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ELEMENTS
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GENERAL LIBRAR
University c
MICHIGAN

METALLURG Y.
A PRACTICAL TREATISE ON THE ART OF EXTRACTING
METALS FROM THEIR ORES.
ohn
BY
J. ARTHUR PHILLIPS,
M. INST. C.E., F.G.S., F.C.S., ETC.,
ANCIEN ÉLÈVE DE L'ÉCOLE DES MINES DE PARIS;
'A MANUAL OF METALLURGY,' THE MINING AND METALLURGY
OF GOLD AND SILVER,' ETC.
1874
AUTHOR OF
ILLUSTRATED BY NUMEROUS ENGRAVINGS ON WOOD.
LONDON:
CHARLES GRIFFIN AND COMPANY,
STATIONERS' HALL COURT.
1874.
[The Right of Translation is reserved.]
LONDON:
PRINTED BY WILLIAM CLOWES AND sons,
STAMFORD STREET AND CHARING CROSS.
30
OS MON
PREFACE.
'
THE First Edition of the Author's Manual of Metallurgy'
appeared in 1852, the second in 1854, and the third in 1858.
Up to the last of these dates no other work on this subject had
been published in England; but we have since had the excellent
volumes of Dr. Percy, and a translation of Professor Kerl's
Metallurgy, with additious, by Messrs. Crookes and Röhrig.
A treatise on the 'Metallurgy of Iron,' by W. Truran, is also
before the public, as well as an admirable manual on the same
subject by H. Bauerman; two small but useful volumes on the
Metallurgy of Copper, Lead and Silver, by Dr. R. H. Lamborn,
forming a portion of 'Weale's Rudimentary Series,' and various
other works of a somewhat similar character, have from time to
time been published within the last fifteen years.
The student has, therefore, within his reach a considerable
number of metallurgical books in the English language; but
some of them are large and consequently expensive, while others
confine themselves to the metallurgy of one of the metals only.
No well-illustrated treatise in a single volume has, however,
appeared, describing with any considerable detail the metallur-
gical operations relating to all the principal metals, and at the
same time serving as an introduction to the general literature
of metallurgy.
The object of the present work is to supply, within mode-
rate limits, such practical information on general principles, and
typical processes, as may not only afford a comprehensive view
of the subject, but also enable the reader to study with advantage
more elaborate treatises and original memoirs. The information
generally is, as far as practicable, brought up to the present
time. In order to do this, various works on metallurgy, as well
a 2
iv
PREFACE.
as numerous papers dispersed through the different English and
foreign scientific journals, have been consulted. Recourse has
also been had to notes which, during the last twenty years, have
been made by the Author, both at home and abroad. These
principally refer to the Metallurgy of Copper, Lead, Silver, and
Gold.
In the case of each of the more important metals, the different
ores from which they are respectively obtained are enumerated
and described, while statistics of their distribution and production
in various parts of the world are also added. Much information
relative to the distribution of iron ore has been derived from
Bauerman's Metallurgy of Iron'; in the case of the other metals
the statistics have either been obtained from official sources, or
compiled from the most trustworthy information available. For
returns relative to the production of France and of the United
States of America, we are indebted respectively to Professor
Daubrée, of the Ecole des Mines, Paris, and to Professor B. Silli-
man, of Yale College, Connecticut.
A great difficulty experienced in collecting statistics relative
to the metal-production of the world arises from the fact that
ores raised in one country are frequently subjected to metallurgical
treatment in another, and the produce is, in the majority of
instances, returned by both.
Allowance for such double returns has, when practicable, been
made, but the complete elimination of error arising from this
cause would be exceedingly difficult. Sometimes no precise figures
have been available, and in such cases estimates founded on the
best procurable data have been substituted.
Both the wet and dry methods of assaying are given with
considerable detail, and when, as in the case of ironstones, the
value of an ore is materially affected by the nature and quantity of
the impurities present, the processes employed for their detection
and estimation are fully described.
The principal works, in addition to those already mentioned, to
which the Author wishes to acknowledge his obligations, are the
following: Gruner and Lan, ‘Métallurgie du Fer en Angleterre,'
published in the Annales des Mines; Gruner, 'De l'Acier et de sa
Fabrication,' also published in the Annales des Mines; Jordan,
Métallurgie du Fer au pays de Siegen,' published in De Kuyper's
Revue Universelle; Dana's 'System of Mineralogy,' and Watts's
'Dictionary of Chemistry.' Many other books and papers have
necessarily been consulted; but the several sources from which
PREFACE.
V
information has been derived will be found duly acknowledged in
the text.
Of the illustrations a large number are new, and have been
reduced by Mr. W. J. Welch from working drawings, a few only
having been retained from the 'Manual of Metallurgy.' Some
have been obtained from foreign sources, particularly from draw-
ings published by the Technical Institute of Berlin under the
title of Sammlung von Zeichnungen für die Hütte.' Others have
been reproduced from papers published in the Transactions of
various societies; a few have been reduced from Truran's draw-
ings; and some six or eight have, with the kind permission of the
Author, been adapted from Percy's 'Metallurgy.'
(
The woodcuts have been drawn to scale, and a sufficient
number of dimensions are generally given to render easy the
determination of any others that may be required.
The Author has much pleasure in acknowledging his obliga-
tions to Mr. W. Hutchison for information relative to lead-smelting
at Couëron, to Professor Ulrich for a description of the process
employed at Oker for the extraction of silver and gold from
copper by sulphuric acid, and to Ober-Berg- und Hütten-Director
Leuschner for drawings of the large blast-furnace at Mansfeld,
and for valuable information relative to the various processes
employed in that establishment. His thanks are likewise due
to Mr. F. W. Rudler for his able assistance during the time.
this volume has been passing through the press.
CRESSINGTON PARK,
AIGBURTH.
June, 1874.
TABLE OF CONTENTS.
COLOUR
OPACITY AND LUSTRE
HARDNESS
·
SPECIFIC GRAVITY
CRYSTALLISATION
MALLEABILITY
DUCTILITY.
TENACITY
8
•
INTRODUCTION.
PHYSICAL PROPERTIES OF METALS.
PAGE
8 FUSIBILITY
∞ ∞ ∞
PAGE
11
ELASTICITY AND SONOROUSNESS
12
9 ODOUR AND TASTE
12
9
POWER OF CONDUCTING HEAT
13
9
CAPACITY FOR HEAT
13
·
10
EXPANSION BY HEAT
13
•
11
VOLATILITY
13
11
ALLOYS
13
•
FUEL.
CALORIFIC POWER OF FUEL
16
PREPARATION OF CHARCOAL IN PILES
Calorific Power of Carbon
18
OR STACKS
51
Carbonic Oxide
19
CHARRING IN FURNACES OR KILNS
57
""
""
Hydrogen
19
PEAT-CHARCOAL OR PEAT-COKE
61
""
""
Berthier's Process for estimating the
CHARRING IN HEAPS
62
Calorific Power of Fuel
ANALYSIS OF FUEL, &C.
19
OVENS
63
CALORIFIC INTENSITY OF FUEL
23
COKE
65
24
CARBONISATION IN HEAPS
66
ESTIMATION OF ASH
24
COKING IN MOUNDS
67
HYGROMETRIC WATER
25
RECTANGULAR KILNS
68
•
""
SULPHUR
25
""
OVENS
71
CARBON AND HYDROGEN
26
IMPROVED COKE-OVENS
76
NITROGEN
26
Breckon and Dixon's Ovens
76
OXYGEN
26
Anchor Oven
79
LITHARGE EXPERIMENTS
27
COLLECTION OF TAR, &C., FROM COKE-
Wood
29
OVENS
80
PEAT OR TURF
33
Silesia
80
•
COAL
LIGNITE OR BROWN COAL
38
Pauwel's and Dubochet's Oven
81
39
Pernolet's Coke-Oven
82.
BITUMINOUS COAL
CANNEL COAL
ANTHRACITE
EFFECT OF HEAT ON FUELS
•
PREPARATION OF ARTIFICIAL FUELS
CHARCOAL.
43
COMPOSITION AND PROPERTIES OF COKE 88
47
WASTE HEAT FROM COKE-OVENS
88
48
CHARRING OF BROWN COAL
89
48
GASEOUS FUEL
90
영영
​50
SIEMENS'S GAS-PRODUCER
92
50
REGENERATIVE FURNACE
96
viii
ELEMENTS OF METALLURGY.
REFRACTORY MATERIALS FOR FURNACES AND CRUCIBLES.
FIRE-STONES, &c.
FIRE-CLAYS
PAGE
100
FIRE-BRICKS
101
CRUCIBLES.
PAGE
104
106
IRON.
Texture
•
WROUGHT OR MALLEABLE IRON
Fusibility
Magnetism.
Rust, &c.
•
•
111
111 SPATHIC IRON ORE; SIDERITE
CLAY IRONSTONES
138
139
112
BLACKBAND IRONSTONE
140
•
112
CLEVELAND IRONSTONE
141
•
•
112
ASSAY OF IRON ORES
144
ON CERTAIN COMPOUNDS OF IRON
113
IRON AND CARBON
113
DRY ASSAY OF IRON ORES. Appa-
ratus necessary
144
State of Carbon in Iron
113
Preliminary operations, fluxes, &c.
146
IRON AND SILICON
117
Classification and Proportion of
Ferrous Silicates .
117
Fluxes
148
IRON AND SULPHUR
118
•
Method of conducting an Assay
149
IRON AND PHOSPHORUS.
118
Swedish Process .
152
•
IRON AND NITROGEN
119
WET ASSAY OF IRON ORES; MAR-
•
IRON AND MANGANESE .
119
GUÉRITE'S PROCESS
152
INFLUENCE OF OTHER METALS ON
Preparation of Standard Solution .
153
IRON
120
Solution of the Ore
153
•
Chromium.
120
Determination of the Iron
154
•
•
ALLOYS OF IRON
120
PENNY'S PROCESS
154
•
IRON ORES.
121
Standard Solution
154
·
NATIVE IRON
121
Estimation of the Iron in an Ore
155
Meteoric Iron
121
MAGNETIC IRON ORE; Magnetite;
Dry and Wet Assay. Comparative
Yields
155
•
Fer Oxydulé; Magneteisenstein. 122
FRANKLINITE
ANALYSIS OF IRON ORES
156
123
Water
156
ILMENITE; Titaniferous Iron Ore;
Titane Oxyde ferrifère; Titan-
eisenstein.
Attack by Hydrochloric Acid, &c.
156
Sulphur
158
•
123
Phosphoric Anhydride.
158
•
HEMATITE; Specular Iron; Fer
Carbonic
158
•
oligiste; Eisenglanz .
123
Titanic Oxide
159
•
GÖTHITE; Fer hydroxide; Göthit .
124
Insoluble Residue
159
BROWN IRON ORE; Fer oxyde hy-
METALLURGY OF IRON
159
•
drate; Brauneisenstein
124
DIRECT PREPARATION OF MALLE-
Pea-iron
125
ABLE IRON
161
•
IRON PYRITES; Fer Sulfure; Eisen-
CATALAN OR FRENCH PROCESS
163
kies
125
AMERICAN BLOOMERY
168
•
SIDERITE; Carbonate of Iron; Fer
CORSICAN PROCESS
169
•
Carbonate; Eisenspath
126
•
STÜCKOFEN, OR HIGH BLOOMERY
DISTRIBUTION OF IRON ORES.
127
FURNACE
170
•
•
MAGNETIC ORES.
128
CLAY'S PROCESS
171
•
TITANIFEROUS IRON SANDS
130
CHENOT'S
172
""
RED IRON ORES
131
YATES'S
173
•
""
•
•
OLDER BROWN IRON ORES
134
""
Black Brush Ore
134
•
NEWER BROWN IRON ORES
135
TERTIARY AND POST-TERTIARY IRON
ORES
137
SIEMENS'S
INDIRECT METHOD OF OBTAINING
IRON-PRODUCTION OF PIG-IRON
AND SUBSEQUENT CONVERSION
INTO MALLEABLE IRON
174
•
176
TABLE OF CONTENTS.
ix
PAGE
PAGE
MECHANICAL PREPARATION OF IRON
Cost of Blast-Furnaces.
260
ORES
176
Heat absorbed for Work done in
WEATHERING OF IRON ORES
178
Blast-Furnaces
261
.
•
ROASTING OR CALCINATION OF IRON
CONVERSION OF GREY CAST-IRON
ORES
179
INTO WHITE
262
•
Roasting in open Heaps
179
Parry's Refinery .
266
Roasting between Walls
181
German Refinery.
267
•
Roasting in Furnaces or Kilns
182
Heaton's Process
268
FLUXES AND SLAGS
190
Henderson's Process
269
THE BLAST-FURNACE AND ITS AC-
PRODUCTION OF WROUGHT-IRON FROM
CESSORIES
196
CAST-IR N IN OPEN FIRES
270
•
THE BLAST-FURNACE
198
GERMAN OR WALLOON FORGE
271
The Rachette Furnace.
207
IRON FOR TIN PLATES
276
•
Blast-Furnaces in the Cleveland
PREPARATION OF MALLEABLE IRON
District
210
BY THE REVERBERATORY PROCESS
277
BLOWING MACHINERY
210
PUDDLING
277
•
•
•
Blowing Engine at the Dowlais
Puddling in Gas-Furnaces
284
Iron-Works
212
Mechanical Rabbles
286
Blowing Engines in the North of
Rotative Furnaces
287
England.
214
FORGE MACHINERY AND OPERA-
Blowing Engines at Creuzot, &c.
214
TIONS
290
HOT-BLAST
216
Hammers
291
Common Stove
217
Squeezers
295
Circular Stove
219
Puddling Rolls
299
+
•
Pistol-Pipe Stove.
Stove used at Neustadt.
Cowper's Stove
Whitwell's Stove
•
Blast-Pipes and Nozzles
UTILISATION OF WASTE GASES
221
Shears
301
221
WORKING PUDDLED BAR INTO MER-
•
223
CHANT IRON; THE MILL
302
•
•
•
225
Re-heating, or Balling .
302
•
227
Mill Rolls, &c.
305
227
Plates and Sheets
308
Method of collecting Gases at Dar-
STEEL
311
laston
229
STEEL BY THE DIRECT REDUCTION
Langen's Apparatus
230
OF IRON ORES
312
•
•
•
Cup and Cone
230
•
Method employed at Grosmont
231
STEEL BY ADDITION OF CARBON TO
MALLEABLE IRON; Cementation.
313
COMPOSITION OF WASTE GASES
232
Hindoo Process
317
•
LIFTS OR HOISTS.
235
Chenot's Process
317
•
•
Lift at Newport
235
Mushet's Steel; Homogeneous Metal
318
Water Balance
237
Case-hardening
319
•
Furnace Hoist, Ayresome
237
STEEL BY THE PARTIAL DECARBU-
Kiln
238
RISATION OF CAST-IRON
319
•
""
""
SMELTING
241
In open Hearths .
319
•
Fuel used in the Blast-Furnace
241
Puddled Steel
321
Blowing-in.
243
Bessemer's Process
326
•
Descent of Charges
243
Bérard's Process .
339
•
·
Tapping
245
Uchatius's Process
340
Blowing-out
246
STEEL BY FUSION OF A MIXTURE OF
VARIETIES OF PIG-IRON
247
CAST- AND WROUGHT-IRON
340
CAPACITY AND PRODUCTION OF
Obuchow's Steel Process
341
BLAST-FURNACES
Charcoal Furnaces
Coke
250
Price and Nicholson's Process
342
251
Siemens-Martin Process
342
254
PARTIAL DECARBURISATION OF CAST-
•
•
Coal in the Blast-Furnace
Anthracite Furnaces
257
IRON BY CEMENTATION
343
•
259
CAST-STEEL
344
•
•
X
ELEMENTS OF METALLURGY.
PAGE
PAGE
HARDENING AND TEMPERING STEEL
346
PHOSPHORUS
349
Damascening
347
COMBINED CARBON
349
ANALYSIS OF CAST-IRON, WROUGHT-
IRON, AND STEEL
MINUTE PROPORTIONS OF FOREIGN
347
METALS
350
►
•
•
SULPHUR
348
EGGERTZ'S PROCESSES
351
·
CARBON, AS GRAPHITE
SILICON
MANGANESE
348
Determination of Carbon
351
348
•
349
Sulphur
Silicon
352
353
•
·
•
>>
COBALT.
COBALT ORES
Smaltine
Cobalt Glance
355
PREPARATIONS OF COBALT
356
+
355
Oxide of Cobalt
356
•
•
355
Smalt
357
•
Cobalt Bloom
Mispickel
355
•
Cobalt Blue, or Thénard's Blue
358
•
355
Printers' Blue
358
•
ESTIMATION OF COBALT AND NICKEL 355
Rinmann's Green
358
NICKEL.
NICKEL ORES
358. Millerite
Copper-Nickel; Kupfernickel
359
Pentlandite
•
White Nickel
359
•
Zaratite, or Hydrated Carbonate of
Nickel Glance
359
·
Antimonial Nickel
359
Nickel
METALLURGY OF NICKEL
359
•
359
359
360
ALUMINIUM.
METALLURGY OF ALUMINIUM
363
COPPER.
COPPER ORES
366
•
NATIVE COPPER; Cuivre natif ; Ge-
diegen Kupfer
Other Minerals containing Copper.
DISTRIBUTION OF COPPER ORES
373
374
•
366
ASSAY OF COPPER ORES
378
•
·
CUPRITE; Octahedral Copper Ore;
Cuivre oxydulé; Rothkupfererz
MELACONITE; Black Oxide of Cop-
per: Cuivre oxydé noir; Kupfer-
schwarz
REDRUTHITE; Vitreous Copper;
Cuivre sulfure; Kupferglanz
COPPER PYRITES; Chalcopyrite ;
Cuivre pyriteux; Kupferkies 368
FRUBESCITE; Cuivre panache; Bunt-
kupfererz.
•
Fusion for Coarse Copper
Refining
Treatment of the Slags for Copper
GERMAN METHOD OF ASSAYING
CORNISH DRY ASSAY
378
•
366
Apparatus employed
378
Preliminary Examination
379
Method of Conducting an Assay
379
357
Fusion for Regulus
379
Calcination of the Regulus
381
·
•
367
382
•
382
383
383
•
369
Roasting; Calcining.
384
1
TETRAHEDRITE; Cuivre gris; Fahl-
Melting for Coarse Copper
384
•
erz.
370
Refining
384
BLUE CARBONATE OF COPPER; Āzu-
rite; Kupferlazur
WET ASSAY OF COPPER ORES. PRE-
370
CIPITATION BY ZINC OR BY ME-
•
MALACHITE; Cuivre carbonaté vert;
TALLIC IRON
385
•
Malachit
371
PELOUZE'S PROCESS
387
•
CHRYSCCOLLA; Silicate of copper;
Cuivre hydraté silicifère
BY POTASSIUM CYANIDE
388
372
METALLURGY OF COPPER
391
•
TABLE OF CONTENTS.
xi
PAGE
PAGE
ENGLISH METHOD OF COPPER-
SMELTING
392
I. Calcination of Mixed Ores
II. Fusion of Calcined Ores with
Raw Ores, Slags, &c.
393
396
III. Calcination of Granulated or
Crushed Coarse-metal.
398
IV. Fusion of Calcined Coarse-
metal with certain Orrs, and
with Slags from Operations
V. and VI.
398
V. Roasting the Fine- or White-
metal
IV. Melting for "Spurstein" or
Fine-metal
V. Grinding the Fine-metal
414
415
VI. Roasting the ground Fine-metal 415
VII. Dissolving out Sulphate of
Silver and precipitating
Cement-Silver by Metallic
Copper
•
415
VIII. Fusion for Black Copper 415
IX. Refining
416
OBSOLETE PROCESSES AT MANSFELD 417
WET PROCESSES FOR EXTRACTING
399
COPPER
419
VI. Refining and Toughening
399
GERMAN HYDROCHLORIC-ACID PRO-
PROCESS FOR MAKING "BEST-SE-
CESS
420
LECTED " COPPER
400
HENDERSON'S HYDROCHLORIC-ACID
MODIFICATIONS OF THE ENGLISH
PROCESS
421
*
METHOD OF COPPER-SMELTING
402
LONGMAID'S PROCESSES.
422
I. Calcination of Ores
402
BANKART'S PROCESS
423
II. Melting for Coarse-metal
III. Melting for White-metal
IV. Tapping Close-Regulus.
V. Running for Blister-Copper
VI. Refining and Toughening
NAPIER'S METHOD OF COPPER-
SMELTING
402
LINZ PROCESSES
423
402
•
I. Poor Sulphides
423
•
403
II. Poor Oxides and Carbonates
424
403
SINDING'S PROCESS
425
404
"HENDERSON'S PROCESS
427
TREATMENT OF BURNT CUPREOUS
404
PYRITES.
428
METHOD OF RIVOT AND PHILLIPS
CONTINENTAL METHOD OF COPPER-
SMELTING-TREATMENT OF COP-
PER SCHISTS IN THE MANSFELD
DISTRICT, PRUSSIAN SAXONY
406
I. Grinding
429
II. Calcination
430
+
III. Lixiviation
432
•
407
I. Burning the Schist
409
WET PROCESS
•
II. Smelting Burnt Ore with Slag
for the production of “ Roh-
stein" or Coarse-metal
BRASS
410
•
IV. Precipitation
MODIFICATIONS OF THE ORDINARY
ALLOYS OF COPPER
Manufacture of Calamine Brass
433
•
434
435
•
436
437
III. Roasting the Coarse-metal
414
Direct Preparation of Brass
438
TIN.
TIN ORES
440
ROASTING IN REVERBERATORY FUR-
CASSITERITE; OXIDE OF TIN; Etain
NACES
446
oxydé; Zinnstein
440
OXLAND AND HOCKING'S CALCINER
447
TIN PYRITES; Etain sulfuré; Zinn-
SEPARATION OF TUNGSTEN; Ox-
kies
441
LAND'S PROCESS
450
DISTRIBUTION OF TIN ORES
442
METALLURGY OF TIN
451
ASSAY OF TIN ORES
444
•
TREATMENT OF TIN ORES IN THE
PREPARATION OF THE ORE
444
REVERBERATORY FURNACE
452
•
ASSAY OF BLACK TIN
445
Smelting
452
•
In brasqued or Black-Lead Cru-
Refining
453
cibles
445
Re-smelting of the Slags and Resi-
Cornish Method of Assay
446
dues
454
Fusion with Potassium Cyanide
446
SMELTING IN THE BLAST-FURNACE,
454
ROASTING TIN ORES
446
ALLOYS OF TIN
455
•
•
xii
ELEMENTS OF METALLURGY.
ANTIMONY.
PAGE
PAGE
ANTIMONY ORES.
457
ELIQUATION OF THE SULPHIDE
460
SULPHIDE OF ANTIMONY; Antimoine
REDUCTION TO THE METALLIC STATE 460
sulfure; Grauspiessglaserz
457
Singling
461
ASSAY OF ANTIMONY ORES
METALLURGY OF ANTIMONY
458
Doubling
461
•
•
460 Melting for Star Metal
461
ARSENIC.
ASSAY OF ARSENICAL ORES
462
•
MANUFACTURE OF WHITE ARSENIC
463
SENIC
PREPARATION OF METALLIC AR-
463
ZINC.
ZINC ORES.
465
DISTRIBUTION OF ZINC (RES .
469
NATIVE ZINC
466
ASSAY OF ZINC ORES
472
RED OXIDE OF ZINC; Zincite; Zinc
FIRE ASSAY.
BY DISTILLATION
472
oxydé ferrifère; Zinkoxyd
SULPHIDE OF ZINC; Zinc sulfuré;
466
BY DIFFERENCE
472
""
HUMID ASSAY.
BY DIFFERENCE
473
•
Blende
CARBONATE OF ZINC; Calamine;
Calamine;
466
VOLUMETRIC ASSAY
471
Ferric Chloride Solution
475
Zinc carbonaté; Zinkspath
467
Standard Solution of Sodium Sul-
SILICATE OF ZINC; Smithsonite ;
Zinc oxydé silicifère; Galmei
WILLEMITE; Anhydrous Silicate of
Zinc
phide
475
468
Estimation of the Zinc contained in
an Ore
475
•
468
METALLURGY OF ZINC.
477
SULPHATE OF ZINC; Goslarite; White
ENGLISH PROCESS
478
Vitriol; Zinc sulfate; Goslarit
OXYSULPHIDE OF ZINC; Voltzite;
Leberblende
469
BELIAN PROCESS
480
•
SILESIAN PROCESS
484
469
•
MERCURY.
MERCURY ORES
491
METALLURGY OF MERCURY
498
•
NATIVE QUICKSILVER;
Mercure
EXTRACTION OF MERCURY BY SUB-
natif; Gediegen Quecksilber
491
CINNABAR; SULPHIDE OF MERCURY;
JECTING CINNABAR TO A PROCESS
OF ROASTING
498
Mercure sulfuré; Zinnober
491
ROASTING IN MOUNDS
499
•
NATIVE CALOMEL; Mercure chlo-
TREATMENT OF MERCURIAL ORES
ruré; Quecksilber-Hornerz.
492
AT IDRIA. Old Process
500
•
Coccinite
492
Continuous Process
502
•
Onofrite
492
ALUDEL FURNACE OF ALMADEN
503
Ammiolite
492
•
NEW ALMADEN, CALIFORNIA.
504
DISTRIBUTION OF MERCURY ORES
492
EXTRACTION OF MERCURY IN RE-
ASSAY OF MERCURY ORES
495
VERBERATORY FURNACES
504
DISTILLATION WITH QUICKLIME IN
AN ATMOSPHERE OF HYDROGEN
DISTILLATION WITH QUICKLIME AND
SODIUM BICARBONATE
METHOD EMPLOYED AT IDRIA
DECOMPOSITION OF MERCURIAL ORES
495
•
IN CLOSE VESSELS BY LIME
GALLERY OF PALATINATE
505
•
505
•
496
RETORTS AT LANDSBERG
505
·
•
497
TABLE OF CONTENTS.
xiii
BISMUTH.
PAGE
PAGE
BISMUTH ORES
508
SCHNEEBERG PROCESS
509
NATIVE BISMUTH; Bismuth natif;
JOACHIMSTHAL PROCESS
510
Gediegen Wismuth
508
•
PRODUCTION OF BISMUTH AT FREI-
ASSAY OF BISMUTH ORES
509
BERG
510
METALLURGY OF BISMUTH
509
LEAD.
LEAD ORES
514
BLEIBERG PROCESS
548
NATIVE LEAD; Plomb natif; Ge-
REDUCTION BY METALLIC IRON IN
diegen Blei
514
REVERBERATORY FURNACES
550
•
OXIDE OF LEAD; Massicot; Blei-
SMELTING IN BLAST-FURNACES
551
glätte
514
SLAG-HEARTH
551
CHLORIDE OF LEAD; Plomb Chlo-
rure; Salzsaures Blei
CASTILIAN FURNACE
553
514
SMELTING RAW ORES WITH METAL-
SULPHIDE OF LEAD; Galena; Ga-
LIC IRON
555
lène; Bleiglanz
515
TREATMENT OF LEAD ORES BY
•
CERUSSITE; Carbonate of Lead;
Plomb carbonaté; Kohlensaures
Blei
ANGLESITE; Sulphate of Lead;
Plomb sulfate; Schwefelsaures
Blei
PYROMORPHITE; Phosphate of Lead;
Plomb phosphate; Buntbleierz
DISTRIBUTION OF LEAD ORES
516
ROASTING, AND SUBSEQUENT
SMELTING WITH METALLIC IRON.
TREATMENT OF SILICEOUS ORES AT
COUËRON.
559
564
517
HORNO DE GRAN TIRO, OR PAVO
SMELTING IN SHALLOW HEARTHS
571
571
•
BACKWOODS HEARTH
571
•
517
ORE-HEARTH OR SCOTCH FURNACE
572
•
·
519
THE AMERICAN HEARTH
575
•
•
ASSAY OF LEAD ORES
524
EXTRACTION OF SILVER FROM LEAD 576
ASSAY OF ORES OF THE FIRST CLASS
524
IMPROVING OR SOFTENING
576
ASSAY OF ORES OF THE SECOND
DESILVERISATION. PATTINSON'S
CLASS
526
PROCESS.
578
ASSAY OF GALENA CONTAINING AN-
MODIFICATIONS OF PATTINSON'S
TIMONY
531
PROCESS.
582
ESTIMATION OF SILVER IN LEAD
DESILVERISATION BY ZINC. PARKES's
ORES
532
PROCESS.
584
•
METALLURGY OF LEAD
537
MODIFICATIONS OF PARKES'S PROCESS
SMELTING IN REVERBERATORY FUR-
IN GERMANY AND ELSEWHERE
585
•
NACES
538
CUPELLING OR REFINING
588
•
FLINTSHIRE PROCESS
538
REDUCING
592
•
MODIFICATION OF THE FLINTSHIRE
GERMAN CUPELLATION.
593
PROCESS AT COUERON
540
REFINING THE BLICKSILBER
596
CORNISH PROCESS.
544
LEAD FUME
597
•
SPANISH FURNACE OR BOLICHE
546
SHEET-LEAD AND LEAD PIPE
598
SILVER ORES
NATIVE SILVER; Argent natif;
Gediegen Silber
SILVER.
602
602
•
NATIVE AMALGAM; Argent amal-
game; Natürlich Amalgam
ARGENTITE; VITREOUS SULPHIDE
603
•
xiv
ELEMENTS OF METALLURGY.
PAGE
OF SILVER; Argent sulfuré; Sil-
berglanz .
603
Stamping Mill
Settling Tanks
Pans
PAGE
643
648
STEPHANITE; BRITTLE SILVER ORE;
Argent sulfure fragile; Schwarz-
gültigerz.
649
•
Separators.
655
·
•
604
Agitator
656
POLYBASITE; Polybasite; Eugen-
Retorting and Melting
657
glanz
604
Tailings
659
DARK-RED SILVER ORE; PYRARGY-
General Arrangement of Reduction
RITE; Argent sulfuré antimonié ;
Works
659
Dunkles Rothgültigerz
605
Chemical Reactions of the Washoe
CHLORIDE OF SILVER;
Argent
Process
660
·
cornué; Hornsilber
605
THE STETEFELDT FURNACE
661
•
•
DISTRIBUTION OF SILVER ORES
606
PROCESSES FOR EXTRACTING SILVER
ASSAY OF SILVER ORES
610
BY THE WET WAY
664
•
BY FUSION WITH LITHARGE, &C.
610
AUGUSTIN'S PROCESS
664
SCORIFICATION
612
First Roasting
665
ASSAY OF SILVER BULLION
613
Roasting with Salt
665
FIRE ASSAY
613
·
Lixiviation and Precipitation
665
HUMID ASSAY
617
ZIERVO EL'S PROCESS
667
•
METALLURGY OF SILVER
623
Roasting
668
TREATMENT OF SILVER ORES BY
Lixiviation and Precipitation
671
•
AMALGAMATION
625
VON PATERA'S PROCESS
673
MEXICAN OR PATIO PROCESS .
625
•
Roasting
673
Rough Stamping .
625
Lixiviation with Water
674
•
Fine Grinding
626
""
Sodium Hyposul-
The Patio
628
•
phite
674
Washing
•
Filtration of Amalgam.
Retorting
Results obtained, &c.
STOVE AMALGAMATION.
HOT PROCESS
AMALGAMATION IN BARRELS .
Amalgamation of Copper Matts
WASHOE PROCESS OF AMALGAMATION
630
Precipitation of Silver .
675
•
631
•
Treatment of Silver Sulphide
676
632
Residues
•
677
•
632
EXTRACTION OF SILVER AND GOLD
•
633
BY SULPHURIC ACID.
677
633
CLAUDET'S PROCESS
€79
•
635
Estimation of Silver in the Liquors 681
641
Precipitation of Silver .
681
642
GOLD.
DISTRIBUTION OF GOLD
684
MECHANICAL AND METALLURGICAL
ASSAY OF AURIFEROUS MINERALS
694
TREATMENT OF GOLD
·
703
•
CUPELLATION
694
PLACER MINING .
703
PARTING
694
PAN.
·
703
•
ASSAY OF GOLD QUARTZ, &c.
695
CRADLE
704
Fusion with Litharge, Carbonate of
Том .
705
Sodium, &c.
696
PUDDLING Box
705
1
Fusion with Red Lead or Litharge
SLUICE
706
only
697
HYDRAULIC MINING
709
•
Auriferous Pyrites
697
•
EXTRACTION OF GOLD FROM AURI-
Inquartation
697
·
FEROUS VEINSTONE
712
Parting
697
ARRASTRA
712
•
•
•
ASSAY OF GOLD BULLION
Determination by the Touchstone,
698
CHILIAN MILL
714
•
STAMPING MILL
714
•
•
&c..
701 | Amalgamation in Battery
714
•
TABLE OF CONTENTS.
XV
PAGE
PAGE
Blankets
715 RETORTING,
AND FUSION
INTO
Amalgamated Plates
719
INGOTS
•
722
Cleaning up
719
CHLORINATION PROCESS
724
·
Amalgamation of Blanket Washings 720
Tailings
722
PARTING BY SULPHURIC ACID
REFINING BY CHLORINE GAS
726
728
PLATINUM.
DISTRIBUTION OF PLATINUM.
733
MODIFICATION
OF WOLLASTON'S
METALLURGY OF PLATINUM
736
PROCESS.
737
•
WOLLASTON PROCESS
736
DEVILLE AND DEBRAY'S PROCESS
738
!
ERRATA.
Page 7, line 2.—The date here given is that of the Strasburg edition of the works
of Paracelsus, which is not the earliest. He was born in 1493 and died in 1541.
Page 7, note*, for Beckman read Beckmann.
Page 363, line 32, for Saint-Claire read Sainte-Claire.
Page 413, line beneath fig. 128, for fire-doors read working doors.
Page 463, line 15, for a magnesium read ammonio-magnesian.
i
LIST OF ILLUSTRATIONS.
FIG.
1. Flatting Mill.
2. Charcoal Pile; vertical section.
3. Charcoal-burning; rectangular heap
4. Charcoal Kiln; vertical section
5.
">
""
plan
6. Peat-charcoal Oven; vertical section
7. Coke Mound; vertical section
•
8. Rectangular Kiln; side elevation
PAGE
10
52
·
•
55
58
58
61
67
69
9.
""
"}
plan
section
""
""
69
Rive-de-Gier; longitudinal section
""
""
20.
99
19
""
23.
""
""
21.
25.
""
26.
10.
11. Coke-Ovens
12. Coke-Oven; ground plan
13.
""
14. Breckon & Dixon's Coke-Ovens; elevation.
15.
16.
17.
""
""
""
18. Anchor Ovens; ground plan
plan of four, partly in section
sectional elevation
front elevation; partly in section
19. Pernolet's Coke-Oven; longitudinal section
horizontal section at different heights
transverse section
22. Siemens's Gas-Producer; vertical section
21.
•
plan; partly section
Re-heating Furnace, front elevation; valves and flues in
69
71
73
74
•
77
78
78
79
80
84
85
86
91
95
""
""
""
section
longitudinal section
sectional plan
•
·
98
99
99
27. Assay Furnace; vertical section
28. Crucible Tongs
144
145
29.
""
30.
""
""
31.
""
146
146
146
32. Shield for protecting the face from heat of furnace
33. Brasqued Crucible
34. Catalan Forge and Trompe; vertical section
35.
""
36. Hearth of Catalan Forge
37. Roasting Kiln, Styria; longitudinal section
146
150.
164
plan, partly in section
165
166
183
38.
""
39.
""
40.
""
41.
3
horizontal section
transverse section
elevation
183
•
184
185
3
""
horizontal section
185
""
""
42.
33
13
Altenberg; vertical section
187
xviii
ELEMENTS OF METALLURGY.
FIG.
PAGE
44.
45.
""
""
48.
""
""
50.
53.
>>
27
""
"}
17
61.
""
Newport
64.
""
""
""
71.
19
43. Roasting Kiln, Dowlais; front elevation
46. Gjer's Calciuing Kiln; one-half in section.
47. Blast-Furnace, Plymouth Iron-Works; vertical section
49. Water-Tuyer; longitudinal section
side view
51. Blast-Furnace, Oldbury; vertical section
52.
54.
Stockton; vertical section
Ditton Brook; vertical section
section through hearth
55. Swedish Charcoal Furnace; vertical section
56. Rachette Furnace; longitudinal section
57.
58.
59. Blast Cylinder, Dowlais; vertical section
60. Blowing Engine, Dowlais .
62. Hot-Blast Stove; transverse section
63. Circular Stove; vertical section
""
65. Pistol-Pipe Stove; transverse section
66. Hot-Blast Stove, Neustadt; vertical section
67. Cowper's Stove; vertical section
68.
69.
arrangement of brickwork
70. Whitwell's Stove; vertical section
??
72. Furnace-top, Darlaston; vertical section
73. Cup and Cone; vertical section
74. Furnace-top, Grosmont; vertical section
75. Furnace Hoist, Newport; elevation
187
longitudinal section
transverse section
188
188
189
•
198
horizontal section
199
200
200
202
•
203
•
204
205
·
206
208
horizontal section above tuyers
transverse section
208
209
211
213
214
218
•
•
219
section through air-box
220
220
221
222
horizontal section
223
224
226
horizontal section
226
·
229
231
232
234
•
76.
""
""
Ayresome Iron-Works; elevation
236
77.
78. Kiln Hoist,
""
""
plan
236
""
""
front elevation, partly section
239
79.
""
""
>>
side elevation.
240
82.
""
plan
84.
85.
87.
""
""
89.
""
90.
""
>>
91.
""
""
92.
""
80. Sand Bed
81. Refinery; transverse section
83. German Forge; vertical section
86. Tilt Hammer; front view.
88. Puddling Furnace; side elevation
vertical section
•
245
262
263
271
"
""
plan
tuyer
272
272
275
sectional elevation
275
278
279
horizontal section
280
""
94.
95.
>>
""
""
Neustadt; longitudinal section
horizontal section
93. Danks's Puddling Machine; longitudinal section
end elevation, partly section
end-piece
96. Helve Hammer, Dowlais; from Truran
285
285
287
288
290
292
•
LIST OF ILLUSTRATIONS.
xix
103.
""
104.
""
105.
19
FIG.
97. Steam Hammer
98. Ramsbottom's Duplex Hammer; partly in section
99. Single Squeezer; from Truran
100. Winslow's Squeezer; longitudinal section
101.
""
102. Puddling Train
end elevation
coupling
PAGE
294
296
296
298
298
299
300
300
300
106. Steam Shears; elevation.
107. Re-heating Furnace; longitudinal section
108.
horizontal section
""
""
109. Wagner's Rolling Mill; front elevation
110. Converting Furnace; transverse section
111. Bessemer Converter; vertical section
112.
Steel Plant; elevation, partly section
113. Calcining Furnace; longitudinal section
114.
horizontal section
115. Melting Furnace; longitudinal section
116.
horizontal section
""
117. Rectangular Furnace, Mansfeld; elevation
301
303
304
307
•
314
L
329
•
331
394
*
394
396
397
410
•
•
118.
119.
""
>>
vertical section
interior of hearth
410
411
27
""
""
120. Six-Tuyer Furnace, Mansfeld; vertical section.
121.
122. Kupfergaarherd
""
412
horizontal section through hearth
413
416
""
123.
vertical section.
416
""
124. Liquation Hearth
125.
11
126. Roasting Furnace; longitudinal elevation
418
section
418
•
430
•
127.
""
128.
""
""
129.
""
longitudinal section
horizontal section through working doors
transverse section through fire-box
•
430
431
431
""
""
""
"}
""
130. Oxland & Hocking's Calciner; plan, partly section
131.
""
132. Tin Furnace; longitudinal section
133.
""
horizontal section
134. Liquation Furnace; vertical section
135. English Zinc Furnace; vertical section
136. Belgian Zinc Furnace; front elevation, partly in section
transverse section
137.
138. Silesian Zinc Furnace, Llansamlet; longitudinal section
448
elevation
•
•
448
452
•
·
453
•
461
479
481
481
484
·
139.
""
""
140.
""
""
""
141.
""
""
142.
""
horizontal section
485
•
transverse section
486
""
end view of retort
longitudinal section of retort .
486
486
143. Apparatus for estimation of mercury
141. Furnace at Idria; longitudinal section
145.
""
""
horizontal section.
146. Aludel Furnace; longitudinal section
147.
""
148. Aludels
149. Gallery; transverse section
150. Retorts, Landsberg; elevation, partly section
496
501
•
501
503
sectional plan
503
503
505
506
XX
LIST OF ILLUSTRATIONS.
FIG.
151. Bismuth Liquation Furnace; vertical section
152. Iron Crucible for Lead Assay
153. Assay Scoop .
•
PAGE
510
530
•
•
530
154.
155.
Mould.
""
"}
530
530
157.
""
elevation
156. Cupel; section
158. Cupelling Furnace; elevation .
159.
160. Muffle
161. Cupel Tongs
533
·
•
533
533
vertical section
533
533
534
162.
Mould
567
•
""
163. Mallet
537
·
164. Smelting Furnace, Couëron; longitudinal section
540
165.
166.
horizontal section.
541
""
""
transverse section through tapping-hole
541
""
""
""
174.
elevation
""
176.
""
177.
179.
""
""
187.
188.
167. Clausthal Furnace; front view
168.
169. Blast-Furnace, Pontgibaud; elevation
170. Five-Tuyer Furnace, Couëron; vertical section .
""
171.
172. Ore-Hearth
173. Pattinson's Pots; plan
175. Refinery; front elevation
horizontal section
transverse section through tuyer
178. German Cupelling Furnace; elevation
180. Sheet-Lead Rolling Mill
181. Lead-Pipe Machine; partly section
182. 183. Arrangement of Apparatus for Wet Silver Assay.
184. Shaking Apparatus for Wet Silver Assay
185. Arrastra; partly in section
186. Amalgamating Barrel
Barrels; transverse section
556
vertical section
557
561
566
horizontal section
567
""
572
581
581
•
589
590
590
·
593
horizontal section
•
591
599
600
620
621
627
637
637
•
""
""
190.
""
""
189. Stamping Mill; front elevation
191. Varney's Pan; elevation .
plan, partly section
•
transverse section
192.
vertical section
""
""
193.
""
as seen from above
638
644
645
650
651
652
195.
vertical section
""
>>
>>
194. Separator; as seen from above
196. Retort and Setting; longitudinal section
197. Stetefeldt Furnace; vertical section.
198.
199. Augustin's Process; side elevation of apparatus
656
657
658
663
section through fire-places.
663
666
200. Ziervogel's Process; transverse section of apparatus
201. Von Patera's Process; transverse section of apparatus
202. Hydraulic Mining; Timbuctoo, California
203. Stamping Mill, with Blanket-Sluices and Riffles; longitudinal section .
671
•
·
675
712
716
204.
""
""
}}
plan
717
205. Hungarian Mill; clevation, partly section
721
•
ELEMENTS OF METALLURGY.
INTRODUCTION.
METALLURGY is the art of extracting metals from their ores and preparing
them for the uses of the artisan and manufacturer. A knowledge of the
principles involved in the treatment of metalliferous substances for the
metals they contain constitutes the science of metallurgy; the various
phenomena observed during metallurgical processes relate either to
chemistry or to physics. Mechanical appliances are also extensively em-
ployed by the metallurgist, and the science of metallurgy is consequently
founded on a knowledge of chemistry, physics, and mechanics.
""*
The history of the art dates from the most remote antiquity, and its
fundamental principles had been discovered and applied to the wants of
mankind, long before the existence of the sciences by the aid of which
their operations have since been explained. Tubal-Cain is stated to
have been "an instructor of every artificer in brass and iron.' In the
days of Moses, at least six metals were known, since, in his direction for
the purification of the spoils of the Midianites, he says: "Only the gold,
and the silver, the brass, the iron, the tin, and the lead, everything that
may abide the fire, ye shall make it go through the fire, and it shall be
clean."t
That silver was at a very early period extracted from ores of lead is
apparent from the following passages, which evidently refer to cupella-
tion. "The house of Israel is to me become dross: all they are brass,
and tin, and iron, and lead, in the midst of the furnace; they are even
the dross of silver."‡ And again, "The bellows are burned, the lead is
consumed of the fire; the founder melteth in vain: for the wicked are
not plucked away. Reprobate silver shall men call them, because the
Lord hath rejected them."§ Strabo quotes Polybius as speaking of an
ore which after being washed seven times, was melted with lead and
became pure silver.
In speaking of gold, which was probably one of the first metals
known, Pliny says: "In these parts of the world in which we live, gold
mines are found, to say nothing of India, where the ants cast it up out
* Gen. iv. 22. † Num. xxxi. 22, 23.
‡ Ezek. xxii. 18.
§ Jer. vi. 29 30.
B
2
ELEMENTS OF METALLURGY.
of the ground, or that which the griffins gather in Scythia. The gold
with us is procured in three ways; among the sands of some great rivers,
such as the Tagus in Spain, the Po in Italy, Hebrus in Thrace, Pactolus
in Asia, and the Indian Ganges, all of which yield gold. Neither is there
any gold finer or more perfect, from being thoroughly polished by the
rubbing and attrition which it meets with in the courses of streams of
water. There is also another method of obtaining gold, viz. by digging
it out of pits which are made for that purpose, or else in the caverns and
breaches which occur by the fall of mountains."* He goes on to say,
“Other minerals after their extraction require fire for their conversion
into metal; but gold, of which we now treat, is gold as soon as it is
found." Again, "Neither rust nor canker alters the weight of gold, or
affects in any way its quality. Salt and vinegar, though such active
solvents, do not make the least impression on it.” He states that "with
respect to its purification it should be mixed with lead." No mention is
made of separating gold from silver, although Pliny observes that all
gold contains more or less silver, and adds that when that metal is in the
proportion of one-fifth, the alloy is called electrum. There were anciently
extensive gold mines in Thasos and other Greek islands. Herodotus tells
us he had himself seen the mines of Thasos, and that a great mountain had
been overturned in searching for the metal. †
Gold was employed in Rome for the purpose of fixing artificial teeth
more than three centuries before the Christian era, and a law of the
Twelve Tables makes exception with regard to such gold, permitting it
to be buried with the dead. The remains of numerous mines have been
traced by Gmelin, Lepechin and Pallas, on the southern and eastern
borders of the Ural mountains; and in them were found hammers and
chisels of copper, as well as various instruments of the same metal, of
which the uses are at present unknown.
From the absence of any
remains of masonry in the neighbourhood, these excavations are inferred
to have been made by a nomadic people, probably the Scythians; and
from no iron tools having been found in any of them, we may conclude
that these operations were carried on before the conquest of Siberia by
the Tartars, who effected the subjugation of that part of Asia, about 150
years before our era.§ Sledges made of large stones, to which handles
had been attached, were also discovered, together with boars' fangs, with
which the gold appears to have been collected, and leathern bags or
pockets in which it was preserved. With such imperfect tools, the
progress made must necessarily have been exceedingly slow, and in one
instance, after reaching a band of rock, and penetrating it for a short
distance, the miners seem to have lost patience and abandoned the works.
Lumps of copper, containing no traces of gold, have also been dis-
covered, although the copper ores of the district are found associated
with that metal, and it is therefore probable that the ancient people who
worked these mines were acquainted with a method of separating gold
from copper.
* Pliny, xxxiii. 4.
Lib. vi. c. 47.
‡ Cic. de Leg. ii. 24.
§ 'Histoire Généalogique des Tartares.'
INTRODUCTION.
3
Smelting was effected in small furnaces made of red bricks; Gmelin
found nearly a thousand such furnaces in the eastern parts of Siberia.
The height and breadth of these were each about two feet, and the
length three. They were furnished with holes in two of their opposite
sides, the one for the introduction of a blast, and the other for the escape
of the metal and slags. In the neighbourhood of the furnaces were
found large quantities of broken pottery, together with numerous heaps
of scoriæ, which indicate that operations to a very considerable extent
had, at some period, been carried on in the locality.
Gmelin likewise found in the same district the remains of various
furnaces which had been employed for the extraction of silver, and
remarked that the lead with which it was associated had been thrown
away in the scoriæ, whilst the whole of the silver was carefully
extracted. By what means this was effected, in this particular case, is of
course now impossible to determine, although it is highly probable that
cupellation in some form was resorted to. Diodorus (iii. 14) informs us,
that gold was purified by being melted and heated in earthen pots, together
with an alloy of tin and lead, to which salt and barley-bran were
added; and that the fire was kept up during five successive days. Hip-
pocrates states that gold was melted by a gentle fire, with the addition
of salt, nitre and alum, and that the same process was employed for
refining silver.
Mercury is first mentioned by Aristotle and Theophrastus under the
name of fluid silver (äpyupos XuTòs); but its nature does not appear to
have been well understood even four centuries later, since Pliny distin-
guishes between quicksilver, argentum vivum, and the liquid silver,
hydrargyrus, obtained by the treatment of native cinnabar. The latter he
supposes to be a spurious imitation of quicksilver and a fraudulent sub-
stitute for it.* With regard to the properties of quicksilver, he observes:
"So penetrating is this liquor, that there is no metal but it will eat and
pass through. It supports everything which may be thrown into it, unless
it be gold only, which sinks to the bottom. It is, besides, very useful for
the purpose of refining gold; to effect which object that metal mixed with
cinders is placed in an earthen pot, and shaken with mercury, which re-
jects all the impurities mixed with it, but in return takes hold of the gold
itself. To expel it from the gold, the mixture is poured on skins, which
on being pressed, allow the mercury to pass through them in drops, whilst
the gold remains in all its purity."+
The above process differs but little from the methods in general use,
for the purposes of amalgamation at the present day; but in this case
Pliny's description is imperfect, inasmuch as the solid amalgam remaining
on the skins would require the separation of the combined mercury by the
aid of heat before the gold could exist in the pure and fine state described.
Tin and lead appear to have been frequently confounded by the
ancients, since their names in Hebrew, Arabic, Greek and Latin are often
indifferently used. The Greeks when they would distinguish the two
Hist. Nat. xxxiii. 6.
‡'Ancient Mineralogy,' by N. F. Moore, LL.D., p. 60.
* Hist. Nat. xxxiii. 8, 1.
B 2
4
ELEMENTS OF METALLURGY.
metals, called tin kaσσírepos, and lead μóλußdos. Pliny appears to have
regarded them as two varieties of the same metal, as he describes them
under the titles of white lead and black, and states that plumbum can-
didum, called by the Greeks kaσσiτepos, was more valuable and com-
manded a higher price than the black variety.
His description of plumbum candidum, and the state in which it was
found, leaves no doubt that this much valued metal was tin, it being
represented as occurring among sand, in the dried-up beds of rivers,
and as only known from the other substances with which it was found
associated, by its dark colour and great weight. "There is likewise found
in the gold mines a kind of lead-ore which they call elutia (stream tin).
The water which is let into the mines washes, and carries down with it,
certain little black stones, streaked and marked with white, and as heavy
as the gold itself. It is gathered with that metal, and they remain
together in the baskets in which the gold is collected." Again :
"You
cannot solder together two pieces of black lead without white lead,
neither can this be united to the other without the aid of oil."
He also says of this metal: "Neither out of white lead can any silver
be extracted; whereas out of the black this is commonly done.”
""
In speaking of common lead, the same author says: "It is much used
for conduit-pipes and for being hammered into thin plates;" and then
goes on to describe the mines of France, Spain, and Britain, which, he
states, when quite worked out and exhausted, become quite as productive
as ever, and indeed even more so, if allowed to remain a short time without
being worked; for which he accounts by supposing the metal to be
produced by the air, which has then free access into the mine. With
regard to the state in which plumbum nigrum occurs, we are informed that,
“Black lead has a double origin; for it is either produced in a vein of its
own, without any other metal; or otherwise it is mingled with silver in
the same mine; being mixed together in the same stone of ore, and they
are only separated by melting and refining in a furnace.* The first liquor
that flows from the furnace is tin (stannum), and the second silver. That
which remains behind is galena, the third element of the vein, which
being again melted, after two parts of it are deducted, yields black lead."
The above passage is obscure : tin, lead and silver, are not often found
in the same stone, and were they thus to occur, the tin would not be the
first to flow out of the furnace. The ore from which the ancients pro-
duced their lead appears to have been galena, a name employed by Pliny
as synonymous with molybdæna, which is described by Dioscorides and
himself as an argentiferous lead ore.
Of the metals employed by the ancients for the manufacture of objects
adapted to the every-day usages of life, copper and its alloys were the most
common; as by far the greater portion of the coins, utensils, and imple-
ments of war, which are occasionally brought to light, are composed of
some alloy of copper; and consequently, the making of these alloys, and
their adaptation to the various wants of mankind, must have formed an
important branch of the manufactures of the Greeks and Romans.
* Hist. Nat. xxxiv. 16.
INTRODUCTION.
5
Accordingly, the author of the 'Natural History of the World,' after
describing the properties of this metal, and stating the localities in which
that of the best quality was found, gives the composition and proportions
employed in the various mixtures then common in Rome, and informs us
to what uses they were severally applied. He also states that copper was
first found in the island of Cyprus, whence two distinct kinds were
exported.* One called coronarium, which, when reduced to thin leaves
and coloured with the gall of an ox, had a golden colour, and was em-
ployed for making coronets and tinsel ornaments for actors, from which
circumstance it derived its appellation. Another variety, which was
named regulare, is not particularly described, except that, like the former,
it would stand hammering, and might thus be made to take any required
form.
The brass of next best quality came from Campania, where it was
the custom to add eight parts of lead to every hundred pounds of copper.
It is also mentioned that in France it was usual to melt copper among
red-hot stones, for the purpose of obtaining a steady heat, as a quick fire
was found to blacken the metal and render it brittle. He further informs
us that the process was completed in one operation, but states that the
quality would be improved by more frequent melting: "Moreover, it
may not be amiss to state also, that all kinds of brass melt best in the
coldest weather. For statues and tables, brass is worked in the following
manner: first the ore, or stone, as it comes out of the mine, is melted,
and as soon as this is done, they add to it a third part of scrap brass, con-
sisting of broken pieces of vessels that have been used; for it is time
and use alone that bring brass to perfection; it is the rubbing which
conquers the natural harshness of the metal. They then. mix twelve
pounds and a half of tin to every hundred pounds weight of the aforesaid
melted ore. The softest alloy is called formall, in which are incorporated
a tenth of black lead, and one-twentieth part of argentine lead; it is this
mixture which best takes the colour called grecanic. The last alloy is
that which is called ollaria, or pot brass, as it takes its name from the
vessels for which it is mostly employed, and this is made by tempering
every hundred pounds weight of brass with three or four pounds weight
of argentine lead or tin."†
The alloys above described are merely modifications of bell-metal or
bronze; but it is not improbable that the ancients were acquainted with
zinc-brass long before this period. Aristotle tells us that the Mossynoecians,
a people who inhabited a country not far from the Euxine Sea, were said
to make copper of an exceedingly fine colour, not by the addition of tin,
but by mixing and cementing it with an earth found in that country.‡
We are also informed by Strabo, that in the neighbourhood of Andêra, a
city of Phrygia, a remarkable kind of stone was met with, which, being
calcined, became iron, and on being fluxed with a certain kind of earth,
yielded drops of a silvery-looking metal, which, mixed with copper,
formed an alloy called orichalcum.§
* Hist. Nat. xxxiv. 8.
+ Hist. Nat. xxxiv. 9.
Arist. de Mirab. op. v,
§ Strabo, Geo. lxiii,
6
ELEMENTS OF METALLURGY.
Sextus Pompeius Festus, who abridged a work of Verrius Flaccus,
a writer of the time of Augustus, mentions cadmia, which he describes as
an earth thrown upon copper in order to convert it into orichalcum.*
On this subject Pliny affords us but little information, merely stating
where cadmia was found, and naming some of its medicinal properties;
but he seems to have regarded it rather as an earth which gave a yellow
colour to copper, than as an ore of a distinct metal, zinc being in no
instance mentioned by him, although he speaks of a kind of brass which
was manufactured in the island of Cyprus from copper and cadmia.
If the foregoing quotations were not sufficient to show that the ancients
were acquainted with zinc-brass, the fact is sufficiently proved by the
-following analyses, published by the author in 1852.†
1.
2.
3.
4.
5.
Copper
Zinc
Tin
Lead
Iron
82.26
81.07
83.01
85.67
79.14
17:31
17.81
15.84
10.85
6.27
1.05
1.14
4.97
1.73
9.18
0.35
0.50
0.74
0.23
99.92
99.93
99.38
100.13
99.79
Specific Gravity .
8.52
8.59
8.50
8.30
8.83
No. 1. Large brass of the Cassia family, about B.c. 20; metal of a
yellow colour. No. 2. Large brass of Nero, A.D. 60; reverse, Rome
seated; metal bright yellow. No. 3. Titus, A.D. 79; metal yellow and
soft. No. 4. Hadrian, A.D. 120; Fortunæ reduci; finely patinated;
metal fine yellow. No. 5. Faustina, jun., A.D. 165; Pietas, without
patina; metal of a whitish colour and very brittle.
That metallic zinc, however, was known to the ancients, there is no
evidence to show, since the metal mentioned by Strabo as given out in
drops from a certain stone when heated, could scarcely have been zinc,
which would have been volatilised if treated in the way described; and
we may therefore suppose, that if the stone referred to by him was an ore
of zinc, it might also have contained some other metal, such as lead, with
which it is often found associated, and which would produce the appear-
ance in question. Ambrose, Bishop of Milan, describes the transforma-
tion of copper into orichalcum, as being effected by means of a drug, and
not by the addition of another metal; from which we may infer that he
was unacquainted with the metallic nature of the material employed,
although, from his calling it a drug, he was perhaps aware of its posses-
sing certain medicinal properties.
A similar description of the manufacture of brass is given by Prima-
sius, Bishop of Adrumentum, in Africa, in the sixth century, and by
Isidorus, Bishop of Seville, in the seventh. Agricola, who wrote in the
sixteenth century, was apparently also ignorant that cadmia contained
Cadmia terra, quæ in æs conjicitur ut fiat orichalcum - Fos. de Ver. Sig.
Watson's Chemical Essays,' iv. p. 91.
*
"?
+ Quart. Journ. of Chem. Soc. of London, 1852, iv p. 252, et seq,
INTRODUCTION.
7
zinc, of which we have no authentic account until we find it mentioned
(1616) by Paracelsus;* and from which it would appear that, although
the manufacture of zinc-brass is of great antiquity, the extraction of the
metal itself is comparatively a modern discovery.
Iron was doubtless employed in very early times, although the uses of
copper and its alloys were probably known at a much earlier period.
Hesiod speaks of iron as having been unknown during the age of bronze,
and Lucretius says, with regard to this metal" Et prior æris erat quam
ferri cognitus usus." Moses compares the deliverance of the Israelites
from Egyptian bondage to their being "brought forth out of the iron
furnace." In the time of Homer iron was well known, but appears to
have been employed more sparingly than bronze, and must have been of
considerable value, since a mass of iron, which had been used by Eëtion as
a quoit, is offered by Achilles as a prize at the funeral of Patroclus.
When the interpreter who accompanied Herodotus, reads to him an
inscription on one of the Egyptian pyramids relative to the amount of
money expended on radishes, onions, and garlic, for the workmen em-
ployed on its construction, he makes the reflection, that if this were true,
how much more must have been paid for iron tools, bread, and clothing.§
If we allow that iron tools were used in building these monuments, this
metal must have been in common use during some portion of the time
which elapsed between the birth of Abraham and the captivity of
Joseph.]]
Aristotle says that iron is purified from scoria by melting, and when
it had been treated thus several times and became pure, it was changed to
steel (στόμωμα). Π
Daimachus, a writer contemporary with Alexander the Great, speaks of
four different kinds of steel, and the purposes to which they were severally
suited. "Of steels (Twv σтоμwµáтwv), there is the Chalybdic, the
Synopic, the Lydian, and the Lacedæmonian. The Chalybdic is best for
carpenters' tools, the Lacedæmonian for files, drills, gravers, and stone
chisels; the Lydian also is suited for files, and for knives, razors, and
rasps.
""**
In speaking of iron, Pliny says: "After copper comes iron, both the
most useful and most fatal instrument of life. With iron, man delves the
earth, plants trees, prunes his orchards, trims his vines, cutting off the
older branches, and thereby throwing more vigour into the grapes; by its
aid man builds houses, cuts stone, and prepares a thousand other imple-
ments; but by it war, atrocity, and villany are effected and rendered
common."†† He also describes iron as occurring in almost every part of
* "Marchasita Aurea," mentioned by Albertus Magnus in the 13th century, is
believed by Beckman and some others to have been zinc.
+ Lib. v. 1286.
Deut. iv. 20.
§ Herod. Euterpe, ii. 125.
Russell's Egypt, p. 89.
¶ Vol. i. p. 590.
** See Stephanus, De Urbibus, word Lacedæmon; and Fabricii Bib. Graec. voľ.
p. 588 (Anct. Mineralogy, p. 59).
+ Hist. Nat. xxxiii. 14
8
ELEMENTS OF METALLURGY.
the known world, but particularly in the island of Elba, where the colour
of the earth indicated the presence of the ore.
Sulphide of antimony, called by the Greeks σríu, and by the Romans
stibium, was from the earliest times, and still is, used in the East for
tinging black the hair, eyebrows, &c.
Pliny's description of stibium as "candida nitensque,"* does not
suit in all respects common sulphide of antimony. In preparing it as a
paint, it is, according to Dioscorides, to be inclosed in a lump of dough,
and buried in coals until reduced to a cinder; after being extinguished
with milk and wine, it is to be again placed upon coals and blown upon
until ignition takes place, but if burned longer it becomes lead.†
Pliny directs cow-dung to be used in the place of dough, but varies so
entirely from the recipe of Dioscorides, that it is evident he had some
other authority before him; yet he likewise recommends moderation in
burning as especially necessary, lest it should be converted into lead (ne
plumbum fiat). The fair inference, therefore, is that the ancients occa-
sionally saw antimony reduced to its metallic state, but failed to
recognise it as a new metal.
PHYSICAL PROPERTIES OF METALS.
The metals are a class of simple substances, possessed of a peculiar
lustre, having the property of conducting heat and electricity with
facility; but both in their chemical and physical properties they differ
very much from one another, and are consequently applicable to a great
variety of uses.
COLOUR.-Most of the metals, when in a finely-divided state, are of a
grey colour, but, when consolidated and polished, approach more nearly
to white. The colours of some of them are, however, very decided: thus
copper is red, gold is yellow, and lead blue.
Alloys formed by the mixture of different metals usually possess to a
certain extent the colours of the metals of which they are composed.
Those resulting from the combination of two or more grey or white
metals will themselves be grey or white; but, if a coloured metal enter
into its composition, the alloy will assume its colour in a marked degree,
although, if the proportion of the coloured metal be small compared with
the amount of that which is not coloured, this is not always apparent. In
some cases, however, as in that of the alloys of gold and silver, a com-
paratively small amount of a white metal has the effect of destroying the
colour of the other.
OPACITY AND LUSTRE.-The metals possess a great degree of opacity,
and are remarkable for a peculiar lustre, called metallic. All, however,
are not equally opaque, as gold, when reduced to extremely thin leaves,
transmits rays of green light. Silver leaf of one-hundred-thousandth of
an inch in thickness is perfectly opaque; but very thin leaves of an alloy
of silver and gold appear of a blue colour when viewed by transmitted light,
* Hist. Nat. xxxiii. 33.
Dioscor., v. 99.
Hist. Nat. xxxiii. 34,
PHYSICAL PROPERTIES OF METALS.
9
The lustre of metals is a consequence of their great power of reflecting
light. When reduced to the state of powder, their peculiar metallic
appearance disappears, but is immediately reproduced by rubbing with a
burnisher, or any other hard and smooth substance.
HARDNESS. The metals differ from one another in no respect more
than with regard to their hardness. Those which are pure are usually
less hard than their alloys, and some of them are so soft as to admit of
being easily scratched with the nail, or even moulded between the fingers.
The following table, arranged by Dumas, shows the relative degrees
of hardness of some of the more common metals :-
Chromium
Scratch Glass.
Titanium
Harder than Steel.
Manganese
Rhodium
Platinum
Nickel
Palladium
Cobalt
Copper
Iron
Scratched by Glass.
Gold
Scratched
Silver
by
Calc
Antimony
Zinc
Tellurium
Spar.
Lead
Scratched by the nail.
Bismuth
Potassium
Soft as wax at 15.5° C.
Cadmium
Sodium
Tin
Mercury
Liquid at ordinary tem-
peratures.
SPECIFIC GRAVITY. The specific gravities of the metals differ very
widely, as among them we find some bodies more than twenty times
heavier than water; whilst others weigh less than their bulk of that
liquid.
The principal metals, arranged according to their specific gravities,
are given in the following table. Water=1; temp. 15·5° C. (60° F.) :
Platinum
Iridium
Gold
Tungsten
Mercury
Palladium
Lead
Silver
Bismuth
Copper
Nickel
•
•
=
TABLE OF SPECIFIC GRAVITY OF METALS.*
11.30-11.80
21.50
21.15
19.50
17.60
•
13.59
11.45
10.50
9.90
8.96
8.80
8.70
•
8.63
Cobalt
Manganese
Iron
Tin
•
8.54
8.00
7.79
7.29
•
Zinc
Antimony
6.86-7.1
•
6.80
•
Tellurium
6.11
•
Arsenic
5.88
Aluminium
2.56-2.67
Magnesium
Sodium
Potassium
Lithium
1.75
0.972
0.865
0.593
•
Cadmium
Molybdenum
CRYSTALLISATION.-All the metals are capable of assuming a crystalline
form under favourable circumstances. Many of them-particularly gold,
silver, and copper-occur crystallised in nature, and are found as cubes
or octahedra, or in some of their derived forms: antimony and bismuth
are, however, exceptions to this rule, and afford rhombohedral crystals.
In order to crystallise a metal artificially, it is sometimes sufficient to
melt a few ounces in a crucible, and, having permitted it to cool on the
surface, to pierce the crust formed and allow that in the interior to flow
out. By this means very beautiful crystals of bismuth may be obtained;
but in the case of some of the less fusible metals larger masses and slower
cooling are necessary to produce this effect, and consequently these are
* Fownes, Elementary Chemistry,' 10th edit. p. 297.
10
ELEMENTS OF METALLURGY.
never found in a crystalline state unless considerable weights have been
fused, and allowed gradually to cool, as sometimes occurs in furnaces in
which their metallurgical treatment is effected.
It also frequently happens that one metal may be precipitated in a
crystalline form by placing a strip of another metal in a solution of its
salts. In this way silver is deposited by mercury, and a piece of zinc
placed in a solution of lead acetate precipitates the latter in feathery
crystals. Gold is occasionally deposited in this form from ethereal solu-
tions, and a stick of phosphorus produces the same effect. Nearly all
the metals yield crystals when deposited from their solutions by electric.
currents of feeble intensity, and it is probably to this action that we are
indebted for many of the beautiful specimens of the native metals which
enrich the cabinets of mineralogists.
MALLEABILITY.—When a piece of metal is struck by a hammer, it
either flattens under the blow or splits with more or less facility into
fragments to the former property the name of malleability is applied,
whilst metals possessing the latter peculiarity are termed brittle. The
malleable metals may be reduced into thin leaves either by the hammer
or by the flatting-mill.
A
This consists of two metallic cylinders (A, B, fig. 1) placed horizon-
tally one above the other. These, by means of cog-wheels, are made to
revolve in contrary directions, as shown by the arrows.
The rollers are so arranged in a frame as to admit
of being placed, through the medium of strong screws,
at any required distance from each other; or, if necessary,
of being brought into actual contact. To reduce a piece
of metal by this means to the form of a thin sheet, it
should be first cast in the shape of a rectangular ingot,
having nearly the same width as the required plate. One
of its ends is then flattened into the shape of a wedge so as to enter
easily between the rollers, which, on being set in motion, draw the metal
in and pass it through to the other side reduced in thickness and pro-
portionately elongated. By repeating this operation several times, and
gradually reducing the distance between the two cylinders, sheets of
almost any degree of thinness may be obtained.
Fig. 1.
B
During this compression of the metals, their molecular structure
gradually undergoes a change, and those which at first are soft and pass
readily through the mill, soon become brittle and difficult to work. They
then require to be softened by being heated to redness, and afterwards
allowed to cool to the temperature at which they are worked. This
process is called annealing.
Gold is the most malleable of metals, and may be made into leaves
of only 200000th of an inch in thickness, each grain of which will cover
a surface of fifty-four square inches. The metals are arranged in the
following list according to their malleability:-*
1. Gold
2. Silver
3. Copper
4. Tin
5. Platinum
6. Lead
7. Zinc
8. Iron
9. Nickel
* Regnault, Cours élémentaire de Chimie,' i. 412
PHYSICAL PROPERTIES OF METALS.
11
DUCTILITY. The above-named metals are also ductile, or capable of
being drawn into wire, but do not possess this property in the same order as
their malleability. Wire is manufactured by passing an elongated piece of
metal through the progressively diminishing holes of a steel tool, called
a draw-plate. By this means wires of almost any length or diameter may
be obtained, as the metal takes the size of the last hole through which it
has passed. Silver, for the purposes of embroidery, is frequently made
into wires th of an inch in diameter. A grain of gold may be drawn
into a wire 550 feet long by enveloping the ingot operated upon in a coat-
ing of silver, and then passing it through the draw-plate. The wire thus
produced will also be found covered with silver, and on removing this
latter metal by dilute nitric acid, an enclosed gold wire, of only 5,000th
of an inch in diameter, will be obtained.
500
1
The following metals are arranged according to their ductility:-
1. Gold
2. Silver
3. Platinum
4. Iron
5. Nickel
6. Copper
7. Zinc
8. Tin
9. Lead
TENACITY.-The power possessed by different metals of sustaining
weights is very variable, and influences in a great degree the usages to
which they may be applied. It is therefore important to ascertain by
careful experiment their relative tenacities, and the various influences
which may affect them in this respect. For this purpose wires of exactly
equal diameters are employed. These are firmly suspended by one end
from a fixed point, and to the other extremity weights are successively and
carefully added until the rupture of the wire is effected. The weight which
causes the wire to break necessarily represents the relative tenacity of the
metal of which it is composed, when compared with others in every
respect similarly treated.
Variations of temperature, even within comparatively narrow limits,
materially affect the tenacity of metals. The following results on this
subject have been published by Baudrimont :-*
TENACITY OF THE PRINCIPAL MALLEABLE METALS AT THE TEMPERATURES 0°, 100°, and
200° C. AS FOUND BY EXPERIMENT, WITH THE TENACITY CALCULATED FOR 1 sq.
MILLIMETRE OF SECTIONAL AREA (0.0155 SQUARE INCH).

Diameter
at 16º.
Tenacity.
Tenacity calculated for 1 sq. mm.
of sectional area.
Metals.
1 millimetre
= 0·03937
inch.
At 00 At 1000 At 2000
At 0°
At 100°
At 200°
!
Gold
Platinum
Millimetres. Grms. Grms. Grms.
0.41250 2,459 2,035 1,722
Grms.
Grms.
Grms.
18,400
15,2
15,224
12,878
0.41000 2,987 2,546 2,281
22,625
19,284
17,277
Copper
0.48000 4,542 3,958 3,296
25,100
21,873 18,215
Silver.
0.39825 3,528 2,898 2,314
28,324
23,266 18,577
•
Palladium
0.39750 4,527 1,031 3,360
36,481
32,484
27,077
Iron.
0.17500 4,940 4,611 5,057 205,405 191,725 210,270
FUSIBILITY.--All the metals admit of being liquefied by the applica-
tion of heat; but the temperatures at which they melt are extremely
* Ann. de Ch. et de Phys. 3 s. xxx, p. 304, 1850.
12
ELEMENTS OF METALLURGY.
various. Mercury retains its liquid form during the most intense colds
of our climate. Potassium and sodium fuse below the boiling point of
water. Tin melts at about 227° C.; lead at 325° C.; and antimony below
redness. Gold, silver, and copper require a red heat; iron, nickel, and
cobalt fuse at a white heat; manganese and palladium are melted only
by the strongest heat of a wind furnace; chromium, molybdenum, and
tungsten, agglutinate but slightly when treated in the same way; plati-
num, iridium, rhodium, titanium, &c., yield only to a powerful voltaic
current, or to the flame of the oxyhydrogen blowpipe.
Fusible
below a
TABLE OF FUSIBILITY OF METALS.*
Mercury
Rubidium
Potassium
Sodium
red heat.
Lithium
Tin
Cadmium
Bismuth
Thallium
Lead
Tellurium
Arsenic
Antimony
•
•
Zinc
Silver
Copper
Gold
·
F.
---39°
101.3
144.5
207.7
356
442
about 442
497
Melting l'oints.
C.
-39.44°
38.5
62.5
97.6
180
227.8
228
259
294
A
561
617
325
Rather less fusible than lead.
Unknown.
773
412
Just below redness.
1,873
1,996
2,016
1,023
1,091
1,102
2,786
" •
1,530
Cast-iron
Pure iron
Nickel
Highest heat of forge.
Cobalt
Manganese
Palladium
Infusible
below a
Molybdenum
Uranium
red heat.
Tungsten
Agglomerate, but do not melt in forge.
Chromium
Titanium
Cerium
Osmium
Iridium
Rhodium
Infusible in ordinary blast-furnaces; fusible
by oxyhydrogen blowpipe.
Platinum
Tantalum
ELASTICITY AND SONOROUSNESS are attributes of the harder metals
only, and are more conspicuous in some of their alloys than in the
metals themselves.
Odour and TASTE.-Many of the metals, when rubbed or otherwise
slightly elevated in temperature, possess a singular and characteristic
odour, and if applied to the tongue leave a peculiar metallic taste. This
property has been attributed to the voltaic action caused by the saliva
between the metals and their impurities; since, however, similar pheno-
mena present themselves when perfectly pure specimens are selected, it
is not probable that this explanation is correct.
* Fownes, 'Manual of Elementary Chemistry,' 10th ed. p. 298.
PHYSICAL PROPERTIES OF METALS.
13
POWER OF CONDUCTING HEAT, ETC.-Some of the metals transmit
heat with much greater facility than others. In the following table the
metals are arranged in the order of their decreasing conducting powers,
and opposite to the name of each body is placed the approximative ratio
of the facility with which it transmits heat:
TABLE OF RELATIVE CONDUCTIVITY OF METALS-SILVER = 100.*
Silver
Copper
Gold.
Brass
Brass (thick)
Tin
Iron
At 12° C.
100⚫
At 12° C.
73.6
Steel
Lead
•
11.6
8.5
53.2
Platinum
8.4
23.6
German Silver
6.3
24.1
Rose's Fusible Metal
2.8
14.5
Bismuth
1.8
11.9
The conductivity of the various metals for electricity is approximately
in the same ratio as their capability of transmitting heat.
CAPACITY FOR HEAT.-The amount of heat required to raise equal
weights of different metals from the same to another given temperature
is very variable. Thus, if we express by 1 the quantity necessary to
raise a weight of water from 0° C. to 1° C., that which must be supplied
in order to elevate the same weight of the following metals to that
temperature, will be as below :—†
Iron
Nickel
Cobalt
Zinc
Copper
Palladium
Silver
0.1138
Cadmium
0.1086
Tin
0.1070
•
Antimony
0.0955
Platinum
0.0952
Gold
0.0593
Lead
0.0570
Bismuth
0.0567
0.0562
0.0508
0.0324
0.0324
0.0314
0.0308
EXPANSION BY HEAT.-Metals expand when heated, and, within certain
limits of temperature, this takes place in a degree proportionate to the
heat to which they are subjected.
The linear expansion of the metals, on being heated from 0° C. to
100°, is given in the following table:—
Gold
Silver
·
Platinum
Palladium
Copper
Iron
•
TABLE OF EXPANSION OF METALS FROM 0° C. to 100°.
0.00155155
0.00190868
0.00099180
0.00100000
0.00171733
0.0012350+
Lead
0.00284836
0.00193765
0.00294167
•
·
0.00310833
•
0.00139167
Tin (from Malacca).
Zinc (cast)
Zinc (hammered)
Bismuth
Antimony
0.00108333
VOLATILITY. All metals are probably more or less volatile, although
a certain number only admit of being readily converted into vapour even
at the highest temperatures of our furnaces: among the more volatile
metals are―zinc, cadmium, mercury, arsenic, tellurium, potassium, and
sodium. Several others have the property of communicating characteristic
colours to flame, and are therefore evidently volatile to a small extent.
ALLOYS. The metals are generally capable of uniting with each
other, and forming a class of compounds possessing more or less the
properties of their several constituents. Alloys are usually more fusible
and harder than the metals which enter into their composition; and as
* Poggendorff's Ann. b. 89, p. 497. † Regnault, Chimie élémentaire,' i. p. 414.
14
ELEMENTS OF METALLURGY.
these properties may be regulated according to the relative amounts of
the various metals employed, an infinite number of modifications may be
obtained. Thus copper is malleable and ductile, but is somewhat diffi-
cult to fuse, and for many purposes does not possess the requisite hard-
ness. In many instances these defects may be obviated by the addition
of zinc, which, without much impairing its malleability, renders it fusible,
heightens its colour, and at the same time communicates to it a proper
degree of hardness.
By the addition of ten parts of tin to ninety parts of copper, an
alloy known as gun-metal is obtained, which is also used under the name of
bronze, for the manufacture of statues, and for various ornamental purposes.
For printers' type an alloy is required at the same time hard, fusible,
and which does not materially contract in cooling. Lead, which is a
fusible metal, is evidently unfitted for this purpose by its softness, whilst
antimony and bismuth are too liable to break under the pressure to which
type is exposed in the process of printing. By combining, however,
antimony, lead, and tin, an alloy is produced which fulfils all these con-
ditions, and furnishes a material well adapted for the purpose intended.
It has been stated that, by alloying the metals, we obtain compounds
possessed of very different ductility, malleability, hardness, and colour,
from those belonging to the bodies which enter into their composition ;
thus gold and lead, and gold and zinc, form brittle alloys, and a small
quantity of arsenic added to copper renders it white. It is also to be
observed that an alloy composed of two metals has seldom a density
corresponding to the mean which should be obtained, by calculation,
from the relative amounts and specific gravities of its constituents.
The following table from Thénard (Traité de Chimie, vol. i. p. 394),
shows in what cases the specific gravity of the compound is superior, and
when inferior to the mean of that of the combined metals :—It is, how-
ever, doubtful whether some of the mixtures specified should be regarded
as alloys.
Alloys possessed of greater specific gravity
than the mean of their components.
Gold and Zinc
""
"}
Tin
Bismuth
Antimony
Cobalt
Silver and Zinc
31
""
""
Lead
Tin
Bismuth
Antimony
Copper and Zine
"1
"
Tin
Palladium
Bismuth
Antimony
Lead and Bismuth
Antimony
Platinum and Molybdenum
Palladium and Bismuth
Alloys having a specific gravity inferior to
the mean of their components.
Gold and Silver
Iron
??
Lead
""
""
Copper
""
""
Iridium
Nickel
Silver and Copper
Copper and Lead
Iron and Bismuth
""
Antimony
Lead
Tin and Lead
29
Palladium
Antimony
Nickel and Arsenic
Zinc and Antimony
FUEL.
15
The action of acids on alloys varies according to the relative amounts
of their constituents. Silver alloyed with a large quantity of gold is
protected from the action of nitric acid, by which, under ordinary circum-
stances, it is readily attacked. Sometimes, however, the reverse of this
takes place, and metals which are totally insoluble in certain menstrua
are made to dissolve in them by the addition of a metal on which they
have the power of acting. In this way, platinum, although of itself in-
soluble in nitric acid, may be dissolved by it when sufficiently alloyed
with silver. Alloys consisting of two metals, the one easily oxidisable,
the other possessing a less affinity for oxygen, may be readily decom-
posed by the combined action of heat and air. In this case the former
metal will be rapidly converted into an oxide, excepting perhaps the last
portions, which may in some degree be protected from further action by
the oxide already formed. The increased affinity for oxygen exhibited by
the more oxidisable metal, in presence of another less affected by this
agent, is probably an electrical phenomenon; the action is in some cases
so rapid as to produce combustion. This occurs when an alloy of three
parts of lead and one of tin is strongly heated in contact with air.
A consideration of the chemical properties of metals belongs rather
to the science of chemistry than to metallurgy; and as the limits of the
present work do not admit of this subject being comprehensively treated,
it has been thought proper to omit it altogether. The study of metal-
lurgy can, however, only be profitably undertaken by those possessing a
competent knowledge of chemistry, which must be acquired by a careful
study of some good text-book, supplemented by a greater or less amount
of laboratory experience.
FUEL.
ANY substance which admits of being rapidly oxidised or burned by
atmospheric air, and evolves during that operation an amount of heat
capable of being applied to economic purposes, is called a fuel. Two
elements only, namely, carbon and hydrogen are thus applied. All fuels
are of vegetable origin, and chiefly consist either of woody tissue or of
various products of its natural or artificial decomposition. Although
vegetable matter is never free from traces of nitrogen, it may be regarded,
practically, as being essentially composed of carbon, hydrogen, and
oxygen, together with small amounts of earthy or inorganic substances.
In all fuels containing carbon, hydrogen, and oxygen, the proportion of
hydrogen may be equal to, or greater than, that required to form water
with the oxygen, but is never less. In such combinations only the hydro-
gen in excess is considered available as a source of heat; so that in the
combustion of a substance of which the composition may be regarded as
carbon and water, the carbon alone is the source of heat. Indeed in
such cases the hydrogen is the cause of the loss of a considerable amount
of otherwise available heat, since it may be viewed as existing in com-
bination with oxygen in the state of water, which must be evaporated at
16
ELEMENTS OF METALLURGY.
the expense of a portion of the heat developed by the combustion of
carbon.
The products of the perfect oxidation or complete combustion of
carbon and hydrogen are respectively carbonic anhydride (commonly
called carbonic acid) and water; and these products are likewise ob-
tained on the combustion of any compound of carbon and hydrogen, or
of these elements associated with oxygen. The amount of heat developed
by the complete combustion of any elementary substance in the same
allotropic condition is perfectly definite, and is the same whether the
combustion be effected rapidly or otherwise. By the perfect or complete
combustion of carbon is understood its conversion into carbonic anhydride ;
when applied to hydrogen these terms imply the degree of oxidation neces-
sary to produce water. In the case of carbon perfect combustion results
in the formation of its highest, and, at the same time, most stable oxide.
With respect to hydrogen it is somewhat different; water is the most
stable oxide of hydrogen, but is not its highest oxide. Peroxide of
hydrogen contains twice the amount of oxygen that water does, but the
affinity by which the second atom of that element is retained is exceed-
ingly feeble.
The pyrometric degree, or intensity, of heat, is perfectly distinct from
and independent of the quantity of heat developed by combustion. The
quantity of heat generated on the perfect combustion of a given weight of
one body may be much greater than that produced by the complete com-
bustion of a similar weight of another body, but the intensity of the heat
in the second case may far exceed that obtained in the first. All other
circumstances being the same, the intensity of the heat developed by the
combustion of a given body will be directly proportionate to the rapidity
of the operation, or inversely, as the time occupied in effecting it. The
term calorific intensity is employed in contradistinction to calorific power,
which expresses the quantity of heat evolved by combustion.
CALORIFIC POWER OF FUEL.-Various methods have been employed
for the purpose of measuring the relative amounts of heat evolved by the
combustion of equal weights of different bodies; but, as this heat cannot
be directly estimated, it must, in all cases, be determined in accordance
with certain effects produced. Any effect of heat may be employed as a
means of measuring its quantity by applying the principle that when two
equal portions of the same substance, in the same state, are acted on by
heat in the same way, so as to produce the same effect, the quantities of
heat are equal. It is first necessary to choose a standard of comparison,
and to determine the effect of heat upon that body. We may thus choose a
given weight of ice at the freezing point as the standard, and we may
define as the unit that quantity of heat which must be applied to this
weight of ice to convert it into water, still at the freezing point. By
this system a quantity of heat is measured by the number of pounds,
grammes, or other agreed weight of ice, at the freezing point, which that
quantity of heat would convert into water at the freezing point. We may
also employ a different system of measurement by defining a quantity of
heat as measured by the weight of water at the boiling point, which it
FUEL.
17
would convert into steam of the same temperature. This method is often
employed in determining the calorific value of fuels.
Another method is to define as the unit that quantity of heat which,
if applied to unit of mass, one pound or one gramme of water, at some
standard temperature, will raise that water one degree Fahrenheit or Cen-
tigrade. According to this method a quantity of heat is measured by the
amount of water, at a standard temperature, which that amount of heat
would raise one degree. The amount of heat required to raise one
gramme of water from 0° to 1° C. is now generally adopted as the unit
of heat.
All that is assumed in these methods of measuring heat is, that if it
takes a certain quantity of heat to produce a given effect on a given weight
of water in a certain state, then to produce the same effect on another
similar amount of water will require as much heat; or that twice the
quantity of heat is required for twice the quantity of water, and so on.
It has been found by experience that more heat is required to raise a
given weight of water near the boiling point one degree than at lower
temperatures. If heat be measured according to either of the methods
described, i.e., by the weight of ice melted or by the quantity of a parti-
cular kind of matter which it can raise from one given temperature to
another, quantities of heat may be treated as mathematical quantities, and
may be added, subtracted, &c., as required.
In the experiments of Rumford the apparatus employed consisted of
a rectangular vessel of thin sheet-copper, inclosing a worm of three
horizontal coils. This vessel was eight inches long, four-and-a-half
inches broad, and four-and-a-half inches deep; containing a worm made
of flattened copper tube, one inch in breadth and half an inch in depth.
The lower end of the worm was secured to a circular hole in the
bottom, near one of the square ends, while the other extremity issued
vertically from the top of the vessel near its opposite extremity. A
funnel-shaped copper mouth-piece, one-and-a-half inch diameter, was
fitted to the lower opening of the worm, and a tube inserted in the
top of the box received a thermometer, by means of which the mean
temperature of the water it contained could be determined. The
substance of which it was sought to ascertain the calorific value was
burned beneath and within the funnel-shaped mouth of the coil; the result-
ing current of air, after communicating the heat developed to the worm,
and thence to the surrounding water, finally escaped from the other
extremity. In order to avoid loss of heat by radiation, the temperature
of the water with which the vessel was filled was reduced, immediately
before the commencement of the experiment, a few degrees below that of
the surrounding atmosphere, and the combustion was continued until the
temperature of the water was raised exactly the same number of degrees
above that of the air. It was estimated that in this way the vessel would
receive as much heat by conduction and radiation, as it lost during the
experiment. In order to reduce as much as possible the loss of heat by
conduction the apparatus was supported on slender wooden pillars. To
test the capability of the instrument to absorb the whole of the heat
C
18
ELEMENTS OF METALLURGY.
developed by the combustion of the substance under examination, the
resulting gaseous products were conducted through a second apparatus
similar to the first, and were found not to augment the temperature of the
water which it contained.
The data required in order to determine the calorific value of a sub-
stance by the use of this calorimeter are as follow :—
Weight of substance consumed
water
copper
Specific heat of copper
Initial temperature of water
Final temperature of water.
•
•
•
N
W
С
t
ť'
In experiments of great precision it would be necessary to make cor-
rections for the glass of the thermometer, &c. ; but in the determinations
of Rumford such extreme accuracy was not attempted. In order to
ascertain the weight of water which, in respect to absorption of heat,
would be equivalent to the copper of which the apparatus is made, its
weight must be multiplied by the specific heat of copper.
Let x represent the amount of heat produced by the combustion of
one part of any given body in atmospheric air; the following formula
will then express the calorific value of that body :-
Nx
(t' −t) (w + cs)
(t'−t) (w + cs)
a
N
For example:-
W =
Let n = 20
17,500
parts by weight.
Then
c = 2,000
0.09515
t
4° C.
t'
13° C.
>>
(13—4). (17,500 + 2,000 × 0·09515)
20
·
7,960;
is the calorific value of the body under examination. Lavoisier, Dulong,
Despretz, and Grassi have investigated the calorific value of various
bodies, but the more recent researches on this subject have been made by
Favre and Silbermann, and by Andrews. The apparatus employed by the
later observers was, in principle, similar to that of Rumford, but was so
constructed as to afford more accurate results; and all necessary correc-
tions were made in the various calculations.
Calorific Power of Carbon. The more recent experiments on
carbon, in the different states of diamond, graphite, and charcoal, have
afforded results agreeing very closely with each other, and the discre-
pancy in the results of the earlier observers may be accounted for by
their having been ignorant that the combustion of carbon, even in
oxygen, always gives rise to the production of a certain amount of car-
bonic oxide. The incomplete oxidation of carbon, resulting in the pro-
duction of carbonic oxide, is attended with the evolution of much less
FUEL.
19
heat than is produced by its complete oxidation and conversion into
carbonic anhydride. As, during the combustion of carbon, a certain
amount of carbonic oxide is invariably produced, it becomes necessary to
determine with accuracy the quantity of this gas resulting from each
experiment. In order to do this, the products of combustion are first
passed through a solution of potassa, by which the CO2 is absorbed,
and subsequently through a tube containing cupric oxide heated to
redness. In this way the CO is converted into CO2, which is passed
through another solution of potassa and weighed. By these means not
only the relation between the quantities of CO and CO, may be deter-
mined, but the total amount of carbon consumed is also ascertained.
From the mean results of a considerable number of experiments 8,080 has
been decided on as the calorific power of carbon existing in the form of
purified wood charcoal.
Calorific Power of Carbonic Oxide.—In order to effect the perfect
combustion of carbonic oxide it is necessary to mix it with one-third of its
volume of hydrogen. To ascertain in each experiment the relative
proportion of the two gases, a portion of the mixture is passed over
heated cupric oxide, and the CO2 and H2O produced are estimated in
the usual way.
The mean of two experiments gave Favre and Silber-
mann 2,403 units of heat as the result of converting one gramme of CO
into CO2.
It follows, therefore, that the amount of CO, containing one gramme
of carbon will evolve 5,607 units of heat. One gramme of carbon has,
however, been found to evolve 8,080 units of heat in passing to the state
of CO2. Therefore one gramme of carbon, by conversion into CO, will
evolve (8,080–5,607)= 2,473 units. It is remarkable that carbon in
passing to the state of CO should evolve less than one-half the heat de-
veloped by its conversion into CO2; but this may probably be accounted
for by the large amount of heat rendered latent on the passage of carbon
from the solid to the gaseous state, in combining with the first atom of
oxygen. The great decrease of temperature which takes place when the
CO₂ formed before the tuyer of a blast furnace is reduced to CO by
means of glowing coal, has been explained by assuming that a chemical
solution and not a combustion of the second atom of carbon takes place.
In this instance, however, the reduction of temperature is to be ascribed
to the large quantity of heat rendered latent by the passage of carbon
into the gaseous state, as well as to the increase of volume experienced
by the products of combustion.
2
Calorific Power of Hydrogen.-From the mean of six determinations
Favre and Silbermann deduced 34,462 as the calorific power of hydro-
gen. In such experiments the weight of hydrogen consumed is calculated
from that of the water collected.
Berthier's Process for estimating the Calorific Power of Fuel.-On
the assumption of the correctness of Welter's theory that the heat
evolved by combustion is directly proportionate to the amount of oxygen
consumed, Berthier proposed to estimate the caloric power of fuel by
burning it into CO, by means of the oxygen contained in litharge, and to
C 2
20
ELEMENTS OF METALLURGY.
ascertain the amount of oxygen abstracted, from the weight of the button
of lead produced. In the case of pure carbon, or fuel consisting of
carbon without any mixture of other reducing agents, this process may
be employed with advantage, and is capable of affording accurate results.
But when hydrogen is present, which is nearly always the case, even
in coke and charcoal, the results obtained are no longer satisfactory ;
this will be evident from the following considerations: One part, by
weight, of hydrogen will reduce the same amount of plumbous oxide as
three parts by weight of carbon. The calorific powers of hydrogen and
carbon are, however, respectively 34,462 and 8,080, or, in round numbers,
as 34: 8. It consequently follows that the calorific power of 1 of
hydrogen as compared with that of 3 of carbon is as 34: 24; so that
the weight of lead which would in the case of hydrogen represent a
calorific power of 34, would in that of carbon be represented by 24 only.
It is, therefore, evident that this process is inapplicable to the exact
determination of the calorific powers of fuels containing variable quan-
tities of carbon and hydrogen. As, however, hydrogen in excess of the
quantity required to form water will alone have any reducing influence
on oxide of lead, the amount of error is less than might be anticipated.
Calculations based on Welter's theory, made on results obtained by
Berthier's method, cannot afford absolutely correct results; but they
deviate so little from the truth that this method, owing to its simplicity,
is still in use, and is of considerable practical value. The results are at
the very highest only one-ninth smaller than those found by calculation
on an analysis of the fuel, and the richer in carbon the substance is,
and the less CO that has, through a careful execution of the assay, been
formed during the experiment, the more nearly will they approximate to
the truth.
Berthier's process consists in heating a known weight of the substance
in fine powder, with a large excess of litharge, which, being de-oxidised
by the combustible constituents of the fuel, yields a button of lead pro-
portionate to the quantity of those substances present. Every atom of
oxygen abstracted from litharge will necessarily give rise to the pro-
duction of an atom of metallic lead, and, consequently, a tolerably
accurate measurement of the relative heating values of different kinds of
fuel is obtained by weighing the button of lead, produced under perfectly
similar circumstances, by a given weight of each variety. When, how-
ever, it is required to ascertain approximately what quantity of water
would be elevated from 0° to 100° C. by the combustion of a given
amount of any particular fuel, it is necessary to refer the results to the
known calorific value of some combustible substance. For this purpose,
carbon, which, according to Despretz, requires 2.666 times its weight of
oxygen for perfect combustion, is chosen. If this be abstracted from
litharge entirely free from the higher oxides of lead, each part of
carbon will afford about 34 parts of metallic lead; and if we admit, in
accordance with the results of the above-mentioned chemist, that the
same amount of carbon will elevate 78·15 parts of water from 0° to 100° C.,
it follows that each amount of lead, corresponding to an unity of carbon,
FUEL.
21
=
2.298
which may be reduced by any kind of fuel, corresponds to
parts of water raised by its combustion from 0° to 100° C.
One Gramme of each Substance.
CALORIFIC POWERS.
Supporter
of Com-
bustion.
Product
of Com-
bustion.
78.15
31
Number of
Grammes of
Water heated
Observers.
1° C.
Diamond
Graphite, native
""
artificial
Carbon from gas retort
Charcoal from wood
Oxygen
""
""
""
""
""
Carbonic oxide
Hydrogen gas
Sulphur, native.
""
•
in the state of flour
Phosphorus
Zinc
Iron
CO 2
""
""
7,770
7,811.5
7,787.5
Favre and Silbermann.
""
""
""
""
8,047.3
""
8,080
23
7,900
Andrews.
င်း
2 227
59
2,473
Favre and Silbermann.
""
H₂O
2,402.7
34,462
""
"9
""
""
19
33,808
""
SO₂
2
2,220.9
""
2,307
Andrews.
Favre and Silbermann.
Andrews.
35
P₂ 05
5,747
59
ZuO
1,301
""
99
""
Fe₂O₁
4,134
""
The following table, from 'Knapp's Technology,' gives Rumford's
results as obtained by his water calorimeter :-
One Pound of the following kinds of Wood,
when burnt, will heat
1. Limetree wood.
Dry wood, 4 years old
Pounds of Water
from 0° to 100° C.
34.707
38.833
""
""
""
""
slightly dried
strongly dried
•
40.131
•
2. Beech wood.
""
3. Elm wood.
Dry wood, 4 or 5 years old
strongly dried.
Wood dried, 4 or 5 years old
strongly dried
33.798
36.476
30.205
•
31.083
•
dried brown
""
4. Oak wood.
30.900
•
""
Common firewood, in small shavings.
The same, in thicker shavings
in thick shavings
>> dried in the air
Very dry wood, in thin shavings
26.272
25.590
•
24.748
•
29.210
•
29.838
thicker
do.
·
26.227
""
""
5. Ash wood.
Common dry wood
The same, dried in air, shavings
""
30.666
•
33.720
shavings dried in an oven
35.449
6. Sycamore wood.
Strongly dried in an oven
36.117
7. Wood of Mountain Ash.
Strongly dried in an oven
Dried brown
8. Wood of Bird Cherry.
Dried wood
Strongly dried in an oven
Dried brown
36.130
32.337
33.339
oven.
36.904
·
31.736
•
22
ELEMENTS OF METALLURGY.
One pound of the following kinds of Wood,
when burnt, will heat
Pounds of Water
from 0° to 100° C.
9. Fir wood (Deal).
Ordinary dry wood
30.332
Well dried in the air, shavings
34.000
in an oven, shavings.
37.379
""
brown, in shavings
33.358
9
in thick shavings
28.695
10. Poplar wood.
Wood, dried in the ordinary manner
34.601
"
strongly dried in an oven
37.161
11. Hornbeam.
Dried wood (ordinary)
31.704
The following table, from The First Report on Coals suited to the Steam
Navy, by De la Beche and Playfair, shows not only the effects actually
produced by several varieties of coal in a well-constructed steam boiler,
but also those theoretically possible, together with the relation existing
between the calorific effect of their various constituents:—

Number
of lbs. of
Water con-
Number
of lbs. of
Water con-
Name or Locality
of Coal.
vertible into vertible into
Steam from Steam from
100° C., by 100° C., by
the Coke the carbon
left by Coal. of Coal.
Number
(f lbs. of
Water con-
vertible into
Steam from
100° C., by
the hydrogen by 1 lb. of
of Coal.
Coal.
Total num-
ber of lbs
of Water
convertible
into Steam
from 100° C.,
Theoretical. Theoretical. Theoretical. Theoretical.
Actual
number of
lbs. of
Water con-
verted into
Steam from
100° C., by
1 lb. of Coal.
Percent-
age of
Coke left
by each
Coal.
Practical.
Welsh Coals:
Graigola
11.301 11.660 1.903
13.563
9.35
85.5
Anthracite
(Jones
and Aubrey)
12.554 12.563 2.030
14.593
9.46
92.9
Old Castle Fiery Vein
10.601
12.046 2.890
14.936
8.94
79.8
Ward's Fiery Vein
12.072
2.542
14.614
9.40
Binea
11.560
12.181
2.912
15.093
9.94
88.10
Llangennech
10.599
10.741 2.519
14.260
8.86
83.69
Pentrefelin
Powell's Duffryn
Mynydd Newydd
10.841 11.749 2.038
11.134 12.126
9.831 11.463
13.787
6.36
85.0
2.966
3.441
15.092
10.15
84.3
14.904
9.52
74.8
Three Quarter Rock
Vein.
7.081
Cwm Frood Rock Vein
8.628
10.325 2.781
11.300
13.106
8.84
62.5
3.488
14.788
8.70
68.8
Cwm Nanty Gros
8.243 10.767
3.165
13.932
8.42
65.6
Resolven
10.234
10.899
3.072
13.971
9.53
83.9
Pontypool
8.144 11.088 3.207
14.295
7.47
64.8
Bedwas.
8.897 11.075 3.766
14.841
9.79
71.7
Ebbw Vale
Porthmawr, RockVein
10.441 12.335 3.300
6.647 10.263 2.548
15.635
10.21
77.5
12.811
7.53
63.1
Coleshill
6.468
10.145
2.654
12.799
8.00
56.0
Scotch Coals:
Dalkeith Jewel Seam
6.239
10.242
2.071
12.313
7.08
49.8
Dalkeith Coronation
Seam.
6.924
10.570
2.202
12.772
7.71
53.5
Elgin Wallsend
6.560 10.454
2.968
13.422
8.46
58.45
Fordel Splint .
6.560
10.933 2.884
13.817
7.56
52.03
Grangemouth .
7.292
10.970 2.722
13.692
7.40
56.6
English:
Broomhill
7.711
11.225 3.638
14.863
7:30
59.2
Irish:
Slievardagh (Anthra-
cite) .
10.895
10.995 1.487
12.482
9.85
90.1
FUEL.
23
CALORIFIC INTENSITY OF FUEL.-By the pyrometric heating power, or
calorific intensity, of a fuel, is understood the degree of temperature
which may be obtained by its complete combustion. This depends not
only on its composition, but on various other circumstances, such as the
purity, dryness, and temperature of the air employed as a supporter of
combustion; the extent of the area of contact which the fuel offers to
the air in a unit of time; the greater or less pressure under which the
combustion takes place; the nature of the products; and the circumstances
under which they are formed, &c., &c. Loss of heat from conduction
and radiation likewise exerts a considerable influence on the practical
results. It is, therefore, evident that to be enabled to calculate the
calorific intensity of a fuel from its ultimate composition and the calo-
rific power of its constituents, it will be not only necessary to take into
consideration the nature of the resulting products, but also to introduce
a number of factors, which complicate the formulæ, and must, without
great care, become sources of error.
Scheerer has calculated the calorific intensity of various bodies from
formulæ based on heating powers as determined by Favre and Silbermann,
and others, on the relative density of the fuel, and the specific heat of the
products of combustion.
The following are examples of the results of his calculations on
heating powers :—
In Oxygen.
In Air.
Carbon burnt to CO₂
9,873° C.
2,453° C.
CO
Carbonic oxide
Hydrogen.
5,316° -7,090°
4,0730
1,310°
2,121° -2,828
2,080°
All calculations made on this subject so far agree with the result of
experience as to show that, practically, the temperature which a fuel is
capable of producing is directly proportionate to the amount of carbon it
contains.
Various methods have been devised for the measurement of very
elevated temperatures, but the indications of the earlier pyrometers
having been found inaccurate, they have generally fallen into disuse. A
method of measuring high temperatures, which may be sometimes found
convenient, is described by Mr. S. Wilson.* It consists in exposing a
given weight of platinum to the action of the heat to be measured, and
then rapidly transferring it to a vessel containing an ascertained weight of
water of known temperature; from the increase of temperature ex-
perienced by the water is calculated the calorific intensity to be measured.
Thus if a piece of platinum weigh 100 grammes, and the water 200
grammes, the temperature being 15.5° C., and the heated platinum,
when dropped into the water, raises its temperature to 32.2° C, then
32·2° — 15·5° – 16·7,° which multiplied by 2 (the weight of water being
* Philosophical Magazine,' ser. iv. vol. iv. p. 157.
་
24
ELEMENTS OF METALLURGY.
In
twice that of platinum) gives 33-4° as the temperature to which a weight
of water equal to that of the platinum would have been elevated.
order to ascertain the temperature to which the platinum has been
exposed, this must be multiplied by 324, the specific heat of water as
compared with platinum, that of the latter being represented by 1.
Therefore 33·4° × 32·4 = 1,082-16° C., which will be the temperature
required. When, however, it becomes necessary to determine the temper-
ature of the interior of a furnace, it is impossible to transfer the substance
heated to the water, in which it has to be cooled without the loss of a
certain amount of heat; and the result obtained must consequently be
to some extent incorrect. The electric pyrometer of Siemens, which
depends in its action on the influence of heat on the conductivity of a
platinum wire, and that employed by Schinz, which is a modification of
the thermo-electric pyrometer of the elder Becquerel, are said to
afford more satisfactory results. A description of these instruments
would, however, occupy more space than the limits of the present work
will, allow, and, consequently, those who feel interested in the subject of
the temperatures of blast-furnaces, and in the chemical and other
conditions influencing the combustion of fuels therein, will do well to
consult the recent works of Schinz and Bell, which are valuable additions
to the literature of this branch of metallurgical investigation.*
The terms ordinarily employed to indicate high temperatures, such as
red heat, white heat, &c., are very indefinite, since in judging of tempera-
ture by the eye, much must depend on the observer, and on the conditions
with regard to light under which the observations may be made.
Pouillet, who examined high degrees of temperature by means of an
air thermometer provided with a platinum bulb, arrived at the following
results:-
Incipient red corresponds to
Dull red
Incipient cherry-red
Cherry red
Clear cherry-red
White
525° C.
Dull orange
1100° C.
700°
Clear orange
1200°
800°
1300°
•
900°
Bright white
1400°
1000°
Dazzling white
1500° to 1600°
•
ANALYSIS OF FUEL, &C.
Fuels which possess the highest calorific powers are not in all cases
to be selected for practical purposes, as they may be subject to disadvan-
tages which more than counterbalance this property. It is therefore
necessary to ascertain by experiment what are the peculiar characteristics
of each, so as to be enabled to select from among a number, such as
may be most economically employed for the particular purposes to which
they are to be applied.
ESTIMATION OF ASH.-If the substance to be examined be a wood,
it should be first reduced to fine powder by means of a rasp, or if it
be friable, such as charcoal, pit-coal, or coke, it may be pounded in an
iron mortar.
* 'Researches on the Action of the Blast-furnace, by C. Schinz;' translated by
William H. Maw and Moritz Müller: Spon. Chemical Phenomena of Iron Smelt-
ing,' by I. Lowthian Bell: Spon.
FUEL.
25
A weighed portion (about 1 gramme) of the pulverised fuel is then
placed either in a platinum or porcelain crucible, and ignited over a gas
flame, until the whole of the combustible matter is consumed. The
residue is subsequently weighed, and from the amount left the per-
centage of incombustible matter present is estimated. In making this
experiment, much time will be saved by placing the crucible a little on
one side, and partially covering its mouth with the lid, for the purpose
of directing a current of air on the burning body. When the substance
to be examined is a caking coal, it is found advantageous not to break
the crust of coke which is first formed, but to allow the mass gradually
to consume from the exterior. If this be not attended to, and it should
contain much ash, small portions are frequently protected by a coating of
earthy matter, and escape complete combustion. In the case of coke it
is sometimes extremely difficult to consume the last portions of carbon,
but this may always be effected either by exposing the crucible and its
contents in an assay muffle, or by subjecting the substance, at a red heat,
to the action of oxygen gas.
The latter process is accomplished by placing a known weight of
pulverised coke in a porcelain crucible over a lamp, and when, from the
accumulation of ash, the combustion becomes sluggish, the vessel is closed
by a cover having a hole through its centre, and through this a current of
oxygen is conducted by a suitable tube, from a gas-holder in which it is
contained. The amount employed is regulated by a stop-cock, and too
rapid action is especially to be avoided.
HYGROMETRIC WATER.-The amount of water present is estimated by
drying a known quantity of the substance in a water or air bath, heated
to 100° C., until it ceases to lose weight. In accurate determinations,
all experiments should be repeated at least twice, as perfect reliance
never be placed in results when this precaution has not been
attended to.
can
SULPHUR.-The sulphur contained in a fuel is correctly deter-
mined by the following process. The substance to be examined is inti-
mately mixed with twice its weight of pure magnesium carbonate, and
placed in a bulb blown in the middle of a tube of hard glass. This is
strongly heated either by a spirit-lamp or gas-flame, at the same time
that a continuous current of oxygen gas is passed through it from an
apparatus attached for that purpose. When the whole of the carbona-
ceous matter has been completely consumed, which is easily perceived by
the whiteness of the mixture, the powder is thrown on a filter, and the
soluble magnesium sulphate washed through. The sulphuric acid in the
filtrate is then thrown down by barium chloride, and from the weight of
sulphate of barium obtained, the percentage amount of sulphur present in
the substance is deduced.
Calcium carbonate may for this purpose be employed instead of the
corresponding salt of magnesium, but as the calcium sulphate is less.
soluble than sulphate of magnesium, the washing on the filter requires to
be prolonged, and a longer time is necessary for the completion of this
operation than for that above described.
26
ELEMENTS OF METALLURGY.
The sulphur may also be more rapidly, but perhaps less correctly,
estimated by igniting in a platinum crucible a mixture of the substance
to be examined with three times its weight of nitre and four times that
quantity of pure carbonate of sodium. When this method is employed,
the fused mass which remains in the crucible is first dissolved in water,
and, after being filtered, is rendered acid by the addition of either nitric
or hydrochloric acid. The filtrate is then treated with a sufficient amount
of barium chloride as above described.
A paper was read by F. Crace Calvert at the Edinburgh meeting
(1871) of the British Association for the Advancement of Science, on the
estimation of sulphur in coal and coke. The sulphur found in coal or
coke often exists in two states, partly as sulphuric acid in sulphate of
calcium, and partly as sulphur combined with iron. The portion existing
as sulphate of calcium does not injure the quality of iron when used in
the production of that metal, as it remains associated with the calcium ;
whilst the portion existing as sulphide of iron greatly deteriorates its
commercial value as a fuel. To determine the amount of sulphur in the
former state, the author proposes to boil the pulverised coke or coal in a
solution of sodium carbonate, which decomposes the calcium sulphate or
calcium sulphide, and sulphur is estimated in the solution. In the
residue from the above operation is found the sulphur combined with iron.
After attacking with aqua regia, the author treats with carbonate of
sodium and heats to near the fusing point. By this means there can
be no formation of insoluble basic sulphate of iron, and the prevention of
precipitation by a salt of barium, stated to occur in liquids containing free
nitric acid, is avoided.
Carbon and HYDROGEN.-These constituents are estimated according
to methods employed for the analysis of organic substances; but the best
results are obtained when a quantity of matter not exceeding half a
gramme is operated on. Experience also shows that the combustion of
fuels is more completely effected by the use of cupric oxide than when
lead chromate is employed, and that whenever the substance burns with
difficulty, as in the case of coal, and more particularly of anthracite, it is
necessary, not only to use a long combustion-tube, but also a certain
portion of dry chlorate of potassium, which, after being mixed with cupric
oxide, is placed at the sealed end of the tube so as to give off oxygen
towards the close of the operation. Instead of using chlorate of potas-
sium, oxygen gas from a gas-holder may be passed through the tube.
NITROGEN.-The amount of nitrogen contained in a fuel cannot be
considered of much practical importance, and it may therefore, in most
instances, be included with the oxygen: if necessary, however, it can be
estimated as ammonia by the method of Will and Varrentrapp.*
OXYGEN. This element is invariably estimated by the loss on
analysis.
Dr. Percy calls attention, as follows, to certain sources of error in
* For directions relative to the analysis of organic substances see A System of
Instructions in Quantitative Chemical Analysis, by Dr. C. R. Fresenius, 4th ed.
p. 451.
Whet
FUEL.
27
analyses of coal:*"When coal contains much inorganic matter, especially
iron pyrites, the usual method of calculating its composition, from the
data obtained in the process of organic analysis, may be erroneous in a
sensible degree. The ashes left by incineration are estimated as inor-
ganic matter, and the proportion of oxygen is found by subtracting the
sum of the carbon, hydrogen, nitrogen, and ashes, from the amount of dry
coal subjected to analysis. By incineration the iron of the pyrites is con-
verted into sesquioxide, and the sulphur, in a greater or less degree, into
sulphuric acid, which may remain in combination with any base in the
ashes, such as lime, capable of forming a sulphate not decomposable at a
red heat. Supposing the whole of the sulphuric acid to be thus retained
in the ashes, for 1 part of iron pyrites there would be an increase of
1, due to oxygen derived from the air during incineration. The whole
amount of this error, provided no correction be made, would fall upon the
oxygen. It is not asserted that the whole of the sulphur is actually con-
verted into sulphuric acid and retained in the ashes, but that a consi-
derable portion of a stable sulphate may be produced during incineration.
will appear from analyses of coal in the sequel. It is certain that
the alumina in the ashes must in great measure exist in combination
with silica as clay, but clay holds water in combination which cannot
be expelled except at a temperature far more than sufficient to decompose
coal. Hence, during the process of organic analysis, water may be
evolved from the clay present in coal, and so occasion an error of
excess in the determination of the hydrogen. This source of error has
been pointed out by Regnault. Carbonate of lime is sometimes present
in coal in very appreciable quantity, in which case carbonic acid would
be evolved during the analysis, and so an error of excess would be caused
in the determination of the carbon. M. de Marsilly has observed, that
however pure a piece of coal may be, and however homogeneous it may
appear to the eye, its different parts do not yield the same proportion of
fixed residue by incineration; and the same is true in respect to the pro-
portion of coke obtained by the calcination of different fragments of the
same lump of coal. Hence, in every case, the proportion of ash and coke
should be determined by operating upon an average sample taken from
the powder of the coal.”
LITHARGE EXPERIMENTS.-In many cases, the calorific value of fuels
may be ascertained with sufficient accuracy without having recourse to an
elaborate analytical examination, and for this purpose the process employed
by Berthier is the most simple one.
The weight of substance operated on may be about half a gramme,
and great care should be taken to obtain it in the finest possible state of
division. If the substance be brittle, such as coal, coke, or charcoal, it is
easily pounded in a mortar, and afterwards sifted; but if it be a variety
of wood which is to be experimented on, the saw-dust obtained by cutting
it with a fine saw, or scratching with a file, should be employed. This
should, according to its supposed richness, be intimately mixed with from
20 to 30 grammes of litharge, and placed in an earthen assay crucible.
* Percy's 'Metallurgy;' Fuel, Copper, &c., p. 84.
28
ELEMENTS OF METALLURGY.
On this is placed from 14 to 15 grammes of pure litharge, and after the
whole has been shaken down, the crucible ought not to be more than half
full, in order to allow sufficient space for the intumescence of the mix-
ture when in a semi-fluid state. The crucible is now stopped by a cover,
which is luted with fire-clay for the purpose of preventing any frag-
ments of coke or reducing gases from the fire from vitiating the result,
and the whole is placed in an assay furnace already lighted, and in which
there is a supply of hot coke. Here it is gently heated during about
fifteen minutes, at the expiration of which time the contents will be in a
state of tranquil fusion. The crucible is now to be covered with coke, and
the draught increased by means of the damper, in order to cause the
whole of the reduced lead to collect in the form of a button at the bottom.
Care should likewise be taken to prevent any loss of metal by volatilisa-
tion, and a moderate temperature only should consequently be employed.
This will usually be effected in about ten minutes, and the crucible is then
withdrawn from the fire and slightly tapped against some hard body, to
throw down any globules which may remain suspended in the fused litharge.
After being allowed to get cold, the crucible is broken and the button of
lead extracted, and from its weight is estimated the calorific value of the
fuel. If the operation has been properly conducted, the button of lead
separates easily both from the crucible and from the melted litharge by
which it is surrounded; but in case of anything adhering to it, its
removal is readily effected by first hammering the button on an anvil, and
afterwards brushing off the small particles sticking to it, with a hard
brush. The results thus obtained from different experiments on the same
substance will be found to agree very closely with one another. But on
comparing the calorific value of a fuel, as obtained by the litharge pro-
cess, with that calculated from its ultimate analysis, the former is found
to be about one-ninth less than that obtained by the latter method. This
process, therefore, although not admitting of great accuracy, is sufficiently
exact for many practical purposes.
The exactitude of such determinations is sometimes also slightly in-
fluenced by the presence of iron pyrites and protosulphide of iron, both
of which exercise a reducing influence on the litharge similar to that pro-
duced by carbon and hydrogen. When heated with this substance, the
sulphur escapes in the form of sulphurous anhydride, whilst the iron
with which it was combined remains with the litharge in the state of
oxide. These reactions determine the reduction of a certain quantity
of metallic lead which interferes with the experiments and, to a certain
degree, vitiates the result.
With few exceptions the operations employed for the extraction of
metals from their ores require the aid of elevated temperatures, and con-
sequently it is important that the metallurgist should be acquainted with
the properties of the various kinds of fuel, and be thereby enabled to judge
under what conditions each may be most economically employed.
FUEL.
29
WOOD.
Wood consists essentially of organic tissue composed of carbon, hydro-
gen and oxygen, with a minute quantity of nitrogen, and a small proportion
of inorganic matter; in its ordinary state it contains large quantities of
water, which may be completely expelled at a temperature considerably
below that at which decomposition of the organic matter would take
place.
The elementary composition of the tissue of all wood is the same,
although various organic compounds with which it is associated may be
very different in trees of different species, e.g., fir trees contain turpen-
tine and oaks tannin. The value of wood as a fuel is almost entirely due
to its vascular tissue, since the associated organic compounds are usually
too small in quantity to afford calorific effects of any practical im-
portance.
The proportion of water differs in various kinds of woods, and is also
considerably affected by the season of the year at which the different
specimens may have been felled. When trees are cut during the winter
months, and therefore not in a state of active vegetation, the amount is
found to be less than if felled in summer when full of sap; and conse-
quently all woods (unless there be some special reason for not doing so)
should be cut during the colder portions of the year.
Some kinds of trees are cultivated, not only for the timber which they
yield, but also on account of the tannin contained in their bark; and such
species are usually cut during the flow of the sap, as they are at that
time more easily barked, and likewise contain a larger proportion of the
compound for the sake of which their bark is collected.
Small shoots and twigs yield a larger percentage of water than the
more solid stem; the difference is also very considerable in woods of
different botanical species, as may be observed by inspection of the fol-
lowing numbers given by Schübler and Hartig.
100 parts of freshly cut wood, from the
White Fir (P. abies) contain
Pine (P. sylvestr.)
Water.
Water
Hornbeam (Carp. betul.) contain
18.6
37.1
Willow (Sal. caprea).
26.0
39.7
Sycamore (Ac. pseudoplat.)
27.0
Red Beech (Fagus sylvat.) ·
39.7
·
Mountain ash (Pyrus aucupar.)
28.3
Alder (Betul. alnus)
41.6
•
•
Ash (Fraxin, excelsior)
28.7
Asp (Popul. tremula).
43.7
Birch (Betula alba)
30.8
Elm (Ulmus campestr.)
44.5
Wild service trce (Cratægus tormi-
nalis)
Red Fir (P. picea.)
45.2
·
32.3
Lime tree (Tilia europæa)
47.1
Oak (Querc. robur)
34.7
Italian Poplar (P. dilatat.)
48.2
Pedicle Oak (Q. pedunculata)
35.4
Larch (P. larix)
48.6
Horse-chestnut (Esculus hippocas-
White Poplar (P. alba)
50.6
tanum)
38.2
Black Poplar (P. nigra)
51.8
It follows that recently cut wood contains from one-fifth to one-half
its weight of water, which not only detracts from its value as a fuel in
the same proportion, but, from its escaping in the form of vapour, must,
moreover, carry off a part of the heat developed by the combustion of the
other constituents.
By exposure to the air green wood soon loses a portion of its water,
30
ELEMENTS OF METALLURGY.
but after a time ceases to diminish in weight, as a sort of equilibrium is
established between the hygroscopic power of the air and that of the
wood. When this occurs, no further drying is effected by continued ex-
posure, and its percentage of water will vary only within very narrow
limits, dependent on the dryness or humidity of the situation in which it
may be placed.
In this state wood is said to be air-dried, and the remaining portions
of moisture can only be expelled by the aid of heat, the last traces being
eliminated with extreme difficulty.
Rumford, who heated specimens of various kinds of air-dried woods
at a temperature of 136° C. until they ceased to lose weight, obtained the
following results :—
Oak wood lost
Elm
Beech
Maple
100 parts of
16.64
Fir wood lost
18.20
Birch
18.56
Lime
18.63
Poplar
17.53
19.38
•
18.79
•
19.55
Generally speaking, the wood employed for fuel is never thoroughly
dried, but retains from 15 to 25 per cent. of water, so that the driest
specimens seldom contain more than 85 per cent. of combustible matter.
Wood kept in a warm room for six months, still retains, according to
Winkler, 17 per cent. of water. Woods are usually divided into two
classes-hard and soft. This distinction is founded on their calorific
properties and on the facility with which they can be worked by edge-
tools.
The former, among which are numbered oak, beech, white and red
birch, elm, and alder, contain in the same bulk a larger proportion of
fibre, and have their vessels more closely packed than those of the softer
varieties, such as pine, fir, larch, lime, willow, and the various kinds of
poplar.
Trees which have grown in poor land and in exposed situations, are
supposed to produce harder and denser wood than individuals of the same
kind, which have been planted in more sheltered localities and in richer
soils. The specific gravity of wood depends in a great measure on its
structure; but as two specimens of the same tree can never be found per-
fectly homogeneous, the results obtained by experiment should rather be
considered as approximative than as representing the true density of the
wood examined. These variations of specific gravity will be also influ-
enced, to a certain extent, by the nature of the soil in which the tree
has grown, as on this will depend in a great measure the quantity and
character of the salts it contains.
From the air inclosed in their cavities, woods are in their ordinary
state generally lighter than the same bulk of water; but when reduced,
by rasping, to the state of fine powder, even the softest varieties are found
to possess a greater density than that liquid. By thus destroying the
pores and liberating the inclosed air, the specific gravity of the following
woods has been found to be-
·
Oak
Linc
•
1.27
1.13
|
Fir
Beech
•
1.16
1.29
FUEL.
31
In the following table are given the respective densities of different
kinds of wood in various states of dryness :-
SPECIFIC GRAVITY OF Different KINDS OF WOOD.

Variety of Wood.
1.
Recently
Felled.
2.
Dried in
3.
Air.
Strongly
Dried.
Birch (Betula alba)
Common Oak (Quercus robur)
1·0754
0.7075
0.663
Pedicle Oak (Q. pedunculata)
1.0494
0.6777
0.663
White Willow (Salix alba)
0.9859
0.4873
0.457
Beech (Fagus sylvatica)
0.9822
0.5907
0.560
Elm (Ulmus campestris)
0.9476
0.5474
0.518
Hornbeam (Carpinus betulus)
0.9452
0.7695
0.691
Larch (Pinus larix).
0.9205
0.4735
0.441
Pine (Pinus sylvestris)
0.9121
0.5502
0.485
Sycamore (Acer pseudoplatanus)
0.9036
0-6592
0.618
Ash (Fraxinus excelsior)
0.9036
0.6440
0.619
0.9012
0.6274
0.598
0.8993
0.6440
0.552
0.8941
0.5550
0.493
0.8699
0.4716
0.434
0.8633
0·5910
0.549
0.8614
0.5749
0.8571
0.5001
0.443
•
0.8170
0.4390
0.431
0.7795
0.3656
0.346
0.7654
0.4302
0.418
0.7634
0.3931
1.2260
•
Mountain Ash (Pyrus auruparia)
Fir (Pinus abies)
Silver Fir (Pinus picea)
Wild Service (Crataegus torminalis)
Horse-chestnut (Esculus hippocastanum)
Alder (Betula alnus)
Lime (Tilia europæa)
Black Poplar (Populus nigra)
Asp (Populus tremula)
Italian Poplar (Populus dilatata)
Ebony
Columns 1 and 2 give the densities determined by Hartig, and column
3 the results obtained by Winkler, who weighed a cubic inch of each
kind of wood.
Wood not only loses weight by exposure to air, but at the same time
decreases in bulk; and in some varieties this takes place to the extent of
one-tenth of its original volume.
By long immersion in water, the soluble and extractive matters con-
tained in woods are dissolved, and therefore the method of transporting it
by rafts, as practised in some countries, is not only found to lessen
its weight, but also to reduce its calorific powers; consequently the
advantages of cheap transport are to some extent counterbalanced by the
inferiority of the wood so conveyed.
The analysis of different kinds of wood yields results differing little
from one another; but in all the varieties yet examined there is a slight
excess of hydrogen over oxygen, although in pure woody fibre they are
combined in such proportion as, by their union, to form water.
The following table, compiled from the results of Petersen and
Schödler, and from those of Heintz, gives the elementary composition of
different varieties of dry wood. The specimens analysed were in each
case taken from the trunk. Dr. Percy, who gives these and numerous
other analyses of wood, calls attention to the fact that a minute amount
of error must exist in all of them, from the presence of a small
32
ELEMENTS OF METALLURGY.
quantity of CO₂ in the ashes; but remarks that it cannot exceed 0.2 per
cent.*
2
ELEMENTARY COMPOSITION OF DRY WOODS.

Exclusive of Ash.
Name of Tree.
C.
H.
0.
N.
Oak
48.94
5.94 43.09
2.03
Beech
Birch
48 29
6.00
45.14
0.57
48.89
6.19
43 93
.
0.99
Hornbeam
48 08
6.12
41.93 0.87
Alder
48.63
5.94
44.75
0.68
Ash
49 36
6.08
44.56
Horse-chestnut
49.08
6.71
44 21
•
Black Poplar
49.70
6.31
43.99
•
Lime
49.41
6.86 43.73
•
Scotch Fir, Old
Spruce Fir
Walnut
Mean
•
49.87 6.09 43.41 0.63
Young
50.62 6.27 42.58 0.53
49.95 6.40 43.65
49.12 6.44 44.44

49.22 6.25 44.02 0.90
The nature and amount of ash left by the combustion of the various
kinds of wood, depend, not only on the species of tree examined, but are
also, to a certain degree, influenced by the nature of the soil on which it
has been produced, as the different inorganic substances which enter into
the composition of plants seem to have, to some extent, the power of
replacing one another in the same way that one substance may be sub-
stituted for another without affecting the form of a crystalline body.
Generally speaking, the ash of wood contains potassium, sodium, mag-
nesium, and iron as carbonates, silicates, sulphates, phosphates, and chlo-
rides.
The following table gives the amount of ash remaining after the com-
bustion of different varieties of wood :
Percentage
Percentage
of Ash.
of Ash.
Fir
Birch
0.83
Elder Tree
1.64
•
1.00
Arbre de Judée
1.70
•
·
•
•
False Ebony
Hazel.
1.25
Lime Tree
1.45
·
•
1.57
•
Oak (branches)
2.50
White Mulberry
1.60
·
•
Oak (bark).
6.00
Saint Lucia.
1.60
The different parts of the same tree do not yield equal proportions of
incombustible matter; the bark and leaves always produce a larger
amount than the branches, whilst the brauches leave more than the
trunk. Woody plants generally yield less than herbaceous ones, which
are also remarkable for containing a larger proportion of silica than is
usually met with in wood.
The published analyses of the ashes of wood are for the most part
* Percy's 'Metallurgy;' Fuel, Copper, &c., p. 65.
FUEL.
33
either imperfect or otherwise unsatisfactory; the following, made by
Böttinger under the direction of Will, appear to be among the most
complete and reliable. In these analyses the calculations have been
made after deduction of the CO2, and charcoal resulting from imperfect
incineration.*
COMPOSITION OF THE ASHES OF WOOD.
1.
2.
4
3.
4.
K₂O
Na₂O
15.80
2.76
CaO
60.35
MgO
11.28
2.79 0.93 15.24
15.99 14.59 7.27
30.36 33.99 25.85
19.76 20.00 24.50
Mn304
18.17 7.61 13.51
Fe₂0, P20, or (Fe"" PO.)
1.84
5.10
2.28
6.18
Fe3O4
7.73
3 ČaỔ, P₂O, or Ca”, (PO,)½
Ca";
3.99
CaSO
2.30
3.31 5.05
2.91
4
NaCl
0.21
1.48 2.52 0.92
SiO2
1.46
3.04 5.27 3.60
•
D
99.99
100.00 99.97 99.98
No. 1, Beech from Switzerland; Nos. 2 and 3, Scotch fir, from the
neighbourhood of Giessen, near which are mines of manganese; ash
No. 2 from a diseased tree, and No. 3 from one that had died; No. 4,
Larch from the same locality as Nos. 2 and 3.
PEAT OR TURF.
In low and moist situations, where water collects and cannot readily
flow off, and in which the loss by evaporation is inconsiderable, large
swamps or moors are formed, and in these marsh-plants of all kinds,
such as sedges, rushes, reeds, mosses, confervæ, and even small shrubs,
grow with great rapidity, and quickly cover the surface with a thick layer
of vegetation. In winter these die, and are, on the return of spring,
themselves covered by another crop of similar plants. These changes
go on from year to year, and finally the ground becomes covered by a
thick layer of vegetable matter in a loose state of aggregation. After a
time, decomposition takes place in the mass, carbonic anhydride and
marsh-gas, together with small quantities of sulphuretted hydrogen (pro-
duced by the reduction of sulphates), are evolved, and finally the whole
attains a considerable density and becomes of a dark earthy colour.
This substance is called peat, and is in many places extensively
employed as fuel. There are but few localities in which small quantities
of this substance are not found; but in some countries, such as Holland
and North Germany, such formations extend over districts of immense
extent, and annually furnish large amounts of fuel.
Sometimes different deposits appear to have taken place at succes-
sive periods; and in this case they are generally divided into parallel
*Annalen der Chemie und Pharmacie,' 50, p. 406. 1844.
D
34
ELEMENTS OF METALLURGY.
horizontal strata by layers of earth or sand of various thicknesses. The
beds nearest the surface are for the most part less compact, and of
a lighter colour, than those found deeper in the series, and are made
up of the roots and stems of plants, which although more or less
decomposed, still retain their original forms.
This porous spongy substance is called turf, and usually becomes
of a darker colour and greater density as its depth increases; finally, it
loses all outward traces of its vegetable origin, and is transformed into
the dark substance called peat.
Peat is turf so far decomposed that but few traces of its original organic
structure remain, and of which the fracture has become compact, and in
some instances even resinous. Its density is also greater than that of
the more recent variety, of which a cubic foot only weighs from four to
six pounds, while the weight of the same bulk of ordinary peat varies
from twelve to twenty pounds.
The cutting of peat is a simple operation. After having laid bare
the surface, the peat is cut by square-pointed shovels into the shape of
rectangular blocks, which are usually dried in the sun, and subsequently
stacked, to be employed as fuel. In some instances the surface of the
ground is covered with water, which, from want of drainage, cannot
be drawn off; in such cases peat is collected by means of an instru-
ment resembling a square-pointed shovel provided with an edge turned
up at right angles for the purpose of affording a hold for the block
after its separation from the mass. To use this tool, a man stands
on a stage raised a little above the surface of the water, and having
thrust the instrument into the peat, withdraws it, together with a square
prism of the combustible, attached by adhesion to its two sides. When
the depth of the water is more considerable, a larger instrument is em-
ployed, which is worked by two men, and provided with a spring for
holding the detached prism with sufficient firmness to allow of its being
drawn to the surface, where the spring is released and the charge
withdrawn.
These are
In Holland and elsewhere, when peat has become too spongy to be
further extracted by the method above described, and has become reduced
to the state of black mud, it is obtained by the use of a sort of dredge,
made of a sharp steel hoop, to which is attached a bag of close network,
which allows the water to flow through, but retains the particles of
peaty matter scraped from below the surface of the water.
allowed to drain in wooden troughs, of which the bottoms are covered
with straw, and in which numerous holes are bored for the purpose of
allowing the escape of water. When the mass has thus attained a
certain consistence, it is trodden down by persons wearing on their feet
large pieces of wood, like snow-shoes, to prevent their sinking into it,
and, when sufficiently firm to resist the pressure of the foot, it is beaten
with a beater of peculiar construction until nearly all the water has been
expelled. It is now cut into blocks not unlike bricks, and stacked under
proper sheds, so as to allow currents of air to pass between the different
layers, and thereby facilitate the drying of the blocks.
FUEL.
35
The amount of water contained in air-dried peat varies considerably,
but is usually from 15 to 20 per cent.; at 120° C. it begins to suffer de-
composition, and when heated to 250° C., not unfrequently ignites. The
specific gravity of uncompressed peat varies from 0-25 to 1.058.
ELEMENTARY COMPOSITION OF DRY PEAT.

Exclusive of Ash.
Locality.
Analysts.
C.
H.
0. & N.
Cappoge, Ireland
Kilbeggan
52.38
62.18 6.79
7.03
40.59
31.03 Kane.
""
Kilbaha
55.62 6.88
37.50
99
Vulcaire, France
60.40 5.95
33.65
Long
60.90 6.22
""
Champ-du-Feu
61.05 6.45
32 88 Regnault.
32.50
""
Mean
58.75 6.56
34.69
The ashes which remain after burning peat are partially due to the
salts originally contained in the plants from which it derived its origin;
but by far the largest proportion arises from earthy matters subsequently
deposited from the water which so frequently covers the surface of the
moors on which it is produced.
The composition of the ashes of peat will necessarily be influenced
to a great extent by the nature of the soil of the neighbourhood in which
it is formed, as the water descending from higher grounds during heavy
rains will always carry with it, in suspension, small particles which are
deposited in the form of sand or mud on reaching the lower lands. In
fact, it is constantly observed that the ashes of peat from a calcareous
district will contain large quantities of lime, whilst a specimen which has
been formed amongst hills of plutonic origin yields an ash in which
siliceous material predominates.
e
In 100 parts of peat + following quantities of ash have been
observed:-
•
Variety of Peat.
Grass Peat, brownish yellow
•
Pitch Peat, from Clermont
Herbaceous, from Burgundy
Brown and herbaceous, from Troyes
Very old Peat, from Vulcaire, near Abbeville
"9
Long
Not so old, from Champ-du-Feu, Vosges
Near Berlin, 1st stage
""
""
2nd
3rd
""
""
Moor in Eichsfeld," 1st sort
""
2nd
""
""
3rd
4th
""
Yellowish-brown, from Dartmoor
Ash.
Observers.
17.30
26.00
Berthier.
7.10
16.00
5.88
•
4.61
Regnault.
5.35
9.30
10.20
Achard.
11.20
21.50
23.0
Buchholz.
30.5
•
33.0
13.43
J. A. Phillips.
D 2
36
ELEMENTS OF METALLURGY.
Peat can only be advantageously employed by the metallurgist in
localities where other fuels are scarce and expensive; the great space
which it occupies, the large percentage of moisture retained by air-dried.
peat, the difficulty of drying the requisite quantities, and the amount of
ash resulting from its combustion, present obstacles to its general use
which are not readily overcome. Various processes have, in different
localities, been employed to improve the quality of peat as a fuel, but, up
to the present time, none of them appear to have afforded results that
can be regarded as entirely satisfactory. In some cases the blocks,
after being partially dried by exposure to sun and air on the surface
of the ground, are stacked in hollow piles, and finally placed in kilns,
through which currents of heated air are conducted. In others the peat
is first worked up into a pulpy mass in pug-mills, and then moulded by
machinery into blocks, which are afterwards kiln-dried. By these means
the quality of the fuel can be materially improved, but the cost of
labour and machinery is so considerable, that the product cannot, under
ordinary circumstances, compete with other varieties of fuel. It is,
however, probable that the increasing price of coal may, ere long, lead
to the discovery of some means by which the large amount of combustible
matter locked up in the peat beds of this and other countries, may be
rendered more extensively available.
The following analyses of the ashes of peat have been selected from
a series of twenty-seven made, under the direction of Sir Robert Kane,
in the laboratory of the Museum of Irish Industry.
ΚΟ
Na₂O
CaO
MgO
A1203
Fe2O3
P2O5
SO 3
HCI
·
COMPOSITION OF THE ASHES OF PEAT.


1.
2.
3.
4.
0.362
0.641
0.744
1.667
1.427
1.875
0.704
2.823
26.113
22.702
40.623
20.907
3.392
6.809
4.352
5.252
4.180
1·109
1.671
2.034
•
•
11.591
29.854
10.368
17.040
•
1.461
2.019
1.114
1.447
·
12.403
16.381
24.208
23.375
•
1.568
1.591
1.052
1.424
0.980
0.737
6.317
6.634
22.519
14.505
3 710
10.682
13 695
1.470
4.981
6.721
99.691
99.693
99.844
100·006
SiO2, in compounds decompos-
able by acids
Sand and Silicates undecompos-
able by acids
CO₂
1. Light spongy surface peat, of a reddish-brown colour and com-
posed almost entirely of Sphagnum, pieces of which are still distinguish-
able; from near Monastrevin.
2. Good compact peat, of a blackish-brown colour, consisting prin-
FUEL.
37
cipally of moss, with a number of Erica and grass roots, with Carex. This
peat, which is used as fuel in Dublin, is from Riversdale bog, near
Kimegad.
3. An exceedingly dense peat, with a conchoidal earthy fracture;
from Athlone bog. Vegetable structure almost obliterated, but, when
apparent, indicates remains of Carex, grasses, and Erica in abundance.
4. A rather dense peat, of a blackish-brown colour, in which the
structure of moss is no longer visible, but abounding in remains of Carex,
grasses, and roots and stems of Erica; from the Curragh or Clombourne
bogs, near Shannon Bridge.
2
In almost every case the amount of CO₂ found was considerably less
than that required for the formation of calcium carbonate, after ad-
mitting the whole of the sulphuric acid to exist as calcium sulphate.
This was supposed to have been caused by the expulsion of CO₂ during
the process of incineration. Regnault, however, has satisfied himself
that the whole of the calcium present in peat does not exist as carbonate,
but as forming part of various organic compounds.
The following analyses of the ashes of American peat are given by
Professor Johnson :- *
COMPOSITION OF THE ASHES OF TEAT-AMERICAN.
1.
2.
3.
K₂O
0.69
0.80
3.46
Na₂O
0.58
trace
Cao
40.52 35.59
6.60
MgO
6.06
4.92
1.05
3
Fe₂O, and A1203
5.17
9.08
15.59
P₂05
0.50
0.77
1.55
SO3
5.52
10.41
4.04
Cl
0.15
0.43
0.70
SiO 2,
soluble
S.23
1.40
CO₂
Sand
19.60
22.28
67.01
·
12.11 15.04
•
•
99.13 100.72 100.00
The specimens of peat affording the ashes analysed were obtained
from three different localities in Connecticut. 1. From Poquonnock;
analysed by Professor G. F. Barker. 2. From Colebrooke; by Mr. O.
C. Sparrow. 3. From Guildford; analysed by Mr. Peter Collier.
Karsten states that peat sometimes contains iron pyrites in sufficient
quantity to admit of its being employed for the manufacture of green
vitriol. In a deposit of peat occurring near Moel-Hafod-Owen, North
Wales, copper was some years since found in sufficient quantities to repay
the expenses of working it for that metal. For this purpose the peat was
* 'Peat and its Uses as Fertilizer and Fuel,' by S. W. Johnson, M.A., p. 47.
New York.
38
ELEMENTS OF METALLURGY.
burnt in kilns, and the ashes subsequently collected for smelting. At
this time the whole of the cupreous peat has been removed, but the water,
which sometimes collects in pools on the present surface, is often slightly
tinged with green from the presence of salts of copper. These are pro-
bably derived from the drainage of a large vein, principally composed
of arsenical pyrites, which passes through the hill at the bottom of which
the peat was found, and which contains a certain amount of copper.
COAL.
Coals constitute an important family which embraces lignite or brown
coal, common or bituminous coal, and anthracite. The chief constituent of
coal is carbon, in chemical combination with varying proportions of
hydrogen, oxygen, and nitrogen; all coals contain a greater or less
amount of earthy impurity, which, being incombustible, remains, after
burning, in the form of ash. From their composition, internal struc-
ture, and other characteristics, there can be no doubt of the vegetable
origin of coals; whether occurring as lignite, in which the ligneous
structure is still apparent, or as common coal or anthracite, in which,
for the most part, mineralisation has so far advanced that every external
trace of their organic derivation has been obliterated. We have satis-
factory evidence that coal in all its species is merely mineralised vege-
tation, which, in part, grew and was submerged, in situ, as peat-mosses,
cyprus-swamps, jungles, forest-growths, &c., and, in part, was drifted by
rivers to seas or basins of deposit. The operations of nature being
uniform and incessant, we have coals of all periods,-peats of the current
epoch, lignites of the Tertiary, &c., bituminous coals of the Carbon-
iferous, anthracites and graphites of the Devonian and Silurian ; the
products differing from one another according to the amount of metamor-
phism to which they may have been severally subjected. The available
coal of Great Britain is of Carboniferous age, but many excellent coal-
fields in India, America, and elsewhere, belong to the Jurassic and
Cretaceous periods, while anthracite and graphite belong to various
epochs. Coals are sometimes so free from earthy matter as to have less
than one per cent. of ash, whilst others are so impure as to be unfit for
fuel, and thus pass into more or less bituminous shales.
The formation of the different varieties of coal by the decomposition
of woody tissue may be explained by the gradual elimination of
hydrogen and carbon as marsh-gas, of oxygen and carbon as carbonic
anhydride, and of oxygen and hydrogen in the form of water. That the
transformation of woody tissue into coal has been accompanied by the
production of marsh-gas may be inferred from the composition of the
fire-damp of coal mines, of which this gas is the chief constituent. It is
not difficult to select from analyses of coals a series illustrating the
gradual passage of woody tissue into anthracite ; a coal consisting almost
exclusively of carbon. The following table, arranged by Dr. Percy,
gives the variable amounts of hydrogen and oxygen contained in different
FUEL.
39
kinds of fuel; the amount of carbon in each case being represented by
a constant quantity.*
Wood (mean of twenty-six analyses)
Peat
Lignite (average of fifteen varieties)
Ten Yard Coal, South Staffordshire
Steam Coal from the Tyne
Pentrefelin Coal, South Wales
Anthracite, Pennsylvania, U. S.
C.
H.
0.
100
12.18
83.07
•
100
9.85
55.67
100
8.37
42.42
100
6.12
21.23
•
100
5.91
18.32
100
4.75
5.28
100
2.84
1.74
It will be observed that through the various stages of conversion the
relative proportions of hydrogen and oxygen gradually decrease.
Nitrogen is present in coal in small proportions (from 1 to 2 per
cent.), and although it does not appear to be an essential constituent of
woody fibre, yet all woods contain albumen, and other nitrogenous
matter, which will readily account for the presence of this element in the
different varieties of fossil fuel.
Sulphur is always present in coal, in which it chiefly exists in the
form of iron pyrites; it may also occur as calcium sulphate, and probably
also combined with the organic elements of coal. Coal always contains
a certain proportion of water, which may be expelled at a tempera-
ture slightly above 100° C. Whether the whole of this exists in the state
of hygroscopic water, or whether, in some cases, a portion of it may not
be present in a state of combination, has not been determined. A coal
may appear to be perfectly dry, and yet lose a large percentage of water
by desiccation.
A sensible amount of inorganic matter is contained in all coal; its
constituents are chiefly silica, alumina, lime, and oxide of iron, which
are, in part, derived from the plants from which the coal was produced,
and partly from the percolation of waters holding these substances
either in suspension or solution. These substances constitute the ashes
which are left by coal when burnt, and its value as a fuel is considerably
influenced, not only by the amount of its ashes, but also by their compo-
sition. Iron pyrites in coal is represented in the ash by an equivalent
amount of ferric oxide, which, when present in large proportion, has
the effect of rendering it fusible and causing it to form clinkers which
adhere firmly to the furnace-bars. The distinction between red and white
ash coals is mainly dependent on the amount of pyrites which they respec-
tively contain. Daubrée has detected arsenic in the Tertiary lignite of
Lobsann, Lower Rhine; and galena, copper pyrites, and micaceous iron
ore are sometimes met with in this country in coals of Carboniferous
age.
.
LIGNITE OR BROWN COAL.-Lignites are composed of fossil plants
more or less completely mineralised and converted into coal; they have
* Percy's 'Metallurgy;' Fuel, Copper, &c., p. 81.
40
ELEMENTS OF METALLURGY.
usually a dull dark brown appearance, compact or laminated, and gene-
rally reveal the texture of wood. When burnt they afford a dull flame,
and evolve much smoke; are poorer in carbon than ordinary coal; their
heating power is less, and, in the majority of cases, they contain a large
amount of ash. Beds of lignite sometimes occur in the New Red Sand-
stone, Oolite, and Cretaceous formations, but chiefly in the Tertiary.
Lignites present a great variety of aspects; some, being almost as hard
as true coal, are known as "stone-coal;" others, being distinctly woody,
are known as “wood coal;"´some, again, consisting of thin layers like
compressed leaves, are called "paper coal;" whilst soft earthy varieties
have received the name of "peat coal."
It thus passes through every gradation of texture from that of the
more compact peats of the present day to that of the bituminous coals
of the older formations. The well-known lignites, or brown coals, of the
continent of Europe are chiefly of Tertiary age, and, from the leaves,
fruit, and stems of palms, &c., which they contain, give evidence of a more
genial climate in these latitudes during that period.
According to Frémy lignites may be distinguished from mere wood
and peat, on the one hand, by their complete solubility in nitric acid and
hypochlorites, and from true coal, on the other, which is insoluble in
hypochlorites, and is only slowly attacked by nitric acid.
The table on the opposite page shows the percentage composition of
different varieties of lignite.
No. 1. Brown; structure fibrous and lamellar; becomes rotten by
immersion in water; does not soil the fingers; coke has a semi-metallic
lustre; does not swell, and cakes but slightly; ash bulky and red;
copper and lead were detected in this coal; on burning, it evolves an
extremely offensive odour; analysed by F. Vaux. 2. Black-brown. This
coal, after being dried, absorbed from the atmosphere 12.7 per cent. of
water in twenty-four hours. 3. Black-brown, with woody structure.
The dry coal absorbed from the atmosphere 15.9 per cent. of water
in twenty-four hours. 2, 3. Analysed by Schrötter. 4, 5. Brown
coal from Prussia; 4, presenting wood-like structure, ash reddish-white;
5, earthy, ash yellowish-brown. The specific gravity and water were
determined on coal fresh from the workings; analysed by F. Bischof.
6. Brown coal; by Baer. 7. Brown coal; analysed by Liebig. 8. Brown
coal; by L. Gmelin. 9. Occurs at a short distance from the sea at
Goneza, province of Iglesias, west of Cagliari; probably belongs to
the true coal-measures; analysed at the École des Mines, Paris.
10, 11. Brought by Dr. Hector from La Roche Percée, Saskatchewan
Plains. 10. Dark brown; compact, in part wood-like, and in part re-
sembling coal from the coal-measures; fracture more or less conchoidal.
11. Cracked into small pieces by exposure to the air; in appearance
much resembling coal from the coal-measures. 12, 13. Collected by Mr.
G. P. Wall in the Island of Trinidad. 12. Black; fracture dull; powder
brown; does not cake when heated in a close vessel; yields 43.15 per
cent. of a non-coherent coke. 13. Black; bright, like good bituminous
coal; when heated evolves an odour resembling that of petroleum.
FUEL.
41
COMPOSITION OF LIGNITES, DRIED AT 100° C. OR UPWARDS.
Exclusive of Sulphur and
Ash.*
No.
Locality.
Specific
Gravity.
C.
H.
0.
N.
S.
Ash.
Water % Coke %
C.
H.
O, in-
clusive
of N.
1
Bovey, Devonshire
1.13 66 31
5.63 22.86 0.57
2.36
2.27
34.66 30.79
69.94
5.95
24.11†.
2 Thallern, Austria
1.41
49.58
3.84 22.68
4.56
19.34 22.53
63.70
65.15
5.05 29.80
3 Gloggnitz
1.36
57.71
4.49 22.14
3.12 12.54 25.15 54.40 68.42
5.33 26.25
:
""
4
Riestedt, Prussia
5 Loderburg
Wittenburg-on-the-Oder
""
1.21 61.13 5.09 31.95
1.22 55.30 4.90 31.95
64.07 5.03 27.55
1.83 31.66
62.27
5.18 32.55
:
:
:
:
6
7
Hesse Cassel
62.60
5.02
26.52
:
66.49 5.33 28.18
8
Sipplingen, Lake Constance.
64.96 3.48 31.56
9
Island of Sardinia
..
10
British North America.
11
Prairies East of Rocky Mountains
12
Island of Trinidad
13
""
""
14
Auckland, New Zealand
15
Tasmania
59.98 4.75 29.42
65.64 4.24 21.97
59.18 3.79 16.85
75.63 5.20 13.57
73.11 5.63 17.08
64.70
69.14
0.49 18.64 14.50
2.96
63.71 5.05 31.24
71.46 4.62 23.92†|
74.14 4.75 21.11†|
2.64 20.50
80.12
5.51 14.37
0.57 3.61 5.90
76.30
5.87 17.83
4.81 18.25 1.34
5.40 18.48 1.26
0.42
10.48 14.12
73.72
5.48 20.80†
0.35
5.37 13.43
74.33
5.80 19.87+
* Except where the amount of sulphur is not given in the eighth column.
† Exclusive of nitrogen.
:
:
:
:
:
7.85 49.50
3.35
5.86
5.50
5.85
17.26
:
0.93 0.70 6.52 13.92
1.05
50.00
60.01
5.31 34.68
:
:
66.29
5.20 28.51



42
ELEMENTS OF METALLURGY.
14. Black; lustre dull; fracture uneven, more or less conchoidal; cleav-
age distinct; more or less translucent. A brown resin occurs, diffused
through this lignite, in pieces varying from the size of a pea to consider-
able masses. 15. In physical characters this lignite is similar to that last
described, and containing resin distributed throughout its substance.
Accompanying the specimen forwarded was a piece of resin as large as
the fist, which was more opaque and less resembling ordinary amber
than that contained in the lignite from New Zealand. The analyses
10-15, both inclusive, were made by Mr. C. Tookey, under the direc-
tion of Dr. Percy. The mode of rendering the results has, in some
cases, been slightly changed, by calculation, in order to adapt them to
the general headings of the table.
The following analyses of the ashes of lignite will be sufficient to
give an idea of their general composition:-
1.
2.
SiO2
45.13 19.27*
Fe2O3
25.83 5.78
A1203
22.47 11.57
CaO
2.80 23.67
MgO
0.52 2.58
K₂0
0.60
1.74
NagO
0.28
SO 3
CO₂
2.37 33.83
⚫90
100.00 99.34
1. From Zwickau, Saxony; analysed by Kremers. 2. From Bruns-
wick; analysed by Varrentrapp. The term lignite is frequently em-
ployed as synonymous with coal occurring in deposits of later date than
the true coal-measures.
The coals of the Monte Diablo district, California, are of Upper Cre-
taceous age, as are also those of Bellingham Bay and Naniamo, Van-
couver. These coals are extensively used on the Pacific coast, and, like
all others of a later geological period than the Carboniferous, contain a
considerable proportion of hygroscopic water. Exposed to the action of
a dry atmosphere they part with their moisture but slowly, and, in
doing so, are liable to become disintegrated. This defect is, however
characteristic of certain American coals of Carboniferous age; the per-
centage of water in some of the Iowa coals being as great as in those
of Monte Diablo. In other respects these Cretaceous coals closely
resemble the highly bituminous varieties from the true coal-measures.
The following proximate analyses of varions Cretaceous coals, in use
on the Pacific coast, are given by Prof. J. D. Whitney, who remarks that
those of the Monte Diablo coals were made very shortly after the first
opening of the mines, and consequently an improvement in quality might
be expected at greater depths.†
* Residue insoluble in acids.
† 'Geological Survey of California,' p. 30.
FUEL.
43
PROXIMATE COMPOSITION OF CRETACEOUS COALS.

Monte Diablo.
Clark & Co.
Black
Diamond.
Bellingham
Bay,
Washington Vancouver.
Naniamo,
Cumberland.
Territory.
Water
13.47
14.69
13.84
8.39
2.98
•
Bituminous substances
40.36
33.89
40.27
33.26
32.16
Fixed carbon
40.65
46.84
44.92
45.69
46.31
•
Ash
5.52
4.58
0.97
12.66
18.55
•
BITUMINOUS COAL. This term is usually applied to coals from the
coal-measures; these burn with a more or less smoky flame, like that of
bitumen, although the presence of this mineral cannot be detected in
ordinary bituminous coal. Coals of this description are brittle and
opaque, with a lustre varying from dull to shining; colour, under ordi-
nary circumstances, black, or brownish-black; when in fine powder
brown-black, or brown; fracture uneven or conchoidal, the fragments
often present more or less cubical or rhombic forms; consist of carbon,
hydrogen, oxygen, nitrogen, and sulphur, with variable amounts of in-
organic matter or ash. When heated in a close vessel they leave a solid
carbonaceous residuum termed coke. Bituminous coals are divided into
various classes in accordance with their peculiar chemical and physical
properties, and their applicability to various specific uses. Many of these
distinctions are merely local, or are dependent on comparatively slight
peculiarities, but the general classification into caking or coking coals,
on the one hand, and free-burning coals, on the other, is both definite and
of great practical importance. Between these two extremes are numerous
sub-varieties, which have, in different localities, received names indicative
of their greater or less similarity to one or other of the types.
When caking coals are strongly heated they become partially fused,
and, when in a pasty state, swell into a spongy mass, giving off bubbles
of gas which, as they escape, burn with a bright flame. Coals of this
description, when reduced to powder and strongly heated in a covered
vessel, agglomerate into a mass of coherent coke. This property of
caking varies in degree, in different coals, from slight agglutination to
almost complete fusion.
The caking of coal does not however take place at a temperature
below that at which its decomposition is effected, and consequently it
cannot be regarded as the result of a mere fusion of its particles; it is, on
the contrary, caused by the action of heat on its constituents giving rise
to the formation of coal-tar, which, becoming subsequently charred,
cements the whole into a solid and frequently sonorous mass. Even the
powder of charcoal, or anthracite, if mixed with a small quantity of pitch
or coal-tar and strongly heated in a closed crucible, will afford a perfectly
solid coke, which, when struck, has an almost metallic ring.
Free-burning coals are those which do not, in burning, cake or
sinter together in any sensible degree, and of which the particles, when
41
ELEMENTS OF METALLURGY.
strongly heated in a closed vessel, do not unite to form a solid coherent
coke. A fire supplied with coals of this description remains open, allow-
ing the air to pass freely through it; whereas many varieties of caking
coal cannot, without an admixture of a free-burning coal, be employed for
metallurgical purposes on account of the stoppage of the air-passages,
caused by its agglomeration into a more or less compact and impervious
mass.
It would appear from the researches of Professor Stein, of Dresden, on
the coals of Saxony, and from the investigations of Dr. Percy on those of
this country, that the property of caking is dependent rather on the proxi-
mate constitution of a coal than upon its ultimate composition, and that a
caking and a non-caking coal may have the same elementary composition.
This subject is, however, one of great interest, and worthy of further
investigation.
It has been asserted on good authority that certain Welsh coals lose
their property of caking after a few days' exposure to the air, and M. de
Marsilly states that strongly caking coal, which affords an excellent
coke when fresh from the pit, yields an imperfectly formed coke, in the
same ovens, after exposure to the atmosphere for six months.
The same observer further remarks that all caking coals, from pits in
which fire-damp occurs, cease to cake when they have been previously
heated to 300° C., and that if they are strongly heated, in a state of
powder, after being raised to this temperature, no agglomeration of the
particles will take place. This statement has been confirmed by
Dr. Percy with respect to the strongly caking coals of Newcastle-on-
Tyne; but, in order to produce this effect to its fullest extent, it was
found necessary to keep them exposed to the temperature specified during
from one to two hours. The more important results of the investigations
of M. de Marsilly may be summarised as follows:-Coal suffers a less
loss of weight by desiccation in vacuo than by exposure to a temperature
of 100° C. It begins to give off gas at 50° C., but its evolution is not
very sensible below 100° C. The amount of gas evolved goes on
increasing to 330° C., when the decomposition of the coal, properly
so-called, probably commences; a liquid product having the odour of
benzine is distilled off at the same time. The loss of weight experienced
by coal at 300° C. ranges from 1 to 2 per cent. Coal from pits subject
to fire-damp disengages carburetted hydrogen to the almost total exclu-
sion of other gases, whereas the gas evolved from the coal of pits free
from fire-damp consists of carbonic anhydride and nitrogen, without any
trace of the hydrocarbons. Coal newly raised evolves carburetted
hydrogen, even under a pressure five times greater than that of the
atmosphere; after being exposed to the air during three months it no
longer gives off any gas at or below a temperature of 300° C.
The caking of coal is also, to a considerable extent, influenced by the
way in which it is treated, since, in some cases, a coal which, if heated in
the usual way, is practically non-caking, will, when rapidly exposed in a
close vessel to a very high temperature, yield a firm coherent coke. The
amount of moisture in a coal has likewise a certain influence on its
FUEL.
45
Newcastle.
Welsh Coals.
property of caking, and when a large quantity of inorganic matter is pre-
sent it is not without effect in diminishing this property, although Stein
has found that a coal containing nearly 22 per cent. of ash may still be
capable of caking.
Strongly caking coal, from becoming agglomerated on the grate, and
thus preventing the free passage of air, is not usually adapted for metal-
lurgical purposes, excepting in the form of coke, and a fuel containing a
large amount of a fusible ash may be equally objectionable, from the
choking of the grate by the formation of clinkers. If therefore a coal
possesses, in a high degree, the property of caking, or yields a large
proportion of fusible ash, it is usually mixed either with a free-burning
variety, or with a coal of which the ash has a tendency to prevent the
formation of clinkers, when mixed with the more fusible ashes of the other.
The following table, extracted from the Third Official Report on
Coals suited to the Steam Navy,' gives the percentage composition of
several varieties of British coal, together with their specific gravities and
the amount of ash and coke yielded by each.
The results obtained by Regnault and Karsten from the analyses of
specimens of various foreign coals are given, page 46.
COMPOSITION OF VARIOUS BRITISH COALS.



Locality or Name of Coal.
Specific
Gravity.
C.
H.
N.
S.
0.
Ash.
Per-
centage
of Coke
left.
•
(Aberamam Merthyr
Ebbw Vale
Thomas's Merthyr.
Duffryn
Nixon's Merthyr
Binea
Bedwas
Hill's Plymouth Works.
Aberdare Co.'s Merthyr.
Gadly Nine-feet Seam
(Resolven
Willington
·
1.305 90.94 4.28 1.21 1.18 0.94 1.45 85.0
1.275 89.78 5.15 2.16 1.02 0.39 1.50 77.5
1.30 90·12 4.33 1.00 0.85 2.02 1.68 86.53
1.326 88.26 4.66 1·45 1·77 0.60 3.26 84.3
1.31 90 27 4.12 0.63 1.20, 2.53 1.21 79-11
1.304 88.66 4.63 1.43 0.33 1.03 3.96 88.10
1.32 80 61 6.01 1.44 3.50 1.50 6.94 71.7
1.35 88.49 4.00 0.46 0.84 3.82 2.39 82.25
1.31 88.28 4.24 1·66 0·91 1.65 3.26 85.83
1.33 86.18 4.31 1.09 0.87 2.21 5.34 86.54
1 32 79.33 4.75 1.38 5.07 included 9.47 83.9
in Ash
Andrews House, Tanfield 1-26
Bowden Close
Haswell Wallsend.
Newcastle Hartley
Hedley's Hartley
Bates' West Hartley
West Hartley Main
Buddle's West Hartley
(Hastings' Hartley .
(Earl Fitzwilliam's Elsecar
Hayland & Co.'s Elsecar
Earl Fitzwilliam's Park)
Gate.
Butterly Co.'s Portland
86.81 4.96 1.05 0 88
85 58 5.31 1.26 1.32
84.92 4.53 0.96 0.65
1.286 83.47 6.68 1.42 0.06
1.29 81.81 5.50 1.28 1.69
1.31 80.26 5 28 1.16 1.78
1.25 80.61 5 26 1.52 1.85
1.264 81.85 5.29 1.69 1.13
1.23 80.75 5.04 1.46 1.04
1.25 82 24 5 42 1.61 1.35
1.296 81.93 4.85 1.27 0.91
1.317 80.05 4.93 1.24 1.06
1.311 80.07 4.92 2.15 1∙11
5.22 1.08 72.19
4.39 2.14 65.13
6.66 2.28 69.69
8.17 0.20 62.70
2.58 7:14 64.61
2.40 9.12 72.31
6.51 4.25
7.53 2.51 59.20
7.86 3.85
6.44 2.94 35.60
8.58 2.46 61.6
8.99 3.73 62.5
9.95 1.80 61.7
1.301 80.41 4.65 1.59 0.86 11.26 1.23 60.9
Butterly Co.'s Langley 1.264 77.97 5.58 0.80 1.14 9.86 4.65 54.9
1.27 79.85 4.84 1.23 0.72 10.96 2.40 57.86
1.285 77.49 4.86 1.6 1.30 12.41 2.30 52.8
Stavely
Loscoe Soft
•
Derbyshire.
46
ELEMENTS OF METALLURGY.
Lancashire.
COMPOSITION OF VARIOUS BRITISH COALS-continued.

Locality or Name of Coal.
Specfiic
Gravity.
C.
H.
N.
S.
0.
Ash.
(Ince Hall Co.'s Arley
Haydock Little Delf
Balcarres Arley
Blackley Hurst
·
Ince Hall Pemberton Yard
Haydock Rushy Park
Moss Hall Pemberton
Four-feet.
Wallsend Elgin
Wellewood
Dalkeith Coronation Seam
Kilmarnock Skerrington
Fordel Splint
Grangemouth
Eglington
Dalkeith Jewel Seam
1 272 82.61 5.86 1.76 0.80
1.257 79.71 5.16 0.54 0.52
1.26 83.54 5.24 0.98 1.05
1.26 82.01 5.55 1.68 1·43
1.348 80.78 6.23 1.30 1.82
1.323 77.65 5.53 0.50 1.73
1.258 75.53 4.82 2.05 3.04
1.20
1.27
Per-
centage
of Coke
left.
7.44 1.53 64.0
10.65 3.42 58.1
5.87 3.32 62.89
5.28 4.05 57.84
7.53 2.34 60·6
10.91 3.68 59.4
7.98 6.58 55.7
76.09 5.22 1.41 1.53
81.36 6.28 1.53 1.57
5 05 10 70 58.45
6.37 2.89 59·15
1.316 76.94 5.20 trace 0.38 14:37 3.11 53.5
1.241 79.82 5.82 0.94 0.86 11.31 1.25 49.3
1.23 79.58 5.50 1.13 1.46 8.33 4.00 52.03
1.29 79.85 5.28 1.35 1.42 8.58 3.52 56.6
1.25 80.08 6.50 1.55 1.38 8.05 2.44 54.94
1.277 74.55 5.14 0.10 0.33 15.51 4.37 49.8
Scotch.
COMPOSITION OF VARIOUS FOREIGN COALS.
Specific
Description of Coal.
C.
H.
O. and N. Ash.
Gravity. Analysts.
Alias, Dép. du Gard
Rive-de-Gier-Grand Croix
Flenû from Mons
Decazeville, Dép. Aveyron
Epinac
89.27 4.85 4.47 1.41 1.322
87.45 5.14 5.63
-84.67 5.29 7.94
82.12 5.27 7.48
81.12 5.10 11.25
1.78
1.298
2.10
1.276
5.13
1.284
2.53 1.353
Commentry
Blanzy
Obernkirchen
Lippe-
Schaumburg
Céral, Dép. Aveyron
Neroi
Saint-Girons
83.72 5.29 11.75 0.24 1.319
76.48 5.23 16.01 2.28 1.362
89.50 4.83 4.67 1.00 1.279
75.38 4.74 9.02 10.86 1.294
63.28 4.35 13.17 19.20 1.410
72.94 5.45 17.53 4.08 1.316
Regnault.
•
Saint-Colombe
75.41
5.59 17.91 1.09 1.305
Leopoldinengrube, Silesia
73.88
2.76
Königsgrube, Upper Silesia
78.39
3 21
2.47 20.89
17.77 0.61 1.285
Karsten.
Sälzer and Neuak, Westphalia
88.68
3.21
8.11
1.288
Hundsnak
90.35 3.20 6.45
1.338
The composition of the ashes of a coal is in a great measure influenced
by the nature of the rock overlying the seam from which it is extracted,
as, besides containing the inorganic elements originally forming part of
the plants, by the decomposition of which the coal has been produced,
they will also to a certain degree consist of various earthy and siliceous
materials, deposited in the pores of the coal by the infiltration of water
from the strata above.
The analysis of the ashes of seven varieties of British coal afforded the
results given in the following table. The alkalies were not estimated.
FUEL.
47
Name of Coal from
No.
which the Ash was
obtained.
COMPOSITION OF THE ASHES OF COALS.

SiO2. Al2O3. Fe2O3. CaO. MgO. SO3. P 205 FeS. Tutal.
1234
1 Dowlais, N. Wales
35.73 41.11 11.15 2.75 2.65 4.45 0.99
98.83
""
""
""
""
24.18 20.82 26.00 9.38 9.74 8.37 0.21 0.38 99.08
37.61 38.48 14.78 2·53 2.71 0.29 2·00
39.64 39.20 11.84 1.81 2.58 trace 3.01
98.40
..
98.08
""
""
5 Bedwas
26.87
56.95
""
6 Porth-mawr,,
34.21
52.00
5.10 1.19 7.23 0.74
6.20 0.66 4.12 0.63. 97.82
98.08
7 Fordel Splint, 37.60
52.00
3.73 1.10 4.14 0.88
99.45
Scotch
Nos. 1-4 analysed by E. Riley; Nos. 5-7 by J. A. Phillips.
CANNEL COAL. This is a compact, brittle, jet-like variety of coal,
sonorous when struck, breaks with a conchoidal fracture, and does not
soil the fingers when handled. It is said to derive its name from the
candle-like light it yields when burning, and is known to Scotch miners
as
"Parrot Coal," from the crackling, chattering sound it emits when
thrown on the fire. Cannel coal occurs in certain districts interstratified
with ordinary coal, and often forms, in the Scotch coal-fields, the upper
portion of a seam of free-burning coal, or even of a bed of blackband
ironstone. It is used chiefly in the manufacture of gas, for which pur-
pose it is in great demand. The "Boghead" coal, in the county of
Linlithgow, the object of a celebrated trial at law in the year 1853, is
one of the most valuable of the brown cannels of Scotland, and is in high
request for the manufacture of gas and paraffin oil. The cannel coals of
Wigan are mined in the immediate vicinity of that town, but thin out in
every direction from Wigan as a centre.
COMPOSITION OF CANNEL COALS.

Locality.
Specific
Gravity.
C.
H.
0.
N.
S.
Ash.
H20% Analysts.
Wigan
Tyneside
Boghead
1.32 78.06 5.80 3.12 1.85
1.20 65.72 9.03 4.78 0.72
1.27 80.07 5.53 8.10 2.10 1.50 2.70 1.91 Vaux.
1.32 84.07 5.71 7.82
2.40 :
2.22 8.95
19.75
Regnault.
Taylor.
Stenhouse.
Dr. Stenhouse obtained the following results as the mean of three
analyses of the ash of Boghead cannel:
SiO2
A1203
Fe₂03
K₂O
NaO
58.31
33.65
7.00
0.84
0.41
•
CaŎ and SO3
traces
·
100.21
48
ELEMENTS OF METALLURGY.
ANTHRACITE.—Anthracite is the ultimate product of the conversion of
vegetable matter into coal. Its structure is perfectly homogeneous, its
fracture conchoidal, and its colour a jet black, with a vitreous lustre,
which frequently exhibits a powerful play of colours.
The results obtained by various chemists from analyses of specimens
of this substance are given below.
COMPOSITION OF ANTHRACITES.
Mire, Braconnière
Locality.
Pennsylvania, America
Sablé, Dép. de la Sarthe
C.
H.
O. and
N.
Specific
Ash.
Gravity.
Analysts.

Rolduc, near Aix-la-Chapelle
•
Vizille, Dép. de l'Isère
•
Isère
Llanguicke, Glamorganshire
90.45 2.43 2.45
91.98 3.92 3.16
91.45 4.18 2.12
87.22 2.49 3.39
94.09 1.85 2.85
94.00 1.49 3.58 4.00
91.44 3.84 3.58 1.52 1.375
4.67 1.462
0.94
2.25 1.343)
1.367 Regnault.
6.90
1.751
1.90
1.730
Jaquelin.
1.650
Wrightson.
Slievardagh, Ireland
80.03 2.30
1.590
H. How.
The present annual production of coal in the United Kingdom is
about 120,000,000 tons.
EFFECT OF HEAT ON FUELS.
Since all the various substances employed for the purposes of fuel
are of organic origin, it follows that they are more or less prone to decom-
position. Chemical combinations are stable within certain limits of tem-
perature only, and when these points are passed, a series of compounds is
produced by fresh groupings of the various elements of which the original
substance was composed. When a substance such as wood is strongly
heated, the arrangement of its elements is broken up, and new compounds
are produced, capable of existing at the higher temperature at which they
are formed. The nature of these products will in a great measure depend
on the degree of heat which has been employed, as those obtained at one
temperature will materially differ, both in quantity and composition, from
those which are formed at another.
The results will moreover be essentially different, according as air is
excluded from or admitted into the apparatus in which the heating takes
place. When air is admitted, the products at first formed are imme-
diately subjected to the action of oxygen, which combines with their
elements to form new bodies, and combustion is finally the result.. If,
on the contrary, decomposition is effected by heat alone in close vessels,
air being excluded, the process is known by the name of dry distillation,
and affords the means of collecting and studying the various products
obtained at more or less elevated temperatures. This operation is of
the greatest importance, as affording the means of modifying various
fuels, so as to adapt them to the particular circumstances under which
they are to be employed. When a piece of wood or coal is strongly
heated, its elements so arrange themselves as to give rise to various
FUEL.
49
gaseous compounds, and these, escaping at an elevated temperature, ignite
and produce flame. This combustion affords sufficient heat to cause the
non-volatile portion of the fuel to combine with the oxygen of the air,
which in its turn produces a fresh supply of gas from that portion of the
mass with which it is in immediate contact. In this way combustion is
supported until the substance is entirely consumed, as the heat evolved
by the combustion of the carbon on the outer surface of the mass causes
the dry distillation of the inner portions with which it is in contact;
whilst the gases thus evolved tend to facilitate the union of the carbon of
the outer surfaces with the oxygen of the air.
When the elements of which a fuel is composed are, by the aid of
heat, forced to abandon their state of equilibrium, the nature of the new
products will be to a certain extent influenced by three different causes.
1stly. By the temperature at which the decompositions have been
effected.
2ndly. By the degree of chemical affinity existing between the various
elements.
3rdly. By their relative degrees of volatility, &c.
Hydrogen and oxygen are volatile bodies, whilst carbon, on the con-
trary, is fixed, and therefore the two former will constantly have a tendency
to separate from the latter, and pass off in the form of gas. Here, how-
ever, chemical affinity comes into play, and causes them to unite with
each other, and form new compounds, either singly or together, with
carbon, a portion of which is thereby made to assume the gaseous form.
The most stable compound of hydrogen and oxygen is water, whilst the
excess of hydrogen which exists in all fuels takes up a portion of the
carbon, with the production of gaseous hydrocarbons, and the united
action of these continually tends to the formation of a series of com-
pounds, the nature of which will in a great measure depend on the
temperature at which they are formed, as those will be constantly pro-
duced which are most stable at the various degrees of heat attained. The
rapid chemical action incident on the production of these varied com-
pounds necessarily produces a further elevation of temperature, and the
consequent formation of new groups.
The greater the proportion of hydrogen contained in a fuel, and the
less the quantity of oxygen, the more numerous are the combinations of
carbon produced, but in no instance are these sufficient in amount to
combine with the whole of the carbon present, a portion of which inva-
riably remains in the solid form in the vessel in which the distillation has
been effected.
Charcoal produced from wood, brown coal, and turf, retains the form
of the original fragment before it was subjected to the action of heat;
and in the case of the former, its mechanical structure is so completely
preserved that the year-rings and cells may be perfectly distinguished, and
the kind of wood from which it was made ascertained.
Coke from bituminous coal, on the contrary, loses more or less com-
pletely the form of the fragments from which it is made, and in the
majority of cases no trace remains of the structure of the original coal.
E
50
ELEMENTS OF METALLURGY.
PREPARATION OF ARTIFICIAL FUELS.
From the large amount of water contained in most varieties of fuel, as
well as from the oxygen which enters into their constitution, it is evident
that, when burnt, a portion of the heat evolved must be rendered un-
available, as the water present will carry off by its evaporation a portion
of the heat produced; the union of the hydrogen and oxygen forming
part of the fuel, will also give rise to the production of water, which has
to be evaporated at the expense of a further sacrifice of heat.
ous
In order, therefore, to obtain a larger amount of combustible matter
in a given weight of fuel, it has long been the custom to expel the aque-
and gaseous portions of such as are required to afford an intense heat,
before applying them to the uses for which they are intended. This is
the object of charring wood, or converting it into charcoal, which opera-
tion has more recently been extended to peat, lignite, and coal; in the
latter case the process is called coking, and the resulting product is
known by the name of coke. By this means, the different kinds of natural
fuels are made to afford a series of artificial ones of respectively higher
calorific values than the substances from which they are severally derived;
their economical preparation, therefore, becomes a subject of import-
ance, not only to the metallurgist, but to all who require the aid of
elevated temperatures.
CHARCOAL.
If we ignite a small splinter of wood, and closely examine the
way in which it burns when the lighted end is held downwards, two
distinct periods will be observed. When the flame has become weak,
from the volatile combustible products having ceased to be evolved,
except in very small quantities, it is observed gradually to die out, and
nothing will remain but the feeble glimmering produced by the slow
combustion of the remaining charcoal, which not affording sufficient heat
to admit of the combustion of the carbon by the oxygen of the air, soon
ccases. If, so soon as the flame is extinguished, the chip be placed in a
close vessel, such as a test-tube stopped by the finger, it will, from want
of air, be quickly extinguished, without any of the glimmering before
noticed; and if a piece of wood be at once heated in a close vessel, so as
to completely char it without first producing ignition, the volatile matters
are driven off, and charcoal is produced without loss of carbon from the
action of the air. In the ordinary methods of preparing charcoal on a
large scale, both these principles are in a manner involved; as in this
case a portion of the wood is consumed in order to sufficiently raise the
temperature to drive off the volatile constituents of that which remains,
whilst the combustible products of distillation are invariably more or less
perfectly consumed. Less frequently the coking is effected in large ovens
or retorts, and in that case the second principle only comes into play.
Whichever of these contrivances be employed, it is essential that
time be allowed for all the oxygen to combine with hydrogen to form
FUEL.
51
water, without which these gases unite with and render volatile a portion.
of the carbon, and thereby diminish the amount of coke produced. Karsten,
who has carefully examined this subject, obtained the following results,
from which the advantage of the slow over the quick method of charring
becomes apparent.
Species of Wood employed.
Percentage Amount of
Charcoal obtained by
Quick Method of
Charring.
Percentage Amount of
Charcoal obtained by
Slow Method of
Charring.
Young Oak
Old do.
•
Young Red Beech
Old do.
16.54
25.60
15.91
25.71
14.87
25.87
14.15
26.15
Young White Beech
13.12
25.22
·
Old do.
13.65
26.45
•
•
Young Alder
14.45
25.65
•
Old do.
15.30
25.65
Young Birch
13.05
25.05
Old do.
12.20
24.70
Birch 100 years old
12.15
25.10
Young Deal (Pinus picea)
14.25
25.25
Old do.
14.05
25.00
Young Fir (P. abies)
16.22
27.72
Old do.
15.35
24.75
Young Pine P. sylvestris
15.52
26.07
Old do.
13.75
25.95
Lime-tree
13.30
24.60
•
The best method of ascertaining the quantity of charcoal yielded by
various kinds of wood is to place a weighed fragment of the wood in a
covered crucible filled with saw-dust or charcoal-dust, and having placed
it in an assay furnace, the heat should be gradually raised to redness, at
which temperature it is kept for about half an hour; when the crucible
must be withdrawn from the fire, and allowed to cool previously to being
opened. Fine sand may also be employed instead of saw-dust for the
purpose of excluding air from the wood. When the crucible has sufficiently
cooled, the charcoal is withdrawn and weighed. This experiment should
be repeated at least twice on each variety of wood, for the purpose of
avoiding error.
PREPARATION OF CHARCOAL IN PILES OR STACKS.-The charcoal-burner
selects for this purpose a dry locality, sheltered, on at least one of its
sides, either by a hill or a portion of the uncut forest; since, if the piles
were constructed in an exposed situation, it would be extremely difficult
to prevent their being so acted on by the wind as to cause an unequal
charring of the wood. When a proper situation has been chosen, which,
to prevent the expense of carriage, should not be far removed from the
place where the wood is felled, a circular piece of ground of the diameter
of the intended stack is marked out. If the soil be sandy and dry, this
is done by merely cutting around it a shallow drain, for the purpose of
carrying off any rain-water which may fall during the process of carboni-
sation; but should there be any reason for suspecting the dryness of the
E 2
52
ELEMENTS OF METALLURGY.
soil, the surface is slightly raised by a covering of stones, logs of wood,
or the smaller branches of trees. The next operation is to cover the
surface with charcoal-dust, obtained from a preceding operation, or, in
default of this, a strew of leaves is sometimes employed. A long post is
now driven into the ground in the centre of the circle, and it should be of
such a length that its upper extremity may remain a little above the top
of the intended mound. Around this, the wood which has previously
been cut into proper lengths, is piled, as shown, fig. 2. The greatest care
Fig. 2.-Charcoal Pile; vertical section.
is taken to avoid large cavities between
the billets; and, for this reason, those
situated immediately around the post
should be made by splitting the larger
branches; in making the mound their
thinner edges are placed towards the
central post.
The more slantingly the billets are
placed against this post, the greater
will be the spaces between them; and,
therefore, the more perpendicularly
they can be piled consistently with
the stability of the mass and the reten-
tion of the external covering, the better will be the subsequent results. It
is also evident that, when logs are piled horizontally in concentric circles
radiating from the centre, considerable spaces must be produced by the
divergence of the outer ends of the billets forming the various rings; and,
therefore, a combination of the two methods, as shown in the figure, is
frequently adopted. All unavoidable spaces resulting from the crooked-
ness of the branches or their radiation must be carefully filled with
small fragments of wood; and when the surface has been thus made even,
and the top or cap has been properly rounded by the addition of refuse
wood, the pile is provided with its covering. This consists of turf, which
is placed on the heap with the grassy side inwards, and is beaten all over
with a shovel, to make it lie closely on its surface. This is again
covered either with damp charcoal-dust or earth, and the whole pressed
down for the purpose of giving it solidity. The covering does not, how-
ever, extend to the foot of the pile, but is supported at a few inches from
the bottom by twigs held in their places by forks, so as to form hoops
around the lower part of the meiler. This open part at the base of the
mound is for the purpose of allowing the escape of the aqueous vapours
generated during the first stage of the operation, since no opening is
allowed at the upper part of the pile, as it would tend to cause a draught
and consume a portion of the wood to be charred.
The dimensions of the mounds depend on circumstances incident to
the neighbourhood in which the charring takes place, but should in no
case be so considerable as not to admit of easy regulation of the tempera-
ture. Heaps of only 10 feet in diameter are sometimes met with, but
these are, generally speaking, inconveniently small, and stacks of from
30 to 40 feet across the base are, therefore, frequently preferred, although,

FUEL.
53
in some localities piles of even 60 feet in diameter are occasionally
employed.
In arranging the billets around the central stake, care is taken to leave
at the bottom a small channel from it to the exterior part of the heap, and
by means of this the fire is communicated to the pile when it is finished
and the external covering has been well pressed down. Sometimes, instead
of leaving this opening, the central stake is composed of three pieces of
cleft wood so arranged and tied together with bands of green branches as
to form a kind of chimney by which fire may be communicated; and in
this case the horizontal passage becomes unnecessary.
When the mound is completed, and the covering securely packed
down, fire is communicated to the centre of the mass, either by throwing
lighted coals down the vertical chimney, or by introducing them through
the horizontal gallery. For the purpose of facilitating ignition, the wood
placed immediately around the stake consists of the half-burnt charcoal
resulting from a preceding operation, which is picked out for that pur-
pose as being more combustible than the ordinary wood of which the
other parts of the stack are composed. When the heap has been ignited,
the hole by which the fire has been introduced is tightly closed with turf
and earth; and the first period, during which the moisture is expelled
from the wood, commences.
At this stage great attention is necessary to prevent the explosion of¸
the heap, from the ignition of a mixture of atmospheric air with the in-
flammable gases produced by the dry distillation of wood. During the
whole of the "sweating" process, large quantities of yellowish-grey
smoke escape, particularly from the uncovered space at the base of the
mound, and the interior of the covering becomes moist from the condensa-
tion of aqueous vapour expelled from the wood by the action of heat.
When the colour of the smoke issuing from the mound has been observed
to change to a light grey, without any of the yellow tint before men-
tioned, the burner hastens to close the open space at the base, and the
charring period commences.
The covering of the pile now requires to be thoroughly repaired, as
the dry wood in the vicinity of the central stake will have become par-
tially consumed, and have caused a sinking of the top or cap of the heap.
The upper part of the covering is, therefore, rapidly removed, the charred
wood forced down by means of a long pole into a compact mass, and the
cavity thus made immediately filled with fresh logs. The covering is
now, with as great expedition as possible, replaced, and any crevices
which may have occurred in it from the sinking of any part of the mound
are stopped without delay, as they would otherwise, by admitting atmo-
spheric air, cause the combustion of a portion of the wood. The stack is
now left to itself for several days, except that small holes are from time to
time made in that portion of the covering which is nearest the ground.
This is done both for the purpose of allowing the escape of tarry vapours
and to admit the requisite amount of air, although the porosity of the
covering of turf, &c., constantly aids in producing these results.
The dimensions of the heap have, at this stage, become considerably
54
ELEMENTS OF METALLURGY.
reduced, and care must be taken to observe whether it has equally dimi-
nished in all its parts, or whether some portions of its surface have sunk,
whilst others are in their original condition, thereby giving an irregu-
larity of outline to the meiler.
If such be the case, the charring has been badly conducted. This
may to a certain degree be obviated, either by covering the sunken and
more perfectly carbonised parts with an additional layer of turf, or by
means of an aperture made in the raised portion, the draught may be
increased in that direction.
Towards the end of the process, and when the wood in the interior
of the mound has become perfectly carbonised, it will be found necessary
to adopt means to effect the charring of those portions which are in
immediate contact with the movable covering.
In this direction the wood is so cooled by radiation and by the con-
densation of aqueous vapours as to escape carbonisation; and the work-
men, therefore, accelerate the draught in this part of the heap by making
a second series of holes in the covering, parallel with those which have
before been described, but at a greater distance from one another. These
are allowed to remain open until the smoke that issues from them is seen
by its colour to be free from watery vapour; and, when this period has
arrived, they are closed, in order to give place to others which are made
at a short distance below them. Holes are never made for this purpose
in the higher part or crown of the pile, as the draught is naturally in
that direction; but in very large mounds, three, or even four, successive
series of openings are not unfrequently made at different heights above
the surface of the ground.
The time necessary for the operation chiefly depends on the size of
the stack. Small mounds are generally carbonised in from six to
fourteen days; but if the diameter be more than thirty feet, at least a
month is required.
If at the termination of the process the covering were removed, and
the heap broken up whilst still hot, the access of atmospheric air would
cause the charcoal to ignite, and the whole would be consumed. On the
contrary, if the covering were allowed to remain undisturbed until the
mass had cooled down, so as to admit of its being removed without
danger, much time would be lost; the charcoal is therefore withdrawn
in small quantities, and with suitable precautions. In order to do this,
the burner lays bare a space of two or three feet at the bottom of the
mound, and, with an iron crook fitted to a wooden handle, withdraws, one
by one, the logs of charcoal. These, which are red hot when drawn out,
are extinguished cither with water or by being buried in damp charcoal-
dust; and as soon as the air begins to act too strongly on the exposed part,
the opening is closed, and another made in a different part of the mound.
This operation, which is repeated until the whole has been removed and
extinguished, is best performed at night, as the slightest spark is then
visible, and the chance of loss from the ignition of the charcoal thereby
reduced.
In some parts of the Continent, another arrangement is employed
FUEL.
55
for the preparation of charcoal; this process is said to yield charcoal of
a better quality than that obtained by the ordinary method. For this
purpose the logs are laid together in the form of a narrow wedge, as shown
in fig. 3, of which the breadth is regulated by the length of the logs; its

Fig. 3.-Charcoal-burning; rectangular heap.
length varies from twenty to thirty feet. The thick end, which is farthest
from that at which the fire is communicated, is from seven to nine
feet in height, whilst the thin end is only about two feet above the level
of the soil. In the erection of a heap of this kind, the burner commences
by driving stakes, a, all round the parallelogram in which the logs are
to be placed. These must project from the surface so as to be of the
same height as the pile is intended to be at the points at which they are
driven; and their outline, therefore, in every respect corresponds with
the form of the pile itself.
These stakes are so placed as to leave a space all round the wedge-
shaped heap of logs which are piled within the inclosure. The billets
used are usually eight feet in length; and, therefore, in order to allow a
space of six inches between their ends and the sides of the inclosure, the
latter is made nine feet in width. The opening thus left between the
ends of the wood and stakes is for the purpose of receiving the covering,
which, on account of the perpendicular sides, could not otherwise be
kept in its place.
Boards or pieces of cleft wood are now applied against the inside of
the posts, and wet charcoal-powder or breeze is stamped down between
them and the logs until the interval is entirely filled. When this is
done, the roof receives a triple covering of twigs, leaves, and, lastly,
charcoal-powder and earth, which is moistened with water and well
beaten down. In each of the long sides of the heap a series of holes is
made in the boarding, but these do not penetrate through the charcoal
coating; and in the lower end a larger one, b, is left for the purpose of
igniting the logs, which is effected by first filling the aperture with
shavings or dry wood, and then throwing some red-hot coals between the
posts and the pile of wood.
When the fire has fairly taken hold of the wood this aperture is closed,
and other holes, of about three or four inches in diameter, are made at a
height of about fifteen inches from the ground, in the same end of the
heap. As soon as the smoke issuing from these assumes a clear blue
colour, they are stopped, and others made higher up in the pile, which in
56
ELEMENTS OF METALLURGY.
their turn are closed as soon as the fire has sufficiently advanced towards
them. By this arrangement the wood in the front of the pile is under-
going the charring process, while that placed behind is merely losing its
more volatile constituents. When the operation is drawing to a close, it
is found necessary to open a series of holes in the sides of the heap just
above the level of the soil, as by this means the charring of the lower logs
which constitute the bottom of the pile is effected. These, from their
proximity to the ground, and the dampness deposited by the sweating of
the wood, would otherwise remain as imperfectly-charred billets; and,
therefore, to prevent this, a series of holes is (when the heap is first
constructed) cut in the planking forming the sides. During the early
part of the operation these are closed by the charcoal-powder, which is
closely packed between the boarding and the wood to be charred; but
when the fire is required to descend to the bottom of the heap, the
draught is made to pass in that direction by removing the damp charcoal-
dust from the apertures left in the planking. As soon as the logs in the
front of the pile have become perfectly charred they are removed, and
being thus withdrawn from the action of heat shortly after the opera-
tion is finished, they not only yield a larger amount of charcoal, but
that produced is of better quality than that afforded by the ordinary
process.
In the foregoing operations the dry distillation of the greater portion
of the wood which constitutes the heap is effected by the combustion
of a certain quantity, which may be considered as the fuel necessary to
produce the required heat. In order to conduct an operation with the
greatest possible economy, care should be taken that no more air be
admitted than is absolutely necessary for the combustion of this amount
of fuel, as any further supply will cause a greater quantity to be consumed
than is required for the dry distillation of the mass.
The success of these processes is also much influenced by the fact
that the smoke and vapours, being evolved contrary to their natural
course, are constantly made to take a downward direction, which not only
affords the workman the opportunity of attentively watching the changes
which are taking place, but also gives him time for taking the necessary
steps to prevent the access of too large an amount of air. Ordinary wood
loses from twenty to twenty-five per cent. of its bulk during the process
of charring; and, therefore, the dimensions of the charcoal produced from
a given quantity of wood are much less than those of the original piles
before the application of fire. This diminution naturally tends to pro-
duce cavities between the fuel and its covering, which, if formed, would
become accessible to air, and thereby cause a useless consumption of
wood; but in the case of the movable coverings employed for this pur-
posc, this inconvenience can never occur, as, in proportion as the size of
the heap becomes less, through the shrinking of the wood, the covering
will be found to sink with it, and is, therefore, much more effective
in excluding air than any fixed roofing which could be substituted for it.
The loss arising from the combustion of a portion of the charcoal is
also diminished by the way in which the charring is conducted. The
FUEL.
57
mounds are always first lighted at the bottom; and, therefore, the lower
portion of the heap will be completely charred before those parts which
are in immediate contact with the covering have become much affected
by heat. In this way, the charcoal which has arrived at the last stage
will, by the heat which it evolves, cause the dry distillation of the wood
immediately around it, which, from the combustible gases evolved, and
the burning of a portion of the wood in its vicinity, protects, by a zone
greedy for oxygen, the portion, already completely charred, from further
action of the air.
These methods have, however, the disadvantage of allowing the
volatile constituents of the wood to escape, and these are more or less
valuable according to the locality in which they are produced. Various
plans have been proposed to prevent this loss. For this purpose it has
been suggested that the covering of the meiler should consist of hurdles
covered with clay, into which pipes for carrying off the volatile products
could be placed: others have proposed that, instead of covering the heap
with earth or sand, slaked lime should be employed, so as to combine
with, and thereby fix, the pyroligneous acid produced. Both these plans
have, however, been found to fail in practice, as the first destroys the
flexibility of the covering, and the second is said to retain but a small
portion of the acid produced.
If the method of carbonisation in long masses or piles be resorted
to, instead of those more usually employed, the gaseous and liquid
products of distillation may be collected by an iron pipe placed in the
highest end of the heap, which, being connected with a worm-tub filled
with water, will discharge the condensed products in the liquid form. In
cases where the site of the stack can, without much inconvenience, from
the facility of carriage afforded by sledges or a stream of water, remain
stationary, the heap may be placed in a funnel-shaped pit, lined with
clay, which, having at its lower part an inclined channel, either of iron
or clay, conveys a portion of the impure acid and tarry matters into
a reservoir, where they gradually accumulate. The time required for
effecting the complete charring of a heap or mound usually varies from
fifteen to twenty days, according to the size of the fire, the dryness
of the wood, the state of the weather, and other circumstances. In
China carbonisation is conducted in pits, which are provided with a
chimney about three feet in height, communicating with the bottom.
After being filled with wood the top is closed by a covering of earth,
through holes in which a draught is produced. Nine days after lighting,
the smoke begins to give indications of the completion of the process,
and, when it has become nearly transparent, the pit and chimney are
hermetically sealed. At the expiration of five or six days from the
stopping of the chimney, the charcoal has sufficiently cooled to admit of
the pit being uncovered for the purpose of its removal.
CHARRING IN FURNACES OR KILNS.-When the collection of the vola-
tile constituents of wood becomes a matter of much importance, the char-
ring is usually conducted in stationary furnaces, from which they may be
conveyed by proper appliances into receivers adapted for that purpose.
58
ELEMENTS OF METALLURGY.
These furnaces are of two kinds. In the first carbonisation is effected
as in the case of the common meiler, at the expense of a certain portion
of the wood, which is consumed in order to produce the amount of heat
necessary for the distillation and charring of the remainder. In the
second variety, the heat necessary for the dry distillation of the wood is
not obtained by the combustion of any part of the charge of the furnace,
but is, on the contrary, raised by the application of a certain amount of
fuel, which is entirely distinct from that from which the charcoal is to be
manufactured.
Figs. 4 and 5 represent a section and plan of one of the many kilns
or furnaces belonging to the first class. In this arrangement the air has
access into the furnace through the bars, a. It is partially filled through
the door, b, and when the charge has been raised to this level, the remainder
of the wood is introduced through the aperture, c, which is left for that

(2.
Fig. 4.-Charcoal Kiln; vertical section.
Fig. 5.-Plan.
purpose in the crown of the arch. When the charging is completed, the
openings, b and c, are closed by doors, against which earth is thrown
for the purpose of excluding the air. The wood is now ignited, by
kindling a small fire in the ash-pit, immediately beneath the grate; and
when it has become fairly alight, the draught is regulated by a sliding
door, d, which admits of being opened or shut at pleasure.
As soon as the walls of the furnace have attained a sufficient heat to
complete the operation, the door, d, is completely closed, and the furnace
left to itself, until the whole of the wood which it contains is converted
into charcoal. The volatile ingredients escape through the aperture, e,
and are more or less completely condensed by passing through a series of
tubes surrounded by water.
The grate at the bottom of these furnaces, instead of being made of
bars of iron, is frequently a kind of trellis formed of open brickwork or
perforated tiles, and when the apertures in these are small, the firing of
the charge is effected through the door, b. When the operation is termi-
nated, all the apertures by which air could be admitted are completely
closed, and the furnace is allowed to cool; the charcoal being finally
withdrawn through the door, b.
FUEL
59
Furnaces of different constructions are in various places employed
for the production of charcoal, according to this principle. Some of these
are made quadrangular, and very nearly resemble in form the boarded
piles before described. Two openings in the lower end, to which doors
are adapted, serve for charging the wood, and withdrawing the charcoal
when made, whilst the requisite supply of air is obtained through aper-
tures in the walls. The first row of holes is made on the same level as
the ground on which the furnace stands; the second at eighteen inches from
the floor; and the third at a distance of about three feet from the first.
When the wood is placed in the furnace, a channel is constructed in
the direction of its longer axis, which corresponds with one of the open-
ings of the lower end of the building. By this opening fire is communi-
cated to the charge, and as soon as ignition of the mass has taken place,
the door by which it was lighted is closed. As the process proceeds, the
apertures are successively closed by plugs of clay, and when the operation
is completed, the whole of the surface of the furnace is covered with that
substance. The gaseous and other volatile ingredients escape through
a pipe placed in the higher end of the furnace for that purpose, and when
the charge has become completely charred, it is allowed to remain un-
touched until it has grown nearly cold. In very large ovens of this
description, the cooling often occupies from two to three weeks since, if
they were opened before being reduced to a proper temperature the air, on
coming in contact with red-hot charcoal, would cause the greater portion
of it to be consumed.
Furnaces of the second kind, i. e., where the heat necessary for char-
ring the charge is applied from without, are chiefly employed where the
charcoal produced is considered to be of less value than the tar, pyrolig-
neous acid, naphtha, and other volatile ingredients, and they are therefore
seldom used by the metallurgist for the preparation of the fuel which he
requires. The coniferous woods yield the largest amount of tar, and are
consequently those which are most frequently subjected to distillation.
when the production of that substance is the most important considera-
tion. The arrangements by which both the tar, &c., and charcoal may
be made available are extremely various, but one of those best adapted for
the purpose consists of an iron cylinder, so set in brickwork, that the
flame and strongly-heated gases escaping from a fire-place below, may
circulate freely around it. The wood to be charred is placed in the
cylinder through an opening which can be hermetically closed. This is
done by a luted door, and the vapours arising from the distillation are
conveyed by an iron pipe into a worm-tub, where those capable of assum-
ing the liquid form are condensed. When the wood in the retort ceases
to give off tarry vapours, the luted door is removed, and the charcoal
withdrawn by long rakes. On being withdrawn from the retort, it falls
into sheet-iron cases, which being furnished with closely-fitting covers,
prevent the combustion of the red-hot charcoal; and in these it is allowed
to cool. By a more recent improvement in the construction of retorts of
this description, the uncondensible gases issuing from the wood in process
of charring are made to afford a portion of the heat necessary for carrying
60
ELEMENTS OF METALLURGY.
on the operation. This is done by conducting the vapours, which escape
condensation by passing through the worm-tubs, under the bottom of
the vessel, in which the wood is heated. When, in this arrangement,
it has been raised to a certain temperature by a fire placed under the re-
tort, and considerable quantities of combustible gases are evolved, they
become ignited on coming in contact with the flame from the grate, and
thus afford sufficient heat for completing the operation.
The average quantity of charcoal produced by the stack or meiler
process from ordinary wood amounts to about 22 per cent. When the
distillation is carried on in close ovens, this quantity is frequently in-
creased to 27 per cent.; but as about 5 per cent. is required for heating
the oven, this method in reality affords results very little superior to
those obtained from the common charcoal-mound.
Mushet, who made a series of experiments on the amount of charcoal
yielded by different kinds of wood, obtained the annexed results. This
investigation was conducted on a small scale, and the woods, before being
charred, were thoroughly dried, and pieces of each sort selected as nearly
alike in every respect as possible. One hundred parts of each kind were
employed, and respectively yielded the following amounts of charcoal :—
Per cent.
Lignum Vitæ afforded 26·0, of a greyish colour, resembling coke.
Mahogany
""
25.4, tinged with brown, spongy and porous.
Laburnum
""
24.5, velvet black, compact, very hard.
Chestnut
>>
23.2, glossy black, compact, firm.
Oak
>>
22.6, black, close, very firm.
Walnut
Holly
>>
Beech
Sycamore
Elm
""
20 6, dull black, close, firm.
19·9, dull black, loose, and bulky.
19.9, dull black, spongy, firm.
19.7, fine black, bulky, moderately firm.
19.5, fine black, moderately firm.
Norway Pine
19.2, shining black, bulky, very soft.
Sallow
39
Ash
""
18.4, velvet black, bulky, loose, and soft.
17.9, shining black, spongy, firm.
Birch
""
17.4, velvet black, bulky, firm.
Scottish Pine
""
16.4, tinged with brown, moderately firm.
Allen and Pepys obtained from 100 parts of the following woods, the
quantities of charcoal as under-
Birch
Mahogany
Lignum Vitæ
Per cent.
15.00
15.75 Fir
Oak
17.25
Box
•
Per cent.
17.40
18.17
•
20.25
These results are generally less than those obtained by Mushet, who
may either have operated at too low a temperature, or not have allowed
sufficient time for the escape of the volatile products.
The specific gravity of charcoal varies with the nature of the wood
from which it has been manufactured, the denser varieties usually afford-
ing the heaviest charcoal, and vice versa. Hassenfratz, who has made the
most careful experiments on this subject, gives the following specific
gravities for different kinds of wood-charcoal:-Alder, 0-134; birch, 0-203;
white beech, 0.183; oak, 0·155; red beech, 0·187; and red larch, 0·176.
Knapp, who made his experiments on a large scale, found the following
FUEL.
61
numbers as the weight of a cubic foot of various kinds of wood-charcoal,
interstices included:-Beech-wood charcoal (split wood) 8 to 9 lbs. ;
charcoal from split oak wood, 7 to 8 lbs. ; pine wood, 5.5 to 7 lbs. ; of the
softer kinds of wood, 4·5 to 5.5 lbs.
The charcoal obtained from wood by the methods above described is
not pure carbon mixed with the inorganic constituents of wood, since,
on being strongly heated in a closed platinum crucible, a considerable loss
of weight is experienced by the expulsion of volatile matter.
The analysis of beech-wood charcoal produced by the ordinary stack
process afforded Faisst the following results, exclusive of ash :—
H₂O
C.
H.
O and N
Ash
3.02 per cent.
7.23
88.89
2.42
1.46
100.00
Charcoal has also the property of absorbing considerable quantities of
water from exposure to the air. Allen and Pepys found that by a week's
exposure to a moist atmosphere, the charcoal of
Per cent.
Per cent.
Lignum Vitæ gained in weight 9.6
Becch gained in weight
16.3
Fir.
Box
•
13.0
14.0
Oak
16.5
Mahogany
18.0
Common charcoal when kept in store contains, on an average, about
12 per cent. of hygroscopic water.
In addition to this facility for taking up aqueous vapours, charcoal
possesses the property of absorbing large quantities of any gas by which
it may be surrounded.
The following table indicates the number of volumes of different
gases which one volume of charcoal is capable of absorbing :-
HCI
NH3
SO2
·
H,S
•
CO₂
90
CO
85
65 N
•
55 Ꮋ .
35
·
9.42
9.25
7.50
1.75
PEAT-CHARCOAL, OR PEAT-COKE.
The charcoal obtained from peat is subject to disadvantages which pre-
vent its general application to ordinary metallurgical purposes. In the
first place, peat usually contains a large amount of ash, and yields only
from 24 to 30 per cent. of charcoal, which must therefore produce a very
large proportion of earthy matter, and is thus rendered entirely useless
for many operations to which it might otherwise be advantageously ap-
plied. If we suppose, for example, that a variety of peat contains 10 per
cent. of incombustible matter, and affords 25 per cent. of coke, it is evident
that the coke thus produced would contain no less than 40 per cent of
ash, which would render it unfit for many of the purposes for which, if it
were more free from ash, it might be employed. Besides this, it is found
impossible to transport peat-charcoal to any considerable distance from the
62
ELEMENTS OF METALLURGY.
place where it is prepared, for, being extremely friable and brittle, it soon
falls to pieces, and is thereby rendered worthless as a fuel. In smelting
furnaces, where it has to sustain the weight of the charges above it, this
charcoal is found to crumble and choke the blast, and it can therefore be
employed only under steam boilers, in forge fires, or in reverberatory
furnaces.
The mounds
CHARRING IN HEAPS. From the circumstance of peat being generally
cut in the form of rectangular bricks, it admits of being piled so as to
leave but few interstices between the blocks; and from being less readily
combustible than wood, the heaps in which it is prepared require a less
perfect covering, and may be built of a smaller size.
commonly employed for making peat-charcoal are from five to seven
feet in diameter, and four feet in height. After a proper situation has
been selected for the mound, a post is driven into the ground, and around
this the blocks of turf are placed in concentric rings. At the bottom are
four channels made of the thickness of a brick, for the purpose of admit-
ting air into the arrangement. These, which are at right angles to each
other, commence at the central stake, and terminate at the periphery of
the circle described by the base of the mound, and are subsequently used
for regulating the rapidity of the carbonisation. When the peat has been
properly arranged, the mound is first covered with earth or charcoal-
dust, which is well packed down to exclude the air. Some dry wood for
igniting the mass is then placed at the bottom of the stake, and the fire
is communicated through one of the channels before described. By the
alternate opening and shutting of these, the combustion is equally effected
in all parts of the mound, and as soon as flame begins to appear from the
crown, which for a small space around the stake is left uncovered, the
opening is closed with turf and earth, and the completion of the charring
is accomplished by means of holes made all round in the covering ;
which, commencing near the top, are brought down by six inches at a
time until they reach the bottom of the heap. In this process, like
that of charring wood, the progress of the operation is known from the
colour of the smoke evolved. Knapp states the produce in charcoal of
the mounds examined by him to have been as follows:-
Gave p. c.
Gave p. c.
in Weight. in Volume.
Peat, not completely air-dried
24
27
air-dried
27
321/10
•
""
from Pfungstädt, very dry
30
29
•
39
of good quality, quite dry
351/
49
from the district of Siegen, very good
23
40
The peat is withdrawn from the mound after being allowed to cool
down to a proper temperature, as the use of water for quenching it is
objectionable, on account of the facility with which the resulting coke
becomes reduced to powder. The amount of charcoal furnished by peat
when the experiments are made on a small scale, is usually greater than
FUEL.
63
those above given, as there is then less loss sustained from the crumbling
nature of the product.
CHARRING IN OVENS.-Although the product obtained from carbonisa-
tion in ovens is not greater than that yielded by the ordinary process,
yet the supply of air and the rapidity of charring are more easily regu-
lated, and consequently the operation is more cheaply executed when
ovens are employed.
One of the best forms given to these ovens is that used at the
manufactory of arms at Oberndorf, in Wirtemberg. These ovens, which
have the form of an upright cylinder 9 feet in height, are closed at the
top by a dome, in which an aperture is left for the convenience of charg-
ing. This cylinder is 5 feet in diameter, and has a fire-brick lining
15 inches in thickness. This is surrounded by the same thickness of
sand, which is inclosed between the lining and another 15-inch wall, so
that the entire thickness of the sand and walls together is 45 inches.
Above the floor of the oven are three tiers of air-holes made by inserting
pieces of musket-barrels in the wall, and which may be closed by stoppers
from the outside.
The door for drawing the charcoal is placed on a level with the floor,
and is closed by an iron slab, against which some sand is thrown for the
purpose of excluding the air. On charging the oven, a channel is left
through its axis for the purpose of igniting its contents, which is done
by throwing some lighted charcoal down the chimney thus made. At
the commencement of the operation both the charging-hole and lower
vent-holes are left open, but as soon as the peat becomes white-hot the
former is shut by an iron plate, and covered with sand. The lower air-
holes are at the same time closed, and those which are placed next above
them opened. When all smoke has ceased to be given off, the whole of
the apertures must be closed, and the furnace and its contents are allowed
to cool together. The coking process is completed in from thirty to
forty-eight hours, but the oven is seldom fit to draw in less than six or
seven days after closing all the air-holes. For this reason a series of ten
ovens is employed, in order to allow of one being charged and another
drawn every day.
Instead of effecting the coking of one portion of the peat at the
expense of another part, which is consumed in the same furnace to obtain
the necessary elevation of temperature, it is sometimes subjected to dry
distillation in a kind of retort specially adapted to that purpose. At
Crouy-sur-Ourcq, near Meaux, an apparatus of this kind was formerly
employed, but we are not aware whether it is still in operation. Fig. 6
is a sectional view of this arrangement; a is the cylindrical coking
chamber, the walls of which are heated by the flame and hot air passing
through the intermediate flue, b. This space itself is divided by par-
titions of fire-tiles into three stages, through the apertures of which the
hot air from the fires, c, ascends and heats the coking chamber. In order
to avoid loss of heat, a cylindrical hollow space, d, is left in the outer
wall of the kiln, which, being constantly full of stagnant air, tends to
prevent the cooling of the furnace. The peat is introduced through the
64
ELEMENTS OF METALLURGY.
&
opening at f, which, as soon as the charging is finished, is closed by an
iron plate and thickly covered with ashes or sand. The flue from the
e
(
C
C
h
vertical section.
fire-place opens above this aperture, and its out-
let is provided with a movable iron cover, g, in
which there is a hole for the escape of the gases.
The bottom of the kiln consists of an iron plate, h,
which, being attached to the iron rod, i, may be
withdrawn or replaced at pleasure. When the
carbonisation is completed, this plate is withdrawn,
and the charcoal allowed to fall into the chamber
below. The volatile products which are generated
during the process are carried off by the pipe, e,
and conducted into a condensing apparatus.
The gases which escape from this are con-
veyed by metallic pipes into the fire-place, c, and
being there consumed, yield a portion of the heat
necessary for carrying on the operation. The
Fig. 6.—Peat-charcoal Oven; product of charcoal obtained from this furnace is
larger than that produced by the methods before.
described, but from the impact it receives in falling from the retort
to the chamber beneath, it frequently becomes much broken, and is
thereby rendered to a certain extent less valuable than if obtained in
larger masses.
Mr. Vignoles, in the year 1849, patented a process for charring peat
by steam superheated to the melting point of lead or tin. "Peat, in the
state of pulp, is thrown in a mass into a cylindrical drum-shaped vessel,
divided, if necessary, into compartments, which is caused to revolve with
great rapidity on its axis; the requisite velocity being such as shall
drive off the water or other fluid from the solid parts of the peat or turf
by centrifugal force." The axis of this cylindrical vessel should be
vertical, and the cylinder should be from 6 to 10 feet in diameter, and
from 1 to 2 feet in depth. The external surface is composed of wire-
gauze or perforated sheet-metal, of which the apertures should be of
such a size as to retain the particles of peat, whilst the water escapes
freely through them. When the peat, as obtained from the bog, is not
sufficiently pulpy, it may be readily reduced to the state of a nearly
homogeneous mud by the operation of edge-stones, or a pug-mill. When
a sufficient amount of water has been expelled by this process, the peat,
in the form of a coherent mass, is removed and moulded into blocks.
These are introduced into large iron cylinders, into which superheated
steam is admitted at a pressure of from 45 to 60 lbs. per square inch.
The charcoal thus produced is stated to be equal to gas-coke; but this
process, although tried on a large scale, and at great expense, by the
inventor, has never come into practical use.
The quality of the charcoal obtained will necessarily vary in accord-
ance with the nature of the peat from which it has been prepared. A
fibrous peat affords a spongy charcoal, while a more compact variety
yields a product of better quality; in all cases, however, the charcoal

FUEL.
65
obtained from peat is friable, and incapable of sustaining handling, or
moderate pressure, without crumbling. This defect would be alone suffi-
cient to render it generally unsuitable for metallurgical purposes, since,
in the first place, it could not be transported to any considerable distance
without great waste, and, in the second, it would be incapable of support-
ing the pressure to which fuel is subjected in the ordinary blast-furnace.
Charcoal prepared from peat which has been much reduced in bulk by
compression, is, to a certain extent, free from this defect; but this pre-
liminary process may increase the cost to such an extent as to preclude
its profitable application to metallurgical operations. Notwithstanding
that peat was, according to Carlowitz, charred in piles as far back as
1712, and peat-charcoal was made in the Hartz, as Vogel informs us, in
1735, none of the attempts which have hitherto been made to utilise this
fuel have been practically successful on a large scale, and further
evidence is required to enable us to arrive at a satisfactory conclusion
with regard to its economic value.
COKE.
The combustible residue which remains after the volatile constituents
of bituminous coal have been eliminated by the action of heat is called
coke. In making this substance, as in the manufacture of charcoal, one
of the chief objects sought is the production of a fuel which shall possess
a higher calorific value than the coal from which it is produced; the
elimination of a large portion of the sulphur present in the original fuel
is, at the same time, accomplished.
We are without any precise information with regard to the date when
coke was first employed. It is, however, reasonable to conclude that
when, on account of its increasing consumption, wood became scarce and
expensive, attempts would be made to extract from pit-coal a substance
which might be advantageously employed as a substitute for ordinary
charcoal. The first experiment would be to subject coal to a process
similar to charcoal-burning, and, in this way, a fuel would be produced
of which the practical value must have been quickly appreciated.
Coke was employed in Derbyshire for drying malt about the year
1640. In Plot's 'History of Staffordshire' (1686), it is stated that coal
was charred in the same manner as wood, that coal so prepared was called
coak," and was capable of producing a heat almost as strong as that
afforded by charcoal. Swedenborg, writing in the year 1734, says that
in certain districts in England coke was employed in the smelting of
iron, but that its use was not brought to perfection. M. de Gensanne,
in his Traité de la Fonte des Mines par le Feu du Charbon de Terre'
(Paris, 1770), describes and gives drawings of ovens erected at Sultsbach
by the Prince of Nassau for the preparation of coke. This arrangement
consists of a series of brick muffles, or retorts, set in a row, in which the
coal is distilled by the heat obtained from independent fire-places. The
products of distillation were also collected, and are recommended for
lubricating cart-axles, and for burning in lamps.
F
66
ELEMENTS OF METALLURGY.
In a work published in 1774, M. Jars gives a drawing of nine kilns
employed at Newcastle for destroying the sulphur and reducing coal
to cinders and "coaks."
Until comparatively recent times coke was most frequently prepared
by burning coal in piles or heaps, and even at the present day this
method of coking is still practised in certain districts.
• Good coke should possess sufficient solidity to enable it to withstand
the pressure of a smelting furnace without crushing, and is of little
value unless obtained in large prismatic pieces not liable to crumble and
form dust. From the difference observed in the properties and composi-
tion of coals, it is evident that all cannot be equally fitted for the manu-
facture of coke, and it is therefore necessary to select such as are best
adapted for the purpose.
The nature of the coke produced from any particular variety of coal
is also considerably influenced by the method of its preparation, as well
as, in a certain degree, by the nature and amount of the ash existing in
the coal from which it is manufactured. Coke which has been made in
large quantities at a time is usually better in quality than that manu-
factured on a more limited scale, as, from the weight of the mass operated
on, the product will be more compact than when smaller quantities are
used, whilst, from the high temperature obtained, the volatile ingre-
dients will be more perfectly driven off. When the ash contained in the
coal is fusible, it melts and forms a kind of cement for the particles of
coke, which is thereby rendered more compact, and less liable to be
crushed by pressure.
From the circumstance of coal being continuously raised in the same
localities, the manufacture of coke is usually carried on by means of
stationary arrangements, but from its being but slightly inflammable, and
requiring a good draught to effect combustion, its production even in the
open air becomes an easy operation.
CARBONISATION IN HEAPS. The earliest method of manufacturing
coke, and one still employed in the present day, is carbonisation in
heaps. When this process is resorted to, no external covering of the
mound is used, and the coking, which is at first carried on with free
access of air, is finally checked by the application of a coating of breeze
or earth when coke has already been produced. The coke heap is
always erected on the same station, which soon becomes covered with a
sufficient amount of breeze for the purpose for which it is used.
Instead of making round heaps, like the ordinary mound for the pro-
duction of charcoal, a long, rectangular mass is generally preferred, as by
this means a much larger amount of coal can be operated on at a time.
The length of these piles is frequently from 150 to 200 feet, and in
order to erect them, a line is first stretched in the direction of the axis of
the heap throughout the whole length of the coke station. Large pieces
of coal are now placed on either side of this, so that by coming together
at the top they form a kind of triangular gallery, running the whole
length of the intended heap. In making this central channel, it is of
importance that the fragments should be so placed as to be upright in
FUEL.
67
relation to the layers of deposition, whilst the larger surfaces must be
placed at right angles to the axis of the heap. A second series of
blocks of coal is then placed on the first, and these are again covered
with others similarly arranged, but of gradually decreasing size, until
the heap has attained a width of six feet on either side of the central
channel, when the whole is covered with a coating of smaller coal about
two feet in thickness, which is arranged without any regard to its strati-
fication, although care is taken that the larger fragments be placed on
the sides of the mound, the top being covered with small dust only. In
order to ignite the heap, stakes are placed at regular intervals from the
top of the pile along the central channel, and these, being withdrawn,
leave a series of chimneys into which burning coals are introduced. The
fire is thus communicated to the mass in so many points at the same
time, that ignition soon becomes general, and coking commences through
its whole extent.
The person in charge of the operation has now to prevent the action
from advancing too far, and as soon as he observes that thick smoke and
flame have ceased to be evolved from any particular part of the mound,
and also that it begins to get covered with a coating of ash, he prevents.
any further action by covering the flame with breeze, which, being
closely packed down, prevents the entrance of air, and quickly deadens
the fire. As the coking advances this is repeated until the whole heap is
covered, when it is allowed to remain two or three days to cool, care
being taken to supply it with a thicker covering on the side which is
exposed to the wind than on that which is opposite to it. When the fire
has become nearly extinguished the coke is withdrawn, and is subse-
quently cooled by the use of water. This method of making coke,
although simple, is far from economical; for, inasmuch as the charring
commences on the outer and upper parts of the heap, and then gradually
proceeds towards the central and lower portions, it follows that the
surface of the heap is coked before the central parts are reached, which
must, however, be fully charred before the air can be excluded. The out-
side of the pile is therefore burning to waste without the possibility of
prevention, and the central portions are but little acted on; at the same
time the surfaces are being uselessly consumed.
COKING IN MOUNDS.-A more economical method of making coke
than that just described, is represented in the annexed woodcut,
fig. 7. A chimney of about three feet in diameter at bottom is loose-
ly built with bricks on

01 Z
租
​1016
the site of the intended
mound, BB. The brick-
work of this flue has a
number of holes, b, made
by leaving out a brick here
and there, and the upper
part, which is made of
solid work for a short
distance near the top, is provided with an iron cover.
B
Fig. 7.-Coke Mound; vertical section.
B
Around this
F 2
68
ELEMENTS OF METALLURGY.
chimney the coals to be coked are placed in a slightly inclined position;
the largest masses are piled nearest the centre of the mound, and the
dimensions of the pieces are gradually reduced towards the outside.
A mound of this kind is generally about twenty-five feet in diameter, and
five feet in height; and when completed, its surface, excepting round
the bottom, to the height of about a foot, is covered with a coating
of damp breeze four or five inches in thickness, which is well packed
for the purpose of excluding the air. A shovelful of burning coals is
now introduced through the perpendicular chimney, which soon commu-
nicates with the mound through the various apertures, b, and the mass gra-
dually becomes ignited, beginning from the bottom and centre, and from
thence spreading in the direction of the covering of cinders. Openings
in the foot of the mound, where there is no covering of breeze, admit
of a certain quantity of air passing through and escaping by the chim-
ney. At the expiration of four or five days the fire will have reached
the covering, which then becomes red-hot. The top of the chimney is
now closed by an iron plate, and the uncovered space around the foot
of the pile is at the same time secured by tightly compressed coke-dust.
After being allowed to remain for two or three days the coke will have
sufficiently cooled, and may be drawn and quenched with water.
In some localities no covering is applied to these mounds, and when
the burning coals are thrown into the central aperture, combustion is
carried on by the air, which on all sides enters freely through the cre-
vices occurring between the fragments of coal of which it is composed.
When any part of the mound becomes coated with ash it is immediately
covered with breeze to protect it from further action, and as soon as the
whole surface is thus protected, the iron plate is placed on the top of the
chimney and the mound allowed to cool.
By this method a less percentage of coke is produced than is obtained
from that now to be described; but it has still one advantage over the
ordinary heap, namely, that the coking proceeds from the centre towards
the circumference.
COKING IN RECtangular KilNS. This method of coking has for many
years been practised in Upper Silesia. The kiln consists of a rectangular
inclosure (figs. 8, 9, and 10), about 60 feet in length by 15 feet in width,
outside measure, which is floored with fire-bricks set on-edge, beneath
which is a layer of furnace-slag broken small, whereby proper drainage
is secured. The inner surface of the walls, which are 5 feet in height,
and, laterally, 8 feet apart in the clear, is lined with fire-brick, whilst
the outside is constructed either of ordinary brick or of rubble-work.
In each of the lateral walls, a, is a series of openings, c, two feet apart,
and the same distance from the floor-line, so placed that those on the
one side are respectively opposite to those in the opposite wall; from
each of the openings, c, is a vertical chimney, d, ascending to the top of the
wall. In order to charge a kiln of this description, one of the openings,
e, in the end, is closed by brickwork, plastered with clay, whilst through
the opposite one the small coal, or slack, is wheeled in and spread over the
bottom, where it is watered and stamped into a layer reaching to the
FUEL.
69
lower edges of the openings, c. Wooden poles, six inches in diameter
at the one end, and four at the other, are now inserted in the lateral
openings in one side, in such a way that their smaller ends rest in
the corresponding apertures in the opposite wall. Wetted slack is
afterwards thrown upon the pieces of wood and carefully stamped down,
and the kiln is then filled up with damped slack, of which every layer, of

e
C
Fig. 8.-Rectangular Kiln; side elevation.
d
a
d
a
Fig. 9.-Plan.
d
C
IB
İA
C

e

Fig. 10.-Section on the line A B (after filling).
from six to eight inches in thickness, is consolidated by treading. When
the whole of the slack has been introduced it is covered with a thin layer
of coal-dust or clay, and the opening in the end of the kiln, through
which the charge has been brought in, is built up with loose bricks and
plastered with clay. When this has been done, the pieces of wood are
carefully withdrawn in the direction of their larger ends, and in this way
a series of channels is formed which is essential to the success of the
operation.
Before lighting, all the chimneys on one side are stopped by placing a
brick, d', on the top of each (fig. 10), those on the other side being left
70
ELEMENTS OF METALLURGY.
open; on this side the draught-holes are stopped by bricks, c', the holes on
the opposite side being open. The kiln is lighted by means of chips and
shavings of readily inflammable wood, inserted in all the unclosed open-
ings, c, and a current of air is established, which traverses the channel in
the direction indicated by the arrows. Six or eight hours after lighting,
the fire will have reached the opposite ends of the channels, when the
chimneys on the left, d', and the holes on the right, c', must be opened; at
the same time the chimneys on the right, d, and the draught-holes on the
left, c, must be closed. According to the state of the weather and the
quarter from which the wind is blowing, the direction of the currents
through the coal may be changed every two or three hours, and should
the coking be found to proceed irregularly, it may be expedient not to
change the direction of the currents in all parts of the kiln at the same
time.
The work of the coke-burner chiefly consists in keeping open the
transverse channels through the coal, and for that purpose he is provided
with a slender iron rod which is somewhat bent at one end.
When a
channel has once become stopped, considerable difficulty is often experi-
enced in re-opening it; and if several of the neighbouring channels are
closed at the same time, the progress of the operation is locally arrested
and the results obtained are unsatisfactory. Any cracks which, during
the process, may occur in the covering on the top of the coal must be
carefully stopped, and in windy weather the draught through the kiln
must be carefully regulated by more or less completely closing the
various chimneys and draught-holes. On a judicious regulation of the
draught will very much depend the quality as well as the yield of coke
obtained.
Under ordinary circumstances the process will be completed in from
eight to ten days; this is indicated by the escape of white flame from the
chimneys, and by the resistance experienced on the insertion of an iron
rod through the covering of the kiln. The openings are now all care-
fully closed and plastered with clay, and at the expiration of from two to
three days the wall, stopping one of the ends, is taken down and the
coke extinguished, and removed. By this method of treatment some
varieties of Silesian coal are stated to yield 80 per cent. of coke of good
quality.
In 1854 the late Mr. E. Rogers, of Abercarn, communicated a paper to
the Institution of Mechanical Engineers in Birmingham, on the manufac-
ture of charcoal and coke by this process, which, as far as it relates to
the production of coke, he believed to be new. Kilns, in some cases of not
less than 15 feet in width, from wall to wall, inside measure, were erected
at various establishments in South Wales, and the flues were carefully
constructed of large blocks of coal, across the interior of the kilns, corre-
sponding to the air-holes in the opposite side. Mr. Rogers was of opinion
that kilns, 14 feet in width, 90 feet in length, and 7 feet 6 inches in height,
would be found more economical than smaller ones. A kiln of these
dimensions contains about 150 tons of coal. In North Wales the saving
in working expenses was stated to amount to 50 per cent., and the yield
FUEL.
71
of coke to be 75 per cent. of the coal employed; the coke is also stated
to possess a greater density and to be of more uniform quality than that
usually produced in the district. Opinions on this subject do not, how-
ever, agree; and in some establishments, at which kilns of this description
were erected, they have, after repeated trials, been abandoned.
COKING IN OVENS.—The foregoing methods of coke-making are now
to a great extent superseded by oven-coking, more particularly in locali-
ties where, the price of coal being high, it becomes a matter of import-
ance that as small a proportion as possible should be lost during the
operation. The ovens used for the production of coke are almost in-
variably heated by the combustion of a portion of the fuel with which
they are charged, and not at the expense of a distinct quantity, spe-
cially consumed in a separate fire-place, for the purpose of raising the
temperature to the requisite degree.
When, on the contrary, coal is charred in order to obtain the gaseous
products of its distillation, and the coke made is regarded as a secondary
product of the manufacture, the operation is carried on in close vessels
heated by distinct fires; but in this case the coke produced is spongy, and
consequently unfit for many metallurgical purposes.
The ovens employed for the manufacture of coke vary so much in form
and dimensions that it would be impossible to give even a brief descrip-
tion of all those in general use; but the principle involved being the same
in all cases, it will be sufficient to explain the construction and manage-
ment of some of those most frequently employed. Fig. 11 represents

emma
Ъ
Fig. 11.-Coke-Ovens.
coke-ovens of a common form. The cavity of the oven, which is about
9 feet in diameter, and 3ft. 6in. in height, is internally lined with fire-
bricks well jointed in refractory clay. The form somewhat resembles that
of a compressed bee-hive, and at the top of the dome is a circular aper-
ture or chimney, which can be closed by an iron plate. A slightly arched
doorway of about 23 feet square is also left at b, for the purpose of charging
the oven and withdrawing the coke. This opening is strengthened by
72
ELEMENTS OF METALLURGY.
a heavy cast-iron framing, c, built into the brickwork and secured in its
place by iron binders. Where large quantities of coke are manufac-
tured these ovens are placed back to back in double rows, with a series of
doors on either side of the long mass of masonry. The charge of each is
about three tons of coal, which is introduced either through the door, b,
or through a charging-hole in the top of the oven, and as this is done imme-
diately after the withdrawal of the former charge, and whilst the oven is
still hot, the coal soon begins to give off large quantities of inflammable
gases, which escape through an aperture in the dome. When the charg-
ing is finished, the doorway, b, is closed by fire-bricks loosely piled up,
but the air has still free access into the furnace through the openings left
in the stopping, which, supplying the necessary oxygen to the gases
evolved, they soon ignite, and the temperature of the oven and its con-
tents is rapidly raised. At the expiration of about three hours the lower
holes in the loose brick wall are closed, to prevent the access of too much
air, which still finds its way through those which are above, and escapes
by the chimney. In some instances, instead of closing the doorway with
loose bricks, an iron door, lined with tiles and provided with draught-
holes, is employed. These are successively stopped by lumps of clay,
and when it is required to exclude the air entirely, it may be done by
applying a sheet of iron against the bricks and luting the edges with
clay.
In twenty-four hours after charging, the upper holes are also closed
by plastering them over, and the oven is allowed to remain twelve
hours with the chimney open, during which time the remainder of the
gaseous matter is expelled by the heat, and passes off in flame through the
opening in the dome. When the flame emitted from this opening ceases,
which usually occurs at the expiration of another twelve hours, it is
covered with an iron plate made tight by a layer of sand, and the whole
is allowed to stand for twelve hours more, for the purpose of moderating
the heat of the oven and its contents.
may
At the expiration of forty-eight hours from the time of charging, the
oven will have sufficiently cooled to admit of drawing, and the door
be now opened without causing much loss by the burning of the coke.
A large iron shovel, d, suspended by a piece of chain to the crane, e, is
now thrust between the coke and the bottom of the oven, and as the
weight on the blade will be supported by the crane, which turns on its
axis, a large mass can be taken out with comparatively little exertion on
the part of the workman. The swinging of the small iron crane enables
the burner to place the heated coke on any part of the paved floor within
the circle described by its extreme end from its point of suspension, and
as soon, therefore, as it is withdrawn it is strewed thinly on the ground
and rapidly cooled with water. When it has been thus extinguished and
has become nearly cold, it is taken up on a grated shovel, g, and transported
by means of iron wheelbarrows either to the place where it is stacked or to
the furnace in which it is to be consumed. The grated shovel is used to
separate the breeze from the large coke, as the former falls through the
intervals between the bars, so that the latter only can be taken up and
FUEL.
73
placed in the barrows. Iron is used in preference to wood for the
barrows, both on account of its being incombustible, and because wooden
ones would sooner become destroyed by constant friction against the hard
and rough edges of the coke. Fig. 12 represents a ground-plan of an
oven of this kind.
Various contrivances have at different times been
employed to facilitate the cooling of the ovens, after
the last stage of coking; but few of these have come
into general use, as the increased expense incurred in
adapting them is in most instances more than equiva-
lent to the advantages to be derived from their use.
One of the methods of hastening this cooling of the
coke is the construction of ovens with air-flues, not

O
Fig. 12.
only under the refractory lining of the bottom, but also round the sides.
During the first stages of the process, all connection between these and
the external air is cut off by dampers, but as soon as it is required to
cool down the oven for the purpose of drawing a charge, the air is
admitted by side openings, and escapes through a set of holes left for
that purpose in the upper part of the brickwork. This causes a draught
and the constant influx of fresh quantities of cold air, which, by reducing
the temperature of the walls of the oven, shortens the usual period allowed
for cooling. Where many ovens are employed, and in localities where
it is desirable that the smoke produced shall be carried as rapidly as
possible from the neighbourhood of the establishment, a flue is con-
structed along the whole range, and by this the smoke and fumes issuing
from the openings in the crown of the ovens are carried off to a suitable
chimney. In this case the flue-holes are usually shut by sliding dampers
worked either by a lever or by a pulley and counterpoise.
Some manufacturers are in the habit of cooling the coke in their
ovens before it is drawn, which is done by well watering it as soon as the
operation is completed, by means of a jet under considerable pressure
supplied by a hose. This is said not only to effect a saving by preventing
any loss by combustion during the time the charge is being withdrawn,
but also, by the decomposition of water, to carry off sulphur in the form
of sulphuretted hydrogen. Care is of course taken that the oven be not
so far cooled as to be unable to inflame the succeeding charge; and, as
the whole of the water is converted into vapour before reaching the
walls, they are not, it is stated, in the slightest degree injured. The coke
thus cooled in the furnace is said to be brighter and more sonorous than
that manufactured in the ordinary way.
Another form of these ovens is much used among the coal mines in
the north of England. This arrangement is that commonly employed in
the neighbourhood of Newcastle, and has the double advantage of retaining
the heat, and requiring but little brickwork for its construction. Each
single furnace is a square chamber ten feet deep, twelve feet wide, and ten
feet high. The top is arched, and the whole thickness of the side walls,
including the internal lining, is but two feet. In the centre of the arch
an aperture, two and a half feet in diameter and lined with a cast-iron
74
ELEMENTS OF METALLURGY.
ring, is left, whilst another is made on the level of the floor; this
opening is supplied with an iron casing provided with a groove in which
the door slides. The door, which consists of an iron framing filled
with brickwork, is suspended by a chain, and is raised or lowered by a
lever. In the brickwork of the door several openings are left, which
however, sometimes dispensed with, and in this case the bricks are
loosely placed in the frame, and admit sufficient air through the crevices
between them for the combustion of the gases issuing from the coal.
are,
The charge, which reaches the base of the arch, requires to remain
about forty-eight hours in the oven before it is in a fit state to be drawn,
which is done by an iron hook used specially for that purpose. In all
other respects these ovens are managed precisely like those last described,
fresh coal being thrown in as soon as the coke is withdrawn, and a certain
amount of air admitted during the first periods of the operation.
Good coke may be manufactured from the small particles and dust of
those varieties of coal which have the property of caking when strongly
heated. Such small fragments will, on being charred in properly con-
structed apparatus, adhere so firmly to each other as to form coke quite
equal to that produced from larger pieces. At St. Etienne a trial was
made by pressing moistened small coal into large boxes provided with
movable pegs corresponding to the channels and air-holes required to
effect the coking. These cases were so constructed as to admit of being
easily taken to pieces after the coal had been properly forced in, and, as
the pegs were at the same time withdrawn, it was thus moulded into a
small heap provided with all its necessary flues and channels. This
process was found to yield good firm coke, but the amount of labour
required to form the mound proved too expensive to admit of its being
advantageously employed, and it was consequently abandoned in favour
of the oven, fig. 13, which is that used at Rive-de-Gier, for coking dust-
coal.

A
A
Fig. 13.-Coke-Oven, Rive-de-Gier; longitudinal section.
This oven consists of a flat-arched cavity with an even floor. Like
those before described, it is without a fire-place; the heat retained by the
walls of the apparatus after the withdrawal of one charge being suffi-
cient to cause the ignition of that which succeeds it.
The floor, a,
of this oven is an oval space, eleven and a half feet wide, and twenty-
three feet in length, composed of a bed of fire-clay six inches thick,
spread out and well beaten on a layer of loose stones, b. This, again,
rests on a mass of rubbish and gravel, C, with which the centre of the
FUEL.
75
foundation is filled, and which forms the immediate support of the
bottom of the oven. For the purpose of charging the coal and with-
drawing the coke, two openings, d, are placed opposite each other at
the extremities of the longer axis of the oven; these are closed by doors,
each two feet high and two feet eight inches wide, made of iron, lined
with fire-bricks, and of which the refractory side is turned towards the
oven. Each of these doorways is provided with cast-iron linings, e,
made with grooves, in which the doors, f, slide when raised or lowered by
means of chains and levers to which they are attached. In the middle
of each door is a small opening, through which the workman can observe
what is going on inside, and thereby regulate his proceedings. The
greatest distance from the roof to the floor is four feet. A small
chimney, G, one foot six inches, in diameter, and one foot five inches in
height, is placed in the centre of the arch, A, for the escape of gas.
The whole of the internal lining, excepting the floor, is composed of
fire-bricks, and the arch is jointed with clay, instead of lime, in order to
render it better calculated to withstand the heat produced. The outside
of the masonry may be of either brick or stone, but should be covered
with a good layer of mortar mixed with sharp sand, for the purpose of
excluding any air, which might otherwise enter through the joints of the
work. Should any crack occur during the working of the apparatus, it is
for the same reason carefully stopped with clay kept prepared for that
purpose.
The oven is charged while still hot from the preceding operation, and
the layer of coal-dust, which is about twelve inches in thickness, should
be evenly spread on the sole by iron rakes. The fine coal is slightly
sprinkled with water before being charged; and, if it be of a very caking
description, the layer on the bottom of the furnace should not exceed
ten inches in thickness.
During the first two hours after charging, the doors are entirely
closed, with the exception of a small slit at the bottom, which affords
just sufficient draught to carry off, through the chimney, the large quan-
tities of gases and vapours which escape from the charge. This stage
of the operation corresponds to the first or sweating period of charcoal
mounds, and it is found that the more slowly and regularly this is
conducted, the larger is the amount of coke produced.
The charge of one of these ovens varies from 120 to 150 cubic feet,
according to the more or less caking nature of the coal operated on. At
the expiration of two hours after charging, the evolution of vapour
rapidly declines, whilst the quantities of inflammable gases given off are
much increased. After a short time, these, mixing with atmospheric
air entering beneath the doors, suddenly ignite with a sort of explosion,
and the yellow smoke which has hitherto been evolved through the aper-
ture in the dome is replaced by a cloud of a darker colour. At this
point the charge is at a dull cherry-red heat, and it becomes necessary to
increase the temperature, in order to expel the last traces of volatile
matter. This is done by raising the doors about three inches from the
bottom of the frame, and the fire soon draws up and yields an increased
76
ELEMENTS OF METALLURGY.
quantity of dusky-coloured smoke. At the expiration of three quarters
of an hour, the smoke gets clearer and less sooty, the heat of the charge
becomes uniform in all parts of the furnace, and the coal begins to
split. At the end of three hours from the first opening of the doors, the
mass of coke is usually split from the surface to the floor of the furnace,
and at this stage the doors are closely shut, and the crevices stopped with
clay. The heat, which has been absorbed by the walls, will now be
sufficient to complete the charring of the coal, and the expulsion of the
last traces of gaseous matter is effected by the same means. After thus
shutting the furnace, the flame issuing from the central chimney still
flickers for a short time over the opening, but gradually becomes more
and more feeble, until it finally becomes extinct. The top of the
chimney is now closed by an iron plate, and the coke drawn with as little
delay as possible, in order to prevent loss of heat before the introduction
of another charge. Each operation requires twenty-four hours for its
completion, and as soon as the coke is withdrawn, it is sprinkled with
water, for the double purpose of cooling it more rapidly, and also of
producing the decomposition of the sulphur compounds which, if
retained, would render the coke less valuable as a fuel.
When one charge is withdrawn, another is introduced into the furnace,
and the process goes on without intermission until it becomes necessary
to allow the oven to cool for the purpose of examining its refractory
lining, which, if made of good bricks, will require to be repaired about
once in six months. At Rive-de-Gier, the annual produce of coke is
found to amount to 69 per cent. of the coal employed, and even the
worst varieties which are there subjected to coking in these ovens afford
from 60 to 65 per cent. of coke.
✓ Coke produced in ovens is usually denser than that obtained either in
heaps or mounds, but, on the other hand, it is said to contain a larger amount
of sulphur, and to be on this account less adapted for certain purposes,
in which that substance is prejudicial, than coke prepared in the open
air. On cooling, good coke splits into prismatic masses, in some degree
resembling columns of basalt. Its colour is steel-gray, almost ap-
proaching in some instances to silvery whiteness; but the surfaces of
many varieties are covered with an iridescence supposed to be dependent
on the presence of sulphur, and is therefore a property by which its
value is not enhanced.
IMPROVED COKE-OVENS.-Numerous patents have at various times
been taken out which have had for their object the utilisation of the
heat afforded by the ignited gases which are generally allowed to pass
directly into the chimney, or into the open air.
Breckon and Dixon's Ovens.-The invention of Messrs. Breckon and
Dixon consists in constructing coke-ovens with flues for the purpose of
conveying the gases, when in a state of combustion, beneath the floor of
the ovens.* These flues communicate with the interior, and the gases
are taken through them before passing into the chimney. The following
description will, with the aid of the woodcuts, enable this arrangement
* Specification filed June 9th, 1860.
FUEL.
77
to be readily understood.* Fig. 14 represents, in elevation, a row of
coke-ovens provided with a chimney through which all the gaseous
products make their escape.

2-
.0.
Fig. 14.-Breckon and Dixon's Coke-Ovens,
Fig. 15 is a plan of four coke-ovens, shown partly in section. Fig.
16 is a sectional elevation of two coke-ovens, showing flues leading to
the chimney. Fig. 17 is a front elevation, also partially in section. These
ovens are shown with regulating valves and iron distributors, for which
a patent was granted March 29th, 1858, but they are by no means
essential to the efficient working of the apparatus; a is the door of the
coke-oven; b, the opening at the top; c, the flues or pipes which convey
atmospheric air, admitted by the regulating valve, d, to the distributors
e; ƒ (fig. 17) is the hydrant.
The improvement claimed consists in the application of flues, g,
constructed under the floor, h, of the ovens. These floors are made of
fire-brick, or other suitable material, resting on the division walls of the
flues, g, which are connected with the interior of the oven by the upright
flues, i, and the circular openings, j, and with the chimney, k, through
the flues, and m. Each orifice, j, is in communication with one of
the outer flues, g, and passes from one to another as indicated by the
arrows. When these gases arrive at the two central flues they ascend
the passages, l, and enter the horizontal flue, m, through which they
escape to the chimney; a damper, n, placed in each of the flues, l, admits
of one or more of the ovens being shut off during repairs, or for other
purposes, without interfering with the action of the others. The coal,
with which the oven is charged, may either be dropped through the
opening, b, or thrown in through the door, a.
When the charge becomes ignited the gaseous products of combus-
tion, escaping through the openings, j, descend the flues, i, into those
Transactions of North of England Institute of Mining
* Drawings from
Engineers,' 1860–61.
78
ELEMENTS OF METALLURGY.

g
d
α
999 9 g
R
m
m
d
a
-
h
a
Fig. 15.-Breckon and Dixon's Coke-Ovens. Plan of four; partly in section.

b
m.
n
n
b
9
9
Fig. 16.-Breckon and Dixon's Coke-Ovens; sectional elevation.
e
a
FUEL.
79
under the floor, g, where they circulate, and finally pass off to the
chimney through the flues, I and m. In this way the floor of the oven
is heated by the ignited gases, which according to the patentees enables a
given quantity of coal to be converted into coke in about one-third less

9
I
b
(L.
d
d
Fig. 17.—Breckon and Dixon's Coke-Ovens, front elevation; partly in section.
time than is required in an ordinary oven. They also state that the coke
produced is denser and of better quality, and that the yield is increased
to the extent of from 10 to 15 per cent. A very similar patent was taken
out by Joseph Dunning in May, 1853.
It was found at one of the collieries in the neighbourhood of Dar-
lington, after a trial extending over several years, that coal, yielding 58
per cent. of coke in ordinary ovens, afforded 69 per cent. in those con-
structed with flues beneath the floor; also that a charge of six tons,
which requires seventy-two hours for conversion into coke in the former,
is in the latter, completely coked in forty-eight hours.
Anchor Oven.-This oven admits of the entire charge of coke being
drawn at once previously to cooling, thus saving a considerable part of
the labour required for discharging the ordinary coke-oven and also the
great wear and tear to the lining of fire-bricks resulting from cooling in
the ovens by the introduction of a jet of water.
In these ovens (fig. 18) the mouth is of the entire width of the
chamber, A, and the anchor, d, e, f, which is of wrought-iron, is placed in
the oven before it is charged with coal, and is thus, at the end of the
operation, imbedded in the coke. When the oven is to be drawn a
chain is attached to the anchor from a winch fixed in some convenient
position, which, when set in motion, draws out the whole charge in
one mass upon a paved flooring, where it is cooled by the appli-
cation of water. In some cases, instead of employing water, a sheet-
iron cover is put over the coke, which, around the lower edge, is kept
as nearly as possible air-tight by the application of damp breeze. In
this way the atmosphere is so nearly excluded that the coke may be
allowed to cool gradually, without experiencing any material loss of
weight through waste by burning. The great size of the mouth of the
oven, which is required when this method of drawing coke is resorted
to, has been urged as an objection to the use of the process, but this, in
80
ELEMENTS OF METALLURGY.
practice, is found to be productive of but little inconvenience. The wear
and tear of the anchor itself is also an apparent objection, but experience
shows that the waste of iron is in reality not great.

d
A
A
A
A
Fig. 18.-Anchor Ovens; ground plan.
The time required for coking in ordinary ovens is usually from forty-
eight to seventy-two hours, but, when an exceedingly hard coke is required,
the operation is sometimes continued during ninety hours. The total
cost of manufacture, exclusive of taxes, agency, and redemption of capital,
varies from about 1s. 4d. to 1s. 6d. per ton.
COLLECTION OF TAR, &C., FROM COKE-OVENS.-In this country large
quantities of tar are annually furnished by the distillation of coal, from
which gas for illumination is obtained, and as the supply may be consi-
dered equal to the demand, the price is so low as to offer little induce-
ment to the manufacturer to take measures for the collection of that
which might be obtained from coke-ovens. In some localities, however,
it becomes a matter of importance that as small a portion as possible of
this substance should be allowed to escape condensation.
Silesia.-At Gleiwitz, in Silesia, the apparatus used for this purpose
is a cylindrical oven, eight feet high and about six in diameter. The
upper part is arched, and has an opening for the escape of gases, which
may be closed by an iron plate. The charging door, which is on a level
with the floor, is closed by piling up loose bricks, and afterwards made
air-tight by applying an iron door on the outside and stopping the
interstices with clay. Besides this door the oven is provided with a
FUEL.
81
series of air-holes made through its walls at different heights from the
floor, and a large iron pipe is fitted into the arched brickwork of the top
for the purpose of carrying off and collecting the tarry vapours which
are evolved. These, together with the gaseous products, are conveyed
to a cistern which condenses and collects the former, and allows the latter
to escape. In the cold season this pipe leads directly to the receiver,
but during warm weather it is connected with a series of zig-zag pipes,
which, passing through cold water, acts as a refrigerator and aids con-
densation. The charge of one of these furnaces is from 35 to 40 cwts. of
coal, and as soon as it has taken fire the larger openings, and all the air-
holes, except the lower row, are closed. When the fire, as seen through
these apertures, has assumed a reddish-yellow colour, the holes are
closed, and those which are immediately above them opened. On closing
the second series of holes, the third is opened, and so on, until the
whole charge has been sufficiently and regularly ignited. The first and
second rows of holes are each allowed to remain open ten hours, the
third sixteen hours, and the fourth and last series three hours; after
which the oven is allowed to remain twelve hours to cool, and the coke
is then drawn and quenched with water.
The coal used in these ovens is slightly caking in character, and each
charge, besides yielding 53 per cent. by weight, or 74 per cent. by
volume, of coke, produces on an average 5 gallons of tar. The same
coal charred in mounds affords only 47 per cent. of its weight of coke,
which is far more spongy and friable than that obtained in ovens. It
is probable that ammonia might also be manufactured from the water
associated with tar thus obtained, although it does not appear that it
is collected for that purpose. In this country the low price of tar
and the supposed injury to the quality of the coke caused by its collection
have prevented the introduction of furnaces on this principle.
Pauwels and Dubochet's Oven. In 1850 a patent was granted to
Messrs. Pauwels and Dubochet for the manufacture of coke and gas. *
This invention is described as having for its object, first, the extraction from
pit-coal of a gas fit for illumination, and the production at the same time
of a coke possessing all the properties requisite for smelting ores, and
generating steam in locomotives; second, the regulation, according to
circumstances, of the pressure of gas in the passages, so as to render the
loss of gas as small as possible. These various results are obtained by
means of distinct apparatus; first, an oven or retort, with its extractor,
and second, a moderator. The oven or retort is constructed of bricks,
cast- and wrought-iron; it is furnished with fire-places for producing the
necessary heat, by the combustion of coal, coke, or other combustible, and
has various flues for the circulation of heat, with a peculiarly constructed
heat-magazine : and, lastly, is furnished with divers apparatus, some used
as channels for the gaseous products, and the others serving either
* The system of Pauwels and Dubochet, as well as that patented by Pernolet, are
described very nearly in the words of their respective specifications. The author
must consequently not be held responsible for the statements made; they possess,
however, considerable interest as showing the direction which has been given to
attempts to render available the various products evolved in coke-making.
G
82
ELEMENTS OF METALLURGY.
permanently or at intervals to isolate the distilling apparatus, properly
so called.
The object of the extractor is to protect the apparatus from pressure;
it is divided into three distinct parts. The first is composed of three vats
full of water, in which as many bells or movable chambers are caused to
work up and down by any convenient motive power made to act upon
suitable shafts and cranks. The second part of the apparatus consists of
two large cylinders, provided with rectangular plungers, united together
and acting as valves, which constitute, with the first part of the me-
chanism, an aspirating and forcing apparatus, the action of which is regu-
lated by the third portion of the apparatus, which consists of a large vat
in which works a bell or movable chamber, something like a gasometer.
The office of this is to regulate and maintain the equilibrium of
pressure.
In order to set an oven to work, it must first be raised to a high tem-
perature by the application of heat, both to the interior and exterior; this
being done, the fires are to be kept up, and as soon as the coal has been
introduced into the oven the doors must be closed, leaving open, however,
for a few minutes the orifice of the extraction chimney, to allow aqueous
vapours to escape, after which the orifice is closed by means of the cover,
and a hydraulic valve is opened at the same time, to allow the gas to
pass through the pipes, which, as well as the interior of the oven, are pro-
tected from pressure by means of the communication then established
between them and the extractor. The gas is thus aspirated or drawn by
the extractor and forced into the various apparatus of which gas-works are
composed. The moderator must be so regulated that its action shall
prevent any variation of pressure on the apparatus and its appendages.
Coke-ovens on this principle are employed at a large establishment in
the neighbourhood of St. Etienne, and at some other places in France,
and the results obtained are said to be satisfactory; but the coke which
we have seen produced in such appliances was darker in colour and con-
siderably less dense than that manufactured at a higher temperature in
ordinary ovens.
Pernolet's Coke-Oven.-A patent was granted, in 1862, to Richard
Archibald Brooman (being a communication from Charles Claude Phili-
bert Nicolas Pernolet) for "Improvements in Coking Ovens, in collecting
and utilising the Products from the Distillation or Carbonisation of Coal
and other matters producing Coke, and in apparatus employed therein."
The invention is described as consisting in the construction, arrangement,
and working of coking ovens, in such a manner, that the following products
are obtained during the manufacture of coke :-First, coke suitable for
metallurgical, railway, and other purposes, in greater proportion than
when manufactured in the ordinary manner; second, gas suitable for
burning and heating; third, tar, and different oils obtainable therefrom;
and, fourth, ammonia and ammoniacal salts.
The apparatus employed is said to be applicable not only to ordinary
coal, but also to anthracite, coke-dust, peat, wood, and other combustible
materials, of vegetable or mineral origin, whether treated separately or
FUEL.
83
mixed with rich coals, resins, or tars. "Nine chief features are comprised in
this invention." They consist, first, in particular arrangements of coking
ovens capable of manufacturing coke from all kinds of coal; second,
in the application to these ovens of a continuous exhaust or draught
for drawing off and collecting all volatile products resulting from the
distillation of combustible matters; third, in a method of condensing such
of those products as are capable of being liquified, and in the preserva-
tion of each of such products so as to utilise them; fourth, in the appli-
cation of the gas produced in the ovens, whether to heating the furnaces of
the coking ovens themselves or other furnaces, or to the reduction of
oxidised ores, or to any other purposes for which carburetted hydrogen
can be employed, especially for lighting purposes; fifth, in pulverising
certain coals which would otherwise produce coke of a bad appearance
and ill adapted for metallurgical and railway purposes, whereas, after pul-
verisation of the coal, coke suitable for locomotives and other uses may be
produced, and that without washing being necessary; sixth, in mixing
rich coal-tar or resin with poor coal, anthracite, coke-dust, peat, and other
combustible materials which do not by themselves produce good coke;
seventh, in the employment of steam thrown on the coke when at its
highest temperature for desulphurising it; eighth, in the employment
of apparatus for loading the ovens with coal and for removing the coke,
whereby these operations are effected more speedily and economically
than in the ordinary manner; ninth, in producing in the same ovens as
those used for the manufacture of coke, common tar, such as that obtained
from gas-works, or other tars richer in oils; and in utilising them in
various ways.
Ovens constructed according to this invention are equally suited for
raw or for washed coal. The distillation is carried on upon a large scale,
say from six to seven tons in an oven, and all the products accessory!
to the distillation, such as tars, ammoniacal waters, and gases for burning
and heating, as well as the coke, being collected separately, may be
utilised. If these ovens are erected near towns the gas can be used for
lighting, or it may be employed in iron-works, where a quick and regular
fire is required. If the gas be not required for lighting or heating it is
burned in the coking-oven furnaces, in which case no other fuel will ordi-
narily be required. When the ovens are used for the manufacture of
coke only, a gas-holder, which in other cases is required to contain the
gas, is dispensed with, as well as the exhauster, and the exhaust will
depend on the draught of the chimney, being increased by the vacuum
produced by the partial condensation of the volatised products.
The coke-oven shown, figs. 19, 20, and 21, is about thirty feet in length;
fig. 19 is a longitudinal section and fig. 20 a horizontal section of two
ovens at different heights. Fig. 21 is a transverse vertical section
through two ovens ; of one through the fire-place and of the other across
the flues at the far end. C, fig. 19, is a truck running on the rails, B, and
constructed in such a manner that its load of coal may be discharged
at will into either of the openings, D, in the arch of the oven. An
ordinary oven requires six truck-loads to fill it; c, c, are hoppers placed
G 2
84
ELEMENTS OF METALLURGY.

M
J
A
S
K
M
C
D
Α
D
F
0
i
1
W.J.WELCH.DELET.SC
T
Fig. 19.-Pernolet's Coke-Oven; longitudinal section.
I
FUEL.
85
M
M
W
M
0%
0¢
α
α
α
a
--A-
FO
Fig. 20.-Pernolet's Coke-Oven; horizontal section at different heights.
T
t
W.J.WELCH SE

86
ELEMENTS OF METALLURGY.
over the apertures, D, to guide the load into the interior of the oven, A.
The coal being thus introduced on to the bed, s, of the oven, is spread
evenly thereon by means of tools introduced at the ends. The two
doors, d, are then lowered by means of the windlasses, G, running on the
rails, g; the hooks, W, which connect the doors, d, with the windlasses,
are disconnected, all the openings, d, closed, and the joints stopped with
sand or earth, so that no air may enter the oven.

A
A
$
asa
a
α
a
Fig. 21.- Pernolet's Coke-Oven; transverse section.
During the time occupied by the removal of the coke and charging the
oven with coal, the fire on ƒ has not been extinguished; so soon, then, as
the mass of coal introduced into the oven is sufficiently heated, the distil-
lation begins; gases, steam, and tar are disengaged and issue by the orifice,
E; they then traverse the pipe, F, and enter the condenser, where the
gaseous products traverse compartments formed of thin metallic plates,
smooth and close to one another, by coming in contact with which
they are gradually cooled. The cooling is accelerated by a continuous.
flow of water falling from a reservoir into chambers, whence the water
spreads on each side so as to run down externally, from top to bottom,
over the sides of the condenser. A wooden casing surrounds the con-
denser, and protects it from the action of the sun and at the same time
affords a passage for a current of air which serves to cool the water.
Following the condenser, where the tar and greater portion of the ammo-
niacal waters are deposited, the gases and the ammoniacal vapours enter
into the first washer, where they traverse from the bottom upwards through
fine showers of ammoniacal water supplied continually by a pump from
a suitable reservoir. The ammoniacal waters may be thus enriched to
any desired degree for subsequent treatment The current of gas thus
purified passes to a second washer, similar to the first, but supplied with
water only, to complete the absorption of ammonia. After the tar, oils,
and ammoniacal waters have been removed from the gas the latter flows
through pipes, M, under the influence of the draught of the chimney,
O. The combustible gases which reach the fire-place of the coke-oven, ƒ,
become mixed with air, which enters through small holes formed around
and in the middle of the nozzle, u. The mixture of gas with air pro-
duces a flame which circulating through the flues, a, conveys heat to the
Thence the products of combustion pass to the flue, T, and after-
wards to the chimney, O. The ovens are divided into sets of ten, each
ovens.
FUEL.
87
group having a separate chimney; v, v, are sight-holes, fitted to the
flues, a, for examining whether the heat is equally spread between the
different ovens of a group and in the various flues of the same oven. By
means of a tap, z, the quantity of gas admitted to the fire-place of each
oven is regulated. The quantity of air admitted around and through the
nozzle, u, is regulated by slide-valves or otherwise, and the distribution of
flame is regulated in the flues, a, by means of fire-brick registers, k. After
a certain time, which varies from two to three days, according to the
nature of the coal used, the whole of the charge is transformed into coke :
if required, desulphurisation is effected.
For this purpose, a steam discharger is conveyed to the front of the
oven on the rails, h; communication between the inside of the oven, A,
and the general passage for the gas and vapours is intercepted by closing
the register, r; connection between the boiler, J, and the door of the oven
is established by the pipe, j, and, by opening a tap, steam is driven into the
interior of the oven as long as may be considered desirable. The doors,
d, are then raised, and after adjusting the discharger in front of the oven,
it is set in motion, and pushes the coke before it out of the oven on to
the inclined plane, I, between dwarf walls, i, where it is covered with coke-
dust to smother it; the discharging occupies from four to five minutes.
The discharger is then withdrawn, the orifices, D, are opened, and the oven
is again charged, as before described, with six or seven tons of coal, which
takes from fifteen to twenty minutes to accomplish; the doors, d, are lowered,
any pitch which may have been deposited is removed, the charging orifices
are closed, the register, r, opened, and the operation commences afresh.
When the coke on the inclined plane, I, is sufficiently cold, it is
placed in trucks which convey it away on the rails, t. Care must be taken
that the following precautions are attended to during the process: First,
that all the joints are kept tight with earth, so that no air may enter
during the operation; second, that a uniform heat is maintained through-
out the ovens; third, that the condensers and washers are regularly
supplied with water. The form and shape of the ovens may be consider-
ably varied without departing from the invention. Impure coals may
be pulverised in any convenient way, or mixed with rich coal, or even
with tar, or pure coal before carbonisation; but the pulverising process.
is very efficacious in order to give solidity and good appearance to the
coke, and in order that coke made from very poor coal may, without
washing, be suitable for use in locomotives and furnaces generally with-
out leaving clinkers on the grate, because, when the foreign matters are
pulverised, the current of air carries them away, so that in this particular
case the pulverisation replaces washing without waste. Where the mix-
ture of coal to be formed into coke is composed of materials which do not
carbonise well alone, and would produce only incoherent products, the
ovens constructed according to this invention answer better than ordinary
ones, because the bituminous parts not being liable to be burnt, a less
quantity is required to produce the agglomeration of poor coal, anthracite,
coke-dust, and other combustible materials incapable alone of being trans-
formed into solid coke.
88
ELEMENTS OF METALLURGY.
The apparatus employed by Pernolet is very similar to that patented
by Pauwels and Dubochet twelve years previously, excepting that the latter
exhaust the gases from the oven by means of a machine, whilst Pernolet
sometimes effects the same object by the draught of a high chimney.
Several experiments were made at Pease's West Colliery, near Darlington,
in the summer of 1860, with a view to collect ammonia from the gases
driven off from coal by the heat of coke-ovens, but the results afforded
no promise of ultimate success, and they were therefore abandoned.
COMPOSITION AND PROPERTIES OF COKE.-Well-prepared coke essen-
tially consists of carbon, inclosing the various inorganic impurities of
the coal from which it has been manufactured. It, however, invariably
retains small quantities of hydrogen, oxygen, and nitrogen. The following
table gives the composition of three varieties of coke :—

1.
2.
3.
C.
93.15
91.30
91.59
H.
0.72
0.33
0.47
N.
1.28)
2.17
2.05
0.
0.90
Ash
3.95
6.20
5.89
No. 1, coke from Durham coal, Richardson; Nos. 2 and 3, coke
from the caking coal of the Mons basin, analysed by M. de Marsilly.
These specimens were dried at between 100° and 200° C. before being
subjected to analysis.
Perfectly dry coke will not generally absorb more than from 1 to 2·5
per cent. of moisture by exposure to a moist atmosphere; and coke, of
which the extinction has been properly conducted, should not retain more
than 3 per cent. of moisture; as, however, coke-burners are not unfre-
quently paid according to the weight of coke produced, without any
stipulation being made as to the percentage of water which it shall
contain, it is not unusual to find specimens in which the amount
varies from 8 to 12 per cent. It is evident that in order to produce
its highest calorific effect, coke should be used in a dry state.
A con-
siderable portion of the slack now employed for the manufacture of
coke is freed from shale and other impurities by some process of washing
before being charged into the ovens.
WASTE HEAT FROM COKE-OVENS.-Ebelmen, who made a series of
analyses of the gases issuing from coke-ovens, arrived at the conclusion
that in those on which he experimented two-thirds of the heat capable
of being produced by the complete oxidation of the volatile products
were rendered sensible in the ovens themselves, and that only one-third
remained to be generated by the oxidation of the gases which escaped
from them. Many attempts have at various times been made to render
available this waste heat by applying it to steam boilers and other similar
purposes; but, in almost every instance, the results have been unsatis-
factory. Obstructions which intercept the heat and prevent the free exit
FUEL.
89
of the gases from the coke-oven are found to be so injurious to the quality
of the coke produced, that no saving arising from the application of waste
heat to such purposes will compensate for the injury done to the coke.
In preparing coke it is essential that no obstruction should be offered
to the free egress of the gases from the oven as they are evolved, and they
should be allowed to mingle with atmospheric air in such proportions as
to produce the highest temperature in the ovens without waste of coal.
The process of coking will be thus carried on with rapidity, and a bright
dense coke, free from volatile matter, will be the result. The admission
of air to the gases in the oven must be regulated by the judgment of the
coke-burner, whose object will be to generate the maximum amount of
heat with the least possible combustion of the coke.
Very trifling interruptions to the exit of the gases invariably retard
the process of coking, and, when this occurs, the coal near the bottom of
the oven is found to be imperfectly coked, thus causing a serious depre-
ciation in its value. Generally speaking, any attempts to utilise the
waste heat of coke-ovens, which materially reduce the value of the
coke produced, will be found commercially valueless.
CHARRING OF BROWN COAL.-Brown coal is of all kinds of fuel the
least adapted for carbonisation; for although it is acted on by heat in
the same way as wood, and produces a less combustible charcoal or coke,
yet it is subject to inconveniences which render its production too costly
for general application. Lignite, like peat, contains a large proportion
of ash, and this percentage will necessarily be greater in the charcoal
produced than in the coal from which it was made. This, from the
tendency which the charcoal would necessarily have to clinker on the
fire, prevents its being used for many purposes for which a fuel of greater
purity could be employed. In addition to this, the action of heat causes
the layers and concentric rings which are scarcely perceptible in the
fresh lignite to separate from each other, and the charcoal or coke manu-
factured is thereby either reduced to such small fragments as to be of
little service as a fuel, or is rendered so extremely friable as to be unable
to bear carriage even to a short distance from the locality in which it is
produced. The carbonisation of lignite in mounds is, however, conducted
on a small scale in the neighbourhood of Cassel; but the situations
where this can be done with advantage are far from numerous.
The following results were obtained by heating pieces of brown coal
in closed crucibles until all traces of their volatile constituents had
ceased to be evolved :-
100 Parts of
Gave of
Charcoal
100 Parts of
Gave of
Charcoal
Earthy Coal from the Basses Alpes 48.5
Lignite from Greece
Lignite from Neundorf
38.4
38.9
""
Coulang
38.1
Friesdorf
28.2
Jahnsdorf
32.8
""
Iceland.
57.5
""
""
Hartenberg
37.2
Auszig
40.1
34.6
""
""
""
Orsberg.
Hegendorf
62.8
Kanden
37.5
""
41.2
Reichenau
38.1
•
""
""
Stöszchen
Pützchen
29.1
29.3
·
""
46.4
Altsattel
40.3
""
•
44.7 Lignite from Verau
35.6
•
90
ELEMENTS OF METALLURGY.
GASEOUS FUEL.
Attempts were made as early as the commencement of the
present century to substitute combustible gases for solid fuel in various
technical operations; but, for a considerable time, they were not attended
with practical success. According to a report, made in 1842 to the
French Academy, by Thénard, Berthier, and Chevreul, the waste gases of
blast-furnaces were first employed by M. Aubertot, in the year 1809, for
roasting ores, burning lime, &c., and, in 1814, he suggested the erection
of suitable apparatus for the employment of waste gases for metallurgical
purposes. In the year 1801 Lampadius had already shown the possi-
bility of employing the waste gases from the carbonisation of wood, and
in 1830 he attempted, at smelting-works near Freiberg, the cupellation
of argentiferous lead by means of gases produced from coal.
Ebelmen states that M. Victor Sire, of Clerval, obtained a patent in
1836 for the manufacture of wrought-iron by means of waste gases from
blast-furnaces. According to a report of the Central Jury of the
Paris Exhibition in 1844, Sire's patent was employed in 1838 at iron-
works on the Lower Rhine, and, in 1841, in the Department of the
Moselle, for the refining of iron, but the process does not appear to have
attracted much attention.
Successful experiments were made in 1837 by Wilhelm von Faber du
Faur, by burning the waste gases of blast-furnaces in a reverberatory
furnace for the purpose of puddling pig-iron.
In the course, however, of the various trials of the employment of
waste gases for this purpose it was soon discovered that every modi-
fication in the working of the blast-furnace produced a corresponding
change with regard to the quantity and composition of the gases evolved,
and that the process of puddling was thereby prejudicially affected.
The collection of the gases also appeared to produce a prejudicial effect
on the operations of the blast-furnace itself. The dependence for a
supply of fuel on the satisfactory working of the blast-furnace was
found so prejudicial as to cause this method of employing waste gases
to be abandoned, and led to their employment in the roasting of ores,
the heating of the blast, the production of steam, and the burning of
lime, bricks, &c. These processes do not require either a very high or a
very uniform temperature, and a large amount of fuel was thus saved.
The utilisation of waste gases has also resulted in the extensive employ-
ment for metallurgical purposes of gases specially prepared in generators
or producers, by which means great saving is not only effected, but
fuels of an inferior description can be rendered serviceable for purposes
for which, if consumed in the ordinary way, they would be totally
unfitted.
Before Faber's process for utilising waste gases had obtained publicity,
experiments were made in the Hartz (1839) by Bischof, with the view of
generating gases in a furnace or producer, and subsequently burning them
by means of a mixture of atmospheric air.
FUEL.
91
Gases thus obtained from peat were found to readily afford the highest
welding heats, but as Faber's method of employing waste gases had in
the meantime come into notice, and appeared to possess the advantage of
requiring no special consumption of fuel, Bischof's results were not at
once appreciated. In 1838 some Austrian metallurgists who visited
Wasseralfingen, in Wirtemberg, where Faber's process was in operation,
came to the conclusion that the employment of waste gases in the
puddling of iron could not afford practical results, and in the following
year commenced experiments, at the iron-works of Jenbach in the Tyrol,
with a view to the preparation of inflammable gases by an imperfect
combustion of small charcoal. These trials, however, gave rise to
dangerous explosions which appear to have finally led to their abandon-
ment. In 1841 Karsten stated it was probable that certain descriptions
of compact fuel, which, from their state of aggregation and low calorific
power, were not then adapted for the purpose of puddling, would, ere
long, be rendered available for that operation by being converted, in a
special apparatus, into carbonic oxide gas, by the combustion of which
the desired result would be effected. The experiments made at Jenbach
having shown the practicability of firing with artificially-produced gases,
further experiments were made, in 1842, at steel-works at St. Stephan,
Styria, with a view of producing gaseous fuel from small brown coal.
The results obtained having been of a satisfactory nature, they were at
once published, and gave rise to the general introduction of artificially-
prepared gases as fuel. This method of firing has been further
developed by Bischof, Eck, and others, but more especially by Siemens,
whose regenerative gas-furnace is suited for almost every metallurgical
operation in which it is required to produce a high temperature in
reverberatory furnaces. As this may be regarded as one of the most
important inventions of modern times with regard to the utilisation of
fuel, it will be necessary to describe not only the apparatus employed
for the preparation of the gases, but also the arrangement made use of for
effecting their economical combustion.
Among the many advantages claimed by Mr. Siemens for his
regenerative furnaces are the following:-
a. The employment of inferior descriptions of fuel, such as slack
coke-dust, lignite, peat &c., together with a saving on the quantity made
use of to the amount of from 40 to 50 per cent.
b. A daily increase of the work done in a furnace of given dimensions
amounting to at least 30 per cent., which is a result of the almost un-
limited calorific power at command, even when only a moderate chimney-
draught is available.
c. Perfect uniformity of heat throughout the furnace, and greater
durability of the brickwork, owing to the absence of ashes, by which the
fusibility of the surfaces with which they come in contact is increased.
d. The production of a flame of such purity as greatly to diminish
waste by oxidation or deterioration of the metals operated on.
e. Great cleanliness and saving of space in works, since the gas-
producers are invariably erected on the outside.
92
ELEMENTS OF METALLURGY.
f. Increased command of the heat employed and of the chemical
effects produced by the flame, which can be immediately checked
when required, or at once changed from an oxidising to a reducing one,
or vice versa.
g. Absence of smoke from the chimney-stack, which, in the neigh-
bourhood of large towns, and in some other situations, is of great
importance.
SIEMENS'S GAS-PRODUCER.-The gas-producer employed by Mr. Siemens
is shown, figs. 22 and 23. Fig. 22 is a vertical section, and fig. 23, a
plan, partly section, on the line P Q. The body of the apparatus, A,
is a rectangular fire-brick chamber, of which the side, B, consists of thick
cast-iron plates, lined with fire-brick, and having a step grate formed
of flat iron bars, b; at bottom the bars, C, forming the grate, are of
wrought-iron, two inches square, and rest on suitable cast-iron bearers
built into the masonry. The fuel employed for the production of gas.
is, in this country, usually bituminous coal, which should not possess the
property of caking in too high a degree, but coke, lignite, peat, and even
saw-dust, may, in case of necessity, be used for the same purpose. The
fuel, whatever may be its nature, is charged into the hoppers, D,
and, on opening the valves in connection with the weighted levers, d,
falls on the inclined plane forming the front of the producer; before doing
this, however, the top of the hopper, from which a charge is about to be
let fall, is closed by an iron lid to prevent the escape of gas during the
operation. In this way the grate is constantly kept thickly covered with
fuel, and the accumulated ash and clinker are occasionally withdrawn
by removing the bars, C, beneath which they are allowed to accumulate
for the purpose of conveniently regulating the admission of atmospheric
air. During the removal of the grate, C, for the purpose of clinkering,
temporary bars of pointed wrought-iron are inserted over the lower
bars, b, and allowed to rest on the brickwork at the back. In this way
the fuel in the cavity of the producer is supported, so that the ash
and clinker may be removed without any interruption to the working
of the apparatus; when coal of good quality is employed, each pro-
ducer usually requires clinkering but once in the course of forty-eight
hours.
A limited supply of air is admitted at the grate, and its oxygen, by
uniting with the carbon of the fuel, forms CO2, which rises through the
ignited mass, taking up an additional atom of carbon, and thus giving rise
to the formation of 2 CO. The heat thus produced distils off hydro-
carbons and other gases and vapours from the fuel as it gradually de-
scends towards the grate, whilst the CO, diluted by the nitrogen of the
air, and a small quantity of unreduced CO₂, mixed with the gases and
vapours distilled from the raw fuel, is finally conducted by a gas-flue to
the furnace.
A pipe, E, supplies a small quantity of water to the ash-pit, whence, as
it evaporates and comes in contact with the incandescent fuel, it becomes
decomposed, giving rise to carbonic oxide gas and hydrogen. The hose,
F, of vulcanised india-rubber, is employed for watering the clinkers as
FUEL.
93
they are withdrawn, in order that they may be rapidly cooled and their
removal from before the producers facilitated. By means of the plug-
holes, G, the workman is enabled to inspect the state of the fires, and,
when necessary, to stir the fuel by the aid of an iron bar.
The sliding
dampers, H, are for the purpose of, at any time, cutting off the gas-pro-
ducers from the stack, I. Any in-draught of air through the crevices in
the brickwork, which would result in the burning of the gas in the flue,
is prevented by constantly maintaining a slight outward pressure in the
gas-channel.
When the furnaces stand on a considerably higher level than the pro-
ducers, the required pressure is obtained without any difficulty; but
when this is not the case some special arrangement becomes necessary in
order to produce this effect. The most simple contrivance for the pur-
pose is a cooling-tube raised to a considerable height above the level
of the producers. The stack, I, is carried up in brickwork, well bound
with iron, to a height of from ten to twelve feet, and the gases are con-
ducted through a horizontal tube of wrought-iron, from which they
pass down, through a similar stack of masonry, to the main gas-flue in
connection with the furnaces. The gases, which rise from the producers
at a temperature of about 550° C., are thus cooled by their passage
through the metallic tube, and the descending column, becoming more
dense and heavier than that of the same length which is ascending, con-
sequently overbalances it. A syphon is thus formed of which the two
legs are of equal length, but of which one is filled with a heavier gaseous
fluid than the other.
Mr. Siemens remarks, with regard to the action of this arrangement:
“This method of obtaining a pressure in the gas-flue by cooling the gas
has been objected to as throwing away heat that might be employed to
greater advantage in the furnace; but this is not the case, because the
action of a regenerator is such that the initial temperature of the gases to
be heated has no effect on the final temperature, and only renders the
cooling of the hotter fluid more or less complete. The only result, there-
fore, of working the furnace with gas of high temperature is to increase
the heat of the waste gases passing off by the chimney-flue. The com-
plete cooling of the gas results, on the other hand, in the great advantage
of condensing the steam that it always carries with it from the gas-pro-
ducer, and, in the case of iron and steel furnaces, in burning wet fuel, it
is absolutely necessary to cool the gas very thoroughly in order to get rid
of the large amount of steam that it contains, which, if allowed to pass
into the furnace, would oxidise the metal.
“There is undoubtedly a certain waste of heat, which might be utilised
by surrounding the cooling-tube with a boiler or by otherwise econo-
mising the heat it gives off, as, for instance, in drying the fuel, but the
saving to be effected is not very great, for, as 100 volumes of the gas
require for combustion about 130 volumes of air, including 20 per cent.
above that theoretically required, the heat given off in cooling 1,000° F.
is no more than would be lost in discharging the products of the com-
plete combustion of the fuel at a temperature 435° in excess of the actual
94
ELEMENTS OF METALLURGY.

166 0
P
H
E
I
I
A
GB 7
H
A
d
E
F
Fig. 22.-Siemens's Gas-Producer; vertical section.
FUEL.
95
temperature of 200°; and this loss is greatly diminished if a richer gas
is obtained."
He further observes that the composition of the gases varies in accord-

La
Ra
Fig. 23.-Siemens's Gas-Producer-Plan; partly section on P Q.
5
Ja

a
al
C

al
a
gas-
ance with the nature of the fuel employed and the management of the
producer. An analysis made, in July, 1865, of the gas from the producers at
the plate-glass works of St. Gobain, France, which were supplied with a
96
ELEMENTS OF METALLURGY.
mixture of three-fourths caking coal and one-fourth non-caking coal,
afforded the following results :-
CO .
H
CHA
CO2
N
Volumes.
23.7
8.0
2.2
4.1
61.5
0.5
100.0
The trace of oxygen present is no doubt due, either to want of care in
collecting the gas, or to leakage of air into the flue; allowing for this, the
corrected analysis will stand as under:
8=582
CH
CO2
N
Volumes.
24.21
8.2 34.6
2.2
4.21
65.4
61.25
The first three of these constituents, or about 35 per cent., are alone of
any use as fuel; the carbonic anhydride and nitrogen present only dilute
the inflammable gases.
REGENERATIVE FURNACE.—In the regenerative furnace the producer-
gases and air employed are separately heated by the waste heat of the
flame, by means of regenerators placed beneath the furnace. These con-
sist of four chambers fitted with fire-bricks loosely stacked together, so
as to expose the largest possible surface to the gases passing through
them; the waste gases from the furnace above are drawn down through
two of these regenerators, heating the upper rows of bricks to a tempera-
ture little inferior to that of the furnace itself, and, passing successively
over cooler surfaces, finally escape to the main flue of the chimney in
a comparatively cold state. The direction of the draught is now re-
versed, and the flame and heated waste gases are employed to heat up
second pair of regenerators; at the same time the gases and air entering
the furnace are passed in an opposite direction, through the first pair,
and coming, at first, in contact with the cooler brickwork below, are
gradually heated in their ascent until, on arriving near the top, they
attain a temperature nearly equal to that possessed by the waste gases.
the
The heated gases and air finally pass up into the furnace, where they
meet and ignite, producing a strong flame, which, after passing through
it, is drawn down the second pair of regenerators to a flue in connec-
tion with the chimney. In this way the temperature of the ascending
gas and air remains nearly constant, until the brickwork of the upper
portion of the regenerator has sensibly cooled; but, by the time this has
taken place, the other two regenerators have become sufficiently heated
and the draught is again reversed. The current of waste gases is thus
made to circulate through the first pair of regenerators, by which they
again become heated, whilst the combustible gases and air, entering the
furnace, are passed up through the second pair. By reversing, in this
FUEL.
97
way, the direction of the draught at regular intervals, almost the whole of
the heat generated is retained in the furnace, whereas, under ordinary
circumstances, a considerable proportion of it will be carried off by the
products of combustion. Thus, whatever may have been the intensity of
the heat produced in a regenerative furnace, the temperature of the gases
escaping to the chimney rarely exceeds 150° C.
In ordinary furnaces the amount of heat carried off by the products
of combustion is far in excess of that which is utilised; since all the heat
below the temperature of the work to be heated is entirely lost. The
economy of fuel effected in the regenerative furnace, by removing this
source of loss and making all the heat of the waste gases available for
raising the temperature of the flame, amounts, on an average, to at least
50 per cent. on the quantity used in an ordinary furnace, and this saving
is greater in proportion as the temperature at which the furnace is worked
is increased.
When the heat of a furnace is not continually lowered by the
introduction of fresh charges of cold materials, the temperature necessarily
increases after each reversal of the direction of the draught, as a very
small proportion of the heat generated is carried off by the waste gases.
By ascending through the regenerators the gases and air become heated
to a temperature nearly equal to that of the flame which had been pre-
viously passing through them in a contrary direction, and, when they
meet and burn in the furnace, the heat of combustion is added to that
absorbed from the regenerators; the flame produced is consequently
hotter than previously to the last reversal, and raises the regenerator
through which it is passed to a higher heat. On again reversing the
draught, this increased heat is communicated to the entering air and gases,
and a still further increase in the temperature of the flame produced is
the result. The temperature that may, in this way, be ultimately ob-
tained by the gradual accumulation of heat in the regenerators and fur-
nace is, in practice, only limited by the difficulty of finding a sufficiently
refractory material for the construction of the apparatus.
The only material practically available for this purpose is Dinas
brick, consisting of nearly pure silica; but, although these bricks perfectly
withstand the temperature required for the fusion of the most refractory
steel, the heat can, nevertheless, be easily so increased as to melt them.
Mr. Siemens calculates that, supposing the direction of the draught of
a furnace to be reversed every hour, 17 lbs. of regenerator brickwork, at
each end of the arrangement, per lb. of coal consumed in the gas-pro-
ducer per hour, would be theoretically sufficient to absorb the waste heat,
if the whole mass of the regenerators were uniformly heated at each
reversal to the full temperature of the flame, and then completely cooled
by the gases coming in. But, in practice, this does not actually take place,
and, consequently, three or four times as much brickwork is required in
the regenerators as is equal, in regard to capacity for heat, to the products
of combustion. It has been found by experiment that a surface of six
square feet in the regenerators is necessary to take up the heat of the
products of combustion of 1 lb. of coal per hour. The arrangement of a
H
2.
98
ELEMENTS OF METALLURGY.
reverberatory furnace on the regenerative principle will be understood by
the aid of figs. 24, 25, and 26.
The first is a front elevation of a re-heating furnace, showing the gas
reversing valves and flues in section. Fig. 25 is a longitudinal section
at A, B, C, D (fig. 26), and fig. 26 is a sectional plan at L, M (fig. 25).
The waste heat escaping from the furnace is arrested and absorbed by
the masses of open brickwork, E, F, E', F' (fig. 25), while the products of
combustion subsequently reach the chimney-flue in a comparatively cool
On first lighting the furnace, the gases pass in through the gas
state.

C
K
K'
N
Fig. 24.-Siemens's Re-heating Furnace, front elevation; valves and flues in section.
regulating valve, G, and the reversing valve, H, and, entering the flue, I,
reach the bottom of the regenerator, E (fig. 25); the air enters through
a corresponding air regulating and reversing valve, behind the valves,
G, H, and passes thence through a flue behind the partition, K, into the
regenerator, F. The currents of unheated gas and air ascend separately
through the regenerators, E and F, and pass up respectively through the
flues, L, M (fig. 26), into the furnace above, where they are lighted and
burn with a flame of moderate calorific intensity. The products of com-
bustion are removed through a similar set of openings at the other end
of the furnace, and passing into the regenerators, E', F', finally escape
through the flue, I', and another behind, K', to the chimney-flue, N. In this
way the waste heat is absorbed by the brickwork of the regenerators, E',
F', whilst the gases pass off to the chimney in a comparatively cold state.
FUEL.
99
At the expiration of about an hour the reversing valves, through which the
gas and air are admitted to the furnace, are turned over by means of
levers attached to them for that purpose, and an inward current is estab-
lished through the regenerating chambers, E', F', which have become
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Fig. 25.-Siemens's Re-heating Furnace; longitudinal section.

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Fig. 26. Siemens's Re-heating Furnace; sectional plan at L, M.
heated by the flame and waste gases which, previously to the reversal of
the valves, had been descending through them. The air and gases now
entering the furnace become heated in their passage through the hot
brickwork of the regenerators, E', F', and, on meeting and entering into
100
ELEMENTS OF METALLURGY.
combustion, produce a higher temperature than that obtained during the
first hour, when cold air and gases only were supplied.
The waste gases, from this combustion at a higher temperature, now
heat the previously cold regenerators, E, F, to a correspondingly increased
degree. After about an hour's working of the apparatus with the current
in this direction, the reversing valves are again turned, and the air and
gases admitted through the chambers, E, F, which are now very hot, and,
consequently, they enter the furnace at a still higher temperature than
before, producing a heat of increased intensity and heating the regenera-
tors, E', F', to a still higher temperature than E, F. On reversing the
current, the air and gases acquire a greater heat than before, and
an accession of heat is thus, step by step, obtained, until the furnace
acquires the temperature required; the heat of the products of combustion
being at the same time so thoroughly abstracted that they arrive at the
chimney-flue in a comparatively cool state.
When the required heat has been acquired by the furnace its tempera-
ture is readily controlled by the supply of air and gas admitted through
the regulating valves, and by the chimney damper, which is more or less
closed as circumstances may require. The regulating valves are raised
and lowered either by a hand-screw or by a notched lever, and consequently
admit of being readily maintained in any required position.
REFRACTORY MATERIALS FOR FURNACES AND
CRUCIBLES.
FIRE-STONES, &C.-Many varieties of rock, rich in silica, are employed
for the refractory linings of furnaces, and before being used for that pur-
pose should be stored for a considerable time in a dry place, in order to
deprive them of moisture. When stratified rocks are made use of, they
should be built into the wall in accordance with their natural bedding, in
order, as far as possible, to prevent exfoliation on the application of heat.
Sandstones, in which the grains of quartz are cemented by a siliceous
or argillaceous cement, are frequently employed for the hearthstones
of blast-furnaces, but those varieties which contain notable quantities
either of lime or of oxide of iron, are not sufficiently refractory. Sand-
stones containing spangles of mica, or grains of iron pyrites, are not,
generally, sufficiently infusible to be so employed; coarse-grained
siliceous stones, such as Millstone-Grit, are frequently made use of for
this purpose.
In the Truckee Valley, State of Nevada, United States of America,
a fire-stone is obtained which presents the appearance of yellowish chalk ;
it is, however, much lighter, floating readily when first thrown into water,
but sinking as soon as it becomes wetted to a certain depth. Sp. Gr. =
1.49. It cuts readily and may be sawn into any required form; it is also
easily worked with the axe.
REFRACTORY MATERIALS.
101
A specimen of this substance, analysed in the author's laboratory, by
A. G. Phillips, afforded the following results:*-

I.
II.
SiO2
73.32
73.32
Fe2O3
3.23
3.18
Al2O3
9.48
9.69
CaO
0.70
0.82
K,O
0.55
0.42
Na₂O
0.62
0.68
H₂Ỗ, combined
7.53
7.49
H₂O, hygroscopic
4.65
4.65
100.08
100.25
Talcose slate and soapstone are sometimes used for the fire-work of
furnaces, and, from the resistance offered by them to the corroding in-
fluence of metallic oxides, they are occasionally found very serviceable.
Serpentine, on account of the small proportion of silica it contains, is
also less readily attacked by metallic oxides than many other rocks, but
is not suited for exposure to very high temperatures. Gneiss is used at
Schmölnitz for the construction of reverberatory furnaces; it is easily
dressed to the required forms, and offers great resistance to high tempera-
tures and to sudden changes of heat. Granite is generally employed in
Cornwall for the outside masonry of lead and tin furnaces, which are in-
ternally lined with fire-brick. Siliceous sand is extensively used by the
metallurgist, both for mixing with the fire-clay employed as a cement
in the construction of furnaces, and for furnace-bottoms. The beds of
the smelting and refining furnaces in the copper-works of Swansea are
made of a sand of which great accumulations are met with at various
points along the neighbouring coast. This sand contains about 87 per
cent. of silica, with a little lime, oxide of iron, and alumina. Sand is also
extensively employed for moulds both in iron and brass foundries.
FIRE-CLAYS.-Clays are essentially hydrated silicates of aluminium,
and on the presence of the water of combination depends their plasticity or
capability of being moulded into any required form, when mixed with a
suitable amount of water. In addition to their water of combination all
clays contain a greater or less amount of hygroscopic moisture, which
may be expelled by heating them to 100° C., without in any degree
impairing their plasticity.
When clays are heated to redness, their water of combination is ex-
pelled, as well as their hygroscopic water, and their property of affording,
when mixed with water, a plastic mass is thereby completely destroyed,
In this dehydrated state clays do not immediately combine with water,
although they absorb it with avidity; without, however, in the least degree
regaining their plastic properties.
* This substance, which is probably the result of geyser action, does not contain
Diatomaceæ or any other microscopic organisms.
Uor M
102
ELEMENTS OF METALLURGY.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
COMPOSITION OF BRITISH FIRE-CLAYS.
SiO 2
63.30
51.80
50.20 51.10 69.25
55.50
67.12
53.05 58.10
66.16
79.40
68.98
Al2O3
23.30
30.40
32.59 31.35
17.90
27.75
21.18 28.13
26.59
22.54
12.25
23.82
K₂O
2.32
2.19
2.02
4.19
1.21
0.07
Na₂O
trace
0.44
0.49
CaO
0.73
0.36 1.46)
1.30
$0.67
0.32
0.17
0.40
1.42
0.50
trace
MgO
0.50
·
0.44 1.545
10.75
0.84
1.20
0.99
trace
0.17
FeO
1.80
4.14
4.63
2.97
Fe2O3
3.52
{2.01
5.31
0.10
1.85
2.48
2.97
1.30
0.39
H₂O, combined
9.69
4.82
5.82
7.57
3.11
5.20
5.54
H₂O, hygroscopic
10.30
13.11
10.47
7.58
10.53
$1.39
2.20
1.41
0.85
Organic matter
(0-90 2.82
1.21
99.43 99.95
99.12 100.55
99.00 99.81 100.44 100.06 100.45 98.57
98.65 100.41
3. Glascote,
7, 8, 9. Dowlais,
11. Ireland; by
1. Stourbridge, Worcestershire; used for glass pots; by C. Tookey. 2. Brierley Hill, Staffordshire; by T. H. Henry.
near Tamworth; by J. Spiller. 4, 5. Newcastle-on-Tyne; by T. Richardson. 6. Newcastle-on-Tyne; by Hugh Taylor.
South Wales; by E. Riley.-No. 7 is considered the best fire-clay of the district. 10. Glasgow; by J. Brown.
T. H. Henry; clay of excellent quality. 12. Lee Moor, Devon; by J. A. Phillips.


REFRACTORY MATERIALS.
103

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
COMPOSITION OF FOREIGN FIRE-CLAys
SiO2, combined
63.57
60.60
66.10
SiO2, as sand
Al2O3
CaO
0.55
27.45 26.39 19.80
0.84
32.08 36.04 32.70)
25.04 21.04 26.40)
29.06 30.04
59.01
60.40
54.06
46.50
55.46
77.32
27.46 24.26 24.09 26.99
34.90
31.71
15.57
0.01
0.56
0.10
1.32
0.55
0.85
0.19 trace
MgO
trace
0.70
0.18
0.34
0.72
0.61
0.82
0.14
0.13
K₂O
0.29
0.21
2.49
0.67
1.14
2.10
2.40
1.20
Na₂O
0.22
0.33
0.68
0·63
Fe2O3
0.15
2.50
6 30
0.45
0.67
0.93 4.04
3.70
2.73
3.00
0·59
0.86
H₂O, combined
8.64
9.20
7.50
9.03
8.45
8.00 10.21 10.60 14.15 13.30
9.37
5.61
H₂O, hygroscopic
1.27
101.63
99.53 99.70
97.54 99.08 98.33 100.79 100.46 100.17
97.70 100.66 100.79
1. Beleu, Ardennes. 2. Dourdan, Seine-et-Oise. 3. Hayanges, Moselle; by Salvétat.-No. 3 used for fire-bricks. 4, 5, 6. Clays
from Belgium; by Bischof. 7. Schöningen, Hanover; by Streng. 8, 9. Kipfendorf, Saxe-Coburg; by Fresenius. 10. Almerode, Hessen-
Cassel; by Berthier. 11. Vallendar, near Coblenz. 12. Mehlem, near Königswinter.
104
ELEMENTS OF METALLURGY.
When clays possess the property of resisting exposure to high tempe-
ratures, without either melting or becoming sensibly softened, they are
called refractory clays or fire-clays. These occur in various geological
formations, but those of the best quality are most frequently procured
from the coal-measures.
The substances found accompanying clays, and in a state of intimate
mechanical mixture with them, are very numerous; but among the most
common of these impurities may be mentioned oxide of iron, calcium car-
bonate, and iron pyrites. The presence of these substances materially
impairs the refractory quality of the clays in which they occur, as, by their
action on a portion of the silica, a series of fusible vitreous compounds
is produced. The degree of heat necessary to effect the fusion of these
compounds is not entirely dependent on the amount of extraneous matter
thus brought in contact with the natural silicate, but is also in a remark-
able manner influenced by their nature and number.
por-
In this way a clay containing a given amount of magnesia is found to be
less fusible than another similarly constituted, excepting that a certain
tion of the magnesia is replaced by an equivalent amount of lime; if iron
oxide be also present the compound will be found proportionately more
easy of fusion. Among the purer varieties of clay, the most refractory
are those in which the proportion of silica is greatest; and reaches its
maximum in those substances which, although exhibiting many of the
physical properties of clays, can scarcely be classified among them on
account of their very large percentage of silica: such, for example,
are the different varieties of earth consisting of the siliceous remains of
infusoria.
The composition of several varieties of British Fire-clay is given on
page 102.
The table of analyses on page 103 gives the composition of several
Foreign Fire-Clays.
FIRE-BRICKS.—The qualities required of fire-bricks differ in accord-
ance with the purposes to which they are to be applied. Sometimes it is
important that they should not become softened in a sensible degree by
continued exposure to very great heat. In other cases it is necessary
that they should withstand great and sudden changes of temperature. It
is often essential that they should be capable of withstanding consi-
derable pressure when strongly heated, and their capability of resisting
the corrosive action of metallic oxides is also a consideration of much
importance.
It is seldom possible to produce a fire-brick capable of fulfilling all
these conditions, and, consequently, such additions of other materials
are made to the clay as will afford bricks suited for the particular
purpose for which they are required. Many varieties of clay which pos-
sess the requisite degree of infusibility are, when subjected to a rapid
change of temperature, liable to split, from the expansion or contraction
of the mass. The chief addition made consists of pure siliceous sand, and
ground and previously-burnt fire-clay, which, without increasing the fusi-
bility of the compound, has the property of rendering the material less
M
REFRACTORY MATERIALS.
105
liable to become broken, through the rapid application of heat or sudden
reduction of temperature.
The manufacture of refractory bricks is conducted in a very similar
way to that of bricks employed for ordinary building purposes.
The fire-clay, after being for some time exposed to the air, is crushed
under a pair of heavy edge-stones, where it is ground either with or
without the addition of silica or of previously-baked clay of the same
description, until it has been reduced to the state of somewhat coarse
powder. This falls through a hole in the bedstone, and is thence
mounted by the buckets of an endless chain into a large cylindrical
sieve, by which it is divided into two classes. The coarser fragments,
which remain on the meshes, are returned under the edge-runners, to be
again ground, whilst the finer particles, which have passed through the
apertures, are conducted by an endless belt to a convenient situation,
where they are deposited under a small continuous stream of water. The
mixture is subsequently incorporated in a pug-mill, and moulded into
bricks in the way adopted for the more common varieties employed for
building purposes. A man and a boy can in this way, with a hand-mould,
make and lay out to dry 1,500 bricks as a day's work. When sufficiently
dried, they are baked during five or six days in kilns containing from
15,000 to 20,000. A ton of coal is, on an average, required for the baking
of every 3,000 bricks, which are all placed lengthways, and separated
from one another by about a finger's breadth in order to allow a free pas-
sage between them of the heated gases produced by the combustion of the
fuel, the whole of which is consumed at the extremity of the pile furthest
removed from the chimney.
The following table gives the composition of fire-bricks from various
localities:
COMPOSITION OF FIRE-BRICKS.

1.
2.
3.
4.
5.
6.
SiO 2
A1203
63.09
29.09
84.65
88.43 69.30
75.36
71.02
•
8.85 6.90 28.50
21.47
26.47
CaO
0.42
1.90
3.40
trace
trace
•
MgO
FeO
0.66
0.35
trace
0.44
•
1.79
trace
Fe2O3
2.88
4.25
1.50
2.00
0.80
K₂O
1.92
0.50
Na₂O
0.31
1.38
0.42
TiO2
2.21
S. trace
100.58 100.00 100.23 99.80 100.00
99.65
1. Dowlais; by E. Riley. 2. From Windsor clay; a mixture of 30
per cent. of clay and 70 of sand; by Richardson. 3. From Pembroke;
used in copper-works; by Napier. 4. Creuzot, France; used for blast-
furnaces; by Berthier. 5. Lee Moor, Devonshire; by Abel. 6. From
same locality; by J. A. Phillips.
106
ELEMENTS OF METALLURGY.
The following analyses of an ordinary "blue fire-brick" from Buck-
ley, North Wales, were made in the author's laboratory, by Mr. W. T.
Gent. Sp. Gr. = 2.28.
I.
II.
SiO2
FeO
72.45
72.63
trace
trace
Fe2O3
4.69
4.78
MnO4
.30
35
Al2O3
20.83
20.70
CaO
.30
• 29
•
MgO
trace
trace
K₂O
.61
.63
Na,O
• 62
'57
H₂O, hygroscopic
.13
· 16
99.93
100 11
The Dinas fire-bricks of South Wales, which are probably the most
infusible bricks employed in this country, consist almost entirely of silica,
and, instead of being chiefly composed of fire-clay, are made from a dis-
integrated sandstone, found in various places in the Vale of Neath.
Two specimens of "Dinas clay," obtained from different mines, ana-
lysed by Mr. W. Weston in Dr. Percy's laboratory, afforded the following
results:*
SiO2
Al2O3
FeO
CaO
K₂O & Na₂O
H₂O, combined
•
I.
II.
98.31
96.73
0.72
1.39
0.18
0.48
0.22
0.19
•
0.14
0.20
0.35
0.50
99.92
99.49
CRUCIBLES.—Crucibles are commonly manufactured either by working
the prepared clay on a potter's wheel, similar to that employed in making
ordinary pottery, or by compressing it in moulds, which thus communi-
cate to the mass the required form. Sometimes, also, although more
rarely, they are prepared by covering with clay a mandrel made either
of metal or of hard wood, and having the exact form and dimensions of
the internal cavity of the vessel required. Crucibles should be capable
of resisting sudden changes of temperature without fracture. They
should also be nearly infusible, be unacted on by the ashes of the fuel
by which they may be surrounded in the furnace, and withstand the
corrosive action and permeation of such substances as melted oxide of
lead. It would, however, be difficult to prepare crucibles capable of
* Percy's Metallurgy'; Fuel, Copper, &c., p. 236.
REFRACTORY MATERIALS.
107
fulfilling all these conditions, and it is consequently found better to select
the mixture to be employed in accordance with the use to which it is to
be applied, than to attempt the manufacture of pots which would be
applicable to every purpose.
When it is desired to prepare crucibles capable of withstanding
sudden changes of temperature, the prepared clay is intimately mixed
with various infusible bodies which impart to the mass the property of
neither expanding nor contracting in a sensible degree on being strongly
heated and afterwards rapidly cooled. These substances generally consist
of siliceous sand, ground flints, calcined clay, graphite, or powdered coke.
The most infusible crucibles are prepared from clays containing the
largest proportion of silica, and in which the amount of lime and oxide of
iron is small. The infusibility of clay, like its power of sustaining sudden
changes of temperature, may be much increased by a judicious admixture
of materials, which, from forming a kind of infusible ground-work,
prevent the crucible from being deformed by exposure to a temperature
by which it would otherwise be destroyed. The most efficient materials
for the purpose are burnt clay, graphite, or powdered coke, added to the
clay in the proportion of about one-fourth; since, if a larger amount were
used, although the infusibility of the crucible might be increased, the
carbonaceous matters would be liable to become consumed by repeated
use, and the crucible be gradually destroyed.
The composition of several varieties of manufactured crucibles has
been examined by Berthier, some of whose results are arranged in the
following table :-

Place of Manufacture.
Crucibles, Hessian
•
from Paris
95
SiO2 Al2O3 Fe2O3 | MgO
•
70.9 24.8 3.8
64.6 34.4 1.0
72.3 19.5 3.9
•
""
""
Glass Pots
""
""
Saveignies, near Beauvais
England, for casting Steel.
St. Etienne, for do.
Nemours.
""
•
Bohemia.
""
71.0 23.0 4.0
65.2 25.0 7.2
67.4 32.0 0.8
68.0 29.0 2.2 0.5
In order that an earthen crucible may be but slightly attacked by the
bodies fused in it, it is necessary that the particles of which it is com-
posed should be finely divided and closely compressed, and also that the
materials of which it is made should not readily form fusible compounds
with the substance operated on.
The metals, and their ores, with the exception of their oxides, generally
exert little action on crucibles made of ordinary fire-clay, although galena,
together with certain other substances, has the property of filtering through
the pores of some earthen crucibles without exercising on their constituents
any apparent chemical action. The degree of facility with which clay
pots yield to the action of metallic oxides is usually tested by the fusion
of litharge, which is maintained in the fluid state until the pot becomes
108
ELEMENTS OF METALLURGY.
pierced by its corroding action, when the time necessary to produce this
effect is noted and compared with similar results obtained with other
varieties of crucibles. Black-lead crucibles, and those in which ground
coke has been incorporated, are attacked by fusible metallic oxides, through
the gradual oxidation of the carbon, which results in the reduction of a
portion of the metal.
manner:-
The degree of fusibility of crucibles and other refractory bodies is
best ascertained by a direct experiment conducted in the following
A piece of the substance to be examined, and which for this
purpose should present numerous sharp edges, is heated, in a refractory
crucible, lined with powdered charcoal, to the fullest extent possible in a
large wind furnace. The pot and its contents are then allowed to cool,
and on afterwards examining the contents, it will be observed whether or
not the thin edges of the broken fragment have become rounded or have
been rendered translucent; in which case it affords a sufficient indication
that a commencement of fusion has taken place.
The permeability of crucibles by liquids may be determined by filling
them with water, and noting what time elapses with each variety before
any appearance of dampness is perceived on the outside.
For the purpose of ascertaining their power of resisting sudden
changes of temperature, crucibles may be thrown, without any previous
annealing, into an intensely-heated furnace and afterwards withdrawn
and at once exposed to a current of cold air.
Crucibles are used both in the unburnt and burnt state. Small
crucibles are usually kiln-burnt before they are used, but the large Stour-
bridge-clay casting-pots, which are extensively employed by brass-founders,
are never previously burnt. They are first gradually and thoroughly
dried by the maker in properly-constructed stoves, and are afterwards
kept for use by the founder on shelves in some dry and warm situation in
the casting-shop. A fire is made in a cold furnace, and covered to a depth
of a few inches with coke, broken to a convenient size. On this the
crucible is placed in an inverted position, and the furnace is filled up
with coke. When the crucible has become uniformly red-hot it is with-
drawn, and immediately replaced with its mouth upwards. It is a some-
what remarkable fact that pots of this description which are at first put
into a furnace with the mouth upwards almost invariably crack.
Four different kinds of crucibles are used by assayers in this country,
viz., the London, the Cornish, the Hessian, and the French; and of these
the two former are, perhaps, most extensively employed.
London crucibles are of a reddish-brown colour and are close in grain,
but are liable to crack, and consequently require to be very gradually
heated; they resist the corrosive action of fused litharge remarkably
well, and, with careful management, are very serviceable for fusions with
oxide of lead. The Patent Plumbago Crucible Company, of Battersea,
have for some years manufactured crucibles closely resembling in appear-
ance the “creusets de Paris," but they are considerably thicker and
decidedly inferior in quality.
Crucibles are manufactured in Cornwall on a large scale for the use
IRON.
109
of copper assayers. They are usually made round, and of two sizes, one
of which fits into the other; those of the larger size are 3 inches in
diameter at top, and 3 inches in height, outside measure. These
crucibles are not capable of withstanding very high temperatures, or
of resisting, for any considerable time, the action of melted litharge.
They can, however, be introduced into a hot furnace without cracking,
and can be more generally employed for metallurgical assays than almost
any other description of crucible. They are made by Michell of Truro,
and Juleff of Redruth, and those of the two makers are, for general
purposes, equally good, although Juleff's crucibles, which are made
of a mixture of Teignmouth and Poole clay and of sand from St. Agnes
Beacon, are somewhat less rapidly acted on by fused oxide of lead.
The shape of the Cornish pots is somewhat inconvenient from their
great flatness at the bottom, but in all cases where sudden changes of
temperature are to be undergone, they are to be preferred to every other
variety, excepting those manufactured by Beaufay, of Paris.
Hessian crucibles are usually sold in nests of six, gradually diminish-
ing in size so as to successively fit into each other. They are made of
a mixture of Almerode clay and sand, and are generally triangular at
top, so that their contents may be conveniently poured from either of
the corners. They withstand a tolerably high heat without softening,
but are liable to be cracked by sudden changes of temperature, and are
readily permeated by melted oxide of lead.
French crucibles are circular and considerably deeper in proportion.
to their width than the Hessian. They are also made of more finely
ground materials, and present a smooth surface both inside and out.
Those made by Beaufay are of excellent quality, and not only withstand
a high temperature, but likewise retain melted litharge for a long time.
without becoming pierced; they are, however, somewhat brittle, and
require that the tongs used for withdrawing them from the fire should
not grasp them too roughly. They are by far the best crucibles for assays
of gold and silver ores, in making which large quantities of litharge
are employed.
Plumbago, or black-lead, crucibles are more frequently employed as
melting-pots for the fusion of metals and alloys than for the purposes of
assaying, and are manufactured of good quality by Mr. Ruel, of High
Holborn, by the Patent Plumbago Crucible Company, and others.
IRON.
Iron is a metal of a bluish-grey colour and dull fibrous fracture, but
is easily made to acquire a brilliant surface by polishing; obtained by
electrolysis it has a specific gravity of 8·1393. It possesses great tenacity,
and is at the same time one of the hardest of those metals which are both
malleable and ductile. The iron of commerce is not, however, chemically
pure; but contains variable quantities of carbon, silicon, sulphur, and
110
ELEMENTS OF METALLURGY.
phosphorus. The presence of these substances materially influences the
quality of the metal, and the purest ores alone are consequently employed
for the manufacture of iron of the best descriptions. Iron, in a chemically
pure condition, may be prepared by reducing ferric oxide by hydrogen
gas at a red heat, or by re-melting the purest varieties of malleable iron
with an oxidising flux.
Some fine iron wire is first cut into short pieces and then partially
oxidised, either by heating it with exposure to the air, or, which is still
better, by passing the vapour of water over it at a red-heat in a porcelain
tube. The partially-oxidised product is subsequently melted under a
glass, free from metallic oxides, in an earthen crucible at a strong white-
heat the operation requiring about an hour at the full temperature of a
good wind furnace. By this treatment the small quantities of foreign
matter which may occur in the metal are oxidised at the expense of the
ferric oxide, whilst the resulting ferrous oxide, together with any small
amount of silica which may have been produced, will combine with the
vitreous flux and form a slag. If the operation be properly conducted,
and the crucible broken, when cold, a button of metal will be found at
the bottom possessing less tenacity and ductility than before its purifica-
tion. The metallic button thus obtained is usually brilliant and well
fused, exhibiting a decidedly crystalline structure, like that observed in
meteorites, after treating them by an etching liquid.
It has before been stated, that chemically pure iron may be prepared
by passing a current of hydrogen gas over pure ferric oxide heated to
redness in a porcelain or hard-glass tube. This reduction takes place at
a low red-heat, but as the metal produced will in this case remain in a
spongy state, and therefore rapidly absorb oxygen, it becomes necessary
to carefully exclude the air. For this purpose either the ends of the tube
may be closed before the blowpipe, or the small glass tubing fitted at
either end of the larger one, by means of corks, may be closed in the
same way whilst the apparatus is still filled with hydrogen. The iron so
obtained has the property of absorbing oxygen with such rapidity as to
cause its ignition on the admission of air, and is thereby converted into
ferric oxide. When, however, the experiment has been conducted at a
more elevated temperature, the reduced iron no longer possesses this
property, and may be freely exposed without danger of ignition.
When, instead of ferric oxide, ferrous chloride is thus treated, the
reduced metal adheres to the sides of the reduction-tube in the form of a
brilliant metallic coating, on which well-defined cubical crystals of metal
may frequently be perceived.
Another method of obtaining pure iron is that adopted by the late
Dr. Matthiessen in his researches on the composition of cast-iron. A
mixture of ferrous sulphate and sulphate of sodium, in nearly equal pro-
portions, is fused in a platinum crucible until sulphurous anhydride ceases
to be evolved. The iron is left in the form of crystalline ferric oxide,
which is separated from the fused mass by treatment with hot water; the
last traces of sulphuric acid being removed by long and careful washing.
The oxide thus obtained is reduced to the metallic state by hydrogen,
IRON.
111
and the spongy metal, after being consolidated by pressure in a steel
mould, is melted in a crucible of caustic lime before the oxyhydrogen
blowpipe. The metal prepared in this way is said to be free from
phosphorus, silicon, and calcium, but contains minute traces of sulphur.
Electro-deposited iron, like palladium, has the property of absorbing
or occluding hydrogen, though to a considerably less extent. On heating
the deposited metal in vacuo, it usually gives up from seventeen to twenty
times its volume of that gas.
This metal is employed in the arts in three distinct conditions, viz., as
cast-iron, wrought-iron, and steel, whose several properties are mainly due
to differences in the amount of carbon contained in each. When iron
contains a maximum amount of this element, usually varying from 2 to
6 per cent., the resulting compound is known as cast-iron or pig-metal.
It is a hard and somewhat brittle substance, which is readily fused at a
high temperature, and is susceptible of being cast into any required form
by being poured, when in a molten state, into properly-constructed
moulds. Cast-iron also forms, in the majority of cases, an intermediate
product in the preparation of wrought-iron and steel.
WROUGHT OR MALLEABLE IRON is the nearest approach to the che-
mically pure metal that can be obtained on a large scale, and rarely con-
tains more than 0.25 per cent. of carbon. In this state it is a soft malleable
and extremely tenacious substance, infusible, excepting at very high tempe-
ratures, and welding at a white heat. If heated to redness, and suddenly
cocled, it retains its softness. Wrought-iron may be produced either by
the direct treatment of ores of that metal or by the conversion of pig-iron.
Those varieties of iron in which the amount of carbon is below the
minimum of that contained in cast-iron, and above the maximum of that
present in wrought-iron, are known as steel. The distinguishing pecu-
liarity of this substance is its property of becoming hardened by rapid
cooling, and softened by being slowly cooled. Steel being in its com-
position intermediate between cast- and wrought-iron, is fusible like the
one, and malleable like the other; but requires a higher temperature for
its fusion than cast-iron, and does not draw so readily under the hammer
as wrought-iron. Steels, in which the proportion of carbon is large, are
known as strong steels, and are harder and more easily fusible than mild
steels, in which the amount of that substance is less considerable.
Texture.—The texture of wrought-iron varies according to the nature of
the processes to which it has been subjected during its preparation. A
piece of iron which has been equally hammered in every direction will, on
being broken, be found to have a finely granular structure; but when it
has been rolled into long bars, in which form it usually comes into the
market, the texture will be more or less fibrous in the direction of their
length. This silkiness of appearance is most distinct in the better
varieties of iron, and structure is therefore one of the best indices of the
quality of the metal. By skilful management this peculiarity may, how-
ever, in a certain degree, be imparted to the commoner varieties, and it is,
consequently, unsafe from this circumstance alone to judge of the value of
iron. It is also found that the most fibrous varieties do not always retain
112
ELEMENTS OF METALLURGY.
ance.
their peculiarity of structure for an indefinite time, but that after a certain
period the grain of the metal sometimes assumes a crystalline appear-
These changes are frequently observed to take place in tension-
rods of suspension-bridges, and in other situations where the metal is
subject to constant vibration. The same effect is produced by friction,
and for that reason the axles of railway waggons are occasionally found
to have acquired a crystalline structure, and are thereby rendered harder
and more brittle than the metal from which they were originally made.
Fusibility.—The melting point of malleable iron has not been accu-
rately determined; according to Pouillet it lies between 1,500 and 1,600°
C., while Scheerer gives it at 2,100° C.
Magnetism.If a mass of iron be either brought in contact with, or
placed at a short distance from a natural or artificial magnet, it becomes
itself magnetic, but loses this property as soon as the exciting magnet is
removed. Steel is less susceptible of the magnetic influence than ordi-
nary iron, but when once the power has been communicated, it is retained
after the removal of the magnet from which it was acquired. Permanent
magnets may be obtained by rubbing a bar of steel either with a loadstone
or with an artificial magnet, and in this way an infinite number of steel
bars may be rendered magnetic without diminishing the power of the bar
by which the effect was produced The magnetic power of iron is much
influenced by temperature, as the magnetic needle is but little affected by
a mass of that metal when made white hot, but on cooling it gradually
regains its magnetic properties.
Rust, &c.—Iron may be indefinitely exposed to the action of dry air, or
even of dry oxygen, without becoming oxidised; but if the air or gas con-
tain any portion of watery vapour, the surface of the metal quickly
becomes coated with a layer of rust. The formation of oxide is much
accelerated by the presence of carbonic anhydride, of which a certain
portion is always present in the air; under the influence of this gas and
oxygen, ferrous carbonate is produced. This absorbs a further amount of
moisture and oxygen from the air, and is thereby converted into hydrated
ferric oxide, whilst the carbonic anhydride which is evolved facilitates the
oxidation of a further portion of metallic iron. When a spot of rust has
made its appearance on a piece of this metal, the oxidation of the remain-
ing portions is materially affected by its presence, for the coating of oxide
formed being electro-negative with regard to the metallic iron which is
beneath it, will give rise to an action by which the metal is rendered
positive. This electric condition of the metal so far increases its affinity
for oxygen as to enable it to decompose water at ordinary temperatures, with
the formation of a further amount of oxide and the evolution of hydrogen
in the gaseous form. Oxide of iron thus produced by exposure to the air
usually contains small quantities of ammonia, the presence of which in
iron rust may be explained as follows:-The water, by the aid of which
the oxidation is effected, contains in solution a certain amount of air, and
consequently of nitrogen, which, by uniting with the hydrogen produced
by the decomposition of water, leads to the formation of this body.
When iron is strongly heated and exposed to the air, its surface quickly
IRON.
113
becomes covered with a coating of black oxide, which, on being struck
with a hammer, easily scales off. It is this property of iron which causes
it to afford sparks when struck with a flint or other hard body. Under
these circumstances, small particles of iron are torn off by the flint, which
produces sufficient heat by friction to render the particles of the metal
incandescent on combining with the oxygen of the air; by allowing
these heated particles to fall on an easily ignitable substance, such as
tinder or amadou, a fire is readily obtained. If, instead of tinder, a piece
of paper be held beneath the metal during the time it is being struck by
the flint, its surface becomes covered with small fragments of black oxide
of iron, fused into minute globules, and readily attracted by the magnet.
ON CERTAIN COMPOUNDS OF IRON.
The metallurgy of iron involves numerous considerations, founded
on a knowledge of reactions not generally described in books on ele-
mentary chemistry, and to these we will therefore briefly call attention.
It may be remarked, generally, that iron is attacked by hydrochloric
acid with the formation of ferrous chloride and the evolution of hydrogen.
By weak sulphuric acid it is dissolved even in the cold, hydrogen gas.
being at the same time given off. Concentrated sulphuric acid also
attacks and dissolves iron, but in this case the oxygen is supplied to the
metal at the expense of the acid, and sulphurous acid (sulphurous anhy-
dride) is evolved. Nitric acid attacks it with the evolution of abundant
nitrous vapours; if the acid be very dilute, iron is dissolved without any
apparent escape of gas, nitrate of iron and nitrate of ammonium being
produced.
IRON AND CARBON.-The combination of iron with carbon can be
effected in various ways, and may be produced, either by the direct action
of carbonaceous fuel, or by certain gases, such as carbonic oxide, at a high
temperature. The essential condition of this combination is contact of
iron, at or above a red heat, with carbon or some gaseous compound of
carbon. Combination with carbon is readily effected when iron, in the
form of compact bars, is imbedded in powdered charcoal and heated to
a temperature at or above redness. This process, which is called ce-
mentation, is applied on an extensive scale to the production of steel; the
same effect is produced by exposing heated iron to the action of com-
pounds containing cyanogen, to the vapour of hydrocarbons, &c. It has
been already stated, that the iron of commerce is divided into wrought-
iron, steel, and cast-iron, according to the amount of carbon contained in
each.
Without carbon, the manifold uses of iron would be greatly
restricted, and we are totally unacquainted with any metal or mixture of
metals capable of fulfilling similar conditions.
State of Carbon in Iron.—It is generally admitted that carbon may
exist in iron in two distinct forms, either in a state of chemical combina-
tion, or mechanically diffused through the mass in the form of crystalline
graphite, which has separated from the molten metal during the process
of cooling. The terms combined and uncombined are respectively applied
to these two modes of existence. Iron containing much graphitic carbon
I
114
ELEMENTS OF METALLURGY.
has a dark-grey, granular, or scaly, crystalline fracture, and is known as
grey-iron. When, on the contrary, the amount of combined carbon is
large the colour of the metal is more or less white with a granular or
crystalline fracture; it is then called white-iron. Grey-iron passes into
white-iron by insensible gradations, and at certain intermediate stages the
two varieties are distinctly visible in the fractured surfaces of the same
pig; this variety constitutes what is called mottled iron. Between ex-
treme greyness on the one hand and absolute whiteness on the other, no
fewer than eight varieties are not unfrequently recognised; these are dis-
tinguished by the numerals from one to eight respectively. Thus, No. 1
is the greyest variety, No. 2 is less grey, and so on to No. 5, when mottled-
iron begins, the amount of white-iron gradually increasing up to No. 8,
in which all traces of grey-iron have disappeared.
When grey cast-iron is dissolved in an acid its graphitic carbon
remains as an insoluble residue, but when white cast-iron is similarly
treated a small proportion only of the carbon present is separated in the
graphitic form. In this case the carbon, which existed in a state of che-
mical combination with iron, unites with the hydrogen liberated during
the solution of the metal, and gives rise to various hydrocarbons, some of
which are liquid, whilst others are gaseous; some of these have a very
offensive odour.
Grey cast-iron may be rendered white by sudden cooling, as in the
process of chill-casting, but this change takes place only on the surface,
the interior of the casting still retaining its grey colour.
Caron concludes, after a careful investigation of the subject, that the
state in which carbon exists in steel depends on the treatment to which
the metal has been subjected. The carbon in the softer varieties is chiefly
in the state of graphite, but is capable of passing into combination by
hardening or hammering; its graphitic character is, however, restored by
annealing.
From this it would appear probable that both chill-casting and the
hardening of steel are due to the passage of carbon from the free to the
combined state. Professor Abel, who has made some investigations on
this subject, obtained results which tend to confirm the above view; he
found that hardened steel wire dissolved in hydrochloric acid without
residue, whereas the same steel when softened yielded a dark flocculent
carbonaceous residue if acted on by the same acid. Much diversity
of opinion still prevails with regard to the atomic composition of the
carbides of iron. Spiegeleisen, or specular pig-iron, the most crystalline
and most highly carburised white metal, is supposed by Karsten to be a
carbide of which the composition is represented by the formula Fe̟C,
which would contain 5.08 per cent. of carbon. All the specimens of
spiegeleisen which have been carefully analysed, however, appear to
contain a notable quantity of manganese, and consequently, if this
earbide really exists, it is more probably represented by the formula
(Fe, Mn),C.
According to Rammelsberg the formula of Karsten cannot be estab-
lished, even if the carbon is supposed to be partially replaced by silicon,
IRON.
115
the largest percentage of the latter element being constantly found in the
most carburised varieties. Gurlt has endeavoured to establish the exist-
ence of a carbide corresponding to the formula Fe, C, supposed to stand
in the same relation to grey cast-iron that Karsten's tetracarbide, Fe4C,
does to white. Percy has, however, shown that the methods of analysis
employed by Gurlt are inexact, and consequently that his deductions
are without value.*
That the carbon contained in white cast-iron does not entirely exist
in a state of combination may be seen from the following analyses, by
Bromeis, of various specimens of cast-iron from Mägdesprung, in the
Hartz :—

Description of Iron.
Combined Carbon. Graphitic Carbon.
Total.
Per Cent.
Per Cent.
Per Cent.
Bright White Iron
White Forge Pig
Spiegeleisen
2.518
0.500
3.018
•
2.908
0.500
3.458
•
3.100
0.720
3.820
In addition to uncombined carbon, dark-grey cast-iron often con-
tains silicon in a similar graphitic state. This is more particularly
observed in cast-iron produced in the blast-furnace from very refractory
ores; spiegeleisen and other white cast-irons are only produced from
easily-reducible ores, and especially from those containing notable
quantities of manganese.
When grey-iron is fused with from 2 to 2 per cent. of sulphur, a
considerable portion of its carbon is separated in a sooty form, and an
exceedingly hard white metal is the result. With smaller quantities a
mottled-iron of great strength is obtained, which, on being broken, presents
a surface showing numerous grey spots inclosed in a network of white
lines. Swedish gun-foundry iron is of this character, and is obtained by
adding to the ordinary charge of the furnace an ore containing a small
admixture of iron pyrites.
Cementation, by which carbon is imparted to malleable iron, so as to
transform it into cement- or blister-steel, may be effected in various ways;
pure carbon, charcoal, coal, and almost all organic substances, can be so
made to react, at high temperatures, on malleable iron as to produce steel.
Solid and gaseous cyanides and nearly all vapours and gases containing
carbon, such as carbonic oxide and the various compounds of carbon and
hydrogen, have the property of imparting carbon to wrought-iron at a
red-heat. Whenever soft iron is heated to redness in presence of any
of these substances carburisation takes place, at first on the surface, and
subsequently, by degrees, from the outside towards the centre. The
superficial hardening or cementation of malleable iron, by heating it
for a short time in contact with leather cuttings or cyanogen com-
pounds, is known as case-hardening.
* Iron and Steel,' p. 126.
*
I 2
116
ELEMENTS OF METALLURGY.
Frémy makes a distinction between carburisation and conversion
into steel, and believes that, in addition to carbon, nitrogen is essential
to the production of the latter. The researches of Marguérite, Boussingault,
and others, however, go to prove that nitrogen does not enter into steel,
either as a necessary constituent, or as a carrier of carbon. The first-
named chemist has in fact shown that pure iron, obtained from the oxalate
of that metal, may be as well carburised by being heated in an atmosphere
of carbonic oxide, as ordinary iron by the usual process of cementation.
He has likewise shown that pure iron may be converted into steel by
being heated in contact with diamond powder in a tube through which
pure hydrogen has been passed so as to expel all other gases. Dick has
also found that electrotype-iron is more readily converted into steel by
cementation, in an atmosphere of hydrogen, than the best commercial
sheet-iron. The metal employed in this case was remarkable for purity
and softness, and being perfectly free from nitrogen, the result obtained
affords evidence bearing strongly against the views of Frémy.
As the case at present stands, the weight of evidence is decidedly
against the necessity of the presence of nitrogen in steel, and it would
appear probable that the older view of Karsten, that its essential qualities.
are mainly due to variations in the amount of carbon present, is after all
correct.
Bauerman remarks that from what has been determined with regard
to the composition of cast-iron and steel, the following propositions may
be deduced:
1. In white cast-iron the greater portion of the carbon present is
chemically combined, whilst in grey-iron it exists as diffused graphite.
2. Neither variety is, however, free either from graphitic or combined
carbon, respectively.
3. Although ordinary white-iron contains chemically-combined car-
bon, there is no conclusive evidence of the presence of any defined
carbide. Spiegeleisen may perhaps be a double carbide of iron and
manganese.
4. Dark-grey iron is not a lower carbide of iron than spiegeleisen,
but is more probably a mixture of malleable iron and graphite, the
chemically-combined carbon in which may be reduced to a minimum by
fusion at a very elevated temperature.
5. Silicon is a common constituent of grey cast-iron.
6. Chill-casting and the addition of sulphur tend to produce whiteness
in grey cast-iron, and a similar change is effected in steel by hardening
or forging.
Mr. Snelus, in a paper on the condition of carbon and silicon in iron
and steel, published in the Journal of the Iron and Steel Institute, 1871,
shows that when very grey pig-iron is reduced by crushing to a coarse
powder, scales of graphite are removed from between the crystalline
facets of the metal. These, on being subjected to the ordinary process
of combustion, become completely converted into CO2, thus showing that
they consist of carbon in a state of almost absolute purity. When
* 'Metallurgy of Iron,' p. 47.
IRON.
117
·
borings of grey pig-iron are sifted through fine gauze, or are subjected to
levigation, the finer and lighter portions contain, in each instance, the
largest amount of carbon. In this way the fine siftings from a Bessemer
pig, containing 3.34 per cent. of graphitic carbon, were found to yield 9.11
per cent. of graphite, whilst the light washings from a Cleveland forge-pig,
containing 7.02 per cent. of carbon, in the form of graphite, afforded no
less than 41-33 per cent. of carbon. It was further ascertained that no
separation of silicon can be effected by this method, since, instead of
increasing, like graphite, in the finer and lighter portions, the amount of
silicon is found to decrease in proportion as the quantity of graphitic
carbon becomes more considerable.
IRON AND SILICON.-Silicon is an element always present in every
form of iron, although its quantity is sometimes very minute, and the
silicon in wrought-iron is possibly due to the cinder enclosed between the
layers or fibres of the metal,
Free silica, unaccompanied by earthy matters, such as lime, limestone,
or clay, with which it might form slag, tends to produce iron rich in
silicon; especially when the temperature is high, and the amount of
carbon present large.
By reducing, in a wind furnace, an intimate mixture of oxide of iron
and sand with charcoal, cast-iron may be obtained containing so much as
13 per cent. of silicon, and, by operating this reduction at the high tem-
perature of a Siemens gas-furnace, Riley obtained cast-iron with 21 per
cent. of silicon. This iron exhibited a highly crystalline structure, and
had a silvery-white colour. There are differences of opinion as to
the conditions in which silicon exists in cast-iron; Snelus is disposed
to believe that it exists only in combination; Bell and Riley differ
from this view, and quote instances in which silicon has separated from
pig-iron.
Siliceous iron is often accidentally made, and is known as glazed or
blazed pig. This occurs whenever a furnace is newly blown-in, and is
probably due to the excess of fuel then employed. When poor materials
are used in the furnace, siliceous pig is the result. Some very poor
blackband ironstone smelted at Dowlais, which yielded only 10 per
cent. of iron, produced a siliceous pig which Riley found to contain
7 per cent. of silicon; and a sample of Scotch pig has been found to
contain as much as 8 per cent. of silicon.
Ferrous Silicates.-The formation of ferrous silicates takes place at
the welding temperature of the metal, advantage being constantly taken
of this circumstance by the smith, who, in order to remove any scale
from the surfaces to be united, makes use of a sprinkling of siliceous sand.
The forge- and mill-cinders produced during the processes of puddling
and re-heating are both essentially silicates of iron represented by the
formula 2FeO,SiO2, which contain about 70 per cent. of ferrous oxide,
become very liquid at a white heat, and often assume a crystalline form
on cooling. Heated with access of air, ferrous silicates are decomposed
with the formation of ferric oxide, and the separation of silica; the
result being a more refractory product, the infusibility of which is due
118
ELEMENTS OF METALLURGY.
to the inability of the oxides to form a slag in the presence of oxidising
influences.
In order to produce slags, having a composition corresponding to the
formula above given, the silica present requires two and a third times its
weight of ferrous oxide; or, what comes to the same thing, for every part,
by weight, of silicon in the slag, more than three and a half parts of
metallic iron are rendered unavailable.
The iron contained in puddling-furnace cinder and in other slags
of analogous composition may be obtained in the metallic state by treating
them in the blast-furnace, either alone or in admixture with the ordinary
charges. Owing, however, to the circumstance that a very large pro-
portion of the phosphorus originally present in the ores is passed into
the slags during the process of puddling, the metal thus obtained is
always of inferior quality. The iron obtained by smelting a mixture of
such products is known as cinder-pig, in contradistinction to mine-pig,
which is obtained by the treatment of ores only. According to Richard-
son, when pure ferrous silicate, having the composition represented by
the formula 2FeO,SiO2, is strongly heated with carbon, two-thirds of
the iron is reduced to the metallic state, leaving a slag of the composition
2Fe0,3SiO...
The effect of silicon on cast-iron is very similar to that of carbon; it
renders wrought-iron hard and brittle, but, owing to the ease with which
this substance may be removed during the process of manufacture, it is
rarely present in sufficient quantity to exert a marked influence on the
quality of wrought-iron.
IRON AND SULPHUR.-The compounds of iron and sulphur materially
affect the smelter, since iron pyrites is frequently present, as an impurity,
in iron ores, and the presence of sulphur imparts to the resulting metal
the defect of red-shortness.
The red-short character of Welsh iron, is, in many instances, although
not always, due to the presence of sulphur; iron may be red-short and
cold-short at the same time; such iron is of the worst possible description,
and is made from ores containing a high percentage of sulphur and phos-
phorus. The exact cause of the production of red-short iron is not
always clear. Riley believes it to be sometimes due to a deficiency of
carbon, as in the best cable-bolt, the most fibrous and toughest iron,
when melted in a clay crucible, and afterwards heated, doubled, and
welded, is very red-short, on account of the burning out of the carbon
by oxide of iron in melting the bar.* In Welsh pig-iron the percentage
of sulphur is always found to increase as the number-quality of the iron
increases.
IRON AND PHOSPHORUS.-Nearly all the phosphorus contained in the
ore and fuel used in the blast-furnace passes into the pig-iron produced.
This has been conclusively shown by a series of analyses made some
years since by Riley at the Dowlais Iron-Works. When the cinder was
grey all the phosphorus passed into the iron, and only when the furnace
* On the Manufacture of Iron and Steel.' A Lecture delivered before the
Chemical Society by E. Riley, March 2nd, 1872.
IRON.
119
was running on a scouring cinder rich in iron did the phosphorus pass
into the slag. Phosphorus, like silicon, renders pig-iron weak, although,
when the amount does not exceed from toper cent., it is doubtful
whether the strength of the pig is affected. Best Yorkshire cold-blast
pig has occasionally been found to contain nearly 13 per cent. of phos-
phorus. This pig was very tender; but when used for making best
iron, did not materially influence the quality of the bars. Its production
was due to the use of a thin seam of clay-band ironstone containing 3·27
per cent. of P₂05.
5*
3
To
Wrought-iron containing less than per cent. of phosphorus is
rendered somewhat harder, but its tenacity is not sensibly affected;
with per cent. it begins to be cold-short, or brittle, under the hammer,
if struck when cold; per cent. of phosphorus renders iron decidedly
cold-short; and 1 per cent. makes it very brittle.
2
4
The tenacity of cast-iron is materially diminished by the presence of
large quantities of phosphorus, so that the metal obtained from some of
the worst varieties of bog ore cannot be safely employed for castings
requiring strength. Such iron has, however, the property of acquiring
great fluidity when melted, and can therefore be advantageously employed
for making small and intricate ornamental castings.
IRON AND NITROGEN. Various chemists have investigated the effects
of nitrogen upon iron and steel, but the results obtained have been of
such contradictory natures that, in the present state of our knowledge,
it is impossible to decide whether or not this element plays an important
part in the process of cementation. Frémy states that when iron wire,
heated to dull redness, is exposed during several hours to a current of
ammoniacal gas, its weight is increased from 12 to 13 per cent.
According to Savart, however, the increase in weight of iron wire thus
exposed during nine hours to ammoniacal vapour amounts to only about
per cent. Between one and two hours after the operation has com-
menced the wire will be found to have acquired a finely-granular texture,
and can be so far hardened by quenching in water as to afford sparks when
struck with a flint. This property of the metal passes off, however, as the
experiment is continued, and at the expiration of from eight to ten hours
an iron of unusual softness is obtained; this is of a dark-grey colour, is no
longer susceptible of tempering, and, when broken, presents a graphitic
fracture. A similar slight incrcase in the weight of the iron operated on
was obtained by Dick, when a spiral of iron wire was heated to redness
in a current of ammoniacal gas during one hour and a quarter; in this
case the increase amounted to, but when a straight and thick wire
was employed the increase was only
1
The amount of nitrogen contained in various kinds of commercial iron,
as well as in an artificial nitride prepared by Despretz, has been deter-
mined by Bouis and Boussingault; the nitrogen in the former varied
fromto per cent., whilst the latter yielded 23 per cent. of this
element.
IRON AND MANGANESE. The presence of a considerable amount of
manganese in spiegeleisen has been already referred to. This description
120
ELEMENTS OF METALLURGY.
of pig was formerly exclusively made on the Continent, but it is now
largely manufactured in this country.
INFLUENCE OF OTHER METALS ON IRON.-Titanium may be present
in pig-iron to the extent of about 1 per cent. when a portion of ilmenite,
or some other titaniferous ore, has been added to the charge. Practically,
smelting titanic ores in this country has proved a failure, and the advan-
tages once said to be derived from the use of ores in which this metal is
present are now generally considered to be more than questionable.
Titanium generally enters into the composition of grey pig-irons, and its
presence, in appreciable quantity, may frequently be detected in them.
In white pig-iron, in wrought-iron, and steel, Riley states he always failed
to detect it, even when titanic ores had been employed for making the
pig.
Chromium.-Chromium steel has been made in America, whence speci-
mens tested in this country were obtained. Chromium is said to partially
replace carbon, and the general impression was favourable to its quality.
This steel, which was examined by Riley, was found to contain chro-
mium, but only in very small quantity.- Vanadium was found, in minute
quantities, by Sefström, in iron made from the magnetic ores of Taberg, in
Sweden, which is celebrated for yielding iron peculiarly adapted for wire-
drawing. More recently, Riley has detected this substance in pig-iron
smelted from the oolitic ores of Wiltshire and Northamptonshire; it has
also been found in the Cleveland ironstone and in the pisolitic ores of
South-western Germany.-Tungsten is said to have the property of render-
ing steel hard and tenacious. When finely-divided grey cast-iron is inti-
mately mixed with tungstic oxide and fused at a high temperature, the
graphitic carbon is, according to Bernouilli, burnt by the oxygen of the
oxide, and a steel is produced which forms an alloy with the reduced
tungsten. When spiegeleisen is substituted for grey-pig no reduction of
tungstic oxide takes place; from this it would appear that carbon in the
combined form is not capable of effecting its decomposition. Of six
samples of "
tungsten steel" analysed by Siewert, four contained from
1 to 3 per cent. of that metal, whilst in the other two, no trace of tungsten
could be detected.
ALLOYS OF IRON.-It is doubtful whether any homogeneous alloy of
copper and iron can be produced by fusing a mixture of the two metals,
but the addition of a small quantity of iron to bronze or brass consider-
ably increases its tenacity. Zinc and iron do not furnish any useful
alloy, although about 7 per cent. of the latter metal may be taken up
when zinc is kept for a long time in a state of fusion in contact with iron,
or when zinc vapours are passed through wrought-iron tubes. Tin and
iron unite in almost every proportion, but their alloys are not employed
in the arts. Lead and iron cannot be made to unite by fusion. The pre-
sence of a very small quantity of antimony renders wrought-iron both
hot- and cold-short. Nickel alloys readily with iron without impairing its
malleability. Cobalt is said to increase the whiteness and brilliancy of
iron, without materially affecting its physical properties. Silver does not
alloy with iron, but gold is readily taken up when the two metals are
IRON.
121
melted together. Faraday and Stodart found that platinum alloyed with
steel, and, when present to the amount of 1 per cent., a very tough and
fine-grained product was the result. Similar alloys were obtained with
palladium, rhodium, and iridosmine.
IRON ORES.
For the purposes of the arts, iron is invariably obtained from the
native oxides and carbonates of that metal.
NATIVE IRON.-The occurrence of masses of native iron apart from
those of meteoric origin, is not placed beyond doubt. According to Dr.
Andrews, grains of metallic iron exist in the basaltic rocks of the Giant's
Causeway, and similar metallic granules have been observed in the lavas
of Auvergne.
Metallic iron is sometimes produced by the ignition of coal seams in
the immediate vicinity of ferruginous deposits. The iron thus produced.
occurs in the form of small button-shaped ingots with a finely striated
surface, and is usually known by the name of native steel. They are
excessively hard and fine-grained, and when broken, present a fracture
resembling that of ordinary cast-steel. A mass of this substance weigh-
ing 16 lbs. 6 ozs., was discovered some years since by Mossier, at
Labouiche, in the department of the Allier, where a burning seam of
coal had formerly existed.
Meteoric Iron.-Large masses of metallic iron have been occasionally
discovered in different parts of the globe, whilst others of similar ap-
pearance have from time to time been observed to fall through the
atmosphere.
These meteorites are easily distinguished from the masses of terrestrial
iron before described, both by their structure and composition, as they
not only invariably contain a greater or less proportion of nickel, which
seldom occurs in ores of iron, but the metal itself is usually found in the
form of a network enclosing crystals of a substance, in appearance resem-
bling olivine, soluble in acids. Meteoric iron is always covered on the
surface with a sort of black siliceous varnish, which effectually protects
the exterior from the rusting action of the atmosphere, although, when
this is removed, the metal is as easily oxidised as common iron. A large
number of masses supposed to be of meteoric origin have been enumerated
as existing in various parts of the world, and have, in some instances, fur-
nished the inhabitants of the countries in which they are found with the
materials for making knives, spears, and other instruments. Among the
most remarkable is that which was discovered by Pallas, in Siberia, origin-
ally weighing about 1,600 lbs. ; that in Brazil, weighing 14,000 lbs., and
that discovered by Don Rubin de Celis in the district of Chaco-Gualamba,
in South America, weighing about 32,000 lbs. The largest masses of
meteoric iron are probably those occurring in Greenland; several others
of large size have been found in Africa, as well as on the continent of
North America. Meteorites of smaller size are, by no means, uncommon.
122
ELEMENTS OF METALLURGY.
The composition of three different specimens of meteoric iron is given
below.

1.
2.
3.
Fe
88.042
90.153
83.02
Ni
10.732
6.553
14.62
Co
⚫455
• 502
·50
Mn
• 132
•145
Cul
⚫066
·080
⚫06
Suf
Mg
⚫050
·082
MgO 24
C
·043
trace
.482
.08
F, N, P
1.2.6
Cl
Gangue
480
SiO, 84
P 19
•
⚫02
•
100.000
99.223
99.57
1. From Siberia; by Berzelius. 2. From Lenarto; by W. S. Clarke.
3. From Knoxville, Tennessee; by J. L. Smith.
No other metal is so universally diffused as iron. It not only exists in
a great variety of minerals, forming one of their essential constituents,
but is so constantly present as an adventitious mixture in mineral sub-
stances, that the chemist seldom makes the analysis of an inorganic body
without detecting this metal. As a constituent of organised bodies it is
extremely common, and is in various forms present in nearly all animal
as well as in the greater proportion of vegetable structures.
A detailed description of the various ores of iron would require more
space than is consistent with the limits of the present work; and for this
reason such only will be noticed as are applied to the purposes of the
arts.
MAGNETIC IRON ORE; Magnetite; Fer oxydulé; Magneteisenstein. Iso-
metric. This substance often occurs in octahedra and dodecahedra. It
possesses a cleavage which is often distinctly parallel to the faces of the
octahedron. It is brittle, of an iron-black colour, and leaves a black
streak.
This ore has a density which varies from 5.0 to 5.2, is strongly
attracted by the magnet, and sometimes possesses independent polarity.
Its chemical composition is as follows:-
Fe
O
•
•
71.28
28.22)
or
(Fe2O3
FeO
Corresponding to the formula Fe3O4 or Fe2O3,
69.
31.
FeO.
Magnetic iron occurs in granite, gneiss, mica-slate, clay-slate, syenite,
hornblende-schist, and chloritic slate, as also, less frequently, in lime-
stone formations, &c. No ore of iron is of more frequent occurrence
than this oxide, which is inferior to none for the manufacture of that
metal.
IRON.
123
A large proportion of the best Swedish iron is obtained from this ore;
it also occurs in the island of Elba, and in great abundance in the United
States of America, Canada, the Urals, &c.
FRANKLINITE. Isometric.-Occurs massive and in octahedra, closely
resembling magnetite but less magnetic; streak reddish-brown; specific
gravity 5·1. The average of several analyses by Rammelsberg gives-
Fe
Mn
Zu
O
45.16
•
9.38
·
20.30
•
25.16
100.00
This composition may be represented by the formula (Fe, Mn),0, +
(Fe,Zn, Mn)O. This mineral is found only in a few localities in New
Jersey, where it occurs in metamorphic Silurian limestone, forming a bed
from twenty to thirty feet in thickness, overlaid by from six to eight feet of
red zinc ore. Both minerals are first treated for zinc, and the residues
afterwards smelted for spiegeleisen.
ILMENITE; Titaniferous Iron Ore; Titane Oxydé ferrifère; Titaneisenstein.
Rhombohedral.-Usually massive; colour dead black; fracture conchoidal.
Specific gravity 45 to 5; contains ferric and ferrous oxides, titanic oxide,
and magnesia, in varying proportions.
HEMATITE; Specular Iron ; Fer oligiste; Eisenglanz. Rhombohedral.-
This mineral, when occurring in crystals, is generally found in complex
modifications of the rhombohedron.
They are of dark steel-grey colour, opaque, except when in very thin
laminæ, in which case they are translucent, and of a deep blood-red
tinge.
It leaves a cherry-red or reddish-brown streak, and has a specific
gravity varying from 4.8 to 5 3. Pure specular iron consists solely of
ferric oxide, of which the percentage composition is-
Fe
•
70·001 Formula, Fe2O3.
30.00
100.00
Red iron ore, or red hæmatite, frequently occurs in reniform masses.
When the ore is amorphous, and does not present any indication of
columnar structure, it is termed compact, and if contaminated with argil-
laceous impurities, it is known by the name of red ochre. Micaceous
iron is specular iron with a foliated structure. Oligistic iron, iron glance,
and rhombohedral iron, are merely other names for specular iron ore.
Jaspery clay iron ore is an ore of a brownish-red colour, with a large flat
conchoidal fracture. It is very compact, and has a jaspery appearance.
The name of lenticular clay iron is given to this substance when it
occurs in small flattened grains, resembling some varieties of oolite, as
at Elbogen, in Bohemia.
This ore occurs both in crystalline and stratified rocks, but the purer
124
ELEMENTS OF METALLURGY.
varieties are usually found in the older formations, whilst the argil-
laceous ores are commonly met with in the more recent. Beautifully
crystallised specimens are obtained from the island of Elba, where iron
mines were worked by the Romans; also from St. Gothard, from Norway,
Sweden, Framont in Lorraine, Dauphiné, and Switzerland. Very brilliant.
crystals are also formed by sublimation in the fissures of volcanic rocks.
Fine specimens of this kind are procured from Stromboli, Lipari, and
Ascension, as also from Etna, Vesuvius, and Auvergne, but those from
the last three localities are usually smaller than those coming from those
first named.
Red hæmatite is found in many parts of Cornwall, at Ulverstone in
Lancashire, Workington in Cumberland, Brixham in Devon, in Saxony,
and numerous other localities.
Red hæmatite, when ground to fine powder, is sometimes used as a
pigment; as a source of metallic iron, it is of great importance, as from
it a considerable portion of the iron manufactured in different parts of
the world is obtained. It does not yield so large a percentage of metal
as the magnetic oxide. The iron produced is of excellent quality.
GÖTHITE; Fer hydroxidé; Göthit. Orthorhombic.-This is an oxide
of iron containing less water than the ordinary hydrated ores. This
variety is comparatively rare, but occurs in the form of acicular crystals.
in various localities. It is found associated with quartz in the cavities
of sandstone at Clifton, near Bristol; in pure black crystals at St. Just
and Lostwithiel in Cornwall, also at Lake Onega in Siberia, and at
Eiserfeld in Nassau.
A specimen of this substance from Eiserfeld, analysed by V. Kobell,
was found to be composed of—
Fe₂03
H₂O
90.53
9.47
100.00
This corresponds to one atom of ferric oxide united to one of
water, and its composition is therefore represented by the formula
Fe2O3, H₂O.
BROWN IRON ORE; Fer Oxydé hydraté; Brauneisenstein.—A mineral
of a brown or brownish colour, yielding, when crushed, a yellow powder.
Its density varies from 3.8 to 4.2, and when pure it yields 56 per cent.
of metallic iron. It usually occurs in the massive form, but varies in
structure according to the locality in which it is produced.
This substance is a hydrated ferric oxide, and is chiefly confined to
the sedimentary formations. A specimen of compact brown hæmatite
from the Lower Rhine, analysed by Vauquelin, afforded the following
results :-
Fe2O3
H₂O
Sio 2
•
•
80.25
15.00
3.75
99.00
IRON.
125
This percentage corresponds to two atoms of ferric oxide united
with three of water, and its formula will consequently be 2Fe2O3,3H₂O.
This ore is frequently found in pseudomorphic forms, among which
cubes and octahedra produced by the decomposition of iron pyrites are
the most common. It also not unfrequently occurs in rhombohedra
formed by substitution of ferrous carbonate; also in the moulds left
by the decomposition of shells and madrepores, whose shapes the mineral
consequently assumes.
It sometimes also forms stalactites, having a fibrous or compact
structure, and, in the centres of these, pieces of metallic iron are said to
have been discovered. In some localities this mineral is found in hollow
reniform masses, enclosing in their centres loose globular pieces of the
same substance.
Pea-iron is one of the forms of this hydrated oxide, and is fre-
quently found in large deposits in oolitic formations, where they either
occur cemented together by the same substance, or exist as detached
bodies.
This mineral often occurs in an earthy state, and when naturally
mixed with a considerable proportion of clayey matter, acquires a peculiar
softness of texture, and is known by the name of yellow ochre.
Brown ironstone is in many countries one of the most plentiful and
valuable ores of iron, and, in the oolitic form, supplies a great number of
French iron-works. In that state it is found in large quantities in
Normandy, Berry, Burgundy, Lorraine, and many other places; and when
washed for the purpose of separating the lighter impurities, yields an
excellent material for the manufacture of iron. It is, however, remarked
that whenever the beds of oolitic iron are found to alternate with cal-
careous deposits, the metal produced is cold-short, and consequently
unfitted for many purposes to which iron of good quality only can be
applied. This is attributed to the presence of phosphorus, derived
from the organic matter present in many limestones, and which has
the property of rendering iron brittle, even when present in minute
quantity.
IRON PYRITES; Fer sulfuré; Eisenkies. Isometric.-Frequently in pen-
tagonal dodecahedra, also in octahedra and cubes, more or less modified.
Colour, yellowish-white to bronze-yellow, with a metallic lustre; streak,
brownish-black; specific gravity from 4.8 to 5.1; is brittle, and strikes
fire with steel; does not yield to the knife. The cleavage is parallel to
the faces of the cube and octahedron; when struck, it breaks with a
conchoidal uneven fracture. It consists of-
Fe
S
45.74
54.26
100.00
Or two atoms of sulphur united with one of iron, and is therefore
represented by the formula FeS2.
Iron pyrites occurs in cubical crystals in veins and in various
126
ELEMENTS OF METALLURGY.
slate-rocks, &c.; in globular concretions imbedded in indurated clay,
chalk, &c.
It also accompanies the ores of other metals, and extends from the
oldest rocks up to the newest deposits. It usually occurs crystallised,
but also in irregular masses and imitative forms; replacing, in many
instances, remains of both animal and vegetable origin.
The crystals from the island of Elba are extremely large and beauti-
ful, and often present pentagonal dodecahedra of three or four inches in
diameter. The Cornish mines furnish cubes of large dimensions, and
very perfect octahedra of equal size are obtained from Sweden. Be-
sides occurring in all districts which produce other metallic mine-
rals, it is abundantly found in many of the coal-fields, where, by its
oxidation and conversion into ferrous sulphate, it sometimes produces
sufficient heat to cause spontaneous ignition of the coal with which it is
associated.
Iron pyrites is never directly treated for the sake of the iron it con-
tains, but is frequently employed as a source of sulphur in manufactories
of alum and sulphuric acid. When heated in the burners attached to
sulphuric-acid chambers, good pyrites yields about 46 per cent. of
sulphur, which is burnt and oxidised in the usual way; but the sulphuric
acid thus obtained always contains traces of arsenic. This mineral (iron
pyrites) frequently contains small quantities of gold and silver, but
these are seldom present in sufficient proportion to allow of their being
profitably extracted.
Very large quantities of cupreous iron pyrites are now annually im-
ported into this country from Spain and Portugal, and after being burnt
for the manufacture of sulphuric acid, the "cinders" are treated for
copper by a process of wet extraction. The ferruginous residues thus
finally obtained yield on an average 96 per cent. of ferric oxide, and are
extensively employed both in the blast-furnace and for " fettling
puddling furnaces; by far the largest portion of that produced, amount-
ing to several hundred thousand tons annually, is used for the latter
purpose.
""
SIDERITE; Carbonate of Iron; Fer Carbonaté; Eisenspath. Rhombo-
hedral.-Occurs in rhombohedra and six-sided prisms, and may easily be
mistaken for carbonate of calcium, from which the crystals differ slightly in
the value of their angles; is more commonly massive, with a foliated and
somewhat curved structure. Sometimes in globular concretions, or lenti-
cular masses. Colour, light-grey, but when externally decomposed becomes
dark-brown or nearly black. Is usually almost opaque, with sometimes
a pearly lustre, but small transparent crystals have been found in the
neighbourhood of St. Austell, in Cornwall, where it occurs in sca-
lenohedra; streak uncoloured. Specific gravity from 30 to 3-85.
When pure, is composed of-
FeO
62.07
CO2
37.93
100.00
IRON.
127
It is consequently a carbonate of iron, represented by the formula
FeO,CO2, or FeCO3. Spathose iron is found in rocks of very different
ages, and is frequently observed to accompany other metallic ores, such
as those of lead and copper. Carbonate of iron is, however, most plentiful
in gneiss, clay-slate, and the coal-formations. The beds of Styria and
Carinthia occur in gneiss; those of the Hartz are found in clay-slate;
whilst the English deposits of clay ironstone, from which a considerable
portion of the iron manufactured in this country is obtained, are princi-
pally confined to the coal-measures and Lias. This mineral is frequently
extracted from the same pits through which the coals are raised to the
surface, and either occurs in reniform and lenticular septaria, imbedded
in clay found in the vicinity of the seams, or forms distinct beds, especially
in the Lias.
All coal-formations do not, however, produce iron ore; the Newcastle
district, which is one of the richest coal-fields, yields so little iron, that
the furnaces which are worked in that district are principally supplied by
ores brought from a considerable distance. The French coal-fields, also,
do not generally yield a sufficient amount of clayey carbonate of iron to
render its extraction a matter of importance; but to this peculiarity the
basin of the Aveyron is an exception, the iron-works of Decazeville being
supplied with both ore and coal from seams in their immediate neigh-
bourhood. The ores treated for metallurgical purposes are always
more or less impure, and usually yield from 30 to 35 per cent. of
iron.
Ores containing manganese are found to produce excellent irons for
the manufacture of steel, whilst the presence of a large amount of mag-
nesia is usually thought to be detrimental to the quality of the metal
obtained.
DISTRIBUTION OF IRON ORES.
The ores of iron are not found in large quantities in the state of
mineralogical purity described in the preceding paragraphs, and the
presence of foreign minerals not unfrequently exercises a material influ-
ence on their commercial value. Thus an ore containing a notable quan-
tity of calcium phosphate or of iron pyrites would be practically useless,
whilst the presence of manganese in a spathic ore, or of combustible
matter in an argillaceous carbonate, would considerably increase its
selling price.
Ores of iron are found in formations of every geological age, but most
abundantly in the older rocks. The richest and most extensive deposits
of iron ores are met with in pre-Silurian strata, such as the Laurentian
and Huronian series of North America, and the older gneiss and schists
of Scandinavia.
Spathose ores are found in large quantities in Devonian rocks; inter-
stratified argillaceous carbonates occur, both in Europe and America, in
rock of the carboniferous period. In this country the most important
deposits of red hæmatite are contained in hollows of the Carboniferous
128
ELEMENTS OF METALLURGY.
Limestone of Cumberland and Lancashire. The principal iron bearing
members of the mesozoic rocks are the Middle Lias, Inferior Oolite,
Wealden, and Lower Greensand, yielding brown hæmatites and carbo-
nates, which, though of low produce, are mined at a cheap rate, and are
therefore of considerable importance. On the continent of Europe large
quantities of argillaceous brown hæmatite are raised from irregular de-
posits in the Oolites. But little iron ore is obtained from the tertiary
rocks of this country, the principal deposit being in Dorsetshire; the
magnificent ores of Elba and Traversella may, however, be of tertiary
age.
Post-tertiary and recent deposits of bog iron ore are studded over the
swamps of North Germany, and lake ores are at the present day being
constantly formed at the bottom of the lakes of Norway, Sweden, and
Finland.
MAGNETIC ORES.-These ores, which, when massive, are usually asso-
ciated with hæmatite, are to a great extent confined to the older crystal-
line rocks of Scandinavia and North America, and generally occur in
irregular beds in hornblendic and chloritic slates, in crystalline lime-
stones, or as irregular veins and masses in rocks of eruptive origin. In the
Laurentian rocks of Canada this ore is abundantly found in the gneiss
and metamorphic limestones of the basin of the Ottawa; it usually occurs
in the form of irregular beds, which, although not of any great lateral
extent, are often of considerable thickness. Although of excellent
quality, they have not been, as yet, extensively worked. One of the
largest deposits of iron ore in Europe is probably that of Gellivara, in
Swedish Lapland, situated about ninety miles from the head of the Gulf
of Bothnia. According to the description of Erdmann and others, it
forms a bold hill rising out of swampy ground, and consists of a number
of parallel bands of magnetic and specular iron ores interlaminated with
hornblendic and quartzose rocks. Some of these beds are between one
hundred and two hundred feet in thickness, and may be traced for a dis-
tance of nearly seven hundred yards. Calcium phosphate is present in
some of the beds, whilst others are apparently free from this impurity;
iron pyrites appears to be almost entirely absent. The ore, on an average,
contains about 90 per cent. of magnetic oxide of iron, and 34 per cent. of
silica. In some of the bands phosphoric acid is present to the extent of
nearly 2 per cent.; others, on the contrary, contain traces only of this
substance. These ores have been known for a very long period, but
from the inaccessible nature of the country in which they occur, little
use has been made of them; the only practicable method of transport
during the winter months is by means of sleighs.
The celebrated mines of Dannemora, in Sweden, are situated on the
lake of the same name, about thirty miles from Upsala. The ore, which
is a fine-grained magnetite, occurs in an irregular belt a mile and a half
in length, and is specially employed for the manufacture of iron of the
highest class. It occurs in crystalline limestone and felsite, and the
workings extend to a depth from the surface of more than a hundred
fathoms; the annual production does not, however, exceed 25,000 tons."
IRON.
129
The following analyses of Dannemora ores, by Ward and Noad, are
given by Bauerman :-
*
1.
2.
3.

Fe2O3
FeO
27.55
28.42
27.50
·
58.93
62.06
56.80
MnO
0.10
0.24
CaO
0.38
trace
1.80
MgO
0.61
1.44
0.80
Al2O3
0.29
S
0.04
0.07
•
CO2
0.12
H₂O
0.11
Sio,
12.54
7.60
13.20
P₂05
trace
100.67
99.59
100.34
Metallic Iron
62.60
65.60
61.16
No. 1, analysis of a compact black ore containing minute trace of
iron pyrites; by Ward. Nos. 2 and 3, from Roslagen, on the east coast
of Sweden, north of Stockholm; by Noad. The first of these, from the
Höcksta mine, is coarsely crystalline, and slightly coherent; the second,
from Sladderö Island, is remarkable from being divided, by joints, into
rhombohedral masses.
The deposit of magnetic iron ore at Traversella, in Piedmont, about
twelve miles from Ivrea, in the valley of Bersella, is one of the most
remarkable of those of the more southern portion of Europe. It occurs
in the form of a crystalline mass of magnetite, associated with numerous
other minerals, such as copper and iron pyrites, chlorite, garnet, augite,
&c., some of which are beautifully crystallised. The workings have been
carried on from time immemorial; about 40 miles of galleries have
been driven, and, at one point, the mass has been removed for a distance
of a quarter of a mile to a depth of 200 yards.
Magnetite occurs at Berggieshübel, in Saxony, in the form of parallel
beds, varying from a few inches to 20 feet in thickness. It is asso-
ciated with red and brown hæmatite, and, at the surface, is contaminated
with sulphate of barium; in the deeper portions of the mine magnetite
predominates, while garnets, hornblende, epidote, and copper ores are
found in some of the deeper workings.
Deposits of magnetite have been worked for several centuries in the
neighbourhood of Arendal, in Norway, where they extend in a line nearly
parallel with the coast, for a distance of about thirteen miles. The ore
occurs in hornblendic and micaceous schists, and chiefly consists of
magnetite without any admixture of hæmatite.
On Lake Wettern, deposits of magnetite, in the form of comparatively
small strings and masses, are found in the Taberg, disseminated through
* 'Metallurgy of Iron,' p. 62.
K
130
ELEMENTS OF METALLURGY.
porphyritic rocks. They form a hill of more than 350 feet in height, and,
although comparatively of low produce, yielding only about 25 per cent.
of metal, yet fuel being cheap in the district, they are worked with advan-
tage. The metal produced is of good quality, and is especially adapted for
wire-drawing. In the Ural, magnetite occurs under somewhat similar
conditions to those which characterise the deposits in the vicinity of
Lake Wettern. At Nischne-Tagilsk, a ridge of rock 300 fathoms in
length, 250 broad, and about 40 in height, is, for the most part, made up
of pure magnetite.
The Cerro Mercado, near Durango, Mexico, a hill 300 feet in
height, is in great part composed of massive magnetite associated with
specular iron ore, brown hæmatite, quartz, and calcite. There are other
large deposits of this mineral on the Pacific Coast which are supposed by
Dana to be of the same geological age as those of Canada and the Northern
States of America.
In this country magnetic iron ores are of comparatively rare occur-
rence, but near Brent, in South Devon, magnetite is found in diorite, form-
ing a deposit of about a foot in thickness; it also occurs on Dartmoor;
at Treskerby, in Cornwall, it is found in a vein associated with tin ore.
The following analyses give the composition of three specimens of
English magnetic iron ore :-
1.
2.
3.
Fe₂03
FeO
MnO
Al2O3
CaO
MgO
62.20
44.40
66.50
16.20
20.00
13.00
•
0.14
0.16
0.56
2.28
5.20
3.60
2.34
0.60
0.56
0.37
1·00
1.52
SiO 2
P₂05
FeS2
0.24
0.10
0.50
0.57
0.07
SO,0.04
0.04
Insoluble residue
H₂O Shygroscopic
combined.
0.281
•
2.50
3.20
0.34)
16.26
24.20
9.40
•
100.82
98.60
98.95
Metallic Iron
57.01
46.63
56.66
1. From Dartmoor, Devonshire; analysed by Riley. On operating on
900 grains of the mineral a solution was obtained in which minute
traces of bismuth, tin, and copper, were detected.* 2 and 3. From Corn-
wall; by Dr. Noad.
TITANIFEROUS IRON SANDS.-Magnetite and titaniferous iron are dis-
seminated through many crystalline rocks in the form of crystals and
minute grains. By the disintegration of such rocks the ferruginous
minerals are liberated, and from their high specific gravity become con-
* Percy's 'Metallurgy; Iron and Steel,' p. 224.
IRON.
131
centrated by the action of water, giving rise to the black sands which are
abundantly found in alluvial gold-diggings and elsewhere. Along the sea
shore of countries in which crystalline and eruptive rocks abound, streaks
of black sand, washed out by the action of the waves, are frequently
found, and, in such cases, the accumulations thus produced are often so
large as to admit of its being employed as an ore of iron. Among the
localities where large accumulations of granular titaniferous iron ores are
found may be mentioned the shores of the Bay of Naples, Taranaki, in
New Zealand, and many points of the north-east coast of British America
the most important deposits are situated along the north shore of the
St. Lawrence, east of the Moisie River. At Moisie, where these sands form
a large portion of the beach, after the prevalence of certain winds, belts
of nearly pure black sands, which have been concentrated by the action
of the waves, are found along the shore. The purer and thicker layers
are separated by shovels from the more siliceous portions, and are after-
wards further concentrated by washing. For this purpose the ore is
subjected to a process of dressing on shaking-tables, 20 feet in length,
and 4 feet in width, upon which, by the aid of a gentle current of
water, the lighter siliceous grains are removed. The ore thus prepared
for metallurgical treatment contains on an average about 5½ per cent. of
insoluble siliceous matter.
When thus freed from the minerals with which they are associated
these black sands consist of nearly equal portions of magnetite and titan-
iferous iron; those treated at the Moisie Iron-Works have been examined
by Sterry Hunt, who found the magnetic portion to yield 66-73 per
cent. of metallic iron and 4.15 per cent. of titanic oxide. The non-
magnetic portion yielded 48.85 per cent. of iron, and 28.95 per cent. of
titanic oxide. A mixture of the two, as found, gave 55.23 per cent. of iron
and 16 per cent. of titanic oxide. Similar iron sands occur at several
points along the coast of Labrador, where they are associated with
quartz, garnets, and felspar.
On account of their fine state of division, iron sands have not been
successfully employed for the production of cast-iron, but at the Moisie
works they are directly converted into wrought-iron, in a bloomery-
furnace, with satisfactory results.
RED IRON ORES.-These are frequently associated with the hydrated
peroxide, particularly near the surface of deposits; where hæmatite is
found in the newer rocks, the whole mass is often more or less mixed
with brown iron ores. The most important deposits of these ores are
found in Cambrian, Silurian, Devonian, and Carboniferous rocks. At
Dalkaralsberg, near Nora, in Sweden, and in the island of Utö, specular
hæmatite occurs with magnetite. In Saxony red iron ores are found
near Eibenstock and Schwarzenberg, in lodes at the contact of mica-
schist, altered Silurian rocks, and granite. Some of these lodes are as
much as 15 fathoms in width, and extend for a distance of nearly 12
miles.
The iron mines of Elba, which are alike celebrated for the length of
time they have been worked and for the beauty and purity of their ores,
K 2
132
ELEMENTS OF METALLURGY.
are, for the most part, situated near the eastern extremity of the island.
At Rio Marina, specular and massive hæmatites rest upon talcose schists
and are covered by crystalline limestone; but for many years the work
has been confined to turning over the rubbish left by the ancients, of
which there are enormous accumulations. At Rio Albano and Terra
Nera the ore occurs in lodes, traversing talcose schists, which send off
branches alternately coalescing into beds, some of which are 100 feet in
thickness. A similar ramifying lode, which produces both hæmatite and
magnetite, is seen in a limestone cliff at Cape Calamita.
Near Marquette, on the southern shore of Lake Superior, a schistose
variety of hæmatite is very extensively developed in Huronian rocks.*
The average breadth of this iron district is six miles, and it extends
westwards from the lake shore for about twenty miles. The strata,
which are much contorted, are chiefly talcose and chloritic schists, passing
upwards into parallel laminæ of red jasper and hæmatite, whose united
thickness is said to be upwards of 1,000 feet. Of this, a large propor-
tion is too highly siliceous to pay for working; but distinct beds of
150 feet in thickness are quarried at the Jackson and Superior Mines.
These deposits are, in addition to their purity and great extent, remark-
able from containing minute octahedral crystals of martite, a variety
of ferric oxide crystallising under an isometric form. Contorted and
finely-laminated specular schists of a similar description, but on a much
smaller scale, occur on the Canadian shore of Lake Superior, and in the
altered Lower Silurian rocks of the Quebec group.
Two celebrated masses of hæmatite, known as the Iron Mountain
and Pilot Knob, are worked near St. Louis, in Missouri. The Iron
Mountain is a flattened dome-shaped elevation about 200 feet in height,
and forms the western extremity of a ridge of reddish porphyry, which
rises considerably above the iron ore, and stretches for more than a mile
to the eastward. The surface of the mountain is entirely covered with
loose pieces of ore, which become more and more conspicuous towards
the summit. Moss-grown blocks, some of which are many tons in weight,
cover the top, and are piled together in the greatest confusion. Pilot
Knob is much higher than the Iron Mountain, its height above its base
being estimated at 650 feet; it is mainly composed of a distinctly-bedded
siliceous rock. For the first two-thirds of the distance to the summit
quartz rock predominates; the upper portion of the mountain consists of
thick beds of iron ore alternating with siliceous rocks. The richest ores
exhibit a distinctly slaty structure, differing entirely, in this respect,
from those of the Iron Mountain, which are compact and without
* There are now in the Lake Superior mining district twenty-four iron mines;
eight of brown ore, four of specular, and four of brown and specular hæmatites, one
of specular and magnetic ore, six of magnetic, and one of flag-ore. The first opening
was made in 1840, the first forge was started in 1849, and the Marquette Railroad
was completed in 1856. There are sixteen blast-furnaces and one rolling mill, all
but three working with charcoal and hot-blast. The rolling mill commenced in 1868,
suspended in 1869, and recommenced in June, 1873. The Lake Superior Mines
shipped 985,521 tons of ore, valued at 4,222,350 dollars, in 1870, and have produced
3,771,939 tons of iron ore and 243,450 tons of pig since 1856.
IRON.
133
cleavage. There are numerous other localities in the vicinity, which,
although not so generally known, yield ores of a quality at least equal to
those obtained from Pilot Knob. The ore of Shepard's Mountain is
magnetic and of high quality; the Russell Bank ore is a fine-grained
hæmatite, very pure, and making excellent iron.
A brilliant micaceous hæmatite is found at Brixham, in Devonshire ;
a soft red variety, after being ground in oil, is sometimes employed as a
paint for iron-work.
One of the largest deposits of iron ore in Cornwall is at Restormel,
near Lostwithiel, where a lode, having an average width of about 15 feet
has been followed for more than a mile. The predominating mineral is
göthite, which occurs in fibrous and mammillated aggregations, as well as
in elongated prismatic crystals of great beauty. This lode also yields
red hæmatite and ores of manganese.
The most important deposits of hæmatite in England are, however,
those of Ulverstone in Lancashire, and Whitehaven in Cumberland, which
occur in the form of irregular masses in Carboniferous Limestone. The
ore is usually in dull, compact masses, but also forms kidney-shaped crys-
talline aggregates; in addition to the compact variety there is a greasy
micaceous ore which is largely employed for lining the hearths of puddling
furnaces. Brown hæmatite appears to be entirely absent in both districts,
and iron pyrites and calcium phosphate are only present in the most
minute proportions.
ANALYSES OF RED IRON ORES.

1.
2.
3.
4.
Fe2O3
MnO
A1203
CaO
MgO
CO₂
P₂05
95.16
90.36
86.50
94.23
0.24
0.10
0.21
0.23
0.37
0.51
•
0.07
0.71
2.77
0.05
0.06
1.46
trace
•
•
2.96
trace
trace
trace
trace
►
•
SO 3
trace
trace
0.11
0.09
FeS2
trace
0.06
0.03
H₂O
Shygroscopic
0.39
•
"
combined
0.17
Insoluble residue
5.68
8.54
6.55
5.18
101.15
100.20
100.56
100.88
Metallic Iron
66.60
63.25
60.55
65.98
1 and 2. From Cleator Moor, Whitehaven, Cumberland; by A. Dick.
1 is a compact red hæmatite containing cavities lined with crystals
of specular iron and quartz. When large quantities were operated
on, minute traces of lead were obtained. 2. A compact and pulverulent
3. Gill-
unctuous red hæmatite, in which traces of lead were detected.
brow, Ulverstone, Lancashire; by A. Dick. This ore is an unctuous
131
ELEMENTS OF METALLURGY.
red hæmatite, intermixed with pieces of limestone, which, being coloured
red, cannot be seen until the specimen is washed. 4. Lindale Moor,
Ulverstone; by J. Spiller. A hard compact hæmatite, affording distinct
traces of arsenic when large quantities are operated on.
A remarkable deposit of red hæmatite has been discovered and is
now in progress of development at Cwm Mountain, in Flintshire. The
ore here occurs almost entirely as a breccia of angular fragments
cemented together by calcium carbonate, and fills large irregular veins
in Carboniferous Limestone. At Whitchurch, near Cardiff, an oolitic red
hæmatite occurs at the base of the Carboniferous Limestone. This
variety is met with in the same geological position in the valley of the
Meuse, Belgium, and on the Cumberland River, Kentucky.
Since the introduction of the Bessemer process the demand for
hæmatite pig has much increased, and ores of this class, consequently,
now fetch a proportionately higher price than they did a few years
ago.
OLDER BROWN IRON ORES.-Irregular masses of brown hæmatite are
met with in the Carboniferous Limestones and lower coal-measure sand-
stones in the Forest of Dean, in the neighbourhood of Bristol, and at
Llantrissant, in Glamorganshire. In the Forest of Dean the ore is a
stalactiform brown hæmatite; the brown hæmatite of Ashton Court,
near Bristol, frequently contains fragments of sulphate of barium por-
phyritically imbedded; at Llantrissant the ore is interstratified between
the upper part of the Carboniferous Limestone, and a black shale roof,
supposed to be a portion of the coal-measures.
ANALYSES OF BROWN IRON ORES.

1.
2.
3.
4.
Fe2O3
MnO
A1203
CaO
•
90.05
0.08
89.76
59.05
52.83
0.04
0.09*
0.81
•
trace
0.63
trace
0.06
0.49
0.25
14.61
MgO
0.20
0.40
0.28
5.70
CO₂
P₂05
SÓ₂
FeS2
SiO2
Organic Matter.
18.14
0:09
0.13
0.14
0.32
trace
trace
0.28
0.09
34.40
• •
1.30
•
H₂O
fhygroscopic
0.24
·
combined.
9 22
7.05
6.14
4.75
Insoluble residue
1.07
2.57
0.04
100.77
101·07
100.68
98.78
Metallic Iron
63.04
62.86
41.34
36.98
1. Black Brush Ore, Forest of Dean, Gloucestershire; contains
* Estimated as MnO2.
IRON.
135
minute traces of copper; by A. Dick. 2. Smith Ore, Forest of Dean; a
comparatively pure, brown hæmatite; by A. Dick. 3. From Llantrissant,
Glamorganshire; by E. Riley. 4. From Froghall, near Cheadle, Stafford-
shire; compact homogeneous and brownish-red in colour; by A. Dick.
Enormous deposits of iron ore occur in Carboniferous Limestone
near the port of Bilbao, in Spain. The mine of Somorrostro is at the
present time most extensively worked, and yields about 1,000 tons of
ore daily. The mines of Moruecos Cerillo and Galdames, in the same
district, are being laid open by an English company, who are laying
down a railway and making preparations for shipments on a very exten-
sive scale. At the Galdames Mine there is a mountain of iron ore
1,200 yards in length, and about 170 yards in height above the river,
which flows at its base. At this elevation the ore is capped by limestone;
the whole face of the mountain is composed of ironstone, but scantily
covered by soil, and rocks of solid ore, without any kind of admixture,
stand up vertical y to a height of 150 feet. The quantity of ore actually
in sight is estimated at between sixty and seventy million tons; but it
is believed that from three to four times that amount may be rendered
available.
The following analyses of ores from this district are by Mr. W. Baker,
of Sheffield:-
ANALYSES OF SPANISH ORES.

1.
2.
3.
SiO2
Fe₂O
A1203
MnO
5.55
1.70
7.65
78.80
79-20
76.00
3.50
6.80
5.80
0.651
2.88
0.83
SO 3
0.068
0.12
0.34
•
CaŎ and MgO
trace
trace
trace
P₂05
none
none
none
H₂O, combined
11.653
9.672
10.128
100.222
100.872
100.748
Loss in drying
0.66
1.8
1.6
Metallic Iron
55.16
55.44
54.20
NEWER BROWN IRON ORES.-Brown hæmatites, for the most part of
an impure and sandy character, are found in the Lias, Oolite, and Lower
Greensand formations almost continuously from the northern parts of
Wiltshire to the Wolds of Yorkshire, passing through Oxfordshire,
Northamptonshire, and Lincolnshire. The ore has usually the appearance
of a dark ochreous oolitic rock, which, when freshly broken, has sometimes
a greenish tinge. The most important deposit is at the base of the
Inferior Oolite, and extends from the neighbourhood of Banbury through
Northamptonshire. These ores, although of low quality, admit of being
quarried at a cheap rate, and, besides being smelted on the spot, are
136
ELEMENTS OF METALLURGY.
largely exported to Staffordshire and South Wales. In Wiltshire the
same ore occurs in the Coral Rag, and in Buckinghamshire in the Lower
Greensand; in the latter locality the bed is not continuous, but nodular
masses of limonite are scattered through a stratum of brown sand about
50 feet in thickness. The nodules of ironstone are frequently hollow
and inclose loose white sand.
ANALYSES OF BROWN IRON ORES FROM THE ОOLITE, &c.


1.
2.
3.
4.
Fe2O3
FeO
50.31
44.67
53.43
64.61
trace
0.86
MnO
0:51
0.44
1·60*
Al2O3
CaO
7.25
7.85
4.19
3.85
11.76
9.29
0.84
0.64
MgO
0.62
0.66
0.72
0.20
Sio,
0.22
0.48
24.81
18.02
CO2
7.98
6.11
trace
P205
1.28
0.55
0.87
0.64
SO 3
·
FeS2
0·17
trace
trace
H₂O
fhygroscopic
16.31
combined
13.61
11.85
11.00
•
Insoluble residue
9.33
13.10
100.43
100.32
100.07
99.81
Metallic Iron
35.37
31.94
37.44
45.22
1. From Wellingborough, Northamptonshire, in the Infericr Oolite;
by E. Riley. 2. From Woodstock, Oxfordshire, Marlstone between
Lower and Upper Lias; by C. Tookey. 3 and 4. From Seend, Wiltshire,
Lower Greensand; by E. Riley.
Red and brown hæmatites occur in the liassic and oolitic rocks
of France under nearly similar conditions to those observed in this
country. The most important deposits are those of La Voulte, in the
Ardèche, where large quantities of a compact earthy red hæmatite are
interstratified in marls belonging either to the Lias or to the Oxford
Clay.
In Wirtemberg and Bavaria the lower members of the oolitic group,
on the north-west side of the Swabian Alps, contain ores of a similar
character; their maximum development is in the neighbourhood of
Aalen and Wasseralfingen, where the thickness of the beds exceeds 18
feet.
Another large area yielding ores of a similar character and of the
same geological age is situated in the Grand Duchy of Luxembourg; this
extends into the French portion of the valley of the Moselle, and forms
one of the most productive of the continental iron districts.
In addition to the stratified deposits before noticed, irregular masses
* Estimated as MnO.
IRON.
137
of loose concretionary brown hæmatite, called Bohnerz, are found filling
cavities and long winding fissures in the Oolites of South Germany.
These pisolitic concretions vary from the size of a pea to that of a
walnut; the larger being generally less perfectly spherical in form than
those of smaller size. The cementing material is usually a ferruginous
clay, which may be removed by washing, leaving an ore containing, on an
average, about 35 per cent. of iron.
The Wealden rocks in the vicinity of Boulogne yield sandy brown
ores occurring in superficial deposits; these chiefly supply the iron-
furnaces at Marquise.
TERTIARY AND POST-TERTIARY IRON ORES.-These ores are of minor
importance, but they nevertheless form no inconsiderable portion of the
iron-making resources of certain countries. Lying near the surface, they
admit of being worked at a cheap rate, and frequently produce iron of
excellent quality.
In England the ores of this class are of very little importance, but in
many parts of Europe they are abundantly developed and extensively
wrought. Large quantities occur in the great plain of North Germany,
which extends from the borders of Holland to the head of the Baltic;
they are also found abundantly in France, where they are worked to a con-
siderable extent. The deposits of Berry, especially those in the valley of
the Cher, are in the tertiary series, and consist of pisolitic ores dissemi-
nated in beds in the argillaceous rocks of the district. Tertiary and
alluvial ores are also extensively employed in the Ardennes and in the
department of the Marne. Oolitic and pisolitic ores are obtained from
the alluviums of the Nivernais, and hydrated oxides and hæmatites are
found in the superficial clays of the Charante, Dordogne, Lot-et-Garonne,
Lot, and Tarne-et-Garonne. These are of very considerable importance,
and are sufficiently pure to admit of being worked in the Catalan forge.
The workings are, for the most part, open to the day, and frequently
descend to a depth of sixty or seventy feet. The sandy deposits of the
Landes also contain beds of hydrated oxides and of bog ores. Burat
estimates that one-third of the production of iron in France is derived
from alluvial ores.
In Sweden, Norway, and Finland, large quantities of a variety of
limonite, known as lake ore, are obtained by dredging from the bottom of
shallow lakes. This ore occurs in granular concretionary forms, varying
in size from linseed to masses of several cubic inches. These ores are
collected during the winter months only, for which purpose a hole, of
some three or four feet in diameter, is made in the ice, through which is
lowered a perforated iron shovel attached to a long wooden handle. Ores
of this description are continually forming, and localities known to
have been entirely exhausted a quarter of a century previously, have, on
being re-worked at the expiration of that period, been found to afford
workable deposits of several inches in thickness. The formation of
these ores is said to be mainly due to organic agency; the iron being
chiefly derived from the oxidation of pyrites and from the decom-
position of such minerals as hornblende, augite, &c., containing ferrous
silicates.
138
ELEMENTS OF METALLURGY.
ANALYSES OF BOG ORES, &c.

1.
2.
3.
4.
Fe₂03
FeO
62.59
70.46
66.33
67.59
3.60
2
MnO2
SiO2
A1,03
CaO
8.52
0.75
1.45
13.04
2.80
7.81
·
•
.5.88
4.18
•
::
0.47
•
·
MgO
0.23
•
•
P₂05
1.50
0.12
0.18
Sand
11.37
Water and Organic Matter
16.02
11.12
26.40
17.81
100.00
100.50
100.00
99.72
Metallic Iron
43.82
49.32
49.24
47.32
1. Bog ore from the neighbourhood of Lingen, Hanover; by Senft.
2. Pisolitic ore from the district of Kandern; by Schenck. 3. Bog ore
from State of New York; by Karsten. 4. Lake ore from Flaten, Werm-
land, Sweden; by Svanberg.
SPATHIC IRON ORE-SIDERITE.—This ore does not so frequently occur
in large masses as do the various forms of ferric oxide, but is nevertheless
found in very considerable quantities in various European localities. Large
quantities of spathose ores are annually raised from the Devonian rocks in
the district of Siegen; the most important mine is that of Stahlberg, near
Müsen, where a nearly vertical lode has been worked since the commence-
ment of the fourteenth century. Its form is somewhat that of a wedge;
its greatest width being 65 feet, and its longitudinal extension 480 feet; it
is inclosed in clay-slate and has been worked to a depth of 130 fathoms
by means of a series of levels driven into the hill. Spathic ores also
abound in the crystalline metamorphic rocks and talcose schists of the
Eastern Alps, as well as in limestones of Silurian or Devonian age.
In Styria, the celebrated Erzberg, or ore-mountain, rises to the height
of nearly 2,500 feet, and, although apparently consisting of a solid mass
of siderite, it is, in reality, only capped by an arch of that mineral, to a
depth varying from 200 to 600 feet, including a few interstratified
schistose partings. The best ore, which occurs in the lower beds, is hard
and crystalline, and of a brownish-yellow colour. Iron and copper
pyrites, quartz, carbonate of calcium, and, more rarely, cinnabar, are
among the associated minerals. The present annual yield is about
110,000 tons, and at least 50,000,000 tons are said to have been laid open
by the workings.
The less considerable, but otherwise similar, deposits of Carinthia are
situated at Hüttenberg and Lölling, north-east of Klagenfurth, and include
numerous lenticular beds, the most productive of which is about 200 feet
in thickness.
In Thuringia a large irregular mass of spathic iron, in Permian rocks,
has been worked for the last 700 years; the principal sources are those of
Mommel and Stahlberg, near Schmalkalden, where the ores are much dis-
IRON.
139
t urbed by intruded porphyritic dykes. This deposit has been followed to
a depth of 300 feet, and its known length is about a mile.
In England there are deposits of carbonate of iron in Weardale, in
Durham, where it occurs in veins in the Carboniferous Limestone, asso-
ciated with ores of lead and zinc. Siderite is also found at Perran in
Cornwall, Exmoor in Devon, and at Brendon Hill, Somerset. Of late
years these ores have been worked to a considerable extent and exported to
South Wales for the production of spiegeleisen. The outcrop of veins of
this mineral is invariably found to be converted, to a considerable depth,
into brown hæmatite by the action of atmospheric air and water.
ANALYSES OF SPATHIC IRON ORES.

1.
2.
3.
4.
FeO
49.77
43.84
47.16
55.64
Fe2O3
0.81
0.81
MnO
1.93
12.64
10.61
2.80
CaO
3.96
0.28
0.50
0.92
MgO
2.83
3.63
3.23
1.77
CO2
37.20
38.86
38.50
38.35
P₂05
trace
S
0.04
H₂O
0.30
0.18
•
Insoluble residue
3.12
0.08
99.96
100.32
100.00
99.48
Metallic Iron
38.95
34.67
36.75
43.27
1. Weardale, Durham; containing minute traces of copper; Tookey.
2. Brendon Hill, Somersetshire; Spiller. 3. Stahlberg, Müsen; Schnabel.
4. Erzberg, Styria; Karsten.
CLAY IRONSTONES.- More than one-half of the total amount of iron
annually produced in this country is obtained from the argillaceous car-
bonates, found either in nodules interspersed through the shales and clays
of the coal-measures and, to a less extent, in some other formations, or in
continuous beds, of considerable thickness, in liassic and other compara-
tively recent rocks. It is mainly to the abundance of her coal-measure
ironstones that England has been indebted for the preponderating produc-
tion of that metal which has enabled her to supply the rapidly increasing
demand for railway and other iron.
Nodular argillaceous carbonate of iron essentially consists of ferrous
carbonate, but always contains a notable quantity of clay or sand, with
variable proportions of the carbonates of calcium, magnesium, and man-
ganese. When freshly broken, the fracture has a light-grey, yellow, or
bluish tint, but eventually becomes brown on exposure, through super-
ficial peroxidation of ferrous oxide. The nodules are frequently so
numerous as to coalesce into beds, and sometimes contain fossils, such
as fish and remains of plants. They are often fissured in such a way as
to suggest the idea of its being the result of contraction by drying; and
the fissures, having been subsequently filled with mineral matter, have
the appearance of veins, which often contain quartz, iron and copper
140
ELEMENTS OF METALLURGY.
pyrites, galena, blende, and calcite. At Dowlais, near Merthyr Tydvil,
in Glamorganshire, the clay ironstone, in addition to the minerals above
enumerated, contains Hattchetine, or mineral tallow, and beautiful
thread-like crystals of Millerite, or sulphide of nickel, occur in the
partially-filled cavities. Clay ironstone is abundant in the coal-fields
of North and South Wales, Staffordshire, Shropshire, Yorkshire, Derby-
shire, and Scotland; while those of Northumberland, Durham, and
Lancashire, are almost entirely without it. This ore is frequently
worked in conjunction with the coal with which it is associated, and is
extracted through the same pits.
The yield of clay ironstone per acre necessarily varies in accordance
with the thickness of the bed and the regularity with which the nodules
are disseminated. Thus the Parkgate Old Black Mine, which has a thick-
ness of 11 inches, yields 1,500 tons per acre; while the Clay Wood
Mine, of exactly one-half the thickness, produces in an equivalent area the
same amount of ore. In the South Wales coal-field there are, at least,
seven distinct districts containing seams of ironstone; the number of
beds in each varies from six to twenty-two, and many of these individual
deposits are themselves sub-divided into several distinct courses. They
sometimes consist of a single layer of spheroidal concretions, or balls, of
all sizes up to a ton or more in weight, but the beds are not usually very
thick, and this is the greatest drawback to their value.
ANALYSES OF CLAY IRONSTONES.

1.
2.
3.
4.
FeO
Fe2O3
35.38
39.38
45.35
52.04
1.20
1.24
MnO
0.94
0.95
0.56
0.92
A1203
0.80
0.82
0.61
1.30
•
CaO
2.78
2.26
2.60
0.53
MgO
2.22
3.72
1.22
0.85
SiO2
0.67
CO₂
25.41
29.38
30.21
32.31
P₂05
0.48
0.47
0.46
0.21
•
SO 3
FeS2
H₂O hygroscopic
(combined.
Organic Matter
Insoluble residue
trace
trace
trace
0.18
trace
0.20
0.13
0.74
.
0.681
1.64
0.46
1.11
1.416
0.23
0.54
1.59
0.51
A
28.00
19.35
15.87
11.14
99.47
100.20
100.98
100.40
Metallic Iron
28.76
31.82
35.74
40.84
1. White Bed Mine, Brierley, Yorkshire; Spiller. 2. Thorncliffe
White Mine, Parkgate, Yorkshire; Spiller. 3. Pins, Dudley, Staffordshire;
Dick. 4. Gubbin and Balls, Bunker's Hill Colliery, Staffordshire; Dick.
BLACKBAND IRONSTONE. This ore was discovered in Lanarkshire by
Mushet in the year 1801, but did not come into extensive use until about
1830. It is a clay ironstone, usually of a dark-brown or black colour,
containing carbonaceous matter. The blackband iron ores of Scotland
IRON.
141
contain from 20 to 25 per cent. of coaly matter, and from 30 to 40 per
cent. of iron. In the western coal-field of Scotland several principal
blackband measures, having an aggregate thickness of 6 ft. 5 in., are
known; all these have been more or less extensively worked, but the
supply has now considerably fallen off. The thickness of deposits of
blackband is subject to great variation, and a band seldom extends
over very large areas without some change taking place in its com-
position. At Airdrie the blackband occurs in workable quantity over
an area of only about ten square miles; whilst its equivalent, in the
form of a thin seam of coal, is found over a district of more than five
times that extent. In Linlithgowshire the stratum, elsewhere affording
blackband ironstone, is represented by the celebrated Boghead cannel coal.
The yield of blackband ironstone is at the rate of 2,000 tons of calcined
ore per acre for each foot in thickness of the deposit. Beds varying from 4
to 9 feet in thickness occur in North Staffordshire, and, after calcination,
the ore is largely exported to the iron-works of South Staffordshire.
In South Wales blackband is found in numerous beds of irregular
thickness and of limited extent. This ore was first discovered in West-
phalia, in 1855; but the quantity does not appear to be large, and in
but a few instances only do blackband and coal occur together. Black-
band likewise occurs in Lower Silesia, and thin layers of this mineral
have been discovered at one or two localities in the Banat.
Carbonaceous spathic ores, locally known as coal brasses, occasionally
accompany coal in South Wales, and differ from ordinary blackband in
containing considerable quantities of the carbonates of calcium and mag-
nesium. Nodules of iron pyrites, occurring under similar circumstances,
are also sometimes called coal brasses.
ANALYSES OF BLACKBAND IRONSTONES.

1.
2.
3.
4.
FeO
53.82
40.77
37.07
42.64
Fe2O3
MnO
CaO
MgO
SiO2
CO.
2
P₂05
0.23
2.72
►
0.23
0.26
1.51
0·90
6.61
5.24
0.28
0.72
7.40
5.26
•
•
2.00
34.39
10.10 clay
2.70
26.41
36.14
36.89
0.23
0.17
FeS2
trace
0.22
H₂O
fhygroscopic
•
•
·
combined
1.00
Carbonaceous Matter
7.70
17.38
9.80
8.87
•
99.93
100.00
100.18
99.55
Metallic Iron
41.60
33.57
28.83
33.12
1 and 2. Scotch blackband; Colquhoun. 3 and 4. "Coal brasses,”
Aberdare, South Wales; Price and Nicholson.
CLEVELAND IRONSTONE.-The Middle Lias, or marlstone rock, which,
in the neighbourhood of Chipping Norton and Woodstock, in Oxfordshire,
142
ELEMENTS OF METALLURGY.
yields an oolitic brown hæmatite, affords iron ore in much larger quanti-
ties in the North Riding of Yorkshire. This stone, where best developed
in the Cleveland district, has a total thickness of about 20 feet, made up
of various interstratified bands of ore and shale; of these the two prin-
cipal members are distinguished as the Pecten and Avicula seams, from
the respective prevalence in them of fossil shells belonging to these
genera. The average workable depth of the ore is from 12 to 17 feet;
the usual produce per acre being estimated at about 20,000 tons. This
ore, which is an inferior carbonate of iron, is usually of a dull bluish-
yellow colour, caused by the presence of ferrous silicate; its structure is
oolitic, with numerous inclosed fossils, and it sometimes contains inter-
spersed crystals of quartz and anatase. A dark blue, or nearly black
variety, found at Rosedale Abbey, is, although oolitic in its structure,
both magnetic and polar.
ANALYSES OF CLEVELAND IRON ORES.

1.
2.
3.
4.
FeO
Fe₂03
MnO
A1203
CaO
MgO
K₂O
SiO2
39.92
34.98
33.17
33.85
3.60
32.67
⚫95
0.48
0.50
0.69
7.86
3.20
3.92
3.15
7.44
11.96
11.90
2.86
3.82
4.51
4.52
1.59
•
0.27
•
·
CO2
7.12
22.85
6.95
29.20
28.00
10 36
P₂05
SO 3
1.86
1.30
0.48
1.41
trace
FeS2
0.11
0 03*
H₂O
Shygroscopic
combined
•
2.97
3.30
3.65
3.76
Organic Matter .
Insoluble residue
trace
0.84
1.64
10.04
13.22
100 41
•
98.97
99.36
98.16
Metallic Iron
33.62
27.21
25.80
49.17
1. Cleveland ore, locality not stated; Dick. 2. Pecten Bed, Gros-
mont, Yorkshire; Tookey. 3. Avicula Bed, Grosmont, Yorkshire;
Tookey. 4. Magnetic ore, Rosedale Abbey; Pattinson.
The following is the return of the amount of iron ore raised and
consumed in the United Kingdom for the year 1871:—†

Cornwall
Devonshire
District.
Somersetshire.
Description of Ore.
Red and Brown Hæmatite
Tons.
21,947
Brown Hæmatite and Magnetite
14,124
(Spathose ore, argillaceous ore, and Hæ-
matite
32,883
Carry forward
•
68,954
* Sulphur.
† 'Mineral Statistics of the United Kingdom of Great Britain and Ireland for the
year 1871,' by Robert Hunt, F.R.S., Keeper of Mining Records.
IRON.
143
District.
Gloucestershire
Wiltshire
Description of Ore.
Brought forward
Oolitic ore
Tons.
·
•
68,954
207,598
•
•
159,894
28,330
•
779,314
•
290,673
415,972
34,075
1,513,080
Oxfordshire
Northamptonshire
Lincolnshire
Shropshire
Warwickshire.
•
Staffordshire, North
Derbyshire
Lancashire
Cumberland
South
•
(North Riding.
West Riding
Argillaceous Carbonate
(Argillaceous Carbonate and Hydrated
Oxide
Argillaceous Carbonate
""
Red and Brown Hæmatite
705,665
492,973
931,048
1,302,703
Yorkshire
Argillaceous Carbonate, and Magnetite
Argillaceous Carbonate
•
4,581,901
407,997
Northumberland and
Durham
Argillaceous Carbonate and Spathose ore
285,297
NORTH WALES
Argillaceous Carbonate and Brown Hæ-`
matite
51,887
SOUTH WALES AND
MOUTHSHIRE
MON-Argillaceous Carbonate, Blackband, and
Brown Hæmatite
969,714
ISLE OF MAN
•
Spathose Ore
75
SCOTLAND
IRELAND
Purple ore from cupreous)
pyrites
Argillaceous Carbonate and Blackband
(Aluminous Ore, Blackband, and Brown
Hæmatite
3,000,000
107,734
..
200,000
Iron ore imported
324,175
Total
•
16,859,059
In 1855, Mr. Blackwell estimated the annual production of pig-iron
in the whole world to be that given in column I. of the following
table; the most reliable statistics of the trade as compiled by an American
metallurgist for the year 1871, will be found in column II.*

I.
II.
Great Britain
United States
3,000,000
6,500,000
750,000 1,912,000
France
750,000 1,350,000
•Germany
400,000 1,250,000
Belgium
•
200,000
896,000
Austria
250,000
450,000
Russia
200,000
330,000
Sweden and Norway
150,000
280,000
Italy
75,000
Spain
72,000
All other countries
300,000
200,000
6,000,000 13,315,000
From the above it will be seen that the annual production of Great
Britain is still nearly equal to that of the united make of all the other
countries in the world.
* 'Journal of the Iron and Steel Institute,' No. III., 1872.
144
ELEMENTS OF METALLURGY.
ASSAY OF IRON ORES.
In order to determine the commercial value of an ore of iron it is
necessary to ascertain not only its percentage yield of metal, but also the
approximate proportion and constitution of the various impurities present,
as well as their probable influence as affecting its fusibility. It is more-
over requisite to determine the nature and respective amounts of other
elements, such as phosphorus, sulphur, &c., likely to affect the quality of
the iron obtained by its metallurgical treatment. The two former ques-
tions may be answered by the results of dry assay, which gives the maxi-
mum amount of cast-iron that, under the most favourable conditions, can
be obtained from the ore in the blast-furnace; the ordinary processes of
chemical analysis must be resorted to for the third.
When it is required to ascertain the exact amount of metallic iron
present, its determination must be effected in the wet way, and the metal
may either be precipitated and estimated as ferric oxide, or one of the
volumetric processes may be employed. The volumetric estimation of
iron is generally more exact and expeditious than any method involving
the precipitation and weighing of the peroxide, and possesses the advan-
tage of being equally applicable to assaying and to the determination of
iron in the complete analysis of ores.
We shall first give a description of the methods of assaying iron ores
by the dry way, and afterwards treat of the processes for the volumetric
estimation of iron; finally, the analysis of ironstones and the estimation
of those constituents which are present in minute quantities only will be
considered.
DRY ASSAY OF IRON ORES.-Apparatus necessary. For the dry assay
of iron ores a wind furnace is required. Fig. 27 is a vertical section, through

D
A
C
B
Fig. 27.-Assay Furnace; vertical section.
IRON.
145
the middle of the grate of one of the furnaces employed in the metal-
lurgical laboratory at the Royal School of Mines. The fire-place, A,
8 inches square by 12 inches deep, is lined with refractory bricks, beneath
which is the ash-pit, B, provided with a register-door for the regulation of
the draught. When a large supply of air is required this door may be
opened to its full width, or it may be closed and the register, c, opened to
a greater or less extent. This consists of a revolving circular disc of
sheet-iron, provided with a semicircular opening, the centre of which
coincides with the centre of the door; behind this, in the door, is another
semicircular opening, of equal size to that in the movable disc, with which
it can be made to coincide, or otherwise, as circumstances may require. In
this
way it can be so adjusted as to regulate with great nicety the amount
of air admitted. The flue, D, communicates with a chimney 60 ft. in
height, with which five other furnaces are connected. The whole of the
brickwork is firmly bound together by cast-iron plates, secured by tie-rods,
and those portions of the lining which are subjected to a high tempera-
ture are made of refractory bricks laid in fire clay. For the purpose of
closing the mouth of the furnace fire-tiles, e, f, are employed, each of
which is clamped with a piece of flat iron firmly wedged at one end; screws
are sometimes employed, instead of wedges, for keeping the clamps in
their places. These covers are of two sizes, and the larger one only re-
quires to be removed in order to take a crucible out of the furnace. The
draught may be regulated not only by the register-door of the ash-pit, but
also by opening the furnace top to a greater or less extent.
The same
result may be obtained by placing a piece of fire-brick in the passage
opening into the flue, or by means of a damper at the top of the stack.
The fuel employed should be either hard coke or anthracite supported on
the grate, g.
The furnace above described must be accompanied with an assortment
of tongs to be employed for various purposes. For charging lumps of
fuel into hollow places, and removing hot crucibles after their
withdrawal from the furnace, tongs of the form represented,
fig. 28, will be sometimes found convenient. Another kind,
intended for removing a crucible from the fire, either by grasp-
ing it with the bent part, or by taking one of its sides between
the jaws, is represented, fig. 29. Fig. 30 is of a different form,
and is chiefly employed for lifting uncovered crucibles, as it
is only adapted for laying hold of the sides of the vessel. All
these varieties are, however, rather short in the handles, and
consequently merely adapted for removing bodies from the
furnace when not very highly heated. For this reason, if they
be employed for taking crucibles from a wind furnace of the
kind just described, it will be found necessary to allow it to
cool for at least half an hour, after the assays are completed, before the
crucibles can be withdrawn. To obviate, to some extent, loss of time, the
tongs represented, fig. 31, are often conveniently employed; these are long
in the handles and are provided with very strong bent jaws, so that they
may be used almost as soon as the crucible is sufficiently hardened to bear

용
​Fig. 28.
L
146
ELEMENTS OF METALLURGY.


Fig. 29.
Fig. 30.
Fig. 31.
removal; but as at this stage the furnace is extremely hot, it is sometimes
difficult to look into the fire, in order to see where to apply the tongs.
This inconvenience is lessened by using a wooden
shield, fig. 32, in which a is a small rectangular hole
into which a piece of blue or green glass is inserted,
and b a handle by which it may be held before the face
of the operator. When this is employed, it should be
held before the person using the tongs by an assistant.
By this contrivance the heat is prevented from reach-
ing the face, whilst the small glazed aperture allows
of the interior of the furnace being distinctly seen.
In addition to the foregoing, it is necessary to be
provided with a large cast-iron mortar, a small anvil, a hammer, and a set
of sieves, of which the various uses will shortly be described.

Fig. 32.
Preliminary Operations, Fluxes, &c.-The assay of an iron ore yields
on a small scale somewhat similar results to those obtained in the large
way, and consequently has the advantage over analysis of affording infor-
mation of a more immediately practical character. Before, however,
operating in the dry way, it may be desirable to obtain some definite
knowledge of the mineral to be treated, in order to determine what fluxes
should be added, for the purpose of affording at the same time a fusible
slag and the largest possible yield of metallic iron. The ores of iron
may be divided into three classes :—
1st. Those which consist chiefly of hydrated ferric oxide.
2nd. Those which contain the metal in the state of anhydrous oxide,
such as red hæmatite and magnetite.
3rd. Spathose ores, which are composed of ferrous carbonate.
Berthier recommends that the preliminary examination of minerals of
the first class should be conducted in the following way. A portion of
the ore is selected, which as nearly as possible represents a fair average
of the mineral to be treated. This is powdered in a large iron mortar,
and then, in order to thoroughly mix the different particles, the whole is
IRON.
147
Of this coarse powder
sifted through a sieve of coarse wire-gauze.
about 2,000 grains must be taken and again pounded in the iron mortar
until the whole has been made to pass through a second sieve of very
fine wire-gauze. The object of first pounding the whole of the sample
selected, and then taking a portion only for the purposes of assay, is to
insure perfect uniformity of composition and a fair representative sample.
Of the finely-pulverised ore, 50 grains are placed in a platinum crucible.
and heated to redness over a gas flame, by which means the water and
carbonic anhydride are driven off. The crucible and its contents are now
again placed in the balance, and if the weight of the calcined matter be
called w, the amount of water and carbonic anhydride expelled will be
represented by (50-w).
The calcined ore may be now thrown away and other 50 grains taken,
which are to be attacked, in the cold, either by acetic or very dilute nitric
acid. This will dissolve only the carbonates of calcium and magnesium
which may be present in the gangue, without interfering with either the
oxide of iron or the silica. Should it not contain any earthy carbonate, no
effervescence will ensue on the addition of an acid, and we may conse-
quently pass on to the next operation; but should effervescence take place,
weak acid is added until it entirely ceases. When this point has been
attained, the residue is thrown on a filter, washed with a little water, dried
and calcined. If we now call this weight w', the weight of the water,
together with that of the carbonates of calcium and magnesium contained
in the mineral will be represented by (50-w'), and consequently (w-w')
will be the united weights of the lime and magnesia present.
Lastly, 50 grains of the powdered mineral are attacked with concen-
trated hydrochloric acid, which is boiled until the undissolved matter
which remains at the bottom of the flask has become colourless. This
consists of the siliceous and argillaceous portions of the gangue, which
will alone remain undissolved, and which, after being thrown on a filter
and washed, are calcined and weighed. The weight of this calcined
residue being represented by w', we shall, on uniting the different results
of the various operations, obtain the following information relative to the
composition of the mineral :—
Water and Carbonic Anhydride
Lime and Magnesia
Silica and Clay
(50-w)
(w-w')
w"
Oxides of Iron and Manganese=50— (50—w)—(w—w′)—w" — (w' — w″).
If the mineral contains but a small quantity of manganese and the
whole of the iron originally existed as peroxide, the weight (w'-w") will
represent the amount of anhydrous peroxide of iron in the ore, and will
correspond to 70 (w' — w') of metallic iron.*
Native carbonate of iron is more or less oxidised by calcination; and,
consequently, the loss of weight experienced during the operation will no
longer represent the amount of water and carbonic anhydride driven off.
* This process, if employed for the examination of an ore containing alumina, &c.,
soluble in hydrochloric acid, would evidently result in an error proportionate to the
amount so dissolved; it therefore cannot be considered as being universally applicable.
L 2
148
ELEMENTS OF METALLURGY.
From the results obtained by this preliminary investigation, the pro-
portion of the fluxes required to form an easily fusible slag may be calcu-
lated. Berthier's method for determining the approximate composition
of an ironstone, although sometimes affording valuable information,
involves too large an expenditure of time to be generally adopted, and a
sufficiently good idea of the nature of the fluxes required may, in most
cases, be derived from a mere inspection of the ore. Magnetites and
hæmatites are usually associated with silica, and require the addition of
both lime and alumina. Spathose ores and other carbonates of iron, when
they do not contain a considerable amount of clay, require the addition of
silica, in the form either of sand or of some silicate, such as glass free
from lead, together with alumina and a little lime; argillaceous carbonates
may on the other hand be fused with lime alone. After a certain
amount of experience has been acquired, but little difficulty will be found
in properly adjusting the fluxes to be employed.
The following are the principal fluxes required: Silica, in the form
either of white glass-house sand or ground flints; any other form of silica
may
be employed if practically free from iron, and in a sufficiently fine
state of division. Alumina; this is best supplied in the form of china-
clay, which, after ignition, contains 53 per cent. of silica and 43 per cent.
of alumina. Fire-clay, shale, or blast-furnace cinder, may also be used,
but they have the disadvantage of containing small quantities of iron.
Lime; unslaked lime in a state of fine powder should be used, when
obtainable, but chalk or any other limestone sufficiently free from iron
may be employed as a substitute; care must be taken that this flux is as
free as possible from sulphates and phosphates. In some cases fluor-spar
may be advantageously substituted for lime. This flux affords a liquid
slag, but is rarely used on the large scale. Glass, free from lead, may be
employed with argillaceous ores; such glass usually containing from
60 to 70 per cent. of silica, the remainder being soda, potash, and lime.
Borax is too fusible to admit of being generally employed as a flux for
iron assays, since it combines with iron oxide at a temperature below that
necessary for reduction; it is nevertheless sometimes used as a substitute
for glass, but, when it is so employed, the proportion of lime should be
increased to such an extent as to materially diminish the fusibility of the
mixture.
Classification and Proportion of Fluxes. The nature of the flux to be
employed will vary according to the composition of the gangue, and
its quantity according to the amount of gangue and the weight of orc
operated on. The object sought is in each case to obtain a sufficient
amount of well-fused, clean slag, to completely cover the reduced button
of metal.
According to Percy, blast-furnace cinder may be taken as a type of
the kind of slag most desirable to obtain; its approximate percentage
composition is as follows:-
SiO2
38
21 parts
A1203
15
or about
1
Cao
47
3
27
IRON.
149
The following mixtures produce, when fused, a slag approximating to
this composition:-
Quartz
China-clay
Lime.
. 1
2 SiO₂ 0.92
1.92
2
[36.5 per cent.
•
¡Al2O3
(Al₂O, 0·82
0.82
15.5
2호
​2.50
48.0
""
Glass
21/SiO
1.75
2
35.0
Materials Al₂O,
0.75
15.0
Lime.
21/1
2.50
50.0
Shale or Fire-clay 3 (SiO2
1.80
35.0
""
{Al2O3
0.90
17.0
Lime.
21
2.50
48.0
The nature and amount of the fluxes to be employed may be ascer-
tained by means of repeated trials; three or four equal weights of the
ore should be treated in the furnace, at the same time, with variable
additions, according to the following table:—*
1.
2.
3.
4.
5.
SiO 2
50
50
30
45
15
Al₂Õ3
25
16
20
18
5
Cao
25
34
50
37
80
The weight of flux used in each case must be one-half that of the ore
operated on, and the most advantageous mixture will be that yielding the
highest produce.
In some German iron-works the following proportions are employed :-
For rich magnetic ores and red
hæmatites
•
,, argillaceous brown ores
""
bog ores
""
spathose ores
furnace-cinder.
25 p. c. fluor-spar.
red}
5
to 20 p. c. chalk
and
20 to 40
30 to 40
""
""
""
""
50
50
""
""
""
10 to 15
20 to 25
""
china-clay 20 to 25
""
""
clalk
20 to 25
""
""
""
""
Method of conducting an Assay.-The fusion may be effected either in
an unlined or in a brasqued crucible. In the former case from 100
to 150 grains of finely-powdered ore are intimately mixed with the
proper fluxes and about 25 per cent. of charcoal-powder, and placed in a
black-lead or clay crucible, of which the cover is luted in its place with
fire-clay. The crucible, with its contents, is now placed on half a fire-
brick laid on the bars of the wind furnace, and at first subjected to a
moderate heat, in order to expel water and carbonic anhydride. After a
short time the temperature is gradually increased, and a full white-heat
is maintained for nearly an hour, when the fuel is allowed to burn down,
and the crucible is taken out to cool. When sufficiently cold it is broken,
and, if the operation has been successful, a smooth well-melted button of
cast-iron will be found at the bottom, covered by a slag having the
appearance of glass or enamel. The button of cast-iron is detached from
* Bauerman, p. 97.
150
ELEMENTS OF METALLURGY.
the slag, and the latter is reduced to powder in a mortar, and examined
with a magnet for any shots of metal it may contain; these, if found,
are added to the principal button and weighed with it.
The assay of iron ores is however best made in crucibles lined with
powdered charcoal, which not only protects the sides of the pots from
being acted on by the fluxes employed, but also serves as the agent by
which the oxide is reduced to the metallic state. On account of the high
temperature to which they are subjected, it is necessary that the crucibles
employed should be composed of the most refractory materials. Those
known by the name of London pots, and sold by the various laboratory-
furnishers, are well fitted for this purpose; but Hessian crucibles will
also bear the necessary heat, although less convenient in form. In order
to line a crucible, it is partially filled with coarsely-powdered charcoal,
slightly moistened with treacle and water, which is rammed into the solid
form by the use of a wooden pestle. When the first layer has become
sufficiently compressed, its surface is scratched with a knife, for the
purpose of making the second stratum adhere firmly to it, and a little
more is added and beaten down as before. The surface of this layer
is again rendered uneven by scratching, and the operation repeated
until the crucible is completely filled. When this is the case, a cavity,
of the form shown, fig. 33, is made in the centre, leaving a lining of
charcoal of about half an inch in thickness on the sides and bottom of
Fig. 33.
the pot. To prevent any of the ore or flux from adhering
to the sides, the interior of the cavity is smoothed by rub-
bing with a round glass pestle, and the upper edges are so
rounded off as to prevent any portion of brasque from falling
into the hollow during the time the mixture is being intro-
duced. When dry, the brasque is carbonised by closely
covering the pot and subsequently heating it to redness, by
which a compact mass of charcoal, completely lining the crucible, is
obtained. When quite cold, a weighed quantity of the powdered ore is
to be well mixed on a sheet of smooth paper, with the proper weight of
flux, and then carefully transferred to the cavity in the lined crucible,
where it will occupy the position b c. Any portions of the powder which
may remain attached to the sides are carefully swept to the bottom by a
stiff feather, and the space, a b, is filled, either with charcoal-powder or
by a charcoal plug. The cover is now fitted, and firmly luted with
fire-clay, with which the bottom of the crucible is also cemented to a
piece of fire-brick, so as to stand about three or four inches above the bars
of the grate. During the first half-hour the register remains nearly closed,
and the firing is carefully conducted to drive off moisture, carbonic
anhydride, &c., and to avoid the cracking of the luting, which would
be caused were the heat too suddenly applied. Afterwards the heat
is gradually increased by further opening the register, and at the end
of an hour it is entirely opened for the purpose of increasing the tem-
perature to the highest possible degree. The operation, when properly
conducted, should altogether require about an hour and a quarter, and at
the expiration of that time the furnace is allowed to cool. As soon as the
IRON.
151
temperature is sufficiently reduced, the crucible is carefully removed by
the aid of proper tongs, and is placed in an upright position until suffi-
ciently cold to admit of being readily handled. It is now to be placed
over a sheet of brown paper, with the view of avoiding loss, and the lid,
which will be found to adhere firmly to the pot, is removed by a blow
from a small hammer. If the operation has completely succeeded, the
iron will be found as a rounded button, covered by a stratum of slag,
resembling in its appearance ordinary bottle-glass, and entirely free from
adhering metallic globules. When, on the contrary, the heat has not
been sufficiently great, or the mixture of fluxes has not been judicious, the
slag will be covered with small metallic beads firmly imbedded in its
surface, from which they cannot be easily detached. If, from want of a
sufficient temperature to effect the fusion, or from an improper addition of
fluxes, the experiment has entirely failed, the ore will be found either in
a partially-melted lump, or merely in an agglutinated mass, in which the
iron, although more or less completely reduced to the metallic state, has
not formed into a distinct button. On breaking the crucible, the button,
with its adhering slag, is carefully removed and crushed by a blow of the
pestle in a large iron mortar. The principal metallic button may be
now readily removed; but as it seldom happens that the slag does not
still inclose small metallic globules, it is necessary to reduce it to coarse
powder, in order that these may be separated. This is most readily
effected by turning out the contents of the mortar on a sheet of paper, and
passing a magnet through the pulverised slag. In this way the metallic
particles are soon collected at the poles of the magnet, and, on being
brushed off by a stiff feather, are placed in the balance with the larger
button before separated.
In order to test the quality of iron thus obtained, the button may be
placed between a fold of thin tin-plate and smartly struck on an anvil by a
heavy hammer. If the fracture present a greyish appearance, and the
button flattens slightly before breaking, it shows either that the ore is
easily reducible, or that a very high temperature has been obtained in the
furnace. A hard white button is often produced when phosphorus is
present, and sulphur imparts to it a reticulated mottled structure. Man-
ganese gives to the metal a light crystalline structure like that of
spiegeleisen, and titanium a dull grey colour and reticulated structure.
The intimate mixture of the ore and fluxes, together with the unlimited
supply of fuel, represents, however, in the assay, a favourable combina-
tion of circumstances not attainable in the blast-furnace, and, conse-
quently, it affords no exact information as to the character of the iron
likely to be produced from an ore on the large scale.
The following conclusions may be deduced from the appearance of
the slag. A perfectly transparent slag, with a green tint, indicates that
silica is present in excess; a light grey or bluish enamel, or a trans-
lucent glass, indicates that the fluxes have been added in suitable
proportions. On the other hand, a rough, dull, stony, or crystalline
slag is produced when alkaline earths are in excess. If, as sometimes
happens, the assay has not been melted, but is merely fritted together,
152
ELEMENTS OF METALLURGY.
and contains reduced iron disseminated as a fine grey powder, both
silica and alumina are deficient, and lime and magnesia are in excess.
A vesicular slag, with iron interspersed as malleable scales, indicates an
excess of silica, which must be rectified by the addition of lime. When
the slag has an amethystine colour it may be considered that small
quantities of manganese are present, while a larger proportion renders
it yellow, green, or brown.
Swedish Process.--In Sweden assays of iron ores are made in small
brasqued crucibles, each about 2 inches in height, and 13 inch in diameter at
its largest end. The weight of ore operated on is usually from ten to fifteen
grains only, and four crucibles are placed in the furnace at the same time;
a piece of fire-brick, about 3 inches square, being used as a stand. As soon
as a white-heat has been reached, the fire is allowed to burn down, and, when
the furnace has sufficiently cooled, the crucibles are removed by lifting
out the stands to which they will be found firmly attached by the partial
fusion of the brick with the ashes of the fuel employed. When cold
they are broken, and the buttons and slags examined in the usual way;
the four results, when the assays have been skilfully made, should
not vary more than or per cent. from each other.
10 1
4
WET ASSAY OF IRON ORES; MARGUERITE'S PROCESS.---This method of
estimating iron is based on the action of protosalts of iron on potassium
permanganate, KMnO4, by which a quantity of permanganate, exactly
proportionate to the amount of iron present, is decomposed.
Thus, in a solution of a persalt of iron, such as results from the
attack of hæmatite by hydrochloric acid, it is only necessary to reduce
the metal so as to form a protosalt, and then gradually to add a solution
of permanganate of known strength. So long as a trace of a ferrous salt
remains to be acted on, the colour of the permanganate is destroyed;
but it will be at length found that the colour of the last drop added is
no longer affected, but that, on the contrary, it communicates a pink tint
to the whole solution. When the iron exists as ferrous chloride the
reaction which takes place is expressed by the following equation:-
10FeCl2+2KMnO,+16HCl=5Fe₂Cl₂+2KC1+2MuCl₂+SH₂O.
It will be observed that two equivalents of potassium permanganate are
capable of converting ten of ferrous chloride into five of ferric chloride;
but it will also be remarked that a slight excess of hydrochloric acid is
necessary.
The various operations requisite for the estimation of the amount of
iron contained in an ore of that metal are the following:-
1. Solution of the ore in acid.
2. Reduction of the ferric salts in the solution, either by sodium
sulphite or by sulphuretted hydrogen, and subsequently boiling, in order
to expel sulphurous anhydride or sulphuretted hydrogen. The reduc-
tion of ferric salts may also be effected by boiling with metallic zinc
until the yellow colour of the solution has disappeared.*
For this purpose we have found sulphuretted hydrogen preferable to either
sodium sulphite, or metallic zinc.
IRON.
153
3. To the solution of the ferrous salt thus obtained, a standardised
solution of potassium permanganate is cautiously added, until a pink
tint makes its appearance, when the number of divisions used is read
off from the graduated burette, and the amount of iron present calculated
therefrom.
The presence of zinc, manganese, tungsten, phosphorus, lime, magnesia,
alumina, and silica does not in the least interfere with the accuracy of the
results obtained.
Preparation of Standard Solution.-Potassium permanganate is a
preparation of considerable stability, and may be kept in a glass bottle
for a long time, without undergoing any change, if preserved from con-
tact with organic matter. To convert a solution of this substance into a
test liquor of known strength, two grammes of pure iron, such as pianoforte
wire, may be dissolved in hydrochloric acid, and, as soon as the solution
is complete, the liquid is so diluted with distilled water as to make it up
to exactly one litre.
This is now divided into two equal portions, to one of which the
solution of permanganate is carefully added from a burette until a
slightly pink colour becomes manifest, and the number of the divisions
necessary to produce this effect carefully noted. In order to test the
accuracy of the first determination, the second portion of the ferrous
solution is now treated in the same way, and the number of divisions
necessary to produce a pink colour again noted. The number of divisions
employed in the two experiments should exactly agree; but in case of
any very slight difference occurring between them, the mean of the two is
taken, and this number employed to calculate the results of the estimation.
Should the permanganate solution be found to be too concentrated, it
is easy, by making a proper addition of distilled water, to reduce it one-
fourth, one-half, or to any other extent that may be considered desirable,
in order to afford a sufficient range on the scale of the burette.
When operating on solutions of iron in hydrochloric acid, it is
necessary that they should not only be cold, but also in a very dilute state,
in order to prevent the reaction of the excess of acid on the permanganate,
and the liberation of chlorine.
Solution of the Ore.-A weighed quantity, from one to two grammes,
of the ore, in a state of fine powder, is introduced into an ordinary flask
of hard glass, and digested with strong hydrochloric acid until nothing
but the insoluble siliceous gangue remains at the bottom. Blackband
ironstone when thus treated leaves a carbonaceous, finely-divided residue,
which must be removed by filtration; but in the case of merely siliceous
and argillaceous matters this is not necessary. The ferric salts present
must now be reduced to the state of protosalts, by the use of either
sodium sulphite, sulphuretted hydrogen, or metallic zinc, in the way
already described.
When titanium is present, the reduction of the ferric salts must not
be effected by the use of zinc, which reduces titanic chloride, TiCl, to
titanous chloride, Ti₂Cl. In such cases the use of sodium sulphite is
to be preferred.
154
ELEMENTS OF METALLURGY.
Determination of the Iron.-When quite cold the contents of the
flask are to be diluted with a considerable quantity of distilled water, and
the standard solution of permanganate is carefully added from a gradu-
ated burette: the contents of the flask are well shaken after each addition
of permanganate, and, on the appearance of a pink colour, the number of
divisions that have been used are noted; the amount of iron being deter-
mined by calculation.
In order to avoid the reaction which may take place between free
hydrochloric acid and potassium permanganate, when the solution is not
sufficiently dilute, and to avoid any error resulting from this cause, sul-
phuric acid may be advantageously employed as a solvent for the iron to
be estimated.
When this course is adopted, the solution, obtained by the attack with
hydrochloric acid, must be evaporated nearly to dryness, sulphuric acid
added, and the liquid boiled, in order to expel hydrochloric acid. The
ferric salts in this solution are, as in the former case, reduced to ferrous
salts, cooled, diluted, and the iron estimated by the addition of a known
quantity of a standardised solution of permanganate.
The iron employed for standardising the solution to be used for the
estimation of that metal, when existing as ferrous sulphate, should be dis-
solved in dilute sulphuric acid; the reaction which takes place is repre-
sented by the following formula :—
10FeSO₁+2KMnO4+8H₂SO₁=5Fe2S3O12+2MnSO4+K₂SO₁+8H₂O.
For this process it is not advisable to use a burette with india-rubber
connector at the end; either Mohr's burette, provided with a glass stop-
cock may be employed, or it may be drawn out at the bottom into a
point, and the india-rubber connector and pinch-cock be adjusted to the
upper end.
PENNY'S PROCESS.-When potassium dichromate, dissolved in water,
is added to an acid solution of a protosalt of iron, the latter is converted
into a persalt at the expense of the oxygen of the chromic acid. The
following equation expresses the reaction with ferrous chloride dissolved
in hydrochloric acid :—
6FeCl₂+K₂Cr₂O,+14HCl=3Fe,Cl¸+2KCl+Cr₂Cl₂+7H₂O.
In this case an indirect method must be employed in order to ascer-
tain when the reaction is finished, since the change of colour is not suffi-
ciently marked to indicate the exact moment when the complete oxidation
of the iron has taken place. For this purpose a weak solution of ferri-
cyanide of potassium (red prussiate of potash) is used, which produces a
blue or bluish-green colour with the protosalts of iron, but is unaltered
by the persalts of that metal.
Standard Solution.-Thirty-six grammes of crystallised potassium di-
chromate, previously freed from hygroscopic water by fusion, and after-
wards pulverised, should be dissolved in 4 litres of distilled water; of
this solution about 100 c.c. will be equivalent to 1 gramme of metallic
IRON.
155
iron. This solution is standardised as follows:-Two or more pieces of
bright iron wire, each weighing from 0·4 to 0.6 gramme, must be dissolved
in dilute hydrochloric or sulphuric acid, in a small flask with a narrow
neck. The acid should be first heated, and the wire then dropped into
it, ebullition being continued until the metal has become completely
dissolved. The solution of iron is now diluted with distilled water so
as to increase its volume to about half a litre. The vessel containing
the acid solution of iron is then placed beneath the burette, and the di-
chromate solution allowed to run slowly into it until the iron has become
completely peroxidised and a drop of the solution no longer gives the
slightest trace of a bluish-green colour when transferred, by a glass rod,
to a white porcelain slab wetted with the solution of ferricyanide of
potassium. The number of divisions on the burette is read off and
noted. Other weighed quantities of wire are proceeded with in the same
manner, and, by the data obtained from the experiments, the number of
divisions equivalent to 1 gramme of metallic iron is calculated; the
mean result being taken as the standard.
Estimation of the Iron in an Ore.-About 1 gramme of finely pow-
dered ironstone is heated with strong hydrochloric acid for about half-an-
hour in a small narrow-necked flask, and, when decomposition is complete,
the solution is diluted with water; a few pieces of zinc are added;
ebullition is kept up until every trace of yellow colour has been removed,
and the solution is either colourless or has only a pale green tint. It is
then transferred to a white porcelain dish, leaving the zinc in the flask
in which the attack was made; this flask must now be well rinsed out,
and the washings added to the solution, care being taken that no par-
ticles of zinc are carried over at the same time. Either sodium sulphite
or sulphuretted hydrogen may be substituted for zinc as a means of re-
ducing a persalt to the state of a protosalt; the use of the last-named
reagent being particularly recommended when very accurate results are
of more importance than a small expenditure of time.
When sulphuretted hydrogen is used as a reducing agent the liquid
must be well boiled, in order to expel the excess of that gas, before
adding the standard solution of potassium dichromate.
Penny's process is generally to be preferred to Marguérite's, for the
following reasons :—
1. The solution of potassium dichromate is less liable to decomposi-
tion by long keeping than that of permanganate, and requires less frequent
standardisation.
2. The result obtained is more reliable, since it is not subject to
error through evolution of chlorine.
3. It occupies less time, as filtration is not generally necessary, even
when carbon or other organic matter is present, and no time is lost in
waiting for the solution to cool, as is the case with permanganate.
Dry and Wet Assay.-Comparative Yields. As the result of dry
assay is cast-iron, a substance sometimes containing above 15 per cent. of
other elements, while the wet assay expresses the amount of pure iron in
the ore, the results obtained by the former method should, in all cases,
156
ELEMENTS OF METALLURGY.
indicate a higher yield than those obtained by wet assay from the same
ironstone.
The following series of dry and wet assays, carefully made in Dr.
Percy's laboratory, will serve to show the usual amount of difference
between the results obtained :

1.
2.
3.
4.
5.
6.
Iron by dry assay 73.30 70.30 59.60 35·30 42.10 34.30
wet
""
•
69.75 68.08 57.57
33.35 37.55 32.13
The wet assays were made by means of a standardised solution of
potassium dichromate, or of permanganate, and the dry assays in brasqued
crucibles by the Swedish method.
ANALYSIS OF IRON ORES.
The complete analysis of an iron ore is an operation which is both
tedious and difficult, involving numerous precipitations, filtrations, wash-
ings, dryings, and weighings, and should only be attempted by a chemist
having considerable experience of mineral analysis. The following is an
outline of the more important processes employed for the systematic
analysis of ores of this class, but the reader who may require more com-
prehensive information on this subject, is referred to a 'Memoir on the
Iron Ores of Great Britain,' founded on investigations, conducted by
Messrs. Dick & Spiller in the laboratory of the Royal School of Mines,
published, in parts, between the years 1856-62. He will also do well to
consult an admirable paper by Mr. E. Riley, in the Quarterly Journal
of the Chemical Society,' Vol. XII., p. 13.*
C
Water. The amount of hygroscopic water present in an ore is deter-
mined by exposing a weighed quantity in a finely-powdered state to a
temperature of 100° C. in a water-bath until it ceases to lose weight;
combined water is estimated by heating the dried ore, or a weighed quan-
tity of the undried ore, to redness in a hard glass bulb, to which is
adapted a chloride-of-calcium tube, of which the weight has been pre-
viously ascertained. By this treatment the water and other volatile
matters are expelled, the water only being retained by the calcium
chloride, so that its amount may be found directly by re-weighing the
tube. When undried ore is operated on, the amount of water lost by ex-
posure to 100° C. must be subtracted from the increase in weight of the
chloride-of-calcium tube, in calculating the percentage of combined water
present.
Attack by Hydrochloric Acid, &c.-A weighed quantity of the finely-
pulverised ore is digested in strong hydrochloric acid until no action
* "On the general occurrence of Titanic Acid in Clays, and the method employed
to estimate it; on the Analysis of Iron Ores and Siliceous Minerals containing Iron;
the separation of Oxide of Iron from Titanic Acid; and the methods of estimating
Iron."
IRON.
157
takes place, and, after boiling for an additional ten minutes, the solu-
tion is diluted with distilled water and filtered. The insoluble matter
which remains on the filter is well washed with distilled water, dried in
a water-bath, ignited in a platinum dish, and weighed.
The filtrate from insoluble matter is now boiled with the addition of
nitric acid or potassium chlorate, for the purpose of peroxidising the iron,
and after being rendered neutral with sodium carbonate, is boiled with an
excess of sodium acetate and filtered hot. The precipitate thus obtained
is washed with hot water, the filtrate received in a flask, rendered alkaline
by ammonia, and a few drops of bromine added. After corking the flask,
it is set aside for twenty-four hours, when it is boiled, and the precipitated
hydrated manganic peroxide separated by filtration, washed, and ignited.
By ignition the manganic peroxide is converted into MnO4, in which
form it is weighed. The filtrate from the last operation may contain lime
and magnesia; the former is precipitated by oxalate of ammonium, and
may be weighed either as carbonate or as sulphate of calcium. Oxalate of
calcium is converted into carbonate by simple ignition, and into sulphate
by the addition of weak sulphuric acid and heating until the excess of
acid has been driven off; the most accurate results are perhaps obtained
by the latter process, although, when the carbonate obtained by igniting
the oxalate is subsequently heated with a little carbonate of ammonium
until all traces of the volatile salt have been expelled, the former method
is sufficiently exact. From the amount of the calcium salt thus found
the percentage of lime present is calculated. To the filtrate from the
oxalate of calcium, sodium phosphate is added, and the solution is set
aside for twenty-four hours, during which time, if magnesia be present,
a crystalline double phosphate of magnesium and ammonium will be
deposited. This, on being heated, gives off water and ammonia, and
is converted into magnesium pyrophosphate, Mg2P₂O,, containing 36.33
per cent. of magnesia.
The precipitate produced in the hydrochloric solution by boiling with
excess of sodium acetate, consisting of basic acetates of iron and alumi-
nium with phosphoric acid, is dissolved in hydrochloric acid and boiled
with excess of caustic potash in a platinum or gold dish. Ferric
oxide will be thus thrown down, while the alumina at first precipitated is
re-dissolved, and may be separated by filtration. The filtrate is acidified
by hydrochloric acid and boiled with the addition of potassium chlorate,
for the purpose of destroying any soluble organic matter due to the action
of the caustic alkali on the filter, rendered nearly neutral by ammonia,
and finally made alkaline by carbonate of ammonium. The alumina,
together with a certain amount of phosphoric anhydride, will, when that
substance is contained in the ore, be now precipitated, and must be
washed, ignited, and weighed.
5
The amount of P₂O, present is subsequently ascertained by a process
shortly to be described for the determination of that body, and its weight
is deducted from the former weighing.
The precipitated ferric hydrate remaining after the separation of
alumina is re-dissolved in hydrochloric or sulphuric acid, and the amount
158
ELEMENTS OF METALLURGY.
of iron determined by a standard solution of either dichromate of potas-
sium or of the permanganate." *
Sulphur.-Sulphur may exist in iron ores either as sulphates, soluble or
insoluble in hydrochloric acid, or as insoluble iron pyrites. The sulphur
present in the form of soluble sulphates may be determined by digesting
a weighed quantity of the ore in dilute hydrochloric acid, filtering, and
adding chloride of barium to the filtrate. The sulphate of barium pre-
cipitated is thrown on a filter, washed, dried, ignited, and weighed, and
from its weight is calculated the percentage amount of sulphur existing
in the state of soluble sulphates. If insoluble sulphates are present
the amount of sulphur they contain may be determined by fusing the
pulverised ore with carbonate of sodium, treating the fused mass with
water, decanting, adding hydrochloric acid in excess to the solution, and
precipitating by barium chloride as before directed. If sulphates soluble
in hydrochloric acid are present at the same time with sulphates in-
soluble in that menstruum, both operations will be necessary for their
separate determination.
The sulphur present as iron pyrites is best determined by fusing the
substance in a finely-divided state, with a mixture of nitre and pure
sodium carbonate, in a gold crucible, dissolving in dilute hydrochloric
acid, evaporating to dryness, and separating insoluble matter by re-
attacking with hydrochloric acid, and filtering. Sulphate of barium is
precipitated from the filtrate on the addition of barium chloride.
Phosphoric Anhydride.—This may be determined by the method first
proposed by Dick. A weighed quantity of the ore is dissolved in hydro-
chloric acid, the insoluble matter is separated by filtration, the iron in
the filtrate reduced to the form of a protosalt by sodium sulphite, and
all free sulphurous anhydride driven off by boiling; a small portion of the
solution is oxidised by nitric acid and added to the remainder, which is
then nearly neutralised with ammonia, acetate of sodium added, and the
mixture boiled. All the phosphoric acid is precipitated, together with a
small amount of ferric oxide, of which a portion goes down as ferric acetate.
The precipitate is collected and dissolved in excess of hydrochloric acid;
tartaric acid, ammonia, and a magnesium salt added, and the liquid allowed
to stand at least twenty-four hours; the precipitate is collected on a filter,
washed, dried, ignited, and weighed as Mg, P₂O, containing 63-67 per
cent. of P₂O5.
2
2
2
Carbonic Anhydride. The amount of CO₂ present is best determined
by dissolving a known weight of ore in hydrochloric acid in a small flask
provided with a safety-funnel, and collecting the gas evolved in potash-
bulbs, after drying it by passing through a chloride-of-calcium tube.
Chemists have now generally given up the use of potash in the analysis of iron
ores; ferric oxide, alumina, and phosphoric anhydride are weighed together, and the
mixture then dissolved in hydrochloric acid. Any silica it may contain is separated
by filtration, the iron is determined by a standard solution, and the corresponding
amount of ferric oxide is deducted from the weight of the mixed precipitate; phos-
phoric anhydride is estimated by a special determination, and its weight also de-
ducted, the residue being alumina. Estimation by loss is generally objectionable,
but experience has shown that this method is most reliable.
IRON.
159
Titanic Oxide.-The amount of titanic oxide present in ordinary iron
ores is usually so small that its determination is not of much commercial
importance. For the processes employed for the exact estimation of this
substance, which are somewhat complicated, the reader is referred to the
memoir before referred to, of Mr. Riley, who has devoted much careful
attention to the metallurgy of iron. It is, however, a mistake to suppose
that titanic oxide is left with the silica in the analysis of iron ores, or
that it is completely separated by evaporation to dryness; a considerable
amount is dissolved by strong hydrochloric acid. In iron ores containing
from 20 to 30 per cent. of titanic oxide it has been found that nearly the
whole had been dissolved by hydrochloric acid, and only a very small
amount remained with the silica.
Insoluble Residue. The insoluble residue from the attack of hydro-
chloric acid is, for commercial purposes, not usually examined, and is
generally returned as "insoluble siliceous matter." With a view to ascer-
taining its influence on the working of the ore, it is, however, sometimes
desirable to determine its exact composition, in which case it may be
fused in a platinum crucible with four times its weight of an equal mixture
of the carbonates of potassium and sodium, and subsequently treated with
hot water, which dissolves out alkaline sulphates, if present, together with
alkaline silicates. The residue, after decanting the aqueous solution and
washing, is treated with hydrochloric acid and evaporated to dryness in
the usual way; the filtrate is added to the liquid obtained by evaporating
the aqueous solution to dryness with addition of hydrochloric acid, re-
treating with hydrochloric acid and filtering. Should insoluble sulphate
of barium or sulphate of strontium have been present in the ore, a pre-
cipitate will be at once formed, and the insoluble sulphates are sepa-
rated by filtration; in the filtrate will be found oxide of iron, alumina,
lime, magnesia, &c., which may be separated and estimated by processes
already described.
METALLURGY OF IRON.
-as
As before stated, iron is employed in three different conditions.
cast-iron, as steel, and as wrought-iron, the differences existing between
these substances essentially depending on the relative amounts of carbon
with which the metal is associated. Cast-iron contains a larger propor-
tion than steel, and steel more than wrought or malleable iron, which
theoretically ought to consist of pure metal without carbon. In practice,
this state of perfection is never attained; but the more esteemed varieties
are found to retain small portions only of carbon.
The ores from which iron is obtained are, on account of their com-
paratively small value, never subjected to complicated mechanical treat-
ment. Pea iron ore is usually found agglutinated by a clay containing
but little iron. This is often separated by agitating the mixture in a
current of water, by which clay is carried off in suspension, while the
ore, from its greater density, remains behind.
160
ELEMENTS OF METALLURGY.
We have seen (p. 110) that ferric oxide is reduced at a red-heat in an
atmosphere of hydrogen gas. This reduction is effected, under similar
circumstances, by carbonic oxide, and, consequently, the reduction of the
oxides constituting iron ores is attended with but little difficulty. The
reduced iron is, however, in such cases intimately mixed with the refrac-
tory gangue, which prevents its particles from uniting and forming a solid
mass. If the gangue were readily fusible, it would be sufficient to heat
the mixture to the temperature at which it would enter into fusion, when
the metallic sponge might be compressed by hammering, and the impu-
rities with which it is associated could be squeezed out in the form of a
vitreous slag. If, on the contrary, the gangue be very refractory, it can
only be fused under such conditions as will cause the metallic iron pro-
duced to combine with a portion of the carbon used as fuel, and the
product will be cast-iron, instead of the malleable metal which would be
otherwise obtained.
The gangue contained in iron ores usually consists either of quartz
or of clay, both which are practically infusible at the highest temperature
of the blast-furnace. In order then, to obtain metallic iron, it is
evident that some means must be taken for fluxing or rendering fusible
these refractory substances. This may be effected in two different ways,
varying according to the nature of the product it is desired to produce.
If a very rich iron ore be operated on, and it be required to obtain a
portion of malleable metal directly, without respect to the actual quan-
tity the ore is capable of yielding, it will be only necessary to heat
it in contact with charcoal or some other carbonaceous substance. By
this means one portion of the oxide will be reduced to the metallic
state by the deoxidising influence of the fuel, whilst the other will,
with the siliceous impurities, form a fusible silicate. It follows, there-
fore, that in the presence of rich ferrous silicates, the carbon will not
unite with the reduced metal and give rise to the production of cast-iron.
If the fused mass be now beaten with a hammer, or compressed by
being passed between a series of rollers, the fusible slag will be ex-
pressed, whilst the metallic sponge, by being subjected to strong pressure
at a high temperature, becomes consolidated, and forms a compact mass.
The amount of iron which by this method passes into the scoria is
dependent on the amount and composition of the gangue, and it follows
that the richer varieties only can practically be made to afford malleable
iron by such treatment.
If, as is usually the case, the object be the extraction of the largest
amount of metal, without regard to temperature, it will be necessary
to add to the ore some substance capable of replacing, to a great extent,
the oxide of iron, which in the former instance united with silica to
form a fusible slag. The only substance sufficiently cheap to admit of
being employed for this purpose, is lime, which is readily obtained
by the decomposition of limestone by heat. When lime is thus added,
the resulting slag chiefly consists of silicates of aluminium and calcium,
which are less fusible than those of aluminium and iron.
To obtain,
therefore, the metal which the ore contains, it must be subjected to a
IRON.
161
higher temperature than would be necessary if a large portion of the
oxide were allowed to remain in the slags, and the iron produced com-
bines with a certain amount of the carbon present in the furnace, and
is converted into cast-iron.
The manufacture of iron by the former method necessitates the em-
ployment of rich ores, and from the nature of the rejected slags the per-
centage of metal obtained is far less than that which they are capable of
yielding.
1
DIRECT PREPARATION OF MALLEABLE IRON.
In ancient times iron was always obtained directly from its ores in
the malleable state, and this method is not only practised by the natives
of India, Borneo, and Africa, but is also still employed in some parts of
Europe and in the United States of America.
By the ancient, or direct process, malleable iron is the immediate
result of the treatment of the ore, while by the modern, or indirect
process, cast-iron is first produced, and subsequently subjected to a series
of operations, by which its conversion into wrought-iron is effected.
Furnaces in which the direct process is carried on are called bloomeries,
and the lump of malleable iron obtained is called a bloom.
In India the direct process appears to have been carried on from time
immemorial, as may be inferred from the large accumulations of slag
found in various parts of the country. The appliances employed are
exceedingly rude, and the scale of operations very diminutive; the fur-
naces are frequently not larger than a chimney-pot, and hours of incessant
toil are required to produce a few pounds' weight of metal.
The ores chiefly employed are magnetic oxides and rich red and
brown hæmatites. The furnaces used may be divided into three typical
kinds of these the first and rudest form is employed in the less civilised
districts, and among the hill-tribes; the second and third kinds are
used in Central India and in the North-west Provinces, and resemble the
simplest forms of the Catalan forge and of the German Stückofen respec-
tively. They are in every way superior to the first, and are capable of
producing considerable quantities of wrought-iron as well as of natural
steel.
The blast is produced by bellows made of the skin of a goat or of a
kid; each furnace being provided with at least two such bellows, fitted
with bamboo nozzles. The anvil is of wrought-iron, very small, square,
and without a beak; the hammer, tongs, and other appliances do not
differ in any material respect from those employed in Europe.
The natives of Borneo prepare their iron from clay ironstone, which
is treated in a furnace built of yellow clay, and tied round by hoops
of bamboo. Its height is a little more than 3 ft., and its external
diameter nearly 10 ft., the thickness of the walls being 2 ft.; it is
square on the inside, narrowing towards the bottom to a rectangular
hearth, 2 ft. long by 1 ft. 7 inches wide. Each furnace has three clay
tuyers with an opening for running off the slags, and an external basin
M
162
ELEMENTS OF METALLURGY.
for their reception. The blowing machine is a single acting cylinder of
wood open at top and closed at bottom, the blast being conveyed from the
lower end to the tuyer by means of bamboo tubes. The piston is
packed with feathers, and the piston-rod is attached to a long bamboo,
which, acting as a spring, brings it back again when pressed down to the
bottom of the wooden cylinder.
The ore, preparatory to smelting, is interstratified with wood, and
roasted in heaps, and, after being broken into pieces of the size of nuts, is
mixed with ten times its bulk of charcoal, and charged into the furnace.
When it has been two-thirds filled with charcoal, the mixture of ore and
fuel is added in sufficient quantity to form a conical heap above its mouth.
The piston is worked at the rate of about forty strokes per minute;
the slag is tapped off every twenty minutes, and a lump of iron, weighing
about 100 lbs., is finally obtained. This is taken out at the bottom of
the furnace by means of wooden tongs, and is removed to a bed of slag,
where it is worked by wooden mallets into the shape of roughly-formed
parallelopipedons; such a mass is the result of the labour of four men
during one day. The mass retains much intermingled slag, which is
removed by dividing it into ten pieces, which are hammered out into bars
suitable for making sword-blades, during which operation a loss of 25
per cent. in weight is experienced. Soft or steely-iron may be produced
at pleasure according to the nature of the fuel employed, and the pro-
portions of the charge. The following description of the process.
employed by the natives of the interior of Africa for the manufacture of
iron is given by the celebrated traveller, Mungo Park :-- *
"The negroes on the coast, being cheaply supplied with iron from the
European traders, never attempt the manufacturing of this article them-
selves; but in the inland parts the natives smelt this useful metal in such
quantities as not only to supply themselves from it with all necessary
weapons and instruments, but even to make it an article of commerce
with some of the neighbouring states. During my stay at Kamalia,
there was a smelting furnace at a short distance from the hut where I
lodged, and the owner and his workmen made no secret about the manner
of conducting the operation, and readily allowed me to examine the
furnace and assist them in breaking the ironstone. The furnace was a
circular tower of clay, about 10 ft. high, and 3 ft. in diameter, sur-
rounded in two places with withes, to prevent the clay from cracking
and falling to pieces by the violence of the heat. Round the lower part,
on a level with the ground (but not so low as the bottom of the furnace,
which was somewhat concave) were made seven openings, into every one
of which were placed three tubes of clay, and the openings again plas-
tored up in such a manner that no air could enter the furnace but
through the tubes, by the opening and shutting of which they regulated
the fire. These tubes were formed by plastering a mixture of clay and
grass round a smooth roller of wood, which, as soon as the clay began to
harden, was withdrawn, and the tube left to dry in the sun. The iron-
* Travels in the Interior Districts of Africa, by Mungo Park, Surgeon.' Loudon,
1790, p. 283-285.
IRON.
163
stone which I saw was very heavy, of a dull red colour, with greyish
specks; it was broken into pieces about the size of a hen's egg. A
bundle of dry wood was first put into the furnace, and covered with
a considerable quantity of charcoal, which was brought ready-burnt
from the woods. Over this was laid a stratum of ironstone, and then
another of charcoal, and so on, until the furnace was quite full. The
fire was applied through one of the tubes, and blown for some time
with bellows made of goats' skins. The operation went on very slowly
at first, and it was some hours before the flame appeared above the fur-
nace; but after this it burnt with great violence all the first night, and
the people who attended it put in at times more charcoal. On the day
following, the fire was not so fierce, and on the second night some of the
tubes were withdrawn, and the air allowed to have freer access to the
furnace; but the heat was still very great, and a bluish flame rose some
feet above the top of the furnace. On the third day from the commence-
ment of the operation, all the tubes were taken out, the ends of many of
them being vitrified with the heat; but the metal was not removed until
some days afterwards, when the whole was perfectly cool. Part of the
furnace was then taken down, and the iron appeared in the form of a
large irregular mass, with pieces of charcoal adhering to it. It was
sonorous, and when any portion was broken off, the fracture exhibited a
granulated appearance, like broken steel. The owner informed me that
many parts of this cake were useless; but still there was good iron
enough to repay him for his trouble. This iron, or rather steel, is formed
into various instruments by being repeatedly heated in a forge, the heat
of which is urged by a pair of double bellows of a very simple construc-
tion, being made of two goats' skins, the tubes from which unite before
they enter the forge, and supply a constant and very regular blast. The
hammer, forceps, and anvil are all very simple, and the workmanship
(particularly in the formation of knives and spears) is not destitute of
merit. The iron, indeed, is hard and brittle, and requires much labour
before it can be made to answer the purpose.'
""
CATALAN OR FRENCH PROCESS.-In the French Pyrenees, and in some
provinces of Spain, malleable iron is obtained directly from the ore by one
operation. In order that this branch of industry may be advantageously
carried on, it is necessary that the ores treated should be not only rich,
but also very fusible, and that charcoal, which is the fuel employed, should
be obtainable at a low price, since every ton of bar-iron produced will
require in its preparation the expenditure of more than three times that
weight of fuel.
The Catalan furnace consists of a quadrangular hearth, composed of
refractory masonry, and attached, like an ordinary smithy fire place to one
of the walls of the workshop in which it is situated. Three distinct
modifications of this smelting hearth are used in different parts of the
Continent, under the names of Catalan, Navarrese, and Biscayan forges;
but as in principle these resemble each other very closely, it will be suf-
ficient to describe, with a certain amount of detail, the Catalan forge,
which is the chief modern representative of the ancient bloomery.
M 2
164
ELEMENTS OF METALLURGY.
The hearth of this furnace is established in a large mass of stone-
work, cemented together with refractory clay, and which, instead of being
built directly on the floor of the foundry, is supported on one or more
small arches, to admit of the escape of moisture, and to preserve the
bottom of the hearth from being injured by any dampness which might
otherwise find its way into the masonry. On the top of these arches is
arranged a layer of fire-clay and iron-slag, which is well beaten down, and
supports a large block of sandstone, which forms the bottom, and on this
are placed the four sides of the hearth, a, b, c, d, as shown, figs. 34 and 35.
The face, a, which is of iron, is called the chio, and from this side of
the furnace the liquid slags are run off through a hole left for that pur-
pose. That opposite is called the cave, and is entirely composed of
masonry held together by refractory clay. This side is somewhat curved
in an outward direction, and is slightly inclined from the bottom towards
the top.
The side of the furnace, c, on the left of the sketch, is called the
porges, and is composed of heavy bars of iron placed one above another,
19
so as to form a kind of vertical wall.
The other side, d, opposite the tuyer, is
known by the name of the ore, or con-
trevent, and is composed of pieces of iron,
having a wedge-shaped section, and so
arranged as to form a rounded surface,
with its convex side towards the fire.
The tuyer, N, by which the blast is
brought into the hearth, has the form of
a truncated cone, and is made by turning
a piece of sheet copper into the proper
form without soldering its edges. This
tuyer rests on the upper plate of the
porges, and encloses the nozzle, T, by
which the furnace is supplied with air,
by a water blowing machine, which is
connected with the tuyer by a leathern
hose. The amount of inclination given to

G
F
T
E
Fig. 34.--Catalan Forge and Trompe; vertical section.
111:
IRON.
165
the nozzle is found to materially affect the working of the furnace, and is
made a mystery of by the workmen employed. In most instances, how-
ever, the tuyer makes an angle of from 35° to 40° with the bottom of the
hearth.
The dimensions most commonly employed for the Catalan furnace are
about as follow: length of the hearth from the porges to the contrevent at
its widest part, 3 ft.; width of the hearth, from the chio to the face of the
cave, 2 ft. 6 inches; total depth, from the surface to the bottom of the
hearth, 2 ft. 2 inches. The distance between the porges and the con-
trevent, at its narrowest part, is usually about 27 inches.
These forges are almost invariably placed on the declivity of a hill,
and are supplied with air by a water blowing machine, called a trompe.
This consists of a large cistern, A, which is supplied with a constant
stream of water, and connected with the box, C, by two wooden pipes, B,
each about 20 ft. in length.

AU
FINCH
"
C
F
T
Fig. 35.—Catalan Forge and Trompe; plan, partly in section.
The lower case, C, which is firmly secured on all sides, and closely
united to the pipes, B, is pierced with two openings, the one, D, near the
bottom for the escape of the water, and another in the lid, at E, through
which the air escapes into the furnace through the tube G, F, T,
The openings of the tubes, B, are, at their point of junction with the
reservoir, partially closed by a sort of wooden funnel, which causes the
water to descend in the middle portions of the upright pipes, instead of
adhering to and running over their inner surfaces, as it would be other-
wise liable to do. A little beneath the openings of these funnels, called
the étranguillons, small openings, g, are cut in an inclined direction
through each tube; these are called the aspirateurs, and serve for the
passage of the air drawn into the apparatus by the downward motion of
the stream of water. The two upright columns, B, are firmly secured
into the lid of the lower case, C, and are placed immediately over, and a
short distance above a wooden shelf, on which the descending currents of
water are, by their fall, broken into foam.
The action of the apparatus may be explained as follows: the water
flowing from the upper basin, A, draws down with it a current of air,
which enters through the holes, g, in the vertical pipes, and passes into the
lower cistern, C. The water which is broken by its fall on the bench below,
escapes by the opening, D, whilst the air which has been drawn with it
into the lower box, escapes by the aperture, E. The position of the boards
constituting the étranguillons is easily regulated by means of wedges,
which allow of the descent of a larger or smaller supply of water, accord-
166
ELEMENTS OF METALLURGY.
ing to the requirements of the trompe. In order, during the working of
the machine, to regulate the amount of air passing into the furnace at the
different stages of the operation, each of the descending columns is pro-
vided with a plug, suspended by a lever and iron rod, and by means of
which the current of water, and consequently that of air also, is readily
controlled by the workmen, without their having occasion to leave the
workshop, into which a chain attached to the other extremity of the lever
is brought for that purpose.
The hammer employed for forging the iron produced is made of cast-
iron, and weighs from 12 to 14 cwts. This is mounted on a wooden
beam, frequently made of beech, and bound, for the sake of imparting
solidity, with numerous bands of iron. The hammer makes from 100 to
150 blows per minute, and is raised by a series of cams, arranged around
the axle of a water-wheel, and acting on the wooden beam at a consider-
able distance from its point of suspension. The anvil is composed of a
block of steely-iron, fastened by a tenon, on a large mass of cast-iron,
which is itself securely bedded either on wooden piles or on a heavy block
of stone, sunk beneath the floor of the foundry.
In order to understand the method of working this forge, let us sup-
pose that a mass of iron, or bloom, has been just extracted from the furnace,
and that the workmen are ready to clean out the hearth for the purpose
of commencing another operation.
To do this they first remove from the hearth the burning charcoal
which it contains, and then carefully scrape off from the sides any por-
tions of scoriæ, or other fused matter, which may be adhering to them.
They now throw burning charcoal into the hearth, which they subse-
quently fill with this fuel up to the level of the tuyer. The hearth is
now divided, either by a shovel or by a piece of sheet-iron, into two
compartments parallel to the face of the porges, and in such a way that
the distance between the porges and the shovel may be twice as great as
that comprised between it and the contrevent. Charcoal is now added in
the space between the shovel and the tuyer, and on the opposite side is
a
Fig. 36.
Ville
PALL
\ / // // \/ //
piled roasted ore reduced to pieces about the size
of eggs. The shovel is successively raised in pro-
portion as the space is filled up, and in this way a
saddle backed heap, a, b, c, fig. 36, is raised against.
the contrevent, which is terminated in one direc-
tion by the side called the chio, and the other by
the face of the cave. The surface, a, b, is now
slightly covered with damp charcoal-powder, and
the space, A, between the heap of mineral and the
porges, entirely filled up with fresh charcoal, in
pieces of moderate size.
When the furnace has been thus prepared, the
trompe is set in action, and the blast is admitted
into the hearth. This is at first done with considerable caution, but the
blast is progressively increased until it is allowed to play into the fire
at its full pressure. Whilst this is going on, the heap of broken ore is

JRON.
167
gradually roasted and reduced, and the workmen, taking advantage of
this opportunity, forge into bars the mass of iron produced by a former
operation, and which for this purpose is commonly divided into four sepa-
rate pieces, or massouquettes. These fragments are placed in the midst of
the mass of charcoal lying between the heap of ore to be wrought and the
nozzle, which furnishes the air necessary for carrying on the combustion
of the fuel, and, after being duly heated, they are placed under the
hammer, by which they are made to assume the required form.
As the operation advances, and the fuel is consumed, fresh charcoal
is added to supply its place, and the powdered mineral, obtained by
sifting the ore as it comes from the mine, is slightly sprinkled over the
surface of the fire. These siftings, which are called greillade, are
slightly moistened with water, after being thrown on the hearth, as they
would otherwise be liable to be blown away by the force of the blast,
and have a tendency to pass too rapidly towards the bottom of the fire,
through the interstices occurring between the fragments of the fuel.
The charcoal in the immediate neighbourhood of the tuyer, on which
the full action of the blast is made to play, becomes rapidly consumed,
with the formation of carbonic anhydride, which, escaping through the
surrounding charcoal heated to redness, is soon reduced to the state of
carbonic oxide. This, from the construction of the furnace, has to pass
through the openings left between the lumps of mineral, before finding
its way into the open air; the mineral, which has now lost all traces
of its volatile constituents, and is very strongly heated, is in a great
measure reduced by this means to the state of spongy metallic iron, while
the carbonic oxide is at the same time converted into carbonic anhydride
and escapes in that form into the atmosphere. Another portion of the
oxide of iron present, instead of being obtained in the metallic state,
merely becomes converted into protoxide, which, uniting with the siliceous
matters of the charge, gives rise to a large quantity of very liquid slag,
which accumulates on the bottom of the hearth, and is occasionally drawn
off by a hole left for that purpose in the face of the furnace called the
chio.
At the expiration of two hours from the commencement of the ope-
ration, the full blast of the blowing machine is admitted to the furnace,
and the greillade, which constantly descends with the fuel, begins to
furnish a certain quantity of slag and spongy iron, which accumulate at
the bottom of the hearth. At this stage of the process, the founder
begins to prepare for the formation of the massé or bloom, and, by passing
an iron bar between the contrevent and roasted mineral, pushes forward
those portions of it which he judges to be in the most forward state in
the direction of the nozzle by which the blast is admitted. Fresh additions
of charcoal and greillade are also successively made during the whole
period of the operation, and at the expiration of about five hours from the
time of its commencement, the entire charge has reached the bottom of
the furnace, where the spongy iron is collected by the workmen with a
long iron scraper, and formed into a bloom, which is afterwards carried
to a hammer, by which the slag is expressed, and its particles closely
168
ELEMENTS OF METALLURGY.
welded together in a compact form. When the bloom has by this means
been welded into a solid mass, it is again put under the hammer, and cut
by a kind of heavy steel knife into two equal portions, called massoques,
which, after being a second time heated in the furnace, are made to
assume the form of elongated prisms. Each of these is subsequently
divided, by a blow of the hammer on the back of the cutter, into two equal
parts or massouquettes, which are drawn out into bars during the first
period of the succeeding operation.
Each charge requires six hours for its conversion into malleable iron,
but during the last hour of fusion, such of the labourers as are not other-
wise engaged are occupied in breaking the ores ready for the next opera-
tion, and sifting the greillade which is to be sprinkled on the surface of
the fire.
The weight of ore treated at each operation, in a hearth of the largest
size, is about 94 cwts., containing from 45 to 48 per cent. of iron; the
fuel consumed averages 103 cwts., and the produce of bar-iron 3 cwts.
The consumption of material per 100 lbs. of bar-iron is, of ore 312 lbs.
and charcoal 340 lbs. ; the average cost of production in 1841 was about
£17 5s. per ton.
The metal obtained by this method consists of a variable mixture of
ordinary and steely-iron, the relative proportions of which are regulated by
the way in which the furnace is worked; for if considerable inclination
be given to the tuyer, and the siftings are plentifully thrown on the
fire, the product is chiefly soft iron, whilst if the nozzle be nearly
horizontal, and the greillade but sparingly supplied, a larger product of
steely-iron is the result.
AMERICAN BLOOMERY.-The Catalan method of iron-making has been
introduced into North America, and is employed in Vermont, at Mar-
quette, at Carp River, and elsewhere. In the arrangement there em-
ployed, the hearths, which are placed in ranges on either side of quad-
rangular masses of brickwork, are supplied with hot air through water-
tuyers of the ordinary construction. The bottoms of the hearths consist
of hollow cast-iron plates, through which a current of cold water con-
stantly passes. The working of these furnaces is conducted in many
respects like that of the ordinary Catalan forge.
The essential difference between the Catalan and American forge con-
sists in the method of charging. In the former the greater portion of
the charge of ore is arranged in comparatively large fragments, at the
commencement of the operation, against the sloping side of the hearth
opposite the tuyer; only the greillade, or small ore, being subsequently
added. In the American forge, on the contrary, the whole of the ore is
more or less continuously introduced, but in a state of finer division; the
charging of the furnace after each operation is thus dispensed with, and
a continuous system of working is introduced. The blast employed has
a pressure of from 1 to 13 lb. per square inch, and is heated to a tempera-
ture varying from 208° to 320° C. by being passed through the syphon-
pipes of an ordinary stove placed above the furnace and heated by the
waste flame.
IRON.
169
The waste heat is further economised by passing the flame and gases
from each pair of hearths into a chamber serving for re-heating the
blooms previously to drawing them into bars; a set of small pipes placed
over the hearth is also employed to heat a portion of the air, which is con-
veyed into the re-heating chamber in order to burn any carbonic oxide
which may have escaped combustion in the hearth beneath. The gases
from this chamber are subsequently made use of for the purpose of
heating the principal blast of the furnace in the way before described.
In the larger American furnaces a bloom of 300 lbs. is produced
every three hours; making the daily produce of twenty-four hours
2,400 lbs.
CORSICAN PROCESS.-In Corsica and along the whole Mediterranean
shore of Italy a furnace very similar to the Catalan was formerly em-
ployed for the direct production of malleable iron; but it is believed
that this process has, at the present time, been everywhere abandoned.
The hearth of this forge consisted of an elongated semicircular basin
formed on the top of a platform of masonry about 3 ft. in height; the
bottom was made of a mixture of charcoal-dust and clay, and the blast
was supplied through a slightly-inclined copper nozzle in connection
with a trompe.
In this arrangement, although the operations of roasting, reduction,
and fusion were carried on in the same furnace, they were nevertheless
divided into two distinct processes, one of which consisted in roasting and
partially reducing the ores; in the second the deoxidation of the half-
reduced ore was not only continued, but the metal was agglomerated and
finally forged into bars.
In order to accomplish the first stage of this process, a small
quantity of charcoal in large pieces was arranged around the tuyer;
this was again surrounded with a circle of broken and calcined ore
from a previous operation, and inclosed in another circular wall
of ironstone and charcoal; on the outside of this inclosure the ore
to be roasted was piled in large lumps, and the whole covered with a
thick layer of charcoal-dust. The lumps of unroasted ore, of which the
outer circle was composed, were so arranged that the larger and heavier
masses were placed at the bottom and firmly imbedded in the brasque of
the hearth.
The smaller pieces were piled on this foundation, and slightly in-
clined towards the well, in order that being supported by the fuel within
the inclosure, they might be less liable to fall. The fire was kindled by
throwing pieces of ignited charcoal into the inner circle, immediately
before the tuyer; this was afterwards covered with large pieces of char-
coal, and the blast produced from a water blowing machine allowed to play
into the hearth. At the expiration of about four hours the processes of
roasting and reduction were complete. The inner circle of roasted ore
had softened and run into lumps, whilst the outside wall of raw mineral
was calcined, and had ceased to give off fumes.
The mixture of slag and breeze, forming a long heap on the platform,
was divided into five equal parts, each of which, with the addition of one-
170
ELEMENTS OF METALLURGY.
fifth part of the agglomerated ore, yielded one lump or massé. It now
remained to work the reduced ore into blooms, which were afterwards
forged into bars; this was done in the furnace employed for the roast-
ing and partial reduction of the ores. Dry charcoal-dust was thrown
upon the hearth, and so arranged as to form two inclined planes meeting
below the tuyer, and which rose to the height of the tap-hole wall in front.
The space beneath the tuyer was filled up with cold charcoal, upon which
was placed a lump of metal surrounded by ignited charcoal. This lump,
which was roughly cylindrical, was at one end welded to an iron bar
serving as a handle. By means of this it was, from time to time, turned,
and, after about twenty minutes, was taken to the hammer to be forged.
While this was going on, a charge of breeze, agglomerated ore, and
hammer-scale from a previous forging, was introduced into the middle of
the hearth. This charge remained in the furnace, and the forging was
continued as if the hearth were filled with charcoal alone; each of the
five portions into which the product of the roasting operation was divided
yielded a lump from which four bars of iron were made.
The duration of the roasting and the working up of the reduced ore,
thus divided into five portions, occupied twenty-four hours; four workmen
were employed in each forge, who worked on six days of the week; but
only during seven months in the year. In this period about 26 tons
of bar-iron were made, at a cost varying from £19 to £20 per ton.
Instead of burning all charcoal, a mixture of that fuel with dried
wood was sometimes used, particularly for the first operation, in which
the roasting and partial reduction of the ore were effected. The iron
prepared in this way was of excellent quality, being extremely soft and
malleable; but the product was, in comparison with the quantity of ore
and fuel employed, very small. The ore, which in Corsica was thus
treated, is a specular oxide of iron, very similar to that worked in the
island of Elba; but although it contains 65 per cent. of metal, 40 pcr
cent. only was obtained by the Corsican process. The consumption of
fuel by this process was not less than 8 parts by weight for every
part of bar-iron produced.
STÜCKOFEN, OR HIGH BLOOMERY FURNACE.-In some parts of the
Continent an apparatus was formerly employed which held a middle place
between the low hearths of the Pyrenees and Corsica and the high blast-
furnaces now adopted for the production of iron from its ores. Those
furnaces, called stücköfen by the Germans, and by the French fourneaux
à pièce, were, in fact, small cupolas, of which the height did not ordi-
narily exceed 15 ft., and of which the diameter at the hearth was about
3 ft. This furnace was furnished with but one arch, by which the
tuyer was introduced, and the extraction of the bloom effected. The
blast was supplied by bellows moved by a water-wheel, and the slag
escaped by a small floss-hole made at a certain distance above the bottom
of the hearth. To remove the Stück or bloom of spongy metal formed in
the hearth, the bellows had first to be removed and a hole made in the
masonry of the furnace, which was afterwards temporarily closed by a
wall of bricks and fire-clay. This furnace, when filled with charcoal,
IRON.
171
was lighted from the tuyer-hole, and when the mass had been properly
ignited, the blast was admitted, and successive charges of roasted mineral
and fresh charcoal supplied. At the expiration of twenty-four hours, a
considerable mass of agglutinated iron was found to have accumulated in
the hearth, the side of which was now taken down and the mass removed,
by strong iron bars, to a heavy hammer, where it was reduced into a cake
of about 4 inches in thickness, and subsequently divided into two equal
parts. These were afterwards refined in a small bloomery of peculiar
form, where they were held, by powerful tongs, exposed to the action
of a blast from a nearly horizontal tuyer, by which means a portion
of the metal flowed to the bottom of the hearth, where it accumulated
in a spongy mass and was drawn out into bars under a properly-con-
structed hammer. In Carniola, where this process was employed in
the treatment of a granular oxide of iron, the mass taken from the furnace
at the expiration of each twenty-four hours amounted to from 18 to
20 cwts. This was afterwards subdivided into smaller pieces, which were
first flattened under a heavy hammer, and then refined by being exposed
to the action of a current of air which played into a bloomery, the bottom
of which was of brasque.
From the great quantities of charcoal required to produce a given
amount of malleable iron, this method has, however, fallen into disuse, as
it is found more economical first to obtain the metal in the state of cast-
iron, and subsequently to oxidise the carbon which it contains by expo-
sure to oxidising influences, than to prepare soft iron directly from the
The best iron manufactured is, however, still obtained from furnaces
in which charcoal is the only fuel employed, as the impurities which
always exist in every variety of mineral combustible, in a greater or less
degree, combine with the metal and depreciate its quality.
ore.
CLAY'S PROCESS:-A patent was granted to William Neale Clay, in
1837, and another in 1840, for processes for the manufacture of iron by
welding together the crude spongy metal obtained by heating rich hæma-
tite with powdered charcoal. The method employed was to crush the
better kinds of red hæmatite into lumps not larger than a walnut, and
these, mixed with one-fifth of their weight of charcoal, coke, coal-slack,
or any other carbonaceous materials, were subjected to a bright red-heat
in a clay retort or other suitable vessel, until the iron was reduced to the
metallic state. As soon as the reduction was considered complete, the
spongy mass was transferred directly to a puddling furnace, either with or
without a further addition of coke; it was then balled in the usual way,
worked into blooms under a tilt-bammer, and afterwards rolled into
bars. Experiments by this process were first made on a small scale near
Glasgow, and afterwards on a more extensive one in the vicinity of
Liverpool; commercially it proved a complete failure, although iron
of excellent quality was sometimes produced. The iron was, however,
frequently red-short; but the chief cause of failure was the length
of time required for reducing the ore, and the consequent heavy expen-
diture of fuel and labour.
It was subsequently attempted to effect the reduction of the ore
172
ELEMENTS OF METALLURGY.
directly in the puddling furnace, but here again waste, in the shape of
cinder, added to a large expenditure of time, fuel, and labour, caused the
process to be abandoned for one in which a mixture of pig-iron, crushed
hæmatite, and carbonaceous matter, was treated in the puddling furnace.
The bar-iron thus produced was tolerably uniform in character, and of
fair quality, fetching about the same price in the market as the better
descriptions of Welsh bars; upwards of 1,000 tons were made by this
process, but at such a heavy pecuniary loss as to cause it to be ultimately
abandoned. Dr. Percy remarks of this process, that although it was not
successful, it is important that the results obtained should be placed
on record.
CHENOT'S PROCESS.—-Specimens of "Éponges métalliques,” or metallic
sponges, were exhibited by M. Chenot in the first International Exhibi-
tion of 1851, in London, together with iron and steel made therefrom.
At the Exhibition at Paris, in 1855, M. Chenot was awarded one of the
"Grandes Médailles d'Or" for his invention; this decision was arrived
at after the English, Prussian, and Austrian jurors had left Paris, and
does not appear to have been favourably regarded by these gentlemen.
Professor Tunner, one of the Austrian members of the jury, published an
energetic protest against this award, and his colleagues, Rittinger and
Percy, appear to have formed a similar estimate of the merits of the
case.
According to Grateau, who, in 1859, published a paper on the
'Manufacture of Cast-Steel by the Chenot Process,' works were erected
for carrying it out near Bilbao, in 1852; at Charleroi, Belgium, in 1856;
at Pontcharra, Isère, in 1856; and at Hautmont, Nord, in 1857. It was
further announced that large works were about being erected in Russia
for carrying out this process; we are not, however, aware whether any of
these establishments, excepting that near Bilbao, are at present in ope-
ration, or whether any of the contemplated extensive Russian under-
takings were carried out. A modification of this process was for some
time employed by the Messrs. Wright, of Mostyn, for the conversion of
purple ore, resulting from the humid treatment of copper ores, into
puddled bars, but the results were, commercially, unsatisfactory.
By this process the ore, if in mass, is broken into lumps of about
30 cubic centimetres, or 1 cubic inch, but, if pulverulent, as in the case
of oolitic ores, it is agglutinated, in certain cases with the addition of
some reducing matter, such as resin, of which about 3 per cent. is added.
Thus prepared, it is mixed with from 1 to 1½ its bulk, or, by weight,
19 per cent. of wood-charcoal.
The furnace in which the reduction is effected consists of a cubical
mass of masonry surmounted by a truncated cone of elliptical section.
Two galleries, at right angles, traverse the supporting masonry, leaving
four pillars at the angles, upon which are arches that support the fire-
places. Within are constructed two vertical rectangular chambers or
retorts, 2 m. long, 0·50 m. wide, and 8.50 m. high; at the bottom and
below the level of the ground is a pit for the reception of the apparatus
for discharging. The retorts slightly but gradually widen from the
IRON.
173
top towards the bottom, in order to facilitate the descent of the reduced
charge; around each of these retorts is a series of vertical flues com-
municating, at bottom, with the fire-places, and, at top, with a flue
opening into the air. The whole is firmly braced with bar-iron, and the
bricks are made with tongues and grooves in order to prevent displacement
and leakage.
If the reduced iron were exposed to the air while still hot it would
take fire, and again be converted into oxide. In order to prevent this, a
“refroidissoir,” or cooler, of sheet-iron is placed below each retort, and
beneath this there is another iron case into which the metallic sponge is
discharged when sufficiently cooled. Below the latter, and on a level
with the ground, is a waggon running on rails.
The charge of a furnace with one retort is 1,500 kilos., about 1½ ton, of
calcined iron ore, and 500 kilos., ton, of wood-charcoal; reduction is
complete at the expiration of three days, when the freshly-formed sponge
is allowed to fall into the cooler, where it remains three days. The
entire elaboration, including reduction and cooling, thus occupies six
days. When perfectly reduced the iron sponge has a light-grey colour,
is soft, and can be easily cut into thin slices with a knife; it may be
ignited by a match, when it continues to burn until the whole is com-
pletely oxidised. Under a pressure, stated at 3,000 atmospheres, this
sponge has been compressed to one-fifth its original bulk. Great heat is
evolved during the process of compression.
The process, as above described, is known as the external or indirect
method of heating; by what is termed the internal or direct method, the
reduction of the ore, instead of being effected by solid carbonaceous
matter, is produced by a heated current of carbonic oxide gas. In this
case, the reducing chamber is connected with gas-generators of the usual
construction, by means of which a gaseous current, rich in carbonic
oxide, is maintained upwards through the column of ore, and burns at top
with its characteristic blue flame. A modification of this direct method
of reduction, which was introduced by M. Tourangin, is said to have been
attended with considerable economy in the cost of constructing the
furnace.
The balling of the sponge is effected in a charcoal-hearth similar to
that employed for the manufacture of iron for tin-plates in South
Wales. During the hammering of the ball, jets of blue flame escape from
it in all directions and the blooms may be rolled without re-heating
into bars 12 inch square; these are cut into lengths, made into piles, re-
heated, and rolled into merchant-bars. The application of sponge-iron to
the manufacture of steel will be subsequently described.
YATES'S PROCESS.-In a pamphlet, published in 1860, by Mr. Frederick
Yates, he gave a detailed description of a method by which he proposed
to effect the direct extraction of iron from its ores in the malleable state.
This process is in principle identical with those of Clay and Chenot, and
the apparatus described is substantially a modification of that of the latter.
The method of which Mr. Yates claims to be the inventor does not
appear to possess the merit of originality, and since nothing has been
171
ELEMENTS OF METALLURGY.
heard of it for several years, it may be concluded that some experiments
which were carried out on a working scale did not afford satisfactory
results.
SIEMENS'S PROCESS. Mr. C. W. Siemens, F.R.S., in a paper read
before the Chemical Society, March 20th, 1873, describes an apparatus
which he has recently invented for the direct production of malleable iron
from its ore; this is now in operation at Messrs. Vickers & Co.'s, Sheffield,
and at his own sample steel-works in Birmingham: Mr. Siemens does not,
however, state what amount of iron he has made by the process.
The furnace consists of a rotative chamber of iron provided with a
refractory lining, in communication with a set of four regenerators of
the usual construction, with reversing-valves and gas-producers.
The rotative chamber rests upon four anti-riction rollers; wheel
gearing being applied, by which either a very slow motion of from four to
five revolutions per hour, or a much quicker one of sixty to eighty, can
be imparted to it. The chamber is 7 ft. 6 inches in diameter and 9 ft.
in length, and has a lining of bauxite 7 inches in thickness; * there is a
tap-hole on the working side for discharging the slag into a cave below,
where it is received into vessels mounted on wheels At the two extre-
mities of the cylindrical chamber are large circular openings, one of
which, on the side of the regenerators, being for the introduction of the
heated gas and air, as well as for the exit of the products of combustion ;
the other, facing the working platform, is closed by a stationary door
hung before it in the usual way.
Although the passage for the introduction of the ignited gases is sepa-
rated only by a vertical partition wall from that through which the pro-
ducts of combustion are carried off, the chamber is very perfectly heated;
care must, however, be taken that the gases enter the chamber with a velo-
city which sends them forward towards the door and causes them to reach
the exit passages only after having twice traversed the length of the
rotator.
Mr. Siemens thus describes the working of this apparatus:" The
ore to be smelted is broken up into fragments not exceeding the size of
peas or beans; to it is added lime or other fluxing material in such a pro-
portion that the gangue contained in the ore and flux combines with only
a little protoxide of iron into basic and fluid slag. If the ore is hæmatite,
or contains silica, I prefer to add alumina in the shape of aluminous iron
ore; manganiferous iron ore may also be added with advantage. A
charge of say 20 cwts. of ore is put into the furnace when fully heated
* The bauxite used for this purpose has the following composition :-
A1203
Sio₂
Fe₂03
53.62
42.26
•
4.12
100.00
To this, after being finely ground, are added 3 per cent. of clay and 6 per cent. of
plumbago-powder, which, by reducing the iron contained in the mineral to the
inetallic state, renders it practically infusible; silicate of sodium or water-glass may
be advantageously substituted for clay in the lining mixture.
IRON.
175
while it is slowly revolving. In about forty minutes this charge of ore
and fluxing material will have been heated to bright redness, and at this
time from 5 to 6 cwts. of small coal, of uniform size (not larger than
nuts), are added to the charge, whilst the rotative velocity is increased in
order to accelerate the mixture of coal and ore. A rapid reaction is the
result; the peroxide of iron, being reduced to magnetic oxide, begins to
fuse, and at the same time metallic iron is precipitated by each piece of
carbon, while the fluxing materials form a fluid slag with the siliceous
gangue of the ore.
The slow rotative action is again resorted to, whereby
the mass is turned over and over, presenting continually new surfaces to
the heated lining and to the flame within the rotator.
66
During the time of this reaction, carbonic oxide gas is evolved from
the mixture of ore and carbon, and heated air only is introduced from the
regenerator to effect its combustion within the rotating chamber. The
gas from the gas-producers is entirely, or almost entirely, shut off during
this portion of the process. When the reduction of the iron ore is thus
nearly completed, the rotator is stopped in the proper position for tap-
ping off the fluid cinder; after this, the quick speed is imparted to the
rotator, whereby the loose masses of iron contained in it are rapidly col-
lected into two or three metallic balls. These are taken out and shingled
in the usual way of consolidating puddled balls; the furnace is tapped
again, and is ready to receive another charge of ore. The time occupied
in working one charge rarely exceeds two hours; and supposing that
10 cwts. of metallic iron are got out per charge, the apparatus is capable
of turning out at least 5 tons of puddled bar per diem. If anthracite or
hard coke is available for effecting the reduction of the ore, it should be
crushed much finer than when ccal or brown coal is used, the idea being
that each particle of the reducing agent should be fully consumed during
the period of chemical reaction. If wood is used, it has to be charged, for
the same reason, in still larger pieces.
"If it is not intended to make iron, but cast-steel, the balls may be
transferred from the rotator to the bath of a steel-melting furnace in their
heated condition, and without subjecting them to previous consolidation
under a hammer or shingling machine.
"It is feasible, however, to push the operation within the rotator to
the point of obtaining cast steel. If this is intended, the relative amount
of carbonaceous matter is somewhat increased in the first instance, so that
the ball, if shingled, would be of the nature of puddled steel, or contain
even some carbon mechanically inclosed.
*
"If now, after removing the cinder by tapping, from 10 to 15 per
cent. of ferro-manganese or spiegeleisen is thrown in, and the heat.
within the rotator is rapidly raised by urging the influx of heated gas and
air from the regenerator, the metallic balls will soon be seen to diminish,
and, presently, a metallic bath only will be found in the furnace, which
* Made by heating to whiteness a mixture of pyrolusite, charcoal, and finely di-
vided scrap-iron in crucibles holding from 40 to 50 lbs. each; the alloy produced
contains from 65 to 80 per cent. of manganese. Henderson's alloy, made in Glasgow,
contains from 15 to 30 per cent. of manganese only.
176
ELEMENTS OF METALLURGY.
may be tapped into moulds, and hammered and rolled into steel blooms or
bars in the usual manner. Experience alone can determine which mode
of working will ultimately prove the best; but it is probable that for the
production of cast-steel on a large scale it will always be more profitable
to transfer the metallic balls to a separate melting furnace; a series of
rotating furnaces working in concert with a series of steel-melting fur-
naces to produce charges of 5 to 6 tons of fluid steel.
"In comparing, upon theoretical grounds, this method of producing
metallic iron with the operation of the blast-furnace, it will be at once
perceived that whereas, in the blast-furnace the products of combustion
consist chiefly of carbonic oxide, and issue from the top of the furnace at
a temperature exceeding 350° C. the result of combustion in the rotative
furnace is carbonic acid, which issues from the regenerative furnace into
the chimney at a temperature rarely excceding 175° C. This proves at
once a great possible saving of fuel in favour of the proposed method,
and to this saving has to be added the fuel required in converting pig-
metal into wrought-iron by the puddling process."
After describing the nature of the various changes which take place
in this furnace, and calculating the amount of heat absorbed by each,
Mr. Siemens goes on to say :-
"In fine, a ton of iron ought to be producible from hæmatite ore with
6.4 cwts. of carbonaceous matter, or say 8 cwts. of common coal, and a ton
of cast-steel with 8.91 cwts. of carbon, or say 11 cwts. of coal. In giving
these figures I do not wish to imply that they will ever be completely
realised, but I maintain that, in all our operations we should fix our eyes
upon the ultimate result which theory indicates, which, owing to the im-
perfect means at our command, we shall never completely realise, but
which we should constantly endeavour to approach.”
INDIRECT METHOD OF OBTAINING IRON - PRODUCTION OF Pig-
IRON AND SUBSEQUENT CONVERSION INTO MALLEABLE IRON.
MECHANICAL PREPARATION OF IRON ORES. In this country iron ores
are rarely subjected to any mechanical preparation beyond breaking or
hand-picking, but on the Continent of Europe argillaceous brown iron-
stone and some other ores of low produce are often separated from
associated sand and clay by sifting and washing in revolving perforated
cylinders of sheet- or cast-iron.
As, however, these operations are for the most part carried out on the
spot where the ores are raised, a description of them would rather come
within the province of a treatise on mining, than that of a work on
metallurgy.
In order to attain regularity in the working of blast-furnaces it is
desirable that the charges of ore and fluxes should be reduced to frag-
ments of nearly uniform dimensions. The size of these should be regu-
lated in accordance with the height of the furnace and the greater or
less degree of facility with which the ore is capable of becoming reduced.
In the hæmatite districts of Lancashire it is usual to break both ore and
IRON.
177
fluxes to the size of ordinary road metal; and in Sweden the hard
magnetic ores of the country are, after roasting, reduced to a still
smaller size; the ore in the Cleveland district is, on the contrary,
charged into the furnaces in blocks from 4 to 6 inches cube. These large
masses can, however, be only used in furnaces of great height, in which,
by the slow descent of the charges, sufficient time is allowed for the
complete permeation of heat through them, while their size allows a free
passage for the upward current of gases. Smaller pieces, although ex-
posing a larger surface to the action of the reducing gases of the furnace,
pack more closely together, and consequently offer greater resistance to
the blast. The ores may be broken, either by manual labour or by
machinery, but there are now but few localities where the former method
of breaking can be advantageously employed, unless hand-picking, for
the removal of siliceous gangue or of some injurious associated mineral is
at the same time resorted to. Various contrivances are employed for the
reduction of iron ore to fragments of a size suitable for the blast-furnace,
but the machine known as Blake's Stone-Breaker is now almost univer-
sally adopted in this country and in the United States of America. This
apparatus is not unlike a pair of ordinary nutcrackers, of which one jaw
is fixed to a vertical support, while the other receives a reciprocating
motion which is communicated to it by a powerful combination of levers
actuated by a rapidly-revolving crank-shaft. The faces of the jaws,
which are made of hard-chilled cast-iron, are vertically corrugated by an
angular grooving, and at each revolution the one which is movable
advances about half an inch towards the other, which is fixed, and imme-
diately returns to its original position. When the jaws open, the stone
which is between them falls downwards, as far as its size permits, and is
subjected to an intense crushing action at the next revolution of the
crank. This is repeated until it has been broken sufficiently small to
allow of the escape of the fragments at the bottom, where they are some-
times received on a picking-table, from which any fragments of objection-
able mineral are easily removed.
A machine of this description, with crank-shaft making from 200 to
250 revolutions per minute, and having jaws 20 inches in depth and
from 9 to 10 inches in width, will, with an expenditure of 15-horse power,
crush from 10 to 12 tons of hard red hæmatite per hour into fragments
containing, on an average, 4 cubic inches.
The corners of the movable jaw are liable to become worn or broken
off by use, and the crushing faces are therefore so made as to admit of
being readily replaced in case of accident or when worn out. The most
serviceable material for the crushing surfaces is obtained by the use of a
mixture of mottled cast-iron and franklinite spiegeleisen cast in chills.
At Finspong, in Sweden, a tilt hammer, striking 60 blows per minute, is
sometimes employed for breaking iron ores for the furnace, but the work
performed in proportion to the power expended is much less than is effected
with Blake's machine.
At Eisenerz in Styria, crushing rollers, somewhat similar to those
employed in Cornwall for crushing copper ores, are used for the reduc-
N
178
ELEMENTS OF METALLURGY.
tion of ironstone to a suitable size for the furnace. These are chiefly
made use of for breaking ores which have been previously roasted, and
appear to be very efficient for this purpose.
A pair of such rollers, set at a distance of 13 inch apart and provided
with springs to prevent breakage, in case of hard pieces of raw ore being
accidentally introduced, will, with an expenditure of about 20-horse
power, reduce 40 tons per hour of roasted spathic ores to a size suitable
for the furnace. In order to do this, the rollers make about 36 revolu-
tions per minute, and the ore, when introduced in fragments of from 20
to 30 cubic inches, is delivered at a maximum size of from 4 to 5 cubic
inches. By slightly reducing the distance between the rolls, and in-
creasing their speed to 42 revolutions per minute, from 60 to 70 tons of
calcined ore may be broken per hour with an expenditure of about
24-horse power. For crushing hard unroasted ore to the dimensions of
ordinary road metal there can, however, be no doubt that Blake's stone-
breaker is a far more efficient machine than any system of rollers hitherto
tried.
WEATHERING OF IRON ORES.-The argillaceous nodular ironstone of
the coal-measures is often contaminated with fragments of adhering shale,
which, when first raised, are not readily separated, but by exposure to
atmospheric influences oxidation and exfoliation are induced, and the
removal of the associated rock becomes easy. Ores also which contain
sulphides, such as iron or copper pyrites, when exposed to air and mois-
ture, become gradually purified by the formation of soluble sulphates,
which are finally, to a great extent, removed by rain.
This process
of weathering iron ores with a view to the removal of sulphur in the
form of sulphates is much more effective when applied to them after
roasting, and this method of treatment is consequently most frequently
adopted.
When spathic ores are subjected to weathering in their raw state, the
oxidation of sulphides and the removal of the resulting sulphates is
usually accelerated, during dry weather, by lixiviating the heaps with
water, and also by occasionally turning them over so as to expose fresh
surfaces. Hard siliceous ores are, in the Hartz, subjected to this treat-
ment for several years before being smelted, but it is evident that this
could only be carried on in the case of works of limited capacity, since,
for a large establishment, the amount of ground which would be thus
occupied would be so great as to render the operation practically impos-
sible.
Spathose ores, when thus treated, experience at the same time a super-
ficial transformation into brown hæmatite, and the same change takes
place, to a more limited extent, with nodules of clay ironstone, more
particularly when carbonaceous matter is not present, or when its amount
is very small.
It is, however, important that care should be taken that the weather-
ing of the ores be not carried too far, as they would then be liable to fall
into powder, and become unfitted for treatment in the blast-furnace. Ores
containing much calcium carbonate cannot be subjected to a prolonged
IRON.
179
weathering after calcination, since the slaking of the lime produced.
during the process of roasting would lead to the disintegration and
crumbling of the ore.
In some of the smaller iron-works in Germany siliceous hæmatites and
magnetites, containing pyrites, are, after crushing and washing, exposed
to the air for a period of from two to three years, in heaps of about three
feet in height; and are, during that time, repeatedly washed with water.
After being thus treated they are again passed through the crusher, and
lixiviated with water during the whole of the following summer. At
Altenau, ores of this class, are, after roasting, exposed for one year to the
action of the rain and air before smelting.
Carbonate of calcium in such ores is, however, a great obstacle to the
removal of the sulphur by lixiviation after roasting, since the caustic
lime formed decomposes the soluble sulphates of iron and copper, causing
those metals to be deposited in the form of hydrated oxides, with forma
tion of calcium sulphate, or gypsum. Calcium sulphate, although, to a
certain extent, soluble in water, is much less so than the corresponding
salts of iron or of copper, and, consequently, the sulphur is removed with
difficulty; under these circumstances any copper which may be present is
retained by the roasted ore.
The removal of phosphoric acid from roasted ores by hydrochloric
acid has been attempted, but without success; at Kladno, in Bohemia,
sulphurous anhydride has been employed for the same purpose, and the
results are stated to be satisfactory.
ROASTING OR CALCINATION OF IRON ORES.-All iron ores, with the ex-
ception of certain varieties of magnetite and massive red hæmatites, are
usually subjected to a process of roasting or calcination before being
taken to the smelting furnace. By this treatment water, carbonic anhy-
dride and other volatile matters are expelled, and, as the fragments of ore
retain very nearly their original size and form, they thereby acquire a
degree of porosity which materially facilitates the changes which they
subsequently undergo in the furnace. The roasting of iron ores has also
the effect of decomposing metallic sulphides, such as iron pyrites, the
whole of the sulphur being ultimately expelled, if the temperature be
sufficiently high; the metal remaining as an oxide. Ferrous compounds,
such as spathic ores, absorb oxygen, chiefly with production of magnetic
oxide, but when magnetite is itself subjected to calcination it often
becomes externally covered with a coating of peroxide. Bauerman
remarks that this action of oxygen, although resulting in a greater
expenditure of fuel for the reduction of the iron to the metallic state, has
an important practical advantage, since ferric oxide is much more indiffer-
ent to the action of silica at high temperatures than is ferrous oxide; the
latter, under such conditions, forming with it a highly basic slag, from
which metallic iron can only be obtained with difficulty.
The roasting of iron ores is effected either in clamps or open heaps,
in heaps within walled enclosures, or in furnaces or kilns.
Roasting in Open Heaps.-This method is principally resorted to in
localities in which fuel, as compared with the price of labour, is cheap,
N 2
180
ELEMENTS OF METALLURGY.
but it has the disadvantage of not only uselessly consuming a large
amount of wood or coal, but, from the imperfect distribution of the heat,
the interior of a pile is often fused into a compact mass before other
portions are sufficiently roasted.
At Königshütte, in the Hartz, calcareous iron ores are roasted during
from eight to fourteen days in heaps of the shape of a truncated pyrainid,
60 feet square at the base, and 9 feet in height.
The floor on which they are built is made of slag, upon which is laid
a bed of ironstone six inches thick, on which a stratum of small coal of
the same thickness is placed. Alternate layers of ironstone and coal are
then added, in such a way that towards the top the thickness of the layers
of ore is increased to 10 inches, while that of the coal decreases to 3
inches. One cubic foot of small coal is required to roast three cubic feet
of ironstone.
Blackband ores are generally roasted without any addition of fuel, as
they usually contain a sufficient amount of combustible matter to burn by
themselves when once fairly lighted. Some varieties of blackband
require a small addition of fuel, but in the case of such ores their roasting
is much facilitated by removing the smaller fragments by screening.
The blackband ores of Hasslinghausen, in Westphalia, contain from
15 to 30 per cent. of carbon, and are roasted, without addition of fuel, in
heaps three feet in height, and of any convenient length and breadth. At
Heinrichshütte similar ores are roasted during from one to three months,
in heaps 10 to 15 feet in height, 20 to 30 feet in breadth at the base,
and of varying lengths. Ores containing a large percentage of carbon
are calcined in larger fragments than those which are comparatively poor
in combustible matter.
Ironstone very rich in carbon should, in order to prevent caking,
be calcined in heaps not exceeding 3 feet in height, whilst ores poor
in coaly matter may be roasted in heaps of much greater height. In
order to ignite these heaps, they are either surrounded by a channel filled
with wood, or holes are left in them at regular distances, which are either
filled with wood or with glowing iron ore from a heap already in process
of calcination. The regulation of the temperature of open heaps is some-
what difficult to manage, and, consequently, a partial fusion of the ore
sometimes takes place, whilst at others the roasting is not complete in
certain portions of the pile.
To prevent this irregularity in the results obtained, the following
arrangement is adopted in some parts of Westphalia. Heaps 120 feet
long, 30 feet broad, and 4 feet high, are inclosed between walls built of
the larger pieces of ore, small openings being left at intervals of about
12 feet along the sides. These draught-holes communicate with pas-
sages in the interior of the heap, filled with wood. The larger blocks
are placed at a distance from these passages, whilst the finer ore is piled
against their sides in order to admit the flame as much as possible into
the interior of the heap. After the pile has become fully ignited, the
surrounding wall of ore is taken down and thrown upon places in which
the fire may exhibit a tendency to come too quickly to the surface. A
IRON.
181
heap of the above dimensions will contain about 17,000 cubic feet of ore,
and usually takes a month to burn completely out.
Ores containing a large amount of coaly matter and pyrites are very
liable to become so highly heated that the fragments near the middle of
the heap become fused into large masses. To avoid this caking, such
ores are, in Westphalia, roasted in heaps only 2 feet in height, and,
when this has burned out, but before it has cooled, a similar layer is
placed upon the first; in some cases a third is added after the second has
burned out.
As the presence of reducing gases tends to prevent the complete
oxidation of sulphur, Grundmann recommends that the heaps, when they
contain much pyrites, should be covered with a coating of small ore in
order to condense the sulphur volatilised without oxidation. This coating
is afterwards carefully taken off; the sulphates remaining in the heaps
being removed by long-continued exposure to air and occasional watering.
He also recommends piling the blocks of ironstone with their planes of
stratification in a vertical position, to facilitate the escape of sulphur,
since the pyrites contained in such ores is usually found interlaminated
between the divisional planes.
In South Wales and Staffordshire the calcination of ironstone in
clamps is generally effected as follows:-A bed of coal, a few inches in
thickness, is spread upon the level surface of the ground, and covered with
a layer of ore about 1 foot in depth; this is followed by fresh layers of
coal and ironstone, until the height of the pile has reached from 4 to 5
feet. It is then lighted at bottom and continues to burn until the whole
of the fuel has been consumed. Should the fire in any part of the heap
come too rapidly to the surface, it must be damped with some ore or
ashes, in order to prevent a partial fusion of the mass; the loss in weight
varies from 28 to 33 per cent., and about 2 cwts. of small coal and † cwt.
of large coal are consumed for each ton of ore roasted.
In Staffordshire and Scotland blackband ironstone is calcined in piles
which have generally a trapezoidal form, and vary from 3 to 9 feet in
height; in order to avoid the production of too high a temperature the
smaller heaps are to be preferred for ores containing a large proportion
of combustible matter. The spathic carbonates of South Wales, locally
known as "coal brasses," are particularly liable to become fused during
the process of calcination, and should consequently be roasted in heaps of
very moderate dimensions.
Roasting between Walls (Stadeln). By roasting within walled
areas the draught, and consequently the temperature, can be more easily
regulated than in heaps not so protected; a better calcination is also
effected with a smaller expenditure of fuel. The expense of both fuel
and labour is, however, greater than in kiln-roasting, and the results ob-
tained are less constant and uniform. Three sides of a square, or rect-
angular area, are usually inclosed within walls, of which the height may
vary from 6 to 12 feet, according to the nature of the ores to be calcined,
and the floor is in such cases more or less inclined. Two ranges of
draught-holes, about 4 inches square, are left in these walls at regular
182
ELEMENTS OF METALLURGY.
intervals, the lower series being close to the ground and the upper row
about 3 feet above them. When the inclosed area is very large it is pro-
vided with air-shafts, which are made by building up large masses of ore,
so as to form chimneys in the interior of the heap, to which air has access
through a system of flues formed on the floor. These flues are sometimes
replaced by a layer of wood, so arranged as to admit of a circulation of air
to the chimneys. This method of roasting is not employed in this country,
but is practised to some extent in the Hartz, where clay ironstone is cal-
cined with an expenditure of from 6 to 8 per cent. of charcoal-dust or
breeze.
Roasting in Furnaces or Kilns.—This method of calcination is gene-
rally to be preferred to the ruder processes before described, since it is
not only more economical as regards the consumption of fuel, but the
temperature obtained is also more completely under control; the product
obtained is consequently of a more uniform character. The furnaces are
generally so constructed as to allow of the operation being carried on
continuously, the raw ironstone being introduced at the top, whilst the
calcined ore is withdrawn from the bottom. The construction of the
kilns employed for this purpose varies considerably in different districts,
but the principle of working is, with but few exceptions, every where the
same. A layer of fuel is first placed at the bottom of the kiln, and this
is covered with layers of ore and fuel, alternately, until the internal
cavity of the apparatus has been filled to the top. The ore, as it becomes
roasted, is withdrawn at the bottom, where air is admitted, and the next
layer descends to take its place, the deficiency being made good by fresh
charges of ore and fuel at the top. In exceptional cases the heat is sup-
plied by fuel burned in side grates, in such a way that the flame and
heated gases only have access to the interior of the kiln. In Sweden,
instead of using solid fuel, the roasting of iron ores is frequently
effected by heat developed by the combustion of waste gases from the
blast-furnace.
•
Kilns of moderate size are usually made either of a cylindrical or
conical form, but very large ones have generally either a flattened, ellip-
tical, or rectangular horizontal section; the corners in the latter case
being rounded off. In large kilns with a circular horizontal section it is
found difficult to maintain a uniform temperature, and the ore in the centre
is consequently liable to agglomerate from becoming too highly heated.
At the mines of Gollrath, near Mariazell, Styria, the ores chiefly con-
sist of undecomposed spathic ironstone, with small quantities of brown
hæmatite resulting from the decomposition and oxidation of carbonate of
iron. The calcination of these ores takes place in continuously-working
kilns in which coal-dust, which could not otherwise be utilised, is the
fuel employed. The form and dimensions of the furnaces employed vary
in accordance with the nature of the ores to be treated, lump ore being
generally roasted in round kilns, 9 feet in diameter and 11 feet in height.
The finer ores are, on the contrary, roasted in a large furnace, 80 feet in
length and 35 feet in width, of which figs. 37, 38, and 39 represent a
longitudinal, horizontal, and transverse section respectively.
IRON.
183

□□□
C
口
​。
n
口
​口
​D
☐ 口
​口
​口
​口
​口
​Fig. 37. Roasting Kiln, Styria; longitudinal sect᛬on.
口
​口
​口
​Π
n




田田
​Fig. 38.—Roasting Kiln, Styria; horizontal section.
184
ELEMENTS OF METALLURGY.
The complicated system of air-holes shown in the drawings is neces-
sary on account of the comparatively fine state of division of the ores,
which interferes with the draught, and tends to prevent the regular calci-
nation of the ironstone. This apparatus is charged with alternate layers
of coal-dust and ore, in the proportion of 12 to 15 tubs, of 73 cubic feet
each, of the former, to about 500 cwts. of the latter; these proportions
are, however, more or less varied according to the working of the ore.
The roasted ironstone is withdrawn from the kilns every six hours, care
being taken not to remove any fragments that may not have become
thoroughly red-hot. The calcined ore thus raked from the bottom of the
kilns is slaked on the drawing tables, a, by means of water conveyed through
pipes for that purpose, and issuing from perforated roses, b. The excess of
water employed, passing through gratings, c, escapes by the gutters, d.

W.J.WELCH.S
ㅁ
​ㅁ
​Fig. 39.-Roasting Kiln, Styria; transverse section.
After being thus slaked, the ore is weathered during from four to six
years, and is periodically watered in order to remove the soluble salts
formed. The average expenditure of fuel is at the rate of 0·23 of a cubic
foot of coal-dust per cwt. of ore roasted, and the loss of weight experienced
amounts to about 22 per cent.
The long weathering, to which it is necessary to expose spathic ores
containing pyrites after roasting in kilns of the construction above
described, is a great drawback to their general efficiency, and has led to
the erection of a furnace, of which fig. 40 is an elevation and fig. 41 a
horizontal section partly above and partly below the bottom ring.
It consists of a number of flat cast-iron rings, each 1 inch thick and
12 feet 6 inches external diameter, placed one above another, so as
to form a series of shelves. The bottom one, which is 2 feet in width,
is supported by eight brickwork piers, a, 20 inches in height; the suc-
ceeding rings, fifteen in number, are only 1 foot wide, and are kept
IRON.
185

f
e
a
α
α
a
Fig. 40.-Roasting Kiln, Styria; elevation.

f
b
C
Fig. 41.-Roasting Kiln, Styria; horizontal section.
186
ELEMENTS OF METALLURGY.
at a uniform distance of 6 inches apart by eight cast-iron supports.
In the centre of the kiln is the cylindrical brick chimney, b, 2 feet
8 inches in diameter, having four holes, c, 3 inches square, in each
course, communicating with the central shaft. The top of this chimney
is capped by a cast-iron plate carrying the pipe, d, by which the activity
of the draught is increased; at bottom it communicates with the ex-
ternal air by a rectangular flue, e. A water-pipe, f, perforated on the
inner side with numerous small holes, surrounds the kiln at the level of
the lower shelf. The furnace is charged by laying a bed of cleft wood
on the ground, radially from the central chimney; this is covered with a
layer of 31 cubic feet of charcoal-dust, on which is placed a stratum of
ore, consisting of thirty trucks, each weighing 205 lbs. On this are laid
charcoal-dust and ore in regular succession, until the furnace, which holds
forty-four such charges, has been filled to the level of the top ring. The
wood is now lighted all round between the pillars, and as soon as the fire
has burnt through to the top, the drawing of the bottom layer may be
proceeded with. Wood is only employed for lighting the kiln, and is not
required afterwards; a charge is removed every twelve hours, and about
six tons of ore are drawn daily; each day the furnace is again filled to
the top by the addition of ore and charcoal. In very stormy weather it is
sometimes found necessary to add three charges in the course of forty-
eight hours. This is, however, if possible, avoided, since it is liable to
interfere with the success of the operation, and screens are frequently
employed to protect the kilns from the action of strong winds.
In order to remove the sulphates, the calcined ore is first quenched
with water from the main, f, the lumps are broken, and it is then exposed
in heaps to the action of the air; these are repeatedly turned and watered
until all the soluble salts have been washed out. The ores contain 12
per cent. of magnesia, of which 4 per cent. is removed, as sulphate, by
washing; this is of importance, as the slags obtained are less fusible when
the amount of magnesia they contain is large. The loss of weight experi-
enced by roasting is the same as at Gollrath, viz., 23 per cent.; the quantity
of charcoal-dust used is 0·32 of a cubic foot per cwt. of ore roasted.
At Altenberg six continuously-working circular kilns, each 9 feet in
internal diameter, and having a total depth of 10 feet 5 inches, are found
sufficient to supply the three blast-furnaces at Neuberg. These kilns are
provided with step grates, as shown, fig. 42, which represents a vertical
section of one of them by a plane passing through the centre of the grate.
The masonry, a, is of ordinary rubble-work, but the interior of the furnace
is provided with a refractory lining, b; the grate, c, is of cast-iron, and the
bottom, d, is composed of plates of the same material.
The ores roasted contain from 5 to 6 per cent. of magnesia, and are
exposed for several years to the action of the atmosphere without lixivia-
tion. From 23 to 24 per cent. of their weight is lost in roasting; about
0.35 of a cubic foot of charcoal-dust is employed per cwt. of ore roasted. At
Säfvenäs, in Lapland, where the waste gases from the blast-furnace are
employed for the calcination of ores, the kiln consists of a nearly ver-
tical cylindrical shaft, 18 feet in height, increasing in diameter from
5 feet at top to 7 feet at bottom.
IRON'
187

a
b
し
​d
d
::
OL
Fig. 42.-Roasting Kiln, Altenberg; vertical section.
The gas coming from the blast-furnace is conveyed by a wrought-iron
pipe, connected with a circular main, which incloses the bottom of the
kiln and is provided with ten jets placed at regular distances from one
another. The necessary amount of air is supplied through apertures
regulated by sliding-plates. From 20 to 30 tons of hard magnetite and
schistose hæmatite are roasted daily; the only fuel employed is a portion.
of the waste gases of a small charcoal blast-furnace.
At the Dowlais Iron-Works, in South Wales, the kilns used have a
rectangular form with rounded ends; the width at top being 9 feet, and at
bottom 2 feet; their length is 20 feet, and their height 18 feet. Fig. 43 is a

ㅁ
​D
ㅁ
​ㅁ
​ㅁ
​ㅁ
​ㅁ
​0%
Дъ
0% 0% 0%
口
​0
α
a
α
a
☐
Fig. 43.-Roasting Kiln, Dowlais; front elevation.
188
ELEMENTS OF METALLURGY.

с
Fig. 44.-Roasting Kiln, Dowlais; longitudinal section.
front elevation, fig. 44 a longitudinal section, and fig. 45 a transverse sec-
tion of one of these kilns, as given by Truran. The floor consists of cast-
iron plates 2 inches in thickness, and the interior is lined with fire-bricks :
in front are two splayed arches extending backwards to the refractory lining
of the kiln, and in each of these are two rectangular openings, a, on the floor-
level, through which the calcined ore is withdrawn previously to being
filled into barrows or waggons for conveyance to the furnace. Above
these openings is a series of apertures, b, employed for the purpose of
regulating the draught. The top edge of the kiln is covered by a flanged
cast-iron ring, c, which protects it from abrasion during the process of
filling. The operation of calcining in these kilns is conducted in the

C
Fig. 45.-Roasting Kiln, Dowlais; transverse section.
IRON.
189
following way :-Two or three coal fires having been lit on the floor,
raw ironstone is placed on top and around them, until the whole floor
is covered with ironstone at a dull red-heat; a fresh layer of iron-
stone, about 9 inches in thickness, is then added, mixed with about 5 per
cent. in weight of small coal, and as soon as this stratum has become
heated to redness another is added. This addition of fresh layers of raw
ironstone and small coal is repeated as fast as the previous layers become
heated to the requisite temperature. In this way the kiln is filled to the
top, and by the time this has been done the lower portions, which were
first ignited, will have become sufficiently calcined for drawing; fresh
charges are thus added at top, so as to occupy the space left by the
sinking of the mass on the inside, caused by the daily withdrawal of
calcined ore from the bottom.
The capacity of a kiln of the dimensions given is about 70 tons, and
the amount of ore calcined weekly amounts to 146 tons; the consumption
of small coal is at the rate of 1 cwt. per ton of ore calcined, whereas, in
clamps, 2 cwts. of small and cwt. of large coal, are required to do the
same amount of work.
Welsh argillaceous ores generally lose 27 per cent. of their weight by
calcination; blackband ironstone from 40 to 60 per cent.; red hæmatite

M
亦
​e
d
fo
Fig. 46.-Gjer's Calcining Kiln; one-half in section.
с
190
ELEMENTS OF METALLURGY.
about 6 per cent.; and Cornish, Devonshire, and similar brown hæmatites,
from 12 to 14 per cent.
In the Cleveland district Gjer's calcining kilns are extensively em-
ployed. Fig. 46 is in part an elevation and in part a section of this kiln,
which consists of a body or shell of fire-bricks only 14 inches in thick-
ness, cased externally with wrought-iron plates. The interior diameter,
at top, is, in the older kilns, 18 feet; at the boshes, or widest part,
forming the junction of the two truncated cones, 20 feet; and at the bottom
14 feet; the horizontal section is everywhere circular. The bottom of
the brickwork rests on a cast-iron ring, a, 4 inches in thickness, which is
supported by cast-iron pillars, b, each 27 inches in height; thus leaving an
open space between the bottom of the kiln and the floor. This is covered
by iron plates 2½ inches in thickness, c, cast in segments, and carrying, in
the centre, the cone, d, 8 feet in diameter at the base, and 8 feet in height.
The total depth from the filling gallery, e, to the foundation plate, c, is
24 feet, and its internal capacity is 5,500 cubic feet. As in the kilns of
South Wales, the amount of fuel required amounts to 5 per cent. of the
weight of ore calcined. The roasted ore is drawn through the openings
between the pillars, and is directed outwards by the slope of the central
cone. The height of the newer kilns of this description is 33 feet, the
diameter 24 feet, and the cubic capacity 8,000 feet. Such a kiln is
capable of calcining 800 tons of iron ore per week, and will burn 24 to
25 tons with one ton of small coal. Around the lower tier of plates
are a number of openings, ƒ, ordinarily closed with doors, which are
occasionally useful in the case of the stone becoming agglomerated. A
double roadway passes over all the kilns, with a gangway between and
outside the two roads.
FLUXES AND SLAGS.-It is essential to the proper smelting of an ore
that both the metal and gangue contained in it should be so fused that
their separation may be readily effected by difference of density. It
nevertheless seldom happens that the minerals treated can be directly
smelted without addition of a proper flux, as the earthy impurities
they contain are found to exert an unfavourable influence on the process.
In many instances the gangue associated with ores of iron consists of either
quartz or clay, both of which are infusible at the ordinary temperature of
the blast-furnace, and can only be melted at the expense of a portion of the
oxide of iron, which, by passing off in the slags, reduces the amount of
metal obtained. If the ore operated on be united to a siliceous gangue,
infusible at the ordinary temperature of our furnaces, it can only be fused
by the addition of a proper quantity of some substance with which it
forms a fusible silicate. If, instead of previously adding a suitable flux,
the ore be at once introduced into the furnace, silicic acid combines
with iron, and a fusible slag is produced, containing a large proportion of
iron, whilst the product of metal will be reduced. In case of the mineral
being associated with an argillaceous gangue, results of a similar nature
will be obtained. Silicate of aluminium is of itself very infusible, but,
on being heated with iron ore it combines with a portion of that metal,
and forms a double silicate of aluminium and iron, which is more readily
fused. If a proper amount of limestone, carbonate of calcium, be thrown
IRON.
191
into a furnace together with the ore, it will, during its descent through
the body of the apparatus, be converted into caustic lime, which, in pre-
sence of silica and alumina, gives rise to the production of fusible double
silicates of calcium and aluminium, in which iron is replaced by calcium.
Should the gangue, on the contrary, be chiefly composed of quartz, it will
be necessary to add both lime and argillaceous matter; but instead of
doing this directly by the use of limestone and clays rich in alumina, it
is more advantageous to effect the same object by a judicious mixture of
such ores as contain the largest quantities of the substances required.
The ores treated in many localities contain a large amount of car-
bonate of calcium, and in such cases it is impossible to obtain satisfactory
results without a due admixture of silicate of aluminium. For this
purpose clay ironstone is frequently employed, although the same result
is obtained by the use of a proper mixture of the slags obtained in some
of the processes to be hereafter described. The fusibility of double
silicates of calcium and aluminium is also influenced by the relative
proportions of their constituents.
The principal flux employed by the iron-smelter is limestone; but in
Lancashire, Cumberland, and other districts in which the ores treated prin-
cipally consist of rich red hæmatites, the addition of argillaceous matter
is also necessary. The shales from the coal-measures were formerly
much used for this purpose, but of late years the aluminous iron ores of
Belfast have, to a considerable extent, replaced them both in the blast-
furnaces of the North of England and also in those of South Wales; a
somewhat similar mineral, called bauxite, found at Baux, in the South
of France, is sometimes employed as an ore of aluminium.
The following analyses, the first by Tookey, and the second by Bell, give
the composition of Belfast aluminous ore and of bauxite respectively:-
Belfast Ore.
Bauxite.
SiO 2
Al2O3
Fe2O3
FeO
CaO
9.87
2.8
34.57
57.4
27.93
25.5
5.08
0.91
0.2
MgO
TiO2
Volatile
0.62
•
3.51
3.1
•
19.36
11.0
·
101 85
100.0
A certain economy of fuel results from the employment of caustic
lime in place of limestone, since the cooling, resulting from the expul-
sion of carbonic anhydride in the furnace, is thereby avoided. At
Ougrée, in Belgium, 26 per cent. of lime was found to replace 40 per
cent. of limestone; the production of metal being increased 2-3 per
cent. and the consumption of fuel reduced 1.6 per cent.
At Königshütte, in Silesia, the substitution of lime for limestone
resulted in a saving of 2.85 per cent. of fuel, and in an increased produc-
tion of metal, amounting to rather more than 3 per cent.
192
ELEMENTS OF METALLURGY.
The addition of fluxes to the ores smelted in the blast-furnace is
regulated by various considerations. When they are of good quality the
most important of these is the production of a readily-fusible slag with
the smallest possible addition of material not containing iron; this is
more especially the case when charcoal is the fuel employed. When,
however, mineral fuel is made use of, it becomes necessary that a slag
should be produced of such a composition, and in such quantities, as to
take up the sulphur which would otherwise, by combining with the iron,
materially deteriorate its quality.
Blast-furnace slags may be regarded as silicates, of which the compo-
sition usually ranges between the following limits:—
2
6
3(CaO,SiO2)+ A103,3SiO, Ca, Al, Si,O₁, and
3(2CaO,SiO2)+2Al2O3,3SiO2 = CH3Al¿Si₂O12-
The slags flowing from charcoal furnaces are generally more siliceous
than those from furnaces in which coal or coke is the fuel employed; the
latter more nearly correspond in composition with the second formula.
In the first, the oxygen of the silica is double that of the bases, and
corresponds to the general formula RO,SiO2 of augite. The oxygen in
the second may be regarded as being equally divided between the acid and
bases, and, like olivine, the composition of this slag may be expressed by
the general formula 2 RO,SiO2. As, however, one metal may be replaced
almost indefinitely by another, it is evident that these general expressions
include substances differing widely in ultimate composition.
According to Bodemann, the most fusible silicate of calcium and
aluminium is represented by the following formula :—
4(CaO,SiO2)+Al2O3,3SiO2=Cª¿Al₂Si,O21.
In this case, also, it will be observed that the oxygen of the silica is
double that of the bases taken together. Slags represented by the above
formula contain :-Silica 56, Lime 30, Alumina, 14 per cent. The follow-
ing analyses of slags produced in various localities, and under dissimilar
conditions of working, will serve to show the nature of the differences in
their composition:-
ANALYSES OF BLAST-FURNACE SLAGS.

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
SiO2
Al₂03
CaO
MgO
FeO
MnO
CaS
•
P₂05
70.23 54.26 35.80 53.79 46.37 38.48 43·07 39.52
6.37 6.76 4.20 13.04 4.30 15 13
20.41 24.56 2.14 25.67 38.64 32.82
0.28 4.06 0.57 7.40 7.44
0.15 9.20 21.16 2.44 0.95
2.70 4.80 29.64 2.20
1.86 1.62
*0.03 2.22 1.90 2.15
trace 0.15.
38.76
27.68
•
14.85 15 11
14.48
22.28
28.92 32·52
35.68
40.12
5.87 3.49
6.84
7.27
0.76
2.53 2.02
1.18
0.80
1.37 2.89
0.23
0.20
0.98
2.00
Alkalies
0.45. 1.92 1·84 1·06† 1·11t
99.86 99.86 97.00 97·71 100.00 100 54 100 35 98·76
•
•
99 26 100·35
* Sulphur.
† Potash.
IRON.
193
Nos. 1, 2, 3, 4 and 5, from furnaces fed with charcoal. 1. From
Rothau; furnace working on agillaceous ores and producing grey-iron ;
Klasek. 2. From same locality; by Klasek. 3. From Rothau, working
on a mixture of sphærosiderite and red iron ore; Klasek. 4. From
Rübeland, green and glassy; furnace producing mottled-iron; Rammels-
berg. 5. Slag from a charcoal-fed blast-furnace at Edsken, Sweden,
producing iron suitable for the production of steel by the Bessemer pro-
cess; Ullgren. 6. From Dowlais; produced when making grey-iron;
Riley. 7. From Dowlais; produced with white-iron; Riley. 8. From
cold-blast furnace, working with coke at Wednesbury Oak, Tipton,
South Staffordshire; D. Forbes. 9. Hot-blast furnace, working with
coke, near Dudley; Percy. 10. Clarence, Durham; produced from
Cleveland ores; Bell.
Slags resulting from the treatment of spathic ores in the blast-furnace
are sometimes, although rarely, entirely free from lime. Analyses made
by Karsten of two slags of this description from Siegen afforded the fol-
lowing results :--
1.
2.
SiO 2
Al2O3
49.57
48.39
9.00
6.66
FeO
0.04
0.06
MnO
25.84
33.96
MgO
15.15
10.22
S.
0.08
0.08

99.68
99.37
1. Produced with grey-iron. 2. Resulting from the production of
spiegeleisen.
Generally speaking, all other conditions being the same, if a slag be
refractory the iron will be grey; if it be very fusible the metal will be
white. The addition of an excess of lime reduces the fusibility of slags,
and causes the iron to become highly carburised; they at the same time
become capable of taking up sulphur in the form of calcium sulphide.
The presence of manganous oxide likewise imparts to slag the
power of taking up sulphur; this property of protoxide of manganese is
of importance in the manufacture of spiegeleisen from spathose ores.
Ferrous oxide increases the fusibility of slags, and, at the same time,
imparts to them a dark-green or greenish-black colour; this will be
observed in the case of the "scouring cinders," which are produced
when a furnace is working with a heavy burden, i.e., when the charge
of ore and flux is unduly large in proportion to the fuel used.
Slags of this description accompany the production of white-iron ;
this results from the reduction of a portion of the ferrous oxide in the
silicate at the expense of the carbon of the cast-iron. The same effect
does not result from the presence of manganous oxide, which is reduced
O
194
ELEMENTS OF METALLURGY.
with less facility, and consequently does not react on the carbon of the
metal.
It is impossible to determine, from the mere inspection of the slags
flowing from a furnace, the character of the cast-iron produced. The
physical characteristics of slags, as far as regards colour, texture, and
fluidity, will vary not only in accordance with their chemical composition,
but also with the working conditions of the furnace in which they are
produced; the relation between the appearance of the slag and the
character of the metal will consequently vary in different districts.
In general the slags produced in furnaces working with a light burden.
are either white or grey. This is caused by the almost complete reduc-
tion and removal of the iron; but when the ores contain manganese an
amethystine tiut may frequently be observed; this is particularly the case
in charcoal furnaces smelting non-aluminous ores.
A heavy burden and a comparatively reduced temperature, on the other
hand, commonly give rise to black or very dark-coloured slags.
The fluidity and vitreous character of slags are, within certain limits,
greater in proportion to the amount of silica present; opalescent slags
usually indicate the presence of a considerable amount of alumina.
Slags containing sulphides of calcium, barium, or manganese, such as
are produced when sulphur is present in the ore or fuel, give off sulphu-
retted hydrogen if allowed to flow over damp ground. If the slag be
sufficiently hot to cause the ignition of this gas, it burns with the form-
ation of water and sulphurous anhydride; if, however, on the contrary,
sulphuretted hydrogen should escape without decomposition, its presence
will at once be recognised by its odour.
If a large quantity of lime be present, the slag has usually a dull,
stony fracture, and when the amount becomes excessive the cinder
readily falls to pieces on exposure to a damp atmosphere; if ground with
one-fourth their weight of caustic lime, such slags form an excellent
cement or mortar for building purposes.
When a furnace is working with a light burden, the slags flow con-
tinuously and steadily, and exhibit a somewhat viscid fluidity, pass-
ing slowly from the liquid to the solid state. The scouring slags from
a furnace working with a heavy burden, on the other hand, flow as freely
as water, but become readily solidified without passing through an inter-
mediate state of plasticity. Hæmatites containing manganese produce
slags exhibiting the usual amethystine tints characteristic of the presence
of that metal; but when blown into bubbles by escaping gases, this
colour disappears, and they assume a pearly-white lustre, and pumice-
like structure. When furnaces treating such ores are burdened so
heavily as to afford white-iron, the slags become dark-green in colour.
In addition to the green and black colours resulting from the presence
of ferrous oxide, the amethystine tints produced by oxide of manganese
and the yellow and brownish-green colourations due to sulphide of man-
ganese, certain others, particularly shades of blue, are common in blast-
furnace slags. Among these a light sky-blue tint, frequently seen in
Swedish slags, has been variously attributed to the presence of vanadium
IRON.
195
and titanium, or to artificial ultramarine resulting from the formation of
sulphide of sodium; but the nature of the colouring agent in such cases
does not appear to have been satisfactorily determined; green and blue
tints are said to be sometimes produced by silicates of zinc.
In many of the smaller iron-works in the neighbourhood of Siegen,
and in other localities in Germany, the slags from the blast-furnace are
crushed in a stamping-mill and washed for the recovery of any entangled
shots of metal they may contain; these are afterwards returned to the
furnace with subsequent charges of ore and flux.
Although they cannot be considered as fluxes, forge- and mill-cinders
play an important part in the economy of modern iron-works. When pig-
iron is exposed in a state of fusion to the action of air, the silicon which
it contains becomes oxidised with the formation of silicates rich in iron,
in which a portion of that metal would appear to sometimes exist as
magnetic oxide. A similar slag is produced when wrought-iron is ex-
posed to a high temperature in the presence of silica. The amount of
iron present in such cinders varies from 40 to 60 per cent., and, in this
respect, they may be considered as equal to the richest varieties of iron
ore; they, however, contain nearly the whole of the phosphorus, and a
considerable portion of the sulphur, originally present in the pig-iron,
and, consequently, their use, if employed in large quantities, tends to
deteriorate the quality of the metal produced.
One of the chief reasons for the deterioration of the resulting metal is,
however, the ready fusibility of these cinders, which causes them, when
added to the charge, to flow down to the hotter portions of the furnace
where the reduction of iron and silicon takes place simultaneously. A
portion only of the iron being thus reduced, the remainder passes into
the furnace-slag, producing a scouring cinder, which not only prevents
the production of highly-carburised iron, but has also an injurious
erosive action on the hearth of the furnace. The use of this product as
an addition to the charge consequently results in the production of an in-
ferior description of cast-iron, usually known as cinder-pig, together with
a loss of iron in the slag, which sometimes contains as much as 20 per
cent. of ferrous oxide.
The cinder obtained from re-heating or welding furnaces contains less
phosphorus and sulphur than that resulting from the operation of
puddling, but its use in the blast-furnace, nevertheless, tends to the pro-
duction of white cast-iron. Various methods have been suggested, with
a view of overcoming the difficulties which attend the smelting of such
cinders; that most generally adopted, however, consists in subjecting
them to a preliminary calcination; but with a view of facilitating their
reduction, they have sometimes been combined with a mixture of lime
and small coal. When ferrous silicates are roasted with free access of
air, oxidation takes place, protoxide of iron becomes converted into either
peroxide or magnetic oxide, and silica is liberated. The resulting pro-
duct, which is exceedingly infusible, is extensively employed, under the
name of bull-dog, for lining the hearths of puddling furnaces. Its infusi-
bility is due to the circumstance that silica and ferric oxide, which are
0 2
196
ELEMENTS OF METALLURGY.
both nearly infusible, do not unite to form silicates, when heated together
in an oxidising atmosphere. When bull-dog is produced from puddling-
furnace cinders containing phosphorus, a partial liquation takes place and
a fusible slag, known as bull-dog slag, is separated, and carries off with it
a considerable portion of the phosphorus. The sulphur present is chiefly
converted into sulphate of iron, which forms a crust on the surface of the
heap, and may either be removed by lixiviation or decomposed by further
roasting. The cinder in this peroxidised state is in a favourable condi-
tion for treatment in the blast-furnace, and is, in composition, not unlike
a siliceous hæmatite.
Lang's process for preparing forge-cinders for the blast-furnace con-
sists in mixing them, in a finely-pulverised state, with milk of lime and
coal-slack or charcoal-dust, so as to form masses, which, when dried,
possess sufficient coherence to withstand the pressure to which they are
exposed in the furnace.
The process of Minary and Soudry, is of a somewhat similar cha-
racter; the finely-divided cinder is mixed with the slack of coking-coal,
and converted into coke in the usual way. It is stated by the inventors
that the iron is completely reduced to the metallic state by the action of
the gases evolved during the process of coking, at a temperature which is
not sufficiently elevated to act upon the silica, and that both phosphorus
and sulphur are eliminated in the form of phosphoretted and sulphuretted
hydrogen. The coke thus obtained is employed for smelting iron ores
in the blast-furnace in the ordinary way. In order to obtain sufficient
coherency it is necessary that the proportion of pulverised cinder added
to the coal should not be too considerable. At Givors, the most satisfac-
tory results were obtained with 40 parts of cinder and 60 of coal, which
yielded a coke containing from 20 to 25 per cent. of metallic iron. When
this coke is employed in the blast-furnace a sufficient amount of lime-
stone must be added, over and above that required for the ore treated, to
effect the removal of the uncombined silica in the form of slag. The
foregoing statements with regard to the complete reduction of the oxide
of iron in the silicate are not in accordance with the results of experiments
made by Dr. Percy on this subject, who found that two-thirds only of
the iron was reduced to the metallic state, leaving behind a silicate in
which the oxygen in the base, as compared with that in the silica, was in
the ratio of 1: 3.
It must, however, be remembered that the experiments referred to
were made on pure ferrous silicates, whereas the cinders treated in the
large way contained an amount of earthy matter which may have caused
the liberation of the last atom of iron. Many reactions of this nature
are more completely effected on a large scale than on a small one, while
the results of laboratory experiments are not always confirmed by trials
made on considerable masses.
THE BLAST-FURNACE AND ITS ACCESSORIES.
For a very long period all the iron manufactured for the purposes of
the arts was produced directly from the ore in a malleable state, and it
IRON.
197
is probable that upon the introduction of larger furnaces, of the class
known as Stücköfen, cast-iron was at length accidentally discovered.
After a time it was found that the production of cast metal, as an inter-
mediate stage in the manufacture of wrought-iron was attended with
many advantages not possessed by the direct process, so that at the pre-
sent day this method is almost exclusively followed.
By the direct process, in which a low charcoal hearth or bloomery is
employed, a portion of the iron in the ore becomes reduced to the metallic
state at a comparatively low temperature, while another part, in the form
of protoxide, combines with silica, forming a fusible basic slag, by which
any excess of carbon is removed from the spongy metallic mass which it
surrounds. This oxidising action of the slag is aided by a blast intro-
duced through an inclined tuyer in such a way as to impinge directly
upon the charge.
For the production of cast-iron, on the contrary, a furnace of con-
siderable height, which may be described as a hearth whose walls are
continued upwards into a body or shaft of variable section, is invariably
employed. In this arrangement the blast is supplied by nozzles laid
horizontally, instead of being placed in the inclined position adopted for
the direct preparation of malleable iron. When this furnace is in opera-
tion, or, as it is called, in blast, it is kept filled to the top with alternate
layers of fuel, ore, and flux, and a constant blast of air is maintained
through the tuyers at a sufficient pressure to pass freely through the accu-
mulated fuel and ore. In this way the incandescent fuel in the vicinity
of the blast is consumed with the formation of carbonic anhydride and the
development of an intense heat, by which the adjacent ore and fluxes are
melted and the iron is reduced to the metallic state. These fused mate-
rials fall into the hearth, where the metal, by its greater density, sepa-
rates from the slag, which, being specifically lighter, rises to the surface
and protects it from the decarburising action of the blast.
The CO, formed in the neighbourhood of the tuyers, coming in con-
tact in its ascent through the furnace with incandescent fuel, becomes
reduced to CO, and such an absorption of heat is thereby caused as to
restrict the area of maximum temperature to the immediate vicinity of the
nozzles. The CO thus produced, which, together with the nitrogen of
the air, passes upwards through the apparatus, on coming in contact with
oxide of iron at a red-heat, is again oxidised at the expense of the oxygen
of the iron ore; CO, and metallic iron being simultaneously produced,
the latter becoming more or less carburised during its subsequent descent
into the hearth.*
2
The alternate production of CO₂ by the oxidation of CO through the
agency of oxide of iron, is continued in the upper parts of the furnace, so
long as there is sufficient heat to effect these changes. The quantity of
CO, is also augmented by the decomposition of limestone used as flux,
while such an amount of CO continuously escapes from the apparatus as to
2
* Mr. I. Lowthian Bell states that carbonic oxide is dissociated in the blast-furnace,
being resolved into carbon and carbonic anhydride by the reaction, 2CO=C+CO₂.—
'Chemical Phenomena of Iron-Smelting,' p. 44.
198
ELEMENTS OF METALLURGY.
form a large body of flame if allowed to ascend freely into the atmo-
sphere. When collected and utilised, this becomes a valuable fuel, and
may be employed for heating the blast, and for various other accessory
operations connected with the establishment.
It is therefore evident that the blast-furnace may be considered as
combining within itself the functions of various distinct metallurgical
appliances. When limestone and raw fuel are employed, the upper por-
tions combine those of a lime-kiln, coke-oven, and gas-producer; the
middle region becomes a large cementation chamber; and the hearth, in
which an intensely elevated temperature prevails, effects the fusion of the
various materials, which, during their descent through the shaft of the
apparatus, have become prepared to undergo the transformations which
there take place.
THE BLAST-FURNACE. The blast-furnace, of which fig. 47 is a ver-
tical and fig. 48 a horizontal section through the hearth, consists in its

·9-
1
-18
Fig. 47.-Blast-Furnace, Plymouth Iron-Works; vertical section.
most primitive form of a shaft or cavity formed of two truncated cones
joined together at their bases. The upper and deeper of these cones,
known as the stack or body, is formed by an interior lining of fire-bricks,
which is again enveloped in a casing of broken scoriæ, or of refrac-
tory sand, which separates the internal lining of the furnace from the
external brick coating, supported by a mass of masonry composed either
of stone or brick. The opening at the top of the furnace is called the
throat, and is often surmounted by a chimney, in which there are one or
more openings, for the convenience of charging the fuel, ore, and flux, with
which the apparatus is at regular intervals supplied. The lower cone,
known by the name of the boshes, is usually constructed of fire-brick,
but a refractory fire-stone is sometimes employed for this purpose.
As this part of the arrangement is subjected to a high temperature,
as well as to the scouring action of the slag, it is of importance that the
IRON.
199
material of which it is composed should be carefully selected, as on the
durability of the boshes mainly depends the length of time during which
the action of the furnace may be uninterruptedly carried on. To prevent
the occurrence of a sharp angle, the two cones forming the body and
boshes are united either by a curve or by a narrow cylindrical belt, of
which the edges are slightly rounded, and a space is thus formed called
the belly.
The lowest division was, in the older furnace, sometimes composed
of large slabs of refractory sandstone, cemented with fire-clay. The
hearth is often somewhat smaller at bottom than at the point, where it
meets the boshes; but this difference of size at the two extremities is in
many instances so small, as almost to give to the hearth, as this part is
named, the form of a prism or cylinder.
The bottom is composed either of fire-stone or of large fire-bricks,
supported on a mass of masonry, in which channels are left open for the

45.
45-
Fig. 48.-Blast-Furnace, Plymouth Iron-Works; horizontal section.
escape of any moisture which may be expelled from the brickwork;
whilst, to keep the whole building perfectly dry, the foundations are
traversed by arched galleries, which intersect each other at right angles
beneath the axis of the internal cavity of the furnace.
Three only of the sides of the hearth are continued to the bottom
the fourth being merely brought to within a certain distance of the base,
where it is supported by strong bearers of cast-iron, firmly fixed into the
masonry of the walls, and on which rests a block of refractory material
called the tymp.
At a short distance beneath the tymp, and a little in advance of it, is
placed the dam-stone, which has a prismatic form, and is securely fixed by
a strong piece of cast-iron which covers its outer side, and is known by
the name of the dam-plate.
At a short distance above the ground-level, passages for the introduc-
tion of the blast are perforated through the walls of the hearth; these are
known as the tuyer-koles and usually vary in number from two to six.
200
ELEMENTS OF METALLURGY.
The arch covering the fore-hearth which is bounded in front by the dam,
is called the tymp-arch and is, in large furnaces, protected by a cast-iron
box or block having within it a wrought-iron serpentinous pipe through
which a current of cold water is conducted, in order to protect the brick-
work from intense heat and from the corrosive action of molten slag.
A semicircular depression on the top edge of the dam, known as the
cinder-notch, forms a passage for the slags, which are often moulded into
large blocks by being run into a shallow iron truck, provided with
movable sides. When the cinder-tub has become full, it is removed and
replaced by an empty one; as soon as it has sufficiently cooled to become
solidified, the block of slag, which, in some cases, weighs several tous,
is lifted from the waggon and thrown on the cinder-heap. In small
furnaces, and particularly in those in which charcoal is the fuel em-
ployed, the front of the dam is formed into an inclined plane, or cinder-
fall, on which the slag solidifies in thin layers, and may be readily
removed by manual labour. In Staffordshire, slags are allowed to collect
in a basin in the floor of the casting-house, called the roughing-hole, and
when sufficiently consolidated are lifted, by means of a crane, upon a
waggon and carried to the cinder-tip.
The tap-hole for withdrawing the molten iron from the furnace is in
the form of a narrow vertical slot passing through the dam and dam-plate,
and extending from the bottom of the hearth to a height of about eighteen
inches above it. This is easily stopped by a packing of sand tightly
rammed into it, and remains closed during the filling of the hearth, but is
readily penetrated by a pointed iron bar at the time of casting.
The space between the top of the arch and the tymp-arch is also closed
either by sand or by a temporary wall of fire-brick and clay, a small passage
for the escape of slag alone being left open. Sometimes the level of the
dam is raised above that of the bottom of the tymp, causing the metal in
the hearth to be covered by a bath of molten slag, from which a stream
flows continuously, as the fore-hearth is not stopped.

Fig. 49. -Water-Tuyer; longitudinal section.

Fig. 50.-Water-Tuyer; side view.
IRON.
201
The tuyers are hollow truncated cones generally of cast- or wrought-
iron, the sides of which are hollow, in order to allow of the circulation of
cold water, as shown, figs. 49 and 50, of which the first is a longitudinal
section and the second a side view. In the axis of the tuyer lies the nose
of the blast-pipe, which is usually of wrought-iron. As tuyers are liable to
leak from becoming burnt, they are, when made of wrought-iron, of sufficient
length to admit of being several times repaired without becoming unser-
viceable from the shortening thus caused. They are placed with their axes
lying horizontally, and with their ends pointing more or less directly
towards the centre of the hearth.
On either side of the tymp, cast-iron plates with vertical notches are
frequently placed for the purpose of affording support to the heavy tools
employed in clearing the hearth, and for other operations connected with
the routine of working the furnace. The filling-hole, or throat, is always
surrounded by a platform of sufficient breadth to allow free passage to
the waggons or barrows by which the fuel, ore, and fluxes are supplied.
In the older furnaces ample space for this purpose is usually found be-
tween the internal ring and the external masonry, but in the more lightly-
built cylindrical furnaces of the present day additional surface becomes
necessary. This is provided by means of an overhanging gallery of cast-
iron supported upon iron brackets.
When the gases are allowed to burn freely at the throat of the furnace
it becomes necessary to provide a chimney to carry the flame clear of the
charging place. This, called the tunnel-head, consists of a cylinder of
brickwork from 8 to 12 feet in height, varying in diameter with the
size of the furnace, rests on the platform, and is strongly bound with
wrought-iron. When the gases are collected for the purpose of being
employed as fuel, the arrangements of the head of the furnace are of a
more complicated nature; some of these will be described when treating
of the employment of waste gases.
In the newer furnaces the conical or spindle-shaped body, with sharp
lines of division between the hearth, boshes, and stack, have, to a great
extent, been replaced by curved outlines; the heavy masses of masonry of
the old furnaces have also been superseded by thin walls of radial bricks,
moulded to the varying sections of the work.
Figs. 51, 52, and 53 will serve to show the nature of the progressive
changes which have, within the last twenty years, taken place in the
construction of the blast-furnace in this country. Fig. 51 is a vertical
section of a blast-furnace at Oldbury, about eighteen years old, blown
with six tuyers. Fig. 52 is one of the older furnaces at the Stockton
Iron-Works, and fig. 53, one of a pair recently erected at Ditton Brook,
near Warrington, which have closed tops, and from which the waste gases
are drawn off to be used as fuel. Fig. 54 is a horizontal section of this
furnace immediately below the level of the tuyers. It will be seen that
the body of the masonry is supported by five brickwork pillars, a. Hot-
blast is employed, heated by the waste gases, and introduced into the
furnace through four tuyers.
When furnaces are slightly built, and are closely hooped or entirely
202
ELEMENTS OF METALLURGY.

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Fig. 51.-Blast-Furnace, Oldbury; vertical section.
cased with iron, they are usually designated cupola furnaces, to distinguish
them from more massive erections, such as the Oldbury furnace. The
superstructure of such furnaces is frequently supported on cast-iron
IRON.
203

-32·0.
1
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-49.0·
1
1
1
1
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W.J.WELCH.DEL.ET.S?
Fig. 52.-Blast-Furnace, Stockton; vertical section.
standards, and they are entirely incased with boiler-plate up to the
throat.
In order that moisture may readily escape, and the brickwork be
201
ELEMENTS OF METALLURGY.

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W.J.WELCH.SC
Fig. 53. Blast-Furnace, Ditton Brook; vertical section.
prevented from splitting, through the pressure of confined vapour, the
masonry constituting the exterior casing of the older furnaces is often
traversed by numerous small channels, by which the drying of the mass
IRON.
205
is facilitated. The work is strongly bound together, on the outside, by
stout iron bands, which are made to bind tightly either by keys or screws
and nuts. When the furnace is rectangular these bands are held together
by long vertical bars, to which they are attached by loop-eyes or strong
screw-bolts, and by this means great strength and solidity are communi-
cated to the building. The dimensions of blast-furnaces differ very much,
according to the period at which they were erected and the nature of the
the ores operated on. The height is extremely variable, some furnaces
being only about 30 feet high, including the chimney; whilst others
reach an elevation of over 90 feet.
The most common height is, however, from 50 to 70 feet, to which
must be added the chimney, which is from 8 to 12 feet in length, formed
of radial bricks, bound together by stout iron rings and girders; door-
ways are left in the sides for the introduction of ore and fuel, The

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Fig. 54.-Blast-Furnace, Ditton Brook; section through hearth.
throat is protected by a large annular plate of cast-iron, and on this the
foundations of the chimney rest.
In building blast-furnaces it is now usual to avoid abruptly-varying
slopes, and the diameter is often continuously increased from the throat
to the boshes, and is thence contracted downward to the hearth bottom
in a somewhat similar way. In Scotland this form of furnace is employed,
with the addition of a wide cylindrical hearth. Slightly-curved stacks,
with conical boshes and cylindrical hearths, are almost universal in the
Cleveland district, but in South Wales the boshes are often conical, while
the stack, which is for a certain distance cylindrical, is terminated by a
species of dome.
In French and German furnaces curved outlines are less common
than in this country, and, in the majority of cases, their hearths are
206
ELEMENTS OF METALLURGY.
proportionately smaller than in ours. Swedish charcoal furnaces are of
considerable height as compared with their diameter, and the hearth and
boshes form part of the same cone, which is usually very acute. The
stack is commonly cylindrical. Fig. 55, from Percy, is a vertical section
of a furnace erected, in 1857, at Sten, near Finspong. In all essential
respects this furnace is similar to those constructed in England, and con-
sists of an inner lining of fire-brick and an outer shell of less refractory
material. The hot-blast stove is heated by the waste gases withdrawn
from the opening, a, in the upper part of the furnace, and the air-pipes

JWEL JOSE
Fig. 55.-Swedish Charcoal Furnace; vertical section.
are so arranged that, when necessary, the blast may enter the furnace
without being heated by first passing through the stove. Nearly opposite
the opening, a, is another, by which a portion of the gas is drawn off for
the purpose of supplying fuel to the kiln in which the calcination of the
ores is effected; the mouth of this furnace always remains open.
་
The height and other dimensions of blast-furnaces differ according to
the nature of the ore treated and of the fuel employed, and no general
rules can be laid down with regard to the form best suited for any par-
ticular class of ore. The most useful guide in the construction of a blast-
IRON.
207
furnace is afforded by the condition of other furnaces when they are
blown out after working the same kind of ore, under similar conditions.
It is evident that, by constructing the various parts in accordance with
the indications thus obtained, a certain amount of fuel may not only be
economised, but the apparatus may be more quickly brought to its best
working condition, than in the case of the most suitable form having to
be obtained by the erosive action of the slags.
An increased production of iron from a given ore can only be obtained
by augmenting the fusing power of the furnace in which it is treated
since it is manifest that fresh charges can be introduced only in propor-
tion to the rapidity with which those which have preceded them are
removed. The power of fusion is mainly dependent on the rapidity with
which fuel is consumed by the oxygen of the blast, and, as the combustion
of fuel is chiefly confined to the region of the tuyers, it follows that by
augmenting the diameter of the hearth an enlarged area of active com-
bustion is obtained.
When a furnace is working satisfactorily the active combustion of
fuel should be confined to the region of fusion, and to the immediately
adjoining zone in which the CO, produced is transformed into CO. The
latter gas and the nitrogen of the deoxygenated air are charged respec-
tively with the reduction of the oxides of iron and the progressive heating
of the materials in the upper portion of the furnace. It therefore follows
that the greater the distance between the zone of active combustion and
the mouth of the furnace the more complete will be the abstraction of
heat from the gases issuing at the tunnel-head. This, of course, only
applies to the sensible heat of the gases; an additional and much larger
quantity may be obtained by their combustion.
The height of a blast-furnace should be mainly regulated by the
character of the fuel employed as regards its power of resisting the
crushing action of a large number of charges forming a high column of
materials; very high furnaces are consequently not used with tender fuel,
and the favourable results obtained from the tall furnaces in the Cleve-
land district are, to a great extent, due to the exceedingly resistant nature
of the coke employed as fuel. The height of furnaces in which anthracite
is employed is not generally great, since the fuel is liable, by decrepi-
tating, to cause obstructions, which are only to be avoided by the use of a
more than usually powerful blast. Such furnaces are, therefore, generally
low, wide, and are blown by a considerable number of tuyers. It is of great
importance that the dimensions of a furnace should be so regulated that
the reduction of the ore may take place at a low temperature, as otherwise
silicates of iron will result, with the formation of scouring slags, and the
production of white cast-iron. The harder a furnace is driven, all other
conditions being the same, the greater will be the deterioration in the
quality of the metal produced, caused by the more rapid descent of the
charges; it consequently follows that to manufacture an increased
quantity of iron, without injury to its quality, it is necessary to employ a
larger furnace.
The Rachette Furnace. With the view of securing a uniformity
208
ELEMENTS OF METALLURGY.
of temperature unattainable in circular hearths of large diameter, various
attempts have been made to obtain this result by the substitution of more
elongated forms. In the Rachette furnace, introduced some years ago

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​Fig. 56.-Rachette Furnace; longitudinal section.

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Fig. 57.-Rachette Furnace; horizontal section above tuyers
into Russia, and since experimentally tried in various parts of Europe, the
hearth is a rectangle, of which the length very much exceeds the width.
Fig. 56 represents a longitudinal section of this furnace, and fig. 57 a
O
IRON.
209
horizontal section above the tuyers; fig. 58 is a transverse section of this
apparatus.
The oblong hearth gradually merges into a shaft, of which the
diameter regularly increases upwards, and which, at the throat, is from
two and a half to three times as wide as the hearth at the level of the
tuyers. This furnace is provided with a series of ramifying, rectangular
air-passages which traverse, at different levels, the outer casing of the stack ;
these communicate with an arched chamber situated below the hearth.
Before the furnace is blown-in, a fire is lighted in the drying-chamber
below the hearth, by which the whole mass of masonry is quickly and
uniformly warmed. The tuyers, which vary in number from twelve to
sixteen, are arranged, on either side of the hearth, in such a way as not to
be directly opposite each other, and a dam and tapping-hole are provided
in each of the shorter sides.
For the purpose of causing greater regularity in the distribution
of the blast, the tuyers are sometimes replaced by a single rectangular
nozzle, placed on each side, which delivers the air in a thin uniform

CHEHI
Fig. 58.-Rachette Furnace; transverse section.
stream along the whole length of the hearth. In the original furnaces of
this class erected in the Ural, the breadth of the hearth at the tuyers is
3 feet, the width at the throat 7 feet, and the total height of the appa-
ratus 30 feet. The cubic capacity of such a furnace is 1,950 feet, and
its daily production of grey pig-iron, when working with charcoal and
cold-blast on magnetic ores containing 67 per cent. of iron, is about
30 tons.
P
210
ELEMENTS OF METALLURGY.
Blast-Furnaces in the Cleveland District. The following table, pub-
lished by Mr. Gjers, in the 'Journal of the Iron and Steel Institute,'
shows the progressive increase in size, &c., of the Cleveland blast-
furnaces, giving their dimensions and capacity in the order of their
respective dates.
!
Date.
Name of Firm.
Furnaces. Height.
Width of
Boshes.
Capacity.
No.
Feet.
Feet.
Cubic feet.
1851
Bolckow & Vaughan
ون
3
42
15
4,566
1853
Bell Brothers
6
Gilkes, Wilson, Pease & Co.
2
44
473
45
10-3
163
6,174
1 + 3/1/
5,100
1854
Cochrane & Co.
1856
1861
1862
1864
B. Samuelson & Co.
Thomas Vaughan
Lloyd & Co.
1865
Bolckow & Vaughan
B. Samuelson & Co.
Bolckow & Vaughan
Gilkes, Wilson, Pease & Co.
Stockton Furnace Company
Norton Iron Company
1858 Thomas Vaughan
Jones, Dunning & Co.
Bolckow & Vaughan
Gilkes, Wilson, Pease & Co.
Whitwell & Co.
Bolckow & Vaughan
6
54
15
7.166
4
55
16
7,175
3
3
2
Hopkins, Gilkes & Co.
2
2
1
1
•
3
•
2
•
4
•
3
·
•
4
1866
Hopkins, Gilkes & Co.
Swan, Coates & Co..
Bell Brothers
1867
Norton Iron Company
Cochrane & Co.
Thomas Vaughan
Stevenson, Jacques & Co.
Gilkes, Wilson, Pease & Co.
Bell Brothers.
Bolckow & Vaughan
Bolckow & Vaughan
6
3
1
•
Lloyd & Co.
""
1869
1870
39
1868 Gilkes, Wilson, Pease & Co.
Stevenson, Jacques & Co.
B. Samuelson & Co.
•
Jones, Dunning & Co.
Bolckow, Vaughan & Co. .
Bolckow, Vaughan & Co..
Thomas Vaughan
Bell Brothers.
Stockton Furnace Company
Swan, Coates & Co.
Cochrane & Co.
•
Gilkes, Wilson, Pease & Co.
B. Samuelson & Co.
1871
Gjers, Mills & Co.
""
Lackenby Iron Company
Bolckow, Vaughan & Co.
60 60 61 60 30 ∞ ∞ II∞ Q H CO THW M N NNAN N N N NIII~~~− ∞ ∞ —~~~~~~
50
14
5,050
54
15
7,116
55
113
6,800
50
16
6,341
50
15
6,000
563
16
7,000
56
16
7,200
58
17
8,000
61
163
7,960
55
16
7,700
60
20
12,778
75
161
11,985
69
20
15,500
70
18
12,000
67
20
15,000
81
19
16,000
70
221/
17,000
75
21
17,700
2
80
20/1/
15.500
2
95/
16
15,050
1
75
20
12,972
2
75
24
20,000
2
75
20
16,090
80
17
11,500
2
85
25
26,000
2
76
23
20,624
1
75
24
22,500
1
70
231/1
1
69
21/
2
80
21/
HNHNHNI
18,000
16,000
18,000
3
73
18
12,000
2
95/
22
25,940
1
951
23
28,800
3
85
25
26,000
4
80
25
25,000
2
80
24
24 613
1
75
233/1
22,229
2
90
30
41,149
2
85
27
32,000
2
85
28
30,000
2
$5
25
26,000
2
85/1/20
2
9512
22
25/
26,676
24
28,950
BLOWING MACHINERY.-The blowing machine ordinarily employed,
fig. 59, consists of a large cast-iron cylinder, A, accurately turned on the
IRON.
211
inside, and provided with a piston, P, made air-tight by a packing often
consisting of tressed hemp. The cylinder is closed at both extremities
by iron ends, and on the cover is a stuffing-box, through which passes the
rod, R, connected with the piston. The cover of the cylinder is pro-
vided with openings communicating with the outer air, and furnished
with valves, v, opening towards the inside. Another valve, v', on the
contrary, opens outwards, and communicates with a lateral chamber, B,
also of cast-iron. The lower end of the cylinder is provided with similar
apertures and valves, those marked v, which establish a communication
between the external air and the space beneath the piston, open inwards,
whilst the opening communicating with the lateral chamber is closed by
a valve, v', shutting in an opposite direction.

R
P
B
A
7"
Ꮴ
Fig. 59.-Blast Cylinder, Dowlais; vertical section.
The better to understand the action of this apparatus, let us suppose
that the piston has been raised to its full height in the cylinder, and has
begun to be again forced down. If the valves v are closed, the air
contained in the upper part of the vessel gradually becomes more and
more rarefied, and the difference of density between the air in this part of
the cylinder, and that of the blast in the chamber, B, will cause the
valve v' to apply itself firmly against the metallic surface before which it
is hung. The valves v, on the contrary, which open inwards, will be
lifted as soon as the difference between the density of the inclosed air and
P 2
212
ELEMENTS OF METALLURGY.
that of the atmosphere is sufficiently great to overcome the resistance
caused by their mechanical adjustments; and in proportion as the piston
descends, the space behind it will be occupied by a supply of atmospheric
air arriving from without.
The motion which causes the air above the piston to dilate, will
evidently at the same time compress that which is beneath, in proportion
as it approaches the bottom of the cylinder, and causes the lower valves v,
opening inwards, to close firmly against the polished metal surfaces to
which they are attached; whilst that marked v', hung in a contrary direc-
tion, will open and allow the air to pass into the chamber, B, whence it
escapes, through the aperture, O, to the pipes connected with the different
tuyers of the furnaces. In this way the upper portion of the cylinder
draws the air from without during the descent of the piston, and forces
that which is beneath it through the chamber into the pipes with which
it is connected. When the piston is raised, the reverse of this takes
place the lower portion receives air from without, whilst the upper dis-
charges that which it contains through the pipes leading to the tuyers.
The machine is by this means made to throw into the furnace a nearly
continuous flow of air, the only time at which the current is interrupted
being that at which the piston has reached the full extent of its stroke,
and before it has begun to move in a contrary direction.
:
As, however, it is of importance that the regularity of the blast should
be maintained, the pipe, O, leading from the chamber, B, is made to com-
municate with a closed reservoir of wrought-iron, where the variations
referred to are lost through the elasticity of the air itself. The piston of
the blowing machine is now almost invariably worked by steam power,
being often attached by a parallel adjustment to the oscillating beam of an
engine. In some cases each machine is provided with two blowing
cylinders acting alternately at each stroke made by the beam, by which
the motion is communicated. The power required to work an apparatus
of this kind necessarily depends on its size, and also on that of the
furnace or series of furnaces which it supplies.
Blowing Engine at Dowlais Iron-Works. The large blowing engine at
the Dowlais Iron-Works, a section of the air cylinder of which is given
fig. 59, was erected, in 1851, by Mr. Truran, and has been described by Mr.
Menelaus in the Transactions of the Institute of Mechanical Engineers. ·
Fig. 60 is a side elevation of this engine. The blowing cylinder, A, is 144
inches in diameter, with a stroke of 12 feet, making 20 double-strokes
per minute, the pressure of the blast being 34 lbs. per square inch.
The discharge-pipe, O, is 5 feet in diameter, and about 140 yards in
length; thus answering the purpose of a regulator. The area of the
entrance air-valves is 56 square feet. The amount of air discharged per
minute, at the above pressure, is about 44,000 cubic feet.
The steam cylinder, C, is 55 inches in diameter, has a stroke of 13 feet,
with a steam pressure of 60 lbs. on the square inch, and works up to 650-
horse power. Steam is cut off when the piston has made one-third of its
course. There is also on one side of the nozzle a small separate slide-
valve for moving the engine by hand when starting. The cylinder-ports
IRON.
213
are 24 inches wide by 5 inches in depth, and the slide-valve has a stroke
of 11 inches with a lap of half an inch. This engine is non-condensing,
and the exhaust-steam is discharged into a cylindrical heating-tank 7 feet
in diameter and 36 feet in length, containing the water employed for
feeding the boilers; beneath the steam cylinder there are about 75 tons
of cast-iron framing, and 10,000 cubic feet of masonry.
The beam is cast in two parts, each weighing about 16 tons, the total
weight upon the gudgeons being 44 tons. It is 40 feet 1 inch from
outside centre to outside centre, and is connected to the crank on the
fly-wheel shaft by an oak sweep-rod, strengthened from end to end by

C
A
M
Пол
M
아
​B
W.J.WELCH.SC
Fig. 60.-Blowing Engine, Dowlais.
wrought-iron straps. The fly-wheel, D, is 22 feet in diameter, and weighs
35 tons. Steam is supplied by eight Cornish boilers, each 42 feet long
and 7 feet in diameter, with a single internal flue, 4 feet in diameter, in
which there is a fire-place 9 feet long.
For some time this engine supplied blast to eight large furnaces,
varying in diameter from 16 to 18 feet at the boshes; it is now,
in con-
junction with three other engines of smaller size, blowing twelve furnaces,
some of which make upwards of 235 tons of good forge pig-iron per week;
the weekly make of the twelve furnaces is about 2,000 tons of forge-pig.
With the exception of the cylinders, which were made and fitted at
214
ELEMENTS OF METALLURGY.
the Perran Foundry, Cornwall, the engine and boiler were made at the
Dowlais works, under the superintendence of the Company's engineer.
Blowing Engines in the North of England. The blowing engines
employed in the North of England are often of vertical construction, and
are sometimes coupled in pairs, having a fly-wheel between them, with
cranks at right angles, as in fig. 61, which represents the arrangement
employed at Newport, near Middlesborough, described by Mr. B. Samuelson
(May, 1871), in a paper read before the Institute of Civil Engineers.

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Fig. 61.-Blowing Engine, Newport.
Blowing Engines at Creuzot, &c.-At the Creuzot Iron-Works, in
France, there are seven blowing engines, of which three are horizontal
and of a somewhat old type. The other four are direct-acting vertical
engines, of which the blowing cylinders, 108 inches in diameter, are
placed below the floor of the engine-house, the steam cylinders, 474 inches
IRON.
215
in diameter, being over head. The two pistons are fixed on one rod, and
their stroke is 6 feet, 63 inches; the piston-rod passes through the top of
the steam cylinder and is attached, at its upper end, to a cross-head
working in metallic guides. From the cross-head a connecting-rod extends
to the crank-shaft; the centre of the latter being 25 feet 10 inches
above the floor of the engine-room, and no less than 44 feet 3 inches
above the base of the engine.
The admission of steam to the cylinder and its release therefrom are
effected by equilibrium-valves worked by cams on a counter-shaft driven
from the crank-shaft by spur-gearing. These engines are of the non-
condensing class, and the steam, which is supplied at a pressure of 60 lbs.
per square inch, is cut off at one-fourth of the stroke; the average number
of revolutions per minute is fifteen.
The blowing cylinders are fitted with a number of flap-valves, one-
half of cach cover being devoted to the inlet and the other half to the
delivery-valves. The blast is furnished at a pressure of 6 inches of
mercury, or rather more than 3 lbs. per square inch, and the quantity
delivered is 90 per cent. of that due to the capacity of the cylinders.
These four engines, which are respectively named the Simoun, Sirocco,
Mistral, and Ouragan, are all placed in one building, and supply blast to
twelve furnaces.
When, instead of employing large engines of the class described, it
is thought desirable to make use of lighter machinery working at a
higher speed, it becomes necessary that the air-valves should be moved
mechanically, instead of allowing them to be opened and shut by the
action of the air itself. This arrangement, coupled with large valves and
passages, prevents all irregularity or jar in the working, provided the lap
and lead of the valves are properly proportioned; and consequently the
piston may be driven at a high velocity, whilst its diameter can be reduced
and its course shortened. This system of construction has been adopted
at different times both in this country and on the Continent, the best
known form being Slate's engine, in which the slide is annular and placed
outside the vertical blast cylinder; it receives its motion by means of a
pair of rods from the fly-wheel shaft. In the arrangement of Thomas
and Laurent the cylinders are horizontal and the air-passages and valves,
which are of a rectangular form, are placed laterally, in the same manner
as the steam-ports and slide-valve of an ordinary horizontal engine.
In Fossey's engine, which was exhibited in the Belgian Department
of the Exhibition of 1862, the slide-valves are replaced by discs, with
radial perforations which are put in slow rotary motion by gearing con-
nected with the main shaft.
In practice the use of blast-engines with slide-valves has not been
found advantageous, owing to the large amount of friction on the valve-
surfaces, and the great wear and tear to which, from its rapid motion,
the machinery is subjected.
In Austria small direct-acting blast-engines, having the steam cylinder
uppermost, are much used for charcoal furnaces; they are generally of
small dimensions, averaging from 25- to 30-horse power, and deliver from
2,300 to 2,500 cubic feet of air per minute.
216
ELEMENTS OF METALLURGY.
Horizontal blast-engines are generally preferred in Rhenish Prussia;
the cylinders are placed on the same line, and the rod which carries the
piston passes through both covers of the blast-cylinder, and runs in guides
on either side. Two engines of this description are not unfrequently
coupled, but they are so constructed that one of them may be readily
thrown off in case it should not be required. An engine of from 30- to
40-horse power is sufficient for blowing an ordinary charcoal furnace, but
a single furnace working with coke requires a blowing engine of from
90- to 100-horse power.
4
The pressure of the blast varies with the nature of the fuel employed
and the burden of the furnace. In some parts of Europe the pressure of
air employed for charcoal furnaces does not exceed inch of mercury,
while in American anthracite furnaces a pressure of 15 inches, corre-
sponding to 7 lbs. per square inch, is often used. In this country,
with tender fuel, a pressure of from 2 to 3 lbs. is employed, but with
hard coke it ranges from 3 to 5 lbs. per square inch.
The practice of blowing several furnaces with one engine, although
mechanically economical, is attended with considerable risk should any
break-down of the machinery take place. It is therefore always desirable
that there should be a reserve of blowing power, and that the work should
be so distributed between two or more machines, that in case of an acci-
dent to one of them the blast may still be efficiently kept up. When there
is but one furnace, a pair of coupled engines, capable of being worked
independently of each other, may be often employed with advantage.
On account of the variations of pressure at the different parts of the
stroke and the pulsations caused by the reciprocating action of the piston,
the blast issues from the blowing cylinder with a somewhat irregular flow.
In order, therefore, to obtain a steady blast from the various nozzles, it
becomes necessary to employ some means for rendering the pressure
constant. This may be effected either by receiving the blast in a reservoir
having a capacity several times greater than that of the blowing cylinder,
or by delivering it into a second cylinder provided with a loaded piston,
which rises when the amount of blast increases, but falls and exercises a
compressing action when the supply of air is temporarily diminished.
The same result may be obtained by the use of a loaded bell floating,
like a gas-holder, in water, but fixed reservoirs of sufficient capacity are
equally efficient, and are now generally preferred. These are usually
made of sheet-iron and had formerly a spherical or dome-like form, but
they are now more frequently cylindrical, and should have a capacity
from forty to fifty times greater than the volume of air delivered per
second by the blowing engine. When, however, the blast-main is long
and of considerable diameter, with two or more engines blowing into it
at the same time, it frequently happens that sufficient uniformity of
pressure can be obtained without the use of a special regulator. In some
of the old iron-works a brickwork chamber, lined with cement, was used
as a regulator for the blast.
HOT-BLAST.—A patent was granted, in 1828, to Mr. James Beaumont
Neilson entitled 'Improved Application of Air to produce Heat in Fires,
Forges, and Furnaces, where Bellows or other blowing Apparatus are
IRON.
217
required.' There is reason to believe that the patentee had originally no
just conception of the great value of his invention, or of the important
influence it was destined to exert on the manufacture of iron. The par-
ticular reference made by him in his specification to smiths' fires and iron-
founders' cupolas, would seem to indicate that he regarded his invention
as being more particularly applicable to such purposes than to the blast-
furnace.
Mr. Neilson, and others with whom he had entered into partnership,
granted a licence, in 1832, to Messrs. Baird, the proprietors of the Garths-
herry Iron-Works, Scotland, in consideration of receiving one shilling per
ton on the iron produced at their establishment. This payment was
subsequently disputed by the licencees, principally on the ground of
insufficient description and want of novelty, but they further contended
that the cold-blast was practically more economical. The trial took
place at Edinburgh in 1843, when the jury awarded the patentees damages
to the amount of £11,867 16s. The value of this invention, which, at a
comparatively recent date, was thus disputed, is now universally admitted,
and the employment of the hot-blast has been proved not only to be
attended with a great economy of fuel, but at the same time has been
found to increase the productive power of the furnace. Heated air is
consequently at the present time employed, to the almost total exclusion
of the cold-blast, in all the principal iron-producing districts of the world;
the latter being retained only for the production of certain special brands
of cast-iron which command a high price, and may therefore be manu-
factured at a correspondingly enhanced cost.
The temperature to which the blast may be advantageously raised
appears to be limited only by the wear and tear of the apparatus and by
the difficulty of keeping it tight when the air is very strongly heated.
The blast is not generally heated beyond 350° or 400° C., but it is found
that by using air heated to 650° instead of 400°, a saving of 5 cwts. of
coke per ton of iron made can be effected. In some cases the blast is
now used at a visible red-heat, or about 700° C., but when such extreme
temperatures are employed the rapid destruction of the metallic pipes
of the stoves renders a special construction of the heating apparatus
necessary.
Common Stove. The apparatus usually employed for producing the
hot-blast consists of a series of parallel or spiral tubes, arranged in a
fire-brick chamber, where they are heated externally, either by the com-
bustion of solid fuel, or by that of the waste gases from the furnace.
One end of these tubes is in communication with a main which supplies
cold air from the blowing engine, while the other is connected with that
which conveys heated air to the several tuyers. In the older stoves the
fire-place is rectangular, and two mains, which are parallel to the longer
sides and circular in section, are provided with a number of sockets into
which the ends of the heating-pipes are cemented.
These pipes, similar in section, and having the form of a syphon
or arch, are placed in the position shown, fig. 62, which represents a
transverse section of a hot-blast stove; their extremities are severally
218
ELEMENTS OF METALLURGY.
attached to the mains, a and b, by means of cement joints. The grate,
c, extends along the whole length of the apparatus, and the flame aud
heated gases, after playing against the under sides of the tubes, pass
around and between them, finally escaping to the chimney by means
of flues provided for that purpose. The cold air from the blast-engine,
entering by the main a on one side, flows continuously through the
arched pipes, where it becomes heated, and passes off to the tuyers by

a
Fig. 62.-Hot-Blast Stove; transverse section.
the opposite main, b. In order to obtain a larger amount of heating
surface, the arched or horse-shoe pipes are now usually made with a
flattened elliptical section instead of a circular one, and inverted V-shaped
pipes are frequently employed instead of those of the arched form shown.
in the engraving. The heating power of the apparatus has also been
augmented by the introduction of stops in the mains, by which the air
is compelled to pass alternately backwards and forwards through the
vertical pipes before being conducted to the furnaces. In all cases the
cold air is introduced at one end of the stove, and passes off to the tuyers
IRON.
219
from the other extremity. The arched pipes of hot-blast stoves are
liable to become broken by the expansion and contraction caused by
variations of temperature, unless they are allowed a certain freedom of
motion; this is frequently provided for by supporting one of the mains
on rollers in such a way as to admit of its moving inwards or outwards,
according as the pipes either contract or expand.
Circular Stove.-Round ovens are now sometimes employed in place

b
Fig. 63.-Circular Stove; vertical section.
of the rectangular stove above described, and, in such cases, the air-
mains are replaced by an annular cast-iron box, having a square or
trapezoidal section; this is divided by a central partition into two hollow
rings, one of which corresponds to the cold- and the other to the hot-air
main of the ordinary stove. The vertical pipes, instead of being arched,
are connected at top by a short horizontal connecting-piece. Fig. 63
220
ELEMENTS OF METALLURGY.
represents a vertical section through the centre of a stove of this kind.
Fig. 64 is a horizontal section through the air-box.
The cold air first enters the outer ring, a, where it is interrupted by

b
W
2
Fig. 64. Circular Stove; section through air-box.

Fig. 65.-P stol-Pipe Stove; transverse section.
a stop, fig. 64, and then reaches the inner ring, b, by ascending a number
of the outer vertical pipes and descending an equal number of those of
the inside series. A stop in the inner ring causes the air to again pass
IRON.
221
through an equal number of the vertical tubes into the outer one, by
which its temperature is still further augmented.
Pistol-Pipe Store.--Another modification, known as the "pistol-pipe
stove,” is made use of in Scotland, Cleveland, and some other districts in
this country, as well as in France, Germany, and other parts of the
Continent of Europe.
In this case the two vertical pipes or limbs are replaced by a single
one divided longitudinally by a division reaching nearly to the top, which
is closed, enlarged, and bent over in the form of a pistol-stock. These
pipes are arranged on either side of a fire-place, as shown, fig. 65, and

f
www
d
a
b
Fig. 66.-Hot-Blast Stove, Neustadt; vertical section.
the cold air which enters one division descends through the other, and,
after becoming heated by the furnace, finally passes off to the tuyers.
Stove used at Neustadt.—At the Neustadt Iron-works, Hanover, a
form of stove is employed of which fig. 66 represents a vertical section.
The heating coil consists of four cast-iron pipes united by semicircular
bends, and three such series are so connected by branch-pipes that the
whole apparatus consists of twelve tubes. The cold air enters at a, and
passing downwards, finally passes off in a heated state at b; the fuel
222
ELEMENTS OF METALLURGY.
employed is the waste gas from the blast-furnace which arrives through
the large wrought-iron main, c, and is supplied to the furnace through jet-
pipes, d. The jets, d, are provided with a central tube, through which air
is admitted, at e, in order to effect the combustion of the gas.
The pipe, f, is one of a series employed for superheating steam. When

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Fig. 67.-Cowper's Stove; vertical section.
waste gas from the furnace is employed for heating ordinary air-stoves,
it is advisable that each stove should have a small fire-place in which a
fire is constantly kept up in order to insure the continual ignition of the
gas. If this were not provided, and the flame should accidentally become
extinguished, air would be liable to find its way into the gas-main in
such proportions as to cause an explosion.
IRON.
223
Cowper's Stove.-Cowper's stove for heating the blast to a very high
temperature is constructed on the principle of the regenerative furnace of
Siemens. Figs. 67 and 68 represent respectively vertical and horizontal
sections of this apparatus, which is inclosed in a wrought-iron cylindrical
casing with a flat bottom, which stands on the ground and has an arched
or dome-shaped top. This is lined throughout with brickwork, and pro-
vided with a circular central shaft, A, whose diameter is about one-fourth
of the whole space between the walls, and extends from the floor nearly to
the roof. Around this is a number of compartments or boxes, B, filled
with bricks, so placed that the apertures left between those in one course
do not exactly coincide with those in the courses either above or below
them, although a passage is, nevertheless, left from the top of the mass of
brickwork to the bottom. The regenerator thus formed is supported on
cast-iron gratings at the bottom or cool part of the stove.

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B
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B
B
B
A
C
B
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Fig. 68.-Cowper's Stove; horizontal section.
The wrought-iron casing is provided with several valves, one of which,
c, fig. 68, is for admission of the cold-blast, another, d, for the gaseous fuel,
and a third, e, for the introduction of the air necessary for its combustion;
the valve, f, is for the exit of the products of combustion, and that marked
j, for the hot-blast. These valves, with the exception of that for the hot-
blast, g, are of the usual construction, but the latter is kept cool by a
current of water, which circulates around it in the same way in which the
cooling of an ordinary water-tuyer is effected. The opening of the different
valves at proper intervals soon becomes a matter of routine, and constitutes
the whole of the attention required beyond an occasional observation to
see that the supply of gas is sufficient.
If, then, we suppose that a stove is at work heating the blast, and it
is wished to again heat the brickwork up to the required temperature, the
224
ELEMENTS OF METALLURGY.
first thing to be done is to put on another stove, and then to shut the hot-
and cold-blast valves, g and c, and allow the air to blow off by means of
the small valve, h, so as to reduce it to atmospheric pressure.
The gas-,
air-, and chimney-valves, d, e, and f, are then opened, and the gas, which
ignites as it enters, gives a large volume of flame up the central shaft,
and over and into the regenerator. In this way the top course of brick-
work is raised to a high temperature, the next course to a somewhat less
one, the third still less, and so on until the bottom course is reached, the
temperature of which is but very slightly elevated; the products of com-
bustion escape to the chimney at about 120° C. As the operation goes
on and larger quantities of heat are absorbed by each course of brick-
work, an elevated temperature penetrates by degrees lower into the
regenerator, until, after the expiration of some hours, the bricks near
the bottom have become nearly red-hot; thus storing up a large amount
of heat in the regenerator.
The gas and the air employed for its combustion are now shut off, and
the chimney-valve closed, the cold-blast valve is opened, and, lastly, the
hot-blast valve, g, is raised.
The stove, as soon as these changes have been effected, again does its
duty of heating the blast to full redness; that is, to a temperature
between 700° and 750° C. The hot-blast pipes from the stove to the
furnace are made of sheet-iron, and are of large size to allow of a
9-inch lining of fire-brick, so as to prevent loss of heat, &c.
Fig. 69.
In order to prevent the choking of the apparatus, which would be
caused by an accumulation of dust, if ordinary chequered work were
employed, (in which a brick stands over each narrow space, although a
little above it, thus effectually preventing the
passage of a brush), an arrangement of the
brickwork shown in vertical section, fig. 69, is
made use of. These stoves are also provided
with blast-pipes for removing the dust by means
of compressed air or steam, each compartment or
set of boxes being cleansed seriatim. The pipe,
i, fig. 67, is of wrought-iron, jointed to a central
pipe capable of revolving, by means of a worm
and worm-wheel, so as to bring its extremity over each of the divisions
in succession, in order to clear out all dust by the action of a violent
current of air. The central pipe is also capable of a slight vertical
motion, to be employed whenever the pipe, i, is required to be used near
the centre of the stove. The pipe, k, shown by dotted lines at the bottom
of the regenerator, is provided with a small sheet-iron cone, or umbrella,
for protecting the workman against falling dust when he applies the pipe.
to blow upwards through the boxes. At the bottom of the stove, where
the cold-blast enters, the temperature is never very high, and can, at
any time, be further reduced by allowing cold air to pass through it for
more than the usual period; when sufficiently cooled, a workman may
enter through the chimney-valve for the purpose of removing the dust.
The construction of the regenerator in compartments, continuous vertically

IRON.
225
but not horizontally, enables the blast to be efficiently applied, inasmuch
as its whole force is confined to one division; it admits also of a brush
with a long flexible handle being passed up between the boxes. The
removal of the dust is further facilitated by apertures, 7, made in both
casing and lining, through which a blast-tube may be inserted, but which,
when not in use, are closed by suitable stoppers. Stoves of this con-
struction designed by Messrs. Cowper and Siemens, are employed by
Messrs. Cochrane and Co. at their works at Ormesby, and their intro-
duction has resulted in an increased make of iron and a considerable
saving of coke in the blast-furnace.
Whitwell's Stove.—A form of stove, which, in common with that of
Cowper, presents the advantage of being constructed of fire-brick instead
of iron, has been introduced by Mr. J. Whitwell, at the Consett Iron-
Works and elsewhere; it is exceedingly durable, withstands a high
temperature without damage, and is readily cleaned.
Fig. 70 represents a vertical, and fig. 71 a horizontal section, through
the cold-air- and gas-passages. Four of these stoves, which are circular,
cach 25 feet in height and 22 feet in diameter, are often worked con-
jointly; they are provided with sheet-iron casings, and each affords 9,000
square feet of heating surface, or, together, 36,000 square feet. The gas
enters at A, air for its combustion being admitted through the passages,
a, in the brickwork, and the flame passes through the apparatus in a
zigzag course, as indicated by the arrows, by channels of which the total
length is about 240 feet. Of the 9,000 square feet of surface, two-thirds,
or 6,000 square feet, become heated to bright redness, as may be seen
through the peep-holes, b, perforating the shell and lining, through which
the interior of the stove may be readily observed. The remaining one-
third of the brickwork of the stove gradually decreases in temperature
until the products of combustion pass off to the chimney through Cat about
300° C. When a stove has been thus heated, the gas inlet, A, and the
chimney-valve, C, are closed, as well as the air-flues, a, and the hot- and
cold-blast valves, B and D, are opened. The cold-blast now enters at D,
and, passing through the apparatus in the reverse order to the gas, is
gradually heated until it attains the temperature of the hottest surface,
when, entering the tube, B, lined with fire-brick, it reaches the furnace
at a visible red-heat. The four stoves at the Consett works are used
in pairs; the blast passing through two of them during the time that the
two others are being heated. The hot-blast main is 3 feet in diameter,
and being lined with 9-inch brickwork, has a clear air-way of 18 inches.
The blast is allowed to pass through the apparatus during two hours,
at the expiration of which time only one-third of the whole surface
remains at a red-heat, below which point, in order that the regular work-
ing of the furnace may not be interfered with, it is not allowed to cool.
The walls at the hot end of the furnace are partly constructed of
ganister, and partly of fire-brick; the other transverse walls, which are
7 inches in thickness, are built of lumps 12 inches long, 7 inches wide,
and 3 inches thick. The weight of brickwork in each stove is nearly
300 tons. The hot-blast- and gas-valves are of iron cast hollow, so that
Q
226
ELEMENTS OF METALLURGY.
a current of cold water may circulate through the shell and seating.
When it becomes necessary to clean one of these stoves, the gas is shut
off, the chimney-valve opened, and the first cleaning door, e, at the hot
end, removed; the movable cover, f, in the crown of the arch is also
lifted. Scrapers, with handles of 4-inch gas-pipe screwed together so as
to make up the requisite length, are now inserted, and the walls on either

A
B
Fig. 70.-Whitwell's Stove; vertical section.
A
m
C
D
Fig. 71.-Whitwell's Stove; horizontal section.
side are scraped down, the dust falling to the bottom. The first com-
partment having been thus cleaned, the cover is replaced, and luted with
fire-clay, the same process being repeated with all the other divisions in
succession. The side doors, g, at the bottom of the stove, are now
opened, and the dust which has accumulated on the floor is removed.
The cleaning of a stove occupies about nine hours, and requires to be
repeated at intervals of from two to three months. In order to allow for
1
1

IRON.
227
the expansion of the brickwork, a space of one inch is left between it and
the wrought-iron casing; this is filled with either dry clay or granu-
lated slag.
At the Consett works a considerable saving of coke has been effected
by the use of these stoves. The furnace to which they have been applied
produces 400 tons of pig-iron weekly with a consumption of 17 cwts. of
coke per ton of metal. The charge is composed of a mixture of two-
thirds calcined Cleveland ironstone, and one-third red hæmatite, yielding
about 48 per cent. of iron. The blast is heated to 730° C., and the gases
escaping at the top of the furnace have a temperature of 250°. A fur-
nace of the same dimensions, and working on similar ores, with a blast
heated only to 450°, consumes 22½ cwts. of coke, and the waste gases are
given off at 470°.
Blast-Pipes and Nozzles.-The blast issuing from the stoves is carried
round the furnace in a circular main which, in the older ones, that are
inclosed in a square casing of masonry, passes through the arched open-
ings traversing the pillars supporting the stack, but in the newer form of
furnaces is, at a certain height above the ground, secured to the columns.
that inclose the hearth. Opposite each tuyer-hole a branch-pipe is
brought down to the proper level; these are turned at right-angles, and
connected with the blast-nozzles. A throttle- or slide-valve is attached to
each branch for the purpose of regulating or cutting off the blast, while
a similar valve of larger dimensions is fitted to the main between the
stove and the furnace.
When cold-blast is employed, a conical nozzle is attached to the
blast-pipe by a short leather tube, but when hot-blast is made use of it is
necessary that all the fittings should be of metal, and means are conse-
quently provided for adjusting the nozzles by the aid of ball-and-socket
joints and telescope-tubes. Water-tuyers are made either of wrought- or
cast-iron, of a combination of both, or of copper or bronze; the latter
are said to possess the advantage of not being readily destroyed by
"ironing;" that is, of being melted by the imperfectly-fused masses of
iron which sometimes adhere to them when the furnace is not in good
working order.
The number of tuyers and the method of their arrangement vary in
accordance with the size of the furnace and the nature of the fuel
employed. Small charcoal furnaces have frequently only two tuyers
placed on opposite sides of the hearth: three is, however, a more usual
number, one being placed opposite the tymp, and the two others on oppo-
site sides of the hearth. In the case of very large furnaces, the tuyers
are sometimes arranged in series, two being placed on either side of the
hearth, and the same number at the back, or three at the sides and either
one or two at the back. Sometimes a special tuyer is added on the tymp
side for the purpose of removing any obstruction caused by local cooling,
and is only used in case of the hearth becoming obstructed by accumula-
tions of imperfectly-fused matter.
UTILISATION OF WASTE GASES.-Shortly after the application of hot-
blast to iron-making, various attempts were made to employ the waste
Q 2
228
ELEMENTS OF METALLURGY
heat escaping from the throat of the furnace for the purpose of heating
the air with which it is supplied.
One of the methods formerly employed for the purpose of attaining
this object consisted in ranging a series of iron pipes around the tunnel-
head, in which the blast was heated by the flame passing out of the
mouth of the furnace. In other instances the pipes were either coiled
around the interior of the upper part of the stack so as to be heated by
direct contact with the ignited material which it contained, or were so
inclosed in brickwork as to become heated by transmission. All these
contrivances have, however, been successively abandoned, since from their
inefficiency and the difficulty attending their repair when they got out
of order their use was not found advantageous.
An improvement on this plan was invented by Mr. James Palmer
Budd, of the Ystalyfera Iron-Works in South Wales. Instead of making
the heating apparatus an integral part of the furnace, the ovens were in
this case so arranged as to allow of their being repaired without inter-
fering with the action of the furnaces with which they were connected.
The stoves were built a little below the level of the throat of the furnace,
which they supplied with hot air, and a chimney, twenty-five feet higher
than the top of the platform, afforded the means of drawing into them as
much of the heated air and flame as might be required. These were
carried from the furnace by a series of flues placed about three feet below
the top, and communicating with the hot-air chamber, in which were
placed the arched pipes, heated by the gases issuing from the furnace.
The chimney and its damper regulated the heat of the stove; cross-
pipes connected the upright pipes, and side-pipes conveyed the blast
arriving by upcast mains to various cross-pipes. The heated air was
afterwards conveyed to the tuyers by downcast pipes. A door was also
placed in the brickwork of the building for the purpose of cooling the
apparatus before entering it to make repairs.
All these contrivances have, however, given place to various systems
for conveying the combustible waste gases in pipes, or culverts, to the
points where they are required to be burnt as fuel. In addition to the
sensible heat which the gases are capable of directly communicating
to any body with which they may be brought in contact, the whole
gaseous column issuing from the throat of a blast-furnace is inflammable,
even after its temperature has been reduced to that of the surrounding
atmosphere. The combustion of these gases, therefore, affords a new and
entirely distinct source of heat. Various patents have at different times
been taken out for methods by which the heat thus lost has been
sought to be usefully applied, but the difficulties attending the combus-
tion of waste gases, added to the comparative cheapness of fuel, for a long
time prevented their being extensively used in this country. On the
Continent of Europe, where fuel was more expensive, the utilisation of
waste gases was much earlier introduced, but at the present time their
employment has become almost universal in all iron-producing districts.
In many small charcoal furnaces, in which the throat remains open,
the gases are taken off by means of iron pipes which perforate the brick-
IRON.
229
work from 10 to 12 feet below the top. In Sweden this plan is generally
adopted, but it can be applied on only a limited scale, and the supply
is liable to be somewhat irregular from the occasional partial stoppage of
the openings by the descending charges.
Another method for collecting the gases is by partially closing the
mouth of the furnace, so as to cause a slight impediment to the escape of
its gaseous products, and then drawing them off by means of proper
flues and tubes to where it is intended they shall be consumed.
In order to do this, a cylinder of cast-iron, of a smaller diameter than
the throat of the furnace, and having a depth equal to its width, is fre-
quently used. This is suspended by a strong flange within the tunnel-
head, and as the mouth of the furnace is constantly kept charged with
mineral and fuel, whilst a clear annular space remains between the iron

b
b
cl
a
α
Fig. 72.-Furnace-top, Darlaston; vertical section.
collar and the lining of the furnace, it is evident that this must be filled
with the gases issuing from the apparatus, which may be readily con-
ducted by means of flues or pipes to any situation where they may
be required for combustion. In furnaces built especially with a view
to economising the heat to be obtained by burning the unconsumed
gases, the internal iron lining is sometimes replaced by an annular
flue made in the brickwork a few feet below the throat. This is con-
nected by several openings with the interior of the stack, and as the
charges thrown into the furnace above this point naturally offer a certain
resistance to the exit of the escaping gases, they find their way into the
annular flue before described, whence they are readily drawn off in any
direction in which they are required, and may be conducted to a distance
of several hundred feet.
Method of collecting Gases at Darlaston.—Fig. 72 is a vertical sec-
tion of the top of a furnace at Darlaston, where this system of collecting
waste gases has been introduced by Mr. G. Addenbroke. There are fifteen
gas-openings, a, around the neck of the furnace, each 23 inches wide and
113 inches high, and consequently presenting an aperture of 270 square
230
ELEMENTS OF METALLURGY.
inches, making a total area of 4,050 square inches for drawing off the
gases. The large gas-flue, b, surrounding the neck of the furnace is
lined with fire-brick, and is 4 feet 3 inches high to the crown of the arch,
having a mean width of 3 feet. The outside of the furnace from a little
below the bottom of the flue upwards is cased with wrought-iron plates,
to which is fastened a light iron gallery, c, for the convenience of clean-
ing the flue, b. A series of openings, e, is made all round the outer side of
the flue, and these are closed by pieces of boiler-plate luted with fire-clay,
and held in their places by cross-bars and wedges; by means of these the
whole of the flue may be cleaned out in the course of a few minutes, at any
time when the blast is off the furnace. The bottom of the flue is placed
at a lower level than the edge of the openings, a, in order that the dust
carried over may accumulate for some time before interfering with the
exit of the gas. The gas-mains are 5 feet in diameter, and, in case of the
top of the materials sinking below the gas-openings, any damage is pre-
vented by shutting the valve, d, when the whole of the gas will burn at
the mouth of the furnace, without injury resulting to the apparatus.
Langen's Apparatus.—When it is desired to utilise all the gases issuing
from a furnace it becomes necessary to close the throat. At Siegburg,
on the Rhine, Langen's apparatus for the collection of waste gases is em-
ployed, the furnace mouth being closed by a lid, in the form of a bell-
shaped tube, resting in an inverted conical ring. This tube may be raised
and lowered by means of a lever, for the purpose of charging, and is at
its extremity provided with a lip which dips into a water-trough in the
gas-main, forming a perfectly air-tight joint. At the time of charging,
the bell is lifted, and, sliding in the water-joint on the gas-tube, allows
the charge in the cup-shaped ring to fall into the furnace. To prevent
accident from explosion, a safety-valve is placed on the top of the
conical tube, and another on the gas-tube.
any
At Hörde, Langen's apparatus has been modified as follows. The
mouth of the furnace, 9 feet in diameter, is closed by a flat lid of cast-
iron which, although it cannot be raised, may be readily turned on rollers,
and is kept air-tight by means of a water-joint; a gas-pipe, 3 feet in dia-
meter, is placed on this lid and kept tight in the same way. This cover
is provided, on its circumference, with four apertures closed by valves
kept tight by water, through which, in quick succession, the charging of
the furnace is effected. Before re-charging, the movable lid is made to
traverse one-eighth of a revolution, thus uniformly distributing the
materials around the circumference of the furnace.
Cup and Cone.-The simplest method of closing the throat of the
furnace, and that which is most generally used, is the cup and cone
charger, fig. 73, first applied by Mr. Parry at the Ebbw Vale Iron-
Works. It consists of an inverted cast-iron cone, a, fixed to the top of
the furnace, and of which the lower aperture is about one half the diameter
of the throat. A cast-iron cone, b, is placed in the furnace below this
cup or funnel, and suspended by a chain, c, to an arch headed lever, d,
carrying a counter-balance at the opposite end. The raising or lowering
of this cone is often effected by a pinion on the shaft of a hand-wheel, e,
gearing into a segmental rack attached to the lever. When the cone is
IRON.
231
raised, it bears against the bottom of the cup, and forms a stopper which
prevents the escape of gas from the top of the furnace. Thus prevented
from escaping by the throat, the gaseous fuel is conducted through an
orifice made in the wall of the furnace, above the level of the charges, and
is conveyed, by means of iron pipes, to any part of the works where its
combustion is to be effected.

d
a
b
Fig. 73.-Cup and Cone; vertical section.
In the Cleveland district a modification of the cup and cone is em-
ployed, the cone being replaced by an external cylindrical stopper, which
is lifted while the furnace is being charged, and lowered as soon as the
charging has been effected. The object of this arrangement is to obviate
the loss of space at the throat, which must necessarily be kept empty
when a cone of the ordinary construction is employed. It is, however,
found that the uniform distribution of the charges, so essential to the
satisfactory working of a furnace, is not secured by the use of this appa-
ratus, and, in order to effect this result, the frustum of a cone is frequently
suspended inside the throat of the furnace.
Method employed at Grosmont.-At Grosmont, Yorkshire, and Barrow-
in-Furness, Lancashire, the waste gas is taken off in a wrought-iron
tube, a, fig. 74, about 5 feet in diameter, which extends five feet down the
throat of the furnace, and is lined on the inside and cased outside with
refractory brick. This tube is supported by a brickwork dome, b, built
in the throat of the furnace, supported by six buttresses of the same mate-
rial. This dome has six openings, c, at the sides, for charging purposes,
and another in the centre, corresponding with the tube, a. The furnace
is provided with the usual brick chimney at top, which has wrought-iron
swing doors corresponding with the openings in the crown. Expansion
boxes are fixed at intervals along the tube by which the gas is conducted
to the boilers and hot-blast stoves, and a flap-valve, d, opening outwards,
is placed at the end of the tube for the purpose of clearing it, and, if
necessary, to act as a safety-valve. As before stated, the most general
method of closing the mouth of the furnace is by means of the cup and
cone, and even in cases where the waste gases are not collected the use
of a conical charger is attended with advantage.
In some of the charcoal furnaces of America the charging is effected
232
ELEMENTS OF METALLURGY.
by means of barrows, which are constructed exactly on the principle of
the cup and cone; and at Rhonitz, in Hungary, cylindrical charging
barrows are employed, by which a portion of the material is dropped in
the centre of the furnace whilst the remainder is distributed in a circle
next the brickwork.

C
Fig. 74.—Furnace-top, Grosmont; vertical section.
COMPOSITION OF WASTE GASES. -The composition of the gases of the
blast-furnace at various heights, has, at different times, been investigated
by Bunsen, Playfair, Ebelmen, Scheerer, Tunner, and others. The results
arrived at by these chemists have, after making due allowance for the
different characteristics of the fuel employed, generally agreed very closely,
and have afforded much valuable information relative to the chemical re-
actions which successively take place. The gases issuing from the throat
of a furnace practically contain the whole of the carbon of the fuel
consumed, with the exception of the comparatively small amount which
has become fixed by the carburisation of the metal.* This escaping car-
bon is chiefly in the form of carbonic anhydride and carbonic oxide gases,
the oxygen of which has been principally derived from the air of the
blast, but is to a less extent due to the reduction of oxide of iron. The
whole of the nitrogen of the air blown in will also be present, together
with small quantities of hydrogen and hydrocarbons, to a great extent
produced by the decomposition of watery vapour.
The following analyses give the composition of the gases issuing from
various blast-furnaces :-
Percentage by Volume.
1.
2.
3.
4.
5.
N
CO₂
CO
CH₁
C₂H₁
H
4
62.34
57.22
8.77
12.01
24.20
24.65
•
55 0
56.64
12.59 11.39
25.24 28.93
55.35
7.77
25.97
3.36
0.93
3.75
0.43
1.33
5.19
6.55
3.04 6.73
* A certain amount of potassium cyanide is also produced in blast-furnaces.
IRON.
233
1. Veckerhagen, Hesse Cassel; Bunsen; fuel, charcoal.
2. Clerval, France; Ebelmen; charge of brown hæmatite, limestone,
and charcoal.
3. Audincourt, France; Ebelmen; charged with brown hæmatite,
forge-cinder, limestone, wood, and charcoal.
4. Seraing, Belgium; Ebelmen; charge, brown hæmatite, mill-cinder,
limestone, and coke.
5. Alfreton, Derbyshire; Bunsen and Playfair; charge composed of
calcined argillaceous ores, limestone, and raw coal. It will be observed
that the nitrogen of the blast, which has passed through the furnace with-
out taking any important part in the reactions which are continually
going on, in each case constitutes more than one-half of the entire volume
of the gases evolved.
The proportion of nitrogen as compared with that of oxygen is, how-
ever, less than in atmospheric air, and, as no appreciable absorption of
this gas takes place in the furnace, it follows that the increase of from
12 to 18 per cent. in the amount of oxygen must be derived from the
solid materials of the charge. This increase in the amount of oxygen
is chiefly the result of the reduction of oxide of iron, and of the elimina-
tion of CO₂ from the limestone employed as flux. In certain cases, and
particularly in that of hot-blast furnaces working on siliceous ores, a
further but very small addition to the quantity of oxygen may be derived
from the reduction of silica.
2
The relative proportions of CO., and CO vary considerably in the
different parts of the furnace; the gases in the upper portion of the hearth
chiefly consist of a mixture of carbonic oxide with nitrogen; but in those
drawn off at higher levels the proportion of CO, is found to increase
almost progressively with the distance from the tuyers. In the imme-
diate vicinity of the blast CO₂ is produced by the complete combustion
of the fuel. Above this point CO₂ is generally reduced to CO by the
action of the carbon present, while in the upper portions of the furnace
the quantity of the former gas rapidly increases, because, at the compa-
ratively low temperature which there prevails, the oxidation of CO by the
oxygen of the ore proceeds more energetically than the reduction of CO₂
by carbon.
2
When furnaces are worked with raw coal, the gases evolved from
them contain, in addition to the products of combustion, small quantities
of various condensible vapours, especially tarry matter and ammonia.
Bunsen and Playfair suggested that the latter might be collected in the
form of sal-ammoniac by passing the gases through chambers containing
hydrochloric acid; and, more recently, the injection of water, in the form
of finely-divided spray, into the gas-pipes, and the use of hydraulic
mains, like those of gas-orks, has been proposed by Dr. D. Price. Up
to the present time, however, no practical application of either of these
suggestions appears to have been made, and it is probable that, if the
manufacture of ammoniacal salts from this source were attempted, con-
siderable difficulties would be found to present themselves.
The gases of blast-furnaces carry over with them notable quantities
234
ELEMENTS OF METALLURGY.

b
U
C
C
W.J.WELCH.SC
Fig. 75.-Furnace Hoist, Newport; elevation.
IRON.
235
of solid matter in the form of dust, which, accumulating in the flues and
gas-mains, requires to be removed from time to time. This principally
consists of silica, alumina, ferric oxide, lime, and sulphate of calcium.
When, as at the Concordia furnace, near Aix-'a-Chapelle, the ores treated
contain zinc, a considerable quantity of zinc oxide is found in the pul-
verulent deposit.
LIFTS OR HOISTS.-When blast-furnaces are situated in the deep
valleys of a mountainous country, it not unfrequently happens that all
the materials necessary for working them may be delivered by means of
a bridge at the top without the aid of machinery. When, however, the
country is flat, it becomes necessary to have recourse to mechanical lifts
for raising the charges.
In the older iron-works, when erected on level ground, inclined planes
are often employed for this purpose, and are usually made with a double
line of railway carried on trestle-work, or with a single line and crossings
for the return trucks. The inclination given to these does not generally
exceed 25° or 30°, and the motive power employed is usually a steam-
engine, giving motion to a winding-drum. The truck in most cases con-
sists of a triangular framework with two pairs of wheels, of unequal
diameters, supporting a platform on which are placed the iron wheel-
barrows used in charging. Chains or wire ropes are used for raising the
load. Where large quantities of material have to be elevated to a con-
siderable height, it is now more usual to employ a perpendicular lift, by
which the charges of fuel are raised by means of cages moving between
vertical guides.
Lift at Newport.-The mode of arrangement and the nature of the
power employed vary in different establishments, but the woodcut, fig. 75,
page 234, copied from a paper, before referred to, read by Mr. Bernard
Samuelson, before the Institution of Civil Engineers, represents an
elevation of the furnace hoist used at the Newport Iron-Works, near
Middlesborough.
The entire lift to the charging platform of the furnaces is 92 feet,
and the motive power, instead of being below, as is frequently the case,
is placed overhead, and consists of a double-cylinder engine, a, provided
with link motions. The diameter of the cylinders is 8 inches, and the
length of stroke 12 inches. On the crank-shaft are two pinions working
into wheels on an intermediate shaft. On the middle of the latter is
keyed a larger pinion, gearing into the main spur wheel, b (represented
by a dotted line), 12 feet in diameter, which is flanked on either side
by a deeply-grooved pulley carrying a steel rope, 1 inch in diameter.
These ropes fit the grooves with a considerable degree of exactitude, and
only pass half round their respective pulleys, the ends being attached in
pairs to the two cages, c. By this arrangement, while one of the cages is
ascending, the other is going down, the work being accomplished by the
friction of the ropes in their respective grooves.
In order to secure equal tension on both ropes, their attachment to
the cage is effected by means of a double lever, which immediately yields
to any unequal stretching of the ropes. The cages are steadied in their
236
ELEMENTS OF METALLURGY.

b
1
b

76.-Furnace Hoist, Ayresome Iron-Works; elevation.

C
이
​. 77.- Furnace Hoist, Ayresome Iron-Works; plan.
IRON.
237
:
upward and downward course by guides fastened to the columns which
support the platform. The weight raised at each journey is about two
tons, although a much greater load can be lifted without any slipping of
the ropes.
It will be observed that the moment the descending cage touches the
ground the strain on the ropes is relieved, so that they will no longer
hold sufficiently in the grooves to enable the ascending cage to be raised
any higher; this slipping of the ropes evidently renders over-winding
impossible. The great length of steam-pipe required for working the
engine at this elevation is not found, practically, to be objectionable.
The engines usually make about 150 strokes per minute, and, calcu-
lating for loading and unloading the cages, they are capable of making
one lift per minute, or of raising 120 tons of material per hour.
Water Balance.-The old water-balance lift consists of two cages
moving vertically, and guided in the usual way, united by a rope or chain
passing over a pulley. Below the floor of each cage is a water-tight box,
provided at bottom with a discharge-valve. When the cage, with the empty
box, is at the top of its course, water is run into it until its weight be-
comes sufficient to overbalance the other cage with its load, the speed of its
descent being regulated by a brake on the pulley around which the rope
or chain passes. As soon as the descending cage reaches the ground the
projecting spindle of the discharge-valve is forced upwards and allows
the water to escape, leaving the cage ready for another ascent as soon as
it is loaded. The principal objection to this arrangement is the difficulty
of preventing leakage from the tanks, by which the lift-house is constantly
kept in a sloppy and untidy state.
Lifts are also sometimes constructed upon the system of Sir W. Arm-
strong, where the cage is lifted by the action of a hydraulic ram, of which
the course is multiplied by means of a chain passing over a system of
compound pulleys. Pneumatic lifts are extremely convenient, and are
now much used in the iron-works of this country.
Furnace Hoist, Ayresome.-Figs. 76 and 77 represent a furnace hoist,
on the pneumatic principle, erected by Mr. Gjers at the Ayresome Iron-
Works, Middlesborough, which consists of a 36-inch cylinder, a, the
whole height of the furnace, made up of flanged cast-iron tubes, lipped
and bolted together and accurately bored throughout. In this cylinder
works a heavy piston, lightly packed with a cotton jacket, which also
forms a balance-weight, and is sufficiently heavy to balance the empty
table, with four empty barrows, and a portion of the load. From this
piston four wire ropes pass over four pulleys, b, overhead, down to each
corner of the table, which is 15 feet square, surrounds the cylinder, and
is guided by four shoes on the table, working in wooden guides on the
cylinder. This leaves plenty of room for four barrows being placed
round the cylinder, the table having a palisading around, with openings
on the two opposite sides, so that the barrows are run on at one side
at the bottom, and run off on the opposite side at the top. The bot-
tom of the cylinder is connected with a pair of single-acting air-pumps
worked by a pair of steam cylinders at an angle of 45°. Between the
238
ELEMENTS OF METALLURGY.
pumps and cylinder is a reversing-slide, so arranged that, by moving it in
one direction, the delivery of air is put in connection with the cylinder
and the exhaust with the atmosphere; by moving it the reverse way, the
exhaust is in connection with the cylinder and the delivery with the
atmosphere. The empty table and barrows being at the top, the piston
will be at the bottom; the engine being started, air is forced into the
cylinder under the piston, and about 2 lbs. pressure will lift the piston
and bring the table down. When the engine is stopped, the full barrows
having been put on the table, the slide is reversed; the piston being now
at the top and the engine started, air is removed from under the piston
and a partial vacuum produced; the atmospheric pressure acting on the
top of the piston now brings it down and the table up, till, arriving at
the top, the engine is again stopped. Heavy ironstone barrows, carrying
about 50 cwts. of stone, leaving about 40 cwts. unbalanced, require a
vacuum of about 4 lbs. to bring the piston down; whereas, coke weighing
only 20 cwts., with about 10 cwts. unbalanced, is brought up with a
vacuum of about 1 lb. The engine is worked, stopped, and started like a
winding engine, the speed at which the table is brought up or down
depending upon the speed at which the engine is run.
The cylinder being open at the top, the rope, shackles, and piston-
packing are always accessible. The air-pumps are simply a pair of small
single-acting blowing engines, exhausting air from one pipe and delivering
into another, the suction-flaps being on one side and the delivery-flaps
on the other.
It will be noticed that the table being connected with the piston by
four ropes, no serious accident could happen unless all were to break at
the same time. No run-away is likely to take place, as the piston can
neither go up nor down faster than air is introduced or removed from
below it. The pull on the ropes being through the elastic medium of
the air, much less strain is thrown upon them than is the case with direct
winding.
Kiln Hoist, Ayresome.-Figs. 78 and 79 are side and end eleva-
tions of a hoist employed at the same works for lifting large railway
trucks upon the depôts and kilns; this is also a pneumatic lift, working
exactly on the same principle as that just described, but is arranged with
two cylinders, a, each of 48 inches diameter with the table between them.
From each piston wire ropes, b, pass over pulleys overhead, and lap once
round, and down to the table corners. The opposite pulleys are keyed
on shafts, c, as shown, so as to maintain parallelism. There is also a
safety chain, d, on each side, which ordinarily does not take any weight,
but comes into play in case of the breakage of a rope. The weight to be
lifted is from 15 to 16 tons, and it requires a vacuum of about 6 lbs. to
bring the pistons down and the table up, the balance being such that it
requires a pressure of 4 lbs. to bring the empty table down.
The engine
to work this lift is precisely similar to that for the furnace lift, but is
worked at a much slower speed. The height to which the trucks are
lifted is 35 fect, and with four furnaces it will be required to lift at least
6,000 tons per week, including the weight of the trucks.
IRON.
239

H
10000000000
d
W.J.NELCH.SC
Fig. 78.-Kiln Hoist, Ayresome Iron-Works; front elevation, partly section.
240
ELEMENTS OF METALLURGY.

b
ODO
J.WELCHES
Fig. 79.-Kiln Hoist, Ayresome Iron-Works; side elevation.
IRON.
241
An empty waggon drop is also employed at the Ayresome works,
which acts on the pneumatic principle, and is constructed similarly to
the lift, with this difference, that the cylinders are only 36 inches in
diameter, and the ropes, table, &c., lighter. Instead of the lift-pistons
having a space beneath them, and being connected with an engine, a
bottom is put into each cylinder on which the pistons come down. Close
above this bottom, on each cylinder, are valves, one set communicating
with the atmosphere, and the other through a pipe with the general blast
main, both sets being actuated by handles on the top of the depôts. The
table being at the top and pistons at the bottom, and both sets of valves
being closed, the empty truck is run on; the balance of the pistons being
such that the table, with truck on, is somewhat heaviest. As long as the
valves at the bottom are shut, however, the table cannot raise the pistons,
as immediately they move a partial vacuum is formed below them; the
moment, however, the valve communicating with the atmosphere is opened,
the extra weight of the table pulls the pistons up, drawing air after them
through the valves. This constitutes an air-brake, and is entirely under
control; the descent can be stopped at any time by shutting the valves,
and the speed of the descent regulated at pleasure. On the table arriving
at the bottom the truck is run off, but, before doing so, the attendant
changes the handles at the top-that is, shuts the valves to the atmo-
sphere, and opens the set communicating with the blast-tubing, thus
increasing the pressure under the pistons to 4 lbs. This is for the pur-
pose of supporting the heavy pistons when the truck is run off; but it
also has an ulterior object, as the balanced weight of the pistons is such
that they will descend against the 4 lbs. pressure, thus forcing the two
cylinders full of air into the blast-tubing. It will thus be seen that for
every empty truck which descends this drop a certain amount of air is
forced into the blast-main. Direct-acting steam hoists are also frequently
employed in the North of England for lifting trucks to the depôts or
kilns, but space does not admit of their description.
SMELTING.
Fuel used in the Blast-Furnace. The fuel used in the blast-furnace is
usually either charcoal or coke, but both raw coal and anthracite are like-
wise extensively employed; turf and wood are also sometimes made use of,
but principally as a mixture with charcoal. Owing to its freedom from
sulphur and other impurities, charcoal yields pig-iron of superior quality,
but the immense consumption of wood entailed renders the manufacture
of charcoal-iron in thickly-populated districts impossible.
The average yield per acre of the best-timbered lands in America is
about sixty cords, a quantity sufficient to produce about twenty tons of
pig-iron, or to supply one of the charcoal furnaces of the Lake Superior
region with fuel for a single day. It is, consequently, evident that, as the
daily supply of one furnace necessitates the clearing of an acre of forest
land, a charcoal smelting-establishment can only be permanently carried
on in a densely-wooded country, either on the sea-board or within reach
R
242
ELEMENTS OF METALLURGY.
of navigable rivers. It is believed that at the present time there are at
most but two charcoal furnaces in blast in this country, and the charcoal
furnaces of Belgium are now reduced to the same number. Much more
iron is also produced in France and Germany by the use of coke than in
charcoal furnaces.
The value of coke as fuel for the blast-furnace is much influenced by
the amount of ash it contains, as well as by its hardness or power of
resisting pressure; the hardest varieties of coke, containing the smallest
percentage of ash, are those best suited for the purpose of the iron-
manufacturer.
When raw coal is employed in the blast-furnace, non-caking varieties,
containing but a small proportion of ash, are selected; since a caking coal
would, if thus used, be liable to form lumps by which the regular working
of the apparatus would become seriously deranged.
Owing to its density and purity, anthracite yields pig-iron of good
quality, but in order to obtain satisfactory results with this fuel, a hot-
blast at a high pressure must be employed. If used in furnaces of the
ordinary construction, its difficulty of combustion would cause a slow
descent of the charges, and a consequent small production of metal. This
difficulty is overcome by enlarging the area of the furnace and admitting
a large quantity of hot-blast equally distributed around its circumference,
by means of numerous tuyers; in some cases as many as sixteen tuyers
have been employed in furnaces working on anthracite.
The un-
desirable property of decrepitating possessed by some varieties of an-
thracite is chiefly characteristic of lamellar varieties; the anthracite of
South Wales, which has a somewhat granular fracture, does not generally
splinter in the fire. Pennsylvania, Scotland, and South Wales are the
principal localities in which anthracite is employed for the production
of pig-iron.
Turf has the disadvantage of being bulky, and, in addition to a large
percentage of ash, contains notable quantities of sulphur; compressed or
artificially-dried turf has sometimes been employed, but its preparation
is expensive, and the results afforded not generally satisfactory. Turf is
usually employed in admixture with charcoal. At Ransko, Bohemia,
where the largest proportion is employed, the mixture used consists
of 70 per cent. of dried turf and 30 per cent. of charcoal.
Air-dried wood may be added to charcoal in the proportion of about
one-third, and artificially-dried wood to the extent of one-half. The
carbonisation of wood or turf in the blast-furnace is liable to cause an
increase of temperature in the upper parts of the stack, and to cause
irregularities in the working; wood must be employed in small pieces,
and consequently its use involves a considerable amount of labour.
The weight of air thrown into a blast-furnace in full work much
exceeds the total weight of all the solid materials employed. A furnace
of a capacity of 7,500 cubic feet, when working on foundry-iron, requires
5,400 feet of air per minute, or about 1,700 tons weekly; when working
on white-iron the same furnace will require about 2,400 tons of blast per
week.
IRON.
243
Blowing-in.-The blowing-in of a blast-furnace is an operation neces-
sitating considerable care, since if too hastily effected great injury to the
masonry would result. When a furnace has been made ready for
blowing-in by building up the tuyer-holes, &c., a quantity of rough
dry timber is placed in the hearth, filling it to the height of from 5 to
6 feet; on this is piled coke until it reaches and fills the boshes. Fire
is now applied to the timber, which quickly communicates it to the coke
above, and regular charges of calcined ironstone, limestone, and coke are
added until the materials reach the throat of the furnace. The relative
amounts of ironstone, limestone, and coke employed vary in different
localities; but in the neighbourhood of Merthyr Tydvil, in South Wales,
they are, according to Truran, often in the proportions of 5 cwts. calcined
ironstone, 12 cwt. limestone, and 4 cwts. of coke.
The furnace having been in this way gradually filled to the throat,
the blast is turned on to the extent of about one-fifth of the volume
usually employed. For a furnace intended to be blown with 4-inch
nozzles the first set should have a diameter of 13 inch; after blowing
about thirty hours, these may be replaced by others 23 inches in diameter;
and at the expiration of three days, these may be exchanged for 31-inch
pipes. By the close of the third week the size may be increased to
33 inches, and in four or five weeks after blowing-in, full-sized pipes
may be used.
Shortly after the admission of the blast, the workmen commence
clearing the hearth below the tuyers for the reception of slags, which
begin to make their appearance about twelve hours after beginning to
blow. In twenty-four hours these will have filled the bottom of the
hearth.
The metal, which usually makes its appearance about twelve hours
after the cinders, will, in a furnace of a capacity of 7,500 cubic feet,
accumulate to the amount of from 3 to 4 tons at the expiration of
sixty hours after the admission of the blast. Eighteen hours later,
another casting of 2 tons of metal may be made, and thenceforward the
castings may be performed at the usual fixed periods. The old method
of supporting the charges of a furnace on a "scaffold" during the
process of blowing-in is now seldom resorted to.
When this system
is adopted, a grate, of iron bars, is made across the hearth on a
level with the top of the dam-plate, and, as soon as the first charge of
ironstone reaches this point, the bars are withdrawn and the blast
turned on.
The number of workmen employed about a blast-furnace is somewhat
varied in accordance with its size and the locality in which it is situated.
In South Staffordshire there are usually three men to each furnace:
one keeper, one stove-man, and one filler; during the operation of
casting these are assisted by others, such as coke-wheelers, limestone-
breakers, &c.
Descent of Charges.-The respective amounts of ironstone, flux, and
fuel, required for the production of iron of a given quality, having been
determined, it is important that their relative proportions should be
R 2
244
ELEMENTS OF METALLURGY.
maintained unaltered in the consecutive charges by the workmen engaged
in filling, and, for their guidance in this respect, weighing machines are
placed in the various barrow-roads over which the charges are transported.
In the case of charcoal furnaces, the different ores and fluxes are usually
made up in suitable proportions in alternate layers one above the other,
and the mixture obtained by making a vertical section of the heap is
charged into the furnace. In coke furnaces, ore and limestone are often
charged separately, or they may be placed in the charging barrows in
distinct strata.
In order to obtain regularity in the action of a furnace, the column
of descending materials should be uniformly heated by the ascending
current of hot gases. There is, however, in practice, considerable diffi-
culty in attaining this result, since the upward gaseous current follows
the sides of the furnace, whereas the flow in the centre of the mass is
comparatively insignificant. The descent of the solid charges, on the
other hand, takes place under very different conditions, because the frag-
ments of which they are composed are sensibly retarded by friction
against the masonry of the furnace. The central portions are not thus
affected, and, descending more rapidly, they have a tendency to become
less heated than portions of the mixture occupying a position in which
the motion is less gradual, and where a more elevated temperature
prevails.
From this cause the central portions of the successive charges, depo-
sited in the throat of the furnace in approximately parallel layers, over-
take the sides of those which precede them in the series, and thus, at a
certain depth below the mouth, the contents of the furnace become
intimately mixed, a nearly uniform heat being the result.
The distribution of the materials in a furnace is also materially
affected by the arrangements adopted for charging, which may leave the
upper surface of the column either horizontal, as an upright, or an
inverted cone, or as a combination of the two, resulting in a conical heap
with a funnel-shaped depression in its centre. When the upper surface
of the charge assumes the form of a cone, the fragments of ore and fuel
dropped upon it from above take up positions in conformity with their
differences of form and density. A large proportion of the ironstone
will remain where it first falls, while the lighter fuel, which is usually in
larger fragments, rolls down the slope and arranges itself around the
periphery of the base, thus establishing the worst possible combination
of circumstances by allowing a free passage to the gases around the
sides, while a dense core of almost impermeable ore accumulates in the
centre.
When the charges are distributed around the circumference of the
throat, the surface forms a conical cup, the lighter fragments rolling
inwards towards the centre, while the ore accumulates in the vicinity of
the walls. This tendency of the fuel and larger masses of ore to settle
in the middle, forming a central, readily-permeable column, results in a
more equal distribution of the draught over the entire horizontal section,
while the bulk of the ore descends slowly through the region most highly
IRON.
245
heated by the current of ascending gases. These conditions are favour-
able to uniform and economical working, but in the case of furnaces
having wide throats, the central draught may sometimes become so active
as to result in an undue consumption of fuel, and the constant contact
with ironstone is liable to produce an erosive action on the brickwork of
the lining.
Where charging plates are employed, or a conical funnel is made use
of, the surface of the materials will present the form of an annular ridge
sloping towards both the centre and the circumference of the furnace.
This condition of the material is obtained by the use of the ordinary cup
and cone, and is considered the most favourable for the regular working
of the apparatus.
For many of the Swedish charcoal furnaces the charges are weighed
in a large iron scoop provided with a wooden handle, and suspended by
a chain above the throat; by means of this the richer magnetic ores
are distributed in a ring next the walls, while the limestone and poorer
varieties of ironstone are spread uniformly over the other portions of the
column.
Tapping.—The removal of the liquid metal is called tapping, and is
effected by piercing, with a long bar, a plug of sand and clay with which,
during the previous operations, a hole communicating with the bottom
of the hearth has been closed. Before proceeding to tap, the workmen

=
-
Fig. 80.-Sand Bed.
prepare moulds for the reception of the liquid metal, by excavating in
sand a series of parallel trenches connected by channels which traverse
all at right angles and place them in communication with the hole at
the bottom of the hearth, by which the liquid metal is withdrawn. The
blast is now shut off, the fore part of the hearth is opened, and the
plug of refractory material rapidly removed; this allows the melted
iron to flow into the channels communicating with the moulds; here it
246
ELEMENTS OF METALLURGY.
assumes the form of semi-cylindrical bars or pigs, united to one another
by one of larger dimensions, called a sow, and from which they are
easily separated by being broken off at the point of connection.
When the whole has been drawn off, the blast is again admitted into
the furnace, and smelting operations are repeated as above described,
until, from the quantity of metal accumulated, a second tapping becomes
necessary.
By the aid of the accompanying diagram, fig. 80, the process of
casting will be readily understood. The sand bed extends for a con-
siderable distance in front of the furnace, and may be either exposed to
the weather or protected by a roof. It is made to slope gradually from
the furnace, and a series of parallel furrows is prepared, having the shape
of the pigs to be cast, with their longer axes directed towards the tapping-
hole. A sufficient thickness of sand is left between the several furrows
to form barriers, strong enough to resist the pressure of the molten
metal, and the ends of the several moulds in each row communicate with
a transverse channel formed in the sand. All these transverse furrows
are in communication with a long main channel, a, running from the
tapping-hole to the lower end of the sand bed. The lower row of
moulds only is at first filled by means of the furrow, b, and, when they
have become sufficiently full, communication between it and the main
feeding-channel, a, is cut off by driving down a spade at d, and piling
against it a little sand. The other moulds are, in succession, placed in
connection with the feeding-channel, by the removal of a small quantity
of sand, the metal flowing last into those nearest the furnace. The
longitudinal moulds form the pigs, and the transverse feeding channels.
the sows.
Blowing out.-Whenever it becomes necessary to put a furnace out of
blast, for the purpose of repairs or for any other reason, the burden is for
some time reduced, in order that the temperature of the hearth may be
increased, for the purpose of removing obstructions only fusible at a
high heat.
The gas-tubes and other metallic fittings of the throat are next
removed, and, charging having been suspended, the contents of the
furnace are allowed to burn down; the last tapping is made from a point
as low down as possible in the hearth.
The hearth is frequently found to be more or less obstructed by im-
perfectly-agglomerated masses of malleable iron; and detached crystals,
or even lumps, of considerable size, of a copper-coloured substance,
TiCN4, which was formerly supposed to be metallic titanium, are found
adhering to the brickwork.
It sometimes happens that, either through want of material or by some
accident to the machinery, it becomes necessary to suspend the operations
of a furnace during several successive days. This may sometimes be done
by hermetically closing the throat and tuyer-holes with sand or clay; but
should the interruption extend over a period of more than a week, cooling
takes place to such an extent as to cause agglomerations liable to render
the abandonment of the furnace necessary.
IRON.
247
VARIETIES OF PIG-IRON.-Pig-iron may be divided into several
qualities, of which the classification is practically determined by the
appearances presented by freshly-broken surfaces. Metal presenting in
the most marked degree a dark-grey fracture, with large and brilliant
graphitic scales, is known as "No. 1 pig;" while the lighter-coloured and
more finely granular varieties are distinguished by numerals up to No. 4.
When the metal ceases to be grey beyond this point, its quality is no
longer indicated by a numerical scale. Further modifications are known
as “mottled" and "white," the former being sometimes subdivided into
"weak" and "strong" mottled; this classification varies slightly in
different localities.
These numbers, as far as 3, are called foundry-pigs, while those
beyond, which are only suitable for conversion into wrought-iron, are
known as forge-pigs. Two extra classes known as Bessemer, Nos. 1
and 2, are made in Cumberland and Lancashire, and command higher
prices than the same numbers in the ordinary scale.
White cast-iron can, under ordinary circumstances, be more cheaply
produced than grey, as it usually results from a heavy burden and an
active driving of the furnace. It smelts at a lower temperature than
grey-iron, but is less liquid; on cooling it passes through an inter-
mediate pasty condition before setting, and contracts very considerably
on solidification. Grey cast-iron, on the contrary, expands in becoming
solid, and is, from this circumstance and from its more perfect fluidity,
well adapted for all descriptions of foundry work.
Where, as in Sweden, the practice is adopted of casting the metal
in iron moulds, the surface, even when the metal is naturally grey, is
whitened to a considerable depth by rapid cooling. Another class of pig-
iron, obtained under similar conditions, consists of alternate layers of
white, lamellar, and dark-grey metal; in some cases the grey-iron occurs
in the form of stars or patches disseminated through a white matrix.
Metal of this kind is in high repute for forge purposes, as it closely
approximates in composition to a mixture of grey-iron and refined metal,
such as is found most advantageous for the manufacture of wrought-iron.
Common white-iron made with a heavy burden of cinder usually
contains a considerable amount of sulphur and phosphorus, and is much
honeycombed on the upper surface of the pig.
The white pig-iron, produced in New Jersey from the residues.
obtained in the treatment of franklinite for zinc, is exceedingly hard, and
is much used in the manufacture of crushing-rolls, stamp-heads, jaws for
Blake's crushing machines, &c.
The white cast-iron, prepared from spathose ores containing man-
ganese, is known by the name of spiegeleisen; it is extremely hard, and
when broken its surface presents an aggregation of bright lamellar
crystals, frequently tinged with blue, sometimes nearly an inch in length.
It contains a large amount of carbon in chemical combination; man-
ganese is also always present, but its amount may vary considerably
without affecting the crystalline character of the metal.
The following table gives the composition of different varieties of
248
ELEMENTS OF METALLURGY.
ANALYSES OF PIG-IRON.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
pig-iron produced in some of the principal British and foreign iron-
smelting districts:
combined
2.35
1.43
3.17
1.07
2 78
C
3.50
3.27
2.50
5.04
4.770
2.80
2.42
graphitic
2.40
2.02
0.12
3.39
1.99
Si
1.17
0.92
0.37 0.84 0.67
0.16
0.41
1.81
0.820
1.85
0.36
0.71
Mn
5.42
2.02 7.39 0.44
0.37
0.10
7.57
1.08
11.120
traco
S
0.06 0.04 0.11
0.02
0.01
0.04
0.08
0.013
trace
0.14
0.87
trace
Fe
trace 0.04 trace
$8.60 94.08 88.84 94.85
0.19
0.28
0.11
0.16
0.006
0.134
1.66
1.08
1.23
95.70
86.74
93.55
95.27
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
(combined
C
graphitic
Si
Mn
0.602
0.858 0.561 0.83
3.574 1.634 0.78
2.301 1.052 1.52
0.066
0.002 0.113 0.27
0.156 0.16
6.900
2.99
{2.61
0.554)
2.795
2.325
1.150$
{
0.04
3.31
3.10
3.44
0.100 0.97
11.500
1.71
4.414
1.900
2.629 2.16
1.13
1.86
0.27
1.837
0.395
1.838 0.50
0.43
0.50
0.137 0.05
0.05
0.039 0.414 0.250 0.11
0.03
0.071
0.50
0.29
0.099 1.807 1.872 0.63
1.24
0.076
Ti
1.150
Fe
96.484 96.44 81.363
90.584 93.780 91.086 94.56
93.470
:

with charcoal from red and brown hæmatites, by the Acadian Iron Com-
cuarcoal from spathic ore; Rosthorn. 4 and 5, Acadian pig-iron, smelted
1, Grey. 2, Mottled. 3, White; from Lölling, Carinthia, smelted by
IRON.
249
pany, Nova Scotia; Tookey; No. 4, large-grained, and highly graphitic;
No. 5, fine-grained pig-iron. 6, White forge-pig, smelted with charcoal
from magnetite and specular schists, Langshytta, Dalarne; Rinman;
contains traces of copper and calcium. 7, Spiegeleisen, containing
traces of copper; Jordan. 8, Grey Bessemer-pig, smelted with coke from
spathic and brown iron ores, Hochdahl, Siegen; Jordan. 9, Spiegeleisen,
from Germany, locality not known, containing 0.310 per cent. copper;
Tookey. 10, South Wales grey cinder-pig; and 11, South Wales common
white-pig; Noad. 12, Mottled iron, from Königshütte, Hartz, produced
with charcoal and cold-blast; Gurlt. 13, Grey-iron, from Rothehütte,
Hartz, produced by charcoal. 14, Grey-iron, from Hasslinghausen,
Westphalia, coke-smelted; Lürmann. 15, Mottled iron, from same
locality; Lürmann. 16, Spiegeleisen, from franklinite, New Jersey,
U.S.; T. H. Henry. 17, Bowling, No. 1 cold-blast pig; Abel.
18, Ystalyfera; No. 3 hot-blast, argillaceous ores smelted with anthra-
cite; Abel. 19, Grey Bessemer-pig, from Tow Law, Durham, smelted
from decomposed spathic ores with coke; contains traces of copper,
cobalt, and lead; Riley. 20, Made at Bilston from Northampton ore
with coke and hot-blast; described as "exceedingly tender iron";
T. H. Henry. 21, Produced from equal weights of Northamptonshire
ore, roasted tap-cinder and flue-, or mill-furnace cinder; T. H. Henry.
22, No. 3 best mine-pig, Dowlais, made wholly from Welsh mine;
contains traces of cobalt and nickel; Riley. 23, No. 2 foundry-pig,
produced at Middlesbrough-on-Tees from Cleveland ore with coke and
hot-blast; Abel. 24, Titaniferous pig-iron made from hæmatite with a
mixture of 7 per cent. of ilmenite; Riley.
The following elaborate analysis, by Fresenius, of spiegeleisen
produced from the famous spathic ores of Stahlberg, near Müsen, is of
much interest on account of the large number of substances which, in
minute quantities, he appears to have estimated :*—
Fe
Mn
82.860
10.707
•
Ni
0.061
•
•
•
•
•
Co
trace
•
•
•
•
Cu
Al
Ti
Mg
•
0.066
•
•
•
0.077
•
0.006
•
•
0.045
Ca
0.091
•
K
0.063
•
Na
Li
As
trace
tracel
•
0.007
•
•
Sb
P
N
0.004
0.059
·
0.014
•
0.014
Si
C
0.997
4.323
SiO2, in the intermingled slag
O, combined in the bases of the slag
0.475
0.190
100.059
* From a printed circular of the Müsen Company. Date of analysis, 1862.
250
ELEMENTS OF METALLURGY.
Peters has given the following as the average composition of the
spathic ores smelted by the Müsen Company :*____
SiO 2
A1203
Fe2O3
FeO
MnO
CaO
MgO
ZnO
•
•
.*
1.62
•
1.63
2.75
•
52.12
0.83
·
·
1.75
2.29
·
0.01
CO2
35.92
•
2
P₂05
0.54
·
FeS2
0.22
H₂O
0.45
Organic matter
0.39
•
100.55
The power of resistance of cast-iron to strains variously applied
differs in accordance with the quality and composition of the metal;
No. 1 pig is soft and deficient in strength, as compared with lower
qualities made from the same ores, and, consequently, for foundry pur-
poses it is customary to so blend the different kinds of metal as to
obtain a mixture suitable for the casting to be produced. Silicon is
believed to prejudicially affect the strength of cast-iron, and it may be from
the presence of a larger amount of this element in hot-blast metal that
its strength is inferior to that smelted by the cold-blast.
The maximum and minimum limits of strength in British pig-iron,
as deduced from experiments made at the Woolwich Arsenal (1856-59),
are as follow:-
Specific gravity
Minimum.
6.886
Maximum.
7.289
Tensile
strength per square inch
•
Transverse
Torsional
Crushing
""
""
""
""
4.85 tons
1.37
1.74
22.54
""
14.05 tons.
4.47
3.44
""
""
58.42
""
""
""
""
Tensile strength was determined by tearing asunder short columns of
1.3 inch in smallest diameter. Transverse strength was determined by
taking the mean of a number of values derived from breaking bars
22 inches long and 2 inches square. Torsional strength was determined
on round bars 8 inches long between the points at which the twisting
force was applied. The crushing strains were deduced from cylinders
1.3 inch high and 0·6 inch in diameter.
The lowest values were obtained from iron made from sandy brown
ores, and the best from hæmatite and from argillaceous carbonates,
smelted either together or separately with cold-blast.
CAPACITY AND PRODUCTION OF BLAST-FURNACES.-According to the
valuable Mineral Statistics of Mr. Robert Hunt, F.R.S, the total pro-
duction of pig-iron in Great Britain during the year 1872, amounted to
6,741,929 tons, or more than double the make of nineteen years ago,
when the great iron industries of Cleveland and Cumberland were compa-
ratively undeveloped; four times greater than in 1840, and three hundred-
* 'Jahres-Bericht; Wagner,' 1857, p. 5.
IRON.
251
fold the make of the year 1750, when the tanners of Sheffield petitioned
Parliament against the importation of American iron, lest the Yorkshire
furnaces should be extinguished, and, wood being no longer required by
them, a supply of bark for the tan-pits should not be obtainable.
Each of the blast-furnaces of that period produced, on an average,
300 tons of pig-iron annually, while some of the largest of them now
yield above 24,000 tons during the same period. In other words, the
produce of a single modern blast-furnace exceeds by one-third all the
crude iron made in the country one hundred and twenty-five years ago.
The greatly increased production of the modern blast-furnace, as
compared with those of older date, is partly due to its larger size, and
partially also to the proportionately large amount of blast with which it
is now supplied. The time necessary for the complete reduction of the
ore, previously to actual fusion, is dependent on many variable elements,
such as its richness, composition, porosity, and density, the nature of
the fuel, &c. It is therefore necessary, in order to obtain any given
result, with regard to either quality or produce, to ascertain by actual
experiment for each particular furnace the amount of blast, burden of
ore, and admixture of fluxes which should be employed. The more com-
pletely the materials are exposed to the action of the ascending gaseous
current, all other conditions being the same, the shorter will be the
time necessary for reduction, and it is consequently important that, by
the use of suitable charging and gas-collecting apparatus, the flow of
gases through the mass should be rendered, as far as possible, uniform.
The free escape of gases from the top of the furnace must especially be
provided for, and on this account methods based upon their collection
above the surface of the charges are to be preferred to those in which
lateral flues penetrating the walls below the level of the throat are made
use of.
If the pressure of the blast delivered to a furnace be kept con-
stant, while the volume is increased, a tendency to produce white-iron
will be developed. On the other hand, by increasing both pressure and
temperature, especially if the ores be of a refractory character, the pro-
duction of mottled or grey iron is likely to be the result.
Charcoal Furnaces.-The charcoal furnaces, or Blauöfen, of Styria,
consist of two truncated cones united by their bases; the throat is very
narrow, and they differ from other blast-furnaces in being without a fore-
hearth. The metal and slag are allowed to accumulate in the hearth,
whence they are removed by frequent tapping, as many as sixteen casts
being sometimes made in the course of twenty-four hours. The ores
treated are chiefly spathic carbonates, poor in manganese, and more or less
changed, by oxidation and loss of carbonic anhydride, into brown hæmatite.
In order to free the ironstone as completely as possible from sulphur, it is,
after roasting, exposed to the action of the weather for a period of from
two to three years. The ores treated contain from 35 to 55 per cent. of
metal, and the object sought is the production of white-pig for the manu-
facture of bar-iron with a minimum expenditure of charcoal. In order to
attain this end the furnaces are worked with a very heavy burden, care
being taken to counteract the tendency to form obstructions, by intro-
ducing, at regular intervals, charges of fuel without ore. Some of the
252
ELEMENTS OF METALLURGY.
ores treated are so constituted as not to require the addition of fluxes, but
they generally contain so large a proportion of lime as to render a
mixture of siliceous and argillaceous materials necessary.
Von Fischer's furnace, Vordernberg, is one of the smallest in the
world, its total height being 28 feet, its width at the boshes 6 feet, and
its cubic capacity 452 feet. The usual charge of this furnace consists of
223 lbs. roasted ore, 15 lbs. clay, and 4lbs. of the granulated pig-iron
recovered by stamping and washing the slags; to this are added 95 lbs.
charcoal. This furnace is tapped at intervals of ninety minutes, fourteen
charges, including a blank one of fuel without burden, being made
during the same period; the daily production of pig-iron is 74 tons.
Von Fridau's furnace, in the same district, is somewhat larger than
the above; its height is 42 feet, its diameter at the boshes is 7 feet, and
its capacity 1,052 cubic feet. The full charge consists of from 6 cwts. of
roasted ore, to which are added 10 per cent. of clay, and about 10 lbs. of
granulated metal from the slags. Fifteen and half cubic feet of soft, pine-
charcoal, weighing 101 lbs., are employed with each charge, and the
burden of ore is gradually raised from 3 to 6 cwts. per charge, and after-
wards successively diminished in a similar way; a blank charge of fuel
without ore being introduced at each change from an increasing to a de-
creasing burden. The daily production of this furnace varies from 18
to 20 tons, and the tuyers, which incline at an angle of 5°, cause the
hearth, to some extent, to act as a refinery.
Both these furnaces are very actively driven; the first tapping taking
place twelve hours after lighting, the subsequent castings being repeated
at intervals of from one and half to two and half hours.
The consump-
tion of charcoal is about 14 cwts. per ton of pig-iron produced; they are
sometimes worked with cold-, and at others with hot-blast. Although
the ores treated are well adapted for the production of spiegeleisen, the
prevailing high price of fuel prevents its being regularly made, and from
the small proportion of lime contained in the charges, considerable quan-
tities of the oxides of iron and manganese are carried off in the slags.
"self-
The blast-furnaces employed in Sweden are, in many respects, similar
to those of Styria, but they are provided with a small and narrow fore-
hearth. Their capacity is usually inconsiderable, varying from 600 to
2,500 cubic feet. The best varieties of Swedish ores are known as
fluxing," and contain earthy materials in such proportions as to afford
fusible slags without further addition. The ores of Dannemora, Lang-
banshytta, and Langshytta are usually of this description, and contain
from 50 to 60 per cent. of iron. At the last-named locality the charges,
even after the addition of from 3 to 5 per cent. of limestone, sometimes
contain above 60 per cent. of iron. The more siliceous hæmatites and
micaceous ores are mixed with calcareous magnetite, and fluxed with
dolomitic limestone; the average amount of iron in the charges varies
from 35 to about 50 per cent.
The siliceous itabirite of Nora requires an admixture of 25 per cent.
of limestone, and at Taberg, where the ore smelted consists of magnetite
disseminated in an eruptive greenstone, the charges only contain about
20 per cent. of iron. At Dannemora, the blast is heated to from 80° to
IRON.
253
100° C., and throughout Sweden the temperature does not usually exceed
200°. The waste gases are withdrawn through an aperture in the side of
the furnace 12 to 15 feet below the throat, and are employed both for
heating the blast and for the calcination of ores. Cold-blast is used at
Finspong for the production of gun-foundry iron.
The average weekly production of the Swedish furnaces ranges from
30 to 60 tons of pig-iron, but at Langshytta the weekly make is 117 tons,
at Sandviken 104 tons, and at Langbanshytta 75 tons per furnace. Gene-
rally speaking, the works are kept in operation during the winter months
only, when ore and fuel can be readily transported by means of sledges.
The consumption of charcoal varies from 16 to 17 cwts. per ton for
white and mottled pig-iron produced, and from 21 to 22 cwts. per ton for
grey metal suitable for foundry purposes, or the preparation of Bessemer
steel; the poor magnetic ores of Taberg require as much as 50 to
60 cwts. of charcoal to produce a ton of pig-iron.
At the well known iron-works at Finspong, Ostgothland, the pig-iron
intended for making cannon is run directly from the furnace into the
moulds; whereas in other foundries it is usual to re-melt the pig-iron in
reverberatory furnaces. The charge in 1857 was, according to Tunner,
composed as follows:—

Lispunds.* Lispunds. Lbs. Avoirdupois.
Ferola ores.
29.8
Jerna
5.4
42.0
625.80
Petang,,
4.1
Stenbo
2.7
Scrap cast-iron
22.35
Iron-borings
22.35
Limestone
96.85
767.35
Charcoal
•
Tunnas.
9
Imperial bushels.
36
The Ferola ores chiefly consist of granular magnetite and quartz, with
a little oligoclase, hornblende, and iron pyrites; the Jerna ore is a richer
and less-compact magnetite, associated with the same minerals as those
from Ferola; the Petäng ores are similar, but are more finely granular,
and contain a considerable percentage of manganese; the Stenbo ore is a
mixture of magnetite and spathic carbonate of iron. These ores yield
from 48 to 52 per cent. of pig-iron of great strength, but containing a
notable quantity of sulphur; this, instead of impairing the quality of the
metal, is believed to increase its strength.f
* Each of 14.9 lbs. avoirdupois.
† With respect to the influence of sulphur on the quality of iron, Dr. Percy
remarks: "I have particularly interrogated the intelligent managers of iron-works,
from every part of England, as to their opinion concerning the influence of sulphur,
in certain proportions, even on bar-iron, and they have, without exception, expressed
the opinion that it is not unfavourable to strength, however it may interfere with the
finish on the surface of the metal."-'Iron and Steel,' p. 554.
254
ELEMENTS OF METALLURGY.
At Marquette, Lake Superior, the ores smelted are a brown hæma-
tite containing, on an average, 40 per cent. of iron, and a specular schist
yielding 60 per cent. of that metal. These ores are mixed in such pro-
portions as to yield 55 per cent. of pig-iron, and are treated in a furnace
40 feet in height, 11 feet in the boshes, and 4 feet at the throat; the gases
are collected in an annular flue inclosed by an iron cylinder. The blast
is introduced at a temperature of 330° C., and at a pressure of about 2 lbs.
per square inch, through two tuyers, each 33 inches in diameter, on opposite
sides of the hearth. A crystalline limestone is used as flux, to the amount
of about 10 per cent., and the consumption of charcoal is approximately
25 cwts. per ton of pig-iron. The weekly production is from 125 to 130
tons of fine-grained dark-grey pig, suitable either for foundry work or for
the manufacture of Bessemer steel.
At the Wyandotte Iron-Works, near Detroit, the consumption of light-
wood charcoal in a furnace of similar dimensions amounts to only 17 cwts.
per ton of pig-iron made. The charges are composed of 500 lbs. of slaty
ore, 40 lbs. Niagara limestone, and 40 lbs. of forge-cinder; the average
yield of iron is about 65 per cent. The ores in the Lake Superior dis-
trict are not usually roasted, but all the materials constituting the charges
are reduced, by means of Blake's stone-breaker, to the size of ordinary
road-metal.
There are still in Prussia two Royal works in which charcoal is the
fuel employed, namely Malapane and Kreuzburger Hütte, each of which
has one furnace. These are 30 feet in height and 7 feet in diameter at the
boshes; fir-charcoal is chiefly employed as fuel.
At Malapane the ores treated are calcined clay ironstones producing
from 30 to 40 per cent. of metal, and earthy brown iron ores of about the
same produce; there are two tuyers of from 1½ to 17-inch in diameter,
and the weekly produce is from 14 to 15 tons. At Kreuzburger Hütte
there are three tuyers each 19 inch diameter, the pressure of the blast is
from to lb. per square inch, and the temperature from 60° to 90° C.
The weekly produce is slightly in excess of that at Malapane.
Coke Furnaces.—The ores smelted in the Siegen district are princi-
pally spathic carbonates and brown hæmatites; the former contain a con-
siderable quantity of manganese. The spathose ores are, for the most
part, obtained in the immediate neighbourhood, but a considerable portion
of the hæmatite is brought from Nassau and elsewhere. Both white and
grey pig-iron of good quality are produced, as well as spiegeleisen; the
first being employed for the production of steel in the puddling furnace
and open hearth, and the two last in the Bessemer process. The older
furnaces were generally very small and were worked exclusively with
charcoal, but since the establishment of railway communication with the
coal-fields in the Ruhr basin, these have been generally superseded by fur-
naces of larger capacity, in which coke and the hot-blast are employed.
This has resulted in greater regularity both in the quantity and qua-
lity of the metal produced, in addition to which the high temperature in
the region of the hearth, resulting from the hot-blast, is found to increase
the quantity of manganese reduced.
The state of oxidation in which manganese exists in the ore also exer-
IRON.
255
cises considerable influence on the amount of that metal contained in the
pig-iron made; when spathose ores are employed, the resulting pig-metal
is more highly manganiferous than when hæmatites containing manganese
are made use of.
At Charlottenhütte the charges for spiegeleisen have the following
composition:-
Roasted spathic ores
Raw brown hæmatite
limestone
Total
Coke
Cwts.
28.8)
7.2 yielding 44 to 45 per cent. of pig-iron.
•
•
•
9.0
45.0
20.0
The coke contains 8 per cent. of ash; number of charges daily, 36;
produce, 30 tons; consumption of coke per ton of metal, 22 to 23 cwts. ;
number of tuyers, 3; back 3 inches, sides 33 inches, diameter; tempera-
ture of blast, 280° to 300° C.; pressure, 33 lbs. per square inch.
In the Müsen district, spiegeleisen was formerly produced from the
Stahlberg spathic ores without the addition of flux, but since it has been
customary to add a certain amount of limestone the percentage of man-
ganese in the pig-iron has been much larger than previously. At the
Charlottenhütte the pig-iron produced usually contains 8 per cent. of
manganese, but this is reduced to one-half when the blast is allowed to
fall from 300° to 100° C.
The ores employed in South Staffordshire are partly clay ironstones
from the coal-measures (“native mine") and partly red and brown hæma-
tites from North Staffordshire, Lancashire, and elsewhere; the make
is chiefly grey-pig for forge purposes. Forge-cinders are extensively
employed in the production of common hot-blast metal; but the best
minc-pig is still made from coke with cold-blast. According to Jones,
this district annually consumes 1,746,500 tons of ironstone, and 150,000
tons of forge- and mill-cinder. The coal of South Staffordshire belongs to
the non-caking class, and is used partly in the raw state and partly coked ;
the coke, which is brittle, contains from 4·2 to 4.6 per cent. of ash, and
from 0.3 to 0.5 per cent. of sulphur. The pressure of blast varies from
21 to 3 lbs. per square inch, and the temperature from 300° to 330° C.; a
small number of furnaces are worked with cold-blast.
The flux is principally Silurian and Carboniferous Limestone; the
average consumption of coal per ton of metal made is, in hot-blast fur-
naces, 55 to 60 cwts., and for cold-blast from 60 to 70 cwts., or, rather, its
equivalent in coke. In addition to this, 2 cwts. of coal are necessary for the
calcination of the ores, and from 15 to 22 cwts. are required in the hot-
blast stoves, as the waste gases escaping from the throat of the furnace
are but seldom utilised in the district. The produce of the furnace is
from 120 to 150 tons weekly, although some of the largest yield from
180 to 250 tons of metal per week.
The furnaces of the Cleveland district, which are remarkable for their
large dimensions, are worked entirely with the hard compact coke from
South Durham, containing from 4 to 10 per cent. of ash, and from 4 to 1
per cent. of sulphur. The ores treated are principally the argillaceous
256
ELEMENTS OF METALLURGY.
carbonates of the district, to which a little red hæmatite is sometimes
added.
The ironstone chiefly smelted in Cleveland is the argillaceous ore
from the Lias, containing, in a dry state, from 33 to 40 per cent. of prot-
oxide, and from 2 to 7 per cent. of peroxide of iron; equal to from 26
to 33 per cent. of metallic iron. By calcination this is increased to 37 or
40 per cent. of metal.
The flux is either raw or burnt limestone, derived chiefly from the
Pennine range, and containing, in its raw state, from 87 to 96 per cent.
of calcium carbonate.
In order to produce a ton of grey foundry-pig from Cleveland iron-
stone, without admixture of foreign ores or of mill-cinder, from 19 to 28
cwts. of coke, and from 10 to 14 cwts. of limestone are required; the
amounts in each case varying in accordance with the quality of the ore
and fuel, and the regularity of the working of the furnace, &c.
In one of the furnaces at Newport, near Middlesborough, described
by Mr. B. Samuelson in his paper read before the Institution of Civil
Engineers, the average consumption of fuel, excluding the six weeks
immediately after blowing-in, was 20.35 cwts. per ton of iron produced;
the minimum quantity used in any one week 18.78 cwts., and the
maximum quantity 22.12 cwts. per ton of iron. The average quantity
of calcined ironstone used was 46.11 cwts. per ton of iron, the minimum
quantity used in any one week 44.16 cwts., and the maximum quantity
48·04 cwts. per ton of iron. The average quantity of limestone em-
ployed was 10-71 cwts., the minimum quantity in any one week
10.35 cwts., and the maximum quantity 11.26 cwts. per ton of iron
made. The average weekly production of pig-iron was 430 tons, and the
maximum 466 tons, but the produce per furnace has been since increased
to from 490 to 500 tons. This furnace is 85 feet in height, 25 feet in
diameter at the boshes, and has a capacity of 30,000 cubic feet; the con-
sumption of fuel and flux, in proportion to the production, is about
15 per cent. less than that in four other furnaces erected in 1863-4, of
which the internal capacity is only 16,000 cubic feet. Three furnaces
erected by Mr. Samuelson at South Bank, in Cleveland, in 1854, have
each a capacity of 5,079 cubic feet, and consume from 32 to 40 cwts. of
coke, and from 14 to 15 cwts. of limestone to the ton of iron; the weekly
production varying from 120 to 160 tons.
The quantity of coal used in the calcining kilns varies from 3·50 to
3.94 cwts. per ton of iron. The number of men employed about the two
furnaces in twenty-four hours, exclusive of platelayers and mechanics for
repairs, but including enginemen for removing the slag, is seventy-seven;
fifty-two in the daytime and twenty-four at night; being one man for
every 11 tons of materials of every kind, including slag, transported, or
one man for every 111 ton of pig-iron produced.
At the Ayresome Iron-Works, in the same district, the property of
Messrs. Gjers, Mills & Co., the weekly make of each furnace is about
400 tons of pig-iron; each ton of metal is produced with an expenditure
of an equal weight of coke, and the blast used is about 6,600 cubic fect
per minute.
IRON.
257
GENERAL LIBRAS
University c.
MICHIGAN
The most productive furnaces, as regards their weekly make of pig-
iron, are those treating the rich hæmatites of Lancashire and Cumber-
land. In the Barrow district, furnaces 56 feet in height and 16 feet
diameter at the boshes, with a cubic capacity of 9,500 feet, required,
according to Jordan (1864), the following materials for the production of
one ton of pig-iron :-

Cwts. Cats.
34 to 34
18
181
·
Red hæmatite, unroasted
Coke from Durham
Limestone
Slack for stoves
53
The gases are generally collected and are exclusively employed in firing
steam-boilers. About 7,000 cubic feet of blast, heated to 350° C., are
supplied per minute through six 3-inch tuyers, at a pressure of 2 lbs. per
square inch. Under these conditions, the maximum production appears
to be at the rate of about 630 tons weekly, but the average produce does
not exceed 575 tons.
The same ores are treated under nearly similar conditions at Kirkless
Hall, near Wigan. The largest furnaces are 80 feet in height and
24 feet in diameter at the boshes, with a cubic capacity of 23,423 feet;
the temperature of the blast is about 480° C., and the pressure from
3 to 4 lbs. per square inch. The composition of the charges and the
weekly produce vary in accordance with the quality of the iron to be made.
We are indebted to Mr. J. Thorburn, Jun., the manager of the Ditton
Brook Iron-Works, near Widnes, Lancashire, for the following par-
ticulars relative to the working of the new furnace, figs. 53 and 54:
weekly produce of pig-iron 300 tons, with a consumption of 26 cwts. of
Lancashire coke per ton of metal; blast, 7,760 cubic feet per minute, at
a temperature of 425° C. and pressure of 4 lbs. per square inch.
The charge contains, on an average, 50 per cent. of metal, and is made
up as follows:
Red hæmatite
Irish ore
•
•
Spanish ore, Bilbao
Staffordshire Red Mine
Purple ore
·
2 parts.
1 part.
1
2 parts.
1 part.
The purple ore is obtained from various works in the neighbourhood at
which copper is extracted by the wet process from burnt Spanish pyrites;
it contains, on an average, 67 per cent. of metallic iron.
Coal in the Blast-Furnace.-The staple produce of South Wales is
white forge-pig, of which a large proportion is converted into rails in
the various local forges; the higher qualities of metal are employed in
the tin-plate works, and a few furnaces working on cold-blast produce
grey pig-iron for foundry use.
The principal ores employed in the Welsh blast-furnaces are "native
mine," chiefly argillaceous carbonates with some blackband; brown
hæmatites from Llantrissant, Forest of Dean, Cornwall, Northampton-
shire, and Spain; red hæmatite from Cumberland, with occasionally a
little from the island of Elba, and spathic carbonates from Somersetshire.
S
258
ELEMENTS OF METALLURGY.
In the eastern district the fuel employed is partly coal and partly
coke, the latter being now exclusively used in the furnaces working on
cold-blast. In the neighbourhood of Swansea a small number of furnaces
are worked with anthracite. Forge- and mill-cinders are largely used in
the production of white forge-pig.
According to Truran, some fifteen years ago, the foundry-iron furnace
at the Dowlais works had a capacity of about 7,500 cubic feet, and was
blown with a blast of 5,390 cubic feet of air per minute. For every
20 cwts. of crude iron obtained, 48 cwts. of calcined ore, 50 cwts. of coal,
and 17 cwts. of limestone were required. The weekly production of iron
was about 130 tons.
The consumption of materials per week was as follows:-Calcined
ore, 312 tons; coal, 325 tons; limestone, 110 tons; air supplied weekly
by the tuyers, 1,695 tons.
For the production of white-iron for the forge, in furnaces of similar
capacity to the foregoing, a larger amount of blast with a different burden
was employed.
The consumption of solid materials to a ton of crude iron averaged
28 cwts. calcined argillaceous ore, 10 cwts. hæmatite, 10 cwts. forge- or
refinery-cinder, 42 cwts. of coal, and 14 cwts. of limestone, with a volume of
7,370 cubic feet of blast per minute; the weekly production of crude iron
was 170 tons. In this case the consumption of solid materials per week
was 884 tons, and the weight of air injected by the blast 2,318 tons.
For the production of iron of inferior quality for the forge, the burden
was composed of the following materials:-Hæmatite, 16 cwts.; refinery-
cinder, 25 cwts.; coal, 36 cwts. ; and limestone, 16 cwts. per ton of crude
iron. The capacity of the furnace and the volume of the blast were the
same as in the last instance. From this furnace a weekly production of
190 tons of crude iron was sometimes obtained, the consumption of
solid materials being 883 tons. The estimated time of the descent of
a charge was from forty to forty six hours.
At the same works, in 1863, the consumption of coal per ton of mine-
pig, from variable mixtures of argillaceous ore and brown and red hæma-
tite, had been reduced to from 23 to 27 cwts.; the make of the furnace
ranging from 172 to 280 tons per week. The larger production, in
relation to the amount of fuel consumed, chiefly resulted from the greater
richness of the charge from the larger amount of red ore used.
The newer furnaces are considerably larger than those formerly
employed, and, when working on white-iron, their production ranges from
250 to 300 tons weekly. The use of the cup-and-cone charger is now
very general, the waste gases are economised, and hot-blast is employed.
The Scotch furnaces each produce, on an average, about 160 tons of
pig-iron weekly ; but in the Llackband districts it is said to be sometimes
as high as 270 tons.
In the State of Indiana the red and specular hæmatites from Lake
Superior, Iron Mountain, and Pilot Knob are smelted with a free-burn-
ing, non-caking splint coal, locally known as block coal, which is used in
its raw state. The furnaces are from 50 to 60 fect in height, 16 feet in
diameter at the boshes, and from 5 to 6 feet in width at the hearth.
IRON.
259
The blast of one of these furnaces at Brazil, near Indianapolis, is
heated by the waste gases to a temperature of from 370° to 450° C., and
is delivered through seven tuyers, each 31 inches in diameter, at a pres-
sure of from 3 to 4 lbs. per square inch. The usual daily consumption
of coal is 70 tons, of ore 45 tons, and of limestone 16 tons; the average
production of pig-iron is 28 tons, or 196 tons per week. It therefore
follows that the consumption of coal is about 21 tons per ton of pig-iron
produced, or, reducing it to its equivalent in coke, about 1½ tons.
A coal, in order to admit of advantageous application, in the raw
state, to iron-smelting, should be non-caking, and as free as possible from
sulphur; hot-blast, at a high pressure, is found advantageous, and the
furnace should be somewhat wide at the throat.
Anthracite Furnaces.--Anthracite is employed for the production of
pig-iron chiefly in South Wales, Scotland, and in the United States of
America.
Anthracite is liable to decrepitate when strongly heated, and some
varieties, when suddenly exposed to a high temperature, become reduced
to a state of absolute dust. In furnaces, in which anthracite is the fuel
made use of, the accumulation of these small particles sometimes be-
comes so great as to materially obstruct the passage of the blast. When
this takes place it is usual to cease charging and to continue the blast,
when, as the solid materials descend, the fine particles of anthracite are
blown away. A greater difficulty, however, experienced in the use of
anthracite, arises from the running together of the slag and decrepitated
particles of fuel into infusible masses which are liable to cause the
furnace to become obstructed.
In the year 1863 the anthracite furnaces at Yniscedwin, South Wales,
were from 25 to 30 feet only in height, since a low shaft is less liable
than a high one to become obstructed by the small particles of fuel
resulting from decrepitation.
Other anthracite furnaces in the same district were from 36 to 40 feet
in height, and were blown at a pressure of from 4 to 6 lbs. per square
inch, with air heated to from 320° to 550° C. The consumption of air
amounted to 6,000 cubic feet per minute, the weekly production was 80
tons, and the consumption of anthracite 23 tons for each ton of pig-iron.
The anthracite furnaces of Pennsylvania are worked with a large
number of tuyers and with a pressure of blast varying from 6 to 7½ lbs.
per square inch.
The ores treated are usually massive magnetites and
hæmatites, containing from 50 to 60 per cent. of iron.
At the Lehigh furnace the charges and produce are as follow:—
Ore, 424 cwts.; limestone, 291 cwts.; anthracite, 393 cwts.; weekly make,
248 tons. The Lackawanna furnace is charged with 381 cwts. of ore,
14 cwts. of limestone, and 33 cwts. anthracite; produce, 268 tons of
pig-iron per week.
Spiegeleisen is made at Newark, in New Jersey, from residues obtained
in the treatment of a mixture of red zinc ore, franklinite, and willemite,
for the production of zinc oxide to be employed as a pigment. The residue
from the furnaces in which the volatilisation of zinc is effected is a black
$ 2
260
ELEMENTS OF METALLURGY.
cindery mass, containing the whole of the iron and manganese of the frank-
linite, and the silica of the willemite, together with some oxide of zinc ;
it is estimated to contain about 25 per cent. of iron, and is smelted with
anthracite in furnaces of small dimensions. Their height is usually only
20 feet, and their diameter at the boshes 7 feet; the blast is introduced at
a temperature of 200° C., and with a pressure of 4 lbs. per square inch;
limestone is employed as flux, and the weekly make is about 25 tons.
The waste gases are consumed in stoves for heating the blast, but before
they can be thus employed the oxide of zinc, resulting from the oxidation
of that metal still retained by the residues, and volatilised in the furnace,
requires to be separated by means of a system of wrought-iron condensers.
This oxide is from time to time removed, and not being sufficiently pure
to admit of being employed as paint, is sent to spelter furnaces for reduc-
tion. The consumption of fuel is at the rate of 3 tons per ton of pig-
iron produced.
Cost of Blast-Furnaces.
In order to afford a just idea of the expense of erecting large blast-
furnaces, with the various necessary appliances, it may be useful to give a
summary of the cost of two furnaces, each of the capacity of 30,000 cubic
feet, erected, in 1870, by Messrs. B. Samuelson & Co., at Newport, near
Middlesborough. The cost of railways would have been greater, by about
£2,500, if the ways, previously laid down to four other furnaces, had not
been made partially available; the time occupied in construction was
fifteen months. It will be observed that the account does not include
interest on capital, and that there is no charge for land; it must also be
remembered that the price of labour and of materials has considerably
risen since the date mentioned, and that the erection of a pair of similar
furnaces could not now be accomplished for the same amount.
SUMMARY OF THE COST OF TWO BLAST-FURNACES AND PLANT, COMPLETE, ERECTED
AT THE NEWPORT IRON-WORKS, MIDDLESBOROUGH-ON-TEES, IN 1870.
Two blast-furnaces
Furnace gallery
Furnace hoist
•
Hoist-engine and house.
Kiln gantry.
Kiln drop
Bunkers
Kiln lift
•
•
Five calcining kilns
Eighteen hot-blast stoves
Eight boilers and fittings
Two pairs of blowing engines
Engine house and tank
Cold-blast main
Hot-blast and horse-shoe mains
Gas down-comer and flues
Chimney
Force-pumps, steam- and water-pipes, &c.
Floor-plates and paving
Two locomotives
Eighteen metal-bogies
Carry forward
£ s. d.
10,517 9 2
857 14 10
973 9 11
•
•
1,082 8 8
·
2,351 15 6
794 5 3
•
1,885 16 4
2,234 17 4
4,327 18 4
6,241 1 8
·
5,132 3 9
4,730 8 4
2.469 3 10
579 16 10
1,198 12
1
1,723 10 8
499 8 10
1,991
0 6
580 11 0
1,750 0 0
522 0 0
52,443 12 10
IRON.
261
Brought forward
Thirty slag-bogies
Twenty charging barrows
£ S. d.
52,443 12 10
733 1 7
One platform weighing-machine
Railways, equal to about 1 mile of single line
Total
90 0 0
30 0 0
3,034 9 11
£56,331 4 4
Heat Absorbed for Work Done in Blast-Furnaces.
The chemical phenomena of the blast-furnace, including the laws
governing the reduction of ores, time necessary to effect the various reac-
tions, quantity and constitution of the gases produced, effect of tempera-
ture, physical condition of the charges, &c., have recently been carefully
and laboriously studied by various metallurgists. The very large amount
of matter which has been written on these subjects renders it impossible to
epitomise the conclusions arrived at in such a way as to render them
generally intelligible; but those who may wish to make themselves more
intimately acquainted with the chemistry of the blast-furnace are referred
to the various published papers and treatises on that subject, and more
especially to the elaborate works of C. Schinz and I. L. Bell, before
referred to.
The annexed table is given by Mr. Bell as showing, at one view,
the actual quantity of heat absorbed for the work done in five different
furnaces in the North of England.*

Particulars.
I.
Clarence.
II.
III.
Clarence. Ormesby.
IV.
Consett.
V.
Consett.
Height of furnace, in feet
80
48
76
55
Cubic capacity, in feet
•
11,500
6,000
20,642
9,400
55
10,300
Materials used:-
Coke, per ton of iron, in cwts.
22.32
28.92
22.00
22.75
18.00
Ironstone
48.80
48.80
48.80
41.67
41.67
Limestone
13.66 16.00
12.50
8.25
8.12
Weight of blast per ton of iron, in cwts. 103 74 128.12
88.94
93.13
71.07
Escaping gases
"?
138.66 | 170·59
125.54
127.86 100.05
Temperature of blast in deg. Cent..
485
485
780
""
gases
332
452
454.5
412 477
718
248
""
Heat evolved by oxidation of carbon 81,536 89,288 75,736 75,944 | 63,584
in cwts. heat units
Contributed by blast
11,919 14,721 16,439 10,528 12,081
Total heat generated in furnace, units
Less heat carried off in gases †
93.455 104.012 92,175 86,472 75,665
8,860 16,409
10,213 13,839
Leaving for furnace work
84,595
87,603 81,962
5,095
81,962 72,633 70,570
|
+ Deducted from gases for heat com-
municated by materials, units
Units added to ditto for latent heat of
steam from H2O of coke
2,496
2,496
2,496
1,100
1,100
313
399
308
319
243
*
C
Chemical Phenomena of Iron Smelting,' by I. Lowthian Bell, p. 161. Spon, 1872,
262
ELEMENTS OF METALLURGY.
CONVERSION OF GREY CAST-IRON INTO WHITE.-REFINING.
Whether carbon forms any definite compound with iron is perhaps
open to a certain degree of doubt. Iron appears to have the power of dis-
solving carbon at high temperatures, and on slowly cooling, carbon is
separated in distinct graphitic scales. If this cooling takes place very
slowly, large crystals are formed, and graphite may be readily removed
from their faces by scraping with a knife. On chilling or suddenly cool-
ing grey-iron, the carbon is retained in a more intimate state of combina-
tion or solution, and cannot be thus mechanically separated. Different
opinions arc entertained as to whether this carbon is chemically combined
or whether it is only carbon, in another form than graphite, simply

A
Fig. 81.-Refinery; transverse section.
dissolved in the iron; the term "combined carbon," in contradistinction
to graphitic carbon, is, however, generally admitted.
With regard to silicon, which is always present in every kind of cast-
iron, much remains to be learnt. It is known that carbon exists in three
different states, and also that silicon assumes the graphitic and crystalline
forms of carbon. It appears, therefore, not improbable that silicon may
exist in, at least, two different states in pig-iron and steel.
When grey cast-iron is fused in an oxidising atmosphere, the silicon
present is oxidised, and, becoming silica, unites with a portion of the iron,
IRON.
263
oxidised at the same time, to form a fusible ferrous silicate. If the
metal be now run into moulds and suddenly cooled, a peculiarly white
iron is produced, which is analogous in composition to that smelted from
poor ores at a low temperature, with a heavy burden of material. The
same result may be obtained by throwing water on the surface of a bath
of molten metal and subjecting the thin plates thus obtained to the action
of air at a red-heat during several hours; this method is employed in
various parts of Germany. The more usual process, however, consists in
9
:
b
C
e
B
C
Ъ
9
T
9
Fig. 82.-Refinery; plan.
melting the metal with coke or charcoal in a rectangular hearth, pro-
vided with tuyers more or less inclined, through which air is blown upon
the surface of the fused metal.
In this country the refinery usually consists of a strong cast-iron
framework, supporting a low brickwork chimney, A, figs. 81 and 82,
which represent, respectively, a transverse section and plan of a refinery
used at the Dowlais Iron-Works. The bottom rests upon a floor of
dressed sandstone, a, about 12 inches in thickness, which is supported
upon a foundation of brickwork or masonry. At each side, and at the
back, within the vertical frames, are fixed cast-iron water-blocks, b,
!

264
ELEMENTS OF METALLURGY.
while a dam-plate, c, fig. 82, of the same material, closes the front,
forming a quadrangular cavity about 4 feet square, inside measure, and
15 to 18 inches in depth. Above the side-blocks, and resting on a ledge
cast for their reception, are the tuyer-plates, d, about 2½ inches in thick-
ness, provided with openings for the insertions of the water-tuyers, and
bolted at their ends to the vertical framing. In front, resting on the
dam-plate, it is usual to have a dust-plate, for the convenience of filling
and working the fire. A little above this, in front, and also above the
water-block in the rear, cast-iron doors 23 feet high are hung to the side-
frames.
At a sufficient distance from the floor of the refinery, and a little in
advance of the dam-plate, is placed the casting-bed or pig-mould, B. A
brickwork or cast-iron cistern, about 30 feet long, 4 feet wide, and 2 feet
deep, is laid at right-angles to the axes of the tuyers, and is slightly
inclined from the hearth. On this rests the casting-bed, composed of
thick cast-iron blocks, e, 3 feet square and 6 to 8 inches in thickness,
having flanges on each side by which they are supported on the edges of
the cistern beneath, and a depression in the upper surface to confine the
liquid metal within the desired limits. This cistern is filled to within
an inch of the under surface of the mould-blocks with water, which is
maintained at this level by a small stream which constantly flows in and
escapes by an overflow-notch. The mould-blocks are provided with
rebated joints luted with fire-clay, and are maintained in close contact
with each other by clamps fitting corresponding snugs cast on the sides
of the moulds. They are often made with a rib running down the centre,
dividing the mould longitudinally in two parts, so as to reduce the
labour of breaking up the plate of refined metal.
The blast is usually supplied through two or three small nozzles on
either side of the hearth, each pipe being provided with a stop-valve, g,
for regulating the quantity. The connection between the movable nozzle
and fixed supply-pipe may be made either by means of short leathern
hose fastened at their ends by screw-clamps, or by ball-and-socket joints,
h; the former method is cheaper, but the latter the more durable.
Refineries are also sometimes constructed with a single nozzle at the
back, in which case the framework, water-blocks, moulds, and all the
other parts are made much lighter, and the fire-place is of smaller dimen-
sions. They are often distinguished as melting down and running-in
refineries; cold pigs from the blast-furnace, old castings, scrap, &c., are
melted in the former, while liquid metal is allowed to flow into the latter
directly from the furnace.
The melting-down refinery is usually placed in a building at some
distance from the blast-furnace, while the running-in refinery is, on the
contrary, generally built immediately contiguous to it; this method of
working, which effects a considerable saving of coal, was first introduced
at Dowlais.
The operation of refining crude pig-iron is usually conducted in the
following way. The floor of the hearth is strewed with broken sandstone
and a fire is lit in the centre; a quantity of coke is now added and a light
IRON.
265
blast is directed upon it. A charge of pig-iron, scrap, or broken castings,
is now piled on the coke, a fresh quantity of fuel is heaped upon the
metal, and the full power of the blast is turned on. The weight of
crude iron constituting a charge varies in accordance with the dimensions
of the refinery, but it may, on an average, be taken at 2 tons, requiring
the consumption of 5 cwts. of coke for its conversion into refined metal.
The broken sandstone on the floor fuses and glazes the surface of the
hearth, while, in the course of an hour, the metal begins to melt, and
dropping through the coke, reaches the bottom. In the course of from two
hours to two hours and a half, the whole of the iron has become melted
and lies under the coke, but the blast is still kept up and fresh coke is
added. By this means a portion of the metal becomes oxidised, and
uniting with the siliceous matter contained in the fuel, as also with the
silica resulting from the oxidation of the silicon present in the cast-iron,
forms a fusible vitreous slag. This slag, which is extremely rich in oxide
of iron, exercises a strong decarburising action on the iron on which it
floats; but in order that these changes may be properly effected, the air
from the different tuyers is allowed to play on the surface of the fused
mass for a considerable time after the whole of the iron has been col-
lected at the bottom of the hearth. During this period the fuel is
observed to be continually lifted by the motion caused in the metal by
the escape of the gaseous carbonic oxide produced by the reaction on the
cast-iron of the rich silicates of iron constituting the slag. When the
decarburisation is judged to be sufficiently advanced, the tap-hole is
opened, and the contents of the hearth are allowed to flow into the
mould, where they are cooled by the addition of a large quantity of cold
water, by which treatment the metal is rendered extremely brittle. The
slags are now separated, and the finc-metal broken into pieces convenient
for transport to the puddling furnace, where it is to be freed from the
remainder of its carbon and converted into soft iron.
The working of the refinery is continuous, so that, as soon as one
charge of metal is run out, the hearth is again prepared for the reception
of a fresh supply. The time occupied in refining each charge will
average about three hours; but white-iron does not require to be blown
so long as grey-pig, which frequently requires from three and a half to
four hours before it is sufficiently refined.
With the running-in refinery the case is somewhat different, since the
metal is run into the hearth in a fused state, and the time and fuel con-
sumed in melting the metal in the ordinary refinery are consequently
saved.
When taken directly from the blast-furnace, 22.3 cwts. of common
forge-, or 21·1 cwts. of good grey-pig, are required to produce 1 ton of
finc-metal, and the expenditure of coke is about 2 cwts. In the melting-
down refinery the loss of metal is somewhat greater, and the expenditure
of fuel 20 per cent. larger.
The loss of weight in refining hot-blast iron is usually greater than
that experienced in the treatment of cold-blast pig, and the metal pro-
duced from blackband is especially difficult of treatment, chiefly owing
266
ELEMENTS OF METALLURGY.
to its ready fusibility, which renders long-continued blowing necessary :
this results in an increased waste, 24 cwts. of crude iron being required
to produce 1 ton of fine-metal.
The tuyers are usually from 13 to 13 inch in diameter, and are in-
clined at an angle of about 38°. In the running-in hearth 94,000 cubic
feet of blast are required per ton of metal treated, but in the melting-
down refinery 136,000 feet are necessary for white-pig, and 153,000
cubic feet for grey-iron. The weekly production of a refinery working
on white-iron is from 150 to 160 tons, and with grey from 80 to 100
tons. The operation of refining may be accelerated by the addition of
basic silicates, such as the slags from re-heating furnaces or forge-scale.
The action of the blast is in this case supplemented by the use of the
flux; the carbon of the cast-iron is in part oxidised by the oxygen of a
portion of the oxide of iron, an equivalent amount of iron being at the
same time reduced to the metallic state. Lime may sometimes be advan-
tageously employed for the removal of sulphur, but it has a tendency to
render the slags comparatively infusible, and can therefore be used in
moderate quantities only; the same result is more efficaciously produced
by the presence of manganese.
The usual thickness of the plates of fine-metal is about 3 inches;
when freshly fractured the surface has a silvery-white colour, the lower
part being compact, with a radiated or columnar structure, while the
top is dull and cellular.
Parry's Refinery.-In Parry's method of refining, the fused cast-iron
is run directly from the blast-furnace into the hearth of a reverberatory
furnace, heated in the usual way, and the blowing is effected by jets of
superheated steam. This is admitted at a pressure of from 30 to 40 lbs.
through numerous water-tuyers inclined at an angle of 45°; the apertures
in these are to inch in diameter, the steam being heated to from 300°
to 400° C. by keeping the orifices from 2 to 3 inches only above the sur-
face of the molten metal. When 4 cwts. of cinder are used to the ton of
pig-iron, 20 cwts. of metal may be drawn, the impurities in the pig being
replaced by refined iron reduced from the cinder. A ton of grey-iron
may be refined by steam in the course of half an hour by the use of
seven jets, each 3 inch in diameter. The forge-cinder used contains 66
per cent. of iron, and the run-out cinder only 26 per cent.; it therefore
follows that about 40 per cent. of iron has been reduced and converted
into refined metal.
Dr. Noad, who has had ample opportunities of making himself
thoroughly acquainted with the working of this process at Ebbw Vale,
gives the following as the result of one week's working of the steam
refinery :-
Cwts. qrs. lbs.
Pigs used
Metal made
Loss
Yield*
396 0 15
·
393 3 1
·
2 1 14
20 0 14
*The quantity of ironstone or other material consumed in the manufacture of
1 ton of iron is spoken of among smelters as "the yield" of that material.
IRON.
267
The proportion of puddling cinder used was 3 cwts. per ton of pig.
The following analyses of metal and slag obtained by this process at
the Ebbw Vale works are by Noad:
Pig-iron used.
Refined metal.
C, graphitic
S
Р
2.40
0.30
2.68
0.32
0.22
0.18
0.13
0.09
•
Mn
Slag
0.36
0.24
·
0.68
•
Forge-cinder added.
Cinder run out.
S.
P₂05
1.34
2.06
0.16
0 13
German Refinery.-At the Government iron-works of Gleiwitz and
Königshütte in Silesia, the conversion of grey-iron into white is effected
in a reverberatory furnace heated by gas. The hearth is constructed of
a somewhat loamy sand, set in an iron frame with hollow sides, and the
molten iron is prevented from attacking it by the rapid circulation of
cold air below the fire-bridge and hearth-plate.
The gas-generator, which replaces the fire-place of an ordinary furnace,
is an oblong chamber, 3 feet 9 inches in width and 6 feet 4 inches in depth,
tapering slightly towards the top so as to facilitate the descent of the fuel.
Air, at a pressure of about 4 lbs. per square inch, is introduced through a
chamber a little above the level of the floor, and is conducted to the fuel
by means of two tuyers communicating with the iron air-chest. The gas,
resulting from imperfect combustion of the coal with which the apparatus
is charged, is burnt at the top of the shaft by the aid of a supply of air
introduced through a long narrow slot-like opening, extending across the
entire breadth of the hearth, and having an inclination of about 30°, so as
to throw the flame downwards in a thin sheet over the surface of the
metal. The air-chest, from which this supply is derived, like the other
near the bottom of the generator, communicates by means of a pipe with
the blowing-engine of the establishment, but the supply of air, both to
the generator and to the inflammable gases produced, admits of accurate
regulation by means of valves on the connecting-pipes. The charge, of
which the weight is 2 tons, is run down in about three hours, when a
small quantity of limestone is added, and the blowing proper commences
by means of two side tuyers which are now introduced into opposite sides
of the furnace, through openings provided for that purpose. The duration
of this operation, after the charge has become melted, varies from two
and a half to five hours, according to the quality of the metal required;
in the latter case perfectly white-iron is the result. One per cent. of
limestone is added, and the loss of metal only amounts to about 5 per
268
ELEMENTS OF METALLURGY.
cent., but the change produced is, as in the common refinery, chiefly con-
fined to the elimination of carbon and silicon; sulphur and phosphorus.
when present in the pig-iron appear to be but slightly affected. The
following estimations by Abel give the percentage proportions of these
elements before and after refining:--
Si.
Р
S
•
Pig-iron.
4.66
Refined iron.
0.62
0.56
0.52
·
0.04
0.03
Iron thus refined is highly esteemed for castings required to possess
unusual powers of resistance, and experiments made to ascertain the com-
parative strain borne by the same iron, before and after refining, show
the strength of the latter to be greater by one-half than that of the
former.
A modification of the ordinary refinery process is used in Carinthia,
chiefly for iron intended for the manufacture of steel. Grey or mottled
pig-iron is melted in a hearth lined with brasque, charcoal being em-
ployed as fuel.
The slags are partially removed from the surface of the
fluid iron and oxidising fluxes added; water is then thrown upon the
metal and the chilled crusts taken off. The consumption of charcoal is
about 5 cubic feet per 100 lbs. of refined iron produced.
Heaton's Process.—A process was introduced some years since by Mr.
Heaton, of Langley Mill Iron-Works, which, although intended for the
production of steel, is essentially a modification of refining; instead of a
blast of atmospheric air, the oxidising agent employed is nitrate of sodium.
The converter is a circular cupola inclosed in an iron casing, &c., having
a movable bottom, kept in its place by iron clamps; this bottom is
filled with nitrate of sodium, in the proportion of one-tenth the weight
of the metal treated, and, in some cases, a small quantity of siliceous sand
is added. In order to prevent it from floating to the surface of the
molten metal without undergoing decomposition, this flux must be covered
by a perforated plate of cast-iron, and, when the bottom is thus adjusted,
fused cast-iron is introduced through a charging-hole at top. During the
first five minutes, the action of the nitrate on the oxidisable matter present
is slight, but on the melting of the covering-plate, which usually occurs
after that interval, a violent ebullition takes place and a bright yellow
sodium flame escapes from the top of the chimney. After continuing
for about a minute and a half, this action rapidly subsides; the bottom of
the converter is then detached, and is, with its contents, removed on a truck
placed beneath it for that purpose. The product of this operation, called
"crude steel," is not sufficiently liquid to be run into ingots, and the
contents of the converter are therefore turned out upon the floor and
broken into fragments of convenient size for further treatment.
This consists of sundry re-heatings, squeezings and hammerings; or
the broken fragments may be melted in crucibles in the ordinary way for
the production of cast-steel.
The following analyses of the material operated on, and of the pro-
IRON.
269
ducts obtained by this process, were published by the late Dr. W. A.
Miller, in 1868:-

C
Si, with a little Ti
S
P
As
Mn
Ca
Na
Fe, by difference
1.
2.
3.
2.830
1.800
0.993
2 950
0.266
0.149
0.113
0.018
trace
•
1.455
0.298
0.292
•
0.011
0.039
0.024
•
0.318
0.090
0.088
0.319
0.310
0.144
trace
•
92 293
97.026
98.144
100.000
100.000
100.000
1. Cupola pig. 2. Crude steel. 3. Steel-iron.
It will be observed that the "steel-iron" contains as much carbon as
ordinary strong steel, and that the amount of phosphorus retained is four
times greater than that contained in best Yorkshire iron, and fourteen to
fifteen times as much as in Swedish Bessemer steel. This process, which
does not appear to have been carried out on a manufacturing scale, was
subsequently examined by M. Gruner and by Mr. G. J. Snelus, of
Dowlais. The analyses of the latter chemist, who has had a large experi-
ence in investigations of this nature, show that the most marked effect of
the use of the alkaline nitrate is the almost entire removal of silicon ;
this is probably to a great extent due to the production of silicates of
sodium.
Henderson's Process.-Henderson's method for the production of malle-
able iron and steel from inferior brands of pig is dependent on the action
of titanic oxide on fluor-spar, by which silicon, sulphur, and phosphorus
are said to be almost wholly eliminated.
The first operation consists in the preparation of titaniferous iron by
fusing 1 ton of low-class pig with 7 cwts. of Norwegian titaniferous iron
ore. The metal thus obtained is charged upon a layer of fluor-spar, regu-
larly spread over the bed of a puddling furnace, and when melted, the
silicon and other impurities are supposed to be removed by the action of
fluorine; the operation is completed, without stirring, under a covering of
slag; the only manual labour required being that necessary for balling-
up the finished iron. The following are given by Bauerman as the im-
purities contained in a sample of malleable iron thus produced :-
M
Ti
C
Si
P
S
. 0.022
·
trace
none
0.140
•
0.062
The almost total absence of carbon in a sample said to have been
"good malleable iron" is somewhat remarkable.
A more simple
270
ELEMENTS OF METALLURGY.
modification of this process consists in using a mixture of fluor-spar
and titaniferous ore directly in the puddling furnace.
Sherman proposes to expedite the process of refining by the use of
very small doses of either iodine or iodide of potassium in the puddling
furnace. This has been experimentally tried both in America and in
this country, but the results hitherto obtained do not appear to justify the
conclusion that the process is likely to become of practical utility.
PRODUCTION OF WROUGHT-IRON FROM CAST-IRON IN OPEN FIRES.
The various processes employed for the production of wrought-iron
from cast are either conducted in open hearths, in which the pig-metal is
melted and decarburised before the blast of an inclined tuyer, or the
transformation is effected by puddling, by which the same operation is
performed on the hearth of an ordinary reverberatory furnace. In both
cases the reactions involved are precisely similar; graphitic carbon first
passes into the non-graphitic or combined state, and is subsequently con-
verted into carbonic oxide, either directly by the oxygen of the blast, or
indirectly by the action of oxide of iron dissolved in the slags. In many
instances this oxidising agent is supplied by the pig-iron itself, which
is always to a certain extent oxidised by the air of the blast during the
process of fusion, while in others it is directly added in the form of
hæmatite, forge-scale, finery-cinder, &c.
White cast-iron does not, like grey, pass, when heated, immediately
from the solid to the liquid state, but assumes an intermediate pasty con-
dition favourable to the removal of carbon and silicon by the action of
the air, or by any other oxidising agent. For the Bessemer process, how-
ever, which essentially consists in the removal of carbon by means of a
current of air blown through the metal from below, grey pig-iron is
exclusively used. As the removal of carbon is, in this case, effected by
the action of air alone, the superior fluidity of grey-iron is manifestly
advantageous, since the plasticity of white-iron would be liable to interfere
with the free passage of the blast. It also appears that, at the very high
temperature which prevails in the converter, graphitic or uncombined
carbon is readily consumed. As a first step in the process of making
malleable iron, grey-pig is frequently subjected to a preliminary oxidising
fusion in a refinery, and the resulting fine-metal, thus freed from a large
portion of the carbon and silicon present in the original pig, may either
be run directly into the hearth in which it is to be transformed into
wrought-iron, or it may be cast in moulds or stripped off the surface in
the form of thin discs, after throwing water on the molten metal.
The various methods employed for the production of malleable iron
in open hearths, although, from their antiquity and comparative simplicity,
of much interest, are nevertheless gradually diminishing in importance;
this arises from the rapidly-extending use of the puddling furnace, which
can not only be employed with fuel and materials of lower quality, but
also admits of the more extensive application of machinery in the elabo-
ration of the resulting iron.
IRON.
271
The numerous methods of refining in the open hearth may be classified
under three heads, according to the number of times the metal requires
lifting or breaking-up, from the period when it is first fused until the
bloom has been made ready for placing under the hammer. In accord-
ance with this distinction the method employed is distinguished as a
single, double, or manifold running-down process, or in Germany, where
several small open-hearth establishments are still in operation, as einma-
lige, zweimalige, or mehrmalige Schmelzerei. This distinction is, in a great
measure, due to the number of hearths employed during the operations
requisite for the conversion of pig-iron into malleable metal.
In the first, or single method, employed in Styria, white pig-iron,
nearly approximating in composition to refined metal, is used, and the
elimination of combined carbon is principally effected by the addition of
oxidising agents, without material assistance from the injected blast; the

3
e
W
B
H
Fig. 83.-German Forge; vertical section.
product is a steely-iron from which the excess of carbon is subscquently
removed by subjecting the bloom to successive welding heats. In the
second, or double process, the metal is run into the hearth or bloomery
from a melting-down or running-out fire, and in the last, of which the old
German or Walloon forge may be taken as a type, the three operations of
converting grey-iron into white, lifting, or breaking-up, and the final
balling are performed in the same hearth.
GERMAN OR WALLOON FORGE.-The working of the German forge may
be described, generally, as follows, although the various operations admit
of more or less modification in accordance with circumstances, and the
custom of the district in which the works may be situated.
This operation is carried on in a small open furnace, of which fig. 83
represents a vertical section, and fig. 84 a ground plan: the quadran-
272
ELEMENTS OF METALLURGY.
gular hearth, H, is formed of thick cast-iron plates. The depth of the
hearth is about 10 inches, and its width from 2 feet to 2 feet 4 inches.
The blast is introduced by the tuyer, t, which projects about 4 inches
into the hearth, and is so inclined that its axis may intersect the opposite

A
C
*
Fig. 91.-German Forge; plan.
face, somewhat above the line of its junction with the plate forming the
bottom.
The tuyer is made of sheet-copper, and is of the form represented,
fig. 85. In this are placed the nozzles of two wooden
bellows, B, set in motion by a water-wheel, and
arranged so as to afford a continuous stream of air.
Fig. 85.
The movable lids of these are raised by cams,
c, placed on the axle, A, of the water-wheel, and the
too rapid fall of the vibrating segments is checked by their being attached
to the levers, e, provided with boxes, w, in which are placed weights,
for the purpose of regulating the rapidity of the descent. The cams, c,
are so disposed around the axle of the wheel that the movable half of
one bellows begins to be raised precisely when that of the other is being
released, and in this way a continuous current of air is constantly kept up
in the furnace.
In front of the fire-place is a cast-iron plate, raised on one side to the
level of the hearth, and on the other inclined to that of the refinery floor.
An aperturc, called the chio or floss-hole, passes through the side of the
furnace, and enters the hearth at the bottom; by this aperture the fusible
slags are occasionally run off. Over the furnace is placed a hood, v,
which is made of brickwork, and being provided with a chimney, serves.
to carry off the smoke and gases evolved during the process. To the
sides of this hood are attached plates of sheet-iron, for the purpose of
screening the workmen from the heat to which they would otherwise be
exposed.
In order to understand the working of this furnace we must suppose
that an operation has been terminated, and that the hearth still contains
a considerable quantity of incandescent charcoal.
The workman begins by filling up the hearth with fresh fuel, and
then gradually admits the blast. In the older forges the supply of air is
regulated by limiting the supply of water on the wheel by which the
IRON.
273
bellows are set in motion, but in some of those of more recent construc-
tion blowing cylinders are employed, and in that case the blast is
adjusted by a valve situated near the tuyer.
The iron to be refined is cast either into pigs of from 10 to 15 feet in
length, or into short bars or thin plates. In the first case the bar is
placed on iron rollers, and its extremity introduced into the middle of
the hearth at a height of from 6 to 9 inches above the bottom. When, on
the contrary, the metal to be refined has been cast into smaller masses,
they are piled to the amount of from 2 to 3 cwts. immediately before
the charcoal with which the remainder of the cavity of the furnace is
filled.
After a short time the metal begins to melt, and passing through the
current of air from the tuyer, falls to the bottom of the hearth. This
period of fusion ordinarily lasts from three to three and a half hours, and
during that time advantage is taken of the heat developed to weld toge-
ther and form into bars the metal refined during the preceding operation.
The drops of melted iron, in passing at a high temperature through the
air furnished by the blast, become partially oxidised, and by subsequent
reaction of the basic silicates of iron formed, a considerable portion of
the carbon is consumed.
On arriving at the bottom of the hearth, the iron thus treated has
become to a certain extent decarburised, and forms a pasty mass beneath
the layer of fuel through which it has passed. The slag, which gradually
accumulates in the furnace, is from time to time run off through the
tapping-hole before referred to, care being taken to retain a sufficient
quantity to carry on the process of decarburisation.
The oxidation of the iron is also promoted by bringing the melting
mass immediately before the current of air thrown in by the tuyer. The
slag run off is preserved for use in the succeeding operation.
When the partially-refined bloom has become sufficiently resistant,
the workman, by the aid of a strong bar of iron, rolls it up in the form
of a ball, and raises it on the top of the fuel, which he now thrusts
down into the bottom of the furnace. Fresh charcoal is at the same time
added, and the pressure of the blast so increased that the mass is again
subjected to strongly-oxidising influences, and a second time reaches the
bottom of the hearth, where, from having now lost a considerable portion
of its carbon, it forms a large spongy mass. The detached fragments
are now collected with an iron bar, and united into one mass. Should
any portions appear to be imperfectly refined, they are again brought
into a position to be directly acted on by the blast.
When the mass has become sufficiently coherent the slag is run off,
and the iron is rolled into a large ball, and removed from the furnace by
strong levers, and subjected to the action of a heavy hammer, by which
the spongy matter is consolidated and welded together, whilst the siliceous
slag is at the same time expressed from its pores. During this operation
the hearth is cleaned out, and the larger proportion of the remaining slag
is drawn off; but a certain quantity is nevertheless retained in the furnace
to assist in the decarburisation of the succeeding charge of cast-iron.
T
274
ELEMENTS OF METALLURGY.
Before again proceeding to charge, it is frequently found necessary to
cool the hearth with water, which is made to circulate beneath the bottom
plate.
The richer slags thus removed are not thrown away, but, together
with the scale produced during the hammering of the mass, are employed
in the next operation during the first melting of the pig-iron.
After being removed from the hearth, the bloom is transported to an
anvil, on which it receives the repeated blows of a heavy hammer, set in
motion by a water-wheel, the slag becoming completely expelled, and the
iron consolidated into the form of a lengthened parallelogram.
The hammer-head commonly weighs from 800 to 1,200 lbs., and is
sometimes made of cast-iron, although wrought-iron is also employed, and
in that case it is provided with a face of hardened steel.
The anvil is, in most instances, composed of cast-iron, which, to give
it greater solidity, rests on a heavy mass of the same material, supported
by a large wooden pile firmly fixed in the floor. The wooden beam
which carries the hammer is strengthened by bands of iron, and is sup-
ported by a strong cast-iron ring, provided with trunnions, on which
it turns when the head of the hammer is raised. These trunnions are
supported by iron bearings fixed in wooden supports. Parallel to the
hammer-beam, and at a short distance from it, is situated a horizontal
axle, moved by a water-wheel, and provided with a series of cams, which,
by coming in contact with an iron band, situated at about one-third part
of the distance from the head to the trunnions, forming the centre of
suspension, first lift the hammer, and then allow it to fall with its whole
weight on the anvil beneath it. To accelerate the fall of the hammer
when lifted to its full height it is made to come in contact with a long
piece of elastic wood, which acts as a spring, and, by causing the rapid
descent of the hammer, prevents the falling beam from coming in contact
with the cam which is next in the series. The extreme range of the
hammer, or the height to which it is raised from the anvil at each blow,
varies from 2 feet to 2 feet 6 inches.
When the working of a piece of iron has been completed, the hammer
is propped to the full height of its course by a wooden support, which is
removed as soon as the succeeding bloom has, by means of proper tongs,
been placed on the anvil. At first the water-wheel is made to revolve
very slowly, and consequently a considerable interval occurs between
each blow; but by degrees a more plentiful supply of water is admitted,
and the hammer soon attains its maximum speed, which is continued to
the end of the operation. Whilst the bloom is being worked on the
anvil, it is so turned by the workmen that all its sides successively be-
come exposed to the hammer; and by this means the slag is rapidly
expelled from the spongy metal, which is speedily formed into an elongated
prism, of which the various parts have become firmly welded together.
This is again subdivided, by a cutter, into three or four fragments, which
are placed above the bloom formed in the next operation, and when suffi-
ciently heated are drawn into bars, under a hammer especially adapted
for that purpose. The mass is divided by a kind of knife, placed on it
IRON.
275
whilst under the hammer, which, in its fall, strikes the back of the cutter,
thus causing it to divide the iron.
£
D
D
The hammer used for drawing the divided bloom into bars is, in most
instances, much lighter, and makes a greater number of blows in a given
time, than that employed for expressing the slag from the bloom when it first
comes from the refinery. This hammer, which has much less lift than the
one just described, is represented, figs. 86, 87. In this case, instead of being
raised directly by cams, the motion
is communicated on the other side
of the centre of suspension; the
cam-axle, as in the other hammer,
being turned by a water-wheel.
Fig. 86 represents a front view,
and fig. 87 a sectional-elevation of
this hammer. A, represents the axle
of the water-wheel, on which are
fixed the cams, c: these are fitted
into a cast-iron ring, which is
firmly secured on the shaft by the
wedges, a, made of hard wood.

اليد
F
Fig. 86. Tilt Hammer; front view.
The beam, B, carries the ham-
mer, F, and is received into an iron
ring, C, which is provided with trunnions, working in bearings between
the perpendicular piles, D, and the cross-bars, E, which are strongly bolted
together.
At the extremity of the beam opposite to that which carries the
hammer, is placed an iron plate, p, which is firmly secured by means of

Tel
D
h
B
F
F
IR
F
I
G
H
Fig. 87.-Tilt Hammer; sectional elevation.
the band, d: against this plate the cams, which are turned in the direc-
tion indicated by the arrow, are successively brought to bear, and by their
pressure raise the hammer fixed on the other end of the wooden beam,
which again falls as soon as the cam in contact with the plate, p, has so
far depressed the end of the lever as to allow of its passing round without
further impediment. A spring, R, is placed under the tail of the beam,
instead of immediately above the head. The faces of the hammer, F, and
of the anvil, G, which rests on the pile, H, are inclined at a certain
T 2
276
ELEMENTS OF METALLURGY.
angle with the floor; the guide, I, serves to steady long iron bars when
worked under the hammer.
The weight of each bloom is in most instances between 1 and 2 cwts.,
and 100 lbs. of cast-iron produce about 85 lbs. of bars. For every 100 lbs. of
wrought-iron obtained, 150 lbs. of charcoal are employed. The bellows are
stopped as soon as the bloom is ready to be placed under the hammer, and
the whole operation usually occupies about five hours. The iron manufac-
tured by this method is of excellent quality. Refineries of this description
are sometimes supplied with heated air instead of the ordinary cold-blast,
and attempts have been made to replace the employment of charcoal by
the use of coke; but the iron produced by this means is so much inferior
to that prepared with the usual fuel as to more than compensate for the
advantages derived by the substitution of the cheaper combustible.
The process above described is called by the Germans Klumpfrischen,
or lump-refining, and differs from the Durchbrechfrischen, because in the
latter the bloom, instead of being rounded together in one mass on the
hearth of the furnace, is then separated into several pieces, which are
successively worked under the hammer.
The French call the first process affinage au petit foyer, and the
second, affinage par portions.
A further distinction between the open-hearth processes may be founded
upon the various methods adopted for working the iron, as it loses its
carbon and becomes converted into malleable metal, or, as that transfor-
mation is called in this country, it comes to nature. When of good quality
the whole charge may be lifted together, and worked in a single mass
before the tuyer, whereas with inferior descriptions the particles of iron,
instead of being allowed to coalesce as they form, are divided into several
portions, which, after being separately decarburised, may either be worked
into one ball or forged separately.
Three principal methods of manufacturing iron in the charcoal hearth
are employed in Sweden :-the Walloon, the Franche-Comté, and the Lan-
cashire processes. The first of these is confined to forges producing the
Dannemora steel-iron. The Franche-Comté and Lancashire hearths are-
covered and provided with flues in which the charge of pig-iron is heated,
previously to fusion, and where the blast is raised to a temperature of
100° C. by being passed through a series of cast-iron pipes; the pressure
employed is from 1 lb. to 14 lb. per square inch.
In the first method the bloom, after shingling, is cut into two pieces
and re-heated in the same fire; while in the Lancashire forge, either a
second hearth, or a gas welding furnace is employed for re-heating. In
both cases the weight of bar-iron produced is about 85 per cent. of that
of the pig-metal operated on, and, under the most favourable conditions,
the consumption of charcoal is about one and a half times the weight of
the finished bars made.
IRON FOR TIN-PLATES.-In South Wales a superior description of iron
employed for rolling into the thin sheets, used in the manufacture of tin-
plates, is made in the charcoal hearth. The pig-metal treated is of good
quality, and is smelted either with anthracite or in a coke furnace blown
IRON.
277
with cold-blast. The charge, which consists of from 5 to 6 cwts. of good
Welsh mine, or hæmatite pig, is first melted in a small coke refinery
with two tuyers, and, after the necessary amount of exposure to the
oxidising influences of the blast, is run off, through an inclined gutter,
into two charcoal hearths placed in front, and at a somewhat lower level.
These hearths are made of cast-iron plates, their bottoms being cast
hollow in order that they may be kept cool by the circulation of a current
of cold air; the charge of refined metal is divided equally between them,
and each is blown by a single tuyer. Water-tuyers are made use of both
in the refinery and charcoal hearths, although cold-blast only is employed
in each case.
In the charcoal hearth the metal is frequently broken up
and raised by the aid of an iron bar, the slags being run off two or three
times during each operation, of which the average duration is little more
than an hour. The whole of the charge is worked into a single ball,
which weighs something less than 2 cwts., and is first shingled under a
tilt hammer and then drawn into a long flattened bar of about 2 inches
in thickness. This is partially cut through transversely, and is broken by
the blows of a sledge-hammer into fragments called stamps, each weighing
about 28 lbs. The fracture of the pieces thus broken off is examined,
and such only as present a finely-crystalline and uniform grain are used
in the formation of the pile from which the finished sheet is made.
In the West Riding of Yorkshire the same method of breaking and
selecting the rough bars is employed in those forges which are most noted
for the superiority of the iron they produce.
The re-heating of the stamps is conducted in a special furnace known
as the hollow fire, consisting of a deep rectangular hearth roofed over at
top. This hearth is partially filled with coke, and is supplied with blast
through a single inclined tuyer introduced near the top of the fuel.
The piles, consisting of the fragments detached from the rough bars by
the process above described, are supported upon a staff or flattened bar of
iron, above the top of the fuel, but fully exposed to the action of the flame
from the hearth. A portion of the waste heat is economised by being
used in a chamber in which the piles are exposed to a high temperature
previously to being raised to a welding heat.
PREPARATION OF MALLEABLE IRON BY THE REVERBERATORY PROCESS.
PUDDLING.—The reverberatory process for converting cast into malle-
able iron, introduced by Henry Cort, in 1784, has now almost entirely
superseded every other in all localities in which mineral fuel is mode-
rately abundant. The comparatively recent introduction of gas-furnaces
has, moreover, been the means of its becoming general, even in wooded
districts and in localities where inferior descriptions of fuel only are
available, since not only wood, but also brown coal and peat, may, when
converted into carbonic oxide, be employed as fuel in the puddling
furnace. The reactions which take place during the operation of puddling
are of a similar character to those of the open hearth, as the decarburisa-
tion of pig-iron is effected by the joint action of a current of atmospheric
278
ELEMENTS OF METALLURGY.
air and of oxidising fluxes. In the puddling furnace, however, a current
of air is obtained by the draught of a high chimney instead of by a
blast, and according to the relative importance of the effect produced
by the action of atmospheric air or by oxidising fluxes respectively, the
process is spoken of as the " dry" or "wet" method of puddling. In
the old process of dry puddling the necessary oxygen is chiefly derived
from atmospheric air, while on the contrary, in wet puddling, or pig-

A
.
С
P
તમ
f
(9
Oh
Cla
ᎢᎬᏂ
B
Fig. 88.-Puddling Furnace; side elevation.
boiling, it is, to a very large extent, furnished by the slags and oxide of
iron added. In either case the conversion of grey-pig into white-metal,
by a preliminary fusion, is advantageous, and the operation is thereby
accelerated.
The fire-place of the modern puddling furnace, figs. 88, 89, and 90,
(slightly modified from Percy) is rectangular and divided from the hearth
by a low fire-bridge; the roof, which is a flat arch, has a gradual slope
IRON.
279
towards the flue.
The fire-bars, a, are movable for greater convenience in
removing the clinker, and a powerful draught is obtained by means of a
brick chimney, b, from 30 to 50 feet in height, strengthened by iron ties;
at top this shaft is furnished with a sheet-iron damper, c, opened and shut
by means of a lever and chain, by which the workman can regulate at
will the amount of air passing through the furnace. The outside walls
are inclosed with strong side-plates of cast-iron, united by flanges and

d
C
·
Fig. 89.-Puddling Furnace; section on C. D. (fig. 90).
bolts, and are bound together by wrought-iron tie-rods across the top. By
this means not only is the perfect solidity of the structure insured, but
the entrance of air through rents in the brickwork is entirely prevented.
The bottom of the bed, d, is formed of cast-iron plates united by tenon-
joints, and supported on dwarf pillars of the same metal. The sides of
this bed are variously constructed, according to the method of artificial
cooling adopted, but they are frequently made of hollow iron castings,
through which a current of air circulates for the purpose of protecting
them from the intense heat of the furnace. The hearth, 6 feet in length,
is terminated at either end by a straight wall of fire-brick, that nearest
280
ELEMENTS OF METALLURGY.
the fire-place being called the fire-bridge, and the other, at the opposite
end, the flue-bridge. The brickwork is made to overlap the top of the
side-frame in such a way as to form a recess for the refractory material
(fettling) with which it is lined. The width of the hearth is 3 feet
9 inches at one end, and 2 feet 9 inches at the other.

C
α
d
e
f
Fig. 90.—Puddling Furnace; section on A. B. (fig. 88),
The depth of the fire-place varies with the nature of the fuel employed,
being greatest when the coals used are but slightly bituminous. For
furnaces provided with the ordinary fire-grate, the best fuel is non-
caking coal, containing but a small amount of sulphur, and burning with
a long flame. The grate-area should be between one-half and one-third that
of the bed; or, taking the latter at 20 square feet, the area of the grate will
be from 7 to 8 square feet. The firing-hole, e, which is usually placed
about a foot above the grate, has no door, but is closed by throwing a
shovelful of coal on a projecting ledge cast upon the iron casing, and
piling it against the opening. The flue-of which the sectional area
varies with the nature of the fuel employed, being for bituminous coal
one-fifth that of the grate, and for anthracite only about one-seventh—
slopes gradually towards the stack. In some cases, a second bed is
placed behind the flue-bridge, on which the pig-iron destined for the
succeeding charge is heated by means of the flame which passes over it on
its way to the chimney; in others when, as in gas-furnaces, a blast is used,
the air is heated by first passing through the hollow side-frames of the
hearth, and afterwards through a coil of cast-iron pipes situated between
the furnace and the base of the chimney. The walls of the stack are of
common brick, with an internal lining of fire-brick, and the working
door, f, which is situated on the same side of the furnace as the fire-hole,
consists of a large fire-tile, set in a cast-iron frame, suspended by a chain
to a lever having a counterbalance-weight at the other end. This is
only opened for the purpose of charging, or for removing the puddled
balls, but a small rectangular or arched notch, g, called the stopper-hole,
is cut out of the lower edge for the introduction of the tools used in
stirring or rabbling the charge. The sill of the working door is about
10 inches above the bottom of the bed of the furnace, and below it is a
tap-hole, h, usually kept closed, through which the slag, or tap-cinder, is
IRON.
281
withdrawn from time to time as may be required. Another portion of the
slag overflows the flue-bridge, and runs down the inclined flue to the
bottom of the stack, where it is allowed to accumulate.
The portion of the bed opposite the working door is of a curved
form, and in the ordinary single furnace is only accessible from one side;
but the larger or double furnaces have doors on both sides, so that two
sets of puddlers may work at the same time on a charge, of which the
weight is proportionately increased.
The working bed, or lining, of the puddling furnace was formerly
composed of sand, but substances rich in oxide of iron are now employed,
and these not only materially assist the process, but also, under certain
circumstances, improve the quality of the metal produced. The cast-
iron bottom is usually prepared for use by being covered with a layer of
tap-cinder or hammer-slag, which is heated until it has assumed a pasty
condition and is then worked down and uniformly spread over its
surface; this is covered by a thin layer of fettling composed of nearly
pure oxide of iron. The thickness of the finished coating need not
exceed 1½ inch, and the first charges should consist of scrap-iron, or of
waste blooms and refined metal. Grey-pig should not be puddled alone
before the refractory lining has become sufficiently consolidated to resist
the action of silica resulting from the oxidation of silicon contained in
the metal.
The side-plates of the hearth require to be lined in a similar manner
with some substance rich in oxide of iron; the best materials for this are
the pure oxides of iron, such as hæmatite, magnetite, or roasted spathose
ore, free from earthy matter. Roasted tap-cinder, known technically as
bull-dog, is extensively used, as is also purple ore, or blue lilly, which is
the residue remaining from the treatment of roasted cupreous Spanish
and Portuguese pyrites by the wet process for extracting copper.*
Other materials, such as limestone, are occasionally employed for
fettling, but in selecting materials for this purpose all such as contain a
notable quantity of quartz or sand should be carefully avoided. The pre-
sence of a certain amount of clay is only injurious as diminishing, in
some degree, the durability of the lining. The most desirable material
for fettling is what is known as best tap, which is the cinder from a
re-heating furnace in which piles of wrought-iron are prepared for rolling
* The average composition of this substance is as follows:
Fe2O3
Pb(as sulphate)
Cu
S
P
Ca.
Na
Co, As and Cl
Insoluble residue, &c.
Metallic iron.
•
•
•
96.00
•
0.75
0.20
0.36
•
•
none
•
0.40
•
0.10
traces
2.11
99.92
67·00
282
ELEMENTS OF METALLURGY.
on a cast-iron bottom, known as a cinder-bottom, in contradistinction to
the ordinary brick hearth covered with sand. A furnace fettled wholly
with best tap so affects the quality of the metal produced, that good iron
may be made even from cinder-pig, and from pig of fair quality the
weight of puddle-bar produced is greater than that of the pig-iron
operated upon. Titanic iron ore, or ilmenite, forms a very durable
fettling, but is liable to render the iron cold-short.
The process of refining iron in the old refinery is still carried on in
many works, but has, to a considerable extent, been superseded by pig-
boiling, or puddling the pig metal without previous preparation. The
process of puddling may be described as including four distinct opera-
tions, namely, the melting-down of the charge; its incorporation at a low
heat, with oxidising fluxes; the elimination of carbon by stirring, with
exposure to air at a high temperature; and, finally, the preparation
of balls of spongy metal suitable for squeezing or hammering. Although
susceptible of considerable modification, the following may be considered
as a general outline of the ordinary method of puddling.
As soon as the charge has been introduced into the previously-heated
furnace, the working door is closed, and the joints, if necessary, luted
with clay; the grate is also pricked, fresh fuel added, and the firing-hole
stopped with slack, in order that no air may enter excepting through the
ash-pit. At the expiration of about a quarter of an hour, when the metal
begins to soften, the puddler introduces a bar or rabble through the notch in
the bottom of the working door, and removes any unmelted lumps from the
sides of the furnace to the middle of the hearth. The fire is now increased
during a few minutes, and as soon as the metal has become uniformly
liquid it is briskly stirred, the temperature being at the same time
gradually lowered by partially closing the damper on the top of the
stack, until the surface of the charge has, by the formation of a covering
of slag, become protected from further oxidation, by the direct action of
the air passing through the furnace. The management of the operation
immediately after charging is more or less varied in accordance with the
nature of the metal treated. With grey-iron, which becomes exceedingly
liquid when fused, the fragments may, when the furnace is sufficiently
hot, be distributed equally over the bed; when, however, it is less highly
heated, the pigs of metal are piled near the fire-bridge, and as the
operation proceeds and the heat increases, the unmelted portions are
drawn into the centre, and forced beneath the surface of the fused slag.
When, on the contrary, white or refined iron is operated upon, it is
advantageous to bring the furnace to a high heat before the introduction
of the charge. By this means the metal is made to fuse more rapidly,
and is less subject to oxidation than when the operation is more
prolonged.
In order to obtain the full benefit of the oxidising power of the slags
it is necessary that they should be intimately incorporated with the metal,
and for this purpose the draught is checked, the temperature lowered,
and the charge, while in a pasty state, well stirred. Hammer-slag, or
mill-cinder, is also added for the purpose of rendering the slags more
IRON.
283
basic, and to compensate for the silica resulting from the oxidation of
the silicon of the pig-iron; as soon as the mass has thus become pasty
the reaction of the oxides and silicates of iron upon the carbon of the
metal becomes apparent, and copious blue flames, resulting from the
combustion of carbonic oxide, make their appearance. The damper ist
now opened, and on the temperature becoming higher, the surface
begins to boil from the rapid escape of CO; some of the slag is run
off, and the action is accelerated by stirring with a hooked iron bar or
rabble. At this point the puddler, using the side of the door-frame as a
fulcrum, sweeps every portion of the bed from the centre towards the
bridges, and in order to prevent the tool from becoming too hot and
adhering to the metal, it requires to be frequently changed. On being
taken out of the furnace it is cooled in a cistern or water-bosh, by which
the adhering cinder becomes detached, and the hook at its end is after-
wards hammered into shape. In proportion as the carbon becomes eli-
minated, the violence of the ebullition is diminished, the mass begins to
stiffen, or come to nature," and malleable iron begins to make its
appearance. To prevent a too rapid agglomeration of the charge, the
contents of the furnace are again broken up, and thoroughly mixed by
stirring; any pasty lumps adhering to the sides are detached, and the
mass is subjected to a final heat for the purpose of rendering the cinder
perfectly liquid, and thereby facilitating its separation from the metal.
CC
The last operation consists in forming the metal into balls; this is
done by detaching from the charge masses each weighing from 60 to
80 lbs., and compressing them with the tool until they have acquired
sufficient coherence to admit of being moved without falling to pieces.
This may be effected either by pressure against the bottom and sides
of the furnace, or by so rolling a small nucleus of metal on the hearth
as to collect other fragments which become attached to it by welding.
As soon as a ball has been thus prepared, the workman, by means of a
strong iron tool, places it close to the fire-bridge on the far side of the
furnace, for the purpose of protecting it against the action of the air
entering the working door and passing off by the chimney; the making
of the second ball is then at once proceeded with in like manner, and
when the whole charge has been balled up, the working door and stopper-
hole are closed and the last heat given.
Finally the balls are drawn, one by one, to the working door, lifted
by means of suitable tongs to the iron table in front of it, and afterwards,
either dragged along the floor, or, more frequently, carried on a small
wrought-iron truck to the machine by which the shingling or first com-
pression of the metal is effected.
The old system of dry puddling is only applicable to the treatment
of white or refined metal, and, as before stated, the oxidation of the
carbon is more dependent on the action of atmospheric air than it is in
pig-boiling; the quantity of slag produced is also considerably less. By
this process, as soon as the metal has been melted down and has assumed
a pasty state, it is broken up and kept constantly stirred for the purpose
of incorporating with it the oxide produced during the operation. The
284
ELEMENTS OF METALLURGY.
charge of the furnace is maintained in a partially fused or pasty state,
and the stirring goes on almost continuously from the running-down to
the balling-up. As, however, the use of sand bottoms is attended with
great loss of iron, and the metal produced is of inferior quality, they
have, at the present time, become almost obsolete.
The charge of a puddling furnace is, in Staffordshire, from 4 to
4 cwts., and from five to seven heats are worked off by a puddler and
his assistant during a turn of twelve hours; the difference of weight
between the pig-iron charged and the puddled bars obtained is from
7 to 10 per cent. The coal consumed is about equal in weight to
the puddled bars made, and the fettling materials required, per turn,
are from 6 to 7 cwts. of bull-dog, and 2 to 3 cwts. of puddler's ore, or
blue billy, to which must be added the mill-scale introduced into the
charges. In Scotland, where dark-grey metal, containing a large amount
of silicon, is puddled without being previously refined, from four to five
heats only, each of 4 cwts., are made in twelve hours; in this case the
loss experienced, from pig-iron to puddled bars, is from 15 to 18 per cent.,
and the consumption of coal, per ton of the latter, varies from 25 to
26 cwts. In Cleveland the consumption of small coal is from 24 to 27
cwts. per ton of puddled bars made.
Wrought-iron of very superior quality is manufactured in the West
Riding of Yorkshire from cold-blast refined metal. The furnace em-
ployed is of comparatively small size, and is provided with a very high
stack, for the purpose of insuring a strong draught. The charge, weigh-
ing 3 cwts., is heated to redness before its introduction into the furnace,
and the melting-down is effected in from twenty to twenty-five minutes;
the whole operation occupies about one hour and twenty minutes, and
nine heats are made in the course of twelve hours. Three or four
balls only are obtained from each heat, which, after shingling under a
helve hammer, are made into stamps from 10 to 12 inches square and
2 inches in thickness; these are broken by the fall of a heavy weight,
and subsequently assorted in accordance with the nature of the fracture
which they severally exhibit. Those which are most uniformly crystal-
line are employed for the manufacture of hard bars, while those showing
a distinct fibre are reserved for making into boiler-plates and wire-rods.
The consumption of coal is about 30 cwts. per ton of fine-metal treated.
In Belgium the coal consumed is usually equal in weight to the puddled
bars obtained, and the loss on cast-iron is from 7 to 10 per cent., accord-
ing to the quality of the metal operated on.
Puddling in Gas-Furnaces.-In Carinthia gas puddling furnaces are
employed, the fuel being air-dried wood, which is converted into gas in
a generator having a capacity of about 14 cubic feet; air is introduced
near the bottom at a pressure of half an inch of mercury, and the com-
bustion of the gases is effected by a second blast brought in imme-
diately above the fire-bridge, through an oblong tuyer extending the whole
width of the hearth. This blast is heated to a temperature of 200° C., by
passing through the hollow side-plates of the furnace, and a second bed,
situated between the puddling furnace and the chimney, is used for heat-
IRON.
235
ing-up the metal which is to constitute the next charge. In Styria,
lignite is sometimes employed for puddling, the consumption being from
22 to 24 cwts. per ton of blooms, and the loss of weight on the metal

Т.
C
a
B
A
h
h
Fig. 91. Puddling Furnace, Neustadt; longitudinal section.
from 6 to 10 per cent.
From 200 to 280 cubic feet of wood are required
to produce 1 ton of blooms, and from 240 to 360 cubic feet of turf are
capable of yielding the same result; the consumption does not appear to
differ materially, whether it be consumed on an ordinary grate or con-

f
A
B
g
C
Fig. 92. Puddling Furnace, Neustadt; horizontal section.
verted into gas. The gas puddling furnace employed at Neustadt (Han-
over), in which turf is the fuel used, is represented, figs. 91, 92, of which
the first is a longitudinal section, and the second a horizontal section
above the level of the hearth. The gas-generator, A, is supplied
286
ELEMENTS OF METALLURGY.
with fuel by means of the hopper, a, and at bottom is provided with a set
of fire-bars, b; the air necessary for the conversion of the carbon of the
turf into carbonic oxide gas is supplied from the blast-main of the estab-
lishment, through the tap, c, passing into the ash-pit beneath the bars.
Another portion of the blast enters the cast-iron sides, d, of the hearth
through the pipes, e, whence, after becoming to a certain extent heated,
it passes off by the pipe, f, to the heater, g, which covers the flue of the
furnace. This is made of cast-iron with a sheet-iron top, and has a
number of divisions cast on the lower plate, through which the blast cir-
culates in a zigzag direction. Here the air, which has become heated by
passing through the sides of the hearth, is further elevated in temperature,
and escaping by the pipe, h, is conducted to the inclined tuyer, i, which
is oblong in form and extends completely across the bridge. The bottom
and side-plates of the hearth, B, are shown in the drawing without any
lining, but this requires to be added before the furnace can be used for
puddling; the heated gases escaping from the apparatus are finally utilised
by passing under and around the steam-boiler, C.
Among the various contrivances employed for puddling cast-iron,
Siemens's regenerative gas-furnace is of great importance. The way in
which this principle is applied is shown, figs. 24, 25, 26, which represent
a gas re-heating furnace on this plan. The difference in general form
between a re-heating and a puddling furnace is not very great, and
consequently it will be easy, on consulting drawings of the one, to
understand the application of the system to the other.
Two men, a puddler and his assistant, usually conduct the working of
each furnace; the former does the heaviest portion of the work, including
making up the balls, while the latter attends to the firing, and also does a
portion of the stirring and rabbling.
The tools employed in puddling are of two kinds; namely, long
straight chisel-shaped bars or paddles, and hooked flat-ended bars or
rabbles. When withdrawn from the furnace, the ends of these are
coated with molten cinder, which is removed by quenching in a cistern
of cold water.
Various attempts have been made to puddle iron by machinery, and
the methods proposed for effecting this object may be classified under two
distinct heads: namely, by imitating the motions of hand-stirring by
mechanical appliances, and by using rotatory or oscillatory hearths.
Mechanical Rabbles.-For some time mechanical rabbles have been
attached to puddling furnaces for the purpose of diminishing the heavy
labour of stirring; they are however useless in the laborious operation
of balling, and their adoption has not become general.
In Eastwood's mechanical stirrer, which is one of the simplest machines
of this class, the rabbling tool is suspended in a stirrup at the end of
a bent lever, which receives a reciprocating motion by means of a crank.
The centre of oscillation of this lever is at the extremity of an inclined
jib, to which a lateral motion is imparted by a rod working on a pin
attached to a screw-wheel, driven by a worm on the crank-shaft. Motion
is given to this arrangement by a chain passing over a pulley, and the
IRON.
287
rabble is moved backwards and forwards across the hearth, once in each
revolution, while at the same time its point of suspension is shifted a
short distance by the movement of the jib, caused by the screw-gearing.
In this way a compound motion is communicated to the tool, which
causes it to travel gradually over every portion of the furnace-bottom.
This apparatus is bolted to the casing-plates of the furnace, and the
driving-pulley is connected to the shaft by a fast-and-loose clutch. The
furnaces of Tooth, Menelaus, and Danks, are themselves movable.
Rotative Furnaces.-The first experiment with a rotative furnace
attended with any degree of success, was that of Tooth, who used a
wrought-iron cylinder lined with fire-brick; this was made to revolve
between a fire-place and the flue leading to a chimney; the flames passed
through the cylinder, and the balls, when ready, were withdrawn from
the end. It was found that the brick lining of this machine rapidly wore
away, and that the iron was imperfectly puddled, as the mass obtained
frequently inclosed a central lump of unchanged cast-iron.
Menelaus improved upon Tooth's machine, and the results obtained
O
C
B
m
m

A
m
Fig. 93.-Danks's l'uddling Machine; longitudinal section.
were much more satisfactory. The apparatus employed was in the shape
of an ellipse; the idea being that whereas in Tooth's machine the iron
was simply rolled round, in the elliptical revolver, from the different.
diameters at various parts, the action would be to so break up the iron as
not to form a cylindrical mass like that produced in Tooth's machine ;
thus in turn exposing every portion to the oxidising action of the air and
cinder. This ellipse was movable, and by means of a crane and a pair of
trunnions it was removed from the fire-place, tilted on end, and the lump
of iron turned out, in one mass, upon a bogie, and taken to the hammer.
288
ELEMENTS OF METALLURGY.
The experiments of Menelaus appear to have, practically, failed to give
satisfactory results solely on account of the difficulty experienced in find-
ing a suitable lining; he first tried ganister (a siliceous material used for
lining Bessemer converters), various descriptions of brick, and ilmenite.
Ilmenite was found to stand best, but it was difficult to fix it in the
furnace, and it moreover made the iron cold-short.
Danks's rotative puddling furnace has for some time been successfully
at work in America, and the Iron and Steel Institute not long since sent
out a Commission to examine it, which reported. very favourably upon its
performance. This machine is represented in longitudinal section, fig. 93,
and in end elevation, partly section through the revolving chamber, fig. 94;
fig. 95 is an elevation of the movable end-piece and flue. The revolving
cylindrical chamber, A, is made with wedge-shaped recesses, which act
mechanically in retaining the initial lining in its place. This first lining
may be composed of any iron ore, free from silica, ground with cream of

four
m
d
m
O
M
O
777.
ď
www
Fig. 94.—Danks's Puddling Machine; end elevation, partly section.
lime; this is introduced in the state of mortar, and when dry becomes
a refractory and sufficiently coherent material to allow of the fettling
being melted upon it without either melting itself or breaking away
from the plates. The ore employed for mixing with the lime should, by
preference, be anhydrous, since otherwise the removal of its water of
combination, by the heat to which it is exposed, is liable to cause the
crumbling of the mass.
Upon this foundation a quantity of any ore, free from silica, may be
melted, and for this purpose the hydrated varieties may be employed, as
their combined water is rapidly driven off. Into the bath of melted ore
thus obtained, large solid lumps of the same material are thrown, and
IRON.
289
these, being cold, cause the melted ore to set round them, and by firmly
fixing them in their places a rough internal lining is produced. It is not
only necessary that these lumps should be moderately free from silica,
but also that their texture should be such as to prevent their crumbling
by heat; this was found to be the case with ilmenite. Best tap-cinder
answers this purpose very well, and, when suitable ores cannot be obtained,
oxidised scrap-iron may be substituted with advantage. The Danks furnace
has a closed ash-pit, the necessary air being supplied by a fan-blast
through the pipe, B; jets of air are also introduced over the fuel by means
of the nozzles, c, in connection with the air-main, C; these, which extend
the whole width of the bridge, enable the puddler in charge of the
machine to regulate the draught, and he has thus complete control over
the furnace.
As time is lost, and a considerable amount of fuel is expended in melt-
ing the charge in the revolving furnace, the pig should either be fused in a
cupola or run directly from the blast-furnace in which it is produced. A
jet of water is directed against the lining on the descending side, for the
purpose of chilling a portion of the cinder and causing it to be carried
under the metal. Mr. Snelus-to whose report, in conjunction with the
other Commissioners, to the Iron and Steel Institute, and to Mr. Riley's
paper on Iron and Steel,* we are mainly indebted for information relative
to puddling by machinery-is of opinion that this has also the effect of
carrying off sulphur from the cinder, as in the case of Parry's steam
refinery.
When grey pig-iron is made use of, the boil commences in about ten
minutes, but with white-pig it begins in two or three minutes only after
melting; after tapping off the cinder, the cylinder is set in motion
and the fire urged; the iron now begins to boil violently, and carbon
becomes rapidly oxidised. But little cinder is produced during this
portion of the operation, and the greater part of it is removed with
the ball. An ingenious arrangement, consisting of a movable end-piece,
fig. 95, at the back of the flue, permits the ball to be removed from the
Danks furnace by means of a fork worked by a crane, by which it is
placed on a bogie and carried to a hammer or squeezer. The revolving
cylinder, A, is supported on friction rollers, d, and is set in motion by the
pinion, e, working in the toothed segments, f. G is the firing-hole, and
h the passage for the flame and gases into the cylinder; i is the chimney-
stack, k the stationary flue, I suspension rods with swivels, m water-
pipes, n water-front of movable piece, o supports, p stopper-hole, q tap-
ping-hole. The firing-hole, G, has a coil of wrought-iron pipe cast into
it for the purpose of allowing the circulation of a stream of water to keep
it cool, and the bridge-plate between the fire and the charge of metal,
has also a coil of water-pipe cast into it for the same purpose.
In Danks's machine the puddling is entirely effected by the fettling,
the carbon, silicon, and phosphorus being almost completely oxidised by
it, and by the cinder introduced. The separation of silicon, sulphur, and
phosphorus, by this apparatus, is more perfect than by hand-puddling,
* A lecture delivered before the Chemical Society, May 2, 1872.
U
290
ELEMENTS OF METALLURGY.
and the inventor alleges that the more silicon and phosphorus the pig
contains the better will be the quality of the iron produced. Strange as
this statement may appear, it is confirmed by Riley, who says that the
views of Mr. Danks seem to be borne out by the results of the working
of the machine in this country.
The present machinery in use at iron-works is totally inadequate to
dealing with such masses of metal as the ball from this rotative furnace,
the weight of such a ball being about 650 lbs. To meet these circumstances,
Mr. Danks has applied a most ingenious and efficient squeezer, which

Z
In
p
0
0
n
k
Fig. 95.-Danks's Puddling Machine; eud-piece.
will be described when treating of forge machinery. Iron thus pro-
duced, after being thoroughly squeezed and re-heated, can be rolled
out at once into a rail or large bar, without the operation, now required,
of rolling into puddle-bar, piling, re-heating, and rolling again.
A revolving puddling machine has also been invented by Mr.
Spencer, of the West Hartlepool Iron-Works. His converter is rhom-
boidal in form, having at its two opposite ends axes at right angles to
the extremities or discs. These are made to revolve on rollers by suitable
gearing. The sides are honeycombed to retain the fettling, consisting of
best tap, which is introduced into the recesses, and fresh tap melted over
it. Experiments made with this apparatus have shown that the silicon
and phosphorus are almost completely removed by it from Cleveland
pig-iron, containing above 2 per cent. of the latter element.
FORGE MACHINERY AND OPERATIONS.-That portion of an iron-works
in which puddled blooms or rough bars are produced, including puddling
furnaces, shingling machines, and puddling rolls, is called the forge;
while those portions of the establishment in which rough bars are re-
IRON.
291
heated and transformed into finished or merchant iron, are known as the
mill. This department comprehends the re-heating or balling furnaces,
together with the mills and other appliances employed in the production
of bars, plates, sheets, or other merchantable forms.
Hammers.—The compression of the rough balls of malleable iron
into blooms is effected by the use of either hammers or squeezers, the
former acting by percussion and the latter by compression. In the
puddling forge, the blooms thus obtained are also converted into rough
bars by passing them, at the same heat, through a rolling mill. Ham-
mers of two kinds only were formerly employed in the preparation of
blooms; in the first, or tilt hammer, the axis is placed between the point
where the cam acts upon the shaft and the head, while in lifting hammers,
or helves, the hammer-block and lifting-cam are both on the same side of
the fulcrum. Both are, however, now very generally superseded by the
steam hammer.
Tilt hammers are usually small in size, and are driven at a con-
siderable speed, being used rather in drawing out bars and finishing
work generally, than for shingling blooms. The shaft is made of one or
inore beams of straight-grained timber, which, in the latter case, are
hooped together with wrought-iron rings, and the pivots either pass
through the shaft or are more frequently attached as trunnions to a
strong broad hoop. The head has usually somewhat the form of a
sledge-hammer; the general arrangement of a hammer of this description
is shown, figs. 86, 87, p. 275.
Helve hammers are of two kinds: the nose, or frontal helvc, in which
the cam acts upon a projection immediately in front of the hammer-
block; and the belly helve, which has the cam-shaft below the level of
the floor, and which acts upon it about midway between the fulcrum
and the head. Hammers of this description, such as were formerly in
general use in puddling forges, have been made of all weights up to
10 tons; but the most usual sizes are from 5 to 7 tons, giving from
seventy to seventy-six blows per minute, with a lift of from 16 to 18
inches. In order to avoid injury to the machine, the hammer is never
allowed to fall directly upon its anvil, and, with this object, when not in
use, a stop, or gag, is placed between them. When this has to be
removed, a piece of iron is placed on the tongue, of sufficient thickness
that, on the cam coming in contact with it, the hammer is lifted clear of
the prop, which may then be removed and the machine again brought
into working order. The foundation usually consists of a solid bedding
of wood, containing from 1,000 to 1,500 cubic feet of oak, capped by a
cast-iron bed-plate, weighing from 10 to 12 tons, and measuring about
24 feet by 7 feet. Two standards, a, fig. 96, for carrying the helve, are
fixed on the bed-plate in strong jaws, and a third, b, for carrying the
cam-shaft, c, is secured in the same way. The helve, which is T-shaped
in plan, is about 8 feet in length, 6 feet in width at the centre of
vibration, d, 2 feet in depth, and 12 inches wide in the middle; at the
end furthest from the point of suspension is a recess 18 inches square, on
the lower side, for receiving the hammer-face, e. The anvil-block stands
U 2
292
ELEMENTS OF METALLURGY.
on the bed-plate under the centre of the hammer-face, and has, on its
upper side, a face, f, similar to that of the hammer. The helve is lifted
by a revolving cam-ring, g, about 5 feet in diameter, having four cams or
wipers on its circumference, which, coming in contact with it, raise it,
and passing onwards, allow it to fall upon the bloom resting on the
anvil beneath. The following are the approximate weights of the castings
employed in the construction of a hammer of moderate size: Bed-plate,
11 tons; helve-stand, 3 tons; helve, 53 tons; hammer-face, 15 cwts.;
anvil-block, 5 tons; anvil-face, 16 cwts.; standards under cam-ring
shaft, 2 tons; cam-ring shaft, 7 tons; cam-ring, 4 tons; four cams,
24 cwts.: total, 41½ tons.
The puddled ball having been placed on the anvil, the helve is lifted

C
VI
Fig. 96.-Helve Hammer, Dowlais; from Truran.
off the prop by a boy, who holds a small iron block beneath the tongue,
which, coming in contact with the wiper, the prop is withdrawn and the
hammer descends upon the ball. The helve is lifted by the several
wipers as they pass in succession, and the ball is converted into a bloom
in from eighteen to thirty seconds, during which time it receives from
fifteen to twenty blows.
The working faces of both hammer and anvil are subject to great.
wear and tear, and require to be frequently replaced; they may be ren-
dered more durable by causing a current of water to circulate constantly
through them; but this expedient, introduced by Condie, the inventor of
the water-tuyer, was never generally adopted.
The steam hammer is now generally preferred to the helve for
shingling and balling purposes, and is thus employed in nearly all the
more recently-erected forges. It essentially consists of a vertical high-
pressure engine, with an inverted cylinder, supported by a framing,
often consisting of two heavy cast-iron standards. The piston-rod,
which passes through the lower cover of the cylinder, is directly attached
IRON.
293
to a heavy block or tup moving vertically between guides on the inner
faces of the standards. In single-acting hammers, steam is admitted on
one side only of the piston, so as merely to raise the tup, which, on the
connection with the boiler being cut off, falls with its whole weight, the
steam escaping by an exhaust-port which is opened when the steam pas-
sage is closed; double-acting hammers are also made, in which the force
of the blow is increased by admitting steam on the upper surface of the
piston, and thus accelerating its descent. The steam hammer possesses a
great advantage over those of the ordinary construction, inasmuch as it
admits of the force of the blow being regulated in accordance with the
requirements of the work in hand. This is done by throttling the
exhaust by means of a properly-constructed valve, and allowing the pis-
ton to fall upon a cushion of steam. This power of moderating the
force of the blow is of great advantage in the shingling of blooms,
since at the commencement it is often desirable to consolidate the ball by
short light strokes, and afterwards, as the iron becomes more compact, to
increase the impact by lengthening the fall. The hammers generally
used in puddling forges vary in weight from 30 to 60 cwts. ; one weigh-
ing 50 cwts is considered of sufficient power to do the work of twelve
furnaces, and may be supplied with steam by a boiler utilising a por-
tion of the waste heat of the establishment. In steel-works, and for
blooming and forging large masses of metal, very heavy hammers, having
blocks ranging in weight from 20 to 50 tons, are sometimes employed;
those of the largest size are usually single-acting, the employment of
steam above the piston being chiefly confined to those of moderate
dimensions. Messrs. Thwaites and Carbutt, of Bradford, are the makers
of a double-acting steam hammer, of which fig. 97, from a photograph
kindly furnished by them, is a side elevation. The framing is princi-
pally of wrought-iron. The hammer-block, A, which weighs 10 tons,
is attached to the piston-rod; the piston is 34 inches in diameter, and
the stroke 7 feet. The slide-valve is tubular, and is so balanced
against the pressure of the steam as to be easily moved by the lever, a ;
the stop-valve for regulating the admission of steam is worked by means
of another lever connected with the rod, b. When not hand-worked, the
stroke of the steam hammer is determined by a tappet coming in contact
with the end of a lever which so moves the slide-valve as to allow the
steam to escape from below the piston through the exhaust-pipe. The
hammer-man standing on the platform, c, has the lever, a, and another
in connection with b, close at hand, and at the same time commands an
uninterrupted view of the work in process of forging. Small hammers,
such as those used instead of the old tilt hammer in steel-works and for
smithy purposes, are frequently made with but one standard, so as to
allow of free working on three sides of the anvil, and, in some modern
hammers, guides below the cylinder are dispensed with. In that case, the
piston is prevented from turning either by an angular piston-rod, or by
the use of one of which a portion has been so planed off as to form a
flattened surface; this, passing through a stuffing-box having a similar
section, prevents any disposition of the piston to turn upon its axis.
294
ELEMENTS OF METALLURGY.
In Condie's hammer the cylinder is cast to the hammer-block, and
the piston-rod is suspended to a suitable support, by a ball-and-socket
joint; large steam hammers require anvils of great weight, and these
should be so arranged as to be entirely clear of the foundations sup-
porting the framing.
A convenient foundation for hammers of moderate size may be con-

b
-
ARB
VULCAN IRON
WORKS
BRADFORD. YORK
A
ส
10
0
C
Q
D
00
100
Oc
W.JANELCH SE
Fig. 97.-Steam Hammer.
structed of squared balks of timber placed on end, and bedded either on
concrete or on a mass of cinders broken small, deposited in layers, and
well beaten. For the very large hammers used in steel-works, such as
Krupp's 50-ton hammer (the maximum lift of which is 10 feet, and of
which the anvil weighs 185 tons,) the substructure is built of solid
IRON.
295
blocks of cast-iron; the foundation of this hammer is composed of eight
masses of cast-iron, weighing in the aggregate over 1,000 tons.
A 30-ton steam hammer is at present being constructed for the use of
the Royal Gun Factories at Woolwich Arsenal. The building for con-
taining this machine will be 150 × 100 feet.
The somewhat unusual size of the proposed machine necessitates
special arrangements for the bed-plates. All of these are of a very
massive and solid character, and consist in the first place of a hundred
12-inch square piles, arranged, at equal distances apart, in the form of a
square, 30 × 30 feet. Around and between the piles, for a depth of
4 feet from the heads, is a bed of concrete. Upon the piles is laid
a cast-iron plate, weighing 115 tons. This plate is in three parts, and
upon it is a double layer of 1-inch elm planks, the upper layer being
placed at right angles to the lower one; on these are laid two layers
of 12-inch oak balks. Upon these comes a second plate of cast-iron,
weighing 150 tons. This plate is cast in two pieces, and covers an area
of 27 × 13.5 feet. Then comes a 2-feet thickness of oak timber, placed
with the grain vertical, or end on, the collection of balks being held
together by an iron strap 6 inches deep by 2 inches thick. These carry
a third cast-iron plate, 12 inches thick, and weighing 130 tons. Upon
this will come a fourth plate, 12 inches thick, and weighing 100 tons, a
thin packing of oak, just sufficient to prevent contact, being interposed
between them.
On the top of the last plate will be placed another thin oak packing,
and then the round anvil-block, which weighs 103 tons, and is 15 feet
in diameter at base, tapering to 12 feet at the top.
Upon this comes a cylindrical anvil, 2 feet 8 inches deep, and 12 feet
in diameter, which weighs between 60 and 70 tons.
These foundations will include nearly 670 tons of cast-iron, so
disposed as to present the utmost solidity, while at the same time
retaining sufficient elasticity to prevent any detrimental consequences
of jar from the blows of the hammer.
In Ramsbottom's duplex hammer (fig. 98), both hammers are simul-
taneously put in motion by a steam-engine consisting of the cylinder, A,
piston, a, and slide-valve, b, &c. The piston-rod is connected to a cross-
head moving in guides, and united to the hammers, B, supported on rollers
running on rails, by double connecting-rods, c. The iron journals, d,
are packed with greased leather, so as to deaden the jar of impact, and
the ingot to be hammered is placed in the cage, e, and can be either
raised or lowered by a lever in connection with the counterpoise, ƒ, or be
moved horizontally on its axis by means of a hand-wheel standing above
the floor-level, but not shown in the woodcut. It follows from this
arrangement that the ingot to be hammered may be raised, lowered, or
turned on its axis, to the right or left, at will.
Squeezers. These machines, by which the compression of a ball is
effected without impact, are now more frequently employed for the
operation of blooming than the old helve hammer. Squeezers are of
two kinds reciprocating and rotary. Those of the first class are again
296
ELEMENTS OF METALLURGY.
distinguished as single and double; the single squeezer, fig. 99, has but
one anvil and one hammer, while in the double squeezer there is a jaw on
each side of the articulation, and it has, consequently, two anvils and two
hammers.

B
B
Fig. 98.-Ramsbottom's Duplex Hammer; partly in section.
The lever, a, carries a plate of cast-iron, which may be either flat or
serrated with parallel corrugations, working against a corresponding fixed
jaw, c, constituting the anvil; motion is communicated to this arrangement
by the rod, b, connected with a crank which is usually attached to the
driving-shaft of a rolling mill. The shingler introduces the ball between

Fig. 99.-Single Squeezer; from Truran.
the jaws of the machine at their widest part, and gradually moves it
forward on the anvil until it comes in contact with the upper jaw,
or hammer. At each stroke of the squeezer-arm the ball is flattened by
the pressure, and a portion of the cinder is expelled; during the up
IRON.
297
stroke it is turned over towards the fulcrum of the arm, where it is finally
reduced to a bloom of about 5 inches in diameter and 18 inches in length.
The up-setting of this bloom, which receives from 20 to 25 successive
squeezes during its elaboration, is effected at the extreme end of the jaws,
where the distance between them admits of the mass of iron being set
on end for the purpose of being pressed longitudinally. The squeezer-
crank usually makes about 60 revolutions per minute, and the time neces-
sary for shingling a ball is therefore from 20 to 25 seconds.
The rotary squeezer generally consists of a strong cylindrical casting,
the inner surface of which is studded with blunt triangular teeth or
corrugations; within this revolves a cast-iron cylinder having the outer
surface similarly roughened.
The fixed circular casing of cast-iron forms about three-fourths of an
entire cylinder, and within this, the revolving drum is placed eccentri-
cally with regard to its axis, in such a way that, their surfaces being
parallel, the distance between them gradually diminishes in the direction
of the line of rotation. The puddled ball enters at the widest part, and
on being carried forward by the movable cylinder, is gradually reduced
in size until it is ejected at the narrower end in the form of a cylindrical
bloom ready for the rolling mill. The speed of the squeezer is about
12 revolutions per minute, and one machine is stated to be capable of
doing the shingling for fifty puddling furnaces: as, however, there is no
means of regulating the distance between the surfaces, it has the dis-
advantage of requiring that the balls should be as nearly as possible
uniform in weight and shape.
For the manipulation of heavy masses of iron, the forging of steel
ingots, and for other purposes where very powerful compression is re-
quired, hydraulic power may often be advantageously employed. The
forging-press of Mr. Haswell, of Vienna, is a machine of this class, and
consists of a large vertical hydraulic press with its ram acting down-
wards against a table serving as an anvil. The large ram is lifted by a
smaller hydraulic press, with which it is connected by means of a cross-
head and side-rods. As the ram rises, the water expelled from the larger
cylinder is returned to an accumulator containing a piston, upon the sur-
face of which steam can be admitted; this is employed for moving the
ram rapidly when the resistance is not considerable and the whole power
of the machine is consequently not required. When, on the contrary, it
is desired to develop the whole force of the apparatus, the connection
between the press and accumulator is cut off by a valve, and it is put
into communication with a pair of ordinary hydraulic forcing pumps,
driven by a large direct-acting steam-engine. It is evident that by using
the speed-piston for comparatively light work this machine may be driven
with considerable rapidity, while, by reserving the slow action of the pumps
for the heavier forgings an immense compressive power may be developed.
A machine of this kind, constructed by De Mayr, of Leoben, communi-
cates a pressure of 764 tons to the surface of the large ram; but as by
this apparatus intense pressure is obtained without impact, it does not
require the massive and costly foundations necessary for steam hammers.
298
ELEMENTS OF METALLURGY.
The squeezer, figs. 100, 101, of which the first is a longitudinal
section, and the second an end view, employed with the Danks rotary
furnace, is known as Winslow's, but has been improved and modified by
Mr. Danks, so as to adapt it to the treatment of very heavy masses of
iron. It consists of two corrugated rollers, a, each about 4 feet in length

d
C
C
T
Fig. 100.-Winslow's Squeezer; longitudinal section.
and 18 inches in diameter, placed horizontally, occupying one plane,
and having the journals fixed in strong frames, b. These rollers are
made to revolve in the same direction at the rate of from 15 to 20 revo-
lutions per minute, and above them is geared a large eccentric or
d
b
cam, c, the periphery of which revolves
at the same rate as the circumference
of the two rollers, a. At the side
of the squeezer-frame is a horizontal
steam hammer, the ram, d, of which
is seen, fig. 101, and which hammers
the end of the bloom as it is being
rotated.
When the bloom has been suf-
ficiently squeezed, which is effected
by two revolutions of the cam, it is
removed by means of a neat lever-
arrangement, and rolled upon the floor;
it is now seized by a pair of tongs,
lifted by a crane used for charging and
drawing at the re-heating furnace, and
placed on a fork, by means of which it
is charged. It is subsequently withdrawn by the same fork, placed on a
bogie, and taken to the rolls.

1:40
Fig. 101.-Winslow's Squeezer; end
elevation.
The Commissioners, however, state that they do not consider this
squeczer an essential feature in machine-made iron; and are further of
IRON.
299
!
opinion that, if means can be devised for handling under the steam
hammer such heavy masses as balls weighing from 600 to 1,000 lbs.,
and of getting them worked in a reasonable time, the result will probably
be an improvement in the quality of the iron produced.
Puddling Rolls.—Although the hammer is still employed in some of
the old open-fire forges of Sweden and Germany for the production of
finished iron, it has nevertheless been generally superseded in all the
chief iron-producing districts, both of Europe and America, by the
rolling mill. The rolls by which the heated metal is drawn into bars
are of two kinds. The first, which are called puddling rolls, serve to
consolidate the blooms after their removal from the hammer or squeezer.
The second kind, known as mill rolls, are employed for the purpose of
extending into bars the masses of iron obtained by cutting puddled bars
into lengths, and subjecting them to a welding heat in a balling or
re-heating furnace.
Two pairs of rolls, fig. 102, constitute a puddling train, one pair being
used for roughing-down the bloom, and the other for finishing it into a

α
a
о
α
Fig. 102.-Puddling Train.
bar. The grooves in the roughing pair are either oval, gothic, or dia-
mond-shaped; generally the first two or three grooves are gothic, and
the others diamond-shaped. Finishing rolls are usually turned with
grooves capable of producing flat bars from 3 to 7 inches wide and from
3 to 1 inch thick. Rolls are supported in pairs one above another, in
a heavy framework or housing of cast-iron, and are so connected by
strong spur-gearing as to turn in contrary directions. Motion is com-
municated to the lower shaft either by steam or by water power, and the
distance between the two rolls is regulated by screws, a, acting on the
brass steps in which their journals or necks are secured. Puddling rolls
are generally from 3 feet 6 inches to 5 feet in length, and from 18 to
22 inches in diameter; the durability of the necks and steps is much
increased by the use of cinder-plates, for the reception of which a narrow
groove is turned in each roll close to the ends, and a piece of thin sheet-
iron of the proper form is inserted before lowering the top roll. The
roughing-down rolls on the left have a series of grooves turned on them,
which gradually diminish towards the right, and are roughened by
indentions cut with a chisel; the finishing rolls, on the right, have a
300
ELEMENTS OF METALLURGY.
series of grooves which diminish in the same direction. The lower
roughing roll is provided with a serrated fore-plate and rest, and the
bottom finishing roll with a rest and guide; the crank, b, works the
squeezer. As the rolls, when at work, are subject to great and sudden
variations of torsional strain, the couplings uniting the different members.
of the train are so made as to have less resisting power than the necks
of the rolls themselves; and they are, at the same time, arranged in such
a way as to be capable of a certain amount of independent motion. The
contrivance by which this is accomplished is shown, figs. 103, 104, and
105, the first being a side view, and the second an end one, of the coupling-
box employed. The necks of the rolls, which are continued a short



Fig. 103.
Fig. 104.
Fig. 105.
distance beyond their bearings, have the form of the aperture in fig. 104,
and slip readily into the coupling-box; one of these is placed on the end
of each of the rolls to be joined, the two being united by a loose bar,
fig. 105, of similar form, but of somewhat less sectional area, called the
breaking-piece or spindle. The collars or coupling-boxes are prevented
from slipping by four wooden stops laid in the depressions of the
spindle and secured by leathern straps or wire bands; the intermediate
shaft, being the weakest part of the train, gives way in case of any
undue resistance occurring, and thus prevents the breaking of the rolls.
A continuous supply of water is necessary in order to keep the rolls and
their bearings cool, and is conveyed through pipes and channels to the
various parts where it is required.
On leaving the hammer, or squeezer, the bloom, while still at a high
temperature, is first passed through the largest groove of the roughing-
down rolls, and afterwards, in succession, through the other grooves of
both pairs of rolls, until it is finally extended into a long flat bar, of which
the surfaces are usually very rough; this is known as "puddled bar," or
"No. 1 iron."
Every time the iron has been passed through the rolls it has to be put.
back again over the upper roll, which is attended with a considerable
expenditure of time and labour. Reversing rolls have sometimes been
employed to avoid this, so that immediately the iron has passed through,
the motion is reversed, and it is passed back through the next groove.
Various other contrivances have been resorted to for the purpose of roll-
ing without unnecessary loss of time, and, among them, the most
approved appears to consist in the use of two or more pairs set in advance
of each other, or in passing the bloom alternately through the grooves of
two mills moving in opposite directions; in some cases the bar is carried
on an iron carriage, by which it is rapidly taken by steam power from
IRON.
301
one pair of rolls to the other. Sometimes, and particularly for merchant
and guide trains, a combination of three rolls are placed one above the
other, in the same housing. Such an arrangement of the rolls consti-
tutes a three-high train, and is driven from the middle; the central roll
gearing forward with the lower, and backward with the upper one, or
vice versa, so that the bar, instead of being rolled only one way, passes
backwards and forwards, alternately, between the grooves of the middle
and upper, and middle and lower, rolls.
The speed of puddling rolls ranges from 35 to about 80 revolutions
per minute; in the Welsh forges the rolls are driven at from 50 to 80
revolutions, but in Staffordshire and Derbyshire they are worked more
slowly.
Shears. The puddled bar, on leaving the rolls, is taken by boys to
the cutting shears, which should be placed opposite the finishing rolls.

d
1
[
a
Fig. 106. Steam Shears; elevation.
It is the general practice to shear puddled bars hot; but when the length
into which they may require to be divided for the mill-piles is not known,
they are laid aside, to be subsequently cut cold; stronger shears are
then required, and the work is performed by men.
The shears usually employed for this purpose consist of two jaws,
terminated by cutting edges of hardened steel, firmly bolted to the iron
limbs to which they are attached. The lower blade is immovably fixed
to a cast-iron support, while the upper one moves on a pin passing both
through it and the cast-iron support of the lower jaw. To the upper
limb is attached a lever, which being connected by a strong rod to a
302
ELEMENTS OF METALLURGY.
crank on a revolving shaft, causes the jaws of the shears to alternately
open and shut at each revolution. In this way sufficient power is trans-
mitted to the shears to enable them to divide bars of iron presenting
considerable sectional area. Instead of driving shears by means of a
crank, or shafting connected with other machinery, they are sometimes
worked by a small independent engine; this is the case in the machine
represented, fig. 106, where the heavy cast-iron lever, a, on which is
secured the upper cutting face, b, is connected by a sweep-rod with the
crank, c, on the fly-wheel shaft, and receives motion from the small
inverted steam-engine, d. Shears are employed for cutting puddled
and other bars into lengths for piling, and also for removing the
rough ends of finished bars and the edges of plates and sheets. When
the length of the cut to be made is considerable, a knife with a diagonal
edge, moving vertically between parallel guides, is usually employed.
These guillotine-shears are much used for cutting boiler-plate, and, as
they require considerable power, are frequently driven by an engine
attached to their framing.
Rails and other heavy bars have their rough ends removed while still
hot, by circular saws; these are from 3 to 4 feet in diameter, and make
from 800 to 1,200 revolutions per minute. They are generally driven by
belts, but in some instances direct-acting steam turbines, on the same
shaft, have been employed.
The yield of puddled iron varies considerably in different localities,
and will depend not only on the nature of the pig-iron operated on, but
to a certain extent also on the skill employed in its treatment. In the
neighbourhood of Dudley, South Staffordshire, the ordinary calculation
is, that 24 cwts. of pig-iron should yield 22 cwts. of puddled bars, and
that about 1 ton, 2 cwts., 2 qrs. puddled bars are employed in the
production of 1 ton of merchant-bar. In South Wales, in 1859, it was
estimated that 27 cwts. of white pig-iron were required to produce 1 ton
of finished or merchant-bar.
WORKING PUDDLED BAR INTO MERCHANT IRON; THE MILL.-After
having been cut by shears into suitable lengths, the puddled bars are
piled in packets, which are heated to a welding heat, and then hammered
and afterwards rolled, or they are at once rolled into bars without
hammering. The elevation to a welding temperature is effected in
special furnaces, known as mill, balling, or re-heating furnaces.
Re-heating, or Balling. The re-heating furnace very closely resembles
the puddling furnace, and has a chimney, a, of similar dimensions, but is
usually 8 or 9 inches wider, and about 2 feet longer; the average area of
the fire-place, b, is 12 square feet.
The dimensions, form, number, and size of doors, &c., of the re-heat-
ing furnace vary considerably, in accordance with the nature of the work
for which it is to be employed; but the following woodcuts, figs. 107
and 108, after Truran, represent a longitudinal section, and a hori-
zontal section, above the level of the hearth, of a furnace, such as is com-
monly employed in South Wales for the conversion of puddled bars into
rails or merchant iron.
IRON.
303
The cast-iron bottom, c, is placed about 14 inches below the working
door, and on it is laid a sand bottom, d, falling from the door both
towards the back of the hearth and towards the chimney. Many re-heat-
ing furnaces are constructed without an iron bottom, and in such cases
the sand forming the hearth is laid on rubble-work, consisting of old fire-
brick, fire-brick ends, &c. Between the hearth, or body of the furnace,

f
{
b
a
Fig. 107.-Re-heating Furnace; longitudinal section.
and the fire-place, a bridge, e, 9 inches in thickness, is carried up to
within 14 inches of the roof, while at the stack end the sand is gradually
rounded off so as to meet the bottom of the flue.
A number of puddled bars, generally from 3 to 4 feet in length, are
placed together to form a pile, of which the sectional area is from 3 to 10
inches square, in accordance with the size of the iron to be made; piles
3 feet 6 inches long, 7 inches wide, and 8 inches high, are a common size
for the larger descriptions of merchant iron. The baller charges four of
these for a heat through the door, f, by placing them singly on a flat iron
bar, called a peeler, and slides them into the furnace, taking care not to
disturb the arrangement of the bars. When charged, the four piles lie
nearly across the furnace, radiating from the door, the ends towards
the back lying about 6 inches lower than those nearest the door.
The door, f, is now closed, and a little fine coal thrown around it to
exclude the air, the damper is raised, the grate cleaned, fresh fuel added
through the firing-hole, g, and the fire urged, so as to produce an intense
heat. The workman's chief occupation, after charging, is to watch the
piles, and to so shift their positions that they may be equally exposed to
304
ELEMEN IS OF METALLURGY.
the fire, and be brought to a welding heat in the shortest possible time.
As this point is approached, the iron becomes externally oxidised, and
forms a scale which covers the surface of the pile, and which, by combining
with the siliceous matter of which the bed is composed, forms a slag,
which, running off freely towards the bottom of the stack, escapes from
the furnace. This is distinguished by the name of flue-cinder from that
produced in the puddling furnace, which is known as tap-cinder. A
small fire is usually placed in front of the stack of re-heating furnaces
to prevent the tap-hole from becoming obstructed by the cooling of
the cinder. At the expiration of sixty minutes a heat, such as that

g
d
pi a:
Fig. 108.—Re-heating Furnace; horizontal section.
described, will be ready, and the piles are then successively grasped by a
pair of heavy tongs, and placed on a bogie, to be carried to the rolls. The
withdrawal of the piles, charging a fresh heat, and repairing the bottom,
will occupy about sixteen minutes; such piles usually average about
4 cwts. each, and consequently a furnace working thirty-six piles in the
course of twelve hours will get through 83 tons of iron weekly. For
smaller descriptions of merchant-bar, the piles are made about 18 inches
long, 3 inches wide, and 23 to 2 inches deep. Sixteen or eighteen such
piles, which take from twenty-eight to thirty minutes to reach a welding-
heat, are charged at once; the time occupied in withdrawing the heat,
repairing and re-charging is about twenty-one minutes, and a furnace.
working on piles of this description will re-heat 31 tons of iron per week.
Bars of the smallest size are rolled from bolts of manufactured iron
called billets, measuring from 12 to 20 inches in length, and having
a diameter of from 1 to 12 inch; for these a smaller furnace is
employed, and from twenty-five to thirty billets are heated at a time.
Cold billets are introduced as fast as hot ones are withdrawn; furnaces
working on billets for guide-iron will heat from 15 to 25 tons per week,
according to the size of the finished bars.
The ordinary weight of the piles for rails is, in South Wales, about
15 cwts.; four of these are placed in the furnace at once and the whole
heat is rolled into blooms, in a triple mill, in five minutes. After a
IRON.
305
second heating, which occupies about thirty minutes, the blooms are each
passed nine times through the rail mill, and become rails. The loss on
the piles, including crop-ends, which are subsequently utilised, is about
20 per cent.
The amount of labour bestowed on the manufacture of merchant iron
varies with the quality it is intended to produce. For the commoner
descriptions it is usual to pile puddled bars, or No. 1 iron, cut into proper
lengths, and these, when brought to a welding heat, are rolled into bars,
either with or without being previously worked into blooms under
the hammer. More frequently, however, No. 2 iron, or that which has
been twice rolled, is used for the top and bottom bars of the pile, when
best iron, or No. 3, is being made. If, after this, the iron be further
piled and welded, it is distinguished as best best, and treble best;
according to the number of re-heatings and rollings to which it may
have been subjected.
As a rough approximation it may be estimated that the amount of
coal consumed for the manufacture, from the ore, of common finished bars,
of No. 2 quality, is about four times their weight; to this must be added
from 9 to 10 cwts. per ton for each additional heat to which the iron may
have been subjected.
The bottoms and tops of rail piles are sometimes covered by slabs
made by doubling and welding together, under the hammer, two or more
puddled blooms, which are then re-heated and rolled, without first having
passed through the intermediate state of puddled bars. The necessity
for the use of single bars for the outside of piles arises from the circum-
stance that butt joints, unless covered, do not weld properly; it is also
necessary that the ends of the bars forming the pile should be cut
square, and that all contact-surfaces should be as free as possible from
scale and rust.
The application of gaseous fuel to re-heating has been described, page
96 et seq., where figs. 24, 25, and 26 represent the method of applying
the regenerative principle introduced by Mr. Siemens to a furnace to be
employed for this purpose. Ekman's re-heating furnace, in which the
fuel employed is carbonic oxide produced by the imperfect combustion
of wood-charcoal, is said to be very efficient. It consists of a cylin-
drical gas-generator, built of fire-brick and inclosed in a wrought-iron
jacket in such a way, that, for a certain portion of its height, there is a
free space left between the casing and lining. Into this annular chamber,
cold air is blown, at a pressure equal to about an inch of mercury, and
after becoming to a certain extent heated, one portion of it is admitted
by means of tuyers to the cylindrical generator, where carbonic oxide is
produced, while another is introduced above the fire-bridge for the pur-
pose of effecting the combustion of the gaseous fuel. Beyond the welding
chamber is a second hearth, where the piles receive a preliminary heat-
ing, before being introduced into the former.
Mill Rolls, &c.-The quality of bar-iron is much improved by ham-
mering, since the rapid consolidation which takes place under the heavy
blows of a steam hammer expels the cinder, while the iron is at a
X
306
ELEMENTS OF METALLURGY.
sufficiently high temperature to allow of its escape. A large portion of the
cinder is, however, eliminated during the operation of rolling the pile
into a bar; but in consequence of the great reduction of temperature
which has taken place before the last groove has been reached, a certain
amount of slag is liable to become inclosed in the iron. Hammered iron
is more homogeneous, has a greater specific gravity, and is superior in
point of strength to that which has not been thus treated; consequently,
in the manufacture of iron of the best qualities hammering should not
be dispensed with.
A train of mill rolls for large iron consists of two pairs; one for
roughing, which may be about 6 feet 6 inches long by 22 inches in
diameter, and the other for finishing, considerably shorter and of some-
what less diameter. The whole of the plant requires to be as strong
and substantial as for the puddling train, but the standards of the finishing
rolls are provided with various tightening and adjusting screws for
maintaining the rolls accurately in their positions. Motion is communi-
cated to the finishing rolls by a pair of pinions and spindles, while from
the bottom finishing roll a coupling spindle communicates motion to the
bottom roughing roll, whence it is transmitted to the upper one by spur-
gearing, keyed on the ends of the pair. This method of driving from
the lower finishing roll possesses the advantage of permitting the use of
larger or smaller roughing rolls, as may be required.
In three-high trains the lifting of the piles from the lower to the
upper level is easily effected when light bars only are being rolled, but
in the case of heavy piles it is attended with considerable labour and loss
of time, unless some special mechanical appliance is employed. The
usual method adopted is to make the feed-plates, or tables, movable, and
to so connect them with a single-acting steam- or water-pressure engine,
that the pile, after passing through grooves between the lower rolls, is
lifted to the upper ones, and, after having passed between them, is
received on a table on the other side, which at once descends to the level
of the lower pair. A similar arrangement is also often used for heavy
plate mills consisting of a single pair, since the pile, after having passed
between the rolls, has in this case only to be deposited on top of
the upper roll to be again carried back to the side from which it
entered.
For rolling bars of small section, which from their flexibility are
liable to become bent or twisted, it is usual to use a three-high train, to
the tables or aprons of which guide-jaws or friction-rollers are attached;
these, which are employed for keeping the ends of the bars straight on
entering the grooves, give their name to the arrangement which is known
as a guide train.
Wagner's rolling mill, of which fig. 109 is a front elevation, is some-
times called "the universal mill" on account of the facility with which it
may be made to produce bars and flats of variable sizes with the same
pair of rolls. This machine consists of two horizontal rolls mounted
and geared in the usual way; to these is added a pair of vertical rolls, a,
fixed in bearings, which can be traversed horizontally on slides by
IRON.
307
means of right and left screws. The simultaneous motion of these
screws is insured by the hand-wheel, b, geared to a shaft carrying two
worms acting on wheels keyed on the screw-spindle. By turning these
the two vertical rolls may either be brought nearer together or removed
further apart; thus regulating at will the width of the bar to be
produced. The vertical rolls, a, receive their motion from the driving-
pinion through bevel wheels geared into similar wheels, sliding on their

d
b
00
mamat
Mamon
www
Te
O •
TLE
Fig. 109.-Wagner's Rolling Mill; front elevation.
shaft in such a way as to follow horizontally the movements of the
vertical rolls. The horizontal top roll is kept up to its bearings by a pair
of counterweights, c, and its distance from the bottom roll is regulated
in the usual way by a pair of screws geared to the hand-wheel, d. A
combination of this kind, under the name of "White's mill," has been
advantageously employed in South Wales for roughing rail-piles.
Very heavy mills, such as those used for rolling armour-plates, are
reversed at each passage of the pile. In Ramsbottom's rolling mill the
rolls are driven, without the intervention of a fly-wheel, by a pair of direct-
acting horizontal engines, coupled at right angles, which are reversed
each time that a heat has passed through the rolls; the rolling is thus
performed alternately in opposite directions. The motion is transmitted
from a pinion, on the crank-shaft of the engine, to a spur-wheel in connec-
x 2
308
ELEMENTS OF METALLURGY.
tion with the rolls which make one revolution for three and a quarter re-
volutions of the engine. The action of Napier's differential friction
gearing for reversing rolling mills, and of Stevenson's reversing gear,
could not be rendered intelligible without a lengthy description, accom-
panied by drawings.
The size and speed of rolling mills vary within very wide limits,
according to the nature of the work to be performed; reversing mills for
heavy plates make only from 25 to 30 revolutions per minute, while
some very small mills employed for special purposes make over 500 re-
volutions in the same time. For ordinary sized merchant-bars, the dia-
meter of the rolls is from 12 to 18 inches, and the number of revolutions
per minute from 80 to 110. Rolls for roughing rail-piles are usually
from 20 to 24 inches in diameter, and, if worked as a reversing train, the
speed does not exceed 30 revolutions; if not reversing, the number of
revolutions varies from 80 to 100 per minute.
Plates and Sheets.-The rolls employed in the preparation of plates
and sheets are of a plain cylindrical form, of the same diameter through-
out, and, in order to increase the hardness of their surfaces, they are in-
variably cast in chills. The distance between the rolls is diminished each
time the pile is passed through, and the top roll requires to be supported
to prevent its coming in contact with the lower one when running light.
This is generally done by supporting the lower step of the top roll on the
ends of a forked rod connected with a lever and weight, so as to slightly
overbalance it. For the purpose of securing accuracy of adjustment and
insuring the perfect parallelism of the two rolls, spur-wheels are attached
to the heads of the setting screws, which are moved through equal spaces
by spur- or bevel-gearing, and carefully-divided hand-wheels. For roll-
ing tapered iron, the setting screws are sometimes provided with self-
acting gear, by which the distance between the rolls is gradually and
uniformly diminished during the passage of the pile.
Armour-plates for ships, which are made up to 12 inches in thickness, and
other very heavy plates, may be produced either by hammering or rolling
alone, or by a combination of the two operations. The material employed
for the manufacture of hammered plates is best scrap-iron, which is
balled, re-heated, and welded, until a slab is obtained somewhat thicker
than the section of. the finished plate, and of which two of the edges are
square and the other two chamfered. These are welded together, with
their tapered edges, on the shorter sides, overlapping, so as to form a sec-
tion of a plate of the required breadth, and finally, the length is made up
by the addition of so many pairs as may be required. For convenience of
handling, a porter-bar or staff is welded to the unfinished plate, and this
being provided with a capstan-head with levers, and supported by a crane,
allows of its being readily turned on the anvil as required. The finish-
ing of the plate and its reduction to the proper thickness are effected at a
moderate red-heat, and water is constantly thrown on its surface to facili-
tate the removal of scale. When finished, it is heated to redness and
annealed by slow cooling.
Rolled armour-plates instead of being built up edgewise are formed
IRON.
309
by the successive superposition of slabs, re-heating and re-rolling. For
the finished plate, large slabs, each about 8 feet long, 4 feet wide,
and 24 inches thick, are piled and introduced into a furnace, in which
they are placed on fire-brick pillars, so as to allow the flame to circulate
beneath them. The door of the furnace is on the side parallel to the axis
of the rolling mill, and when the pile has become sufficiently heated it is
transferred to a truck, running on a railway, which takes it directly to the
mill. After passing between the rolls,it is received, on a similar truck,
on the other side, and is passed backwards and forwards by reversing the
rolls, until sufficiently reduced in thickness. The tops of these trucks
are either inclined towards the rolls or they receive the plate upon fric-
tion-rollers in such a way that it may be readily pushed forward; the
action of the mill being sufficient to force it up the inclined surface on
the opposite side. After leaving the rolls, and while still hot, the plate
is rendered perfectly smooth by the passage over it of a roller weighing
about 7 tons; when cold it is transferred to the table of a planing-
machine, where all its edges are dressed square.
Plates and sheets are classified in accordance with their thickness: the
former term embraces all strengths exceeding No. 4 of the Birmingham
wire-gauge, corresponding to a thickness of 0.238 inch; all less thicknesses
are sheets.
Sheet-iron is classified as follows:
Singles,
Doubles
including from No. 4 to No. 20 gauge 0.238 to 0.035 in. thick.
Trebles, or lattens
20
25
25
""
""
""
27
""
""
0.035 0.020
0.020 0.016
""
""
""
For the heavier classes of plates, the piles are built up of bars, which,
instead of having their longer sides parallel cross each other alternately;
the coverings at top and bottom being flat slabs, from 9 to 14 inches
in width and from 1 inch to 1 inch in thickness, made by doubling two
puddled blooms under the hammer and rolling, at a heat, to the proper
size.
16
The pile for boiler-plates, which when finished measure 6 feet in
length, 3 feet in breadth, and have a thickness of 3th, is about 20 inches.
long, 7 inches high, and 12 inches broad. It is first reduced to a roughly-
squared bloom by passing it lengthwise through three grooves in the
blooming rolls, then four times in the direction of its breadth through
the plate-roughing rolls, and finally, three times lengthwise through the
finishing rolls.
The pile for sheets of large size, such as singles of No. 12 gauge,
which are 6 feet in length by 2 in width, weighing about 70 lbs. each,
is made up of scrap and crop-ends produced in making top and bottom
plates. About twenty such piles are placed in the furnace at one time,
and each is first rolled into a bar 3 feet 6 inches in length and 7 inches
in breadth, and then cut transversely into two equal parts. Each of
these portions is now passed through the roughing rolls the wide way,
until it has assumed the form of a plate having nearly the required
thickness, and of a width represented by the length of the original
half-pile. After being passed lengthways three or four times through
310
ELEMENTS OF METALLURGY.
the finishing rolls, the two sheets, produced from the halves of the
original bloom, are passed through together three or four times; they
have now become nearly cold, and after being softened by heating to
low redness in an annealing furnace, are cut to the proper size and
finished.
Thinner sheets are rolled in a similar way, excepting that they are
made from smaller piles; in rolling lattens, after the first annealing heat,
four plates are passed through together, and, after the final heat, eight
thicknesses are passed at the same time. The thin sheets, or black plates,
intended for tinning are made in a similar way, but as the unfinished
work is doubled after every heating, as many as sixteen thicknesses are
at last passed through at the same time; they are finally cut to their
proper sizes, pickled in weak sulphuric acid, and their surfaces polished
by cold rolling.
For the production of small square bars, such as nail-rods, the slitting
mill, in which the rolls are replaced by arbors carrying steel discs, is
commonly employed. In this arrangement the discs on the upper arbor
interlock with those on that which is beneath it, thus constituting a rotary
shearing mill with several pairs of cutters. When a flat bar of iron is
passed between these cutters, in the same way as in an ordinary rolling
mill, it is divided into slips or rods of rectangular section, which are
delivered on the other side in a somewhat bent and twisted condition,
from the pressure of the cutters; these are afterwards straightened and
made up into bundles for the use of nail-forgers. The bar is steadied,
while passing between the cutters, by guides, and a tank above the
framing contains water, which is allowed to fall upon the slitters in
several small streams, for the purpose of keeping them cool.
Iron made from ores containing a considerable amount of phosphorus
is always cold-short; thus, the characteristic of Cleveland iron is cold-
shortness. Cold-short iron is also produced when any siliceous materials
are used for fettling; both phosphorus and silicon, therefore, appear to
make iron cold-short.
The exact cause of the production of red-short iron is not always very
clear. Red-short iron is produced from ores that are deficient in phos-
phorus, and the addition of that substance, by the introduction of Cleve-
land pig, or some similar variety, produces the best results, when mixed with
hæmatite pig or the purer charcoal irons. The red-short character of Welsh
iron cannot always be attributed to the absence of phosphorus, as it is in
many instances, although not always, undoubtedly due to the presence of
sulphur. Iron may at the same time be both red-short and cold-short
this, which is the worst possible description of iron, is produced from ores
containing a high percentage of both sulphur and phosphorus. Red-
shortness is believed to be, in some cases, due to a deficiency of carbon in
the wrought-iron, since the most fibrous and the toughest iron acquires
this property if melted in a clay crucible and afterwards heated, doubled
and welded.
Mr. Mattieu Williams considers that burnt iron results from dissolved
oxygen, or rather that oxide of iron is disseminated throughout the metal;
;
IRON.
311
his experiments on this subject do not, however, appear to be fully con-
clusive.
The waste heat of puddling and re-heating furnaces is frequently em-
ployed for the generation of steam, and it is sometimes also made use of
for heating the blast; another method of utilising waste heat has been
described under the head of "Gaseous Fuel."
The following summary of mills and forges at work in this country
in 1872 is from Mr. Hunt's Mineral Statistics':—
County.
No. of
Works.
No. of Puddling
Furnaces.
No. of Rolling
Mills returned.
ENGLAND:-
Northumberland
Cumberland
Durham
•
Yorkshire (Cleveland District)
•
25
54
4
86
10
21
1,135
62
•
11
492
36
>>
(Leeds and Bradford District)
13
282
54
"}
(Sheffield and Rotherham Dis-
10
363
58
trict)
Derbyshire.
108
18
Somersetshire
1
19
2
•
Lancashire
Gloucestershire
South Staffordshire
North
Shropshire.
NORTH WALES.
SOUTH WALES :-
Glamorganshire
1
6
2
·
125
2,155
329
8
446
168
9
181
24
•
11
178
40
•
5
66
7
17
594
93
Brecknockshire
Monmouthshire
1
20
2
12
637
49
SCOTLAND
19
.486
57
Total.
276
7,311
1,015
STEEL.
Every description of ironstone is capable of affording cast-iron and
wrought-iron; but the properties of the product obtained will vary both
in accordance with the nature of the ores employed, and with the method
of treatment resorted to, since all will not effect, in an equal degree, the
elimination of foreign substances. The metal obtained will consequently
be more or less tenacious or brittle, hard or soft, pure or impure; in all
cases, however, the names "cast-iron" and "
and "wrought-iron" will be
applied to the extreme results. In the same way all intermediate pro-
ducts which cannot be classed with cast-iron on the one hand, or with
wrought-iron on the other, may be called "steel."
The crude product obtained from the reduction of iron ores in
the blast-furnace is known as "cast-iron;" it is not malleable, particu-
larly when hot, but may be hardened by sudden cooling. The term
“wrought-iron” is applied to the inore or less refined metal produced
¡
:
312
ELEMENTS OF METALLURGY.
either from pig-iron or directly from iron ores; it is malleable, both hot
and cold, but it is not capable of being tempered.
Steel forms an intermediate link between ordinary cast-iron and
wrought-iron, uniting, in a certain degree, the properties of both; its
distinguishing characteristic is its capability of being hardened or
softened at pleasure by rapid or slow cooling It cannot, however, be
said where steel begins or where it ends; it is a member of a series
commencing with the most impure pig-iron, and ending with the softest
and purest malleable iron.*
According to Frémy, steel is not simply a combination of carbon
and iron, but is a nitro-carbide, the presence of nitrogen being essential
to the production of steel. He, however, subsequently became aware that
not only does wrought-iron contain nitrogen, but also that it is present
in larger proportion than in ordinary cast-steel; and, as the case at
present stands, the weight of evidence is decidedly against the necessity
of the presence of nitrogen in steel. The older view of Karsten, that
its essential qualities are due to variations in the amount of carbon
present, is now generally admitted to be more probably correct. At
all events, it is now thoroughly established that nitrogen occurs in steel
in very small proportions only; and that if its presence be necessary
to the constitution of steel, it must be still more necessary to that of
wrought-iron and pig-metal.
Steel may be produced-first, directly from iron ores; secondly, by
the addition of carbon to malleable iron; thirdly, by the partial decar-
burisation of pig-iron; fourthly, by diluting the carbon in pig-iron by
the addition of malleable iron.
STEEL BY THE DIRECT REDUCTION OF IRON ORES.-By the Catalan
process, previously described, steely iron, fer aciéreux, is produced under
certain special conditions of working. The most important of these
conditions are as follow: The employment of a small quantity of
greillade, and a large proportion of charcoal; the ore is frequently
and gradually pushed forward from the contrevent towards the tuyer;
the slag is tapped frequently, and ample time must be allowed for the
formation of the massé or bloom. It is also generally considered that
the tuyer should be less inclined, and that the contrevent should have
more slope; towards the end of the process less blast should be given
than in the case of soft iron. The denser varieties of charcoal should
be employed, and the presence of manganese in the ores treated is
desirable. Much will, however, depend on the skill of the furnace-man ;
as, with the same materials, one man will produce a large proportion of
steely-iron, while another will obtain little or none.
Although in this case steel is produced in one operation, yet the ore
must first be reduced, and the resulting metallic iron subsequently car-
burised by contact with incandescent charcoal. By this process uniform
carburisation cannot be secured; the bars, obtained by hammering out
the resulting blooms arc therefore broken on the anvil, and the various
* Karsten gave this definition of steel as long ago as 1823. Annales des Mines,'
1824, vol. ix. p. 657.
STEEL.
313
fragments selected and classified in accordance with their respective
fractures.
A patent was granted in 1791 to Samuel Lucas for making cast-steel
by melting rich iron ores with carbonaceous matter-charcoal, horn,
bone-dust, or other cementing substances. Patents were obtained for
substantially the same process by David Mushet in 1800, and by John
Isaac Hawkings in 1836. In 1854 a patent was granted to Samuel Lucas
for an improved method of manufacturing steel, which essentially con-
sisted in interstratifying the bars of iron in an ordinary converting
furnace with lumps of iron ore. It is directed that the bars should not
be allowed to touch the iron ore, as they would adhere to it; and a
claim is inserted in the specification for the conversion of iron ore into
steel without the presence of bar-iron.
A patent was obtained by William Edward Newton, in 1856, for im-
provements in the process of manufacturing steel, &c., being a communi-
cation from abroad. The iron ores are directed to be reduced to fragments
of about forty to the cubic inch, mixed with charcoal or other carbon-
aceous matter, and, if necessary, with suitable fluxes, in alternate layers,
and kept heated to whiteness during about forty-eight hours in a suitable
cementing vessel. After cooling, the ore thus treated is either melted in
crucibles, to form cast-steel, or worked up in a furnace into spring-steel.
Some years since experiments were made at the Dowlais Iron-Works
by Mr. E. Riley, on the direct production of cast-steel from iron ores;
it was, however, found, that although steel of excellent quality was
sometimes produced, uniform results could not be obtained.
s;
STEEL BY ADDITION OF CARBON TO MALLEABLE IRON. Cementation.-
This is an old process, but of its history little is known. Beckman
states that there is no allusion to it in the writings of the ancients
but it was well described in 1722, by Réaumur, in his treatise on the
art of converting bar-iron into steel. This treatise is illustrated with
engravings, in which converting furnaces, similar in all essential respects
to those now in operation, are represented.
When it is desired to purify cast-iron as completely as possible, the
operation of fining must be prolonged until wrought-iron is produced, and
from this steel is obtained by recarburisation. This is the method
usually pursued in the Bessemer and Siemens-Martin processes for the
direct production of cast-steel; but, as in these operations the recarburi-
sation of the iron is effected by the introduction of cast-iron, the
impurities contained in it become incorporated in the ultimate product.
When, therefore, steel of fine quality is required, the carburisation must
be effected on the principle of cementation, by the use of carbonaceous
reagents.
The furnace in which this operation is conducted, is represented in
the accompanying woodcut, fig. 110. It consists of an oblong rectangular
chamber, divided into two parts by a long and narrow fire-place, a,
which passes through its centre and is provided with a door at either
extremity, by which fuel is supplied. On each side of this is a chest
or converting pot, b, made either of fire-brick or fire-stone, and so
314
ELEMENTS OF METALLURGY.
supported on flues as to allow of the heat and flame passing beneath the
troughs through openings, in connection with the chimneys, c. By these
d
Ъ
རྒྱུུ!
Fig. 110.-Converting Furnace; transverse section.
the smoke and heated air escape
from beneath the arch, which is
thrown over the two chests and
the fire-place by which they arc
heated. In the brickwork at the
ends of these troughs man-holes, d,
are left for the purpose of intro-
ducing the iron bars into the fur-
nace; these are bricked up during
the working of the apparatus, but
when it has cooled they allow of
the workmen entering either to
charge the bars of iron, or to re-
move the steel produced by their
cementation.
The whole furnace is built
under a conical hood, e, of from 30
to 40 feet in height, which serves
both to prevent loss of heat by
radiation, and to carry off the smoke
and gases generated by the com-
bustion of the fuel employed.
The converting chests vary from
8 to 15 feet in length, and from 23
to 3 feet in width and depth; the
smaller cases are found to produce
steel of the most uniform quality,
but are less economically worked
than those of larger size.

The depth of the fire-place de-
pends both on the nature of the fuel
employed, and on the dimensions of the cases to be heated: the space
between these is usually about 18 inches in width, but in some instances
one chest only is employed, and under these circumstances it is placed
immediately over the grate on which the fuel is consumed. The degree of
heat applied is regulated by opening or closing openings in the arch, and
by limiting the amount of air passing into the furnace through the grate.
4
The iron to be converted is in the form of straight bars, usually about
3 inches in width and 3 inch in thickness; in order to allow for ex-
pansion these must be somewhat shorter than the chest in which they arc
to be placed. Charcoal, which has passed through a riddle, of to
inch mesh, is first spread evenly over the bottom of each chest, and on
this a layer of bars is laid longitudinally, flat side downwards, with very
small spaces only between them. When the iron is too short to extend
the whole length, the empty spaces are filled up with short pieces or ends
of bars. This first layer of bars is covered by a stratum of charcoal
STEEL.
315
about half an inch in thickness; on this another layer of bars is placed,
and so on in succession, iron bars alternating with layers of charcoal, until
the chests are filled. A thick layer of charcoal is now placed upon the
top, and the whole is plastered over with grinders' waste, or "wheels-
warf," a substance produced by the wear of the siliceous grindstones
employed by cutlers and others in the manufacture of articles of steel.
This consists of disintegrated siliceous sandstone mixed with finely-divided
and partially-oxidised particles of steel, which combine more or less com-
pletely with the silica, and a compact air-tight covering is the result; when
grinders' waste is not obtainable, clay may be substituted for it. As soon
as the charging of the chests has been effected, the man-holes are stopped
with bricks, and the fire is lighted, care being taken to keep up a tempe-
rature of glowing redness during periods varying in accordance with the
nature of the steel it is desired to produce. Spring-steel requires seven
days, shear-steel eight days, and steel for welding from nine to ten days;
the
progress of the operation is, from time to time, ascertained by means
of trial-bars, which are inserted and removed through holes left in the
ends of the chests, and from an inspection of the fracture of these, when
cold, a judgment is formed of the degree of carburisation which has been
attained. The ends of these bars protrude beyond the furnace, and care
is taken to prevent access of air by carefully claying-up the openings left
between the iron bars and the sides of the trial-holes. When the
cementation has attained the desired point, fuel is no longer supplied
to the grate, and the furnace is allowed to cool during several days
before commencing to remove the charge. As soon, however, as the tem-
perature has become sufficiently reduced to allow a man to enter, the bars
are taken out, broken, and assorted in accordance with the indications
presented by their fractured surfaces. Iron produced from Swedish
magnetic ores is employed in the production of the best kinds of cement-
steel, and, generally speaking, hammered bars are preferred to those made
by rolling. The smaller forges, situated in the eastern part of Sweden,
and working in connection with the Dannemora mines, produce the most
esteemed brands; the iron of Löfsta, known as ‣ iron, is one of
those having a very high reputation. The charge of a furnace of the
usual dimensions consists of from 16 to 18 tons of bar-iron; as before
stated, chests of moderate size are found to afford more satisfactory
results than very large ones, since in the latter, a uniform temperature
cannot be maintained throughout. Consequently, the bars towards the
centre will be carburised in a less degree than those situated nearer the
bottom, sides and top of the chest.
On "drawing a heat" a portion of the charcoal is always found to
have retained its original form, while the remainder has become reduced
to a soot-like dust; the whole is now sifted and washed, in order to free
it from the finer particles, and, when dry, the portion which has not
passed through the meshes of the sieve is added to an equal bulk of fresh
charcoal, and well mixed with it. The mixture thus obtained is found to
afford more satisfactory results than entirely fresh charcoal, which
requires a longer time to effect the complete conversion of the iron.
316
ELEMENTS OF METALLURGY.
The addition to charcoal of small quantities of carbonate of barium,
alkaline carbonates, ferrocyanide of potassium, or of organic matter con-
taining nitrogen, has at different times been recommended, but none of
these substances are practically in use, excepting for case-hardening.
The physical properties of the bars before and after conversion
differ very considerably; the colour of the fractured surfaces of the
carburised bar has no longer the bluish tint of malleable iron, but has
acquired a reddish-white aspect not unlike that of bismuth, and the
texture has become scaly and crystalline.
The most remarkable characteristic of the carburised bars, and that
from which this product derives the name of blister-steel, is however
the blistering of their surfaces. When the blisters are small in size,
and are distributed with a certain amount of regularity, it is an indication
that the steel is of good quality; but, when, on the contrary, they are
large and follow particular lines, it is indicative of a want of homogeneity
in the iron used.
Much diversity of opinion has been entertained with regard to the
cause of these blisters, which are evidently due to gaseous expansion
from within, while the iron, from being exposed to a high temperature,
is in a soft state. The most probable explanation appears to be that
they are due to the action of the cementing material on particles of slag,
consisting of ferrous silicates, enveloped in the metal, and, as the reduc-
tion of the iron in these to the metallic state will be attended with the
formation of carbonic oxide, the evolution of this gas would account for
the formation of the blisters. Another explanation of the production of
blisters on the surface of the metal was offered by the late Mr. T. H.
Henry. This chemist found that a bar of iron which previously to con-
version contained 0.577 per cent. of sulphur, retained 0.017 per cent.
only after cementation; so that 97 per cent. of the sulphur had been
removed during the process. From this it was argued that the sulphur
must have escaped in the form of disulphide of carbon, which is always
formed when carbon and sulphur are brought together at a red-heat.
This substance is highly volatile, and its escape in the form of vapour
was thought sufficient to account for the blisters found on the surface of
the steel. The hypothesis of Mr. Henry, although ingenious, appears
less probable than that by which the formation of the blisters is attributed
to the evolution of carbonic oxide.
The average increase of weight experienced by iron during its con-
version into blistered steel amounts to from to 3 per cent.; and the
amount of coal consumed is from 75 to 90 per cent. of the weight of steel
produced. Blistered steel may be used for steeling the faces of hammers
and sledges, but its texture is not sufficiently uniform for general pur-
poses; by re-heating and drawing, or by faggoting, welding and hammer-
ing, or rolling, it is converted, in accordance with its degree of carburi-
sation, &c., into spring-steel or shear-steel. The former is produced by
drawing out bars of mild blister-steel at a low heat, and the latter by
making blister-steel into piles or faggots, re-heating in a hollow fire, and
drawing into bars. The surfaces of these faggots are covered with clay
STEEL.
317
during the process of re-heating; this, by forming a vitreous slag, protects
the combined or dissolved carbon from the action of the blast. After
being once subjected to this treatment the product obtained is known as
single-shear; by doubling the bars and repeating the process double-shear
is produced.
Hindoo Process.-According to Mr. Josiah Marshall Heath, wootz, or
Indian steel, is prepared from iron, made in the ordinary Hindoo furnace,
by fusion in crucibles made of refractory clay, in which is placed, together
with the metal to be converted, a certain portion of finely-chopped
wood, for which purpose that of the Asclepias gigantea or Cassia auriculata
is preferred. The quantity of iron put into each crucible does not usually
much exceed a pound in weight, and, after covering the pots with one or
two green leaves of the Convolvulus laurifolius, they are closed with a
little wetted clay, and placed in the sun to dry.
When the clay plugs have become sufficiently hardened, from twenty
to twenty-four of these crucibles are built, in an arched form, on the
bottom of a small blast-furnace, and strongly heated during from two to
three hours with a blast produced by two bellows, each made of a bullock's
hide. At the expiration of this time the conversion is considered to be
completely effected; the furnace is then allowed to cool, and the cru-
cibles are removed and severally broken, when the steel is found in the
form of a rounded button occupying the bottom of each pot.
The cakes of steel thus obtained are prepared for drawing into bars
by exposing them, during several hours, in a charcoal fire to a tempera-
ture slightly below their melting point. The fire is urged by bellows,
and the cakes are turned over before the blast; from this circumstance
Mr. Heath arrives at the conclusion, that in order to insure complete
fusion of the contents of the crucibles, the addition of a large excess of
carbon is necessary, and that this excess in the too-highly carburised steel
is oxidised in the way above described.
The following analysis of wootz is by the late Mr. T. H. Henry; the
specimen operated on was in the shape of a bar, 4 inches long and 1 inch
square, weighing 4,760 grains:-
C
(combined
uncombined
•
Si
ககக
As
Fe, by difference
•
•
1.333
0.312
•
•
0.045
0.181
•
•
0·037
98.092
100.000
Chenot's Process.-The production of sponge-iron by this process has
been already described, and it therefore only remains to explain by what
means the carburisation of the metallic sponge is effected. For this
purpose it is either intimately mixed with charcoal-powder or other
solid material rich in carbon, such as a mixture of resin and charcoal, or
it may be impregnated by imbibition with some substance rich in carbon,
such as wood tar or fatty matter. The ground sponge, after having been
immersed in the carburising liquid, is allowed to remain until complete
318
ELEMENTS OF METALLURGY,
saturation has taken place, and, when necessary, a gentle heat is employed
for the purpose of facilitating imbibition. The metallic sponge, when
thus saturated, is drained and torrefied in a close vessel during one hour,
and when fatty matters have been employed as the carburising agent, the
sponge, after having been impregnated in lumps, is ground with the
addition of 75 per cent. of fresh sponge to which no addition of carbon
has been made. This is done to prevent over-carburisation, and the pro-
duction of too hard a steel. After having been thus prepared it is com-
pressed into the form of small cylindrical masses occupying about two-
thirds its original bulk, and these are melted in crucibles in exactly the
same way as ordinary blister-steel. The siliceous and earthy ingredients
of the ore form a slag which floats on the top of the molten steel, and,
immediately before pouring, this is thickened, by the addition of a little
sand, and then removed by skimming. The charge of each crucible is
from 18 to 25 kilos., and the operation occupies, on an average, four hours.
Steel of fair quality has been produced in the way described, but the
expense of fusion is necessarily great, since the compressed sponge
occupies a much larger space than an equal weight of blister-steel, and
consequently the charge of crucibles of the same capacity will be pro-
portionately less.
1
100
Mushet's Steel; Homogeneous Metal.—A patent was granted in 1800 to
David Mushet for a process for manufacturing cast-steel by fusing
malleable iron in crucibles with a proper addition of carbonaceous
matter. Different qualities of steel may be obtained by varying the
proportion of carbon, a small quantity producing a softer variety than a
larger one. The specification states that "steel produced with any pro-
portion of charcoal not exceeding Too will generally be found to possess
every property necessary to its being cast into those shapes which require
great elasticity, strength, and solidity; it will also be found generally
capable of sustaining a white heat, and of being welded like malleable
iron; indeed, as the proportion of charcoal or other carbonaceous matter
is reduced, the qualities of the steel will be found to approach nearer to
those of common malleable iron." In his well-known 'Papers on Iron
and Steel' Mr. Mushet thus describes the properties of the metal pro-
duced: "When iron is presented in fusion to 40 or 1 of its weight
of charcoal, the resulting product occupies a kind of middle state betwixt
malleable iron and steel. It then welds with facility, and may be joined
to iron or steel at a very high welding heat. Thus combined with carbon
it is still susceptible of hardening a little, but without any great alter-
ation in the fracture. It possesses an uncommon degree of strength and
tenacity, and is capable of an exquisite degree of polish, arising from its
complete solidity and the purity of fracture conveyed to it by fusion."
T
1
150
It will be observed that the process patented by Mr. Mushet is nearly
identical with that by which wootz has, from ancient times, been pre-
pared by the Hindoos. In 1839 a patent was granted to William Vickers
for the production of cast-steel by melting 100 parts of iron borings
with 3 parts of black oxide of manganese and 3 parts of ground charcoal.
The use of scrap-iron is also claimed, the proportions specified being
STEEL.
319
28 lbs. of scrap, 2 lbs. 3 ozs. of oxide of manganese, and 3 lbs. of
charcoal.
Case-hardening.-This is a rapid process of cementation, by which
the surface of wrought-iron may be converted into steel. An iron box is
often employed as the cement-chest, and the charcoal used is, in most
cases, obtained by charring some animal matter, such as horn, leather,
or hoof. The objects to be case-hardened are imbedded in the charcoal
in the usual way, and afterwards exposed for a short time to a moderate
heat, either in a smith's forge or in some suitable furnace. When
removed from the fire, the articles are hardened by being heated to redness
and plunged, while still red-hot, into cold water.
Small articles may be rapidly case-hardened by sprinkling a little
ferrocyanide of potassium on their surfaces when red-hot; as soon as
the powder has disappeared the work is quenched in cold water in the
usual way, and, if the process has been properly conducted, the portions
covered by the salt will have become externally so hardened as to resist
the file.
STEEL BY THE PARTIAL DECARBURISATION OF CAST-IRON. In open
Hearths. When, instead of causing carbon to combine in due proportion
with malleable iron, steel is produced in an open hearth by the partial
carburisation of cast-iron, the resulting product is known under the name
of raw-steel, and may be employed for many purposes to which that
obtained by cementation is commonly applied. This variety was for-
merly somewhat extensively manufactured on the continent of Europe,
particularly in Styria and Carinthia; but the process has at the present
time been almost entirely superseded by more improved methods. The
crude iron best adapted for this purpose is that obtained from spathose
ores and containing a considerable quantity of carbon, such as spiegel-
eisen, or the strongly-mottled variety known as blumige Floss, which is
speckled with grey upon a white ground.
After having filled the hearth with burning charcoal, six or seven
plates or slabs of lamellar cast-iron are successively melted before the
blast of the tuyer; these are from an inch to an inch and a half in
thickness. At the commencement of the operation a certain quantity
of rich slag and iron-scale, struck from the blooms by the large hammer,
is added to the charge, which, melting on the surface of the cast-iron when
in a fluid state, assists in the oxidation of the carbon which it contains.
When the first slab is in a liquefied state, and has collected at the
bottom of the hearth, it is at first nearly fluid, but being there subjected
to the oxidising influences of the rich slags by which it is covered, it
rapidly loses a portion of its carbon, and becomes thickened into a pasty
mass. At this point another slab is fused by being brought directly
before the blast, and this, falling in drops to the bottom of the hearth,
again gives fluidity to the whole mass of metal there accumulated. Under
the united influence of the blast and the oxidising slags, this in its turn
loses a portion of its carbon, and becomes pasty. A third slab is now
melted in the same way as the two former ones, but care is taken that
the falling drops of liquid metal may be received on the centre only of
320
ELEMENTS OF METALLURGY.
the molten mass collected at the bottom of the hearth. The middle of
the lump only is now melted by the fused cast-iron, this being sur-
rounded by a ring of spongy metal which does not assume the liquid
form. This operation is repeated until six or eight slabs have been suc-
cessively melted, at the expiration of which time from 200 lbs. to 300 lbs.
of spongy iron will have accumulated at the bottom of the furnace. The
slags are, at this point of the operation, run off, and the metal is raised
from amongst the fuel by which it is covered, and divided into wedge-
shaped fragments by being cut according to a series of lines radiating
from its centre to the circumference. By operating in this way, the
several masses of crude metal will be found to have a nearly similar com-
position, but as the cake from which they are cut is itself far from homo-
geneous, the different parts of the same fragment seldom exhibit precisely
the same degree of carburisation. It consequently follows that these
Masseln, which are now drawn into bars, will yield rods of very different
composition at different points of their length. To remedy this defect,
and to give at the same time greater density to the finished steel, the
bars of rough metal are handed over to a workman, who, after having
heated them red-hot, and subsequently cooled them by plunging in cold
water, raises each bar by one of its ends, and allows it to fall heavily on
an anvil placed for that purpose on the floor of the workshop. By this
treatment the most brittle part of the bar is detached, and on striking a
still harder blow in the same way, another and less carburised fragment
is broken off, whilst the larger portion, which remains in his hands,
merely consists of a peculiar steely-iron, which, in many countries, is
used for the teeth of harrows, for plough-shares, and other agricultural
implements.
The parts broken off are assorted according to the structure of the
fractured ends, and are subjected to a series of manipulations destined.
to communicate to them greater density and uniformity of composition.
For this purpose care is taken to weld together a piece of hard steel, and
one which is less carburised; the bar thus obtained is afterwards heated,
and hardened by being plunged into water, and this is again broken as
before described, and subsequently united into one bar.
It is easily
understood that by this treatment the desired result will be ultimately
attained; but this is produced at a considerable expense of labour and
fuel, and is attended with the loss of a greater or less portion of the crude
steel employed. The steel made by this process is, when carefully pre-
pared, of excellent quality, and was at one time, for many purposes,
preferred to that obtained by the cementation of malleable iron.
Forges of this kind are usually small, and are worked by water-
power. Each contains two fires and a hammer; a small water-wheel com-
monly gives motion to the bellows and another to the hammer. The
latter weighs from 5 to 6 cwts., and makes from 65 to 110 blows per
minute, with a lift of about 2 feet. Four men, with the two fires
will produce from 14 to 15 cwts. of crude steel blooms in a double-
shift of sixteen hours; under ordinary circumstances the consumption of
charcoal is about 30 cubic feet per cwt. of steel produced, but by using
STEEL.
321
hot-blast, and placing a covering over the hearth, this may be reduced to
about 22 cubic feet. The Carinthian process does not differ materially
from the Styrian, but the hearth is larger, and the weight of metal
operated on greater. In addition to performing the work of a refinery
the hearth, in this case, has also to do duty as a re-heating fire; the steel
produced amounts to from 70 to 80 per cent. of the pig-iron operated on,
and the consumption of charcoal is from 40 to 50 cubic feet per cwt. of
steel produced.
In the Siegen district, where, before the introduction of the process
for making steel by puddling, spiegeleisen was treated in the open hearth,
small charges of from 60 to 80 lbs. were melted down upon a mass of
mottled iron which thus formed the bottom of the lump. The slag was
tapped to within about 3 inches of the bottom, shortly after the com-
mencement of fusion, and additions of spiegeleisen were made in diminish-
ing quantities, from 40 lbs. at the fifth to 20 lbs. at the seventh and last
charge. During these successive additions the mass was constantly main-
tained in a pasty semi-fluid condition, and, at the expiration of eight hours,
a bloom, weighing 4 cwts., was obtained. This was divided into seven
or eight pieces, which were tilted into bars, of which the weight amounted
to about 70 per cent. of that of the pig-iron employed.
Puddled Steel.-Puddled steel appears to have been produced at
Frantschach, in Carinthia, as long ago as 1835, but after repeated trials
the process was ultimately abandoned. Bischof made puddled steel in a
gas-furnace at Mägdesprung in the Hartz, in the year 1846, and during
several years experimental trials were made by various ironmasters both
in Westphalia and Bavaria. In 1849, some of the Westphalian manu-
facturers had succeeded in overcoming all practical difficulties, and in the
following year puddled steel was regularly fabricated, and had become an
established article of commerce. Steel so produced appears to have first
begun to attract attention in this country at the International Exhibition
of 1851, where Messrs. Lehrkind, Falkenroth & Co., of Haspe, near
Hagen, showed bars and blooms of puddled steel; rolled puddled steel
was also exhibited by Boeing, Roehr, and Lefsky of Limburg, and by
some other German manufacturers.
In the Exhibition of 1862, there were numerous examples of puddled
steel, and by this time Riepe's process, which Messrs. Lehrkind & Co.
appear to have employed, had been introduced into this country. This
method of producing steel was first practised in England at the Mersey
Steel and Iron Works, Liverpool, and a valuable paper on the subject was
communicated in 1858, to the Society of Arts, by Mr. W. Clay, the then
manager of that establishment; a licence had also been granted to the
Low Moor Iron Company, who, at that date, had already produced about
1,000 tons of puddled steel.
In the specification of Riepe's patent, the process is described as
follows: "I employ the puddling furnace in the same way as for making
wrought-iron. I introduce a charge of about 280 lbs. of pig-iron, and
raise the temperature to redness. As soon as the metal begins to fuse and
trickle down in a fluid state the damper is to be partially closed, in order
Y
322
ELEMENTS OF METALLURGY.
to temper the heat. From twelve to sixteen shovelfuls of iron cinder, dis-
charged from the rolls or squeezing machine, are added, and the whole is
to be uniformly melted down. The mass is then to be puddled, with the
addition of a little black oxide of manganese, common salt, and dry clay,
previously ground together. After this mixture has acted for some
minutes, the damper is to be fully opened, when about 40 lbs. of pig-
iron are put into the furnace near the fire-bridge, upon elevated beds of
cinder prepared for that purpose. When the pig-iron begins to trickle.
down, and the mass on the bottom of the furnace begins to boil and throw
out from the surface the well-known blue jets of flame, the said pig-iron
is raked into the boiling mass, and the whole is then well mixed together.
The mass soon begins to swell up, and the small grains begin to form in
it, and break through the melted cinder on the surface. As soon as these
grains appear, the damper is to be three-quarters shut, and the process
closely inspected, while the mass is being puddled to and fro beneath
the covering layer of cinder. During the whole of this process the heat
should not be raised above cherry redness, or the welding heat of shear-
steel. The blue jets of flame gradually disappear while the formation
of grains continues, which grains very soon begin to fuse together, so that
the mass becomes waxy, and has the above-mentioned cherry redness. If
these precautions are not observed the mass would pass more or less into
iron, and no uniform steel product could be obtained. As soon as the
mass is finished so far, the fire is stirred to keep the necessary heat for
the succeeding operation, the damper is entirely shut, and part of the
mass is collected into a ball, the remainder being always kept covered
with cinder slack. This ball is brought under the hammer, and then
worked into bars. The same process is continued until the whole is
worked into bars. When I use pig-iron made from sparry iron ore or
mixtures of it with other pig-iron I only add about 20 lbs. of the former
pig-iron at the later period of the process, instead of about 40 lbs. When
I employ Welsh, or pig-iron of that description I throw 10 lbs. of best
plastic clay in a dry granulated state on the bottom of the furnace before
the beginning of the process. I add, at the later period of the process,
about 40 lbs. of pig-iron as before described, but strew over it clay in
the same proportion as just mentioned.”
According to the statements of more recent writers on this subject, it
appears, however, to be doubtful whether the process can be efficiently
conducted at the low temperature specified by Riepe, and in the course
of subsequent litigation the term "cherry redness" was explained as
meaning a bright red-heat when the furnace was illuminated by direct
sunlight. The use of the highest temperature obtainable in the puddling
furnace was, at a later period, claimed by another patentee..
There is no essential difference between puddling for the production
of wrought-iron and that for the production of steel, excepting that in
the former case the decarburisation is more completely effected than in
the latter. The crude irons most suitable for conversion into steel are
such as are rich in carbon and manganese, and consequently spiegeleisens,
together with certain varieties of flowery-pig, are well adapted for this
STEEL.
323
purpose. Generally speaking, the furnace used is somewhat smaller than
the ordinary iron-puddling furnace; or rather, the dimensions of the fire-
place and chimney remaining the same, the size of the bed is somewhat
diminished, in order, when required, to command a proportionately
higher temperature. The charge is introduced in the form of fragments
of nearly equal dimensions, and is so distributed over the surface of the
bed that all may become fused about the same time, and without the
formation of any large quantity of oxide.
The charge of pig-iron does not commonly exceed from 3 to 3 cwts. ;
in the preparation of puddled steel it is, however, necessary that the
charge should not only be perfectly fused, but also that it should be
covered by a stratum of liquid slag, which has the effect of regulating, or
rendering uniform, the oxidation of the carbon. The presence of prot-
oxide of manganese in the slag is likewise advantageous as contributing
to its fluidity, without at the same time increasing its decarburising
influence.
The melting-down and stirring or rabbling is effected at a higher tem-
perature than that employed when puddling wrought-iron, and usually
occupies from forty to forty-five minutes; the formation of the steel balls
is, however, conducted at a lower temperature than those of wrought-iron,
and, at this stage of the operation, the furnace should be filled with gases
of a neutral or reducing character.
Fluxes of a more or less oxidising nature, in accordance with the
quality of the pig-iron under treatment, are added during the operation
of melting-down; and towards the close of the puddling process the
presence of a poor, and therefore slightly oxidising slag, in a state of
great liquidity, is required. The presence of viscid highly-oxidising
slag would materially accelerate the fining, but would also be liable to
result in a too complete decarburisation of the metal, by which the
quality of the steel would be prejudicially affected; the decarburising
action of the slags is regulated by the addition of clay, quartz, poor
slags, mill-cinder, &c., as may be required. Sometimes addition of per-
oxide of manganese is made immediately before balling, or a mixture of
peroxide of manganese, clay, and salt is added at intervals during the
stirring. The contents of the furnace are well stirred during the second
period of the process, and should the iron separated in a malleable form
accidentally become decarburised to too great an extent, it may be brought
back to the proper condition by dissolving it in the still-unaltered pig-iron
beneath. When the metal commences to rise, the operation of fining is
promoted by closing the damper until the charge begins to thicken, when
the heat is gradually raised, and the mass is repeatedly worked with an
iron tool; this stirring or rabbling occupies from forty-five to fifty
minutes.
The appearance of the particles of metal, which are constantly brought
to the surface of the covering of liquid slag by stirring, affords a toler-
able indication of the progress of the operation and of the nature of the
product which will be obtained. When the metal thus raised above the
surface of the slag is brilliantly granular, it indicates that the process is
Y 2
324
ELEMENTS OF METALLURGY.
progressing satisfactorily, and that the steel produced will be fine-grained
and of good quality. If, on the contrary, the mass is coarsely granular
and presents a flaky appearance, the steel will be likely to be coarse in
texture and imperfectly refined.
The whole of the charge may either be balled-up at once, or only a
portion of it, according to the nature of the steel required and the skill
of the workmen employed; in some cases each ball is shingled as soon as
it is finished, a new ball being formed in the meantime. In the puddling
of iron a certain amount of decarburisation takes place during the ope-
ration of balling; but in the case of steel this is, as far as possible,
prevented by shutting the damper and filling the furnace with flame and
smoke, thus producing a neutral or non-oxidising atmosphere. When the
furnace is heated by gas, the same result is obtained by shutting off the
top blast.
The shingling of the balls is conducted at a lower tempera-
ture than that employed for malleable iron, and those which cannot be
immediately taken to the hammer are rolled in slag, so as to give
them an external varnish, which tends to prevent oxidation. In order to
prevent the decarburising action of the slag, the balls should be shingled
as quickly as possible; slags, when highly basic, act rapidly upon the
combined carbon.
The fact of the partial decarburisation of pig iron requiring the
expenditure of a larger amount of fuel than the more complete removal
of its carbon, in the manufacture of wrought-iron, can only be explained
by the slowness of the operation, caused by the peculiar circumstances
under which the reactions are produced.
The time required, under ordinary circumstances, to work off a heat
for wrought iron and for steel will be, respectively, as follows:
Melting down
Stirring
Boiling and fusing
Iron.
•
30 to 40 minutes.
30 35
""
""
25 30
Steel.
40 to 50 minutes.
•
45 50
""
20 25
""
""
Balling
10
95 to 115
10
115 to 135
The consumption of fuel in puddling iron varies considerably, not
only with its quality, but also with the nature of the metal originally
operated on, and of that finally produced; it may, however, be taken
roughly at from 100 to 125 per cent. of the puddled bars obtained. In
puddling steel, however, from 130 to 135 per cent. of good round coal
will be consumed; and, should the quality be indifferent, it may sometimes
reach as high as 160 per cent.
The loss in puddling steel is less than that occurring in the pro-
duction of wrought-iron; in puddling alone, it varies from 6 to 9 per
cent.; if the loss on re-heating be included, it will amount to from 15 to
20 per cent.
From 1,800 to 2,000 lbs. of shingled steel balls can be produced from
one furnace in twelve hours; when puddling wrought-iron from eight to
STEEL.
325
nine charges are worked during that time, but with steel from six to
seven charges only can be obtained.
The puddled balls, on being placed under the hammer, emit a bluc
flame, due to the combustion of carbonic oxide; and as they are less
compact than those of wrought-iron, they require more careful manage-
ment, first receiving very light blows and afterwards heavier ones. For
the purpose of being drawn into bars, the blooms are re-heated, either in
a reverberatory furnace or in a hollow fire. In large establishments
puddled steel is generally re-heated in reverberatory furnaces, and sub-
sequently treated by steam hammers and rolling mills; but in small
works the re-heating is usually conducted in hollow fires, and the
drawing-out is effected by the aid of a tilt hammer.
At Lohe, in Siegen, where white crystalline pig-iron is operated on,
twelve charges, each weighing 350 lbs., are treated in the course of
twenty-four hours; the loss on puddling is 9 per cent., with a further loss
on re-heating and hammering of 11 per cent. Of the steel produced, 78
per cent. is of first quality, while the remaining 22 per cent., being more
or less mixed with iron, is less easily broken than that of first quality.
The consumption of coal per 1,000 lbs. of puddled steel amounts to
2,000 lbs.; of which 1,680 lbs. are employed for puddling, and 320 lbs. for
re-heating the blooms in a hollow fire.
At Geisweide, in the same district, 240 lbs. of mottled charcoal pig-
iron, somewhat poor in carbon and manganese, are puddled with 80 lbs. of
spiegeleisen, the total weight of the charge being 320 lbs. In thirteen
shifts of twelve hours each, 68 charges, or 21,760 lbs., of pig-iron are
worked, yielding 18,500 lbs. of steel and 3,260 lbs. of iron. The con-
sumption per 100 lbs. of steel and iron produced, is 113.4 lbs. pig-iron
and 131 lbs. coal. Gas-furnaces are stated to be much better adapted for
the production of puddled steel than those heated by solid fuel; at Kirch-
unden, in Siegen, the saving effected by the introduction of gaseous
fuel, is stated at from 35 to 40 per cent. upon the coal, and from 9 to 10
per cent. upon the pig-iron.
At Zorge, in the Hartz, equal weights of white radiated pig-iron and
grey charcoal-pig, are treated in charges of 4 cwts.; in the course of
twenty-four hours, from nine to eleven charges are puddled, alternately
for steel and wrought-iron, with a loss of 11·68 per cent. on the pig-iron.
In the production of 100 lbs. of blooms, 13 cubic feet of soft charcoal and
11 cubic feet of hard charcoal are consumed; weighing together 1821 lbs.
Turf, which has been experimentally tried, resulted in a loss of 17.2 per
cent. of iron.
The blooms of steel are re-heated in hollow fires, with a consumption
of 1·74 cubic foot of coal per 100 lbs. of the finished product, and a loss
on the metal amounting to from 11 to 12 per cent. According to inves-
tigations made by Janoyer, Lan, Gruner, Zander, Schilling, and others,
the chemical reactions of the steel-puddling process are similar to those
of the process of puddling for soft iron. Schilling, who has published an
elaborate series of analyses of the metal and slags produced at different
stages of this process, as carried out at Zorge, obtained some valuable and
326
ELEMENTS OF METALLURGY.
somewhat remarkable results. The charge consisted of a mixture of
equal weights of white pig-iron from Gittelde, and grey-pig from Zorge.
Ten successive samples were taken from the puddling furnace during
the working of a heat; in the fourth, graphitic carbon had entirely dis-
appeared, while that in a combined state had become reduced to 2·49 in
place of 2.60 per cent. This reduction in the amount of carbon was found
to be almost regularly progressive up to the tenth sample, which con-
tained 0.94 per cent. The silicon in the first sample amounted to 0.99
per cent, and in the second it had increased to 1.50 per cent.; in the
sixth it had been reduced to 0·11 per cent., and this proportion did not
subsequently vary up to the close of the operation. Sulphur was present
in the first sample, to the extent of 0.09 per cent., in the sixth this had
become reduced to 0.012 per cent., and traces only could be found after-
wards. Phosphorus, present to the amount of 0.48 per cent. in the first
sample, progressively decreased until it reached the minimum of 0.075
per cent. in the ninth; and did not subsequently alter. Manganese
which, in the first sample, was present to the extent of 2.01 per cent., had,
in the tenth, been reduced to 0.27 per cent. No increase of carbon was
observed in the earlier stages of the process, as recorded by Calvert and
others. This, Schilling ascribes to the use of a gas-furnace and the intro-
duction of an excess of air by the top blast.
Samples of the slags were taken cach time that a sample of the metal
was withdrawn, commencing with No. 4, and were not found to vary
materially in composition. The silica in the slag taken with the fourth
sample of metal was 20.98 per cent., and in the tenth, 20.52 per cent.
Phosphoric anhydride was found in all, to the extent of 5.25 per cent.
Ferric oxide was present in the first sample of the series to the amount of
7.12 per cent., while in the last there was but 6.24 per cent. The ferrous
oxide present in the different samples, varied from 58.98 in that taken
with No. 4, to 62.14 in that taken with the last. Alumina was present
in all, to the extent of about 3 per cent., while of lime and magnesia, the
quantities being about equal, the amount varied from 1 to 2 per cent.
In these slags, the oxygen ratio of acid to bases is about 1:14; but
the large and perfectly constant amount of phosphoric acid present
appears somewhat inexplicable. It is ascribed, not to the oxidation of
phosphorus contained in the pig-iron, which is obviously too small in
quantity to produce such an effect, but to the ash of the wood burnt in the
gas-generator, and carried over by the draught. This explanation does not,
however, appear satisfactory.
Bessemer's Process.-Publicity was first given to this process in
1856, when Mr. Bessemer read before the Mechanical Section of the
British Association at Cheltenham a paper entitled 'The Manufacture
of Malleable Iron and Steel without Fuel.' At that time the process had
not been sufficiently perfected to yield satisfactory commercial results,
aud the general want of confidence on the part of the trade was so great
that Mr. Bessemer was induced to erect independent steel-works in Shef-
field, where the method was ultimately brought to its present state of
efficiency. His first success, however, was achieved at Edsken and
STEEL.
327
Sandviken, in Sweden, at the works of the so-called Högbo Company.
This process essentially consists of blowing large quantities of at-
mospheric air, divided into numerous small jets, through a bath of
molten cast-iron, thus effecting the rapid oxidation and consequent com-
bustion of carbon, silicon, and certain other substances present in the
pig-iron. The very high temperature which is thus developed in the
converting vessel is sufficient to keep liquid the resulting decarburised
iron, instead of leaving it in the viscid pasty condition in which it is pro-
duced in the puddling furnace.
The blast is injected at a pressure of from 18 to 20 lbs. per square
inch, and the very high temperature attained is obviously the result of
the intimate contact thus caused between the air and the various oxidis-
able bodies present. This oxidation takes place simultaneously through-
out the whole mass, and not, as in the process of puddling, only at the
surface, or where the metal comes in contact with cinder or some other
oxidising agent. The increase of temperature goes on progressively
from the moment the blast is first turned on until it is again shut off;
the various substances becoming oxidised in the same order of succession
as they are respectively eliminated by refining and puddling. The silicon
is thus first transformed into silica, which, uniting with oxide of iron,
forms a liquid cinder; if the blowing be continued after the oxida-
tion of the whole of the carbon has been effected, the heat will be kept
up by the combustion of the iron itself, and a product is ultimately
obtained which possesses all the properties of burnt iron. As before
stated, it has been suggested that iron, after losing its carbon, may
possess the property of absorbing oxygen, like silver or copper, and that
the oxygen so absorbed causes the characteristic red-shortness of burnt
iron.
This process, although not adapted for the production of ordinary
wrought-iron, as was originally intended by Mr. Bessemer, is, nevertheless,
capable of affording, at a comparatively cheap rate, steels of good quality
and possessing a great range of hardness; it is at the present time
not only much employed throughout European countries, but is also
being extensively introduced into the United States of America. The
conversion of pig-iron into steel may be effected by two distinct modifi-
cations of this process: either the decarburisation of the charge may be
arrested at the exact stage by turning off the blast at the proper moment,
or the metal may be first completely decarburised, and subsequently
brought back to the composition of steel by the addition of spiegeleisen
or some other highly-carburised variety of pig-iron. By the first method,
which is still to some extent employed in Sweden, the state of the charge,
and consequently the period at which the blast should be discontinued, is
determined by the appearance of the flame issuing from the converter.
The results obtained by the second method, which was originally sug-
gested by Mr. Mushet, are of a more certain and uniform character, and
it is therefore now generally preferred.
Experience has everywhere shown that in order to obtain steel of
good quality it is necessary to employ pig-iron of exceptional purity.
It
328
ELEMENTS OF METALLURGY.
should in the first place be almost absolutely free from sulphur, phos-
phorus, and copper, as the process is, practically, incapable of reducing
to any great extent the proportion of those bodies existing in the
original pig-iron. On the other hand, the presence, within certain limits,
of silicon and manganese is considered desirable, and, until the whole of
the latter has been eliminated, oxidation of the iron takes place to a very
limited extent; the silica resulting from the oxidation of silicon combines
with manganous oxide and forms a very liquid slag, which has however
the disadvantage of exercising a corrosive action on the siliceous lining
of the converter.
The English iron best adapted for use in the Bessemer converter is
grey-pig smelted from Cumberland hæmatite, and of the quality indicated
by the Nos. 1 and 2; it should contain at least 12 per cent. of silicon and
not more than 0.2 per cent. of phosphorus. At Essen, Westphalia, the
pig-iron preferred for treatment by the Bessemer process is smelted from
a mixture of spathic ores and hæmatite; it contains 5 per cent. of carbon
and 2 per cent. of silicon; it also averages 1 per cent. of manganese,
0.06 of phosphorus, and 0·04 of sulphur.
The furnace or converter employed in the production of Bessemer
steel may either be stationary, like that still used to a certain extent in
Sweden, or it may be suspended on trunnions, by means of which it can
be caused to make, vertically, one-half of a revolution.
The fixed converter, which was at one time generally employed in
Sweden, and which is still sometimes used in that country, consists of a
wrought-iron casing lined with fire-brick and provided on one side with
a spout, by means of which it receives its charge of molten cast-iron; a
series of tuyers is placed in a circle round the bottom, and the whole
is covered by a dome having an inclined hood, through which the gases
evolved during the operation make their escape. The liquid metal is run
into this converter after turning on the blast, so as to prevent the iron
from filling the tuyer-holes, and the blowing is continued until the
charge is run off by means of a tap-hole provided for that purpose.
The movable converter universally employed in England, and now
generally adopted on the continent of Europe, fig. 111, affords great
facilities for discharging the metal, and also allows of the charge being
retained for a considerable time after the blast has been shut off. An
external shell or casing, made of wrought-iron plates riveted together, is
suspended by means of a stout wrought-iron hoop, carrying trunnions
supported by cast-iron standards. One of these is solid, and carries a
pinion, gearing into a rack on the extension of the piston-rod of a small
direct-acting water-pressure engine; the other is 'hollow, and forms a pas-
sage for the blast. The lining requires to be composed of the most
refractory material which can be obtained; fire-bricks are sometimes
employed for this purpose, but, in this country, the fine-grained siliceous
sandstone from below the coal-measures, known as "ganister," is found to
answer better than any other material. It is first finely ground, and may
be used either with or without an admixture of powdered fire-brick; in
either case it must be intimately incorporated with a small quantity of
STEEL.
329
water, by which it is rendered so far coherent as to retain its form when
tightly rammed between the outside casing of wrought-iron and an
inside wooden core, which is afterwards withdrawn. The older con-
verters, of which the form was very nearly that of a soda-water bottle
with the bottom flattened and the neck turned on one side, were, for the
convenience of lining, made in two parts, which were united by bolts and
nuts. The form given to the newer converters is more cylindrical, and
the bottom, which is removable, is retained in its place by cotter-bolts.
Beneath the bottom of the converter .(fig. 111, of which the form is
somewhat old), is the tuyer-box, a, which is a cylindrical chamber com-
municating with the hollow trunnion, b, by means of the curved pipe, c.
The tuyers, d, are slightly-tapered cylindrical fire-bricks, each perforated

a
a
и
C
h
b
Fig. 111.-Bessemer Converter; vertical section.
with seven parallel holes, of about half an inch in diameter. From five
to seven of these tuyers are usually arranged in the bottom of the
converter, at equal distances from each other; the lower ends pass
through a perforated guard-plate, forming the top of the air-chamber,
with which they are maintained in close contact by stops supported
by horizontal arms, which can be turned aside whenever the intro-
duction of a new nozzle becomes necessary. The rack for turning
the converter on its axis gears into the pinion, e; in the older establish-
ments the cylinders of the water-pressure engine were placed horizon-
tally, but a vertical position is now more generally preferred, since less
ground-space is occupied by this form of construction. The engine is in
either case double-acting, and is worked by hand-gearing situated at a
330
ELEMENTS OF METALLURGY.
considerable distance. An arrangement for turning on and cutting off
the blast by the rotation of the converter itself is shown in connection
with the hollow trunnion, b; the valve, which is constructed on the double-
beat principle, has its spindle prolonged through the top of the tubular
pillar, and is so weighted at ƒ as to keep it closed, when its fall is not
mechanically interfered with. Attached to the valve-spindle is the lever,
g, articulated at h, while to the trunnion is keyed the eccentric disc, i,
which, pressing against the lever, lifts the valve and turns on the blast
as soon as the apparatus is in a proper position for blowing; on the other
band, when the converter is lowered for the purpose of pouring, the pres-
sure of the eccentric is taken off the lever, and the valve is closed. By
this arrangement the blast is admitted and cut off at exactly the right
moment, and quite independently of any care or attention on the part of
the workmen; perfect uniformity of action in this respect being thereby
insured.
In a Bessemer plant, fig. 112, two converters, a, are usually placed on
opposite sides of a circular casting-pit, in the centre of which is a vertical
hydraulic cylinder, the plunger of which carries a cross-arm, b, formed
of two parallel iron girders strongly connected by bolts and distance-
pieces; to one end of this is attached the ladle, c, its weight being
balanced by a counterpoise on the other end. This counterpoise is pro-
vided with gearing by means of which it can be gradually removed
towards the centre in proportion as the ladle becomes emptied, and its
weight is consequently diminished. The ladle is made of sheet-iron
lined with fire-clay, and is provided with a tapping-hole in the bottom
which is closed by the end of a bent iron bar also coated with clay; the
other end of this bar turns downward on the outside of the ladle, and is
connected with a hand lever, by means of which the plug in the tapping-
hole may be raised or lowered at pleasure. The ingot-moulds are
arranged around the periphery of the casting-pit in such a way as to be
immediately under the tapping-hole, when the ladle and its support are
made to revolve vertically on the central pivot; this motion is effected by
means of spur-gearing, similar to that employed for the rotation of
railway turn-tables.
This gearing is worked by a man standing on a platform, who has
also the control of machinery by which, after a cast, the ladle is turned
over on its bearings for the purpose of removing any adhering cinder or
waste. The valve by which the central ram is raised, carrying with it
the ladle and support, is usually in charge of a man, who also works the
tipping engines of the converter, and who is stationed at sufficient height
above the ground to command a distinct view of all the operations.
Power for the various hydraulic apparatus is obtained from a small
steam-engine working force-pumps in connection with a pair of accumu-
lators. Each converter is usually capable of holding from 3 to 6 tons of
pig-iron, and, during the operation of blowing, occupies the position of
that shown on the right hand, the flame and sparks being carried into a
chimney by means of the hood, d. The hydraulic engines, e, are
STEEL.
331

d
€
a
h
g
I
h
71
Fig. 112.-Bessemer Steel Plant; elevation, partly section.
d
:
What
332
ELEMENTS OF METALLURGY.
employed for tipping the converters, and a horizontal rack on the side of
one of the girders is used as a slow-motion adjustment for bringing the
tap-hole immediately over the centre of the mould. This is worked by a
hand-wheel on the platform carrying the ladle. The transversing motion
is obtained by means of a pinion gearing into a large spur wheel, ƒ, on
the central plunger, and is worked by a wheel which is also placed on
the movable platform. The cranes, g, are worked by hydraulic power,
and are employed for removing the ingots from the casting-pit.
The method of conducting the process in this country is generally as
follows:-The charge of pig-iron, usually amounting to from 3 to 6 tons,
is melted either in a reverberatory furnace, or less frequently in a cupola ;
and the converter, which has been previously heated to redness by being
filled with ignited coke, is first reversed, so as to remove any unconsumed
fuel, and afterwards brought to a horizontal position to receive its charge
of molten metal, which is run into it through a wrought-iron gutter lined
with sand.
The converter is now slowly brought back to a vertical position, the
blast being at the same time turned on; the flame which at first issues
from the neck is of a yellowish-red colour, is but slightly luminous, and
is not accompanied by a large amount of sparks. The reactions taking
place at this period, which lasts from four to six minutes, are similar to
those produced in the reverberatory furnace during the first stage of
puddling; graphitic carbon passes into the combined state, silicon be-
comes oxidised, and silicates of iron and manganese are formed. This
stage of the operation is followed by a period of active ebullition, during
which the combined carbon is rapidly oxidised by the blast, carbonic
oxide is evolved in large quantities, the flame increases in brilliancy, and
showers of sparks and fragments of burning iron are abundantly thrown
out. This boiling period lasts for about six or eight minutes longer, at the
expiration of which time the intensity of the action begins to diminish,
fewer sparks are evolved, and the flame acquires a characteristic bluish-
violet tint. This marks the commencement of the last, or fining, stage,
and as soon as the whole of the carbon has been consumed, the flame
ceases, but is immediately succeeded by a stream of white-hot gas,
chiefly consisting of nitrogen; if, after this stage has been reached the
blowing be further continued, the temperature will be kept up at the
expense of the decarburised iron, which becomes rapidly oxidised. As
soon as the appearance of the flame indicates that the almost total
removal of the carbon has been effected, the converter is again turned
back to the horizontal position, and about 10 per cent. of spiegeleisen,
or some other pig-iron of nearly similar composition, is added; this is
run in from a furnace through a sand-lined gutter, in the same way that
the charge was originally introduced.
After the addition of the spiegeleisen it was formerly customary to
again turn on the blast during a few minutes, but this is now discon-
tinued, and the contents of the converter are at once emptied into the
ladle; this is brought into the proper position to receive it by lowering
STEEL.
333
the central plunger and moving it horizontally by means of the spur-and-
pinion gearing before described. The ingot-moulds, h, are of cast-iron,
open at both ends; they have frequently a circular or octagonal section,
and are somewhat smaller in diameter at top than at bottom. As soon as
the ladle has been charged, it is raised sufficiently to clear the top of the
moulds, arranged in a semicircle on the floor of the casting-pit, and is so
turned as to bring the tapping-hole over the centre of each in succession ;
the plug is then lifted, and the mould beneath it filled. All the others
are in turn filled in the same way, care being taken, in each case, not to
allow the molten steel to impinge against the side of the mould, since it
is found that this is liable to result in the production of an unsound
ingot. As soon as a mould has been filled, a small quantity of sand is
sprinkled on the surface of the metal, which is then covered by a piece
of sheet-iron, which is secured in its place by an iron cross-bar passing
through eyes on either side. In charging, it is necessary that the blast
should be admitted before the converter is turned so as to again assume a
vertical position, since otherwise the fused metal would flow back through
the tuyers, where it would solidify and cause obstruction. The self-acting
arrangement by which the opening and shutting of the valve is caused by
the rotation of the converter on its axis, secures the admission of air at
the right moment, and precludes the possibility of the stoppage of the
tuyers taking place through any want of attention on the part of the
workmen.
The Bessemer plant at the Imperial establishment at Neuberg, in
Styria, was erected under the direction of Tunner; the two systems
were for some time tried competitively, but the Swedish process was
very soon abandoned. Since the close of the year 1865 the iron has
been tapped directly from the blast-furnace, and the reverberatory furnace
and cupola have only been retained for the purpose of testing new
varieties of pig-iron. At Neuberg, as elsewhere, it has been found that
hot working, resulting from strongly heating the converter and a high
temperature of the iron, essentially contributes to the success of the
operation; iron is tapped for the purpose of recarburising, from the
furnace yielding the original charge of the converter. Before casting,
the mixture is allowed to stand from three to five minutes in the con-
verter after it has been turned down; a portion of the gas is thus disen-
gaged, and the resulting ingots are thereby rendered less cavernous.
has been found in this establishment, as in England, that although pig-
iron containing 0.10 per cent. of phosphorus is quite suitable for the
manufacture of rails, it is necessary for the production of steel of good
quality that the original iron should not contain above 0·04 per cent. of
phosphorus.
It
The following interesting series of analyses, published by the autho-
rities in charge of the Imperial works at Neuberg, enables us to follow
the gradual transformation which pig-iron undergoes in the Bessemer
converter. The pig-metal operated on was smelted from spathic ores
with charcoal.
334
ELEMENTS OF METALLURGY.
PIG-METAL AND PRODUCTS.
Grey Neuberg
Pig-iron.
Metal taken
after the Period
of Scorification.
Metal taken
towards the
Close of
Ebullition.
Burnt Iron
taken before
the Addition
of Pig-iron.
Final Product.
Mil Steel,
No. 6.
C
(graphitic
3.180
combined
0.750
2.465
0.919
0.087
0.234
Si
1.960
.443
0.112
0.028
0·033
P
0.010
0.040
0.045
0.015
0.044
S
0.018
traces
traces
traces
traces
Mn
3.460
1.645
0.429
0.113
0.139
Cu
Fe
0.085
0.091
0.095
0.120
0.105
90.507
95.316
98.370
99.607
99 445
100.000
100.000
100.000
100.000
100.000
towards the
Close of
Slag taken
before the
Addition of
Slag taken at
the Moment
of Casting.
Slag from the
Blast-furnace.
CORRESPONDIng Slags.
Slag taken
after the Period
of Scorification.
Slag taken
Ebullition.
Pig-iron.
SiO2
Al2O3
40.95
46.78
51.75
46.75
47.25
8.70
4.65
2.98
2.80
3.45
FeO
0.60
6.78
5.50
16.88
15.43
MnO
2.18
37.00
37.90
32.23
31.89
CaO
30.35
2.98
1.76
1.19
1.23
MgO
16.32
1.53
0.45
0.52
0.61
K₂O
0.18
traces
traces
traces
traces
Na₂0
0.14
traces
traces
traces
traces
S
0.34
0.04
traces
traces
traces
P
0.01
0.03
0.02
0.01
0.01
99.77
99.79
100.36
100.36
99.87
The first of the foregoing tables clearly shows that copper and phos-
phorus are not oxidised in the Bessemer process, but that sulphur, whẹn
present in very small proportion only, finally disappears; silicon and
manganese, more especially the former, are rapidly oxidised, while iron
does not unite with oxygen, to any considerable extent, until silicon,
manganese and carbon have been almost entirely eliminated.
In Sweden nine grades of Bessemer steel are distinguished, according
to their relative degrees of hardness, estimated by their tempering power.
They are respectively designated by the numbers, 1, 14, 2, 24, &c., passing
from the hardest to the softest. At the works of Siljanfors these various
numbers were found to correspond very nearly with the following propor-
tions of carbon :
No. 1
2.00 per cent. of carbon
5
1223 MHH LO
""
11
"
27
2-1/2
31
4
43
1.75
""
1.50
1.25
•
1.00
•
""
""
0.75
0.50
0.25
•
0.05

STEEL.
335
No. 1 links white pig-metal with the hardest steel; it may be forged
with difficulty but does not weld. No. 5, on the contrary, is homogeneous
metal, welding perfectly but having no tempering power.
In Austria, where, as in Sweden, very pure pig-irons are treated
by the Bessemer process, superior products are obtained. Tunner, the
well-known metallurgist, has adopted a system of classification which
differs but slightly from that employed in Sweden; he has, however,
omitted the first two Swedish numbers, which rather belong to white
pig-iron, and has replaced the half numbers by entire ones, from one
to seven.
At the Imperial works at Neuberg, the proportions of carbon corre-
sponding to the several numbers of hardness, are as follow:-

Numbers of
Hardness.
Proportions of Carbon.
Observations.
No. 1
1.58 to 1.38 per cent. Cannot be welded, and is rarely used.
1.38
1.12
""
123+ L
•
1.12
0.88
4
0.88 0.62
""
""
0.62 0.38
??
""
6
0.38 0.15
""
""
""
7
0.15 0.05
""
""
""
Welds easily; used for bits, chisels, &c.
Used for cutting-tools, files, &c.
Mild steel, for tires, &c.
(Tempers slightly; steel for boiler-plates and
axles.
Does not temper; steel for pieces of machinery.
It will be seen from these results that 0.25 per cent. of carbon, more
or less, is sufficient to cause steel to pass from one grade to another.
This is confirmatory of the theory which supposes, all other conditions
being the same, that the hardness of steel will practically be proportionate
to the amount of carbon it contains.
It has been pointed out by Jordan that a very large proportion of the
heat developed by this process for manufacturing steel is due to the
combustion of silicon, which, when converted into silica, combines with
ferrous oxide and other bases, and covers the surface of the bath with
a liquid slag; in the case of carbon, however, a considerable portion
of the heat developed is abstracted by the carbonic oxide produced,
which, escaping in the form of gas, is uselessly consumed at the mouth
of the converter. He also states that in certain localities in the south of
France the process can only be efficiently carried out by charging the
converter directly from the blast-furnace, as the operation of re-melting,
which usually results in the loss of 1 per cent. of silicon, so far reduces
the proportion of that element as to render the resulting metal unsuitable
for this method of treatment.
Manganese may, to a certain extent, replace silicon as a producer of
heat, as in cases where the pig-iron operated on has been smelted from
spathic ores. Silicon, although an essential component of good Bessemer
pig, should not be present in excess, and, as a general rule, it should not
336
ELEMENTS OF METALLURGY.
exceed the amount of carbon in the iron. The presence of a very large
quantity of silicon in pig-iron intended for treatment by the Bessemer
process may be prejudicial to the result in two different ways: first, by
giving rise to the formation of an increased amount of slag, resulting in
a large loss of iron; secondly, by the difficulty experienced in accom-
plishing its complete removal by the time the elimination of the carbon
has been effected.
With such iron it may happen that although the operation, as indi-
cated by the usual cessation of flame, may appear to have terminated, a
sufficient proportion of silicon may be retained in the decarburised metal
to render the resulting steel brittle and useless. That this sometimes
occurs has been shown by Snelus, and it will be further observed on con-
sulting the following series of analyses, by this chemist, of metal taken
at Dowlais at different stages of the blow, that the removal of the silicon
takes place almost coincidently with that of the carbon.

1.
2.
3.
4.
5.
6.
(graphitic
combined
2.070
Si
•
•
S
P
0:051
0.064
•
Mn
0.086
trace
trace
1.200 2.170 1.550 0.097 0.566 0.519
1.952 0.795 0.635 0.020 0·030
0.014 trace trace trace trace
0.048
0.067
trace
0.030
trace
0.055 0.053
0.309 0.309
0.039 0.039
Cu
Ratio of carbon to silicon 1.6:1
2.7:1
2:1:1 4.8:1 19:1
17:1
1. Fused charge of pig-iron. 2. Metal at the close of first stage.
3. Metal after blowing nine minutes. 4. Over-blown metal, thirteen
minutes from start, before the addition of spiegeleisen. 5. Steel from
ingot. 6. Steel from finished rail. On comparing these analyses
with those made at Neuberg (p. 334), it will be seen that in both
cases the phenomena are substantially the same. It will, however, be
remarked, that the amount of copper is much larger in the Styrian steel
than in that from the Dowlais works. This arises from the fact that the
pig-iron employed at Neuberg is smelted entirely from spathic ores,
which almost invariably contain traces of that metal, whilst the copper
in the Welsh steel is entirely due to the spiegeleisen added at the close
of the operation.
From a very excellent report to the Iron Office of Sweden, on the
German, Austrian, and English manufacture of Bessemer steel, based on
data collected in 1870, during a journey in those countries by E. Bruse-
witz, which is published in the Jern-Kontorets 'Annaler' for 1871,
p. 199, we extract the following analyses :*-
* 'Journal of the Iron and Steel Institute,' No. I., part II. Feb. 1872,
STEEL.
337
ANALYSES OF BESSEMER STEEL,
C.
Si.
Mn.
P.
S.
Steel made direct from the blast-furnace
without addition of spiegeleisen:
At Westanfors, in Sweden
Ditto
Ditto
0.085 0.008 trace
0.300 0.014 0.179
0.700 0.032 0.256
0.025 trace
0.033 trace
trace
Ditto
0.950 0·017
0.463
0.032 trace
Ditto
1.050
0.067
0.355
trace
"
Barrow-in-Furness (for coarse
0.200
0.179
0.214
0.026 0.030
wire).
Germany (for rail-heads).
0.138
0.306
Ú⚫386
0.134 0.040
""
""
(for 1ails) from iron
0.150
0.091
0.264
0.132 0.025
poor in manganese
Germany (for rails, from mix-
ture of Workington hæmatite-
pig with German manganife-
rous pig
0.046
0.634
0.638
0.093 0.015
""
from Neuberg (for boiler-plate))
direct from blast-furnace
0.250
0.016
0.136
0.010
""
from Neuberg (iron first re-
melted in cupola)
0.300 0.056
0 273
0.041 0.040
The mechanical appliances employed at the works of the London
and North Western Railway Company, Crewe, for the treatment of
Bessemer steel are exceedingly complete and efficient.
The steel is pre-
pared in ordinary converters, and, when the ingots are of large size, care
is taken to work them while still hot, in order to economise fuel. When
this is done, a short re-heating restores to the outer surface the tempera-
ture of the interior, whereas when an ingot has been allowed to become
cold it is difficult to sufficiently heat the centre without at the same time
burning the outside. The rail-ingots, each weighing about 5 cwts., are
re-heated in a vertical position in a Siemens regenerative furnace with a
revolving hearth; a distance of 4 inches is maintained between the
several ingots, and the hearth makes one revolution in the course of two
minutes. Rail-ingots were formerly hammered before being passed
through the rolls, but they are now taken directly to the roughing mill,
and the quality of the rails does not appear to have suffered from the
omission of hammering.
The rolls employed for this purpose, instead of being complete
cylinders are simply cylindrical sectors which are attached to strong
arbors, to which an oscillating motion, backwards and forwards, is com-
municated either by racks or by connecting-rods. By the use of these
"cogging mills" of Mr. Ramsbottom, the drawing-out of the ingot in
both directions is rapidly effected; this is especially important in working
steel, for which very gradually diminishing grooves and a low tempera-
ture are essential. The finishing rolls do not differ from an ordinary
train, and make from 80 to 100 revolutions per minute. The ingots,
after a re-heating of from two to two and a half hours, are passed
six or seven times through the roughing mill; they are then re-heated
Z
338
ELEMENTS OF METALLURGY.
for half an hour, and passed nine or ten times through the finishing
rolls.
Tire-ingots, which have the form of a frustum of a cone, and of
which the height is about 20 inches, are always worked under the
hammer; the thickness of the disc is by this means reduced at least
one-half; the centre is punched, and the hole is increased in width
until it is about 20 inches in diameter. To effect this, four re-heatings
are necessary and the tire is then finished between the ends of vertical
rolls.
For working very large ingots, Ramsbottom's duplex hammer is em-
ployed. It is found that when a large mass of hot metal is subjected
to hammering on one of its sides, the compression extends to a very
limited distance only; the surface receiving the blow is enlarged while
the centre of the ingot is unaffected. This defect is lessened by strik-
ing the mass simultaneously on two opposite sides, as is done by the
double hammer employed at the Crowe works, where it has been in
operation during the last four years. In the case of ingots of excep-
tionally large size, an hydraulic forging-press of the kind used by
Mr. Haswell, of Vienna, may often be employed with advantage.
The largest number of converters in any one establishment in this
country is at Barrow-in-Furness, where there are eighteen of the size
known as 7-ton; but charges of 6 tons only are blown in them. The
space occupied by the molten iron is in all cases small as compared with
the total capacity of the converter, since it is necessary to provide sufficient
room above the surface of the fused metal to prevent its ejection during
the period when ebullition is most active.
The number of charges worked daily in each converter does not
usually exceed five; for although the actual blowing does not occupy
more than fifteen or twenty minutes, yet a considerable amount of time is
consumed in the various preliminary operations, such as melting the
charges, &c. The loss of weight on the pig-iron is usually about 15 per
cent. in addition to 7 per cent. in the reverberatory melting furnace ;
thus making the total loss of weight about 22 per cent. The lining of a
converter has generally to be renewed after working from seventy to
eighty charges, but some of the tuyers require renewal after every third
or fourth operation.
The following table is from the 'Mineral Statistics of Great Britain
and Ireland,' by R. Hunt, F.R.S.:-
LIST OF WORKS HAVING BESSEMER CONVERTERS IN GREAT BRITAIN IN 1872.

No.
Name and Situation of Works.
1 Henry Bessemer and Co., Sheffield .
2
John Brown and Co., Limited, Sheffield .
Number of
Converters.
Capacity of
Converters.
Tons.
22222
3
5
10
7
6
STEEL.
339
LIST OF WORKS HAVING BESSEMER CONVERTERS IN GREAT BRITAIN IN 1872-cont.

No.
Name and Situation or Works.
3 Charles Cammell and Co., Limited, Sheffield
Weardale Iron Co., Tow Law.
KTH 10
4
5
CO
6
The Glasgow Bessemer Steel Co., Limited, Atlas`
Works, Glasgow
Samuel Fox and Co., Stockbridge Works, Deepcar
7 Lloyds, Foster, and Co., Old Park, Wednesbury
Bolton Iron and Steel Works, Bolton
Number of
Converters.
Capacity of
Converters.
8
9
London and North Western Railway, Crewe
10
Lancashire Steel Co., Gorton
11
Mersey Steel and Iron Works, Liverpool
•
12
Manchester Steel and Railway Plant Co., Gibraltar`
Gibraltar
Works, Newton Heath, Manchester
13
14
Barrow Hæmatite Steel Co., Barrow
The Dowlais Iron Co., Dowlais
15
Ebbw Vale Co., Ebbw Vale
16
17
18
19
Steel Ordnance Co., Limited, Greenwich
West Cumberland, Workington
Phoenix Iron Co., Rotherham
•
Carnforth Hæmatite Iron Co., Limited
•
84
2
Tons.
5
23/
3
5
3
3
5
6
5
40 00 00 CE 30 LO TO LO
4
4
22++~~~ +
3호
​CO LO SO LO 1-∞ ∞
4
4
3
18
6
6
5
6
5
6
7242NN
Bérard's Process.-As before stated, the removal of sulphur and
of phosphorus, more particularly the latter, cannot be effected by the
Bessemer process. Bérard has attempted to surmount this difficulty by
the use of a double reverberatory furnace heated by gas, in which the pig-
iron is worked alternately with air and with gaseous hydrocarbons. The
air produces oxidation and elevates the temperature of the charge, while
the hydrogen is supposed to remove sulphur and phosphorus. The
apparatus employed is somewhat complicated, consisting of two rever-
beratory furnaces joined together, each heated by gas from a generator;
the hot air and gas enter in the usual way from a double battery of
annular tuyers. A compartment filled with incandescent coke is placed
between the two furnaces, and is separated from each by a small open-
work brick wall; the hearth is formed of a box of heavy sheet-iron and
lined with a brasque containing a considerable proportion of clay.
The gas intended to heat the double furnace enters alternately through
either battery; if supplied by that on the right the products of combus-
tion pass to the left, traversing the compartment filled with incandescent
coke. Carbonic anhydride is here reduced to carbonic oxide, so that the
atmosphere of the furnace on the left will, for the time being, be more
reducing than that of the furnace on the right. When the difference in the
temperature of the two furnaces becomes too great, the direction of the
gaseous current is changed, so that each receives, in turn, a current of
heated gases in a state of combustion, and of gases rendered reducing in
the way described. Both hearths are charged with pig-iron, and two
tuyers, inclined at an angle of 45°, are made to dip into each bath; they
are made of refractory clay, and may be either advanced or withdrawn
z 2
340
ELEMENTS OF METALLURGY.
by means of racks. Each is composed of several parallel nozzles, and
arrangements are made by means of which hot air and gaseous hydro-
carbons are injected alternately through them. The latter are prepared
in a sort of cupola furnace, blown by a mixture of air and steam; they are
conducted into a gasometer, whence a special blowing machine forces
them through a heating apparatus into the bath of molten iron.
The gases of the generator are desulphurised by lime, like gas
employed for illumination, and the bath in the furnace in which active
combustion is taking place is blown with hot air, while the other is
supplied with a blast of gaseous hydrocarbons. Two charges are thus
fired simultaneously, or rather they are alternately exposed to the action
of atmospheric air and reducing gases.
The experiments of M. Bérard do not appear to have been as yet
practically successful, and the results which have been hitherto obtained
are not of a sufficiently definite character to enable a correct judgment to
be formed with regard to the probable future of the process.
Uchatius's Process. This process, which was patented in 1855,
consists in effecting the partial decarburisation of pig-iron by fusion in
contact with ferric oxide or some other substance capable of yielding
oxygen. The pig-iron is first granulated by running the fused metal
into water, and the granulated cast-iron thus obtained subsequently
mixed with about 20 per cent. of roasted spathic ore, and 4 per cent. of
fire-clay; this mixture is melted in clay crucibles in an ordinary cast-
steel furnace. The softer kinds of welding cast-steel may be obtained by
the addition of wrought-iron in small pieces to the above mixture, and
the harder kinds by the addition of charcoal; the weight of the cast-
steel obtained, when no addition of wrought-iron is made, is said to
exceed that of the pig-iron by about 6 per cent.
The process has been tried in this country, and the principal ob-
jection to it seems to have been want of uniformity in the quality of the
product obtained; it however appears to be employed with success in
Sweden, and samples of steel so produced were shown in the Swedish
department of the International Exhibition of 1862.
STEEL BY FUSION OF A MIXTURE OF Cast- and Wrought-IRON.—The
manufacture of steel by "reaction," in which wrought-iron is kept
for a longer or shorter period immersed in a bath of molten cast-
iron, has been long understood, and the result obtained appears to be
partly due to the cementation of malleable iron at the expense of the
carbon of the cast, and partly to admixture of the two. Réaumur, in his
treatise entitled 'L'art de convertir le Fer Forgé en Acier,' (1722), says,
“Iron is transformed into steel by immersing it for a short time in
melted cast-iron," and adds, "this process for manufacturing steel is
employed in some countries, and has been described by Vanoccio Birin-
guccio ('De la Pirotechnia,' 1540, lib. i. cap. 7). Réaumur says in
addition, that steel may be likewise obtained by fusing wrought-iron
with cast, and that he had obtained steel in a common forge by thus
mixing with cast-iron sometimes one-fourth and at others one-third of
wrought-iron. He also states that cast-iron may be softened by crocus
STEEL.
341
Martis, red oxide of iron. In 1798 Clouet states that iron or cast-steel
may be obtained by melting pig-metal with oxide of iron.
Hassenfratz describes two furnaces which were used in England as
early as 1812 for the manufacture of cast-steel by reaction:* “The
mixture intended to produce steel is melted in ordinary reverberatory
furnaces, in the lower part of which a kind of crucible is contrived. The
metal, placed near the bridge, is heated, melts, and flows into the cru-
cible, where it accumulates. The cast-iron becomes covered by slags,
not only those contained in the iron, but also those formed by the partial
fusion of the earthy glass that flows from the hearth. If the slag be in
sufficient quantity, the bath is left at rest so long as the surface appears
to bubble and carbonic oxide is disengaged and burns in the form of a
strong flame. When ebullition ccases, a piece of green wood is introduced
into the bath, and the liquid metal is stirred below the slag, in order to
facilitate the separation of those scoria which remain in the cast-iron and
adhere to the metal.
"At the moment the fining of the pig-iron commences, the principal
workman introduces a small ladle into the bath and removes a little of the
cast-iron from below the slags. He pours this into a test-ingot and tries
it at the forge. He continues to take assays until what is taken out can
be forged. Then he examines the grain of his steel; if it be too soft he
throws bars of over-cemented steel into the bath, to supply carbon without
changing the mode of fining; if it be too hard, he throws into it clippings
of wrought-iron, and sometimes even old iron, to dilute the carbon by
increased volume, or to burn it partially; then he removes the scoriæ
and pours into the mould the cast-steel, which is immediately forged into
a commercial product."
Obuchow's Steel Process.-By this process white charcoal pig-iron
of good quality is re-melted in a cupola furnace and tapped into a large
crucible, previously heated to bright redness, containing malleable iron
or steel scrap, together with magnetic iron ore, titaniferous black sand
and clay; arsenious oxide and nitre are subsequently added. In some
cases addition is made of magnetite and arsenious oxide only. After
receiving the charge of molten pig-iron, the crucible is heated until its
contents have become perfectly liquid, when the nitre and arsenious oxide
are added, and the whole is well stirred.
The steel is cast in vertical cast-iron moulds, and, when sufficiently
cold, is drawn out under tilt hammers; the proportion in which the
ingredients are mixed must manifestly exert an essential influence on the
quality of the product obtained.
The following analyses of Obuchow's common steel are by Chodnew :-
c/graphitic. 0·15)
combined.
1.25
1.02)
Si
0.01
trace
Fe
98.79
98.75
100.00
100.00
* Hassenfratz: 'Siderotechnie,' vol. iv. pp. 93–98. 1812,
342
ELEMENTS OF METALLURGY.
This steel is said to be principally employed in the manufacture of
cannon, &c.
guns,
Price and Nicholson's Process.—A patent was granted in 1855 to David
Simpson Price and Edward Chambers Nicholson for a method of manu-
facturing cast-steel by melting together malleable iron and refined metal
that is, pig-iron freed from the chief portion of its silicon; the relative
proportions of cast- and wrought-iron are to be adjusted in accordance
with the nature of the cast-steel it is desired to produce. Shortly after-
wards Mr. Gentle Brown obtained a patent for the manufacture of cast-
steel by fusing bar-iron with good charcoal pig. A patent was granted in
1862 to Charles Attwood for producing the same result by similar means.
Siemens-Martin Process.-The production in the reverberatory fur-
nace of cast-steel by the solution of malleable scrap in molten pig-iron, in
accordance with the method proposed by Price and Nicholson, Brown,
and others, has recently been brought to a considerable degree of perfec-
tion by the use of the Siemens regenerative gas-furnace. The first
experiments carried out on a working scale were made by M. Martin, at
Sireuil, near Paris, in 1865; but the practical success of the process
appears to have been mainly due to the adoption of the gas-furnace of
Mr. Siemens.
The furnace employed has only a single door, which is in the middle
of one of its longer sides, while on the opposite one, and at the lowest
part of the hearth, is a tapping-hole and a channel, through which the
metal is conducted for casting; the horizontal section is a rectangle with
the corners removed. The hearth is composed of refractory sand, sup-
ported on an iron bottom kept cool by a current of air, and is repaired
after each operation by ramming fresh sand into any holes which may
have been produced. On the casting side of the furnace an iron tramway
with waggons, or a revolving platform, brings the ingot-moulds succes-
sively under the tap-hole until the casting is finished. Alongside the
melting furnace is an ordinary reverberatory furnace with a flat hearth,
in which the pig-iron and packets of scrap, added during the operation,
are heated to redness. At Sireuil the pig-iron employed is principally
obtained from the blast-furnaces of St. Louis, near Marseilles, and from Ria,
near Prades; the charge is from 1,500 to 2,000 kilos (3,300 to 4,400 lbs.).
The furnace, after being heated to whiteness by gas passing through a
Siemens regenerator, is first charged with a certain weight of pig-iron,
which, to prevent chilling the furnace, is previously heated to redness in
the auxiliary furnace before mentioned. When the pig-iron has become
melted and the bath is very hot, wrought-iron is added in quantities of
from 10 to 20 kilos at a time. Additions of red-hot iron are made at
intervals of from twenty to thirty minutes, each addition being followed
by a vigorous stirring, in order that the wrought-iron may be more readily
dissolved and more thoroughly disseminated in the bath.
Iron ores may be employed instead of wrought-iron, but, from their
great difference of density and from other causes, this mixture works less
casily than the other; the product is not homogeneous, and the hearth is
strongly attacked.
STEEL.
343
In either case it is evident that the operation is completely under con-
trol, since the proportion of wrought-iron or of iron oxide may be either
increased or diminished, so as to yield at will a more or less carburised
product. The operation may, like the Bessemer process, be conducted
in two different ways: the decarburisation may be either effected gradually,
and arrested at the right moment, or the metal may be first burnt and
subsequently recarburised by the addition of pig-iron of suitable quality.
The second method is that usually adopted by M. Martin.
When the assays taken show that the metal has been sufficiently fined,
pig-iron heated to redness is charged in place of wrought-iron or iron ore,
and, after the whole has been thoroughly stirred, another sample is taken,
which determines approximately the further amount of pig-iron to be
added. After two or three successive additions have been thus made
samples are withdrawn every half-hour until metal of the proper quality
is obtained, when the charge is tapped off into ingot-moulds. Four suc-
cessive assays made at Sireuil by M. Verdié, in presence of M. Gruner,
who records the results, gave the following percentages of carbon:-
No. 1 contained 0.44 per cent.
2
""
ร
3
4
0.54
0.76
0.87
""
""
""
No. 1 is decarburised iron. The two following assays were made after
successive additions of pig-iron. No. 4 is ordinary steel of moderate
hardness.
Each operation occupies from seven to eight hours, so that, if re-
quired, three charges could be worked in the course of twenty-four
hours; but as it is necessary to clean and repair the hearth after each
fusion it is customary to make but one heat in a turn of twelve hours.
For ordinary steel about equal weights of wrought-iron and cast-iron are
ordinarily taken, the proportions being varied according as hard or soft
steel may be required.
The following are the mixtures employed by M. Martin: for mixed-
metal 1,000 parts of wrought-iron, and from 1,100 to 1,200 parts of pig-
metal. To produce tool-steel 1,000 parts of wrought-iron are mixed with
800 or 900 parts of pig-iron. In order to obtain mild steel, or homo-
geneous metal, 1,000 parts of wrought-iron are added to 700 or 750 parts
of pig-iron. From one-sixth to one-quarter of the pig-iron is reserved for
addition at the close of the operation. The loss experienced varies with
the relative proportions of wrought-iron and pig-iron; it is greater in
proportion as the steel is more completely decarburised, but may on an
average be estimated at 6 per cent. The amount of coal consumed in
working a charge consisting of a mixture of wrought- and cast-iron, toge-
ther weighing 2,000 kilos, is 2,340 kilos; and the weight of the ingots
obtained varies from 1,800 to 1,820 kilos. The normal manufacture of
Sireuil, in 1868, was homogeneous metal for gun-barrels.
PARTIAL DECARBURISATION OF CAST-IRON BY CEMENTATION.-The
fact that articles of cast-iron become softened if imbedded in ferric
344
ELEMENTS OF METALLURGY.
oxide, and maintained for a considerable time at a high tempera-
ture, was published by Réaumur so long ago as 1722. The invention of
this process is, however, generally ascribed to Mr. Samuel Lucas, to
whom a patent was granted in 1804 for a method of softening cast-iron
by cementation with "ironstone ore, or some of the metallic oxides,
lime, or any combination of these." The castings to be softened are
packed in cast-iron crucibles, containing finely-powdered red hæmatite,
and arranged in rows one above another in a furnace somewhat re-
sembling the ordinary cementation chamber. When the furnace has
been charged, all the openings are carefully closed and the fire is lighted,
the temperature being gradually raised so as to reach a red-heat in about
twenty-four hours; the firing is subsequently continued during from
three to five days according to the thickness of the layer of malleable
metal required.
When withdrawn from the furnace, articles which have been sub-
jected to this treatment present the appearance of ordinary malleable
iron, but are lighter in colour; their fractured surfaces are white, and
finely granular, and occasionally present a silky appearance not unlike
that exhibited by soft steel. When the thickness of the object is at all
considerable a kernel of unchanged cast-iron is frequently left in the
centre; this may sometimes be broken by bending without occasioning
the rupture of the external skin of malleable iron.
The principal application of this process is to small articles of hard-
ware, such as keys, buckles, gun-furniture, stirrups, bits, &c. Bauerman
states, however, that it has recently been applied by Mr. McHaffie, of
Glasgow, to such parts of machinery as toothed-wheels and screw-pro-
pellers; the latter having been successfully adopted in steamers employed
in sealing and whaling in the Greenland seas, where ordinary screws are
liable to be broken by contact with floating ice. The stratum of malle-
able metal thus obtained on the surface of cast-iron may be externally
converted into steel by a process of case-hardening, so that the same
object may, at different depths, be successively composed of cast-iron,
wrought-iron, and steel; cheap articles of cutlery, prepared in this way,
are known in the trade as run-steel goods.
CAST-STEEL. Although blister-steel may, by repeated workings under
the hammer, be drawn into bars possessing tolerable uniformity of com-
position, yet this treatment is necessarily attended with a certain loss of
carbon and consequent reduction of hardness. The requisite uniformity
of structure may, however, be obtained by breaking up the crude bars
obtained by cementation, and fusing the fragments in crucibles from
which air is carefully excluded. The contents of these crucibles, when
melted, are poured directly into cast-iron moulds, but where very large
masses of cast-steel are required, a great number of crucibles are either
emptied into a foundry-ladle before casting, or the pouring is so arranged
that, by bringing up constant relays of fresh pots, a continuous stream of
liquid metal is kept up. In this way castings of as much as 40 tons in
weight have sometimes been made by Krupp of Essen, who employs
crucibles containing 70 lbs. of steel. The material employed is stated
STEEL.
345
to be a mixture of puddled steel and wrought-iron, with addition of car-
bonaceous matter; each furnace holds from 2 to 24 pots, and their
removal is facilitated by a mechanical lifting-apparatus placed below
the ash-pit. The manufacture of cast-steel was introduced at Sheffield
by Huntsman, in 1740, and has been continued almost without modifica-
tion to the present day.
The general arrangement of a steel melting-house is exceedingly
simple. The melting-hole, or furnace, is a rectangular cavity, from
18 inches to 2 feet square, and about 3 feet in depth to the grate, lined
either with fire-brick or ganister. The top is on a level with the floor,
the grate-bars and ash-pit being readily accessible from a cellar beneath ;
the cover is a square fire-tile, set in an iron framing with a projecting
handle. A little below the mouth is a short rectangular flue, having a
considerably less area than that of the furnace itself, and communicating
with the stack, which, in order to command a sufficiently active draught,
should not be less than 40 feet in height.
Several furnaces are arranged parallel with the walls on opposite
sides of the melting-house, thus leaving in the centre of the floor a
clear space for the moulds. The crucibles are made of a mixture of re-
fractory clay from the coal-measures, with ground potsherds and coke-
dust, and are usually from 16 to 18 inches in height, and from 6 to 7
inches in diameter at the mouth. Two crucibles are generally placed in
a furnace, the charge of each varying from 35 to 80 lbs. They are
supported on discs of fire-clay standing on the grate-bars, but before
being used require to be annealed by being gradually heated to redness
in an open fire. This is done by placing them, in batches of about
twenty, bottom upwards, together with their covers, on a layer of red-hot
coal supported on a grate; the spaces between them are now filled
with coke, and they gradually become heated to redness. The red-hot
crucibles are removed to the melting furnaces, and placed on their
respective stands; the fires are replenished with coke, and as soon as the
crucibles have become heated to redness, which takes place in about twenty
minutes, they are charged with blister-steel. This is broken into small
pieces, properly assorted, and introduced through a wrought-iron funnel;
after which the cover is placed upon the pot, and the full heat of the
furnace kept up for four or five hours. A fresh addition of coke requires
to be made about every three-quarters of an hour.
As soon as the whole of the charge has become completely fused,
which is ascertained by removing the cover and feeling the inside of the
crucible with a long, pointed, iron rod, the surface of the metal is skimmed
from any adhering slag, and the pot is lifted out of the furnace by means
of tongs with strong concave jaws. The ingot-moulds, which are made
of cast-iron, are often covered with a coating of carbon by being wiped
with oil while still hot, or they may be washed with a mixture of clay
and water, ground to the consistency of cream. As soon as the pot has
been withdrawn from the furnace it is placed in the teaming-hole, which is
a small pit in the floor, containing broken pieces of coke, where it is
allowed to cool for a short time previously to pouring. When an ingot-
346
ELEMENTS OF METALLURGY.
mould has been filled, its mouth is covered either by a shovelful of dry
sand or by a plate of sheet-iron.
When the first charge has been poured, the crucible, after being freed
from any adhering slag, is returned to the furnace, in readiness for a
second melting. The amount of metal now withdrawn is somewhat
less than that melted during the first fusion; the time required for the
operation is also less, and the consumption of coke is proportionately
diminished. The first melting occupies from four to five hours, while the
second and third only require from two to two and a half hours each.
After from three to five successive meltings, the furnace is allowed to
cool, since the very high temperature which would otherwise be attained
would so corrode the surface of the lining as to greatly increase the area
of the furnace, and thus cause waste of fuel. The total amount of fuel
consumed is usually from three to three and a half times the weight of
the ingots produced; but if the coke employed be of bad quality it may
reach as high as five times the weight of the cast-steel made.
In France, steel is sometimes fused in pots heated in narrow reverbe-
ratory furnaces capable of receiving a large number of crucibles at a
time, and Siemens's regenerative gas-furnace has also been applied to steel-
melting with considerable advantage. The crucibles are arranged on the
hearth of a furnace having a removable arch, and the fusion of 1 ton of
ingots, instead of requiring 3 tons of coke, is effected by the consumption
of 1½ ton of ordinary coal-slack.
The
The fractured surfaces of ingots of cast-steel vary in appearance, in
accordance with their hardness. The softer kinds are bright and finely
granular, while the harder varieties exhibit distinct crystalline plates
arranged in parallel bands at right angles to the surfaces of the mould, so
that in a square ingot they exhibit a tendency to form a cross.
ingots produced are in all cases more or less unsound, containing vesi-
cular cavities, which can only be removed by re-heating and hammering.
This is effected at a low temperature, and access of air to the furnace
during the operation is, as far as possible, prevented.
HARDENING AND TEMPERING STEEL.-All varieties of wrought-iron
containing above 0.25 per cent. of carbon possess the property of
becoming hardened by sudden cooling from a high temperature. Steel
thus treated is found to possess a lower specific gravity than before
hardening, but on being again heated, and allowed to cool gradually, its
original density, softness and malleability are restored.
In manufacturing objects of steel, the metal is filed or turned into
the required form when in a soft state, and is subsequently hardened by
being strongly heated and rapidly cooled.
In doing this, however, it is difficult to arrive directly at the exact
degree of hardness best fitted for the purpose to which the instrument
is to be applied, and it is therefore customary to give to the metal in the
first instance a considerable degree of hardness, and afterwards to soften
it by an operation called "tempering." In this the workman is guided
by the various colours assumed by the surface of the metal during the
progress of the operation, and when the proper colour makes its
STEEL.
347
appearance the object is suddenly cooled. These tints, some of which
are extremely brilliant, are probably occasioned by films of oxide cor-
responding with considerable exactitude to the degree of heat to which
the metal is exposed, and they consequently serve as a tolerably accurate
guide in determining the hardness which the object will acquire on being
cooled.
The following colours appear in succession on the surface of a
plate of steel when exposed to a progressive heat. A piece of polished
and hardened steel, subsequently heated to 220° C., has a faint yellow
colour, and is well suited for lancets and other instruments requiring
an extremely fine edge. When tempered at 230°, a faint straw colour
tint is obtained, which is well adapted for razors and surgeons' ampu-
tating knives. Steel seasoned at 243° is of a full yellow colour; this
is tougher than the above, and is the tint to which penknives are usually
tempered. At 255° it acquires a brownish-yellow tint, which is the
colour best fitted for cold-chisels and shears for cutting metals.
Axes and plane-irons are tempered at about 265°, which develops a
brown shade intermixed with purple spots. For table-knives and cloth-
shears a temperature of 277° is employed, which gives a purple colour to
the metal so treated. For swords and watch-springs the metal is cooled
when of a bright-blue colour; this tint very nearly corresponds with a
temperature of 288°.
At 293° steel assumes a fine blue colour, and is at this stage well
adapted for small shears and ordinary chisels; at 316° it takes a dark-
blue colour, which is that best fitted for large saws, the teeth of which
require to be bent by hammering.
The experiments of Stodart and Faraday have shown that when steel
is alloyed with either platinum, silver, rhodium, or iridium, its hardness
becomes much increased by the addition of but very small quantities of
these metals; but such alloys have never been applied to the manufacture
of ordinary cutlery, and are consequently matter of scientific interest
rather than of commercial importance.
Damascening, by which a surface is obtained covered by a variety of
figures resembling the water-lines on certain kinds of silk, is produced
by repeatedly drawing out, doubling up and welding together, a bar com-
posed of a mixture of steel and iron, and subsequently treating with an
acid. When an article, such as a sword-blade or gun-barrel, made of
this mixture is washed with a weak acid, its surface becomes, in a greater
or less degree, unequally attacked, as the surface of the iron retains its
metallic lustre, while that of the steel is left covered with a black
firmly-adherent coating of carbon. This gives rise to the peculiar wavy
figures which may be observed on the once celebrated sword-blades of
Damascus.
ANALYSIS OF CAST-IRON, WROUGHT-IRON, AND STEEL.
Preparatory to its examination, the metal must be reduced to a suit-
able state of division, either by boring, turning, or planing; in the case
348
ELEMENTS OF METALLURGY.
of white-iron, it may be reduced to a coarse powder in a steel crushing-
mortar. It is generally considered preferable, in order to obtain an
average sample of a pig, to bore completely through it, so that a fair
proportion of the graphite, which is occasionally found concentrated
towards the centre, may be included in the borings. The borings
obtained in this way are, when necessary, further reduced and thoroughly
mixed by trituration in a wedgwood or large agate mortar. In the
analysis of pig-iron the proportions of the following constituents are
usually determined: namely, carbon, distinguishing the graphitic from
that in the combined state; silicon, sulphur, phosphorus and manganese,
and in certain cases such metals as arsenic, lead and copper are
estimated; the amount of aluminium, magnesium and calcium is some-
times also determined.
SULPHUR. About 10'grammes of the borings are slowly dissolved in
concentrated hydrochloric acid, and the evolved gases may be passed
through a solution of lead acetate slightly acidified with acetic acid; the
sulphuretted hydrogen disengaged precipitates lead as sulphide, which is
collected on a filter and washed, and subsequently converted into sulphate
of lead, from the weight of which the percentage of sulphur is calculated.
Instead of conducting the gases through a solution of lead acetate, they
may be passed through an ammoniacal solution of nitrate of silver;
silver sulphide will be precipitated, together with a small quantity of a
dark-coloured compound resulting from the action of the evolved hydro-
carbons on the silver salt. The precipitate is separated by filtration,
and dissolved in fuming nitric acid. Hydrochloric acid is added, and
the whole evaporated nearly to dryness. The silver chloride is removed
by filtration, and the sulphuric acid in the filtrate thrown down by
solution of barium chloride.
The contents of the flask, after the metal has been fully acted upon,
are transferred to a porcelain basin and evaporated to dryness, the mass
digested with concentrated hydrochloric acid, and water afterwards
added. The insoluble residue, consisting of silica and graphite, is washed
by decantation, and collected in a platinum dish; the decanted liquid
is reserved for the estimation of manganese, &c.
CARBON, AS GRAPHITE.—The mixed silica and graphite are separated
by the action of a warm solution of pure potassa; the silica is dissolved,
and the graphite (which remains insoluble) is washed with water, and
dried by exposure for some time to a temperature of about 120° C., after
which it is weighed. Upon subsequently burning the graphite in a muffle
it usually leaves a small quantity of a reddish ash, which must be de-
ducted from the former weight; this, after fusion with nitre and sodium
carbonate, may be separately examined.
SILICON. The silica dissolved by potassa is recovered in the usual
manner by evaporation with hydrochloric acid; the residue is digested
with acidulated water, collected on a filter, washed, dried, ignited and
weighed. The amount of silicon in the iron is calculated from the
silica obtained. After weighing, the silica may be examined for titanic
oxide, which may also be present in the filtrate.
STEEL.
349
MANGANESE. The hydrochloric acid solution, separated from silica
and graphite, may be divided into two equal portions, one of which,
representing five grammes of iron, is sufficient for the estimation of
manganese. The iron in the liquid having been peroxidised by nitric
acid, the solution must be neutralised by addition of sodium carbonate;
sodium acetate is added, and the liquid boiled, when the iron will be
completely separated as insoluble basic acetate. The filtrate containing
manganese is rendered alkaline by ammonia, and, after the addition of
a few drops of bromine, is boiled during from ten to fifteen minutes.
The hydrated oxide of manganese, which is thus separated from the
liquid, is collected, washed, dried, ignited, and weighed as Mn,O,, which
furnishes, by calculation, the quantity of manganese present.
PHOSPHORUS.-For the estimation of phosphorus about 5 grammes
of the borings may be acted upon with warm nitro-hydrochloric acid in
a flask with a long neck, and, after complete solution of the metal, the
contents of the flask are transferred to a porcelain basin, and evaporated
to dryness; the residue is moistened with concentrated hydrochloric
acid and again heated to expel nitric acid. The residue is dissolved in
hydrochloric acid, the solution diluted, filtered, nearly neutralised with
carbonate of ammonium, and the iron in solution reduced to protoxide
by the addition of sodium sulphite to the gently-heated liquid; the sub-
sequent addition of dilute sulphuric acid expels excess of sulphurous
anhydride. Sodium acetate and a few drops of solution of ferric chloride
are then added, and the liquid boiled; the phosphoric acid is thus pre-
cipitated as basic ferric phosphate with some basic acetate.
The liquid
is rapidly filtered with as little exposure to the air as possible, the
precipitate slightly washed, and dissolved in hydrochloric acid, the solu-
tion neutralised with ammonium carbonate, and a mixture of ammonia
and ammonium sulphydrate added; it is then gently heated to insure the
conversion of the phosphate of iron into sulphide. The latter is after-
wards removed by filtration, washed with dilute sulphydrate of am-
monium and the phosphoric acid precipitated from the solution in the
usual manner, as ammonio-magnesian phosphate, and weighed as mag-
nesium pyrophosphate, from the weight of which the amount of phos-
phorus is calculated.
When the amount of phosphorus present is small, the following
process may be advantageously employed for its determination. Dissolve
about 5 grammes of the metal to be examined in nitro-hydrochloric acid,
and evaporate nearly to dryness; take up again by addition of a few
drops of nitric acid, dilute with water, filter, add molybdate of ammo-
nium, and allow it to stand twenty-four hours in a warm place. The
yellow precipitate which falls is separated by filtration, washed with a
weak solution of ammonium nitrate, and dissolved in dilute ammonia,
slightly warmed; the phosphoric acid is re-precipitated by addition of
the usual magnesium solution, and the resulting salt ignited, and weighed
as magnesium pyrophosphate.
COMBINED CARBON.-In order to determine the amount of combined
carbon, 5 grammes of the metal may be dissolved in an acid solution of
350
ELEMENTS OF METALLURGY.
cupric chloride; the insoluble residue which remains after the complete
action of this solvent is collected and washed, and, when dried, sub-
mitted to combustion with cupric oxide in a current of oxygen; a
gas combustion-furnace is most conveniently employed for this purpose.
The total amount of carbon in the metal is calculated from the weight
of carbonic acid (carbonic anhydride) absorbed by solution of potassa in
the usual manner. The carbon existing in a state of combination will
be represented by the excess afforded by this process over that of
the direct estimation of carbon in the form of graphite as already
described.
Instead of operating as above directed, about 5 grammes of the metal,
in small pieces, may be introduced into a flask, covered with water, and
iodine added. The mixture is, from time to time, shaken, and is allowed
to stand until all the free iodine has been taken up; more iodine is now
added, care being taken to prevent heating; for every part of iron ope-
rated on about five parts of iodine are required. If the metal has been
reduced to a finely-divided state the operation will be complete when the
whole has been dissolved; when, on the contrary, the iron has been used
in the form of chippings of considerable size, the action may be arrested
as soon as a sufficient weight has entered into solution. In this case
the portions remaining undissolved must be taken out, carefully washed,
and re-weighed; the second weighing, deducted from the first, will then
represent the weight of the dissolved metal.
The solid residue is separated from the brown solution by decantation,
and is then carefully washed by the same means; the final washings are
filtered through a tube, of which the end is drawn out and closed by a
plug of asbestos; after being finally washed it is dried, and when dry the
tube with its contents, together with the remaining portion of dry solid
residue, is introduced into a porcelain or hard glass tube, mixed with
cupric oxide, and its combustion effected by the aid of a current of
oxygen. The resulting CO₂, after passing through a tube containing
calcium chloride, is absorbed by caustic potassa and weighed in the
usual way. From the weight of CO₂ obtained, the amount of total carbon
is calculated. From this must be deducted the amount of graphitic
carbon, previously determined, and the difference will represent the com-
bined carbon present. Bromine may be employed in place of iodine,
but the results obtained are not so accurate, being generally too low.
2
MINUTE PROPORTIONS OF FOREIGN METALS.-About 30 grammes of the
iron or steel should be employed in the examination for metals precipi-
tated by sulphuretted hydrogen, e.g., lead, copper, &c. The metal to be
examined is dissolved in hydrochloric acid, and the solution, diluted,
partly neutralised with sodium carbonate, and submitted to the action
of sulphuretted hydrogen. After saturation with the gas the liquid is
allowed to stand at rest for several hours, and the small quantity of
precipitate which subsides is examined for the various metals by ordinary
analytical processes.
Chromium and vanadium are to be looked for in the carbonaceous
residue obtained by dissolving a considerable quantity of the iron in weak
STEEL.
351
acids; aluminium, calcium and magnesium may be estimated in the
filtrate by the usual processes.
EGGERTZ'S PROCESSES.
Determination of Carbon.-This is a process, founded on the use of
standard solutions, and is based on the fact that when carbide of iron is
treated with nitric acid, slightly diluted and warm, the combined carbon
is converted into a highly-coloured organic product, while graphitic
carbon remains unattacked.
By addition of water the solution may be brought to the colour of a
standard liquid, obtained by dissolving a given weight of a steel of known
composition, and the proportion of carbon in the metal under examina-
tion is subsequently determined by measuring the volume of its solution.
Pure nitric acid diluted to a density of 1.20 is employed, and the
quantity of metal operated on is usually 0·10 gramme. The steel, in the
form of filings which have been previously passed through a metallic sieve
of which the meshes are less than 0.004 inch in diameter, is attacked,
in a test tube or small flask, by acid of the density above specified. If
the metal contains but little carbon, from 1·5 to 2 c.c. of acid will be suf-
ficient for the solution of 0·10 gramme of filings, but if the amount of
carbon be large, as in the case of spiegeleisen, from 4 to 5 c.c. will be
required. By the aid of a moderate heat, solution is almost immediately
effected, attended by effervescence, and black flocks, in greater or less
abundance, will be observed floating in the liquid. In order to obtain
uniform results it is necessary that the trials should be conducted at the
same temperature and under similar conditions; to this end the tube in
which the solution is being prepared is placed in a water bath and kept
constantly at a temperature of about 80° C. The black flocks, above
alluded to, are seen gradually to dissolve with evolution of bubbles of
gas, and the liquid becomes proportionately darker in colour.
At the expiration of three hours complete solution is effected, and the
tube and its contents are rapidly cooled by being plunged in cold water.
The liquid is then poured into a burette, graduated to tenths of a c.c.
Finally, it is diluted with water until its colour exactly corresponds with
that of the standard solution obtained by dissolving an equal weight of
steel of which the composition has been previously ascertained; this solu-
tion, for comparison, must be contained in a tube having the same diameter,
and made of similar glass to that of the burette. The similarity of
colour may be judged by comparing the two by transmitted light, holding
them between the eye and a window, or, still better, by placing the tubes
side by side before a sheet of white paper placed opposite the light. After
a little experience, a degree of exactitude will be obtained which is repre-
sented in volume by from one to two-tenths of a c.c.; this will indicate
the proportion of carbon to within two hundreths of 1 per cent., if the
standard solution be prepared by making it up to as many c.c. as the
type steel contains tenths of 1 per cent. of carbon. As, according to
Tunner's scale, the proportion of carbon varies 0-25 per cent. in passing
352
ELEMENTS OF METALLURGY.
from one number of hardness to another, this is found in practice a
sufficiently accurate approximation.
In order to obviate the necessity of making a standard solution for
every set of determinations, various coloured liquids have, at different
times, been employed, with a view of establishing a permanent scale.
Caramel, or burnt sugar, which has, among other substances, been employed
for this purpose, gives various shades of brown and yellow, but they are
by no means stable; partially-decomposed solution of indigo in sulphuric
acid is said to retain its colour for a considerable time. Hetman recom-
mends the use of a solution containing a mixture of potassium dichromate,
and nitrate of cobalt; but, in the majority of cases, direct comparison with
a standard solution of a given weight of steel, of known composition, is to
be preferred.
The following determinations of carbon in various kinds of Swedish
iron and steel are by Eggertz:
Per Cent. of Carbon.
Softest Swedish Bessemer iron contains 0.08
Soft steel
0.75
Best quality of cast-steel
1.40 to 1.50
""
Natural forge-steel
0.99 2.44
Cement-steel
0.50 1.90
""
""
Cast-steel
0.86 1.94
݂ܕ
Hardest-melting cast-steel
1.80
"1
""
Malleable cast-iron
0.88 1.52
""
Draw-plate steel.
3.30 ""
This process cannot be employed for the comparison of steels obtained
from different materials, or by different methods of treatment; in con-
firmation of this, Gruner states, that at Neuberg, a variety of coke-pig
yielded by the Bessemer process a steel corresponding in physical pro-
perties to No. 3 of Tunner's scale, while, according to the carbon it con-
tained, it was only No. 6. This was a good ordinary cast-steel, very hard
and difficult to weld, and by analysis, as well as by Eggertz's method,
afforded only 0.3 per cent. of carbon; by analysis, however, it was found
to contain nearly 1 per cent. of silicon, which, to a certain extent, may
replace carbon in steel as well as in cast-iron.
Sulphur. The ordinary methods of determining the amount of
sulphur contained in iron and steel not only necessitate a consider-
able expenditure of time, but they also require an amount of analy-
tical skill not always at command in establishments of limited extent.
Eggertz has, therefore, sought a more rapid process, by which, without any
pretence to accuracy, an approximate estimation may be made of the
amount of sulphur present in pig-iron, wrought-iron and steel. The
basis of this process is the more or less darkened shade acquired by a
silver plate exposed to the action of the sulphuretted hydrogen evolved
from an attack of a given weight of the metal under examination.
One gramme of distilled water and 0.5 gramme of strong sulphuric
acid are poured into a stoppered bottle about 0·025 m. in diameter and
0.15 m. in height; into this, in the state of a finely-divided powder, is
introduced 0.10 gramme of the metal to be examined, and a piece of thin
silver plate is immediately hung in the upper part of the flask, by means
STEEL.
353
of a fine platinum wire retained between the neck of the flask and its glass
stopper. At ordinary temperatures, the metal will be completely dissolved
in about fifteen minutes, and the silver plate may then be removed for
examination. After numerous experiments, Eggertz has arranged a scale
of colours corresponding to the varying amounts of sulphur present, esti-
mated as hundredths of 1 per cent. This method of estimating small
quantities of sulphur may be conveniently used for the determination of
quantities of less than 0.10 per cent., and is applicable to pig-irons of
high quality, such as those produced in Sweden; it is not, however, to
be recommended for iron obtained with mineral fuel from the ordinary
ores of this country.
Silicon. The accuracy of determinations of silicon in iron and steel
is not unfrequently impaired by the presence of a notable amount of in-
termingled slag, which, being a mere mechanical impurity, has no relation
whatever with the chemical composition of the metal. In order to obviate
this difficulty Eggertz has devised a method of estimating silicon in the
presence of slags, which is based upon the fact that when iron is acted on
by bromine or iodine it dissolves, and the silicon which is liberated is
transformed into a form of silica completely soluble in a boiling solution
of sodium carbonate, while that in combination as slag, should any be
present, is not thus acted upon.
About 3 grammes of metal in the form of finely-divided filings, pre-
viously sifted through a sieve of the degree of fineness specified when
describing the determination of carbon, are treated with five times their
weight of iodine in 15 c.c. of water, contained in a beaker of six or seven
times that capacity. The water used should have been previously boiled,
for the purpose of freeing it from air, and, as the operation should be con-
ducted at a low temperature, the beaker must be kept cool, either by ice
or by a current of cold water. As soon as the complete solution of the
iron has been effected, the liquid is diluted to three times its original
volume by a further addition of cold water, and, after being well stirred,
is allowed to settle. The lighter portion of the graphitic carbon remains
in suspension, and is, with the greater bulk of the solution, poured upon
a wetted filter in a small glass funnel. To the heavy insoluble residue,
which is retained in the beaker, a few drops of hydrochloric acid are
added, and the whole is well stirred with a glass rod; if this should be
followed by a disengagement of gas it is proof that the whole of the
metal has not been dissolved, and after the addition of a little sodium car-
bonate, to neutralise free acid, more iodine is introduced and complete
solution effected, The whole of the residue is now transferred to the
filter and washed with distilled water until the addition of potassium
ferrocyanide ceases to indicate the presence of iron. The filtrate is
evaporated to dryness with addition of hydrochloric acid, for the purpose
of recovering any traces of silica it may contain, and the original
insoluble residue, which may contain graphite, silica, and unattacked
slag, is transferred, without drying, to a large platinum dish, where it is
treated with a saturated solution of sodium carbonate.
After being
heated for about one hour in a water-bath, during which time it is
2 A
354
ELEMENTS OF METALLURGY.
occasionally stirred with a platinum spatula, the alkaline silicate is care-
fully decanted from the insoluble residue upon a filter. A fresh quantity
of sodium-carbonate solution is now added, and, after heating during
another hour in the water-bath, the whole is thrown upon a filter and
carefully washed. The alkaline solution is now evaporated to dryness
with the addition of hydrochloric acid, and to the dried residue hydro-
chloric acid is first added, and afterwards water. After boiling, the silica
is separated by filtration, dried, ignited, and weighed. To the weight
thus obtained is added that of the silica resulting from the evaporation of
the iron solutions, and from the total is calculated the percentage amount
of silicon present in the metal; the insoluble residue may contain graphite,
slag, and titanic oxide.
By this process, Eggertz has found that the amount of silicon in good
bar-iron may vary from 0·01 to 0-10 per cent.; Krupp's steel afforded
0.30 per cent., while ordinary cast-steel, of good quality, contains traces
only. Iron, from a charcoal hearth, destined for the manufacture of wire,
contained 0.33 per cent. of silicon, while in armour-plates it amounts to
from 0.75 to 3·00, and in rails sometimes to as much as 5·00 per cent.
COBALT.
Cobalt is a metal of a steel-grey colour, and is susceptible of re-
ceiving a high polish; it is reduced from its oxides by ignition with
charcoal more easily than iron, and than some of the more difficultly-
fusible brittle metals; but when thus obtained it contains carbon.
Cobalt in its purest state is obtained by ignition of its oxalate. If
either oxalate of cobalt, or a mixture of oxide of cobalt with charcoal, be
strongly heated in a wind furnace, with a little powdered glass, free from
lead, a button of fused metallic cobalt will be obtained. Cobalt may
also be reduced from its oxides by hydrogen; but unless the heat applied
be considerable, the reduced metal is pyrophoric, taking fire in contact
with air, and giving rise to the production of Co304.
Cobalt fuses somewhat more readily than pure iron, and is attracted
by the magnet. It is capable of receiving a slight magnetic power when
rubbed with a magnet; and, according to Pouillet, this power is not de-
stroyed by the strongest red-heat. Its specific gravity is about 8.54. It
is not altered by the action of air and water at ordinary temperatures,
but when very strongly heated it takes fire, and is converted into the
3-oxide. It decomposes aqueous vapour at a red heat, and is dissolved
by hydracids; by dilute oxygen acids it is, by the aid of heat, slowly
dissolved with evolution of hydrogen gas. This metal unites by fusion
with antimony and arsenic, the combination being attended by incandes-
cence; the resulting alloys are brittle, and have an iron-grey colour.
Metallic cobalt is not employed in the arts.
COBALT.
355
COBALT ORES.
The principal ores of this metal are the following:-
Smaltine, CoAs,.-Occurs in octahedra, cubes and dodecahedra, more
or less modified. Colour, tin-white, inclining to steel-grey; structure,
granular and uneven; specific gravity, 6-4 to 7-2. This ore essentially
consists of cobalt and arsenic, and is found in veins associated with silver
and copper. Occurs in Cornwall; in Bohemia; at Freiberg, and, more
abundantly, at Schneeberg in Saxony.
Cobalt Glance, CoASS.-Lustre, metallic; colour, silver-white, in-
clined to red; streak, greyish-black. Occurs at Tunaberg, Riddarhyttan,
and Hokansbö, in Sweden, in large, well-defined crystals; also at
Skutterud, in Norway.
It is likewise met with at Querbach in Silesia, Siegen in Westphalia,
and at Botallack Mine in Cornwall. The most productive mines are
those of Vena in Sweden, which were first opened in 1809. This ore of
cobalt is also found in California, &c.
Cobalt Bloom.-Occurs in thin oblique crystals, having a well-defined
cleavage and foliaceous structure. It is also found as an incrustation on
other minerals, and in compact reniform masses. Its colour is a pinkish-
purple, resembling that of peach-blossom; when scratched it affords a
greenish streak. This mineral is generally associated with silver and
lead, and with other ores of cobalt, and is abundantly found at Schneeberg
in Saxony, Saalfeld in Thuringia, and Reichelsdorf in Hesse Cassel. It
is also found in England, in the counties of Cornwall and Cumberland,
but does not occur in this country in sufficient abundance to render its
extraction of commercial importance. Its percentage composition, accord-
ing to Bucholz, is 39 cf oxide of cobalt, 37 arsenic anhydride, and 22
of water: formula Co,As₂O,,8H₂O. When heated it gives off arsenical
fumes, and, fused with borax, affords a bead of a fine blue colour.
Mispickel sometimes contains from 5 to 9 per cent. of cobalt.
ESTIMATION OF COBALT AND Nickel.
The ores of cobalt and nickel are usually very complex in composi-
tion; they are, however, almost invariably found together, and conse-
quently the methods employed for their estimation and separation from
each other, as well as from the various metals with which they aro
generally associated, will be described as one series of operations.
The ore is finely crushed, and, according to its richness, from 4 to 7
grammes may be taken for analysis. If the mineral contain much sulphur
or arsenic, it is first roasted in a porcelain crucible in the muffle, in order
to dispel the greater proportion of these substances. The residue is then
well boiled with hydrochloric acid, to which a little nitric acid has been
added, until the metallic oxides are completely dissolved. The solution
is slightly diluted with water, nearly neutralised with ammonia, more
water added, and then boiled with an excess of acetate of sodium, by
which iron and aluminium are separated in the form of basic acetates;
*
2A 2
356
ELEMENTS OF METALLURGY.
the precipitate thus obtained will also contain arsenic. It is best to re-
dissolve this precipitate, after washing, in hydrochloric acid, and, after
neutralising part of the free acid with ammonia, to precipitate a second
time by acetate of sodium and boiling, as a small quantity of cobalt and
nickel is generally carried down in the first precipitate of basic acetates.
The two acetate solutions are now mixed and carefully neutralised with
ammonia. They contain all the cobalt and nickel, and possibly some
manganese, zinc, copper, bismuth, and lead. On passing sulphuretted
hydrogen through the solution, cobalt, nickel, zinc, copper, bismuth, and
lead are thrown down as sulphides, leaving the manganese in solution
along with any earthy oxides present in the ore. These sulphides are
collected on a filter, washed, dried and roasted, dissolved in hydrochloric
acid, and the copper, bismuth and lead removed by passing a stream of
sulphuretted hydrogen through the acid solution. The filtrate is now
evaporated nearly to dryness, the salts taken up with water, a little acetate
of sodium and a few drops of ammonia added, and then freely acidified with
acetic acid. On passing sulphuretted hydrogen through this acetic acid
solution the zinc is thrown down by itself as sulphide of zinc. The
filtrate from the sulphide of zinc contains the whole of the cobalt and
nickel, which are finally precipitated as sulphides by making it alkaline
with ammonia and again passing sulphuretted hydrogen. The sulphides
of cobalt and nickel are thrown on a filter, washed, dried, thoroughly
roasted, and weighed. After roasting, the nickel exists as NiO, the cobalt
as Co3O4. These oxides may be reduced at a full red heat by means of
hydrogen gas, and the nickel and cobalt weighed as metals.
It now remains only to separate the cobalt from the nickel. The
oxides or metals are dissolved in hydrochloric acid and the excess of acid
driven off by evaporation. The chlorides are dissolved in water and the
solution poured into a flask, with the addition of an excess of freshly-
precipitated carbonate of barium, together with a few drops of bromine.
The flask is loosely corked and the fluid allowed to stand six or eight hours,
with frequent agitation. The cobalt is precipitated as peroxide, while
the nickel remains in solution. The precipitated cobaltic oxide and
the excess of carbonate of barium are well washed and dissolved in
hydrochloric acid, and, after separating the barium by sulphuric acid,
the cobalt is precipitated by potash. After washing, drying and igniting,
it is either weighed as Co₂O4, or reduced to the metallic state by hydrogen.
The filtrate from the cobalt, containing the nickel, is of a pure green colour.
After removing the baryta by means of sulphuric acid, the oxide of
nickel is thrown down by potash and weighed. From the weight of the
oxide of nickel thus obtained, the percentage of this metal present is
calculated. The yield of cobalt is usually returned as Co₂O4.
PREPARATIONS OF COBALT.
Two compounds of cobalt are extensively employed in the arts,
namely, oxide of cobalt and smalt.
Oxide of Cobalt.-In the preparation of oxide of cobalt on a large
scale, the speiss, or matt resulting from the fusion of arsenical ores of
COBALT.
357
cobalt, is first subjected to calcination. The roasted speiss is subsequently
dissolved in strong hydrochloric acid, and iron, arsenic, &c., precipitated
by the gradual addition of milk of lime. When the precipitate thus ob-
tained has subsided, the clear supernatant liquors are drawn off into vats,
in which sulphuretted hydrogen is passed through them so long as any
metallic sulphides are produced. As soon as these have completely
settled, the clear liquid is again drawn off, and the oxide of cobalt pre-
cipitated by the addition of bleaching powder. The hydrate thus obtained,
heated to redness, constitutes blue oxide of cobalt, and after being heated
to whiteness becomes the prepared oxide of commerce.
These oxides, which are principally made in Birmingham by the
nickel refiners, are employed in the potteries and by glass-makers,
enamellers, and others, who use them, either alone or in conjunction with
various fluxes, for imparting a blue colour to their wares.
Smalt. The preparation of smalt, which is a double silicate of cobalt
and potassium, was invented in Saxony about the year 1550, and is the
only process in connection with the ores of cobalt which can be regarded
as a metallurgical operation. Smalt is applicable to all purposes for
which a cheap durable blue is required as a surface-colour. A pigment
of this kind is attackable only by agents capable of decomposing glass;
smalt is, consequently, more permanent than the majority of colours.
The ore destined for the manufacture of smalt is first roasted in a
reverberatory furnace having in communication with it chambers for con-
densing the arsenical fumes which are evolved. After having been suit-
ably roasted in this furnace, the ore is mixed with pure siliceous sand
and carbonate of potassium. Zaffres are ores of cobalt, which contain a
sufficient amount of silica to form a blue glass with the addition of car-
bonate of potassium only. The fusion of the mixture is effected in large
earthen pots arranged in a furnace similar to that employed in the manu-
facture of plate-glass. From the great fusibility of the ingredients, the
whole will have become completely melted at the expiration of eight hours,
and during this time the mass is often stirred until the glass appears
homogeneous, and a speiss containing a little cobalt and a considerable
amount of nickel, together with arsenic, iron, &c., has sunk to the
bottom. The smalt is now laded out from the pots with a large iron
ladle, and thrown into a reservoir through which a current of water
constantly flows; by this treatment it becomes split into fragments, and
its subsequent pulverisation is consequently much facilitated. When the
pots have been nearly emptied, each ladleful withdrawn will consist of a
mixture of speiss and smalt; the former, being completely liquid, readily
separates from the more viscous glass which adheres to the ladle, whilst
the metallic matts are run into cast-iron moulds. These, during the time
they remain hot, give off dense arsenical vapours, and are therefore
placed in niches in the brickwork of the furnace, so as to be in direct
communication with the chimney.
The deeply-coloured blue glass, after being removed from the vats
into which it has been thrown, is ground with water to the state of an
impalpable pulp between large granite millstones.
358
ELEMENTS OF METALLURGY.
The blue pulp thus obtained is passed, in suspension in water, through
a series of wooden vats, in which the coarser particles are first deposited,
and where the powder which gradually settles is classified in accordance
with its order of deposition. From these vats the pasty smalt, after
being allowed to drain, is removed to drying-kilns, and is finally sifted
through fine metallic sieves to remove lumps, and packed for the market.
Cobalt Blue, or Thénard's Blue, is prepared by precipitating a solution
of nitrate of cobalt by phosphate of potassium, and adding to the result-
ing gelatinous deposit from three to four times its volume of freshly-
deposited alumina, obtained by the addition of carbonate of sodium to a
solution of common alum. This mixture, after being well dried and
calcined, affords, when properly ground, a beautiful blue pigment.
Printers' Blue is the colour used for printing the ordinary blue
patterns on china. It is mixed with oil, printed on paper, and transferred
to the biscuit-ware; the colour is developed during the process of glazing.
This colour is prepared by fritting silicate of cobalt with nitre, and
adding a little sulphate of barium.
Rinmann's Green is a permanent green pigment prepared by precipi-
tating a mixture of the sulphates of zinc and cobalt with carbonate of
sodium, and igniting the precipitate after careful washing. It may be
also made by mixing a solution of nitrate of cobalt with either nitrate or
oxide of zinc, and subsequently evaporating and igniting.
NICKEL.
Nickel
This metal is closely allied to iron and cobalt, being associated with
them, not only in meteorites, but also in the majority of its ores.
is a silver-white metal, ductile and malleable, and but slightly more
fusible than iron, which, according to Deville, it surpasses in tenacity.
Nickel, containing small quantities of carbon, is more fusible than the
pure metal; its specific gravity is 8-279, but this may be increased by
forging to 8.666. Nickel, previously heated, burns in oxygen gas like iron;
the pulverulent metal obtained by the reduction of oxide of nickel by hydro-
gen at a low red-heat is pyrophoric. When oxide of nickel is strongly
heated with charcoal in a wind furnace it becomes reduced to the metallic
state, and, by combining with a portion of the carbon present, gives rise
to the formation of a fusible carbide, which collects in the form of a
button at the bottom of the crucible in which the fusion has been con-
ducted. When treated either with hydrochloric or weak sulphuric acid,
this metal dissolves with the evolution of hydrogen gas; it also dis-
solves readily in nitric or in nitro-hydrochloric acid.
NICKEL ORES.
The ores of nickel, with but few exceptions, have a pale colour and
metallic lustre. In some respects they resemble those of cobalt, but are
NICKEL.
359
distinguished from them by not communicating a blue colour to borax
when fused before the blowpipe. Specimens of native nickel are said to
have been obtained from the Erzgebirge, but it is not found in sufficient
quantities to constitute an article of commerce.
Copper-Nickel; Kupfernickel.-This is a mineral of a pale copper-
colour, affording a brownish-red streak. It occurs massive, and has a
metallic lustre. It is extremely brittle, and has a specific gravity vary-
ing from 7.3 to 7.5. This ore is essentially composed of 44 parts of
nickel and 56 of arsenic; formula, NiAs. When heated before the blow-
pipe it gives off alliaceous fumes, and subsequently fuses into a pale-green
globule, which darkens on exposure to the oxidising flame. Copper-
nickel is generally found associated with the ores of copper, silver, and
cobalt, and is principally obtained from the mines of Saxony; small
quantities have, however, been raised in this country, particularly at Pen-
gelley and St. Austell Consols mines in Cornwall, and at the Bathgate
silver mine in Scotland.
Among the other ores belonging to this class, although, from their
scarcity, of less commercial importance than the above, may be mentioned
the following:-
White Nickel, formula NiAs2, an arsenical ore, found at Reichelsdorf
in Hesse Cassel, and at Schneeberg in Saxony. It contains from 20 to
30 per cent. of nickel.
Nickel Glance, formula NiAsS, another arsenical ore, containing
sulphur, occurring both massive and in cubical crystals. This mineral,
which is of a steel-grey colour, is found in Sweden, in the Hartz, and at
Schladming, Austria. It contains from 20 to about 38 per cent. of
nickel, and has a specific gravity of about 6·7.
Antimonial Nickel, NiSb, containing 29 per cent. of nickel and no
sulphur. It is a pale copper-coloured mineral from Andreasberg.
Millerite is a brass-yellow sulphide of nickel, occurring in delicate
capillary forms; it is found in small quantities in Bohemia, Saxony,
Cornwall, South Wales, &c.; contains 64 per cent. of nickel, and has a
density of 5.3; formula NiS.
Pentlandite, a double sulphide of iron and nickel Fe₂NiS, of a bronze
yellow colour, containing from 18 to 21 per cent. of that metal, is
obtained from Southern Norway. A somewhat similar mineral, contain-
ing from 10 to 12 per cent. of nickel, has been discovered in the
neighbourhood of Inverary, in Scotland, and is also noticed by Mr. King
as occurring in the La Motte Mine, Missouri, United States. Another
sulphide of nickel containing bismuth, has been found in some of
the German mines, which have also produced specimens of arseniate
(arsenate) of nickel of a beautiful apple-green colour.
Zaratite, or Hydrated Carbonate of Nickel, usually occurs as an in-
crustation on other minerals. It is nearly transparent, of a bright
emerald-green colour, and has a vitreous lustre. Another ore of nickel,
of a brown, or nearly black colour, and containing variable quantities of
sulphur, is found in connection with ores of cobalt at La Motte.
360
ELEMENTS OF METALLURGY.
METALLURGY OF NICKEL.
The nickel of commerce is chiefly obtained from copper-nickel,
from pyrites containing nickel, and from the speiss obtained as a secondary
product during the treatment of nickeliferous ores for smalt, &c. Various
processes are employed for the preparation of metallic nickel, but the
details of the various operations in use in this country are usually kept
secret by the manufacturers.
Berthier dissolves either roasted speiss or Kupfernickel, together with
the quantity of iron found by previous experiment to be necessary for the
removal of arsenic, in boiling nitro-hydrochloric acid containing an excess
of nitric acid, and evaporates to dryness. The residue is treated with
water, which leaves a large quantity of undissolved ferric arseniate,
and carbonate of sodium is added to the filtrate, which is kept constantly
stirred until the precipitate begins to exhibit a green tint; by this means
the remainder of the ferric arseniate will be thrown down, together with a
portion of the cupric oxide. Should the precipitate, which is white when
first deposited, not eventually become brown, it is an indication that the
amount of ferric oxide present is not sufficient to effect the complete re-
moval of the arsenic; more ferric chloride must consequently be added,
and ferric oxide be precipitated by the cautious addition of carbonate of
sodium. The filtrate is treated with sulphuretted hydrogen, and the
clear liquid, separated from sulphide of copper, &c., is boiled with excess
of carbonate of sodium. The precipitate, chiefly consisting of a mixture of
the carbonates of cobalt and nickel, is, after being thoroughly washed,
diffused in water, and a current of chlorine is passed through it as long
as this gas continues to be absorbed. After exposure to the air for the
purpose of allowing the escape of any excess of chlorine, the liquor is
filtered, and from the filtrate so obtained oxide of nickel, free from oxide
of cobalt, may be precipitated by an alkali.
Cloez (Jahresb. 1857, p. 619) dissolves finely-pulverised and perfectly-
roasted Kupfernickel in strong hydrochloric acid, and adds an excess of
acid sulphite of sodium. The mixture is afterwards vigorously boiled
until the whole of the arsenic acid has been reduced to arsenious acid; the
excess of SO, is driven off; sulphuretted hydrogen is subsequently passed
through the lukewarm solution in order to precipitate arsenic, copper, anti-
mony, lead, bismuth, &c., and the mixture is allowed to stand for twelve
hours. The whole is now thrown upon a filter, and the filtrate evaporated
to expel excess of acid; water is finally added, and iron and cobalt pre-
cipitated, after oxidation by chlorine, by addition of carbonate of barium
or carbonate of calcium. The dissolved baryta, or lime, is removed by
sulphuric acid and separated by filtration; carbonate of sodium added to
the filtrate yields a precipitate of pure carbonate of nickel, which is sub-
sequently ignited and reduced. Solutions of speiss in nitro-hydrochloric
acid may be treated in the same way after first expelling the nitric acid
by boiling with excess of hydrochloric acid.
The principal nickel works in this country are situated in the neigh-
bourhood of Birmingham, the details of the various operations being, as
NICKEL.
361
far as practicable, kept secret; the general routine practised in these
establishments is, however, understood to be as follows: The ore, or
speiss, or a mixture of the two, is first fused in a reverberatory furnace,
with addition of lime and fluor-spar as flux; the slags thrown away, the
resulting matt, or speiss, finely ground, and subsequently roasted until
arsenious fumes cease to be evolved.
The roasted product is now treated with hot hydrochloric acid, in
which it becomes almost completely dissolved, the solution is diluted
with water, the whole of the iron peroxidised, and the iron and arsenic
precipitated by neutralising the liquor and subsequently boiling. Sul-
phuretted hydrogen is passed through the clear liquors, separated from
the precipitate above referred to, until a filtered sample becomes black on
the addition of ammonia. The precipitate by sulphuretted hydrogen is
separated and washed, and the solution treated with chloride of lime
(bleaching powder), to which is added a little caustic lime to neutralise
the acid liberated. By this means oxide of cobalt is precipitated, and,
after being washed and ignited, is ready for the market; the nickel is
precipitated by addition of milk of lime to the liquor from which the
cobalt has been previously thrown down.
The reduction of nickel oxide thus obtained, is frequently effected by
a process of cementation. For this purpose a number of cylinders of
refractory clay are set vertically in a furnace, so that the flame may play
around them on all sides; these are open at top, and terminate at bottom
in truncated cones projecting below the fire-bars, and through which the
charge is removed. The dried oxide of nickel, either in lumps or in
small cubes, intimately mixed with powdered charcoal, is introduced
at the top of these cylinders, and a strong heat externally applied. The
reduced metal retains the form of the lumps or cubes of oxide introduced,
and is from time to time withdrawn through orifices in the bottoms of
the cylinders; a fresh charge is at the same time introduced at the top,
so that the operation becomes, to a certain extent, continuous.
The hydrated oxide of nickel produced in the wet way is sometimes
mixed in a pasty mass with about 5 per cent. of flour and a little syrup
and water. This mixture, which has the consistency of dough, is beaten
into a frame, and subsequently cut into cubes of something less than an
inch square; these are dried, and afterwards reduced to the metallic
state in crucibles or in tubes in which they are heated to whiteness whilst
surrounded by charcoal-dust.
According to Aubel, nickel has been fused before the tuyer of a
Rachette furnace, and Montefiore states that it may be melted in much
larger quantities in the apparatus devised by Deville and Debray for the
fusion of platinum.
The chief use of nickel in the arts is for the preparation of the white
alloy usually known as German silver; it is also a constituent of the
coinage of Belgium, of Switzerland, and of the United States of America.
German silver is an alloy of copper, nickel, and zinc, in variable propor-
tions. According to Miller, the alloy resulting from fusing together
51 parts of copper and 18-4 of nickel, and subsequently adding 30.6
362
ELEMENTS OF METALLURGY.
of zinc, is of good quality. This mixture is in the ratio of Cuz,
Zna, Nią.
Within a very few years the price of this metal has risen from 4s. to
11s. per lb., and its present production, which is estimated at 600 tons
annually, appears to be rapidly becoming unequal to the demand.
ALUMINIUM.
Aluminium is a white metal, possessing a colour between that of
silver and zinc. It is malleable and ductile, but requires repeated
annealing during the operations of rolling or drawing into wire. Its
specific gravity varies from 2.5, when obtained by fusion, to 2.7 after ham-
mering. The melting point of aluminium has not been accurately deter-
mined, but it lies somewhere between that of zinc and silver. This metal
when pure is not acted on by moist air, but slowly decomposes steam at
a red-heat; it is not attacked by cold nitric acid, and only slowly on
boiling; dilute sulphuric acid has no effect upon it, but it is readily dis-
solved by hydrochloric acid with evolution of hydrogen. It is not
attacked by sulphuretted hydrogen or even by sulphide of ammonium,
and consequently preserves its lustre in an atmosphere in which silver
would rapidly become blackened. The vegetable acids exert no per-
ceptible action on aluminium, and this metal is consequently well
adapted for culinary vessels, particularly as any small quantities of
alumina which might be formed would be perfectly innocuous. The
hydrates of potassium and sodium, in a state of fusion, do not act upon
aluminium, but their aqueous solutions dissolve it readily with formation
of aluminate of potassium or of sodium and evolution of hydrogen. It
may be fused without any kind of flux, and may be readily cast into any
required form; precipitated from its solutions by electrolysis at low
temperatures, it crystallises in octahedra, which appear to be regular.
Aluminium heated in a close vessel does not exhibit the slightest ten-
dency to volatilise; it combines with sulphur at very high temperatures
only, and is acted on but slightly by ammonia.
The minerals from which aluminium may be extracted are perhaps
more widely and plentifully distributed than the ores of any other metal,
although, owing to the great stability of its compounds, it is only recently
that it has been obtained in an isolated state. Its oxide forms the base of
all clays, pure kaolin containing 36 per cent. of alumina, or about 19 per
cent. of the metal; on a commercial scale this metal is usually prepared
either from bauxite, a hydrated mixture of ferric oxide and alumina, con-
taining about 50 per cent. of the latter, or from cryolite, a double fluoride
of aluminium and sodium, containing 13 per cent. of aluminium. The
estimation of the quantity of aluminium present in an ore is a chemical
rather than a metallurgical question. It is, however, invariably weighed
as Al¿О¸, usually obtained by precipitation from its solutions by means
ALUMINIUM.
363
=
of either ammonia or carbonate of ammonium; the precipitate is col-
lected on a filter, and, after washing and drying, is ignited and weighed.
From the weight of alumina found, the percentage of aluminium may
be readily calculated.
METALLURGY OF ALUMINIUM.
This metal was first obtained in the elementary form by Davy,
shortly after his discovery of the alkali and alkaline-earth metals; he
does not however appear to have succeeded in obtaining it free from
an admixture of potassium. In 1827 Wöhler obtained it in the form of
a grey powder, by the reduction of its chloride, and some years later he
succeeded in preparing it in the form of minute globules. The reduction
of this metal has not hitherto been accomplished except by the aid of
electrolysis, or of one of the metals, potassium or sodium, which have a
greater affinity for chlorine and fluorine than has the aluminium with
which they are in the first instance combined; in practice, sodium is in-
variably employed to effect this decomposition, partly on account of its
greater cheapness and steadiness of action, and partly because its lower
atomic weight enables it to perform a larger amount of work than an
equal weight of potassium.
Oersted prepared aluminium chloride by exposing an intimate mix-
ture of alumina and charcoal at a high temperature to the action of a
current of chlorine. The chloride of aluminium formed, volatilised,
and was collected in a suitable receiver; this he mixed with potassium
amalgam, and on subjecting the mixture to heat, potassium chloride was
formed, and aluminium combined with the mercury; this last was
expelled by distillation, and a button of aluminium remained behind.
The method of preparation at present adopted is in principle the same as
that employed by Wöhler, and depends on the action of sodium at a red-
heat on the chloride or fluoride of aluminium, or, still better, on the
double fluoride of aluminium and sodium.
We are indebted for much of our present knowledge of aluminium to
Saint-Claire Deville, whose first researches were published in the year
1854. The process which he first employed consisted in passing the
vapour of chloride of aluminium over metallic sodium maintained at a
red-heat in a tube either of copper or iron. Metallic aluminium was
thus obtained, mixed with the chlorides of aluminium and sodium, which
were removed by washing with hot water. The globules of aluminium
were consolidated by heating to the melting-point and causing them to
unite by pressure. The metal thus obtained was subsequently re-melted
and cast into bars.
The reduction of aluminium may be effected in an earthen or an iron
crucible in the following way: 40 parts of the double chloride of alumi-
nium and sodium, 20 parts of chloride of sodium, 20 parts of fluor-spar or
cryolite, the latter being preferable, all finely pulverised and perfectly
dry, are placed with from 7 to 8 parts of sodium, in alternate layers, in
the pot, and the whole gradually heated until reaction begins to take
364
ELEMENTS OF METALLURGY.
place;
the heat is now increased to bright redness, and the fused mass,
after being well stirred with an iron rod, is poured into a mould. By
this process two parts of aluminium may be obtained in a compact mass,
and one-fourth of that quantity in the form of divided globules inclosed
in the resulting fusible slag. The metal thus prepared is somewhat
contaminated by silicon derived from the crucible, which is more or less
attacked by the sodium and aluminium, as well as by the fluorides pre-
sent in the slag; this may be, to some extent, obviated by lining it either
with calcined alumina or with aluminate of calcium. When iron crucibles
are employed, the aluminium produced is found to contain a certain
amount of that metal.
If large quantities are operated upon, the reduction is conducted in a
reverberatory furnace; a mixture of 10 parts of the double chloride of alu-
minium and sodium and 5 parts of either fluor-spar or cryolite is heated
with 2 parts of metallic sodium. The double chloride and the cryolite,
or fluor-spar, are mixed in the state of fine powder with sodium in small
ingots, and the whole is charged upon the bed of the furnace, which has
been previously heated to the required temperature. An intense reaction
at once takes place, a large amount of heat being developed, and the
complete liquefaction of the mass is effected. As soon as the reaction
is complete, the furnace is tapped in the usual way, and its contents run
off into a receiver prepared for that purpose. The slag thus obtained
separates into two layers, of which the upper consists, to a large extent,
of common salt, while the lower one, which is less fusible, chiefly con-
sists of fluoride of aluminium. On pulverising and sifting the latter, an
additional amount of aluminium is obtained in the form of flattened
shot; the fluoride of aluminium may be subsequently employed for the
preparation of alumina. This process, which has been patented in France
and in this country by MM. Rousseau Frères and M. Paul Morin, is
particularly advantageous, inasmuch as the reduced metal is but little
contaminated by silicon.
In preparing aluminium from cryolite, which occurs abundantly
in West Greenland, the pulverised mineral is mixed with half its
weight of common salt, and the mixture arranged in alternate layers
with sodium in an earthen or iron crucible; the proportion employed
being 2 parts of sodium to 5 of cryolite. A layer of pure cryolite is
placed on top, and the whole covered with common salt. The crucible
and its contents are heated until complete fusion of the mass has been
effected, when it is well stirred with an iron rod and set aside to cool.
On breaking the pot, the aluminium will be found accumulated at the
bottom in the form of large globules, which are collected and re-melted.
This is the process as originally practised by Professor H. Rose in
Berlin, and by Dr. Percy and A. Dick in this country; it is now con-
ducted on a manufacturing scale by MM. Tissier, at Amfreville, near
Rouen.
Aluminium alloys readily with most of the metals; with zinc and
tin it forms brittle alloys; with iron it unites in all proportions, forming
alloys which are both hard and brittle. When iron is present to the
COPPER.
365
amount of 7 to 8 per cent. its alloys crystallise in long needles. Alloyed
with even a small proportion of silver, aluminium loses its malleability.
An alloy of aluminium with 3 per cent. of silver, is employed for
casting ornamental articles; it possesses the colour and lustre of silver,
and is not blackened by sulphuretted hydrogen. Aluminium-bronze is an
alloy usually of 10 parts of aluminium and 90 of copper; it has the
colour of gold, is extremely hard, and takes a fine polish; it is very
malleable, and possesses a tenacity equal to that of steel.
COPPER.
This metal appears to have been known in remote antiquity; and,
alloyed with about one-tenth of its weight of tin, it was anciently employed
for making edge-tools and instruments of war. Copper has a strong red
colour, is very malleable, ductile, and tenacious, and when warmed or
rubbed exhales a peculiarly disagreeable and characteristic odour.
The copper met with in commerce is not chemically pure, but is con-
taminated with other metals, such as lead, iron and antimony. Pure
copper may be precipitated by electrical agency from a solution of a pure
salt of that metal, and the variety of copper known as best-selected is
very nearly pure; tough-cake and tile-copper contain traces of arsenic,
nickel, tin, iron, sulphur, &c.
Chemically pure copper may be obtained by reducing cupric oxide.
to the metallic state, by passing over it a stream of hydrogen gas, while
heated in a hard-glass tube. Under these circumstances the reduction
takes place below a red-heat, and the metal which remains in the tube is
found in the state of a powder, readily assuming a metallic lustre when
rubbed between two hard surfaces.
The specific gravity of this metal varies slightly, in accordance with the
nature of the treatment to which it has been subjected; hammered or rolled
specimens have a greater density than ordinary fused copper which has
not been thus compressed. The density of copper varies between 8·78
and 8.96; it melts at a heat slightly above the fusing point of silver, and
when heated to whiteness gives off distinct metallic vapours, which have
the property of imparting a green colour to flame.
When copper at ordinary temperatures is exposed to the action of
perfectly dry air its surface is not oxidised; but if acted on by a damp
atmosphere, and particularly when acid vapours are present, it quickly
becomes covered with a green substance, known as "verdigris."
Water is decomposed by copper when heated to whiteness in an atmo-
sphere of steam: oxide of copper is formed, and hydrogen gas set free.
A concentrated solution of hydrochloric acid attacks copper, when in a
state of fine division, with considerable facility; but when the metal is
exposed to its action in more solid masses its solution is attended with
some difficulty.
366
ELEMENTS OF METALLURGY.
it.
The presence of the stronger acids does not determine the decomposi-
tion of water by this metal. When dissolved in concentrated sulphuric
acid, sulphurous anhydride is plentifully evolved.
Nitric acid, even when cold and considerably diluted with water,
dissolves copper with great facility, and gives rise to the rapid evolution
of nitric oxide, which, coming in contact with the oxygen of the air,
produces large quantities of the characteristic red fumes caused by the
resulting compound.
The tenacity of copper is less than that of iron, but greater than that
of either gold, silver, or platinum.
COPPER ORES.
NATIVE COPPER; Cuivre natif; Gediegen Kupfer. Isometric.-This
metal frequently occurs in a native or malleable state, and is in all pro-
bability the result of certain electro-chemical influences, by which sulphate
of copper arising from the oxidation of its various sulphides is caused
slowly to deposit the metal which it contains.
Native copper is most frequently met with in irregularly-shaped
masses, occupying the fissures of the rocks in which it is found; but it
sometimes also occurs in a crystalline state, and in this case the crystals
are either cubes, octahedra, or some immediately-derived form.
Native copper is both malleable and ductile; has a red colour, metallic
lustre, and shining streak; possesses no traces of cleavage, and readily
fuses before the blowpipe into a well-defined metallic globule, which, on
cooling, frequently becomes externally coated with a thin layer of black
oxide.
In some localities specimens of this metal occur in a perfectly pure
state, but it more frequently contains traces of other metals, and particu-
larly iron and silver.
Native copper is met with in the copper mines of Cornwall, Brazil
and Siberia, as also abundantly in the district to the south of Lake
Superior, where masses exceeding 150 tons in weight have sometimes been
extracted. Splendid crystallised specimens are also procured from Siberia
and from the island of Naalsö, one of the Faröe Isles, where it accom-
panies fibrous mesotype in amygdaloidal trap.
The crystals of copper are, generally speaking, far from regular, some
of their faces being much more developed than others: the crystalline
form is usually most perfectly represented at the extremities of branches
produced by the union in rows of compressed and less perfect crystals.
The minerals of which copper forms an essential constituent are
numerous and important, but we shall chiefly confine our attention to
such as are metallurgically treated, and are consequently entitled to be
ranked among the ores of copper.
CUPRITE; Octahedral Copper Ore; Cuivre oxydulé ; Rothkupfererz. Iso-
metric. This oxide is remarkable for its fine cochincal-red colour, which
may be most distinctly observed in transparent and translucid specimens.
This oxide frequently occurs in well-defined crystals of a ruby-red
COPPER.
367
colour; its lustre is semi-metallic, streak shining and reddish-brown,
fracture hackly or sometimes conchoidal, and its cleavage, which is much
interrupted, parallel to the faces of the octahedron. When crystals of
this mineral are opaque, they are sometimes of an iron-grey tint on the
surface, but their peculiar red colour at once becomes apparent when they
are reduced to the state of a finely-divided powder. This mineral has a
density of 5.99; its composition is as follows:-
Cu
88.80
11.20
These proportions are represented by the formula Cu₂O.
Octahedral copper oxide is found in many of the Cornish mines;
particularly in those near Redruth, and at the Phoenix mines, near
Liskeard.
Isolated crystals, sometimes an inch in diameter, were formerly
obtained at Chessy, in the neighbourhood of Lyons; and many splendid
specimens have been brought from the Banat and from Katherinenburg,
in Siberia. This oxide is sometimes also found in extremely slender
reticulated crystals; specimens of this variety are occasionally obtained
from the mines of West Cornwall and from some of those on the Rhine.
MELACONITE; Black Oxide of Copper; Cuivre oxydé noir; Kupfer-
schwarz. Isometric.-In many copper mines a black substance is found,
which stains the fingers when handled, and is principally composed of
cupric oxide mixed with various carthy impurities. Analysis shows that
this substance sometimes contains sulphur and arsenic, and often con-
siderable quantities of the oxides of iron and manganese.
From this circumstance it would appear that black oxide of copper,
which in many localities is obtained in sufficient abundance to render its
extraction an important consideration, is the result of the decomposition
of other ores, such as copper pyrites, and that the sulphur and arsenic
which it still retains are merely the result of an incomplete decom-
position of such minerals.
This substance is commonly found disseminated among other ores of
copper, and sometimes occurs in shining botryoidal concretions or dull
friable masses.
REDRUTHITE; Vitreous Copper; Cuivre sulfuré; Kupferglanz. Ortho-
rhombic.-Sulphide of copper is of an iron-grey colour, and is often
iridescent; found in crystals, but more frequently in compact lamellar
masses; pseudomorphic crystals of this mineral, have occasionally been
discovered. The specimens obtained from the Cornish mines, and espe-
cially from Cook's Kitchen, in the neighbourhood of Redruth, frequently
present themselves in thin hexagonal tables. This ore is friable, and
when scratched affords a shining lead-grey streak.
When pure it may be readily cut with a knife, and is fusible in the
flame of an ordinary candle. Its density varies, according to the texture
of the specimen, from 5.5 to 5-8, and the crystals possess a distinct
cleavage, parallel to the faces of the original prism.
Sulphide of copper is almost always contaminated with a certain
368
ELEMENTS OF METALLURGY.
amount of sulphide of iron, by which its hardness and fusibility are con-
siderably modified; but specimens obtained from the Siegen district are
comparatively free from this impurity.
The composition of a specimen of this mineral, from Tellemark,
Norway, analysed by Scheerer, was found to be as follows :—
S
Cu
Fe
20.36
79.12
0.28
99.76
Its composition will therefore be expressed by the formula Cu₂S.
Although in this country magnificent crystals of vitreous copper are
sometimes obtained from the Cornish mines, they are nevertheless almost
exclusively confined to Cornwall; the more compact and massive varieties
occur in Siberia, Saxony, the Banat, and, according to B. Silliman, in
Nova Scotia.
COPPER PYRITES; Chalcopyrite; Cuivre pyriteux; Kupferkies. Tetra-
gonal.—This mineral is distinguished by its strong metallic lustre and
deep brass-yellow colour. It usually occurs in amorphous masses, with
an irregular and slightly conchoidal fracture: it is also found in mam-
millated, stalactitic, and botryoidal forms, as well as in tetrahedral and
octahedral crystals. Its specific gravity varies from 4.1 to 4.3, and when
strongly heated on charcoal before the blowpipe it readily fuses into a
dull-black globule, which, from the presence of iron, speedily becomes
magnetic. When mixed with a little carbonate of sodium, and similarly
treated, it yields a button of metallic copper; if dissolved in nitric acid
or in aqua regia it affords a solution which, on the addition of ammonia,
assumes a fine blue colour.
The following analyses give the composition of specimens of this
mineral from two different localities :-
From Cornwall.
Analysed by R. Phillips.
From Sayn.
Analysed by H. Rose.
S
Cu.
35.16
35.87
30.00
34.40
Fe
32.20
30.47
Gangue
2.64
0.27
100.00
101 01
Its composition will consequently be represented by the formula
Cu₂S,Fe¿S¸, or CuFeS2.
This mineral is found in lodes or veins, which usually occur either in
granite or in clay-slate, although it is also sometimes met with in
serpentine, gneiss, and other rocks. It is most commonly associated in
these deposits with iron pyrites, blende and galena, together with car-
bonates and other ores of copper.
COPPER.
369
The principal localities in which this valuable ore is found are Corn-
wall and Devon, in England; in Saxony; at Eisleben and Sangerhausen,
Prussia; at Goslar, in the Lower Hartz; at Schemnitz and Kremnitz, in
Hungary; at Fahlun, in Sweden; in the Ural Mountains, in Russia; as
also in China, Japan, and in South Australia; formerly at Chessy, near
Lyons, in France.
The Cornish copper ores, so extensively treated in the neighbour-
hood of Swansea, are chiefly composed of this mineral, and constitute a
large proportion of the total amount of copper ores raised in the United
Kingdom.
This ore, although of common occurrence, is not, however, brought
into the market in a very concentrated state, as, from the comparative
cheapness of fuel in the neighbourhood of the furnaces and the facilities.
afforded by a short water-carriage, it is found more economical to treat
the poorer ores, than to concentrate them, beyond a certain point, by
means of a better system of mechanical preparation.
The ores sold at Redruth, in Cornwall, where the mineral products
of the western division of that county are disposed of, rarely yield above
8 per cent. of metallic copper, and even 6 per cent. of metal may be
considered an average of the produce of the total quantity of ore sold.
ERUBESCITE; Cuivre panaché; Buntkupfererz. Isometric. This ore,
which holds a somewhat important position among copper-producing
minerals, has a reddish-brown colour, and metallic lustre; its surface is
commonly iridescent with different shades of blue, purple and red, from
which circumstance it is called cuivre panaché, by French mineralogists.
Fused before the blowpipe, it presents similar reactions to those
obtained from ordinary copper pyrites, but when found in a crystalline
form the crystals are either cubes or octahedra, of which the faces are
not usually well defined. It occurs in the compact form, associated with
other ores of copper, in Chili, Cornwall, Siberia, Silesia, Norway, and the
Banat; also at Killarney, in Ireland, and in the cupreous shales from
the neighbourhood of Mansfeld, in Germany.
In this country the crystallised variety has, as yet, only been found in
Cornwall, where, among other localities, it occurs in the Dolcoath and
Tincroft mines, in the neighbourhood of Redruth.
This, like ordinary copper pyrites, is a double sulphide of copper
and iron; analyses of two specimens, by Varrentrapp and Phillips,
afforded the following results:

From Cornwall; From Killarney;
Varrentrapp.
Phillips.
Cu
58.20
61.07
S
26.98
23.75
Fe
14.84
14.00
Gangue
0.50
100.02
99.32
2 B
370
ELEMENTS OF METALLURGY.
The specific gravity of the crystallised varieties varies from 4.9 to 5·1,
and the different faces of the crystals are, in many specimens, slightly
curved; formula, 3Cu,S,Fe₂S, or CuFeS¸.
TETRAHEDRITE; Cuivre gris; Fahlerz. Isometric; tetrahedral.-
Usually occurs massive, but sometimes crystallised, in well-defined cubes
and tetrahedra. Its colour varies from steel-grey to iron-black, and when
scratched it yields either an unchanged or a slightly brown streak. It has
a conchoidal fracture, and sometimes an imperfectly-developed cleavage
parallel to the faces of the octahedron. It is brittle, and has a density
varying from 4·6 to 5·1.
23
Dana considers that the general composition of this mineral may per-
haps be represented by the formula 4Cu₂S+Sb₂S, or Cu.Sb,S,, in which
each of the different metallic constituents may be, to a greater or less
extent, replaced by the substitution of other isomorphous elements; so
that sulphide of arsenic may be substituted for sulphide of antimony,
sulphide of silver. for sulphide of copper, &c.
This mineral frequently contains zinc and silver, and occasionally
mercury. The following analyses of different specimens of this ore will
serve to illustrate its variable constitution:
Locality.
S.
Sb.
As.
Cu.
Fe.
Zn.
Ag.
From Clausthal; Rose
24.73
28.34
;
34.48
2.27 5.55 4.97
Wolfach; Rose
23.52
26.63
25.33
3.72 3.10 17.71
• •
Corbières; Berthier
25.30
25.00
1.50
34.30
1.70 6.30 0.70
""
Gersdorf; Rose
26.33
16.52
7.21
38.63
4.89 2.76 2.37
roth
Locality not named; Klap-} 10-00
14.00
48.00 25.50
0.50
•
Some of the finest crystals of this substance have been obtained from
the mines near St. Austell, in Cornwall; and very beautiful complex
crystals of a bright polished aspect are found at Andreasberg, in the
Hartz; Kremnitz and Kapnick, in Hungary; Freiberg, in Saxony; and
Dillenburg, in Nassau. Besides occurring in the above localities, the
massive variety is found at Schwatz, in the Tyrol; in Siberia and else-
where. This mineral is not only important as an ore of copper, but is
frequently much increased in value on account of the silver which, in
greater or less quantity, it almost invariably contains.
BLUE CARBONATE OF COPPER; Azurite; Kupferlazur. Monoclinic.-
This mineral, which occurs both in mammillated concretions and in well-
defined and very brilliant crystals, is of a beautiful blue colour, and is
sometimes perfectly transparent, although more commonly only trans-
lucent. Its specific gravity varies from 3.5 to 3.9; lustre, vitreous or
adamantine; fracture, conchoidal, and streak of a somewhat lighter
blue than that of the mineral itself. When acted on alone before the
blowpipe it is melted by the oxidising flame into a black globule. By
the reducing flame a bead of metallic copper is obtained. It dissolves
with effervescence in nitric acid, and yields a solution affording all the
COPPER.
371
common reactions of copper. When fused with borax in the oxidising
flame a glass of a bright-green colour is produced.
Its composition, according to analyses by Phillips and Karsten, is as
follows:-

Specimen from
Chessy;
R. Phillips.
Specimen from
the Banat;
Karsten.
CuO
69.08
69.08
CO₂
25.46
25.72
H₂O
5.46
5.20
100.00
100.00
3
The above numbers correspond to the formula 2(CuO,CO,)+CuO,H₂O,
or 2CuCO₂+CuH2O2. This mineral occurs associated with the red oxide
and the green carbonate of copper, and is found both in primitive and
secondary formations. Some of the chief localities from which blue
carbonate of copper has been obtained are, Chessy near Lyons, Siberia,
and the Banat. Specimens of this ore are also found at Redruth, in
Cornwall; Alston Moor, in Cumberland; in the Cuban mines, and in
large quantities at Burra Burra, in South Australia. When obtained in
sufficient quantity this substance constitutes a valuable ore of copper; it
is likewise, when ground to a fine powder, occasionally used as a bluc
pigment; but from having a tendency to lose its original hue and to
become green by exposure to light and air, it is but little employed for
this purpose.
MALACHITE; Cuivre carbonaté vert; Malachit. Monoclinic.--Green
carbonate of copper is remarkable for its fine emerald-green colour, of
which the same specimen usually exhibits a great diversity of shades.
When in a crystallised state, this substance is found in various forms
derived from the oblique prism; but it is more frequently met with in
mammillated, reniform, and compact amorphous masses.
Malachite, although rarely found in the crystalline forms above de-
scribed, frequently presents itself in the shape of variously-modified
octahedra, produced by the conversion of cuprite into carbonate, as also
in oblique prisms of a fibrous internal structure derived from the decom-
position of the blue carbonate. It is likewise found in stalactiform
masses, having a fibrous radiated structure made up of several suc-
cessive layers, of which the extent and thickness are readily apparent
and well defined. It is sometimes met with in a friable and pulverulent
form, and is in that case commonly associated with various sandy or
earthy impurities.
Malachite is found in considerable quantities in the Ural Mountains,
in the mines of South Australia, in the island of Elba, formerly at Chessy,
in France; in the old mine at Sandlodge, in Shetland; in the Banat,
the Tyrol, and in some of the Cornish mines. It is, from its high per-
centage of metal, a valuable ore of copper, but it is also highly prized by
2 B 2
372
ELEMENTS OF METALLURGY.
the lapidary for various ornamental purposes. Such varieties as are suffi-
ciently compact are often cut into snuff-boxes or mounted as brooches,
studs, and other articles of jewelry; in Russia polished plates of this
mineral are made up into tables, cabinets, and various objects of luxury.
The density of this ore varies from 3.6 to 4·0; lustre, adamantine, in-
clining to vitreous; streak of a rather paler green than the mineral itself.
Its percentage composition is as follows:-

From Siberia; Also from Siberia;
Vauquelin.
Klaproth.
CuO
70.10
71.70
CO2
21.25
20.50
H₂O
8.45
7.80
99.80
100.00
The above numbers indicate that the composition of this mineral may
be represented by the formula CuO,CO₂+CuO,H,O or CuCO,+CuH₂O₂.
Malachite is advantageously employed for mixing with various sulphides
of copper during the operations of smelting, in which it serves as an
economical and effective flux. It is also sometimes employed as a green
pigment for the use of artists; it affords a valuable material for the manu-
facture of the various salts of copper, and may be converted into blue
vitriol by solution in dilute sulphuric acid and subsequent crystallisation.
CHRYSOCOLLA; Silicate of copper; Cuivre hydraté silicifère; Kiesel-
kupfer. Cryptocrystalline; often resembling opal in texture; earthy. In-
crusting various minerals, or filling crevices, sometimes botryoidal. Accom-
panies other ores of copper; chiefly occurs near the surface. Colour,
mountain-green, bluish-green, passing into sky-blue or turquoise-blue.
Found in the copper mines of Cornwall, Hungary and Tyrol; in
Saxony, Bavaria, South Australia, at Keweenaw Point on Lake Superior,
and various other localities in North America.
Its composition varies considerably, from the presence of impurities, as
is generally the case with amorphous minerals, resulting from alteration.
Analyses of two specimens of this mineral from different localities
afforded the following results:

From Coquimbo,
Chili; F. Field.
From Cornwall ;
Berthier.
SiO2
28.21
26.00
CO₂
3.70
CuO
39.50
41.80
Fe2O3
2.80
2.50
A1203
4.97
H₂O
24.52
23.50
Gangue
2.50
100.00
100.00
Probable formula: CuO,SiO,+2H2O, or CuSiO3,2Aq.
COPPER.
373
OTHER MINERALS CONTAINING COPPER.-The other minerals of which
copper forms an essential ingredient are extremely numerous and inte-
resting; but as they seldom occur in sufficient quantities to constitute,
properly speaking, ores of this metal, they present greater interest to the
mineralogist than to the smelter.
Selenide of Copper is a rare mineral, isomorphous in composition with
redruthite; it is of a tin- or silver-grey colour, is fusible like the sulphide,
and is readily cut with a knife. The arsenides of copper are numerous,
but of little importance in a commercial point of view. Condurrite is an
arsenide of copper of a tin-white to steel-grey colour; found in the mines
of Cornwall. Euchroite, which is found at Libethen, in Hungary, is an
emerald-green mineral, containing 33 per cent. of arsenic anhydride, and
48.0 of oxide of copper. Aphanesite is of a dark-green colour, inclining
to blue, and contains 30 per cent. of arsenic anhydride and 54 of cupric
oxide. This variety comes from Cornwall. Erinite, from Limerick, in
Ireland, occurs in mammillated coatings, is of an emerald-green tint, and
contains 38.8 per cent. of arsenic anhydride and 59.4 of cupric oxide.
This has been shown by Church to be a Cornish species. Copper-mica,
found in Cornwall and Hungary, is of a grass-green colour, and occurs in
remarkably thin lamina; it contains 21 per cent. of arsenic anhydride
and 58 of cupric oxide.
Of the phosphates of copper there are three distinct varieties
Pseudo-Malachite, Libethenite, and Thrombolite. The first is found in some
parts of Hungary, and near Bonn, on the Rhine; it is of a dark or emerald-
green colour, and occurs either in very oblique crystals, or as a massive
incrustation on the surface of other minerals. The second-specimens
of which are found in Hungary, Cornwall, &c.—is a dark or olive-green
substance, occurring either massive or in slender crystals, and containing
64 per cent. of oxide of copper. The third and last variety is a green
phosphate, occurring in Hungary, and containing only 39 per cent. of
cupric oxide.
Sulphate of Copper is found in a crystallised state in many of the mines
from which copper pyrites and the other sulphides of copper are ob-
tained. This salt when produced by natural causes resembles in every
respect that obtained by artificial means; it crystallises according to the
triclinic system, has a fine blue colour, and is formed by the oxidation of
the sulphides of copper.
Atacamite, a hydrated oxychloride of copper, is a mineral of a beauti-
ful green or greenish-black colour and vitreous lustre. It occurs in
massive fragments, in rectangular prisms and octahedra; gives off fumes
of hydrochloric acid when heated before the blowpipe. This mineral is
found in Cornwall, Saxony, South Australia, in the neighbourhood of
Vesuvius, and in the desert of Atacama, between Chili and Peru. In
Chili this mineral is sometimes ground into powder, and sold under the
name of arsenillo, as a sand for dusting letters.
The other minerals containing copper are rare, and are consequently
not of importance as a source of that metal.
374
ELEMENTS OF METALLURGY.
DISTRIBUTION OF COPPER ORES.
Copper not only occurs in many different forms of combination, but
its geographical distribution is also very extensive, and its geological
range equally wide. Ores of this metal are found in rocks of all ages,
from the Laurentian to the Cretaceous, but their deposition appears to
have gone on with greater activity during the Permian period than during
any other. To this era are ascribed many of the copper veins of Corn-
wall, although traversing much older rocks; the Kupferschiefer of Ger-
many, so extensively worked in the district around Mansfeld, is of the
same geological age.
The principal portion of the copper produced in this country is
obtained from the mines of Cornwall and Devonshire; but the Ecton
mines in Staffordshire at one time furnished considerable returns, and
Parys mine in Anglesea once yielded large supplies. Wales has from
time to time furnished a limited quantity, and Ireland contributes about
700 tons of copper annually. The production of copper in the United
Kingdom has very much decreased since 1862, when it amounted to
14,843 tons; in 1872 it had been reduced to 5,600 tons; and the present
annual yield of the mines of this country probably does not exceed this
amount.
In France there were formerly mines of considerable interest at
Chessy near Lyons. These deposits, which occurred at the junction of
mica-slate with Triassic and Jurassic rocks, chiefly consisted of azurite
and cuprite; but after furnishing the cabinets of Europe with the finest
known specimens of these minerals, they became rapidly exhausted.
The most important copper-producing district of Prussia is that
around Mansfeld, where mining has for centuries been carried on in the
Kupferschiefer, immediately beneath the Zechstein. The copper-bear-
ing stratum seldom exceeds 18 inches in thickness, but extends with
wonderful regularity over an area of many square miles of country; the
portion which is smelted constitutes from 10 to 18 per cent. of this
seam, and contains copper in the form of inclosed particles of various
disseminated sulphides. The proportion of copper in the ore averages
about 2 per cent., while that of silver does not exceed th of 1 per cent.
The various Mansfeld establishments, which are worked with consum-
mate skill, treat about 175,000 tons of ore annually, and, in addition to
about 4,000 tons of copper, yielded, in 1871, fine silver to the amount of
36,490 lbs. A small quantity of copper is annually produced in the
neighbourhood of Sicgen, and near Kupferberg in Lower Silesia. The
production of copper in Prussia in 1871 was 8,000 tons.
1
70
The principal copper mines of the Russian empire are in the Ural
Mountains, the Altai, the Caucasus, and in Finland; but the latter are
of minor importance. The copper ores of the Caucasus are said to be
abundant, and there is evidence of their having been worked at a very
carly period; the present yield of these mines, as well as of those in
the Altai, is not considerable. There are extensive mines in the Ural
Mountains, as well as on their western flank, where certain beds of Per-
COPPER.
375
mian age are cupriferous, and possess a remarkable analogy with the
Kupferschiefer of Mansfeld. These beds do not extend westward
beyond 500 versts from the Ural chain, and the proportion of copper
decreases as they recede from the mountains.
The copper deposits on the eastern side of the Ural produce, how-
ever, the largest portion of this metal furnished by Russia; the prin-
cipal mines are the Gumeschewskoi, the Bogoslowskoi, and those of
Niny Tagilsk. The Gumeschewskoi mine, which has been worked for
more than a century, is opened on irregular deposits of ore, chiefly
malachite and cuprite, in an argillaceous shale. The mines of Bogos-
lowskoi are worked in Silurian limestone, much traversed by trap dykes,
along the line of contact with which copper occurs in irregular bunches;
crystals of native copper, unsurpassed in beauty and regularity, are
obtained from this locality. At Nijny Tagilsk the main features are
the same, namely, deposits of ore in connection with igneous rocks tra-
versing Silurian limestone. The amount of copper furnished yearly by
Russia is estimated at between 6,000 and 7,000 tons.
The districts of Schmölnitz, in Upper Hungary and Tsiklova, in
the Banat, produce copper. The copper mines of the Schemnitz district
have considerably decreased in importance. The total annual production
of copper in the Austrian empire is believed to be about 3,500 tons.
The quantity of copper furnished by the Scandinavian peninsula is
small, but has somewhat increased within the last ten years. The mines
of Alten, in Norway, are said to be in the most northern position of any
in the world, being in latitude 70°. The mine of Stavanger is of some
importance, as are also those of Röraas, where there are no veins, the ore
being disseminated in chloritic slate, forming fahlbands, or metalliferous
beds. The copper deposits of Sweden resemble those of Norway. There
are eight groups of mines or mining districts, principally in the province
of Dalecarlia. Fahlun has long been celebrated for its copper mines;
but its importance is much diminished, and it is now nearly exhausted;
the ores are poor, and do not yield above 4 per cent. of metal after being
hand-picked. The annual production of copper in Sweden and Norway
is estimated at about 2,500 tons.
The amount of copper produced from Spanish ores is somewhat con-
siderable. The most remarkable deposits are those of Rio Tinto and those
belonging to the Tharsis Sulphur and Copper Company, situated in the
province of Huelva. Both these mines have been worked at various times,
from the Roman period to the present. Since 1787 considerable quantities
of copper have been annually obtained from the former by precipitation
by means of iron from the waters issuing from the ancient workings.
From the latter mines some 200,000 tons of cupreous iron pyrites are
annually imported into this country, which on an average contain
about 2 per cent. of copper. This is first burnt for the production of
sulphuric acid, and the resulting cinders are treated for copper by the
wet process. The total production of copper from Spanish ores, in-
cluding copper precipitate imported into this country, is estimated at
about 7,500 tons annually.
In Portugal, at San Domingos, near the mouth of the river Gua-
376
ELEMENTS OF METALLURGY.
diana, there are extensive mines of cupreous pyrites worked by Messrs.
Mason and Barry of London; these annually export to this country
about 175,000 tons of ore, of the same produce for copper as those from
the Spanish mines; there is also a small quantity of copper ore raised
from workings situated at a distance of a few leagues from Oporto. The
total annual production of copper from Portuguese ores and precipitate
is probably about 5,500 tons.
The only copper mines of any importance in Italy are those of Monte
Catini, which are contact-deposits, for the most part in serpentine. A
certain amount of copper of good quality is annually exported from
Turkey, and copper ores occur at Tenès and near the Mouzaïa Pass, in
Algeria; at the latter place the veins are inclosed in rocks very high in
the geological series, belonging, it is believed, partly to the Gault and
partly to the Tertiary period.
Copper is found in the East Indies and in Japan; about 1,000 tons
annually are said to be exported from the latter country. South
Australia produces large quantities of rich copper ores, yielding metal
of good quality; a large portion of this ore is now smelted in the
colony. The celebrated Burra Burra mine, eighty-six miles from
Adelaide, was first opened in 1845, and at once began to yield large
quantities of the red oxide and green carbonate of copper. In 1850 the
production from this mine was 18,962 tons of ore, averaging from 24 to
26 per cent. of copper. The produce of this mine is now comparatively
inconsiderable, but the total annual yield of the colony probably ex-
ceeds 11,800 tons of copper; the principal mines at present worked are
those on Yorke's Peninsula.
Large quantities of copper ore have for some years been imported
from the Cape of Good Hope. The annual yield from this source is com-
puted at 7,500 tons of 32 per cent. produce.
Among the important copper mines of Chili are those of Corrisal,
north of the valley of Huasco, those of San Juan and La Higuera
between Huasco and Coquimbo, besides numerous others in the vicinity
of Coquimbo. Large quantities of gold were obtained from the upper
portions of the veins in this district previously to the close of the last
century; as the production of gold fell off that of copper increased.
In 1845 there were more than fifty mines in the province of Coquimbo
producing ores containing from 20 to 25 per cent. of metal; a portion
of these was smelted on the spot, while the remainder was sent to this
country for treatment. The principal vein of the Cerro Blanco district
was worked for silver to a depth of 100 fathoms below the summit of
the mountain; here the ore changed gradually to fahlerz and galena, and,
still deeper, the grey copper ore was replaced by copper pyrites. The
present annual production of copper in Chili and Bolivia is estimated at
about 46,500 tons. A portion of the ore is smelted in the country, and
the remainder either run into regulus, or exported in the raw state. The
copper mines of Peru are but imperfectly developed, and the annual
returns small.
The mines of Cuba were formerly of great importance, but of late
years their production has been very much restricted. Copper ores are
COPPER.
377
found scattered in considerable abundance throughout Mexico, but mines
of this metal are not worked to any considerable extent. The most
important copper-producing region of the United States is that lying on
the southern shore of Lake Superior, where native copper is found
in true veins in trappean rocks and their associated conglomerates,
which, for the most part, cover beds of sandstone, ascribed by Whitney
to the Lower Silurian period. The most remarkable feature of this dis-
trict is that the copper does not exist in the form of an ore, but almost
exclusively as native metal; masses of nearly pure copper weighing over
150 tons have sometimes been met with, and require to be cut with
chisels into fragments of convenient size before they can be brought to
the surface. Copper pyrites occurs, to some extent, in the Silurian
sandstones and limestones of the Mississippi valley, but the deposits are
not extensively worked. Copper-bearing veins are found in numerous
localities, extending from Vermont to Tennessee, and are worked in
various places. In Montgomery and Chester counties, Pennsylvania,
copper veins traversing the New Red Sandstone and older metamorphic
rocks are somewhat extensively worked. The total production of copper
in the United States was, in 1872, 12,600 tons.
In Canada there are the copper mines on the northern shore of Lake
Huron, and the Acton and Harvey Hill mines in the neighbourhood of
Quebec, but the annual production of the Dominion is by no means large.
During the last eleven years Chili and Bolivia have supplied
1862
1863
·
35,430 tons
1868
23,977
1869
""
1864
36,355
1870
45,007 tons
46,163
47,355
""
1865
42.721
1871
•
37,986
""
1866
•
35,366
1872
44,124
1867
•
40,966
""
The entire supplies of copper which have been available since 1865
for the United Kingdom are estimated by Messrs. J. Pitcairn Campbell
and Co., of Liverpool, as follow:

1866.
1867.
1868.
1869.
1870.
1871.
1872.
Imports of foreign ore,
regulus, bars, &c., into 41,903 47,629 55,046 54,672 55,574 45,466 53,026
Liverpool
Ditto into London and
other outports
6,843 4,932 5,012 4,600 8,000 11,000 19,000
Cornish salês, estimated in 8,700
fine
Irish and other British
Copper made from pyrites,
&c., in this country
8,027 7,779 6,433 5,606 4,682 | 4,129
S00 1,500 1,500 1,300 1,300 1,100 965
2,000 2,848 3,000 6,500 8,000 9,625 13,000
60,246 64,936 72,337 73,505 78,480 71,873 90,120
Total exports to all parts in 1870
""
""
""
•
1871
1872
51,949 tons
54,340
45,273
""
The annual production of copper in the whole civilised world is pro-
bably between 126,000 and 130,000 tons.
378
ELEMENTS OF METALLURGY.
6
ASSAY OF COPPER ORES.
CORNISH DRY ASSAY.-In an exhaustive paper by M. Moissenet, pub-
lished in the Annales des Mines,'* on the English method of assaying
copper by the dry way, he justly remarks that within certain limits this
process is not less practical from being somewhat inexact; its object is
rather to furnish the smelter with the commercial value of an ore than
to indicate the exact amount of copper which it contains. In point of
fact, the Cornish assay affords, on a small scale, results similar to those
obtained by the smelter on a large one, and any impurities prejudicially
affecting the produce in the one case, will equally affect the results in
the other.
Apparatus employed.—The furnace employed for copper assaying in
Cornwall is of the form represented in fig. 27, page 144, and should be
about 10 inches long, 9 inches wide, and 14 inches in depth to the
grate; in a furnace of the dimensions stated, three fusions for regulus,
or four calcinations, may be made at the same time. The fuel employed
is invariably coke; but the size and number of the furnaces used vary
in accordance with the requirements of the assayer.
The well-known Cornish crucibles are always employed. They are
usually sold in nests of two, and, less frequently, of three. The largest
size, about 4 inches in height, is used for calcining ores and for fusions
for regulus; the small and middle-size pots are employed for calcin-
ing regulus, fusion for coarse copper, and refining, according to the
richness of the ore and the quantity operated on. These crucibles are
generally used without covers, and when several assays are being made
simultaneously, in order to prevent mistakes, each is marked with a
mixture of red oxide of iron and water before being placed in the
furnace.
The assayer, in addition to various tongs of convenient shapes for
handling red-hot crucibles and removing them from the fire, must be
provided with stirring rods, mould-plates for receiving the fused assays
when poured from the crucible, hammers, chisels, and an anvil for
testing the copper buttons, bronze or cast-iron mortars, an iron slab
about 18 inches square for breaking down slags upon, and sieves about
9 inches in diameter with from forty to fifty meshes to the linear inch,
for preparing samples. He also requires copper scoops for transferring
fluxes, &c., to the crucible, a regulus-bowl about 10 inches in diameter
and 5 inches in depth, kept partially filled with water for cooling the
poured assays, and which has a small annular shelf running round it
below the water-level on which the assays to be cooled are placed.
Forceps for picking up prills, &c., a ladle for drying samples or washing
ores, and flux-spoons for measuring out fluxes, are also necessary. The
flux-spoon is made of copper, and is usually 13 inch in width and 1 inch
deep; a balance capable of turning with grain when laden with 500
grains must be likewise provided.
1
25
Special weights, of which the unit is termed a cent, are used by
* Vol. XIII. p. 183.
COPPER.
379
2)
1
Cornish assayers for the purpose of facilitating calculation; the system
adopted is to divide 400 grains into 100 cents taken as a standard,
the smallest weight being, or 0.25 grain. Assays are reported on
100 parts and the unit subdivided into ½, 1, 3, and, so that the
produce of a sample is stated to be 71, 83, 125, 173 per cent., &c.
The fluxes and reagents used are as follow: Common salt, dried or
fused borax, glass free from lead, lime, fluor-spar, nitre, soda-ash, tartar
or cream of tartar, sulphur, charcoal or finely-powdered coal, iron pyrites,
and white flux, for refining.
Refining, or white flux, is prepared by deflagrating in a large crucible
three parts, by measure, of nitre, two of cream of tartar, and one of
common salt; carbonate of sodium, or carbonate of potassium, mixed with
a small percentage of nitre, may be used in place of ordinary refining flux.
Preliminary Examination.—The samples to be assayed usually reach
the assayer in a moist state in brown-paper parcels, each weighing about
1½ lb. After drying at a temperature of about 100° C. each sample is
ground, sifted, and mixed. If the ore is one which the assayer has not been
in the habit of testing, a small portion of it is washed, either on a shovel,
in an evaporating dish, or in a drying ladle; this is done with a view
of ascertaining, approximately, its quality and the proportions of copper,
sulphur, arsenic, gangue, &c., it contains. By practice in this manipulation
it becomes easy to determine beforehand whether, in the next operation,
the ore will or will not require calcination, whether nitre or sulphur
should be added, &c. An experienced assayer will in most cases, by
a simple inspection of the sample, decide correctly as to the mode of
treatment to be adopted; it is consequently only in cases of doubt that
washing is resorted to.
Method of conducting an Assay.—The characteristic peculiarity of the
Cornish method of assaying is the general preliminary concentration of
the copper in the form of regulus. Until within a comparatively recent
date this method of treatment was universal, and even rich carbonates and
oxides were always assayed on this principle. The relative proportions
of the various fluxes employed, as well as the smaller details of manipu-
lation, are slightly varied by different assayers in accordance with the
results of their individual experience; but in all cases the Cornish
method of assaying comprises the following operations:
1. Fusion for regulus.
2. Calcination of the regulus.
3. Fusion for coarse copper.
4. Refining.
5. Treatment of the slags for the copper they contain.
1. Fusion for Regulus.-The quantity of ore operated on varies in
accordance with its richness in copper; 400 grains are commonly used
for ores containing under 10 per cent. of copper; 200 grains for ores
between 10 and 30 per cent., and 100 grains for samples in which the
copper amounts to more than 30 per cent. The fluxes are not weighed,
but merely measured in the flux-spoon, their proportions being so
380
ELEMENTS OF METALLURGY.
adjusted as to yield a fusible slag with the gangue and oxide of iron,
resulting from the oxidation of pyrites, &c. They should also produce a
slag which separates easily from the regulus, and the amount of nitre,
sulphur, &c., should be such as to result in the formation of a regulus
containing about 50 per cent. of copper.
Yellow copper ore, without admixture of iron pyrites, contains a
larger amount of iron and sulphur than is required to form a regulus of
the richness desired.
Vitreous copper ore, on the other hand, requires iron and sulphur, in
order to produce a proper regulus. These may be supplied by the addi-
tion either of iron pyrites or of a mixture of sulphur and oxide of iron.
In order to obtain from copper pyrites a button of regulus containing
about 50 per cent. of copper, it is necessary to oxidise a large portion of
the sulphur present. This may be done either by a partial roasting
("warming"), by partial roasting and the addition of nitre in the sub-
sequent fusion, or, simply, by the addition of nitre. Either of these
methods may be adopted; the first and second require considerable expe-
rience with regard to the amount of roasting necessary, the third is more
simple and direct.
Rich oxides and carbonates may be fused directly for coarse copper,
care being taken to retain the slags for subsequent treatment; native
metal and bar-copper only require refining.
The raw, or more or less calcined, ore is intimately mixed with the
various fluxes required, introduced into a crucible of the largest size, and
over the whole is spread a layer of common salt or dried borax. When
a preliminary roasting has been resorted to, the crucible employed for that
purpose must be preserved for the subsequent fusion. This roasting
is conducted in crucibles, which, when placed in the furnace, are packed
round with coke to their full height, so that they may be as uniformly
heated as possible. A dull red-heat is maintained during the operation,
which is continued until the blue flame, due to burning sulphur, ceases, and
this usually occupies about ten minutes; if much iron pyrites is present
more time will be required. During the first part of the fusion effer-
vescence takes place from the escape of various gases, but this gradually
subsides, until, at the close, the surface of the slag becomes perfectly
tranquil. The crucible is now removed from the furnace, and after
having received a rotary motion for the purpose of washing down any
particles adhering to the sides, its contents are rapidly poured into an
iron mould.
As soon as the slag has solidified, the assay is seized with a pair of
copper forceps, dipped two or three times into water, and left to cool on
the circular shelf fitted around the inside of the regulus-bowl. This has
the effect of fissuring the slag in all directions and causes the regulus to
separate easily from it; should any slag adhere to the button obtained, it
will generally be on the upper surface, and may be removed by a slight
tap from either a light hammer or the edge of a spatula. After the
regulus has been thus carefully separated from the slag, the latter must be
COPPER.
381
examined to see that it contains no inclosed globules of regulus. If any
are found they must be picked out and added to the principal button pre-
viously obtained, taking care to avoid the addition of particles of slag.
In order to save time, the regulus is sometimes poured into one cavity of
the mould and the slag into another. In order to do this successfully,
however, a considerable amount of practice is required; but if there is
any doubt of the cleanness of the slag, or the regulus has not been per-
fectly separated from it, it may be remelted with the addition of a little
sulphur. The button of regulus thus obtained must be added to that
previously separated from the slag by pouring.
A good regulus should be reddish-brown in colour, slightly convex on
its upper surface, very much fissured, and easily reduced to powder.
When the regulus is too coarse it is more or less flat, and is often
vesicular on its upper surface; it is also comparatively hard, and varies in
colour from iron-grey to brass-yellow. When a coarse regulus has been
obtained there is but little fear of the slag retaining copper, but the cal-
cination of the regulus is not so readily effected. When the ore operated
on is very poor it is sometimes desirable to obtain a coarse regulus in
order to insure the complete separation of the copper.
When regulus is too fine the button is more or less spherical, and is
smooth, bright, and semi-metallic in appearance. Externally its colour is
nearly black, but when freshly broken the fractured surface is of a dark
bluish-grey colour, and presents a very compact structure.
Such a
regulus is more difficult to calcine than one which is not too fine, and
there is also in such cases danger of the slags retaining a certain amount
of copper.
2. Calcination of the Regulus.-The regulus is first reduced to a fine
powder in an iron or bronze mortar; after its removal a little coke-
dust is rubbed down in the mortar for the purpose of removing the last
particles and is added to the powdered regulus. In this finely-divided
state the mixture is introduced into one of the smaller or middle-size
crucibles, according to the quantity of regulus to be operated on, and
several calcinations are carried on in the furnace at the same time. The
furnace is filled with fresh fuel to within a short distance of the top, and
the crucibles are arranged upon it with a slight inclination forward, so
that air may readily pass over the surface of the powdered regulus. A
round stirring-rod of wrought-iron, about ths of an inch in diameter,
flattened at one end to a chisel-edge, and having a ring turned at the other,
is inserted into each crucible; when not held in the hand these are allowed
to lean against some support in order that they may be retained in their
positions. The calcination is commenced at a dull red-heat, which is
gradually increased to bright redness, in proportion as the contents of the
crucible are enabled to bear it, without becoming agglomerated. The
time necessary for complete calcination is usually about half an hour;
stirring must be constantly kept up during the first fifteen or twenty
minutes, after which it need only be occasional. When clotting occurs,
the regulus must be removed from the crucible, ground with a little coke-
3
Ι
382
ELEMENTS OF METALLURGY.
dust, and again calcined; if, however, agglomeration, to any considerable
extent, has taken place it is better to throw away the assay and begin
afresh. The calcination is complete when the odour of burning sulphur
is no longer evolved, and the sample is then said to have been roasted
sweet. When this occurs the crucible and rod are removed from the
fire, and when cold, any portion adhering to the rod is carefully scraped
off into the crucible. The same crucible is employed for the subsequent
fusion. The calcination both of the raw ore and regulus is sometimes
conducted in a scorifier heated in a muffle furnace; calcination is more
readily effected by this means and the operation is much expedited, but in
Cornwall it is almost universally performed in crucibles.
3. Fusion for Coarse Copper.-The flux employed for this operation is
usually a mixture of tartar and nitre in such proportions that the tartar
is in excess of the amount required to make carbonate of potassium by
ignition with the latter. In addition to this some assayers add borax,
others usc pounded glass, some use neither, while many employ common
salt. In the metallurgical laboratory of the School of Mines a mixture
of tartar or charcoal with carbonate of sodium is employed, but the
amount required will of course depend on the weight of calcined regulus
to be treated; the addition of an excess will not, however, be attended
with serious inconvenience. A mixture of 50 grains of nitre, 180 of
tartar, and 36 of borax, is sufficient for the reduction of a calcined
regulus weighing, previously to roasting, from 48 to 50 grains. For
a button, weighing from 90 to 100 grains, 85 grains of nitre, 220 of
tartar, and 50 of borax should be employed. These amounts are not,
however, weighed, since, with practice, it becomes easy to measure, with
sufficient accuracy, the quantities required.
The calcined regulus is mixed with proper fluxes in the crucible
employed for its calcination, and then introduced into a fire of coke
heated to bright redness; fusion takes place in from ten to fifteen minutes,
and as soon as effervescence ceases the melted contents are poured into
a mould. When the slag has become set, the assay can be cooled by being
dipped into water, or it may be allowed to remain in the mould until
sufficiently cold to handle. The slag should be black and glassy, and
neither it nor the inside of the crucible should present any streaks or
patches of red, due to the presence of copper. These slags are retained
for subsequent fusion, although in many cases they are practically free
from copper.
4. Refining. The crucible employed in the previous operation is
placed well down among the coke in the assay furnace, in such a position
as to be directly under the line of junction of the two bricks forming the
cover, and when it has become red-hot the button of coarse copper is
dropped into it. The furnace is now nearly closed, and the operation
closely watched through the opening between the bricks. Fusion is soon
effected and a slight evolution of gas takes place from the dull surface of
the metal. After the expiration of a short time the film of oxide begins
rapidly to disappear from the surface of the button, which becomes
COPPER.
383
perfectly bright at the edges, and reflects a bluish-green light from its
centre, producing the appearance technically known as the "eye" or
"star." Some refining flux, or refining flux and salt, previously placed
in a copper scoop ready for immediate use, is now introduced upon the
top of the fused button, and the furnace is again closed; in about two
minutes after the introduction of the flux the crucible is withdrawn from
the fire and its contents rapidly poured into a mould. When it has
sufficiently set, the button, which is covered with slag, is removed
between the jaws of a pair of forceps and held with its lower side
beneath the surface of the water in the regulus-pan; by this means the
slag is easily detached, and the whole operation of refining does not
usually occupy above seven minutes. The button of copper when fine
is nearly flat and has its upper surface coated with a thin film of an
orange-red colour. The metal in this condition is soft, malleable and
tough, breaking with difficulty, and presenting a closely-fibrous fracture.
It is, however, more commonly somewhat dry, presenting a slight depres-
sion on its upper surface, and when broken exhibiting a granular fracture
which has a purple tint. When not sufficiently refined the button, both
externally and when broken, presents, to a certain extent, the appear-
ance of coarse copper; in this case refining must be repeated. Salt is
generally used in refining, as it not only checks the too rapid action of
the refining flux, but also probably aids in the separation of antimony,
arsenic, &c.
5. Treatment of the Slags for Copper.-The slags resulting from the
operations of reducing and refining are subsequently treated by fluxing
with a couple of spoonfuls of tartar or a little powdered charcoal. By this
means, the copper retained by the slags will assume the form of a small
button or prill, the weight of which must be added to that of the prin-
cipal button. The prill obtained usually weighs from 1 to 5 grains,
according to the nature of the assay and the skill of the operator. Cornish
assayers always refine the copper thus obtained from re-melting the
slags, but the quantity is often so small that the error resulting from
omitting this operation would practically be unimportant.
GERMAN METHOD OF ASSAYING.-The method of conducting copper
assays in the smelting establishments of central Europe differs essen-
tially from that adopted in this country, and the results obtained are
stated to be somewhat higher.
The apparatus employed consists of an ordinary muffle furnace;
crucibles of the form commonly known as "skittle pots"; scorifiers of fire-
clay about 2½ inches in diameter, and an assortment of tongs, hammers,
&c. In addition to borax, salt, glass, and powdered charcoal, graphite
and metallic lead and arsenic are employed; black flux, prepared by
deflagrating a mixture of two parts of crude tartar and one of nitre, is
used as the reducing agent.
The process includes the three following operations:-
1. Roasting; calcining.
2. Melting for coarse copper.
3. Refining.
384
ELEMENTS OF METALLURGY.
1. Roasting; Calcining.-About 4 grammes of dry ore are weighed out,
mixed with one gramme of powdered graphite, and spread upon the bottom
of a scorifier. This is introduced into a heated muffle and is almost con-
tinuously stirred during fifteen or twenty minutes, after the lapse of which
time sulphurous fumes should be no longer given off. The scorifier is
then removed from the muffle and allowed to cool, the assay carefully
brushed from it into a bronze or cast-iron mortar, where it is finely
ground, and, after being again mixed with 1 gramme of pulverised
graphite, it is subjected to a second calcination similar to the first. At
the expiration of about fifteen minutes the mass will have generally
assumed a reddish-brown appearance, and the evolution of sulphurous.
fumes will be no longer perceived.
When either lead or antimony is present in an ore, the roasting
requires to be conducted with considerable care, since if the assay were
too strongly heated its surface would become fused, and its further
calcination materially interfered with.
2. Melting for Coarse Copper.—After roasting, the metals in the assay
will be principally in the state of oxides, and the object of the fusion,
which now follows, is to collect the whole of the copper in the metallic
form, while the principal portion of the metals with which it is associated
passes into the slag as oxides. The calcined ore is carefully removed from
the scorifier or roasting-dish, and is mixed in a mortar with from 3 to 3½-½
grammes of black flux; this mixture is introduced into the crucible, and
upon it are placed, without mixing, 8 or 9 additional grammes of black
flux; on this are placed 1½ to 2 grammes of powdered glass and 1 gramme
of borax. The whole is covered by a layer of from 8 to 12 grammes of
common salt, and lastly, a piece of charcoal of the size of an ordinary
bean is added; when the ore is rich in copper and no lead is present,
addition is made, with the glass and borax, of from to 1 gramme of
metallic arsenic. The crucible is now covered and placed in the muffle,
where it is gradually raised to a white-heat, the fusion being completed
in about thirty or thirty-five minutes. When complete fusion has been
effected, and the slag is in a perfectly liquid state, the crucible is with-
drawn from the muffle, and, after being allowed to cool, is broken and
the button of metal extracted. This must not be covered by a crust of
sulphides, and the slag should be glassy, and of a dark-green colour,
without any traces of red.
3. Refining.—As in the case of the Cornish assay, this process has for
its object the removal from the copper of the various other metals by
which it is contaminated. In order to effect this, advantage is taken of
the property possessed by copper of remaining, practically, unchanged
when exposed in a fused state to the action of a current of air, so long as
a more oxidisable metal is present. The metals thus oxidised in the
presence of borax, which is added for that purpose, are taken up and
carried off as a fusible slag. The scorifier employed for refining the
coarse copper, often consists of a fragment broken from the side of
a pot in which a fusion has been already effected; in this, which has
been previously heated to bright redness in the muffle, is placed the
COPPER.
385
button of copper to be refined, wrapped in paper with its own weight of
borax.
As soon as the copper shows a convex perfectly-clear surface, and is
surrounded by a thinly-fluid ring of borax, the mouth of the muffle is
opened, and a current of air allowed to play over its surface. If the
surface of the copper be not clear, but is covered with a black coating,
at the time the muffle is at a white-heat, a further addition of borax must
be made. Should this not result in the production of a bright surface
a small piece of lead must be dropped into the scorifier and the heat
of the furnace increased to its maximum. When the button of coarse
copper is very impure and does not contain above one-half its weight
of pure copper, it must be first placed on the scorifier with borax only,
the lead being added towards the close of the operation. A small portion
of the lead thus added escapes in the form of fume, while the greater
part passes into the slags. Arsenic is to a very great extent volatilised,
but a portion is retained in the slag. The removal of nickel by scorifi-
cation is extremely difficult and necessitates a large addition of lead,
which results in a considerable loss of copper.
When the copper has become fine it brightens like silver, but less
distinctly. Care must be taken that the temperature of the muffle at the
moment of brightening does not much exceed that at which pure copper
solidifies. The assay, which in brightening exhibits a peculiar greenish
light, is now removed from the furnace, cooled, quenched in water, freed
from slag, and weighed. A good assay button is exteriorly of a pure
copper-colour, is ductile, uniformly granular, and rose-red in the fracture.
When a button has not been sufficiently refined it is externally red, but
its fracture is grey; an over-refined button is dark red on the surface
and brittle, the fracture being rather smooth than granular.
Refining on the cupel is in use in some of the smelting works of the
Hartz; it is not more accurate than the above, although perhaps more
suitable for copper containing large quantities of lead.
WET ASSAY OF COPPER ORES. PRECIPITATION BY ZINC OR BY METALLIC
IRON. This method of estimating copper is especially adapted for ores
containing little or no arsenic, and consists in attacking the mineral to
be examined by a mixture of nitric and hydrochloric acids, the sub-
sequent expulsion of the nitric acid, and the precipitation of the copper
from its chloride, by zinc or by metallic iron.
The mineral to be operated on must be first pulverised and passed
through a fine sieve. Of this powder, 100 grains are weighed and intro-
duced into a narrow-necked flask of hard German glass. Nitric acid is
now cautiously added, and the flask gently warmed on a sand-bath;
since if the flask were too suddenly heated, or too large a quantity of
acid were added at a time, violent ebullition might ensue and a loss on
the assay be the result.
When the evolution of nitrous vapours entirely ceases, or they become
much diminished in quantity, add gradually hydrochloric acid, place the
flask in an inclined position on the sand-bath, and cause its contents to
2 c
386
ELEMENTS OF METALLURGY.
boil gently. This must be continued until the residue, if any remain,
appears to be free from metallic stains.
The contents of the flask must now be carefully transferred to a
porcelain dish and evaporated to dryness, with the usual precautions.
When sufficiently cool, moisten the residue with hydrochloric acid, heat
gently, and afterwards add water, boil, and filter into a beaker.
A piece of zinc or polished wrought-iron, about 2 inches in length,
3 inch in width, and inch in thickness, is now attached to a string and
lowered to the bottom of the beaker. It is essential to the success of
this operation that the whole surface of the metal should be completely
covered by the liquid, otherwise a portion of the precipitate would
become oxidised and the results vitiated. The contents of the beaker
must now be kept in gentle ebullition until the whole of the copper
present has been thrown down, which is ascertained by the liquor becom-
ing colourless. This may be confirmed by trying a drop of the liquid on
the surface of a piece of clean sheet-zinc, or by the blue colour produced
by the addition of ammonia in excess to solutions containing copper.
After having ascertained that the whole of the copper has been
thrown down, carefully clean with a feather the piece of metal which
has been used as a precipitant, and then decant off the supernatant liquor
by the aid of a small glass syphon, and repeatedly wash with warm
water, until the precipitated copper is entirely free from any traces of
chloride of zinc or chloride of iron.
The washing water is finally decanted, leaving the precipitated copper
in the bottom of the beaker, which is now placed in a water-bath or in
a warm place near a furnace, until it has become completely dried.
In this operation it is necessary to so regulate the heat as to prevent
the oxidation of the copper, by which the accuracy of the result would
be, to some extent, impaired.
The copper thus obtained is subsequently brushed into a watch-glass,
by the aid of a camel-hair brush, and weighed; on deducting from this
weight the tare of the watch-glass, the result represents the percentage
of copper present.
When the mineral operated on contains either lead or antimony no
appreciable trace of these metals will be found in the copper precipitated.
If large quantities of lead be present, it is, however, best to add sulphuric
acid or sodium sulphate, and to filter previously to the precipitation of
the copper.
If no perceptible oxidation of the precipitated copper has taken place
its weight will sufficiently indicate the produce of the ore; it is however
safer to check the result so obtained by converting the metallic copper
into cupric oxide, from the weight of which the yield of the ore is
readily calculated. The conversion of the finely-divided copper into
cupric oxide may be effected by exposing it to a red-heat, in an uncovered
porcelain crucible, until its weight becomes constant; or the copper may
be transformed into nitrate by the addition of a few drops of nitric acid,
and cupric oxide obtained by subsequent ignition. As this oxide is
highly hygroscopic it must be weighed rapidly and while still warm.
COPPER.
387
Still more accurate results may be obtained by dissolving the pre-
cipitated copper, and estimating its amount by a standardised solution of
potassium cyanide.
PELOUZE'S PROCESS. The amount of copper contained in many ores
and mineral substances, of which this metal forms one of the con-
stituents, may be determined with a considerable approach to accuracy
by the following process invented by Pelouze:-
The substance in which the copper is to be estimated must be dis-
solved in an acid capable of effecting its complete solution, and an excess
of ammonia afterwards added, by which the copper is held in solution
with the production of the characteristic blue colour. Into this liquor,
whilst in a state of ebullition, a standardised solution of sodium sulphide
is poured from a graduated burette, which determines the precipitation of
the copper in the form of a dark-brown oxysulphide of that metal. If
this precipitation be effected with proper precautions, and a little am-
monia added from time to time, as the metallic solution nearly approaches
saturation, it becomes easy to determine at what precise period the whole
of the copper has been thrown down, as the liquid entirely loses its blue
colour when the last traces have been deposited. If the liquor contain
no other substance which can be precipitated by the solution of alkaline
sulphide, it will be easy to calculate the amount of copper present from
the volume of the solution poured from the burette, since each division
of the instrument corresponds to a definite and previously-ascertained
quantity of copper.
To determine the strength of the test solution of sodium sulphide, a
definite weight, say 0·50 gramme of perfectly pure copper, should be
dissolved in a proper quantity of nitric acid, and to this liquid ammonia
is added, until the deposit at first formed has entirely re-dissolved and a
bright blue solution, free from cloudiness, is obtained. Into this liquor
the solution of sodium sulphide is gradually poured from the burette in
which it has been measured, and when the contents of the flask begin
to lose colour it is repeatedly shaken, and afterwards allowed to settle.
At this point of the operation, the liquid from the graduated measure
is dropped into the copper solution with great caution, in order that
the point at which precipitation ceases to take place may be noted with
accuracy. By making two or three experiments of this kind, and taking
the mean of the results obtained, it is easy to discover with what weight
of metallic copper each division on the graduated burette corresponds;
data are thus afforded for the determination of the inverse proposition,
namely, what quantity of copper is contained in a solution in which the
weight of that metal has not previously been ascertained.
If, as an example, we suppose it has been ascertained by experiment
that to precipitate from its solution 1 decigramme of pure copper, 280
divisions of the burette are required, and that to decolourise a given
copper liquor exactly 372 divisions have been employed, it follows that
the solution in question contains a quantity of copper corresponding
372
to × 0·10 = 0·132 gramme.
280
2 c 2
388
ELEMENTS OF METALLURGY.
This method is said to be applicable to solutions containing other
metals besides copper, as experiment indicates that the results are in no
way interfered with by the presence of either iron, tin, zinc, cadmium,
lead, or antimony, as the alkaline sulphide does not begin to react
on these metals until after the copper has been completely precipitated
in the form of oxysulphide. It is, however, absolutely necessary that
the iron should be peroxidised by the addition of a few drops of nitric
acid, and boiling, previously to the supersaturation of the liquor by
ammonia, as the presence of ferrous oxide materially interferes with the
result.
On the addition of the ammonia to the liquid to be examined a
deposit of the oxides of some of the other metals which it contains takes
place; but unless these are extremely abundant they are not found to
vitiate the results, and consequently do not require to be separated by
filtration, unless the quantity be so large as to prevent the colour of
the liquid from being distinctly seen.
This method of estimating copper is not, however, to be depended on
in cases where cobalt, nickel, mercury, or silver is present; but the
last-named metal may be readily removed from the solution by the
addition of a few drops of hydrochloric acid, which will cause it to be
precipitated in the form of insoluble chloride, readily removable by
filtration.
As the alkaline sulphide is liable to become more or less changed by
oxidation it requires to be re-standardised immediately before it is used.
BY POTASSIUM CYANIDE. This method of estimating copper was first
made known by Mr. Henry Parkes in 1851, and is the most accurate and
convenient of all the various processes for assaying copper ores by means of
standard solutions. This process depends on the circumstance that when
cyanide of potassium is added to a blue ammoniacal solution of copper
the latter gradually loses its colour, and finally becomes colourless. The
amount of cyanide necessary to discharge the whole of the colour from
an ammoniacal solution is, all other circumstances being the same,
directly in proportion to the quantity of copper present; it is con-
sequently easy, by means of comparative experiments, to establish a
standard by which the amount of copper in a given weight of ore may
be determined.
The only apparatus required is an ordinary Mohr's burette of 50 c.c.
capacity and 18 inches in length; this is supported vertically by a
wooden stand, which admits of its being either raised or lowered by means
of arms with screws sliding upon an upright pillar. A great number of
assays may be conducted at one time by the same person by the aid of a
series of such burettes arranged on a stand and supplied with the same
titrated solution. Where a large number of assays have to be made
daily, the burettes may be connected with a large stoneware or glass jar,
supported on a convenient shelf, containing the titrated solution, with
which they are filled by means of syphons connected with the bottom of
each, by glass T-pieces and india-rubber tubes provided with spring
clips.
COPPER.
389
The best cyanide for this purpose is that known as photographic
cyanide, as solutions prepared from it may be kept a long time without
becoming either discoloured or muddy. To prepare a standard solution,
260 grammes of photographic cyanide may be dissolved in 4 litres of
distilled water; this liquid should be kept in green-glass bottles free
from lead. The solution is standardised as follows: about 1 gramme of
chemically pure and perfectly clean copper is dissolved in dilute nitric
acid, and the solution boiled until all nitrous fumes have been expelled ;
it is then diluted with water, and ammonia in excess added. The blue
solution thus obtained is made up to 750 c.c. and divided into three equal
portions of 250 c.c. each. The burette is now filled to the level of the
uppermost division with the standard solution of cyanide of potassium,
and as soon as the copper solution has become quite cold the beaker
containing it is placed under the burette, and the cyanide of potassium
is run into it in small quantities at a time, care being taken towards the
close to avoid the addition of the smallest quantity more than is neces-
sary. The cyanide solution is finally introduced by successive small
additions until the blue colour has been completely discharged, and has
been replaced by a very faint tint of violet. The number of divisions
necessary for the decolourisation is now read off and noted, and the second
and third portions of the copper solution proceeded with in the same
manner. The mean of the three results is taken, and from it is calcu-
lated the amount of copper corresponding to each c.c. of the cyanide
solution used; with the proportions above specified it will be found that
about 145 c.c. are equal to 1 gramme of copper. The above is the
average strength of the standard solution employed in the various copper-
works in which that metal is extracted by the wet process from burnt
Spanish pyrites; for the assay of richer ores a standard solution of twice
the above strength may be conveniently employed. For practical pur-
poses the standard will not require to be checked more frequently than
once a week.
In order to make an assay by this process, a weighed quantity of
copper ore may be placed in a flask, moistened with sulphuric acid, and
nitric acid added. The whole is now digested at a gentle heat, with the
occasional addition of nitric acid, until coloured nitrous fumes are no
longer evolved. As soon as the ore has been completely decomposed
the contents of the flask are transferred, without filtration, to a beaker of
convenient size, diluted with distilled water to about 300 c.c., and excess
of ammonia added. The intensely-blue solution thus obtained is allowed
to become quite cold, and the separated ferric hydrate falls to the bottom,
where the insoluble gangue has already collected. Without separating
these, the standard solution of potassium cyanide is gradually and cau-
tiously added, with occasional stirring of the solution, until the blue
colour has entirely disappeared and has been replaced by a faint violet
tint. The number of divisions necessary to produce this effect are read
off, and from the quantity of standard solution employed the percentage
of copper contained in the ore is calculated. The method of doing this
will be readily understood by the aid of the following example :-
390
ELEMENTS OF METALLURGY.
145 divisions of the burette equal 1 gramme of copper, 2 grammes of
copper ore require 30 divisions for decolourisation; consequently
Divisions.
145
Divisions.
Copper.
: 30 :: 1.0 :
0·2069 × 100 = 10 345 per cent.
Copper.
0.2069
When a sulphurous ore is operated on, it will, in the majority of cases,
be completely oxidised by a mixture of sulphuric and nitric acids; but
should any globules of sulphur remain they may be taken out after the
dilution of the solution, ignited, and the residue attacked by nitric acid
and added to the copper already dissolved. The attack of some varieties
of ore is best made by aqua regia.
Owing to the influence exercised by varying quantities of ammonia
and of ammonium salts upon the decolourisation of copper solutions by
cyanide of potassium, it is necessary that both the test solution, originally
prepared, and the various cupreous solutions subsequently assayed, should
contain, as nearly as possible, equal amounts of ammonia. The pre-
sence of ferric hydrate imparts a greenish tint to the ammoniacal solution,
and its proper shade is best observed by placing the eye on a level with
the top of the liquid.
Iron.-This metal, in the state of ferric hydrate, does not interfere
with the results, excepting that it takes some time to settle after the
stirring which accompanies each addition of the standard solution; its
effect is consequently only to slightly increase the time occupied in
making an assay.
Lead and Bismuth are, likewise, without effect upon the result.
Arsenic does not interfere with the results excepting in the presence
of iron, when it forms an arseniate soluble in ammonia, and giving rise
to a brownish colour in the liquid. The removal of the arsenic may be
effected by adding magnesium sulphate in excess. As soon as a precipi-
tate is no longer formed, and the solution has acquired its characteristic
blue colour, the assay may be proceeded with in the usual manner.
Manganese is not often found in copper ores in sufficient quantities to
materially affect the results. When present it may be completely re-
moved by adding to the ammoniacal solution sodium carbonate, with a
few drops of bromine, and boiling; it will thus be precipitated as man-
ganic oxide, and when the cupreous solution has become cold the assay
may be proceeded with as though the ore had not contained manganese.
Silver.—Should this metal be contained in the ore in such quantity as
to exercise, practically, any influence on the assay, it may be removed
by adding a few drops of hydrochloric acid to the solution, and filtering
before the addition of ammonia; it is evident that when hydrochloric
acid has been used for the attack, silver cannot exist in the resulting
solution.
Zinc, Nickel and Cobalt.-These metals would, if present, render the
results obtained utterly unreliable, and in such cases the copper must be
first separated by precipitation. This may be effected by means of a
piece of either iron or zinc, in the way already described, care being taken
COPPER.
391
ナ
​that nitric acid is not present; the precipitate thus obtained is subse-
quently dissolved in nitric acid, and the amount of copper present deter-
mined by the standard cyanide solution in the usual way. Instead of
precipitating the copper in the metallic state, it may be thrown down as
sulphide by sulphuretted hydrogen, and the sulphide re-dissolved and
subsequently estimated by potassium cyanide. Sodium hyposulphite
may also be employed as the precipitant.
METALLURGY OF COPPER.
A large proportion of the ores of this metal consist of mixtures of
various sulphides, and all the ordinary methods employed for their metal-
lurgical treatment are dependent on the relative affinity for sulphur and
oxygen possessed respectively by copper and the different metals with
which it is associated. Copper has a stronger affinity for sulphur than
iron, which is the metal with which it is most plentifully found, possesses
for the same body. Iron, in the presence of sulphur and oxygen, appro-
priates the latter, and, uniting with silica, forms a liquid slag; while
copper and sulphur, combining, give rise to a fusible regulus or matt. In
almost all cases, therefore, the treatment of copper ores consists in a
system of alternate roastings or calcinations, and fusions,* by which iron
is gradually removed as silicate, while copper is progressively concen-
trated in a series of sulphides, gradually increasing in richness.
Any oxide of copper that may result from the process of calcination
is, during the subsequent fusion, converted into sulphide at the expense of
sulphide of iron; a silicate of that metal and a copper regulus being the
result. The siliceous slag thus carries off the greater portion of the
iron originally present in the ore, while the regulus contains, practically,
the whole of the copper in a comparatively concentrated form. This
product is again subjected to further calcination, and afterwards fused with
siliceous matter, preferably associated with natural oxides or carbonates
of copper. Another slag is thus obtained at the expense of the chief
part of the iron retained in the first regulus, while that now produced is
much richer in copper than that resulting from the first fusion. Similar
operations are repeated until impure metallic copper, together with a
liquid slag, is produced, and in some cases a small quantity of very rich
regulus. Any regulus thus obtained is subsequently added to that pro-
duced from similar operations, and consequently the final result will, in
all cases, be impure metallic copper; this is afterwards rendered ductile
and malleable by being subjected to a process of refining.
The details of the processes by which copper is obtained from its
ores by smelting vary greatly in different localities, and it would conse-
quently be impossible to describe more than a very limited number at
such length as to render them intelligible. We shall therefore confine
* Copper-smelters in this country make a distinction between calcination and
roasting; the latter term being by them exclusively applied to operations of the
character of No. V. (p. 393). This difference is recognised when treating of the
English method of copper-smelting, but in all other portions of this volume the
terms are employed as being synonymous.
392
ELEMENTS OF METALLURGY.
V
ourselves to two of the most important methods now in operation, each
of which may, at the same time, be regarded as typical of the class to
which it belongs. The examples chosen for this purpose are—
1. The English method of copper-smelting, as conducted in South
Wales and Lancashire.
2. The Continental method, as applied to the treatment of the
cupreous schists of Mansfeld, Prussia.
The first is employed for a large proportion of the copper-production
of the world, and is specially adapted for securing regularity of yield
and the best commercial results from ores of very varying percentage
and composition.
The second is made use of for the treatment of an ore which, although
exceedingly poor, occurs in very large quantities, and never varies
materially in composition. The various processes employed at Mansfeld,
including those by the aid of which the extraction of silver is effected,
are the result of the experience acquired by a succession of intelligent
and carefully-trained superintendents during a long series of years, and
the whole system has thus been brought to a very high degree of
efficiency and perfection.
ENGLISH METHOD OF COPPER-SMELTING.
The ores treated by this process may be classified as follows:
1. Copper pyrites, with iron pyrites, unmixed with either oxide or
carbonate of copper; the gangue is usually siliceous.
2. Mixtures of various sulphides containing less iron pyrites than the
above, with small proportions of native metal, and of the oxides and
carbonates of copper; gangue generally quartzose.
3. Chiefly oxidised ores, containing inconsiderable quantities of sul-
phur; these, for the most part, consist of a mixture of oxides and car-
bonates with a little native copper, and are usually accompanied by a
more or less siliceous gangue.
This method of copper-smelting is somewhat varied, in accordance
with the nature of the ores to be treated and the quality of the copper it
is desired to produce; it never comprehends less than six distinct opera-
tions, but often more.
Under ordinary circumstances the following general conditions should
be observed in making up the working mixtures :—
a. The mixture of ores operated on (Classes 1 and 2) should not con-
tain less than 9, or more than 14, per cent. of copper; if poorer than
the one the amount of fuel consumed will be excessive, and if richer
than the other it will be difficult to obtain clean slags.
b. The furnace mixture should, after calcination, fuse readily, and
afford a clean slag without the addition of any kind of flux.
c. The matt or coarse-metal resulting from the fusion, after calcina-
tion, of the furnace mixture, should contain, approximately, 35 per cent.
of copper.
In making up the working mixture, oxides and carbonates are not
COPPER.
393
used, but they are subsequently employed for special purposes at various
stages of the treatment.
It would however be impossible to lay down any invariable rule to
be followed in copper-smelting, as the ores and other cupreous materials
operated on by the smelter vary so considerably in character that his
operations must, to a great extent, be guided by his personal judgment
and experience.
Neglecting small quantities of various substances exercising no mate-
rial influence on the ultimate results, the average composition of the ores
smelted at one of the Swansea works was, for a considerable period,
according to Mr. J. Napier, as follows:-
Cu
Fe
13
29
S
SiO2.
24
•
•
34
100
The six distinct processes essentially constituting the English method
of copper-smelting are the following:
I. Calcination of mixed ores.
II. Fusion of calcined ores and metal-slag from No. IV. Products,
coarse-metal, and ore-furnace slag, chiefly thrown away.
III. Calcination of granulated or crushed coarse-metal.
IV. Fusion of calcined coarse metal with ores belonging to Class 3,
and slags from operations V. and VI. Products, fine- or white-metal,
containing about 70 per cent. of copper, and metal-slag, smelted in
operation II.
+
V. Roasting the fine- or white-metal. Products, blister-copper, con-
taining about 95 per cent. of copper, and roaster-slag, added to charge
in operation IV.
VI. Refining and toughening. Products, marketable copper and
refinery-slag, added to charge in operation IV.
Reverberatory furnaces are exclusively employed in the English
method of smelting. These are of two kinds: calciners and melting
furnaces.
I. Calcination of Mixed Ores.-This operation is conducted in a rever-
beratory furnace, one of the older forms of which is represented in figs. 113
and 114; the first being a longitudinal, and the second a horizontal section,
but without the fire-bridge, on the line A, B, fig. 113. The hearth, which
is 16 feet in length by about 12 feet 6 inches in width, is formed of fire-
brick grouted with fire clay. The arch descends rapidly from the fire-
place, F, to the flue-holes, H, by which the gases generated by the oxidation
of the ore, together with the products of combustion of the fuel, pass into
a flue in connection with a high chimney. Air is admitted, either by an
aperture, d, which may be partially or entirely closed by a damper sliding
in a groove, or by means of openings in the fire-bridge, which is often
traversed longitudinally by a channel communicating freely with the atmo-
sphere. Some of the more modern calciners are considerably longer in
{
394
ELEMENTS OF METALLURGY.
proportion to their width than that shown in the woodcut, and have a false
arch or screen extending a few feet from the fire-bridge in order to protect
the ore in that part of the furnace from becoming too highly heated. In
other cases, calcination is effected in a close furnace, or muffle, and the
sulphur is utilised for the manufacture of sulphuric acid. The furnaces

A
α
ER
B
H
Fig. 113.—Calcining Furnace; longitudinal section.

៣.
កា
9841052
F
龍眼
​康
​Fig. 114.-Calcining Furnace; section on A B.
of this kind employed in copper-works near St. Helen's are fired with
gas, and provided with Siemens's regenerative apparatus; the results
obtained are stated to be highly satisfactory.
The ordinary calcining furnace, whatever may be its form, is provided
with rectangular openings or doors, a, immediately behind which are,
COPPER.
395
usually, openings, e, in the hearth. During the time the furnace is in
work these holes are closed by iron plates, which are removed at the
close of each operation in order to allow of the roasted charge being raked
into the chambers, C, situated beneath. The arch of the furnace supports
two large cast-iron hoppers, S, in which is placed the mixture of ores to
undergo the process of calcination. These are provided with sliding
doors at their lower extremities, by the withdrawal of which the ore may
be caused to fall directly upon the bottom of the calciner.
In the smelting works in the neighbourhood of Swansea the clinker is
generally allowed to accumulate in the fire-place to such an extent as to
form a bed of considerable thickness, and upon this, which is kept suffi-
ciently open to allow of the passage through it of the necessary amount
of air to sustain combustion, small coal is burnt; this would, to a great
extent, fall through the bars of an ordinary grate. The fuel employed
is a mixture of free-burning and binding coals; usually in the propor-
tion of two parts of the former to one of the latter.
When the clinkers have, through repeated accumulations, become
raised to a sufficient height from the bars, their further increase is
prevented by occasionally causing the fall of the lower portions by the
use of a long iron bar. In this way is formed, throughout the mass, a
sufficient number of channels to yield a free passage to the air necessary
for combustion, and which, in passing through the interstices of the
heated clinker, acquires a considerable elevation of temperature; these
apertures, although sufficiently numerous for the passage of air, are, as
before stated, too small to allow the finely-divided coal to descend into
the space beneath the bars. The oxygen of the air, which has become
highly heated by passing through the bed of clinkers, is, on travers-
ing the fuel, principally converted into carbonic oxide, which, together
with nitrogen and sundry products of distillation, passes over the fire-
bridge into the furnace. Here it takes fire, and is consumed at the ex-
pense of air entering either by the opening d, or through the fire-bridge,
as well as by various small holes left in the iron plates, by which the
lateral openings are partially closed during the roasting. In this way
the whole internal cavity of the furnace is constantly occupied by a long
sheet of flame, caused by ignited carbonic oxide, which burns on coming
into contact with a stratum of atmospheric air so admitted as to spread
immediately over the surface of the hearth. The ore is consequently
exposed to a current of air, above which is a parallel sheet of burning
carbonic oxide, which is inflamed where it comes in contact with the
oxidising stratum, and thereby affords the amount of heat necessary to
carry on the operation.
The working of a charge of ore commences without any interval in
the action of the furnace, and is begun immediately after the withdrawal
of the calcined ores resulting from the preceding operation. The charge
varies in weight from 3 to 35 tons, and is introduced by withdrawing
the sliding dampers from the bottom of the hoppers, in which it is
placed during the working of the preceding parcel. As soon as it has
been let down, it is spread evenly over the surface of the hearth, by
396
ELEMENTS OF METALlurgy.
long iron rakes, successively introduced through each of the working
doors, which are closed immediately the bottom of the furnace has been
properly covered. After the expiration of two hours the doors are again
removed, and the ore is stirred with long iron paddles, in order to
expose new surfaces to oxidising influences.
This operation is repeated at intervals, and after the expiration of
from twelve to twenty-four hours the roasting is sufficiently advanced.
In order to withdraw the charge, the workmen open the working doors, a,
and after having removed the plates of iron covering the openings, e, they
draw the ore through the apertures with iron rakes, and cause it to fall
into the arched chambers, C, from which, when sufficiently cooled, it is
removed and charged into the fusing furnace employed for the next
operation.
II. Fusion of calcined Ores with raw Ores, Slags, &c.—The furnace in
which this operation is conducted is represented in figs. 115, 116, and has
a hearth, A, about 14 feet long by 11 broad; the first is a longitudinal,

Lirit..
NNNNNN
NNNNNNNNNREN
H
"
M
Fig. 115.-Melting Furnace; longitudinal section.
and the second a horizontal section. The fuel employed in South Wales
generally consists of a mixture of free-burning and caking coal, consumed,
as in the former case, on a layer of clinker, supported on an open fire-
grate, F. In Lancashire, free-burning coal only is used. Sand is made
use of for the bottom of this furnace, and this is so lowered at the part B
as to afford a kind of internal basin. To form a charge, calcined ore, from
operation I., is fused with slags from operation IV., the products obtained
being a regulus known as coarse-metal, containing about 35 per cent. of
copper, and ore-furnace slag, which is thrown away. After stopping the
tap-hole, a, with a mixture of clay and sand, a charge weighing about
3 tons, and frequently composed of 2 tons of calcined ore and 1 ton of
raw ore of Class 2, is let down into the furnace through the hopper, H,
and spread evenly over the bottom of the furnace; the slag is thrown in
through the door, d, after which all openings are closed and the fire is
COPPER.
397
made-up. The operation in this furnace is usually effected in from five
to six hours, when the fused mass, consisting of melted regulus and slag,
is well stirred; after this, the latter is skimmed off and raked through the
door, d, at the end opposite the fire-place, whence it falls into a series of
open sand-moulds, M, where it assumes the form of nearly rectangular
blocks. The furnace is now, a second time, charged with a mixture of
calcined ores and slags, and the operation is conducted as before; this is
repeated until, at the expiration of twenty-four hours, the bed of the

NNNNNNNNNNN
1
F
W
Fig. 116.—Melting Furnace; horizontal section.
furnace has become full of regulus, when the tap-hole, a, is opened and
the regulus granulated by being run through a gutter into a pit, V, nearly
filled with water. This is lined with brickwork, and in the bottom is
placed a perforated wrought-iron box, in which the granulated coarse-
metal is received, and is subsequently withdrawn by the aid of the winch,
W, and drained. The resulting slags, chiefly consisting of silicates of iron,
contain numerous disseminated fragments of quartz, which give to the
whole a somewhat mottled appearance and pasty consistency. It is im-
portant that these slags should have a proper degree of fluidity, since if
too stiff they are liable to retain shots of regulus, and if too thin the
workmen find it difficult to skim them from the top of the regulus
without drawing out at the same time a portion of the matt.
Any regulus which may be thus accidentally drawn out of the
furnace collects, for the most part, in the bottoms of the sand-moulds in
which the slags are collected, and is afterwards carefully removed. The
398
ELEMENTS OF METALLURGY.
slags, when sufficiently cold, are broken and subjected to careful examina-
tion; those portions which contain a sufficient amount of regulus are
preserved for remelting with the roasted ores, while the remainder is
rejected as useless.
In many copper-works, and particularly in those in the neighbourhood
of St. Helen's, Lancashire, the coarse-metal, instead of being granulated
in water, is tapped into sand-moulds and afterwards crushed, either
between rollers or under an edge-mill, previously to calcination.
from the ore-furnace should not, on an average, contain above
cent. of copper.
1
Slags
&
per
III. Calcination of granulated or crushed Coarse-metal.—The furnace
employed for calcining the coarse-metal usually resembles in all respects
that used for roasting crude ores in the first operation. The chief object
of this process is the elimination of a portion of the sulphur and
the oxidation of the iron, which is the more readily effected on account
of the removal of the earthy and siliceous matters present in the raw
ores. The charge varies from 3 to 4 tons, and the calcination is usually
complete in twenty-four hours. When the coarse-metal is first introduced
into the furnace the temperature is for some time carefully regulated,
the heat being afterwards cautiously increased until, at the expiration of
about fourteen hours, bright redness has been attained. This tempera-
ture is maintained until the charge has been in the furnace twenty-four
hours, care being taken to stir and turn it over from time to time. The
plates covering the holes, e, fig. 114, are now removed, and the charge is
scraped through them into the chambers, C, beneath the furnace.
IV. Fusion of calcined Coarse-metal with Ores belonging to Class 3, and
Slags from Operations V. and VI.-The object of this fusion, which
usually occupies from five to six hours, is to eliminate, in the form of
silicate, a further portion of iron, and to produce a regulus richer in
copper than is coarse-metal; the products are metal, or fine-metal, very
rich in copper, and metal-slags melted in operation II. The fusion is
effected in a furnace so similar to that employed for operation II. as to
require no special description; at this period are introduced the rich
foreign oxides and carbonates, belonging to Class 3, containing but little
iron. The charge generally weighs from 50 to 52 cwts., and is con-
stituted in accordance with the nature of the ores which the smelter may
have at his disposal; it is often made up nearly as follows: 30 cwts.
calcined coarse-metal, 16 cwts. of rich carbonates and oxides, and 5 cwts.
of roaster- and refinery-slags from operations V. and VI. In addition to
these, copper-scale and furnace-bottoms are occasionally added in certain
proportions. In all cases the charge should be so constituted that, as
nearly as possible, the whole of the sulphide of iron present may become
decomposed at the expense of oxide of copper, and that the oxide of iron
so formed may, in the form of silicate, pass off in the slags. Towards the
close of the operation the charge is well stirred, and shortly afterwards
the slag is skimmed off and drawn out of the furnace through the door, d,
below which sand-moulds are prepared for its reception. The regulus is
finally tapped off into sand-moulds below the tap-hole, which is on the
COPPER.
399
side of the furnace, and should be in the state of white-metal, containing
about 75 per cent. of copper. This sulphide is very nearly represented
by the formula CuS, although it always retains small quantities of iron.
V. Roasting the Fine- or White-metal. This operation is carried on
in a reverberatory furnace, similar to the ordinary melting furnace, but
generally provided with an air-way in the bridge, and with a lateral
door through which the pigs of regulus from operation IV. are in-
troduced; the products are blister-copper, containing about 95 per cent.
of copper and roaster-slag. The pigs of regulus are placed on the
blade of a long paddle, and each is transported to its proper place on
the hearth of the furnace, of which the temperature becomes consider-
ably reduced during the introduction of the charge. The weight of the
charge is ordinarily from 3 to 3 tons, and the heat is so regulated that
the pigs may be completely melted at the expiration of from six to eight
hours. During this time air is allowed to circulate freely through the
furnace, and sulphurous acid (sulphurous anhydride) is abundantly
evolved. The slag formed on the surface of the melted regulus is twice
skimmed off during the operation; the first time immediately after the
complete fusion of the charge, and the second shortly before tapping. A
peculiar frizzling sound is emitted from the bath of fused regulus, which
is maintained in a state of constant ebullition. After the contents of the
furnace have been for a considerable time in a state of fusion, the tem-
perature is sufficiently lowered to cause the surface of the regulus to
become pasty, and it is then thrown up into crater-like elevations pro-
duced by the escaping gases. When the temperature begins to fall too
low the door is closed, and the mass again brought to a fusing heat, at
which it is maintained for some hours, during which time sulphurous
acid continues to be freely evolved.
Before the close of the operation, which lasts about twenty-four
hours, the openings admitting air into the furnace are closed, and the
slags resulting from the combination of silica, derived from the hearth
and from the sand adhering to the pigs of regulus, uniting with oxides
of iron and copper, are skimmed off the surface, and the blister-copper
is tapped into sand-moulds. The slags resulting from this operation are
added to the charge in operation IV.
VI. Refining and toughening.-The furnace employed for the opera-
tion of refining is similar to the ordinary melting furnace, excepting
that its bottom inclines in all directions towards a point near the door
next the chimney. There is also another door at the side, but there is
neither a hole in the roof for charging, nor a tap-hole. The products
obtained are marketable copper, and refinery-slag, which ultimately forms
part of the charge in operation IV. The charge of the refinery consists
of about 8 tons of blister-copper, which is introduced through the side
door and is piled in the form of a hollow heap, extending to the arch of
the furnace; the cakes being so arranged as to allow a sufficient space for
the free circulation of air between them. The complete fusion of the
charge is usually effected in about four hours, when the slags are removed
by skimming, and the fused metal is exposed during from fourteen to sixteen
400
ELEMENTS OF METALLURGY.
hours to the oxidising influences of the air passing through the furnaces.
The charge is from time to time rabbled and the slag skimmed off, and
at the expiration of the time specified the charge should be in the state
of dry copper. In order to see whether the process of oxidation has
been sufficiently prolonged, the refiner takes out a sample in a small iron
ladle, and from the fracture of this sample he is enabled to judge of the
progress of the operation.
Copper in this dry state contains a certain proportion of oxygen in
combination, and in order to eliminate this it is subjected to the pro-
cess of toughening. When the charge is found to be sufficiently saturated
with cuprous oxide the slag is skimmed off, and two or three shovelfuls
of anthracite or free-burning coal, as pure as can be obtained, are thrown
on the hearth and spread over the surface of the liquid metal. This
covering of carbon tends to the reduction of the oxide of copper formed
on the surface of the metal, and after a short interval, during which the
coal is allowed to act alone, a long pole of green wood (generally birch)
is plunged into the fused copper. Under the influence of the elevated
temperature to which the wood is thus exposed, large quantities of reducing
gases are evolved by its decomposition, attended with strong ebullition of
the metal; the reduction of the oxide is thus determined with much
greater rapidity than by the action of the coal alone, but which never-
theless not only assists in the removal of oxygen, but also prevents the
absorption of a further amount when the surface of the liquid metal is in
a state of rest.
When the fused copper has, by this means, been kept in a state of
ebullition during some fifteen or twenty minutes, the refiner takes a
sample from the furnace by inserting into it a small ladle-shaped mould
about 1 inch in diameter and inch in depth. The sample thus
obtained, which is thicker in the centre than at the circumference, is
tested with regard to malleability by flattening on an anvil, and after
being partially cut through with a cold-chisel is fixed between the jaws
of a vice, and bent backwards and forwards until broken.
As soon as the charge is found, from these trials and from the colour
of the copper, to have reached tough-pitch, the pole is taken out, and the
coal pushed back from the opening, through which the metal is removed
by iron ladles and transferred to cast-iron moulds. When the copper is
found to be in a proper state for removal from the furnace, it is necessary
that this should be effected with the least possible delay, since it
would otherwise be liable to again become somewhat dry through the
absorption of oxygen. Should this occur, poling must for a short time
again be resorted to; and if the metal becomes overpoled this defect is
readily obviated by a short exposure to the oxidising influences of the
air. When copper is intended for rolling, a few pounds of lead are
sometimes added, and well mixed with the charge immediately before it
is laded into moulds.
PROCESS FOR MAKING "BEST-SELECTED COPPER.-Dr. Percy, who
derived his information from Mr. Keates, of the firm of Newton, Keates,
& Co., makes the following observations on the subject of best-selected
COPPER.
401
copper:* "The introduction of the manufacture of brass, on a large
scale, into this country, does not date much further back than the year
1680, and the manufacturers were not long in discovering that copper
taken indiscriminately, as it occurred in the market, frequently produced
brass quite unfit for manufacturing into battery, sheets, and wire, and
they rightly attributed this to its impurity. The English copper gene-
rally in use at the beginning of the 18th century was derived from
Cornish ores, which were then, to a greater extent than at present,
mixed with tin; and it is most creditable to the sagacity and practical
skill of the smelters of that day that they devised a mode of remedy-
ing the evil which, in effect, has not been improved upon by their
successors."
The details of the processes by which copper of this quality is pre-
pared from ordinary ores, vary considerably in different works, although
the principle involved is in all cases the same. Advantage is taken of
the circumstance that when copper ores contaminated by the presence of
other metals, such as antimony, arsenic, tin, lead, nickel, &c., are reduced
to a state of regulus, and afterwards so roasted as not to contain a suffi-
cient amount of sulphur to convert the whole of the metals into matt,
a certain proportion of the copper will, during the subsequent fusion,
be liberated in the metallic form. The copper so set free falls to the
bottom of the moulds in which the contents of the furnace are tapped, and
retains a very large proportion of the impurities by which the quality of
the product would be impaired. The material usually operated on is
fine-metal, which is melted down and roasted during a certain time, in
accordance with the judgment of the furnace-man. When ready the con-
tents of the furnace are tapped into a series of sand-moulds, joined
together by gutters in the upper parts of the partition walls which sepa-
rate them from one another. The mixture of regulus and copper alloy
containing the impurities to be separated is tapped into the first of these
moulds, and when this becomes full, the melted matter flows over into the
second, and so on until the whole of the charge has been run out. The
total number of moulds may be from sixteen to eighteen, according to
the weight of the charge, and the size of the sand beds prepared to
receive it; from six to eight pigs of reduced impure copper will be
found in the bottoms of those nearest the tap-hole. The regule is
removed, by means of a hammer, from the tops of each of these as soon as
it has sufficiently cooled to admit of being conveniently handled. About
one-fourth of the total amount of copper present is reduced in this
method of making best-selected copper, and the regule obtained is again
subjected to similar treatment; a further production of impure copper
is the result of the second fusion. The total amount of copper thus
abstracted as impure will be about one-half the quantity contained in the
material originally charged into the furnace. The bottoms obtained as
the result of these fusions may, according to circumstances, either be
roasted, refined, cast into rectangular plates, and sold as tile-copper, or, if
found advantageous, it may be made into cake-copper.
* 'Metallurgy,' Fuel, Copper, &c., p. 329.
2 D
402
ELEMENTS OF METALLURGY.
MODIFICATIONS OF THE ENGLISH METHOD OF COPPER-SMELTING.
The general routine of the different processes employed for the metallur-
gical treatment of copper ores by the English method is not only varied
in accordance with the quality of the copper it is intended to produce,
but also to meet the circumstances of the varying nature of the supply of
cupreous materials available.
The large quantities of "copper precipitate" now supplied by the
numerous wet-extraction works, added to the amount of Chili regulus which
is constantly imported into this country, have resulted in the introduction,
in the copper-works in the neighbourhood of St. Helens, where the
larger proportion of this precipitate is worked up, of certain modifications.
of the ordinary processes. We are indebted for valuable information
relative to this subject to Mr. J. Smith, of Messrs. Newton, Keates &
Co's. works.
The following are the various operations now generally followed in
the copper-works at St. Helens :
I. Calcination of ores.
II. Melting for coarse-metal.
III. Melting for white-metal.
IV. Tapping close-regulus.
V. Running into blister-copper.
VI. Refining and toughening.
I. Calcination of Ores.-A charge of from 5 to 6 tons of sulphur-ores
and regulus is introduced into a Siemens furnace heated with gas,
supplied from a generator. The ore is spread over the bed, and the gas
circulates around the brickwork of a chamber like an oven or muffle,
which is in communication with sulphuric-acid chambers. The charge is
stirred every two hours through the doors, and is kept at a red-heat during
about 96 hours, when it is drawn with iron rakes, and is usually found
to contain from 6 to 7 per cent. of sulphur.
II. Melting for Coarse-metal. This is carried on in an ore furnace,
in which the sharp-slags obtained from the skimming of No. III. process
are worked.
This is the usual reverberatory copper furnace, and is
heated with slack. A charge of about 36 cwts. is introduced and kept at
a strong heat for about six hours. When the door is removed, and the
charge is found to be in a liquid state, the coarse metal falls to the bottom
and the fusible slag floats above it. The furnace-man then skims off
through the front door, the slag, which should be free from copper, or
ought at any rate not to contain more than of 1 per cent.
Once every twenty-four hours the coarse-metal is tapped into sand
beds at the side of the furnace, and should not contain above 33 per cent.
of copper. The charge consists of poor calcined ores and a small quantity
of poor raw ores, with the sharp-slags from No. III.
III. Melting for White-metal.-A charge of about 40 cwts. of a
mixture of coarse-metal from the preceding operation, Chili regulus,
calcined rich sulphides, and raw carbonates, is placed in a furnace similar
to the last. The door is closed, and the heat increased for about four
hours, when the charge will be found to be in a liquid state. The
COPPER.
403
furnace-man skims off the slags floating on the surface, until he comes to
the metal, which he can readily distinguish. The slags from this opera-
tion are termed "sharp-slags," and are those melted in operation II. for
coarse-metal. The metal is tapped at the side, exactly as in operation
II., and contains about 66 per cent. of copper.
IV. Tapping Close-Regulus.-This process is termed "selecting," as
the metal is divided into two qualities, one for making best copper and
the other for common.
About 40 cwts. of a mixture of coarse-metal, calcined Chili regulus,
calcined rich sulphide ores, and copper precipitate obtained from the
various local precipitate-works, is placed in a furnace of the same con-
struction as the last, where it remains until the charge becomes perfectly
liquid. It is then tapped at the side, at the pitch called close-regulus,
when it is found that, in combination with reduced copper, the impurities
fall through the regulus to the bottom of the moulds; when it is cold
the workman separates the upper portions from the lower by means of a
hammer.
The upper portion consists of sulphide of copper, the lower contains
the other metals, such as tin, antimony, arsenic, lead, &c.
The following analyses made in the author's laboratory-the first by
W. T. Gent, and the second by A. G. Phillips-give respectively the com-
position of close-regulus and of bottoms, obtained from works at St. Helens
employing the modified processes described.

Close-Regulus.
Bottoms.
I.
II.
I.
II.
Cu.
75.55*
75.62
89.63
89.80
Pb.
2.05
2.01
4.75
4.60
Sn.
trace
0.06
1.54
1.73
Sb.
trace
trace
trace
trace
As
0.35
0.28
1.62
1.57
Fe
1.44
1.39
0.30
•31
•
A1203
Mn
Ni.
trace
trace
•
trace
trace
trace
trace
0.66
0.48
0.76
0.94
S
Sio,
19.50
19.60
1.07
0.96
0.29
0.25
99.84
99.69
99.67
99.91
V. Running for Blister-Copper. This is effected in a furnace called
the "roaster," in which three kinds of material are separately treated,
according to the quality of the copper required, namely, white-metal, from
No. III. process; close-regulus, from No. IV.; and bottoms separated
from it.
One method of treatment answers for all:-About 7 tons of white-
metal are placed in the roaster, the temperature of which is raised, and
* A minute portion of this copper was in the metallic state.
2 D 2
404
ELEMENTS OF METALLURGY.
+
the metal reduced, at first slowly, to a liquid state, while a current of air
is allowed to pass freely through the furnace. When it has been working
about forty-eight hours the evolution of sulphur will be observed to have
ceased, and the sulphides will be converted into blister-copper, which is
run into beds of sand. The same is done in converting close-regulus
and bottoms into "blister"; in the first case about thirty hours are
required, in the latter only eighteen, owing to the bottoms containing
much less sulphur than the close-regulus.
VI. Refining and toughening.-A charge of about 8 tons of blister-
copper is put into the refining furnace, which is of the same construction
as the other copper furnaces, excepting that the bottom slopes down
towards the front door, where there is a cavity to enable the men to dip
their ladles when lading out the copper. The charge is roasted for about
four hours at a gentle heat, with a current of air, in order to liberate any
sulphur that may remain after the last operation.
The heat is now raised until the metal becomes liquefied, when it is
skimmed to free it from slag. After having been alternately rabbled and
skimmed for about six hours, it is brought to the pitch of dry copper.
It is then agitated or poled with large poles, so as to remove the oxygen,
by which means the copper is brought to tough-pitch. Samples are
removed by small ladles, hammered, and broken in the vice; when the
fracture and colour of the metal indicate that it is in a fit condition it
is at once laded into moulds.
In Chili, where the ores consist of a mixture of sulphides, oxides,
carbonates, silicates, and oxychloride of copper, smelting is conducted
in reverberatory furnaces, with coal as fuel, and comprises three opera-
tions only, namely, fusion for regulus, roasting for spongy regulus, and
roasting for pimple-copper or blister-copper. The copper arrives in this
country in bars, usually weighing about 14 cwt. each, and, according to its
state of purity, it is either at once refined or subjected to a preliminary
roasting. Pimple-copper contains a larger amount of sulphur than
ordinary blister-copper, and is therefore taken to the roasting furnace
before it can be refined.
In this country "best-selected copper usually fetches about £2 per
ton above the price of ordinary "tile" or "ingot."
The usual forms in which copper is sent into the market are as
follow:
Cakes
Tiles
Ingots
•
cwts. qrs. lbs.
19 in. × 12 in. x 12 in.; weight 1 1 0
19 × 121 X
""
""
11
""
× 31,, × 13
0 1 3
14 to 16 lbs.
NAPIER'S METHOD OF COPPER-SMELTING—A patent granted, in 1846,
to Mr. James Napier for "Improvements in Smelting Copper Ores,"
was for some time carried out at the Spitty Works, near Swansea.
The results, however, do not appear to have been satisfactory, since it was
speedily abandoned and the old method of working resumed.
In all the methods employed for the separation of copper from its ores
it is of importance to separate, at the earliest possible stage of their
COPPER.
405
treatment, the large quantities of earthy and siliceous matters with which
they are invariably associated.
To do this the ore is commonly roasted in a reverberatory furnace
or otherwise, either until a sufficient amount of oxide of iron has been
produced to form a fusible slag, by combining with the silica present
in the ore; or, as this would frequently necessitate a very prolonged
calcination, such a mixture of ores is operated on as will afford fusible
and tolerably liquid slags when strongly heated, after a less complete
roasting than would be requisite in the other case. In this way ores rich
in lime and oxide of iron are commonly added to those in which siliceous
matters predominate, and vice versa; and thus, by a judicious mixture,
fluid slags are produced at a much less expenditure of time and
money than would be required for the separate treatment of the several
ores.
The ordinary routine followed in the English and Welsh copper-
works, although more or less modified in different establishments, is in
all cases an expensive and somewhat tedious operation; and the object
sought by Mr. Napier's process was to obtain equally good results
in less time and with a smaller expenditure of fuel. The ordinary
method, as we have seen, always includes at least six distinct operations,
whilst this method reduced their number to five.
By this method a mixture of Cornish ores, made according to prin-
ciples before laid down, is first calcined, and subsequently mixed, after
its removal from the furnace, with a proper proportion of partially-
calcined rich sulphides, such as those formerly imported from Cuba, care
being taken that the quantities of each be so arranged as to afford a
fusible slag by the combination of their gangues with oxide of iron.
This mixture is made in such proportions that, besides producing a
clean slag, it affords a matt containing above thirty and less than fifty
per cent. of copper. The fusion of this mixture is conducted in an
ordinary melting furnace similar to that employed in the second ope-
ration of the old process, and after the removal of the slags from the
surface of the bath a small quantity of salt-cake is thrown on the fused
sulphides; 1 cwt. to 13 cwt. of salt-cake, together with 20 or 30 lbs.
of fine coal, is added to every ton of regulus operated on. When these
substances have been thrown into the furnace they are thoroughly
mixed with the charge by a continued rabbling with an iron paddle;
and after having been allowed to remain a sufficient time to admit of
the reduction of the sulphate of sodium by the action of the coal, which
is usually completed in the course of a few minutes, the regulus is
tapped into sand beds, where it receives the form of rectangular blocks.
These are allowed to remain in the moulds until they become set; but as
soon as they have acquired sufficient solidity to bear removal they are
thrown into a tank of water, in which they crumble into a fine sandy
powder. This is now washed with water, and after being allowed to
dry is calcined until the whole of the sulphur is expelled, which, from
the fine state of division of the powder, is accomplished in from twenty-
four to thirty hours. The powder, now thoroughly calcined, or as it is
406
ELEMENTS OF METALLURGY,
technically called, roasted dead, is mixed with a proper quantity of mala-
chite, or any other copper ore free from sulphur but containing excess of
silica; after having added the requisite proportion of carbonaceous matter,
it is charged into a melting furnace and again fused. This operation,
which occupies from six to eight hours, yields metallic copper, and a
slag containing but little metal, either in the form of inclosed shot or
in that of combined oxide.
Besides being supposed to be more expeditious and less expensive
than the ordinary method of treatment, this process was believed to yield,
from a given parcel of ore, copper of a purer description than could be
obtained by the ordinary methods, as the sulphide of sodium produced
by the decomposition of the salt-cake, and subsequently dissolved by the
water into which the hot pigs are thrown, would, it was thought, carry
off with it in solution such impurities as tin and antimony. The copper
obtained from the fourth operation is in the same condition as ordinary
blister-copper.
METHOD OF RIVOT AND PHILLIPS.-This method, which was patented in
France in 1846 by the late M. Rivot, formerly Professor of Chemistry
at the Ecole des Mines, and M. E. Phillips, Ingénieur des Mines, is
dependent for its action on the fact, that at elevated temperatures
iron has a greater affinity than copper for oxygen. Advantage is
taken of this circumstance in the following way: The ore, if suffi-
ciently rich—or, if not, a mixture of the ore with a portion of the
regulus obtained from a fusion in the ordinary way,—is first reduced
to the state of fine powder, and then roasted dead, so as to expel
the last traces of sulphur. When this has been effected, iron bars
are introduced through apertures left in the sides of the hearth, which
are closed during the former part of the operation. On the introduc-
tion of these bars they become rapidly attacked at the expense of the
oxygen of the oxide of copper, which is thereby reduced to the metallic
state, whilst the oxide of iron formed unites with silica, and gives rise to
a fusible slag which is extremely liquid and entirely free from any
inclosed granules of metallic copper.
This process has never been tried on a working scale; but during
the progress of the experiments made at Paris, in a small furnace spe-
cially erected for that purpose, metallic copper of good quality was fre-
quently obtained in one operation. When, however, arsenic is present in
considerable quantity in the ores treated, it is found to affect materially
the quality of the copper produced.
The process of Rivot and Phillips has the very serious disadvantage
of consuming a quantity of iron nearly equivalent in weight to the copper
produced, which is, in a practical point of view, an objection not readily
overcome.
COPPER.
407
CONTINENTAL METHOD OF COPPER-SMELTING-TREATMENT OF
COPPER SCHISTS IN THE MANSFELD DISTRICT, PRUSSIAN
SAXONY.
The ore treated at Mansfeld is the well-known Kupferschiefer of the
Germans, which occurs in a bituminous seam below the Zechstein, a forma-
tion of Permian age. The thickness of the copper-bearing shale is
seldom above 18 inches, and of this from 4 to 5 inches only will usually
repay the expenses of smelting. Mining, which is sometimes carried on at
a depth of eighty fathoms from the surface, is particularly laborious in
this district, since the thinness of the deposit renders it necessary
for the workman to conduct all his operations while lying on his
side. Smelting has long been carried on in the neighbourhood of Mans-
feld; Agricola, who wrote about the middle of the sixteenth century,
minutely describes the way in which the ores were burned in heaps in
the vicinity of Eisleben, as a preliminary to fusion. The existing smelt-
ing works are situated near the towns of Mansfeld, Eisleben, and San-
gerhausen. The various mines and smelting works, which were before
1852 possessed by separate companies, were at that date united under a
single direction, of which the chief office is in Eisleben; the result
being the establishment of an admirable system of management, which
has secured large and continuous profits to the proprietary.
The following analyses, by Berthier, give the composition of three
different specimens of Mansfeld schist :-
1.
Unburnt.
2.
3.
Roasted.
Roasted.
SiO2
40.0
SiO2
50.6
43.8
A1203
10.7
Al2O3)
23.4
17.2
Fe2O3
5.0
MgO J
CaCO3
19.5
CaO
7.8
18.0
MgCO3
6.5 CuO
2.8
2.5
•
CuFeS2
6.0
Fe2O3
9.0
7.2
K₂O
2.0
S
4.0
2.4
H₂O
10.3
H₂O and CO₂
0.8
6.0
100.0
98.4
97.1
It will be observed, on comparing Analyses 2 and 3, that the com-
position of these schists, as might be anticipated, varies considerably ;
but, according to Berthier, they fuse readily in a brasqued crucible with-
out any addition of flux, and afford compact vitreous slags free from
cavities. The proportion of copper in the ores worked varies from 2 to
5 per cent.; but the average yield will be nearly 2 per cent.; the amount
of silver present in the ore is th of 1 per cent., which is about equal
to 1 lb. of silver to 200 lbs. of copper. In addition to these metals, lead,
cobalt and nickel are present in small quantities; sulphate of nickel
408
ELEMENTS OF METALLURGY.
is one of the products prepared in the establishment on a manufacturing
scale.
The fuel employed is principally coal and coke, a large proportion of
which reaches the works from England via Hamburg; another portion
is however supplied by the German coal-fields, and gas-coke is collected
from the neighbouring towns and from various cities where large quanti-
ties of gas are consumed. Formerly wood and charcoal were exclusively
made use of in the smelting works; but, although the company still
possesses a very large extent of woodland, it is now found more profitable
to sell the timber and charcoal, and to obtain from a distance supplies
of fuel better suited for the work. Brushwood answers as fuel for
muffle furnaces and for calcining; the brown coal of the neighbourhood,
when mixed with coal of a superior quality, is also employed for rever-
beratory furnaces. In addition to the slags, which, for the sake of freeing.
them from copper, are passed through the furnace with the various charges,
fluor-spar is sometimes employed; it is chiefly used with highly siliceous
materials, and is found abundantly in the immediate neighbourhood of
some of the works.
As at present conducted, the method employed for the treatment of
copper schists in the Mansfeld district comprehends the following
operations:-
I. Burning the schists in heaps for the purpose of removing a portion
of the sulphur, together with the water and bitumen, and to reduce the
material to a mechanical condition suitable for smelting.
II. Smelting the burnt ore with slags and fluor-spar in blast-furnaces;
products, coarse-metal or "Rohstein" and slags, the latter being often
moulded into blocks for building purposes.
III. Roasting the coarse-metal in heaps for the purpose of eliminating
sulphur and oxidising iron.
IV. Concentration of the copper in the roasted coarse-metal by fusion
in reverberatory furnaces, and granulation of resulting fine-metal or
Spurstein"; products, fine-metal, containing 65 per cent. of copper,
with some silver, and rich slag sent back to operation II.
((
V. Grinding granulated fine-metal.
VI. Roasting the ground fine-metal; the chief portion of the copper
is thus transformed into cupric oxide, while the silver is converted into a
soluble sulphate of silver.
VII. Dissolving out the sulphate of silver with warm water, and pre-
cipitating cement-silver from the solution by means of metallic copper.
VIII. Mixing the residues from this lixiviation with suitable fluxes,
and smelting in a cupola furnace; products, black or blister-copper,
a rich matt, which is again passed through the same furnace, and slags,
which, if found to contain less than per cent. of copper, are thrown
away.
IX. Refining; either performed in a reverberatory furnace by a pro-
cess very similar to that made use of in this country, which produces
Raffinadkupfer, malleable copper, or in the German hearth, producing
Gaarkupfer, rosette copper. This latter is either sold in that state,
COPPER.
409
or is subjected to a second process of refining in a somewhat similar
hearth.
The following description of the various processes employed in the
Mansfeld district for the treatment of Kupferschiefer will serve to
render intelligible the series of manipulations to which it is subjected
for the extraction of copper and silver.
I. Burning the Schist.-This has for its object the combustion or
volatilisation of a large proportion of the bitumen, as well as the expul-
sion of water, arsenic, &c.; a portion of the sulphur is also eliminated
at the same time, but care must be taken to retain a sufficient quantity to
form a good coarse-metal with the copper and a portion of the iron.
This operation, which partakes more of the nature of burning than of
roasting, is accomplished in large heaps constructed in the immediate
vicinity of the smelting furnace, but generally at a higher level.
In order to construct a heap of this kind a number of faggots of dry
brushwood are laid side by side on the pavement of the roasting yard in
such a way as to mark out the intended boundary of the mound, thus
inclosing a space of from 200 to 300 feet in length, and 30 to 40
feet in width. This area is traversed, longitudinally, by a line of
faggots arranged along its centre, across which two or three rows of
similar faggots are placed at right angles; where these rows cross one
another a small pile of bundles of brushwood is erected. The schist
is now piled loosely upon the faggots until a rectangular heap, from
7 to 10 feet in height, and containing from 400 to 900 tons, has been
formed; fire is now applied to the wood on one side, and the flames
gradually spread, through the channels filled with faggots, to the heaps of
fuel at their intersection, which act as chimneys to the mass. Schist
made into heaps shortly after its extraction from the mine is found to
burn more readily than when put together dry; this arises from the fact,
that as soon as the water is expelled, the layers of shale open, leaving
interstices by which the mass is rendered permeable to the air, whereas,
if previously dried, it crumbles, and a compact heap is the result. The
best conditions are obtained when the blocks are put together during the
winter while in a frozen state, and gradually thaw after the completion.
of the heap. When the schist has once become well ignited it goes on
slowly burning until the whole of the bitumen has been consumed; this
occupies a greater or less time, in accordance with the state of the weather
and size of the heap, but the smaller ones generally require from eight
to ten weeks, and the larger from three to four months. It sometimes
happens that during very strong winds so much heat is developed as to
cause the ore to melt and run together into masses. This not only results
in considerable additional expense, as it makes the heaps very difficult to
break up, but also drives off the sulphur so completely that the roasted
material requires to be smelted with raw ores containing a considerable
proportion of sulphides. In order to avoid this inconvenience it is usual
to erect screens of rough boarding in the direction of the prevailing
winds, or to cover the exposed portions of the heap with a layer of finely-
divided and closely-packed ore. Ten pounds of wood are, on an average,
410
ELEMENTS OF METALLURGY.
consumed for each ton of schist burnt; the reduction in bulk which takes
place during the operation is about 10 per cent., and the loss of weight
is 16 per cent.
II. Smelting burnt Ore with Slag for the Production of "Rohstein'
or Cvarse-metal, &c.—The roasted ore is taken from the pile in which it


||--
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A
Fig. 117.-Rectangular Furnace, Mansfeld;
elevation.
Fig. 118.-Rectangular Furnace, Mansfeld;
vertical section.
is burnt directly to the smelting furnace, where it is fused with a mixture
of slags and fluor-spar, the products obtained being coarse-metal and
poor slags. This fusion always takes place in a blast-furnace, of which
the form and dimensions vary considerably; all the older furnaces are
rectangular, and are from 15 to 20 feet in height; the newer ones, on the
contrary, are circular, and have a total height of above 30 feet. Figs. 117
and 118 represent one of the rectangular furnaces employed at Mansfeld
for the fusion of roasted ores. The first is a front elevation, and the
second a vertical section through the axis of one of the tuyers; the
lining in the vicinity of the hearth is highly refractory, being constructed
of a variety of sandstone found in the neighbourhood; the upper portion,
A, is lined with fire-brick, and the outer walls are built of ordinary
masonry.
The blast is supplied through tuyers, t, placed either in the back of
COPPER.
411
the hearth or in the two opposite lateral faces of the furnace, and at the
same height from the bottom. On a level with the floor are two aper-
tures, b, fig. 119, which communicate, by means of the channels, c, with two
external basins, B, each about 3 feet in diameter and 14 inches in depth,
hollowed in a bed consisting of a mixture of clay and coke-dust. The

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b
B
B
Fig. 119.-Rectangular Furnace, Mansfeld; interior of hearth.
slags and matts flowing constantly out of the furnace are received into
one or other of these basins, and when one has become full the aperture
by which it communicates with the hearth is closed, and the other
opened.
The blast, which is heated to about 185° C., enters the furnace at a
pressure of from 7 to 8 inches of water; the materials to be charged are
placed on a platform near the top, and usually consist of about 86.5 per
cent. of roasted schist from operation I., 6.5 per cent. of fluor-spar, and
7·0 per cent. of slag from operation IV. The fuel used is either English
or Westphalian coke, or gas-coke; when the former is employed, 12 to 14
cubic feet are required per ton of roasted ore smelted, but in the latter
case 16 to 18 cubic feet will be consumed. The fuel is introduced in
layers, alternately with the ore and flux, and a fresh charge is added as
soon as flame makes its appearance at the top. In this way the complete
fusion of the mass is effected, the gangue, uniting with a certain propor-
tion of oxide of iron, forms a fusible slag, while the copper, in combina-
tion with iron, silver and sulphur, yields a liquid regulus or coarse-
metal. The slag and regulus flow together into the basins, B, where the
latter, from its greater density, accumulates at the bottom, while the
lighter slag floats on its surface, and, in proportion as the basins fill,
is dragged aside by the workmen and pressed into blocks for building.
The basins, B, being used alternately, the coarse-metal which has col-
lected in one of them is allowed to cool while the other is being filled,
and, when sufficiently set, is removed in the form of circular plates, which
are lifted from the surface of the still liquid portion remaining in the
bottom of the cavity. This is done by means of an iron bar which is
inserted in the regulus while still in a liquid state.
412
ELEMENTS OF METALLURGY.
As soon as a plate has been separated it is broken with sledges, any
adhering pieces of slag being picked out and returned to the furnace

سيد
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f
α
h
i
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Fig. 120.-Six-tuyer Furnace, Mansfeld; vertical section.
in which the fusion is effected. The coarse-metal obtained amounts to
about 10 per cent. of the weight of the burnt schist smelted; it contains
COPPER.
413
from 30 to 40 per cent. of copper and a little more than 1th of 1 per cent.
of silver, together with iron, cobalt, nickel, zinc and sulphur.
In addition to the ordinary rectangular furnaces, two circular furnaces of
much larger dimensions have recently been erected; these are each blown
by six tuyers and are provided with apparatus for the collection of the
waste gases. Through the courtesy of Ober-Berg- und Hütten-Director
Leuschner, we are enabled to give drawings of the large furnace built at
the Krug Hütte; fig. 120, is a vertical section through its centre, and fig.
121, a horizontal section at the level of the tuyers. The foundation
consists of a solid block of masonry, A, provided with proper channels
for the escape of moisture. The furnace is supported on eight short

4
Sof
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ASU
k
k
W.J.WELCH.SC
Fig. 121.—Six-tuyer Furnace, Mansfeld; horizontal section through hearth.
cast-iron pillars, a, carrying an iron ring, b, and is lined with fire-brick.
The blast, which is heated to a temperature of 280° C., enters the furnace
by six water-tuyers, c, under a pressure of 2 lbs. per square inch, while
the throat, which is closed by the cup-and-cone arrangement, d, admits
of the waste gases being collected by means of the openings, e, and the
wrought-iron pipes, f. The charges are introduced in the usual way;
the slags flow off constantly at g, and the coarse-metal is from time to
time tapped off at h, on the opposite side of the furnace; this flows
through the iron gutter, i, into the cross-spout, k, fig. 121, with serrated
ends, from which it falls into a cistern of water, where it is granulated.
A furnace with two tuyers, and blast heated to 100° C., will smelt from
414
ELEMENTS OF METALLURGY.
7 to 8 fuders (21 to 24 tons) of burnt ore in the course, of twenty-four
hours; a furnace with three tuyers will smelt 12 fuders in the same
time. With a furnace blown by four tuyers, 17 fuders of ore can be
smelted in twenty-four hours, while the large furnace with six tuyers
smelts from 40 to 45 fuders of ore, with an expenditure of from 12 to
14 cwts. of coke per fuder.
III. Roasting the Coarse-metal.—This is accomplished in rectangular
stalls inclosed on three sides by permanent stonework walls, while the
front is closed by a loose one of uncemented stones, which is taken down
whenever the roasted regulus is required to be removed. Each stall is
capable of containing from two to three hundred cubic feet of coarse-metal
and fuel. The bottom of the area is first covered with a layer of wood,
and upon this are piled from 20 to 25 tons of coarse-metal, broken into
fragments weighing from four to six ounces each. The front wall is now
built up, the brushwood ignited, and, in order to moderate the draught, a
layer of damp breeze, about four inches in thickness, is spread upon
the surface of the heap. When the wood which serves to kindle the pile
has been consumed, the mass will have become sufficiently heated to
cause it to continue to burn at the expense of its sulphur, &c. At the
expiration of from ten to twelve days the fire will, in most cases, have
burnt out. The front wall is now removed, and, as soon as it is sufficiently
cold, the roasted regulus, which will have experienced a loss in weight of
from 12 to 15 per cent., is removed. The greater part will be found
to have been sufficiently roasted, but a certain portion will require
to be subjected to a repetition of the same process. This may either
be allowed to accumulate until a sufficient quantity has been collected to
fill a separate stall, or it may be added to the next charge of coarse-metal
operated on ; in the former case, as a considerable proportion of its sulphur
will have been eliminated, the proportion of firewood required will be
greater than is necessary to effect the calcination of coarse-metal.
IV. Melting for "Spurstein" or Fine-metal. The furnace employed for
this operation very closely resembles that used in this country for melt-
ing for coarse-metal. Until within the last ten years the roasted coarse-
metal was fused in a blast-furnace, but this has been superseded by the
Welsh smelting furnace introduced from Swansea, by Hüttenmeister
Ziervogel, at about the date above stated.
The charge usually consists of 13 cwts. of a mixture of once-roasted
and twice-roasted coarse-metal, 2 cwts. of slag from operation II., and
24 cwts. of siliceous sand. This mixture is charged into the furnace
through a hopper in the usual way, and, at the expiration of eight hours,
will have been reduced to a perfectly liquid condition; the regulus will
have fallen to the bottom, and will be covered by a stratum of siliceous
slag. As in the furnace employed in this country for the production of
coarse-metal, the slag is raked off and withdrawn through the door, and
a new charge let down into the hearth and smelted as before. Once in
twenty-four hours, or oftener if required, the tapping-hole is opened and
the fine-metal which has accumulated in the bottom of the furnace is
granulated by being run into a tank of water; this granulated regulus is
COPPER.
415
subsequently dried, and is sent to the mill, in which it is reduced to fine
powder previously to being treated for the extraction of silver. The
slags raked from this furnace contain a small amount of copper, and are
smelted in operation II., with a mixture of roasted schist and fluor-spar.
The fuel employed is a mixture of brown coal and English bituminous
coal, in the proportion of two of the former to one of the latter, burnt on
a step grate. About 10 cwts. of this are consumed for every ton of roasted
coarse-metal treated.
V. Grinding the Fine-metal. The granulated fine-metal is ground
between granite mill-stones driven by water power, and the resulting
powder is bolted in a hollow cylindrical sieve, having about 15,000 aper-
tures to the square inch; those portions which fail to pass through this
sieve are returned to the mills to be re-ground. The finely-divided
regulus thus obtained is subsequently collected from the various small
establishments in which it is ground, and taken to the Gottesbelohnungs-
hütte, where the extraction of the silver is effected.
VI. Roasting the ground Fine-metal -The concentrated and finely-
ground sulphide, which contains 67.50 per cent. of copper and 0·3520 per
cent. of silver, or about 0.50 per cent. of silver in the metallic copper, is
subjected to a process of careful roasting, by which the copper is, for the
most part, converted into an insoluble oxide, while the silver is trans-
formed into a readily-soluble sulphate of that metal. This is effected in
reverberatory furnaces, with precautions which will be given in detail
when describing Ziervogel's process.
VII. Dissolving out Sulphate of Silver and precipitating Cement-Silver by
Metallic Copper.-This operation is conducted in a series of tubs, in some
of which the solution of sulphate of silver is effected, while in others the
precipitation of the dissolved silver is determined by the introduction of
metallic copper, both in the form of bars and in a granulated state. The
method of conducting this operation will be described when treating of
the metallurgy of silver.
VIII. Fusion for Black Copper.-The residues retained in the tubs in
which the lixiviation for sulphate of silver has been conducted contain
from 70 to 75 per cent. of copper, chiefly as oxide, and have been freed
from silver to within 0.035 per cent. This is now converted into black
copper, by fusion in a blast-furnace, similar to figs. 117, 118, 119, but
varying somewhat in its dimensions. For this purpose it is mixed with
8 per cent. of clay, worked into balls 4 inches in diameter, and dried on
a platform at the level of the top of the furnace; these balls have an
addition made to them of about 10 per cent. of siliceous sand, 5 per cent.
of pyrites, or of gypsum, and from 10 to 15 per cent. of slag from the same
operation or from process IX.; a little rich regulus, resulting from the
same operation, is also added. This mixture is charged into the furnace
alternately with layers of coke; the blast is cold, and amounts to 150
cubic feet per minute at a pressure of about an inch of mercury. The
reducing action of the furnace thus converts the principal portion of the
oxide into metallic copper, while the sulphur in the pyrites and gypsum
serves the purpose of cleansing the slags. Three products consequently
416
ELEMENTS OF METALLURGY.
escape continuously from the hearth of the furnace, and are collected in
the external reservoirs prepared for their reception; namely, black copper,
a rich regulus, and a siliceous slag. These arrange themselves in
accordance with their respective specific gravities. The slag, which rises
to the top and amounts to about 30 per cent. of the total result of the
operation, is from time to time, dragged off, and when it has become
sufficiently cold is broken and sorted; the pieces containing matt are
again returned to the furnace, while that which contains less than per
cent. of copper is thrown away. Beneath the slag, and forming a layer
between it and the impure copper below, is a rich matt, composing about
5 per cent. of the entire product; this is removed, and again, without
delay, added to the charge which is being passed through the furnace.
The black copper, which amounts to 66 per cent. of the fall of the
furnace, contains 98.5 per cent. of pure copper, and, after being removed
from the receiving basin, undergoes the process of refining.
IX. Refining. The copper produced at the Mansfeld works is de-
livered to commerce in two distinct forms, namely, as Raffinadkupfer and
as Gaarkupfer.
The first, or refined copper, is cast into ingots and bars, and possesses
to the fullest extent the ductility and malleability of the best descrip-
tions of English copper. Gaarkupfer, or rosette copper, is sold in the


M
A
cl
α
Fig. 122.-Kupfergaarherd.
Fig. 123.-Kupfergaarherd; vertical section.
form of thin round discs, and is used for making alloys, but is not suffi-
ciently malleable for hammering or rolling.
The refined copper, which is brought to tough-pitch, is produced in
reverberatory furnaces, and is poled in the ordinary way. Black copper
for the production of rosette is treated in the small German hearth, or
Kupfergaarherd.
Fig. 122 represents a perspective view, and fig. 123 a vertical section,
of this arrangement; it consists of a hemispherical basin, a, about
24 inches in diameter, excavated in a mass composed of four parts of
pounded charcoal, four parts of fire-clay, and one part of sand. This
is surrounded by a low platform, c, level with the top of the basin,
which is, on one side, furnished with a small door, d. When the
hearth has been freshly lined, it is necessary, before proceeding with
another operation, to dry it by the introduction of a few shovelfuls
of ignited charcoal, which is allowed to remain until the hearth is
completely dry. As soon as this is the case, the cavity is filled with
COPPER.
417
fresh charcoal, fragments of impure copper are arranged opposite the
tuyer, t, and the blast is gradually admitted. When the first charge of
crude metal has been thus melted, a further quantity is added, care being
taken at the same time to supply the hearth with a proper amount of
fuel. The scoriæ formed during the progress of the operation escape
through a tap-hole, which communicates with the cavity in which the
refining is effected, a little above the level of the top of the mass of
masonry, m.
The first slags obtained are of a greenish colour, and contain a large
quantity of oxide of iron. During the fusion, sulphurous anhydride, and
sometimes antimonial vapours, are evolved.
The next slags are of a deep-red colour, and are extremely rich in
cuprous oxide. When the whole of the black copper constituting a
charge has been fused in successive small quantities, the workman takes
samples, from time to time, by means of an iron rod, and, from the
appearance of these, he is enabled to judge of the working of the
furnace and the state of the metal it contains. As soon as the process
is found to be sufficiently advanced, the blast is stopped and some water
is thrown on the surface of the metal, which is afterwards freed from
the fragments of charcoal by which it is surrounded. The slags are
then carefully raked from the surface of the metallic bath, on which a
little water is again thrown to solidify the upper surface, which is at once
withdrawn, by an iron crook, in the form of a thin circular plate. When
the first disc has been thus removed more water is thrown on the surface
of the metal, and a second film is coagulated and lifted off. These ope-
rations are repeated until the whole of the copper has been removed
from the furnace.
The rosettes thus obtained do not exhibit the malleability and duc-
tility of ordinary commercial sheet-copper, and in order to communicate
to it these properties it is necessary to subject it to a final operation
of toughening. For this purpose the rosettes are again melted in a
furnace, similar to that above represented; and as soon as the discs are
fused, and have fallen into the small concave basin, the surface of the
bath is sparingly covered with small pieces of charcoal, by which, after a
certain time, the oxide is reduced, and the metal attains its state of
greatest malleability.
OBSOLETE PROCESSES AT MANSFELD.-The ancient method of ex-
tracting silver from black copper by liquation was employed in the
Mansfeld district up to the year 1836. The efficiency of this process,
which is described by Agricola, depends on the following principles: If
lead and copper be fused together, the two metals will unite and form
an alloy; and if this mixture be rapidly cooled, after being run out of
the furnace, they remain in a state of intimate admixture. If, on the
contrary, the alloy be slowly heated to near its point of fusion, or be
allowed to cool very gradually after being in a liquid state, the two
metals will separate, and the lead will contain nearly the whole of the
silver originally in combination with copper, whilst the latter metal
retains only a small portion of the lead added. The silver may now be
2 E
418
ELEMENTS OF METALLURGY.
separated from the lead by cupellation, and the copper freed from that
metal by an operation of refining.
Three parts of black copper and from 10 to 12 parts of lead, already
containing a certain proportion of silver-if such is to be procured—
are fused together in a cupola furnace; instead of metallic lead, litharge
containing silver is sometimes employed. The fused alloy, on flowing
from the furnace, is poured into cast-iron moulds, where it is rapidly
cooled by the help of water, and from which it is removed in the form
of large circular cakes. These discs are subsequently heated on a liqua-
tion hearth, in order to extract the argentiferous lead in the liquid form,
while the associated copper remains unmelted, and forms a porous mass,
retaining nearly the form of the original cakes of alloy.
This hearth, figs. 124 and 125, consists of two slightly-inclined plates
of cast-iron, so placed as to leave between them a small space, S, beneath

וי
M
C
Fig. 124.-Liquation Hearth.
which is a hollow channel, C, left in the mass of masonry, M, which sup-
ports the iron plates. The discs of alloy are placed perpendicularly on
these, and are kept at a short distance from each other by means of
wedges, whilst the open sides of the area are closed, after charging the
alloy, by thick plates of sheet-iron, F. The fuel employed, which is
wood charcoal, is introduced between the metallic discs, after which the
الالان
WHAZY
VIIMINAL
ZUMINDE
TINKIN
WALLA
wedges are withdrawn, and some
wood is placed in the channels, C,
by the combustion of which the
charcoal in the upper part of the
hearth is readily ignited; the draught
is produced by small chimneys, d,
left in the masonry of the furnace.
As the temperature of the cakes be-
comes more and more elevated, the
lead, which is the most fusible metal
present, begins to melt, and, flowing on the surface of the iron plates,
falls into the channels, C, and is conducted, by a slight depression in the
floor, into the exterior basins, b. In proportion as these reservoirs

IIIINE
Fig. 125.-Liquation Hearth; section.
COPPER.
419
become filled, the lead is removed, with an iron ladle, to a mould, where
it receives the form of small lenticular cakes. The copper, still retain-
ing a certain amount of lead and silver, remains, in the form of half-
fused spongy masses, in the position in which it was first placed. The
lead thus separated by liquation contains a large portion of the silver,
as, from the circumstance of the alloy of silver and lead being more
fusible than the pure metal, a small quantity only of silver is retained
by the lead which remains associated with spongy copper on the hearth
of the furnace.
These porous masses of copper are, however, still capable of afford-
ing a certain amount of argentiferous lead, if submitted to a higher
temperature, and for this purpose are heated in a peculiarly-constructed
apparatus, known as a sweating furnace.
The spongy masses of copper, remaining after the liquation of the
lead and silver, are charged on the hearth of the furnace, and rest on
the brick piers by which the bottom is divided longitudinally into flues.
These spaces are filled with wood, which is ignited, and the door closed.
The draught is established through openings, in connection with a
chimney, by which the smoke and heated air are carried off.
This treatment determines the separation, in a liquid form, of a
further portion of lead, which becoming oxidised is chiefly converted
into litharge, which falls to the bottom of the flues, together with a small
quantity of oxide of copper dissolved in the oxide of lead. By operating
in this way, black copper is obtained still further freed from lead and
silver than that coming from the liquation hearth, and in the spaces
between the piers will be accumulated litharge containing silver, and a
small proportion of oxide of copper. This mixture was employed at
Mansfeld as a source of lead in the cupolas in which the fusion of the
black copper with lead was conducted.
The black copper was formerly refined in a reverberatory furnace some-
what resembling the German cupelling furnace to be hereafter described.
A method for the separation of silver from copper matts by amalga-
mation was in operation at Mansfeld up to 1849.
WET PROCESSES FOR EXTRACTING COPPER.
It has long been known that the waters issuing from certain copper
mines contain a considerable amount of that metal in the form of sulphate.
Agricola states that in his time the waters of a mine near Schmölnitz,
in Hungary, eroded iron and converted it into copper. Cupreous waters
of this description are most plentifully discharged from mines of which
the workings are extensive, and where sulphides of iron and copper are
disseminated over extensive areas; these are converted by oxidation into
sulphates of iron and copper, and the resulting solutions are sometimes
sufficiently concentrated to enable the copper to be extracted with profit.
This is done by bringing the cupreous waters in contact with either
wrought- or cast-iron, which, abstracting the sulphuric acid from the
copper, the latter is precipitated as a crystalline powder, while sulphate
2 E 2
420
ELEMENTS OF METALLURGY.
of iron is carried off in solution; the copper precipitate thus obtained is
fused and refined in the usual way. At the Rio Tinto and Tharsis mines
in Spain, and at San Domingos in Portugal, considerable quantities of
precipitated copper are annually obtained from the waters issuing from
workings on large bodies of cupreous pyrites. Some of these excavations
date from the Roman period, and recent mining operations have brought
to light numerous wooden wheels and other drainage-appliances evidently
belonging to that date. The water from the Wicklow mines in Ireland
also holds a small quantity of cupric sulphate in solution, and, in order
to extract the copper, it is conducted through a series of troughs in-
terrupted at intervals by deep tanks or hutches. In these troughs,
which are inclined at an angle of from 7° to 10°, pieces of iron are so
placed that the water flows constantly over them, and cement-copper is
precipitated; this is from time to time swept down into the tanks, and
at intervals collected and sold. The waters from the Amlwch mines,
near Holyhead, likewise afford a certain amount of copper annually, and
those of many mines in Cornwall and elsewhere are similarly treated
for the copper they contain in solution.
GERMAN HYDROCHLORIC-ACID PROCESS.—In the vicinity of the village
of Twiste, in Waldeck, several considerable beds of sandstone, to a
greater or less extent impregnated with green carbonate of copper, have
long been known. This ore, although varying considerably in its pro-
duce, yields, on an average, from 1 to 2 per cent., and was formerly raised
and smelted in large quantities; but this method of treatment not having
produced satisfactory results, the operations were finally abandoned.
The insoluble nature of the quartzose gangue with which the copper
is associated, suggested, some twenty years since, to Mr. Rhodius, at that
time the proprietor of the Linz metallurgical works, the possibility of
treating such ores by means of hydrochloric acid, and a large establish-
ment for that purpose was erected about the year 1855.
The arrangement employed consisted of a crushing mill for the
reduction of the cupreous sandstone to a small size, sixteen dissolving
tubs to effect the solution, and a considerable number of tanks and reser-
voirs for the reception of the copper-liquors and the precipitation of the
metal, by means of scrap-iron. Each of the sixteen dissolving tubs was
13 feet in diameter, and 4 feet in depth, and was furnished with a large
wooden revolving agitator, set in motion by shafting connected with a
water-wheel. This apparatus was sufficient for the treatment of 20 tons
of ore daily, and the consequent production of from 7 to 8 cwts. of copper.
In 1856, when the author visited Twiste, the ore was raised and brought
into the works at a cost of 4s. per ton, and each operation was completed
in twenty-four hours the liquors being removed from the tanks to the
precipitating troughs, by means of wooden pumps.
The acid employed at this establishment was procured from alkali
works in the vicinity of Frankfort; it contained 16 per cent. only of real
acid, and cost, delivered at the works, 2s. per 100 lbs. Each ton of
sandstone operated on required 400 lbs. of acid, which was diluted with
water down to 10 per cent. before being added to the ore. In order to
COPPER.
421
precipitate one ton of copper, 1 ton of scrap-iron was used, and the
residues removed from the washing vats after the operation, retained but
one-tenth of 1 per cent. of copper.
How long this process was successfully carried on we are not aware,
but are informed that the works ultimately became unprofitable on
account of a falling off in the yield of the ores. In a volume published
in September, 1857, the works at Twiste were described by the author,
who made the following observations relative to the general applicability
of the method:
*
"It is probable that this extremely simple process for treating the
poorer carbonates and oxides of copper, may be practicable in many other
localities; but in order to be enabled to treat them with advantage it is
necessary that the ore should be obtainable in large quantities at a cheap
rate, and that it should contain but little lime or any other substance,
other than copper, soluble in dilute hydrochloric acid.”
HENDERSON'S HYDROCHLORIC-ACID PROCESS.-Mr. W. Henderson's pro-
visional specification is dated the 30th September, 1857, and is for
"Improvements in Treating certain Ores and Alloys, and Obtaining
Products therefrom, and in Recovering or Reproducing all or Part of the
Materials used."
“These improvements relate first to the treatment of copper and some
other metals, when they occur in the state of carbonates or oxides in ores
containing much silica; secondly, to the treatment of ores of copper and
several other metals when they occur in the state of sulphurets combined
with iron; thirdly, to the treatment of certain alloys of copper and tin,
called white-metal.'
"The first class of ores I treat in the following manner: The ore
is crushed and introduced into tanks or vats made of wood, stone, or other
suitable material; muriatic acid sufficient to cover the ore is also intro-
duced. If the ore is poor and consists of a loose friable rock, the acid
may be very weak, and at ordinary temperature be used cold. For a 23 per
cent. copper ore, acid of from 1·025 to 1.050 answers very well. The
richer the ore the acid will generally be required stronger [sic]. The
exceptions I will explain hereafter. To economise acid and obtain a
solution of uniform strength the vats are worked in a similar manner to
the black-ash vats commonly in use in alkali works."
""
After describing the precautions to be observed in treating the solu-
tions obtained, either with lime or calcium carbonate, in order to pre-
cipitate the metals, the patentee goes on to say: "When convenient I also
use scrap-iron for precipitating the copper.' It will therefore be
observed that Mr. W. Henderson's process differs from that which had
been previously described as in use at Twiste only in respect to the
mechanical appliances employed for washing.
This process for extracting copper from poor siliceous ores has for
several years been used at Alderly Edge in Cheshire, where it was
originally introduced by Mr. Henderson.
The copper here occurs, chiefly as carbonate, in Triassic Sandstone
* 'Records of Mining and Metallurgy,' p. 184. E. & F. N. Spon.
422
ELEMENTS OF METALLURGY.
(Bunter Sandstein of the Germans), of which very large quantities have
been raised and treated; but the results obtained are not believed to leave
a large margin of profit at the ordinary price of copper.
LONGMAID'S PROCESSES.-In the year 1842 Mr. William Longmaid
took out a patent for "Improvements in Treating Ores and Minerals, and
in Obtaining various Products therefrom, Certain Parts of which Improve-
ments are applicable to the Manufacture of Alkali." This invention con-
sists in roasting ground iron pyrites with common salt in a reverberatory
furnace, by which sulphate of sodium is produced, while any copper that
may be present is transformed into soluble cupric chloride.
"The copper
may be separated from the solution either with iron, as is well understood,
or, as I prefer, by the addition of lime slaked in water, forming a milk of
lime." The specification goes on to say: "The solution from which the
copper has been separated may, if required, be concentrated by boiling,
and set aside to crystallise in suitable vessels, very fine crystals of sulphate
of soda being obtainable."
In the specification of a second patent, granted in 1844, for "An Im-
provement in the Manufacture of Copper, Tin, Zinc, and Peroxide of
Iron," Mr. Longmaid makes the following observations: "I have dis-
covered that there are circumstances under which, and situations where,
ores containing copper, tin and zinc, with sulphur, may with advantage
be treated with common salt for obtaining the metallic parts, without
depending mainly on the profits derivable from the sulphate of soda."
The liquors obtained by the lixiviation of ores which have been furnaced
with addition of common salt will contain various metals in solution,
together with sulphate and chloride of sodium. "And I wish it to be
understood that this invention is confined to treating ores containing
copper, tin, or zinc. The copper contained in any liquor obtained as
above explained may be precipitated, as is well understood, by means of
iron, and the milk of lime may be subsequently employed for separating
the zinc associated with an excess of lime and with some oxide of iron.
"The oxide of tin separates from the liquor by gravity with residuary
matters; and if they be not broken fine enough for the washing process
to separate the oxide of tin, they are to be broken before washing, to
separate the tin in the ordinary manner. If the whole of the copper
and zinc be not converted into the soluble form by the first operation, the
insoluble residue may be treated with weak muriatic acid obtained by
condensing that product (as is well understood) as it is evolved from the
furnace where the ores are being treated with common salt, as above ex-
plained, or weak muriatic acid, otherwise obtained, may be employed.
to dissolve the copper and zinc not before rendered soluble in water, and
these metals may be separated from the solutions thus obtained, as above
explained."
This process was worked for several years at St. Helen's, where the
copper was first precipitated by iron, and the liquors subsequently
evaporated down for salt-cake; it was abandoned about the year 1863.
At the works of Messrs. Allen, near Newcastle, it was likewise followed
in its entirety for many years, but was ultimately so modified as to be
COPPER.
423
applied only to the burnt pyrites obtained from vitriol kilns, and the
recovery of sulphate of sodium was no longer effected.
BANKART'S PROCESS.-A process for treating the various sulphides of
copper was patented in 1845 by Mr. Bankart, who carried out his in-
vention on a somewhat extensive scale at the Red Jacket Copper Works,
near Neath. The material operated on was Cuban ore, furnished by the
Cobre Mining Company, and was chiefly composed of copper pyrites con-
taining from 14 to 25 per cent. of copper. This mixture was first reduced,
by mechanical means, to the state of a fine powder, and then exposed in a
furnace to a low red-heat for several hours, with free access of air. By
this treatment a portion of the sulphur is oxidised and driven off, whilst
another portion is converted into sulphuric acid, which combining with
oxide of copper, formed during the operation of roasting, sulphate of
copper, or blue vitriol, is produced.
The ore is next removed into large vats provided with false bottoms,
where it is immersed in boiling water, which, by filtering through it,
dissolves and carries away in solution the sulphate of copper, leaving
oxide of copper and peroxide of iron, associated with the siliceous
matrix. This residue is now again roasted with a due admixture of the
same mineral in the raw state; and the sulphur of the latter, which
would otherwise have gone off in the state of sulphurous anhydride,
receives, through the agency of peroxide of iron, an addition of oxygen,
by which it is converted into sulphuric acid; this again acts on free
cupric oxide, and uniting with it, forms cupric sulphate, to be again
extracted by solution in boiling water, as before.
This process is repeated three times, and on the last occasion the
fresh ore added consists of iron pyrites only; this is for the purpose of
furnishing sulphuric acid to any cupric oxide which may be present in
the calcined ore, and which might not otherwise be extracted.
To obtain metallic copper from these solutions, wrought- or cast-
iron is immersed in the liquid, when, by a well-known chemical
reaction, sulphate of iron is formed, and copper is deposited in a
pure crystalline metallic state, requiring merely a simple fusion to
convert it into ingots, which may be refined and toughened in the
ordinary way.
This process, which displays considerable ingenuity, has, in its ori-
ginal form, been for many years abandoned; although, in a somewhat
modified one, it was worked for a short time by the Bede Metal Com-
pany at Jarrow-on-Tyne, within the last five years. It was finally super-
seded by the ordinary process of calcination with salt.
LINZ PROCESSES.-At Linz, on the Rhine, the following processes
were introduced about the year 1856, and are still employed for the
treatment of poor copper ores, consisting of sulphides, oxides and car-
bonates of copper. These are divided into two classes, and are treated
differently.
1. Poor Sulphides.-These, which contain on an average about 2½ per
cent. of copper, are roasted in a kiln 10 feet in height and 3 feet in
diameter, into which the ore and fuel are charged in alternate layers.
424
ELEMENTS OF METALLURGY.
The ore, which descends slowly to the bottom, is withdrawn, almost free
from sulphur, from a suitable aperture left for the purpose, and is then
crushed to the state of a coarse powder between iron rollers.
The calcined ores are taken to a series of tanks sunk in the ground
and lined with blocks of basalt. These are provided with a double
bottom, also of basalt, so arranged as to form a permeable diaphragm, and
on this is placed the roasted ore; some coarser fragments are charged
first, the finer particles being laid upon them. The space or cavity thus
left between the falso bottom and the bottom of the tank is connected by
means of flues lined with fire-brick, with a series of retorts, constructed
of refractory tiles, and through which a current of air is caused to pass
by means of a ventilator or other suitable blowing apparatus set in
motion either by steam or water power.
The treatment of the ores by the aid of this arrangement is con-
ducted as follows: A quantity of the roasted mineral to be operated on
is placed in the tanks, with the precautions above described.
The retorts
are heated to redness, and charged to a depth of about 2 inches with
finely-divided blende, the blast being, at the same time, gradually ad-
mitted. The sulphurous anhydride thus generated is forced, by the
current of air, through the flues, where it becomes mixed with steam
supplied by a small boiler, and ultimately reaches the chambers beneath
the diaphragms, on which are placed the roasted ores.
These are pre-
viously damped by the addition of a small quantity of water, of which
about 4 inches are allowed to accumulate in the bottoms of the tanks.
In this way oxidation takes place, and the sulphuric acid generated
attacks the oxide of copper formed during the preliminary roasting,
giving rise to the production of sulphate of copper, which percolates
through the basaltic diaphragms into the reservoirs beneath.
The liquors which thus accumulate are from time to time distributed
over the surface of the ores by means of a leaden pump, and the opera-
tion is continued until nearly the whole of the copper originally present
has been extracted, when, by shifting a damper, the gases are diverted
into the bottom of another tank, similarly arranged. The liquors from
the first tank are now removed by a pump, to be distributed over the
surface of the ores in the second, and the operation is continued until
the mineral which it contains ceases to be further acted on by the acid
vapours. When sufficiently saturated, the cupreous liquors are drawn
off into convenient troughs, and the copper is precipitated by scrap-iron.
The resulting sulphate of iron is subsequently obtained by crystallisa-
tion, and is packed in casks for the market.
By operating as above described, ores yielding but 1 per cent. of
copper may be treated with advantage, since the sulphate of iron pro-
duced, and the increased value of the roasted blende, are stated to alone
cover the expenses of the operation.
The roasting of 1 ton of ore by this process is said to require
3 cwts. of coal, while the same amount of blende is desulphurised by an
expenditure of 4 cwts. of fuel.
2. Poor Oxides and Carbonates.-These contain, on an average, a little
na
COPPER.
425
more than 1 per cent. of copper, which exists principally in the form of
either malachite or azurite. Instead of treating these ores as in the former
case with sulphuric acid, hydrochloric acid obtained from a neighbouring
alkali manufactory is the solvent employed. The ore is first crushed and
then charged into large wooden vats, where it is covered with dilute
hydrochloric acid, and allowed to remain during ten days; the solution is
then drawn off into precipitating vats, in which the copper is thrown down.
by metallic iron. The residue remaining in the vats retains but of
1 per cent. of copper, and is thrown away as useless.
10
Instead of attacking the poor oxides and carbonates with weak hydro-
chloric acid, as above described, the waste liquors, from which sulphate of
iron has been partially removed by crystallisation, are sometimes em-
ployed. These, in addition to free sulphuric acid, contain sulphates of
iron and aluminium, which, in the presence of carbonate of copper, give
rise to the formation of soluble cupric sulphate and ferric and aluminic
hydrates, which are precipitated.
The copper in solution is subsequently drawn off into precipitating
tanks, where it is thrown down in the usual way by scrap-iron.
SINDING'S PROCESS.-A process invented by Mr. Sinding, a Norwegian
metallurgist, intended to supersede the use of iron for the precipita-
tion of copper in the treatment of low-produce ores by the wet way, was
experimented on in this country in 1856.
This invention consists in a method of preparing, at a cheap rate, the.
sulphuretted hydrogen, by means of which the copper is thrown down.
The method of roasting and obtaining a solution of copper is the same in
Sinding's as in Bankart's and the older methods of making cement-copper.
Sulphuretted hydrogen is in this case prepared from fuel and ordinary
iron pyrites. For this purpose any fuel, capable of affording hydro-
carbon gases by distillation, may be employed. These gases are sub-
sequently employed in conjunction with the vapours of sulphur obtained
by the distillation of pyrites. When these are brought in contact with
each other at a low red-heat, the hydrogen combines with the sulphur,
giving rise to sulphuretted hydrogen, while the carbon is deposited in the
form of a fine black powder.
The apparatus for generating the gas has two divisions; the first of
these is a square chamber, in which the fuel is distilled, while at the
bottom is situated a tuyer by which a blast is introduced. The top of this
chamber is closed by a cast-iron box, fitted with a sliding top and bottom,
by means of which the fuel is introduced, without allowing any escape of
gas. This apparatus is adapted for the employment of coal; but when
wood is made use of the under part of the generator is made smaller than
the upper, and the blast-pipe placed higher up, so as to cause the fire to
burn from the upper part of the arrangement downwards.
The generator communicates with the second chamber by means of
a horizontal canal, in which air is mixed with the gases in quantities
regulated by stop-cocks fitted on the blast-pipes.
The second chamber, containing the pyrites, is nearly a cube eight
feet each way, and is covered by a slightly-arched roof. At the bottom
426
ELEMENTS OF METALLURGY.
of this chamber are openings for the purpose of allowing the escape of the
gases into the precipitation chamber. To prevent the apertures being
closed by pyrites, they are protected by a brick roof. There are also
openings at the sides for removing spent pyrites, and one in the end for
the introduction of a fresh supply.
The working of this apparatus is conducted as follows:-
The generator is first filled with fuel, which is ignited; and the blast,
coming in at the bottom, supports combustion, while carbonic anhydride is
reduced by passing through the ignited fuel in the upper portion of the
arrangement. The fresh fuel on the top is distilled by the heat of the
escaping gases, and gives off gaseous hydrocarbons. The gas passing
off from the generator is consequently a mixture of carbonic oxide and
hydrocarbons. On coming in contact with the blast in the flue a portion
of this gas is burnt, and it is essential that a portion of it only should be
consumed; the object being to obtain enough heat to distil sulphur from
the pyrites, leaving sufficient hydrogen to effect the formation of the
necessary sulphuretted hydrogen. By a proper regulation of the blast
in the canal, the pyrites-chamber is filled with flame of such a smoky
nature as to be scarcely luminous; by this means the pyrites is heated to
low redness, sulphur is given off, and the odour evolved soon indicates
that sulphuretted hydrogen is being formed. One ton of pyrites is cal-
culated to yield by this method 5 cwts. of sulphuretted hydrogen gas. The
pyrites employed for this process may be that from which copper is to be
subsequently obtained, since by this means the operation of roasting
is materially facilitated. The precipitation takes place in an air-tight
wooden chamber, divided into compartments, so arranged as to cause the
gas entering at one extremity to pass in a zigzag direction to the other.
The top is formed by the bottom of a tank, into which the liquor contain-
ing copper in solution is pumped. The bottom of this tank is pierced
with holes, through which the liquor trickles through an atmosphere of
sulphuretted hydrogen, by which the copper is precipitated in the form of
sulphide. The liquor now escapes at the bottom, and is again pumped into
the cistern at top, and so on until the precipitation is complete. It is sub-
sequently run off into reservoirs, where the black precipitate is allowed
to settle, and the clear liquid afterwards drawn off. The precipitate is
first dried, and afterwards run down into a regulus yielding 70 per
cent. of copper, from which metallic copper can be made in one operation.
The solution, which usually contains large quantities of iron, should not
be much exposed to the atmosphere previously to being subjected to the
action of the gas, since by this means ferric oxide would be formed,
which, by becoming reduced to ferrous oxide, would cause a serious waste
of sulphuretted hydrogen.
At the date of the experiments which were made in this country by
Mr. Sinding and Mr. P. J. Worsley, the process was stated to have been
for several years in successful operation in Norway; it does not appear,
however, to have ever been introduced, on a working scale, into any part
of the United Kingdom. The Bede Metal Company, at Jarrow-on-Tyne,
for some time employed sulphuretted hydrogen for precipitating their
COPPER.
427
copper, but the bulky nature of the precipitate obtained was found to be
a great objection to the process.
"HENDERSON'S PROCESS."-In 1860 Mr. William Henderson filed a
specification for "Improvements in Treating certain Ores and Alloys,
and in Obtaining Products therefrom."
"These improvements relate, first to the treatment of copper and
several other ores, when they exist as or have been reduced or converted
to the state of oxides, carbonates, or other salts of copper, or other metal,
and especially when associated with silica and other matter insoluble in
dilute acids.
"Secondly, to the treatment of ores of copper, lead, zinc, antimony,
silver, cobalt and several other metals, when they occur as sulphurets,
mixed or singly, and combined with sulphur and iron, as iron pyrites, con-
taining all or either of these metals, or partially calcined or burnt, and
being then a mixture of oxides, sulphates and sulphurets, with or without
silica.
"And thirdly, to similar compounds when they exist wholly as oxides.
or salts, and associated with much silica."
Ores of the first class he proposes to attack, either with or without
a preliminary roasting, by sulphuric acid, and to evaporate the resulting
sulphate of copper to dryness in leaden pans, the anhydrous sulphate of
copper being subsequently so heated as to drive off the sulphuric acid
which is condensed in a leaden chamber. The resulting oxide is then
mixed with carbonaceous matter and a small quantity of siliceous ore, and
is smelted in a reverberatory furnace in the usual way; the products will
be blister-copper and slag free from regulus.
"The second class of ores I treat as follows: If the proportion of
sulphur existing in the ore is more than one and a half times as much as
the metal or metals to be extracted, it should be reduced to at least that
amount by calcination, or if the ore contains much silica the proportion
of sulphur may be even lower than an equal proportion. The ores are re-
duced to fine powder, the finer the better, and mixed with from 5 to 50
per cent. of common salt. The mixture is then placed in retorts or close
calcining furnaces, having flues or pipes communicating with the interior
of the furnace or retort, and a condensing apparatus. In these furnaces.
the mixture is subjected to various degrees of heat, according to the nature
of the ore and the metal or metals contained in it. If the ore contains
much sulphur and little silica, the heat must be applied carefully at first
and gradually increased, stirring at short intervals. When the ore is one
of copper or zinc, and has been previously burnt or calcined, the mixture
of salt and pulverised ore may be at once subjected to a bright red-heat;
the volatilised chlorides passing into the condensing apparatus are con-
densed with water. The ore is withdrawn from the furnace whenever it
ceases to smoke strongly, and if any copper or other metal still remains
in the calcined ore it is only necessary to wash it with the hot acid solu-
tion that runs from the tower or condensing apparatus; by these means
the last trace of copper or other metal is readily extracted. The
The copper
or other metal is obtained from these solutions by precipitation with iron,
428
ELEMENTS OF METALLURGY.
lime, or an alkali, and the sulphate of soda may be afterwards obtained
by evaporation and crystallisation. When a mixed ore is under treat-
ment containing metals whose chlorides volatilise at different tempera-
tures far removed, such as copper and tin, copper or zinc and arsenic,
lead and antimony, I employ a furnace with two or more beds, all heated
by the same fire or fires, each bed having a separate condenser. By these
means the arsenic, tin,* or antimony are volatilised in the upper or colder
beds and separately condensed, and the copper, lead, or zinc in the lower
and hotter beds.
“The third class of ores I treat exactly as the second class, the silica
taking the place of the sulphur and decomposing the salt at a red-heat."
It will be seen that the method of treatment patented by Mr. Hender-
son for ores of the second and third classes does not materially differ
from that of Mr. Longmaid, excepting that the former proposes to volati-
lise and subsequently to condense a large proportion of the copper.
The amount of copper thus volatilised is, practically, found to be of
little importance, but considerable quantities of chlorine and hydrochloric
acid are evolved from the furnaces in which the calcination of the mixture
of ore and salt is effected; these are condensed and advantageously
employed for the lixiviation of the roasted ores in the way shortly to be
described.
At the period when Mr. Longmaid was carrying out his invention
the supply of ores suitable for his process was exceedingly limited, and
was chiefly derived from the mines of Cornwall and Devon; by the time,
however, his method, in a more or less modified form, had been incor-
porated into the patents of Mr. Henderson, Spanish and Portuguese
cupreous pyrites had found their way extensively into the English
market.
These, after being used as a source of sulphur, furnish an excellent
material for such treatment, and various works were shortly afterwards
established for extracting copper from "burnt ores" by calcination with
salt and subsequent lixiviation. Although Mr. Henderson failed to
effect the volatilisation of copper to the extent he appears to have
expected, and the other portions of this method had, for the most
part, been anticipated by Mr. Longmaid, there can be no doubt that
to Mr. Henderson is due the credit of first appreciating the peculiar
suitability of burnt Spanish and Portuguese pyrites for treatment by
calcination with common salt. Mr. Henderson seems, however, to have
considered himself entitled to more than this, since he commenced an
action against the proprietors of certain works in which he alleged his
patent had been infringed; these proceedings were, however, withdrawn
before the case came to trial.
TREATMENT OF BURNT CUPREOUS PYRITES.-About 400,000 tons of
cupreous pyrites are annually imported into this country from Spain and
Portugal, in addition to which a few thousand tons are each year ob-
tained from the Stavanger Mines in Norway. The Spanish and Por-
* When ores containing stannic oxide are thus treated chloride of tin is not
formed.
COPPER.
429
tuguese pyrites are remarkably uniform in their composition, and the
limit of variation in the amount of copper present may be taken at
about 1 per cent. A specimen of this mineral from the mines of San
Domingos, in Portugal, which yield nearly one-half of the cupreous
pyrites consumed in this country, was found by Mr. F. Claudet to have
the following composition:-
S
49.00
As
0.47
•
Fe
43.55
5-
Cu
Zn
Pb
CaO
3.20
•
0.35
0.93
0.10
•
H₂O.
Siliceous residue.
0.70
0.63
1.07
100.00
Oxygen and traces of}
This pyrites, after being burnt for the manufacture of sulphuric acid,
leaves a residue representing about 70 per cent. of the weight of the
raw ore, and which is treated in the wet way for the copper it contains;
an average sample of burnt San Domingos pyrites was found on analysis
to have the following composition :—
S
•
As
3.76
0.25
Fe
•
58·25=83% Fe2O3
Cu
4.14
Zn
0.37
•
Co
traces
•
Ag
traces
·
•
Pb
CaO
H₂O
•
O, loss, &c.
1.14
•
0.25
3.85
•
26.93
•
Insoluble residue.
1.06
.
100.00
The treatment of these residues for copper comprehends the four
following operations:-
I. Grinding and sifting.
II. Calcination with salt.
III. Lixiviation.
IV. Precipitation of the copper by iron.
I. Grinding. For this purpose the ordinary Cornish crusher is com-
monly employed, and, in order to insure uniformity of mixture, the salt
is added to the burnt ore previously to grinding. Coarsely-crushed
rock-salt, added in the proportion of from 12 to 15 per cent., is
generally used. Before, however, proceeding to grind the burnt ore, it
is necessary to ascertain the exact amounts, respectively, of copper and
sulphur which it contains, since on the relations existing between these
bodies depends, to a great extent, the success of the operation. In the
majority of cases the amount of sulphur should exceed that of the copper
430
ELEMENTS OF METALLURGY.
by about per cent. The estimation of the former is effected by means
of barium chloride, and the resulting sulphate of barium weighed; the
latter is estimated by the use of a standardised solution of cyanide of
potassium.
When the proportion of sulphur in the burnt ore is less than that
above stated, an addition must be made of finely-ground unburnt pyrites;
if, on the contrary, sulphur is present in excess, the ore must be mixed
with other burnt pyrites from which the sulphur has been more com-
pletely expelled. The mixture of burnt ore, salt, and, when necessary,
raw pyrites, is passed through a sieve having five meshes to the linear
inch, and is then ready for the next operation.

k
k
k
Fig. 126.-Roasting Furnace; longitudinal elevation.
II. Calcination. The furnaces in which this mixture is subjected to
calcination vary considerably in their construction; at the various works.
belonging to the Tharsis Sulphur and Copper Company muffle furnaces
are exclusively employed; at the Bede Metal Company's works at Jarrow-
on-Tyne, automatic furnaces, with revolving hearths, are to a considerable
extent used; but in the majority of cases long open furnaces fired by
gas are preferred.

n
Z
г
万
​b
Fig. 127.-Roasting Furnace; longitudinal section.
Figs. 126, 127, 128, and 129, represent the ordinary open gas-furnace
in use in a great number of the Lancashire extraction-works. The first is
a longitudinal elevation, the second a longitudinal section, and the third
a horizontal section through the working doors; fig. 129 is a transverse
section through the centre of the fire-box, ɑ. This furnace is 30 feet in
length, and 11 feet in width, outside measure. The gas from the pro-
ducers is conveyed to the different furnaces through the flue, A, fig. 129,
and, entering the box, a, is admitted to the five parallel flues, b, separated
COPPER.
431
from each other by the brickwork pillars, c, the supply being regulated
by dampers, d, fig. 127. A sufficient amount of air to consume a portion
of this gas is admitted by apertures, e (fig. 127), at the end of each flue,
which can be closed by sliding doors, while the portion which remains
unconsumed is burnt by the aid of a further supply of air admitted by the
openings, f, into the chimneys, b', situated at the opposite extremity of each

6
Z
김
​Z
Z
Z
Z
h
Fig. 128.-Roasting Furnace; horizontal section through fire-doors.
of the five flues. In this way a long flame is made to travel in the direc-
tion indicated by the arrows (fig. 127), and the bottom of 4-inch rebated
tiles, g, is, at one end of the furnace, most strongly heated from beneath,
while, at the other, the greater portion of the heat is communicated from
above. By this means a tolerably equable temperature is maintained
throughout the whole length of the apparatus, and the products of com-
bustion, together with the gases and vapours evolved from the charge,

h
I
h
h
non o
n
0
m
A
a
Fig. 129.-Roasting Furnace; transverse section through fire-box.
escaping by h, are conveyed to the main flue, I, and pass through an
ordinary condensing tower, filled with open brickwork, in their way to the
chimney.
The mixture of ground ore and salt is charged, by means of a high-
level railway, through the hoppers, k, and is at once evenly spread over
the surface of the hearth, where it is kept at a dull red-heat and fre-
quently stirred by paddles or rakes, through the doors, l, until an assay
432
ELEMENTS OF METALLURGY.
indicates that it is in a fit state for drawing. This is determined in the
following way:-A fair sample of the charge is obtained by removing a
small portion with a paddle from every part of the hearth; about one
ounce of this is taken, and after being finely ground in a cast-iron mortar
it is boiled with water, which is subsequently poured off. This operation is
repeated, successively, three times, and the residue afterwards boiled with
dilute hydrochloric acid, which is in its turn poured off, and excess of
ammonia added to it; finally, the residue from hydrochloric acid is
boiled with nitric acid, and ammonia added in excess. If it be found by
these trials that the attack by hydrochloric acid only acquires a slightly
blue tint, and that the nitric acid solution is entirely, or very nearly,
colourless, the charge is ready to be drawn, since it indicates that, prac-
tically, the whole of the copper has been rendered soluble in water.
When, on the contrary, the nitric acid solution contains copper, it shows
that calcination has not been continued for a sufficient length of time,
and should the hydrochloric acid solution, on the addition of an excess
of ammonia, become decidedly blue, it is probable that the amount of
sulphur present in the charge is not sufficient to effect the necessary
chemical transformations. The fire-bridge, m, at the far end of the
furnace has pillars, n, extending to the arch, which give it stability and
prevent its destruction by the tools of the workmen; the flame con-
sequently enters the hearth through a series of rectangular apertures, o.
•
During the process of roasting, the sulphur becomes oxidised, and
sulphate of sodium and soluble cupric chloride are formed; unless, how-
ever, the charges are properly compounded and carefully worked at a
suitable temperature, a large quantity of comparatively insoluble cuprous
chloride will be produced, and a serious loss of copper in the residue will
be the result. The charge is 3 tons 5 cwts., and the time required for fur-
nacing is about six hours; the hydrochloric acid and chlorine which are
evolved, together with a small quantity of iron and copper chlorides,
are passed into a condensing tower, packed with open brickwork, through
which a constant shower of water is caused to descend. These waters,
which are somewhat acid, are employed for the lixiviation of calcined
ore, and, in addition to hydrochloric acid and chlorine, contain iron and
traces of copper.
III. Lixiviation.-The calcined mixture of burnt ore and salt is raked
from the furnace, through the doors in one of its sides, and, while still hot, is
charged into lixiviating tanks, which are usually from 10 to 11 feet square,
and somewhat less than 4 feet in depth. These are made of wood tightly
caulked, and are provided with a removable false bottom, either of per-
forated tiles or of fire-bricks, supported on other bricks resting, on edge,
on the floor of the tank. Upon this is placed a layer of cinders three
inches in thickness, forming a sort of coarse filter, on which are charged
about 15 tons of the calcined ore. The plug-hole between the bottom of
the tank and the filter bottom is now closed, and either hot water, weak
liquors, or tower-liquors are run in, until the surface of the ore has been
covered to a depth of several inches. This is allowed to remain about two
hours, when it is run off into proper receivers, and the tank again filled
COPPER.
433
with hot water, weak liquors, or tower-liquors. In this way each tank
receives from nine to ten successive washings, and at about the seventh
washing a little hydrochloric acid is sometimes added; all the liquors
which drain from the several tanks after the addition of acid are collected
in a separate receiver, and, instead of being run into cisterns containing
scrap-iron for the precipitation of the copper, they are employed under
the name of "weak liquors" for washing the next series of tanks filled
with freshly-furnaced ore. The operation of washing occupies about
forty-eight hours, and the residual purple ore, which is sold for fettling
puddling furnaces, as well as for other purposes, and of which an analysis
is given, page 281, should not contain above 0.15 per cent. of copper.
The testing of the tanks is conducted in a very similar way to that of the
furnaces.
Considerable quantities of fume are deposited in the flues connecting
the various furnaces with the condensers; these are from time to time
cleaned out, and the deposit treated for the copper it contains. A sample
of dry dust, obtained in cleaning a flue at the Widnes Metal Works, in
connection with eight calciners working on San Domingos ores, was
found to have the following composition :-
A$203
Bi₂03
•
Sb2O3
ZnO
Fe₂03
РЬО
2.97.
2.21
0.23
4.06
15.98
2.00
CuO
Al2O3
CaO
MgO
K₂O
Na₂O
25.33
•
trace
2.38
trace
•
0.23
•
1.81
NaCl
SO 3
2.73
40.32
SiO 2
trace
•
100.25
This analysis is chiefly interesting as showing the large number of
metals contained in the ores treated.
IV. Precipitation.—In establishments in which the silver is extracted
from burnt pyrites by Claudet's process, the liquors from the first three
washings, which contain, practically, the whole of that metal, are first
treated with a soluble iodide, and the iodide of silver is allowed to settle.
The copper-liquors drawn off from the iodide of silver are, in such cases,
added to the weaker solutions from subsequent washings; but when the
silver is not thus separated the whole of the copper solutions, with the
exception of the weak liquors, are at once run directly into the preci-
pitating tanks. These are commonly 12 feet square and 4 feet in depth,
and are partially filled with clean scrap-iron; precipitation of the copper
being accelerated by boiling the liquors by the introduction of a jet of
steam. In the course of about eight hours complete precipitation of the
copper will have taken place, and, when stains of this metal are no longer
2 F
434
ELEMENTS OF METALLURGY.
deposited on a brightly-polished knife-blade when dipped into the liquors,
they are first allowed to settle, and are subsequently run off.
In order to separate the precipitated copper from the undissolved iron
the mass is turned over with an iron fork and the larger pieces of that
metal picked out. The remainder is now washed on perforated cast-iron
plates, through which the particles of precipitated copper pass into
a properly-constructed receiver; the fragments of iron are raked off
their surface and returned to the precipitating tanks. The precipitate
thus prepared will contain from 70 to 80 per cent. of metallic copper,
and may be either smelted directly for blister-copper, or, what is
preferable, fused with fine-metal, and afterwards subjected to a process
of roasting.
MODIFICATIONS OF THE ORDINARY WET PROCESS.-The Tharsis Sulphur
and Copper Company calcine the mixture of ore and salt in close furnaces
so constructed as to completely separate the vapours and gases eliminated
from the charge, from those which are the products of combustion; the
former are passed through an ordinary condenser filled with coke, while
the latter are taken directly to the chimney. This arrangement has the
advantage of effecting better condensation than can be obtained by the use
of the open furnace, but the expenditure of fuel is considerably greater.
In some establishments, instead of precipitating the copper by the use
of scrap-iron, sponge-iron is employed. This is prepared by heating a
mixture of coke-dust and purple ore in a reverberatory furnace, and
drawing the reduced metal into cast-iron vessels, which are hermetically
closed until they and their contents have become nearly cold. When
sufficiently cooled, the spongy metal is ground under edge-runners, and
sifted through a very fine sieve. The precipitation of copper is very
rapidly effected by the use of sponge-iron, but the precipitate obtained
invariably contains a considerable percentage of iron.
The amount of sulphate of sodium produced during the treatment of
burnt pyrites in the wet way is very considerable, and various attempts
have, at different times, been made to effect its recovery by crystallisation
or otherwise. For some time operations of this nature were conducted
in different works with somewhat satisfactory results, but the recent great
advance in the price of every description of fuel has rendered the
majority of these processes unprofitable.
At the Bede Works the waste liquors were for some time converted
into soda-ash by a process invented by Mr. T. Gibb, the manager; sul-
phate of sodium in the waste liquors was converted into sodium sulphide by
balling with coal-dust, and carbonic anhydride passed through the liquors
obtained by lixiviation. Carbonate of sodium was thus formed, and the
sulphuretted hydrogen evolved was employed for the precipitation of
copper from the solutions obtained by washing calcined ores; we believe,
however, that the processes adopted were of a somewhat complicated
nature, and that experiments on this method of treatment have, for the
present, been suspended.
{
COPPER.
435
ALLOYS OF COPPER.
The addition of zinc materially affects the colour of copper; if added
in small proportion only, the alloy assumes a golden-yellow colour; if
the percentage of zinc be greater a pale-straw colour is obtained, and if
zinc predominates, the colour of the alloy is greyish-white or iron-grey.
Various alloys of this kind, of which the most important is known by
the name of brass, are employed in the arts. The proportions of the
two metals best calculated for the production of fine brass seem to be
about two parts by weight of copper to one of zinc.
Brass solder consists of two parts of brass and one of zinc, to which
a little tin is occasionally added; but when the solder is required to be
very strong, as for uniting the edges of tubes intended subsequently to
undergo the process of drawing, two parts of common brass and two-
thirds of a part of zinc may be employed. Mosaic gold consists, approxi-
mately, of 65 parts of copper and 35 of zinc.
of about 78 parts of copper and 22 of zinc.
gold are merely different names for an alloy
which is composed of three parts of copper and one of zinc, separately
melted in different crucibles, and afterwards mixed and incorporated by
stirring.
Bath metal is composed
Pinchbeck and Mannheim
similar to Prince's metal,
Copper is sometimes externally converted into brass by exposure, when
at a red-hcat, to the vapour of zinc; in this way are prepared the copper
bars from which the so-called "gold wire" of Lyons is manufactured,
Copper is also extensively alloyed with tin, in combination with which
it yields many valuable compounds, variously named in accordance with
their respective compositions and uses.
Gun-metal, of which cannon are made, consists of, about, copper 91,
tin 9.
Bell-metal is composed of, about, copper 78, tin 22.
The alloy of which gongs and cymbals are manufactured has usually
the following composition: copper 80, tin 20.
Alloys of copper and tin, although still important, were evidently
more so before iron was extensively used, since prior to that period they
were employed in the manufacture of cutting instruments. For this
purpose a mixture of 90 parts of copper to 10 of tin was most commonly
used, although a little lead was occasionally added, apparently with a
view of imparting to the alloy a certain degree of toughness.
The preparation and fusion of these different mixtures is, according
to the quantities required, conducted either in a reverberatory furnace,
or in strongly-heated crucibles.
German silver, an alloy of copper, zinc and nickel, has been long
known and extensively used in China, and was formerly imported into
Europe under the name of packfong. In 1776 it was first recognised as
an alloy of copper and zinc with nickel, and from being afterwards
largely manufactured in Germany it received the name of German silver.
It is now extensively prepared in various parts of England, but particu-
larly at Sheffield, where it is manufactured into spoons, forks, and various
2 F 2
436
ELEMENTS OF METALLURGY.
other articles for domestic use; these are plated by the electrotype pro-
cess, and employed as a substitute for silver.
The following analyses, given by Lamborn, serve to show the com-
position of several varieties of this alloy :—

Cu.
Ni.
Zn.
Chinese packfong
43.8
15.6
40.6
English German silver
61.3
19.1
19.1
Berlin argentan
52.0
26.0
22.0
Sheffield German silver
57.0
24.0
13.0
A spoon made by Messrs. Zernecke of Berlin, and analysed so long
ago as 1826, was found to be composed of an alloy consisting of cop-
per 57·1, manganese 19.7, and zinc 23.2 per cent. Mr. J. Fenwick Allen,
of the firm of Messrs. Newton, Keates and Co., St. Helens, who men-
tions the above fact in a paper 'On the Alloys of Copper, Tin, Zinc,
Lead and other Metals with Manganese,' read at the Liverpool meeting
of the British Association, 1871, has devoted a considerable amount of
attention to this subject, and has prepared several tons of an alloy of
copper and manganese, to which he has given the name of "standard
metal."
This is produced by heating, in a Siemens regenerative furnace, a
mixture of carbonate of manganese with oxide of copper and charcoal.
As a simple alloy, in which the proportion of manganese ranges from
5 to 30 per cent., it is both malleable and ductile, and possesses a tenacity
considerably greater than that of copper. With zinc, a compound alloy,
resembling in some of its qualities German silver, is obtained.
The alloy of copper and manganese combines with tin, lead and other
metals, and from these mixtures castings are made, and applied as
bearings for machinery, and for other similar purposes. The waste of
manganese from oxidation which occurs every time an alloy rich in that
metal is subjected to fusion is very great, and will, it is feared, materially
restrict the practical application of such compounds.
Although the foregoing are some of the more important alloys of
copper, there are numerous others which are occasionally employed by the
artisan. With iron it appears to combine in very small proportions only,
with aluminium it forms an alloy of considerable malleability and great
hardness, and which is capable of taking a high polish.
BRASS.-Brass, for which the old name is latten, is essentially an alloy
of copper and zinc.
The first brass-works erected in England are said to have been put into
operation in 1649 at Esher, in Surrey, where rosette copper, imported
from Sweden, was exclusively employed in the manufacture; the pro-
prictor having, however, become involved in a disastrous lawsuit, the
establishment was ultimately broken up. Birmingham, where the trade
is stated to have been first introduced in 1740, by the Turner family, is
now the principal seat of the brass industry of this country. Brass is
COPPER.
437
harder than copper, and consequently better calculated to resist wear; it is
also in a high degree malleable and ductile, so that it is easily rolled into
sheets and readily hammered into vessels of any required shape. It can,
moreover, be worked by the process of stamping into numerous orna-
mental and useful objects, and admits of being drawn into fine wire; it
fuses at a lower temperature than copper, and is capable of receiving
a more delicate impression of the mould. Finally, it turns easily in the
lathe, its colour is agreeable, it is capable of receiving a high polish, and
it possesses over copper the advantage of greater cheapness.
Until a comparatively recent date brass was exclusively made by the
old process of cementation, which has become almost entirely superseded
by directly alloying copper with metallic zinc.
The general name of brass is applied to alloys of copper and zinc
into the composition of which the two metals enter in very different pro-
portions. The following table, compiled from Mr. Mallet's figures (Report
of the Meeting of the British Association at Glasgow, 1839), gives the
proportions and peculiarities of several varieties of brass:-
Cu.
Zn.
Colour of Alloy.
Fracture.
Remarks.
88.60
11.40
83.02 16.98
Reddish-yellow
Finely crystalline.
Yellowish-red.
Rolled brass.
79.65 20.35
""
74.58 25.42 Pale yellow
•
66.18 33.82
Full yellow
49.47 50.53
31.52 68.48
Silver-white
·
24.50 75.50 Ash-grey
""
""
""
Coarsely crystalline.
Conchoidal
Finely crystalline
Mosaic gold.
German brass.
(German watchmaker's
brass.
Very hard and brittle.
Brittle.
Manufacture of Calamine Brass.-This very ancient process, by which
for a long period brass was exclusively manufactured, seems to have disap-
peared from among the industries of the United Kingdom. The various
operations of this process are conducted in the following way: The furnace
employed consists of a circular chamber lined with fire-bricks, contracted
above to a circular opening serving as a chimney; the bottom is closed by
a cast-iron plate, in which are twelve holes, symmetrically arranged around
one larger hole in the centre. Through this central hole are withdrawn
the ashes and clinkers, which fall into an ash-pit, communicating, by means
of an arched air-way, with a long passage or vault by which air is con-
veyed to the furnace from the outside, and through which access to
the ash-pit is obtained. Over the holes in the bed-plate, with the excep-
tion of that in the centre, are placed cast-iron tuyers or nozzles, 6 inches
in length, 2 inches in diameter at bottom, and 1 inch at top, inside
measure; the space between the nozzles is filled up level with their upper
extremities with refractory bricks set in fire-clay, so as to form a level
floor 6 inches in thickness. This forms a substitute for the ordinary fire-
grate; the air necessary for sustaining combustion entering through the
different nozzles. Several of these furnaces are usually constructed in a
438
ELEMENTS OF METALLURGY.
row, and over the whole is built a brickwork chamber terminating in a
cone open at the top like that of an ordinary glass-house. These furnaces
have no chimney excepting the mouth, which is kept more or less closed
by a sliding cover consisting of a circular fire-tile set in an iron framing.
The crucibles employed are round, and are made of fire-clay, each
being 12 inches in height and 8 inches wide at top; the central
crucible, sometimes called the king pot, is often a little larger than the
others, being capable of holding 120 lbs. of metal, whereas the others
contain only 84 lbs. each.
The charge consists of 100 lbs. of finely-ground and well-calcined cala-
mine or blende, and 40 lbs. of ground coal. These are intimately mixed,
dry, and then passed through a sieve of eight holes to the linear inch h;
this mixture is subsequently damped and then passed through a much
coarser sieve, after which it is mixed with 66 lbs. of granulated copper,
bean-shot, and is then ready for charging.
As the operation of making brass is carried on continuously, the mix-
ture is introduced into the crucibles while they are still red-hot from the
treatment of a previous charge, and their mouths are severally covered by
large pieces of coal, while the spaces between the different crucibles are
filled with coal broken into pieces of the size of the fist. The mouth of
the furnace is now partially closed for one hour and a half, for the
purpose
of transforming the coal into a kind of coke; the orifice is then still further
closed for a short time, and the coke properly arranged between the dif-
ferent pots, care being taken to keep all the air-holes open. The heat is
now progressively raised by the gradual removal of the cover, and, if skil-
fully conducted, the operation will be completed in about ten hours.
In order to collect the brass which has been formed, the king pot is
first taken out, and its contents well stirred with an iron rod flattened at
the end; one of the side pots is next removed, treated in the same manner,
and the brass, which collects at the bottom, poured into the king pot. All
the other side pots are successively treated in the same way, and the brass
which has been collected in the central pot is finally skimmed and poured
into moulds. Dr. Percy states, on the authority of an old calamine-brass
maker, that good pots lasted, on an average, sixteen days, and were not
allowed to cool during that period.
Direct Preparation of Brass.-This may be effected by melting together
a mixture of copper and zinc, either in crucibles or in a reverberatory
furnace. When this operation is conducted in crucibles the zinc should
be added to the copper immediately after the latter has entered into
fusion, and the ingots of copper should be heated to redness previously
to their introduction into the pots. In making castings, and in the re-
inelting of brass, there is always a considerable loss of zinc through
volatilisation, for which allowance must be made when arranging the
mixture. Granite moulds were formerly used for casting ingot-brass, but
iron is now generally employed.
Muntz's metal, or yellow-metal, which has entirely superseded copper-
sheathing in the merchant service, is generally prepared in reverberatory
furnaces, the ziuc being gradually added to the melted copper. Before
TIN.
439
tapping, samples of the alloy are taken out of the furnace in the same way
as the copper proofs made use of in the process of refining; these are
cast into oblong ingots, hammered, and broken in a vice; the quality of the
mixture being judged of in accordance with the appearance presented
by the fracture. This should be close and finely-granular, but if the
first trial should not prove satisfactory more zinc is added, and the
mixture well stirred; this is repeated until the fracture of a sample ingot
indicates that the right proportions of the two metals have been reached.
The necessity for this method of testing is caused by the great facility
with which zinc becomes volatilised, and consequently, although the
proper quantities of the two metals may have been charged into the
furnace, it is impossible to make accurate allowance for the amount
of zinc which may be driven off. It also frequently happens that the
charge of a furnace is made up with a mixture of old yellow-metal, new
copper, and zinc; in such cases the difficulty of making due allowance
for loss of zinc will be still greater. When ready the metal is tapped
into a large ladle and either poured or laded into close cast-iron ingot-
moulds, the interior of which has been either oiled and subsequently
dusted with charcoal, or more commonly washed with a mixture of
wood-ashes, or clay, and water.
Yellow-metal may contain from 50 to 63 per cent. of copper and from
37 to 50 per cent. of zinc.
From the circumstance that tin is not, practically, a volatile metal,
the preparation of bronze is, comparatively, an easy operation, and may
be conducted either in crucibles or in an ordinary reverberatory furnace.
TIN.
Tin is a white metal, with a lustre closely approaching to that of
silver, and with a specific gravity of 7.29; it possesses a characteristic
taste, and has an odour which becomes evident when a piece of this
metal has been slightly warmed by being held for some time in the
hand. It is very malleable, and may consequently be reduced to thin
leaves by hammering; at the temperature of 100° C. this property is
considerably increased. This metal, although flexible, is not elastic, and
when bent emits a peculiar crackling sound, which is most distinct in
the purest specimens; a perceptible elevation of temperature is caused
by the repeated bending and straightening of a bar of tin. It melts at
a temperature of 227.8° C., and when very strongly heated, gives off
distinct fumes, but experiences only a slight loss of weight. Tin exhibits
a great tendency to crystallise; this property may be readily made
apparent by slightly attacking its surface by some acid capable of
removing the exterior. When this has been done, the metal assumes
a mottled appearance, caused by the irregular reflection of the fern-like
crystals brought to light by the action of the acid. A process of this
kind is sometimes resorted to for the purpose of improving the appear-
Uor M
440
ELEMENTS OF METALLURGY.
ance of articles made of tin-plate, which, after being thus treated, and
subsequently covered by a coating of transparent and slightly-coloured
varnish, present a variegated and somewhat prettily-marked surface.
Tin may be obtained in the form of crystals, by fusing a considerable
weight in a ladle, or crucible, and allowing it to cool gradually on
a heated sand-bath; as soon as a solid pellicle has formed on the surface,
it is pierced by a hot iron bar, and the internal portions, which still
exist in a liquid state, are allowed to run out. By operating in this way
crystals of considerable size, though rarely exhibiting sharp and well-
defined edges, will be found lining the cavity from which the liquid
metal has been removed. Tin may be deposited from its solutions in a
crystallised state by electric agency, and is by this means obtained in
the form of brilliant elongated needles.
The tin of commerce is never quite pure, but is more or less con-
taminated by the presence of various other metals, particularly arsenic.
To obtain tin in a state of great purity, granulated tin may be attacked
by nitric acid, and the resulting insoluble residue washed, first with
hydrochloric acid and subsequently with hot water. The residue is
now reduced to the metallic state by fusion, with the addition of a little
charcoal, in a brasqued crucible. Tin is but slightly affected by exposure
to the air at ordinary temperatures, but when fused its surface is rapidly
covered by a crust of a greyish colour, consisting of a mixture of metal
and stannic oxide. This oxidation of tin takes place very rapidly at high
temperatures, and when the metal is heated to whiteness, is attended by
distinct combustion; at a full red-heat it decomposes water, with evolu-
tion of hydrogen gas. It is dissolved in strong hydrochloric acid, and
its solution is also effected when it is attacked by warm dilute sul-
phuric acid; concentrated sulphuric acid, aided by heat, acts upon
metallic tin, with liberation of sulphurous anhydride and sulphur, and
the eventual production of stannic sulphate Sn(SO4)2. Tin is not attacked
by the strongest nitric acid (sp. gr. 1.52), but by acid of a density of 1·42
it is violently acted upon, with formation of a white, crystalloid, in-
soluble substance, metastannic acid, Su,O₁₂H2,4H2O or Sn¸О105H2O. Tin
is oxidisable by fused caustic potash or soda, and more readily so by a
fused mixture of an alkaline nitrate with an alkaline hydrate or carbonate.
5 11
TIN ORES.
CASSITERITE; OXIDE OF TIN; Etain oxydé; Zinnstein. Tetragonal.-
The tin of commerce is obtained from the native oxide of that metal,
which belongs exclusively to the older formations, and is chiefly met
with in veins traversing granite, gneiss, or mica-slate. Oxide of tin has
a specific gravity varying from 6-3 to 7.1. Its colour is usually brown
or black, but sometimes red, grey, white, or yellow. It has an imperfect
conchoidal fracture, a grey streak, and a highly adamantine lustre.
When pure, this mineral consists of tin 78.62, oxygen 21.38. It is,
however, frequently associated with other metals, particularly arsenic and
iron, and, more rarely, with columbium.
TIN.
441
A specimen of cassiterite from Cornwall, analysed by Klaproth, gave
the following results:-
Sn
77.50
•
21.50
0.25
0.75
100.00
Fe2O3
SiO 2
The composition of this mineral is expressed by the formula SnO..
The most commonly-occurring crystals are rectangular prisms termi-
nated by four triangular planes, which may be more or less modified on
their edges and angles. It sometimes also affords modifications which
give rise to the formation of eight terminal planes at each summit, which
may, themselves, also be modified.
Oxide of tin is infusible when heated alone before the blowpipe,
and is not readily reduced to the metallic state without the aid of fluxes.
It is insoluble in acids; but when heated on a charcoal support, with
the addition of carbonate of sodium, readily affords minute globules
of metal.
Cornwall is one of the localities most productive of this mineral;
it occurs associated with copper and iron pyrites, wolfram, mica, talc,
and tourmaline, together with axinite, and other silicates. Tin mines are
also worked in Saxony, Austria, and Bohemia; in Peru and Bolivia; in
China, Malacca, and especially on the islands of Banca and Billiton, in the
Indian Archipelago, whence large quantities are annually imported into
this country. This oxide also occurs in Galicia, Spain; in Sweden; in
the Department of the Haute Vienne in France; in Greenland, Russia,
Brazil, Mexico, Chili, Australia, and the United States of America.
TIN PYRITES; Etain sulfuré; Zinnkies. Probably tetragonal. This
mineral has hitherto been found in a crystalline state only in Huel
Rock Mine, in the parish of St. Agnes, Cornwall, whence rectangular
crystals, possessing cleavages parallel to the faces of the primitive form,
have occasionally been obtained. Tin pyrites is of a yellowish-grey
colour, and has a strong metallic lustre; it commonly occurs in granular
amorphous masses, and has a specific gravity of 4.35. It affords a black
streak, and presents an uneven fracture. When heated before the blow-
pipe, sulphide of tin fuses into a black slag, which is extremely difficult
of reduction. It is attacked by nitric acid, and affords on subsidence an
abundant white precipitate of metastannic acid. Two analyses of tin
pyrites yielded the following results :—

Kudernatsch.
Klaproth.
Sn
25.55
26.5
•
Cu
29.39
30.0
•
Fe
12.44
12.0
S
29.64
30.5
97.02
99.0
442
ELEMENTS OF METALLURGY.
This mineral does not occur in sufficient quantity to admit of being
metallurgically treated, and cannot, therefore, be strictly regarded as
an ore of tin.
DISTRIBUTION OF TIN ORES.
Tin has, more than almost any other metal, a characteristic mode
of occurrence, being invariably found in the older crystalline and meta-
morphic rocks.
The only ore yielding tin in commercial quantities is cassiterite,
which occurs in four different forms of deposit. Firstly, in true veins or
lodes, from which the larger proportion of the tin annually produced in
this country is obtained. Secondly, in beds or flats, usually connected
with true veins, but passing into the inclosing rocks, and often forming
beds parallel to their stratification. Thirdly, in Stockwerke, which chiefly
occur in granite, and consist of numerous minute veins of cassiterite
passing through the rock in all directions. Fourthly, as stream-tin,
which consists of water-worn nodules and grains of tin oxide occurring
in alluvial sands and gravels. This variety of tin ore is obtained by a
process of washing very similar to that employed for the separation of
alluvial gold. Although this metal has been in use from remote anti-
quity, Cornwall, up to a comparatively recent date, produced the prin-
cipal portion of that annually brought into the market. About the year
1710 rich deposits of tin ore were discovered in the island of Banca, in
the Malay Archipelago, and more recently in the neighbouring island of
Billiton, and in various parts of Australia.
In the county of Cornwall, where ores of this metal have been con-
tinuously raised from the time of the Phoenicians, the deposits compre-
hend all the different varieties previously enumerated; those of stream-
tin have, however, become almost entirely exhausted. Tin veins usually
occur either in granite or in killas, which is a metamorphic clay-slate,
and are generally most productive in the vicinity of the line of junction
of these rocks. The gangue of stanniferous deposits consists in most
cases of quartzose matter, and the minerals associated with cassiterite
are remarkably constant, consisting of wolfram, mispickel, apatite, topaz,
mica, tourmaline, &c.
During the years 1835 to 1838 the annual production of tin in Corn-
wall and Devon amounted to between 4,000 and 5,000 tons; since that
time it has steadily increased, until in 1871 it amounted to 16,898 tons
of black tin, equivalent to 11,320 tons of metal; during the same year
the imports into the United Kingdom were about 9,000 tons, and the
exports about the same quantity.
In Saxony a small quantity of tin is annually raised, but the amount
appears insignificant when compared with that produced in England, of
which it has been estimated at about one-fifteenth. The chief Saxon
and Bohemian localities are Altenberg, Geyer, Zinnwald, and Auersberg
in the Erzgebirge, and Schlaggenwald near Elbogen.
At Geyer the rock in which the ore occurs is a granite, consisting
chiefly of decomposed felspar, and containing apatite, tourmaline, and
TIN.
443
fluor-spar. The tinstone is in small parallel veins and is disseminated
through the adjacent rock; the veins, which are rarely more than 2 inches
in width, merge into the inclosing rock without exhibiting any distinct
walls.
At Zinnwald the tin occurs in masses of granite which rise through
porphyry, the most productive deposits being composed of quartz and
cassiterite in nearly horizontal layers; in some cases, however, the whole
rock is stanniferous.
At Altenberg true Stockwerk deposits occur, consisting of a por-
phyritic rock, intersected by numerous small interlacing veins of tinstone.
In 1854 Whitney estimated the annual value of the tin raised at Alten-
berg at £10,000.
From France and Spain tin is to a great extent absent, rarely occur-
ring in workable quantities; a few tons are, however, annually produced
in both countries, the ore being obtained from Brittany, and from several
localities in Galicia.
The second great centre of production includes Banca and Billiton,
or Blitong, in which all the ore worked is in the form of detrital or
stream-tin. Veins have, however, been found in considerable numbers,
but not of sufficient size to pay for working. The alluvial deposits are
in most cases covered by beds of variously-coloured clays to a depth of
from 10 to 15 feet, and rest on a stratum of white clay, which is con-
sidered an infallible indication of the limit of the stanniferous beds. It
is stated that the stream-tin of Banca is derived from the granite or
rocks immediately contiguous to it, and that tin is only found in valleys
the streams of which take their rise in these rocks.
In addition to the tin produced by these islands, there is also a
certain quantity annually raised on the Malayan peninsula.
In 1871 the quantity produced in Banca amounted to 134,906 slabs,
weighing 4,320 tons; whilst that raised in Billiton during the same year
is estimated at 99,700 slabs, weighing 3,190 tons.
In the United States of America cassiterite has been found in several
localities, but never in workable quantities. Small quantities have been
raised at Temescal, near Los Angeles, in California. In South America
tin mines are worked in Bolivia and Peru. The annual production of
this metal in South America is estimated at 1,200 tons.
Stream-tin has been found in several localities in Mexico, notably in
Guanaxuato and Zacatecas, as also in Durango, where it is associated
with topaz.
Within the last few years tin has been found in large quantities in
Australia, but up to the present time mining for this metal has been
but little developed.
Mr. T. F. Gregory, Mineral Land Commissioner, reports that in
Queensland the richest deposits have been found in stream-beds and
fluviatile flats on their banks, the paying ground varying from a few
yards to five chains in width.* The aggregate length of these alluvial
* 'A Report on the Tin Discoveries in Queensland,' Quarterly Journal of the
Geological Society. Feb. 1st, 1873, p. 1.
414
ELEMENTS OF METALLURGY.
deposits is stated to be about 140 miles on the River Severn, and some 30
more on its various tributaries; 10 tons per linear chain of the creck-
beds is stated to be a fair average yield of oxide of tin, though in some
instances the quantity reaches as much as 30 tons. The tin-bearing
veins have not as yet been fully investigated, but appear to be of cou-
siderable promise. Up to July, 1872, 850 claims had been taken up,
most of which had their frontages on watercourses. The inhabitants of
the tin-fields number from 1,200 to 1,500, but if all the claims be worked
at least 5,000 miners will be required.
Mr. G. H. F. Ulrich, in an article on tin-ore discoveries in New
England, New South Wales, tells us that the predominant rocks are
granite and basalt, inclosing subordinate areas of metamorphic slate and
sandstone.* The richest mining area is that of the Elsmore Company,
near the township of Inverell, where the cassiterite occurs in quartz
veins running through a porphyritic granite. The most important
deposits, however, are in dykes of a softer granitic rock, of which
75 per cent. consists of greenish mica, and the remainder of felspar,
quartz being rarely present. Through these dykes tinstone is thickly
disseminated, not only in small crystals, but in irregular veins, and in
nests and bunches, yielding lumps of pure cassiterite of as much as
50 lbs. in weight.
The conclusion arrived at by Mr. Ulrich is, that the granite of the
district is one vast Stockwerk. The drift is also exceedingly rich, and
consists of recent granitic detritus; samples washed in the prospecting
dish yielded from 3 ozs. to 6 lbs. of black tin per 20 lbs. of material.
It appears, however, that scarcity of water may interfere with the pro-
fitable working of some of the deposits.
In conclusion, Mr. Ulrich says that "the produce of such as can be
worked will doubtless, in no long time, sensibly affect the tin markets of
the world; in fact, it seems not unlikely that the production of tin ore
in this part of Australia will reach, if not surpass, that of all the old tin-
mining countries combined."
The quantity of tin lying on the surface in Australia has been
estimated at twenty-five times the annual produce of this metal in
Cornwall.
The present total annual production of tin in the world may be
roughly estimated at between 25,000 and 28,000 tons.
ASSAY OF TIN ORES.
PREPARATION OF THE ORE.-Before proceeding to the assay of any
description of "tin-stuffӠ it is necessary to first isolate the oxide of tin
from the siliceous gangue and the various sulphurous and arsenical ores
with which it may be associated.
This may be accomplished, in a somewhat rough way, by treatment
* Observations on some of the Recent Tin-Ore Discoveries in New England, New
South Wales,' Quarterly Journal of the Geological Society, Feb. 1st, 1873, p. 5.
† Any veinstone or other rock containing a workable amount of oxide of tin is
called "tin-stuff."
TIN.
445
similar to that by which the concentration and purification of tin ores are
conducted on the large scale. With this view the pulverised mineral
may be first roasted, and afterwards washed in an evaporating basin, or in
some other convenient vessel, until the lighter substances with which it
is associated have been removed. In the tin-mining districts of Cornwall
and Devon a large round-pointed shovel is employed for this purpose,
and after cach successive washing the heavier portions, which have not
been carried off in suspension, are further reduced in size by grinding
under a heavy hammer, of which the faces are slightly rounded; the
assay is subsequently roasted and again washed. Roasting has for its
object the decomposition of arsenical pyrites and of various associated
minerals containing sulphur, which, from their greatly-reduced density
after calcination, are then easily removed by water. In Saxony, a
small hand shaking-table is employed for the same purpose, but it
possesses no advantage over the ordinary vanning-shovel. Instead, how-
ever, of resorting to washing and roasting, the removal of arsenical and
sulphurous minerals may be more completely and expeditiously effected
by boiling the pulverised material in excess of nitro-hydrochloric acid,
by which arsenical and common pyrites, copper ores, &c., are completely
dissolved. The insoluble matters remaining in the flask will chiefly
consist of tin oxide and silica, with sometimes a certain amount of
tungstic acid, which latter may be removed by digestion with ammonia.
What now remains will be a mixture of oxide of tin with silica, from
which the latter may be removed either by careful vanning, or, still
better, by digestion with hydrofluoric acid in a platinum dish. When
arsenical or ordinary iron pyrites containing tin is to be assayed for that
metal, it may be attacked by nitro-hydrochloric acid, washed by decanta-
tion, and treated with ammonia. It is then transferred to a platinum
dish and digested with hydrofluoric acid; these operations must be
repeated until pure cassiterite remains in the capsule. In the majority
of cases it will be unnecessary to treat with ammonia after any but
the first attack by aqua regia.
ASSAY OF BLACK TIN.-The nearly pure oxide, in the state in
which it is delivered by the miner to the smelter, or after the gangue
has been attacked first by aqua regia and subsequently by hydrofluoric
acid, in the way described, may be reduced to the metallic state by various
processes.
In Brasqued or Black-Lead Crucibles.—A weighed quantity of from
200 to 400 grains of the oxide may be placed either in a brasqued crucible
and carefully covered, or it may be mixed with one-fifth its weight of ground
charcoal or anthracite, and introduced into an ordinary plumbago pot
and placed in an assay furnace.
During the first quarter of an hour the heat must be gradually raised
to dull redness, after which it is elevated to a full bright redness, at
which it should be kept for about ten minutes. The crucible and its
contents are now carefully removed from the fire, without knocking, and
allowed to cool, when the pot is broken, and the button of tin removed
and weighed. In order to recover any particles of metal which may be
446
ELEMENTS OF METALLURGY.
disseminated through the brasque in the form of minute globules, it
must be removed and carefully washed; the weight of the metal so
obtained is added to that of the original button. In the same way, any
unconsumed charcoal-powder or anthracite added to the assay in the
black-lead crucible must be carefully vanned, and, should any metal
adhere firmly to the sides of the pot, it must be removed, cleaned, and
its weight added to that of the original button.
Cornish Method of Assay.—In Cornwall, assays of black tin are usually
conducted in a naked plumbago pot, which is first made red-hot, and
the assay, consisting of 2 ozs. of washed ore mixed with a little culm,
introduced. In case the assay should not fuse readily, a little fluor-
spar is added, and after exposure during a quarter of an hour to a full
red-heat, the tin is rapidly poured into a small ingot-mould, and the
slag examined for metal by pounding and washing.
Fusion with Potassium Cyanide. The crucibles employed for this pur-
pose, when 200 grains of black tin are operated on, should be of about
3 ozs. capacity, and must be prepared by ramming into the bottom of
each a layer, of about half an inch in thickness, of commercial cyanide of
potassium. The requisite amount of finely-powdered tin ore is now
intimately mixed with from four to five times its weight of potassium
cyanide, and placed in a crucible prepared as previously directed. This,
with its contents, is now moderately heated in an assay furnace, and,
after having been kept for about ten minutes in a state of tranquil fusion,
the pot is removed, gently tapped to facilitate the formation of a single
button, and allowed to cool. By operating in this way very accurate
results are obtained, and with ordinary care, a difference of more than
per cent. should not occur between two assays of the same ore.
In estimating the amount of tin present in pyrites, or in any other
very sulphurous or arsenical material, it would be inconvenient to operate
on a quantity exceeding 400 grains. The amount of tin oxide obtained by
treating such a quantity with nitro-hydrochloric acid, and subsequently
with hydrofluoric acid, will, in many cases, not exceed a few grains, and
a very small crucible must consequently be employed for its reduction
by cyanide of potassium; this crucible may either be inclosed in a larger
one and heated in the assay furnace, or be placed naked in the muffle.
On breaking the crucible after complete fusion, the reduced tin will be
found to have assumed the form of a button of almost silvery whiteness
covered by a layer of glassy flux. In order to collect any traces of metal
occurring in the form of minute shot, the flux must be dissolved in hot
water, and any metallic globules which may be found weighed with the
principal button.
ROASTING TIN ORES.
Tin ores, after the most complete concentration which can be effected
by washing only, are usually contaminated with variable quantities of
arsenical and ordinary pyrites.
ROASTING IN REVERBERATORY FURNACES.-For the removal of these the
ores are taken to the burning-house, where the sulphides and arsenides
TIN.
447
are decomposed by roasting in reverberatory furnaces. These are from
12 to 15 feet in length, and from 7 to 9 in width; the hearth is hori-
zontal; and the arch, which is about 2 feet in height in the neigh-
bourhood of the fire-bridge, sinks gradually towards the chimney. This
arrangement is provided with but one opening, closed by an iron door,
placed at the extremity furthest removed from the grate, and imme-
diately under a brick hood, by which the sulphurous and arsenical fumes
are directly carried off into the chimney, without annoyance or injury
to the workmen.
In connection with the flues of these furnaces are condensing chambers,
in which the arsenious oxide is deposited in a crystalline form. This is
subsequently purified by a second sublimation, in order to convert it into
the white arsenic of commerce.
From 6 to 10 cwts. of ore constitute a charge for one of these
furnaces, and this requires from twelve to eighteen hours, according
to the amount of pyrites present, before it is sufficiently roasted. The
charging of the furnace is effected by a small hopper in the centre of
the brick arch; and as soon as the proper quantity of ore has been intro-
duced it is regularly spread over the surface of the bottom. At the
commencement of the operation the heat is very gradually raised until it
reaches dull redness, at which temperature it is afterwards kept during
several successive hours. At intervals during the process of calcination
the mineral is stirred with an iron rake, so as to expose new surfaces.
When the ore has been sufficiently roasted, which is indicated by its
ceasing to evolve white fumes, an iron plate fitted into the floor of the
furnace is removed, and the charge, while still red-hot, is raked through
the aperture, and falls into an arched chamber beneath, where it is
allowed to cool. The calcined ore is now again subjected to the process
of washing; and the impurities, which have been decomposed and chiefly
transformed into ferric oxide, are, from their reduced specific gravity,
readily removed. When the ore is contaminated with copper pyrites,
it is, after being carefully roasted, allowed to remain for some time ex-
posed to the atmosphere previously to being again washed, as a portion of
the sulphide of copper is thus oxidised and converted into sulphate, which,
being soluble in water, is readily removed. If tin ores contain much
copper, it is usual to treat them, after their removal from the burning-
house, with dilute sulphuric acid, by which copper oxide is readily dis-
solved, while the oxide of tin remains unaffected. After this treatment
with sulphuric acid, the ore is washed in pure water, and under the name
of black tin, is ready to be transferred to the smelter.
The old reverberatory furnace has to a great extent been superseded
by Brunton's calciner, with a rotative hearth, in which manual labour for
turning the ore is entirely dispensed with.
OXLAND AND HOCKING'S CALCINER.*Brunton's rotative calciner has
now to some extent been replaced by the calciner of Messrs. Oxland and
Hocking, figs. 130, 131, which is especially adapted for the treatment of
rank ores, containing a considerable amount of arsenic and sulphur.
* We are indebted to Mr. Oxland for the drawings and description of this apparatus.
A
A
D
k
n
0
р
mr.
Fig. 130.- Oxland and Hocking's Calciner; plan, partly section.
I
C
У
h
k
Ն
n
C
m
M
1
Fig. 131-Oxland and Hocking's Calciner; elevation, partly section.
448


TIN.
449
This apparatus consists of a fire-box, A, from which the heat and
products of combustion pass through an iron tube, B, made of boiler-
plates, lined with fire-bricks placed on edge. The tube, which is from 30
to 40 feet long, is supported in an inclined position, but varying in in-
clination according to the character of the ore treated. It is supported
on three pairs of friction-wheels, C, and rotated by gearing, D, generally
driven by a turbine or by a water-wheel. At the lower end it passes into
the fire-chamber, and is so arranged as to deliver the ore passing through
it, by an opening, e, in the arch, into the ore-chamber or wrinkle, F. At
the upper end it communicates with the flues or condensing chambers, G.
The ore, brought from the floors in a wet condition, is dried by being
spread on the cast-iron plates, g, covering these chambers. It is fed into
the hopper, h, by a boy who also attends to the fire. The tube revolves
at the rate of from three to eight revolutions per minute; the ore is
raised by four projecting lines of bricks parallel with the axis, leaving
room for the continuous running-in of the dry ore from the hopper.
When the ore has been raised sufficiently high on one of these shelves it
falls off in thin streams through the hot gases passing up the tube. It
thus becomes sufficiently heated for the sulphur and arsenic to take fire,
and to burn with such energy that before the ore arrives half-way down
the cylinder the greater portion of the arsenic and much of the sulphur
is driven off. The heat evolved by the combustion of arsenic and sulphur
is thus rendered available for heating the upper portion of the tube. As
the partially-calcined ore passes onwards beyond this point, the remain-
ing arsenic and sulphur are not in sufficient quantity to produce the tem-
perature required for the completion of the calcination; hence the
provision of a small fire-place, H, for supplying the deficiency. Through-
out the whole of the tube, the lines of shelf perform the duty of passing
the ore in finely-divided streams through the heated gases, in such a way
that no particle can escape full exposure to the oxidising influences
required for perfect calcination. It is found that the arsenic burns
off first, and that its removal is completed some time before the last por-
tions of the sulphur are eliminated. The calcined ore, passing from the
lower end of the tube into the burnt-ore chamber, at a bright red-heat,
contains only traces of arsenic and but a small proportion of sulphur.
When required it is withdrawn from the chamber, F, through the door, f.
Heated air for the perfect combustion of the coal in the fire-place, and
for the oxidation of the sulphur and arsenic, is supplied through the
channel, i, at the back of the arch.
By carefully controlling this supply of air and maintaining a small
consumption of coal, economy of fuel is not only effected, but another
important result is obtained, namely, the passing of a minimum quantity
of air through the calciner. The arsenious anhydride produced is con-
sequently condensed more easily than by the use of the reverberatory
furnace or of Brunton's calciner, and perfect condensation is effected with
less costly condensing chambers.
The consumption of fuel is small, and the condition of the calcined
product is well suited for subsequent operations. By the rotation of the
2 G
450
ELEMENTS OF METALLURGY.
tube the crown, after being fully heated, is brought down under the ore,
becoming in its turn the bed; thus preventing the loss of heat necessarily
incurred in other furnaces from the crown only being exposed to heat,
while the bed is covered by the ore.
The condensation of the arsenious oxide is much promoted by
covering the condensing chambers with cast-iron plates, so that the damp
ores placed upon them to dry, may, by rapidly cooling them, cause a pro-
portionately rapid condensation. Until recently, condensing flues and
chambers were usually constructed with thick walls covered by stone
arches: but at Devon Great Consols and at East Pool Mines, Cornwall,
great advantage has been derived from building flues of thin brick-
work, and covering them with cast iron plates; the openings used for
removing the arsenic are in like manner closed by cast-iron plates.
Any fine ore carried off by the draught is deposited in the divisions k and
l of the condenser, and is removed from time to time by the first door m.
The arsenious oxide is deposited in the compartments n, o, p, &c., and
removed through other doors, while the sulphurous anhydride passes
on by the main flue to the chimney.
Large quantities of crude arsenious oxide are produced in the mines
of Devon and Cornwall. At New Great Consols, near Tavistock, nearly
200 tons of arsenious oxide are obtained per month in the production of
about 20 tons of marketable tin ore, and at East Pool from 50 to 60 tons
per month are produced in dressing about 25 to 30 tons of black tin.
This crude arsenic, of a grey colour, is sold to the arsenic manufacturers,
by whom it is refined before it is finally sent to the market.
The calcined product obtained consists principally of oxides of iron
and copper, containing sulphur and traces of arsenic, occasionally cobalt
and nickel, and in some localities a large proportion of wolfram, with
silica and alumina; oxide of tin is usually present in quantities varying
from 5 to 20 per cent.
The ore is removed from the receiving chamber and cooled by moisten-
ing with water; it is now known as burnt witts, and is taken to the
burning-house floors, where, by treatment in circular buddles, the tin is
concentrated by the removal of the oxides of iron and earthy matters, until
it contains from 50 to 60 per cent. of black tin. It is then again calcined
for the separation of the last traces of sulphur and arsenic, again passed
through the circular buddles, washed in kieves or tubs, and finally con-
centrated until it will produce by assay from 60 to 70 per cent. of "white-
metal," i.e. metallic tin.
SEPARATION OF TUNGSTEN; OXLAND'S PROCESS. If wolfram be
present in large quantities, the black tin, with which it is associated, is
much reduced in value. This mineral cannot be separated from tin ore
by any process of washing, since their specific gravity is nearly the same.
The calcining operations already described have no effect on this sub-
stance; but a process introduced by Mr. R. Oxland, first at Drake Walls,
and subsequently at East Pool, is said to effect a perfect separation.
This process consists in the conversion of wolfram (tungstate of iron
and manganese) into tungstate of sodium, which being readily soluble
TIN.
451
in water is thereby removed, leaving the oxides of iron and manganese
in a finely-divided state, and so light as to be readily separated from black
tin by washing. A reverberatory furnace is used, of which the peculiar
characteristic consists in the employment of a cast-iron bed. The charge
is introduced into this furnace through a hopper in the crown of the arch
and is spread upon the iron bed, and exposed to the flame passing from the
fire-place through the body of the furnace. The products of combustion
pass over the bridge down to a flue formed by a diagonal partition of
brickwork, which conducts it to the front of the furnace under the iron
bottom, and then, returning on the other side, to the chimney. Thus,
the whole of the bed is enveloped in the heated gases passing off from
the fire-place. The charge consists of from 10 to 11 cwts., according
to the quality of the ore, and is prepared by mixing soda-ash with
the dry ore in such proportions as to contain so much sodium as to be
slightly in excess of that necessary to combine with tungstic acid. If
the mixture be comparatively coarse-grained, a larger quantity can be
operated on at a time than when it is in the state of slimes. The charge
is carefully turned over, so as to bring the whole to a bright red-heat.
It is known to be working well when it frizzles, becomes apparently moist,
and is slightly adhesive to the tools used in stirring. If well worked, the
charge should be drawn in from two and a half to three hours, and is
then in better condition than if exposed to a stronger heat or for a longer
time. It is drawn in successive quantities, as soon as it is ready, through
an aperture in the hearth, into a vault beneath, whence it is taken as
wanted to the lixiviating vats, where, by treatment with water while still
hot, the tungstate of sodium is dissolved and run off into receivers. By
successive affusions of water the whole of the saline matters are obtained
as a clear liquid, the mass of the ore serving as a filter. The strong
solutions obtained are either set aside to crystallise, or are evaporated to
dryness in iron pans, affording crude tungstate of sodium, containing about
70 per cent. of the dry salt.
After lixiviation has been completed, the residue in the vats is conveyed
to the dressing-floors, where, by washing with water, the oxides of man-
ganese and iron, the residual constituents of wolfram, are carried off in
suspension, making the water thick and of a reddish-brown colour. This
process was for many years in operation at Drake Walls Mine, but the wolf-
ram having now disappeared from the lode there is no longer any necessity
for its use; at East Pool it is still employed. Salt-cake or crude sulphate
of sodium may be advantageously substituted for the more expensive
soda-ash, but as it requires skilful management it is not generally used.
Tungstate of sodium commands a limited sale for dyeing, for the manu-
facture of non-inflammable starch, for the production of bronze-powder,
and for some other purposes.
METALLURGY OF TIN.
Tin-smelting is in this country invariably conducted in reverberatory
furnaces; blast-furnaces were, however, formerly employed for the pur-
pose, and old smelting works, called Blowing-Houses, where this method
2 G 2
452
ELEMENTS OF METALLURGY.
of treatment was at one time followed, are still to be found in a dis-
mantled state in various parts of Cornwall and Devon.
TREATMENT OF TIN ORES IN THE REVERBERATORY FURNACE.—The
treatment of tin ores in the reverberatory furnace comprehends three
distinct operations, namely, smelting, refining, and re-smelting the slags and
residues; all are conducted in a furnace of which fig. 132 is a longitu-
dinal and fig. 133 a horizontal section, a little above the level of the
hearth. The form and dimensions of these furnaces vary in different
establishments, but the length of the hearth in that given as an illustra-
tion, which is in daily use at the present time, is 12 feet and its greatest
width 8 feet.
Smelting. The ore, which usually contains about 65 per cent. of tin,
is mixed with one-fifth of its weight of small anthracite, culm, and is

C
· · - - Pa - - - - -
T
E
Fig. 132.-Tin Furnace; longitudinal section.
slightly sprinkled with water, for the double purpose of rendering it more
easy to charge, and also to prevent any portion from being carried off
mechanically by the draught. The charge is thrown upon the bottom, A,
through the door B, and the heat of the furnace is maintained by the fire-
place, C, which is supplied with coal through the door, D; the charge is
subsequently spread by means of tools inserted through the door, E.
Each furnace is provided with a separate chimney, with which it is con-
nected by means of a diagonal flue, not shown in the drawings. The
temperature is gradually increased during the first five hours, at the ex-
piration of which time the charge is well worked up with a rabble; this
stirring is repeated at the end of five hours and three quarters, and in six
hours from the time of charging, the tapping usually takes place. Three
products are thus obtained-metal, "glass," and slag. The slag, which
is in reality a mixture of unconsumed culm with metallic tin and various
associated impurities, is raked through the door E, and is subsequently
stamped and washed. The tin and glass are run off through the tap-
hole, ƒ, into the float, G, which is lined with fire-clay, and has sometimes
a nearly rectangular form.
TIN.
453
The glass (vitreous slag), when sufficiently chilled, is removed from
the surface of the tin in the float, which is skimmed and laded into
moulds which give to it the form of slabs.
Refining. This operation comprehends two distinct operations, eliqua-
tion and poling or tossing. The slabs of metallic tin resulting from the
first operation are arranged on the hearth of a reverberatory furnace in
all respects similar to that employed for smelting the ore, and the
temperature is gradually raised. By this treatment, the more readily.
fusible tin is eliquated, and flowing over the surface of the hearth, and
escaping by the tap-hole, f, is collected in the cast-iron pot, H, which is

H
A
B
C
ດ
E
Fig. 133.-Tin Furnace; horizontal section.
set over a small independent fire-place. A less fusible product, con-
sisting chiefly of a mixture of iron, tin and arsenic, remains on the bed
of the furnace.
The charge of the kettle, H, consists of about 7 tons of eliquated tin,
which is kept hot by the fire beneath it. This is refined by forcing into it,
by means of a crutch, supported by an iron jib, a piece of green wood;
that of the apple-tree is generally preferred.
When tin of second quality, or, as it is called, "unrefined tin," is
being prepared, this boiling is continued during one hour only; the dross
which has risen to the surface is then skimmed off and thrown back into
the furnace, after which the tin is laded into ingots. Tin still continues
to flow into the kettle during the time the metal is being dipped out, and
cast into ingots. In making "refined tin” the bath of eliquated metal is
poled during several hours; the dross removed from the surface is nearly
identical with the hard-head remaining, after liquation, on the bottom of
the furnace.
454
ELEMENTS OF METALLURGY.
Instead of boiling the metal by the introduction of billets of green-
wood, the same effect is sometimes produced by tossing. When this
process is employed, the agitation is produced by the workmen con-
tinually lifting the melted metal in a ladle, and letting it fall from a
considerable height into the refining-pot. The scum thus brought to
the surface is carefully removed by skimming, and the metal finally
laded into moulds.
Re-smelting of the Slags and Residues.-The slags in the basin sepa-
rate into bottle-slag, so called on account of its resemblance to bottle-
glass, and a heavy black slag. The bottle-slag is thrown away, but the
heavy black variety is re-smelted in the furnace with lime and, occasion-
ally, a little fluor-spar. The crude metal thus obtained, together with
the slag, is run off, and the greater portion is now obtained as bottle-
slag; the heavy black residuary slag is again separated, and subsequently
stamped and washed for the extraction of the buttons (prillions) of metal
disseminated through it.
The comparatively infusible residues resulting from the process of
liquation are preserved, and, when a sufficient quantity has been collected
to form a charge, it is subjected to liquation at a more elevated tem-
perature than is necessary for ordinary tin; the crude tin thus obtained
is again returned to the furnace to be liquated, and the resulting metal
is either boiled or tossed.
A specimen of hard-head, from which as much as possible of the tin
had been removed by the processes described, afforded by analysis the
following results:-
Fe
Sn
62.50
17.25
•
As
S
19.02
•
1.26
100·03
Tin slags are essentially ferrous silicates, containing a little tin, and
often a considerable amount of tungsten.
The total consumption of fuel per ton of metallic tin produced varies
from 30 to 35 cwts.
SMELTING IN THE BLAST-FURNACE.-The furnaces formerly used in
this country were 6 feet in height from the bottom of the hearth to the
throat by which the ore and fuel were introduced. This was placed near
the opening of a flue, by which the dust and fumes carried away by the
blast were conducted into a chamber at the base of a high and somewhat
narrow chimney. This chamber was not over the mouth of the furnace,
but was placed behind it in such a way that the flue had a slightly-
inclined direction. The furnace, the masonry of which was of granite,
was lined with fire-bricks, and had an opening in the side opposite the
charging-hole, through which were inserted two nozzles supplied by a
wooden blowing machine set in motion by a water-wheel. The tuyers
were inserted at a short distance from the bottom, which was gradually
sloped down to a receiving basin of the usual form. A short distance
TIN.
455
from this, and at a lower level, was a second basin, somewhat larger than
the first; near this, and at a still lower level, was a third, in which was
conducted the process of refining; the fuel employed was charcoal. In
smelting with this furnace it was necessary to keep it constantly filled
with a proper mixture of ore and charcoal; and the reduced metal,
received in the first basin, was subsequently run off into the second, in
which it was allowed to stand for some time. The slags which collected
on the surface of the first basin were removed when sufficiently hardened,
and divided into two classes, for subsequent treatment. Those containing
metallic shot were stamped and washed, whilst those which retained tin
in a combined state were broken with a hammer and taken back to the
furnace. The tin forming the upper zone of the second basin was suf-
ficiently pure for refining, and was therefore laded into the third re-
ceptacle, where it was subjected to boiling by the introduction of blocks
of green wood, and afterwards laded into moulds. The heavier metal
which sunk to the bottom of the receiving-basin was subjected to liqua-
tion. The refining-pot was of cast-iron, and was kept warm by a small
fire placed beneath it.
In the Erzgebirge, a blast-furnace of about 10 feet in height is em-
ployed. The sides are formed of large pieces of granite, and the hearth
is a block of the same material, lined with. brasque, and having a con-
siderable fall towards the breast. The fused matter escaping from this
cavity, flows continuously into an exterior basin of granite lined with
brasque. This is furnished with a tapping-hole, by which its contents
may be withdrawn into a small iron vessel placed at a lower level. The
charcoal and ore are introduced by successive charges, and the blast is
furnished by a blowing machine. The slags produced float on the sur-
face of the metal collected in the basin, whence they are removed by an
iron hook, as soon as they have sufficiently consolidated. When the
reservoir has in this way become filled with metal, the tapping-hole is
opened and its contents are run into the iron vessel, where the process of
refining is conducted by boiling with green wood. The slags are divided
into two classes: the richer are, without any mechanical preparation,
fused with succeeding charges of ore; the poorer, after being stamped,
are washed for the purpose of separating the metallic granules which
they contain.
6
10
By this process every ton of tin smelted requires for its reduction
1 ton of charcoal, and the percentage loss of metal is much greater
than in the reverberatory furnace. From this it is evident that the
latter is, generally, the more economical method of treatment.
Grain-tin is prepared by heating blocks of that metal, and when the
temperature has been sufficiently elevated to render the mass brittle and
to cause the block to assume a crystalline structure, it is broken either
by a fall or by a blow from a heavy hammer.
ALLOYS OF TIN.
Tin is extensively employed for the manufacture of tin-plate, which
is thin sheet-iron, externally coated with that metal. Pewter is an alloy
456
ELEMENTS OF METALLURGY.
of tin and lead, in the proportion of four parts of the former to one of
the latter. Solders are also alloys of tin and lead in varying proportions;
fine solder is composed of two parts of tin and one of lead; tin solder,
used in the manufacture of articles of tin-plate, consists of a mixture of
equal proportions of the two metals; plumber's solder is made by mixing
together one part of tin with two of lead.
Large type are made of an alloy of lead and antimony only, but tin
enters somewhat largely into the composition of the mixture used for the
smaller descriptions; type of the size ordinarily employed for printing
newspapers contains from 1 to about 20 per cent. of tin. Tin alloyed
with antimony constitutes Britannia metal, the best varieties being com-
posed of tin with just sufficient antimony to give it hardness.
The addition of bismuth to alloys of tin and lead has the effect
of lowering their melting-point to an extraordinary degree; an alloy of
two parts of bismuth to one of lead and one of tin melts below 100° C.
Tin combines with copper in all proportions; ordinary gun-metal is
a mixture of 10 per cent. of tin with 90 of copper. Genuine bronze is a
compound of copper and tin only, but that used for statuary usually
contains a certain proportion both of lead and zinc. Bell-metal is a
bronze containing a very large proportion of tin. "Tom of Lincoln" is
composed of 22 per cent. of tin and 78 of copper; "Big Ben" of about
24 per cent. of tin and 76 of copper.
ANTIMONY.
Antimony is a brilliant metal, of a white colour, slightly inclining to
blue. It fuses at a temperature just below redness, and contracts but
little in becoming solid.
It is extremely brittle, and possesses a strongly-crystalline texture, so
that when broken it exhibits well-defined facets, indications of which may
be observed on the surface of the cooled ingot. It is slowly but dis-
tinctly volatile at a white heat in a closed vessel, but admits of being
distilled with tolerable facility in a current of hydrogen gas.
Antimony is not sensibly affected by exposure to air at ordinary tem-
peratures, but is rapidly oxidised when exposed to it in a state of fusion.
When fused and strongly-heated antimony is allowed to fall from a certain
height, combustion, accompanied by the production of a thick white
smoke, immediately takes place. This white vapour is chiefly antimonious
oxide, Sb2O3.
This metal does not occur in commerce in a state of purity, but is
contaminated with variable quantities of iron, lead, arsenic and sulphur.
To separate these, it may, after being reduced to a fine powder in an iron
mortar, be intimately mixed with one-tenth of its weight of nitre, and
subsequently fused in an earthen crucible.
By this treatment, the impurities, together with a portion of the
ANTIMONY.
457
antimony, become oxidised, and on breaking the vessel, after having allowed
it to cool, the antimony is obtained as a metallic button, the surface of
which will be covered with a fern-like crystallisation. The purification
of this metal may likewise be effected by fusing it, when in a finely-
divided state, with a small quantity of its oxide. Fineness of grain is
regarded as an indication of the purity of metallic antimony.
When in a state of fine division, antimony is attacked by hydro-
chloric acid with the evolution of hydrogen gas, but is not acted on by
dilute sulphuric acid. When attacked by hot concentrated sulphuric
acid, it becomes oxidised with evolution of sulphurous anhydride. Nitric
acid attacks antimony; the degree of oxidation varying with the strength
of the acid. Aqua regia readily attacks antimony, and gives rise to the
formation of a trichloride, soluble in an excess of hydrochloric acid.
ANTIMONY ORES.
Antimony, although occasionally found in a native state, is usually
combined with sulphur, and is often associated with galena. It also
exists in combination with oxygen and arsenic. Native antimony crystal-
lises in forms derived from the rhombohedron, and is often associated
with small quantities of iron and silver.
SULPHIDE OF ANTIMONY; Antimoine sulfuré; Grauspiessglaserz. Or-
thorhombic. This substance, which is the only mineral sufficiently
abundant to be regarded, practically, as an ore of antimony, is of a lead-
or steel-grey colour, which is liable to tarnish on exposure.
The cleavage is parallel to the shorter diagonal, and the crystals are
commonly divergent, columnar, or fibrous. It also occurs in granular
amorphous masses. Its specific gravity varies from 4.50 to 4.62; its
streak has the colour of the mineral itself, and on being heated on char-
coal before the blowpipe, abundant white fumes and an odour of sulphur
are evolved.
This ore, which is commonly associated with iron, zinc, lead, silver,
quartz, and sulphate of barium, occurs in veins traversing granite, clay-
slate, &c. Its most celebrated localities were formerly Felsöbanya and
Schemnitz, in Hungary; Stolberg, in the Hartz; and Auvergne and
Dauphiny, in France. Mines of sulphide of antimony have also been
worked in Spain, Corsica, and in the county of Cornwall; of late years
the chief supply of antimonial ores has been obtained from Borneo.
The analysis of a specimen of this mineral from Arnsberg, West-
phalia, afforded Schnabel the following results:-
Sb
S
Fe
72.02
27.85
•13
100.00
It is consequently a sulphide of antimony, of which the composition
is represented by the formula Sb,S3.
Antimonious oxide, Sb2O3, occurs, though rarely, as a mineral
458
ELEMENTS OF METALLURGY.
(Valentinite), in shining white crystals belonging to the trimetric system.
It is found in veins at Przibram, in Bohemia; at Braünsdorf, in Saxony;
and at Malaczka, in Hungary. It occurs also in regular octahedra,
namely, as Senarmonite, in the province of Constantine, Algeria; it is
therefore dimorphous. Tetroxide of antimony, sometimes called anti-
monious acid, Sb2O4, is found native as Cervantite, or antimony ochre, at
Pereta, in Tuscany. Antimony also occurs as red antimony, antimony
blende, or kermesite, Sb.,O,+28b,S3; likewise as sulphide combined with
various other metallic sulphides, particularly with those of lead and
silver.
We have been unable to obtain any reliable statistics with regard to
the annual production of antimony, but the amount raised in this country
is exceedingly small. The imports of antimonial ores into the United
Kingdom, chiefly from Borneo, are said to be about 2,000 tons annually.
ASSAY OF ANTIMONY ORES.
From the ready fusibility of this metal its ores admit of reduction at
a moderate heat. For the purpose of assay, ores of antimony may be
divided into two classes: the first comprehends all compounds in which
the metal is either native or combined with oxygen, and in which little
or no sulphur is present; the second consists of native sulphide of
antimony, and all other antimonial compounds containing large quan-
tities of sulphur. .
Class 1. All substances belonging to this division are, when free from
earthy or siliceous impurities, readily reduced to the metallic state by
being moderately heated with finely-divided charcoal. Their assay may
be conducted in an earthen crucible lined with charcoal, without the
addition of any flux.
The volatility of this metal renders it necessary to avoid the appli-
cation of too strong a heat; and when the ore examined is contaminated
with siliceous impurities the addition of some suitable flux becomes neces-
sary. For this purpose the ore may be either intimately mixed with two
parts of black flux, or with one part of carbonate of sodium, and 0.25 of
finely-powdered charcoal. In this case, lining the crucible is unneces-
sary, and after it has remained in the fire until its contents are in a state
of tranquil fusion, it should, on being withdrawn, be gently tapped against
some hard body, to collect the fused metal into a compact button. When
the crucible has become cold it is broken, and the button extracted and
weighed. Care is, however, necessary in detaching it from adhering slag,
since, from its brittleness, it would otherwise be liable to become broken,
and a portion consequently lost.
This method is likewise applicable to substances which, although
principally composed of oxides of antimony, nevertheless contain small
quantities of sulphur; as the sulphide yields with black flux just one-
half of its antimony, only a very small portion can, in such cases, be
retained in the slags. When oxide of iron is present in the substance
treated, that metal is reduced at the same time as the antimony, and
ANTIMONY.
459
uniting with it forms an alloy, by which the result obtained is to some
extent vitiated.
Class 2. The assay of substances belonging to this class may either
be made by first roasting the sulphide, and subsequently fusing the
oxidised residue with black flux, or by directly fusing the crude mineral
with the addition of black flux and finely-divided metallic iron or with
iron scale. The roasting of sulphide of antimony is, from its fusibility
and the facility with which it is sublimed, an operation requiring much
care in its execution; it must consequently be conducted at a very low
heat, and be constantly kept stirred with a slight iron rod, until all
smell of sulphur ceases to be evolved. The residue is then fused with
three parts of black flux, and a button of antimony is obtained, as in the
treatment of oxidised minerals belonging to the first class.
The antimony contained in the sulphide of that metal is also readily
liberated by fusion with metallic iron in a state of fine division. The
sulphide of iron thus produced has, however, so very nearly the same
density as metallic antimony, that their separation can only be obtained
by keeping the contents of the crucible for a considerable time in a
state of fusion. When this precaution is taken, two distinct buttons are
obtained on breaking the crucible; the one, which is at the bottom, is of
a white colour, and crystallised in large plates, whilst the other is of a
bronze-yellow tint, and consists of sulphide of iron containing slight
traces of antimony. These are carefully detached from one another, and
the button of antimony weighed. The long-continued heat necessary to
produce this separation has, however, the effect of causing the loss of a
notable amount of antimony by sublimation, which is an inconvenience
that cannot be entirely obviated by the most careful manipulation.
In operating in this way, it is also of importance that only the
amount of iron necessary to combine with the sulphur present should
be added to the pounded sulphide, as any excess of that metal would
combine with antimony, giving rise to an antimonide, of which one portion
would contaminate the reduced metal, whilst another might be retained
in the slag.
For the reduction of pure sulphide of antimony, 42 per cent. of iron
in the form of filings is required; these should be free from rust, and in
the finest possible state of division, as when larger pieces are employed a
considerable amount of antimony is lost by volatilisation before they can
be fully acted upon by the sulphide. Cast-iron must not be employed
for the reduction of sulphide of antimony, as it is not only less readily
acted on by sulphur than is wrought-iron, but the slag produced adheres
so firmly to the reduced metal as to be difficult of removal.
If, instead of employing iron and sulphide of antimony alone, a certain
proportion of carbonate of sodium and charcoal be added to the contents.
of the crucible, similar results are obtained, and a slag is produced con-
taining sulphide of iron and sulphide of sodium.
A good mixture for this purpose consists of 100 parts of sulphide of
antimony, 42 of metallic iron, 45 of carbonate of sodium, and 5 of finely-
powdered charcoal. When thus treated in a lined crucible, and at a
460
ELEMENTS OF METALLURGY.
moderate temperature, pure sulphide of antimony affords from 65 to 67
per cent. of metal.
Instead of using metallic iron for this purpose, the oxide of that
metal, iron scale, or any ferruginous matter may be employed, provided
it be capable of affording, when heated with charcoal and an alkaline
flux, a large percentage of metallic iron. When iron scale is employed,
it should be added to the sulphide in the proportion of 45 parts of the
former to 100 of the latter; this, with the addition of 100 parts of car-
bonate of sodium, and 15 of charcoal, will, with careful firing, afford 67
per cent. of metallic antimony.
Mitchell states that the best method of assaying sulphide of antimony
is to mix it intimately with four parts of cyanide of potassium, and after-
wards to heat it gently in an earthen crucible. The heat required in
this case is so extremely low, that little if any of the metal is lost by
sublimation; while by all other processes, a notable quantity, often
amounting to 5 or 6 per cent., is driven off. It is consequently evident
that the assay of antimony must rather be considered as a commercial
approximation than as being rigorously exact; when pure sulphide is
operated on its examination will be of but little value, since every 100
parts of that mineral correspond to 72.8 of antimony.
METALLURGY OF ANTIMONY.
ELIQUATION OF THE SULPHIDE.-From the fusibility of sulphide of
antimony, its separation from the siliceous and earthy gangues with
which it is associated is readily effected by a simple liquation conducted
at a moderate heat. On the Continent this operation is carried on in
vertical retorts; but in this country a reverberatory furnace has some-
times been employed.
At Malbosc, in the department of the Ardèche, France, the separation
of sulphide of antimony from its associated gangues is effected by means
of an apparatus, of which fig. 134 represents a vertical section. For this
purpose the mineral is placed in large earthen retorts, R, of which four
are set in each furnace. An aperture is left at the bottom of each, which
corresponds with a similar opening in the tile, by which they are sup-
ported. Beneath these, in separate chambers, C, are the earthen pots, P,
in which is received the melted sulphide as it descends from the cylinders
above.
The fuel consumed is fir-wood, and the sulphide obtained is converted
into metallic antimony, by roasting in a reverberatory furnace, and sub-
sequent reduction by a mixture of 20 per cent. of pulverised charcoal,
previously saturated with a strong solution of carbonate of sodium.
REDUCTION TO THE METALLIC STATE. To obtain metallic antimony,
the sulphide is sometimes roasted in a reverberatory furnace until the
sulphur has been expelled, and a grey residue remains. This is after-
wards mixed with one-tenth its weight of crude tartar, and reduced in
large earthen crucibles. The metal obtained by this process is, with the
exception of a certain admixture of iron, tolerably pure, and is at once
ANTIMONY.
461
ready for the market. The English process for antimony-smelting is
conducted in large crucibles made of refractory clay, mixed with small
quantities of plumbago, which are heated in circular wind furnaces.
In order to obtain metallic antimony from its sulphide, by the English
process, three distinct operations are required, namely, Singling, Doubling,
and Melting for Star Metal.
The furnaces used in this process are 3 feet in depth and 14 inches
in diameter. The crucibles are 15 inches in depth, 103 inches wide at
top, and 9 inches at bottom, inside measure; the fuel used is coke.

NAWA
R
MANA
NAK
WANN
Fig. 134.-Liquation Furnace; vertical section.
Singling.-This consists in fusing 40 lbs. of raw ore with from 20 to
22 lbs. of the clippings of tin-plate, by which treatment two products,
sulphide of iron and impure metallic antimony, are obtained. In some
cases a small quantity of slag from the next operation is also used.
Each fusion requires about 13 hour, and at its termination the charge is
poured into a conical mould, and, when sufficiently cold, the antimony is
separated from the ferruginous matt by which it is covered.
Doubling. The impure metal from the first operation is subsequently
fused in a similar crucible with the addition of sulphate of sodium and a
small quantity of slag from the third process. The charge of each
crucible is 80 lbs. of crude antimony, 2 lbs. of salt-cake, and a small
quantity of slag from the star metal. This fusion occupies 1 hour and
20 minutes.
Melting for Star Metal.— About 60 lbs. of the metal obtained from the
doubling process (bowl metal) are broken into small fragments, to which
are added 2 lbs. of pearlash and 5 lbs. of the slags obtained during a
previous fusion for star or French metal. The fusion usually occupies
somewhat less than 1 hour, and when it is completed the metal is cast
into rectangular ingots, care being taken that each shall be completely
covered with slag. If this be not attended to the necessary crystal-
462
ELEMENTS OF METALLURGY.
line surface is not obtained. The ores operated on in this country
chiefly consist of the rich sulphides of antimony from Borneo.
In works where antimonial ores are smelted by means of crude tartar,
the scoria which cover the surface of the metal are not thrown away, as
they retain a certain proportion of antimony in combination, from which
a secondary product, constituting a coarse kind of kermes mineral, is ob-
tained. These slags contain sulphide of potassium and antimonious
oxide, and, on being treated with water, undergo a decomposition by
which kermes is precipitated: this, under the name of "kermes by the
dry way," is sold as a veterinary medicine.
The brittleness of this metal prevents its being extensively employed
in a pure state, but its alloys are much used. The most important of
these is type metal. Antimony, in the form of a soluble tartrate of anti-
mony and potassium, is the tartar emetic of the apothecary; and antimony,
with a mixture of lead, forms the alloy on which music is engraved. A
similar mixture is much used in alkali works for pumps and taps, for
raising and drawing off sulphuric acid.
*
ARSENIC.
Arsenic is a brittle metal, of a steel-grey colour, and possessing a
strong lustre. When heated to 180° C., it sublimes without first entering
into fusion, and at the same time emits an odour resembling that of
garlic. In close vessels it may be sublimed without change; but, if air
be admitted, it is rapidly converted into a white oxide. When exposed
to air and moisture, it usually acquires, on its surface, a dark film,
which is only superficial; but it has been observed that some specimens
may be kept in open vessels for several years without losing their
lustre, whilst others are in a short time oxidised throughout their
whole substance, and fall into powder. This difference has been accounted
for by supposing arsenic to exist in two allotrophic conditions, namely,
as As and as As2. The first of these, which is deposited in the hotter
parts of the receivers in which it is collected, is of a whiter colour than
the other, and is highly crystalline; the second is found in the cooler
portions of the receivers, is amorphous, darker in colour, and is more
readily oxidised.
Arsenic is combustible, and burns with a bluish white flame, and the
formation of arsenious oxide As03. This oxide, which is generally
known by the name of “white arsenic," is the most common preparation
of this metal. It is obtained by roasting, in a reverberatory or other
furnace, ores containing arsenic. The white arsenic of commerce is pro-
cured during the treatment of arsenical ores of tin, arsenical ores of
cobalt, and ores of copper.
ASSAY OF ARSENICAL ORES.-Digest the finely-pulverised ore in strong
nitric acid until all action, on the addition of fresh acid, is at an end.
ARSENIC.
463
Evaporate nearly to dryness, to expel excess of nitric acid, dilute mode-
rately with water, and filter. The filtrate will contain the arsenic in the
form of arsenic acid, probably with sulphuric acid, resulting from the
oxidation of sulphur; solution of nitrate of lead is added, and a mixture
of arseniate and sulphate of lead will be thrown down. The liquid is
removed by decantation, and the precipitate digested with weak nitric
acid by which the arseniate of lead is dissolved, while the sulphate of
lead remains. This is separated by filtration, and the filtrate neutralised
with sodium hydrate, which throws down the arseniate of lead; this
must be collected, dried, and weighed. Every 100 parts of this precipi-
tate corresponds with 22.2 of metallic arsenic, or 29 parts of arsenious
oxide. The above process, which is comparatively expeditious, is recom-
mended by Mitchell in his 'Manual of Assaying,' but we have not had
occasion to test the accuracy of the results obtained. Arsenic may be
estimated with considerable accuracy as a magnesium arseniate; but in
the presence of iron and various other bodies, the operation becomes a
• process of quantitative analysis, for which some text-book on that subject
should be consulted.
MANUFACTURE OF WHITE ARSENIC.-None of the makers of white
arsenic in Devon or Cornwall, excepting the Great Devon Consols Com-
pany, manufacture it directly from raw ore; the grey flue-deposit of
the tin mines is generally employed. At Devon Consols raw ore is
roasted in Oxland and Hocking's calciner, and much of the arsenic pro-
duced is, without further preparation, sufficiently pure for the market.
When any of it is found to be a little grey it is re-sublimed.
A common reverberatory furnace is used for the re-sublimation of
crude arsenic, but, to prevent discolouration by smoke, either coke or an-
thracite is used as fuel. A large proportion of the sublimed white arsenic
is deposited in an amorphous state, but some of it is found in the form of
beautiful octahedral crystals. The whole is ground between French burr-
stones, and packed in casks for the market. All the white arsenic pro-
duced in this country comes from Devon and Cornwall. Devon Consols
collects 200 tons of white arsenic monthly; New Great Consols about 200
tons, and East Pool from 50 to 60 tons of grey arsenic.
Freshly-prepared arsenious oxide is perfectly colourless and trans-
parent, but becomes opaque by exposure. It is largely employed by
glass-makers, and in the manufacture of emerald green. The production
of arsenious oxide in this country in 1872 was 5,171 tons, of the total
value of £17,964.
PREPARATION OF METALLIC ARSENIC.-Arsenious oxide when heated
with carbonaceous matter becomes reduced to the metallic state. Metallic
arsenic is prepared either by the reduction of arsenious oxide, or by the
direct decomposition of arsenical pyrites at a high temperature in retorts,
usually arranged in a gallery.
At Altenberg, in Saxony, a mixture of 1 cwt. of arsenious oxide with
a cubic foot of powdered charcoal, is submitted to reduction and sublima-
tion in iron pots. A charge so constituted necessitates the consumption
of eight cubic feet of large coal and three and a half cubic feet of slack.
464
ELEMENTS OF METALLURGY.
At Reichenstein, in Silesia, the mixed Schlich operated on contains on
an average 23 per cent. of arsenic. The furnaces employed for working
these ores have each twenty-six glazed earthen tubes or retorts, varying
in length from 26 to 28 inches, and each 5 inches in diameter; they are
provided with receivers resting upon supports of masonry. Of these
twenty-six retorts, thirteen are placed on either side of the furnace, seven
in the lower row and six in the intermediate spaces above. The chamber
inclosing the receivers is provided with an iron door, which is kept shut
till the close of the operation; the arsenical fumes and products of com-
bustion escape through apertures in the arch, which is covered by a
conical chimney, like that placed over a cementation furnace. This fur-
nace is charged with 5 cwts. of schlich, which in the course of ten hours
yields 100 lbs. of arsenic, of which 90 lbs. are sold in the light-coloured
crystalline state, and the remainder as dark-grey arsenic.
Arsenic is used in small quantities in the preparation of various
alloys, and particularly in the manufacture of shot. When a small
quantity of this metal is mixed with lead, it is found not only to impart
to it a certain degree of hardness, which is advantageous, but it likewise
gives to it a tendency to form into regular globules, which facilitates the
manufacture.
ZINC.
Although the ores of zinc have probably been employed from remote
antiquity for the purpose of converting copper into brass, the metal itself
does not appear to have been known in Europe prior to the commence-
ment of the sixteenth century; as we find it first distinctly mentioned by
Paracelsus, who died in the year 1541. It is, however, stated by Beck-
mann and others to have been first described, under the name of “ marcha-
sita aurea," in the thirteenth century by Albert of Bollstädt, commonly
known as Albertus Magnus. Its colour is bluish-white, and when re-
cently broken it presents a brilliant crystalline surface. At ordinary
temperatures zinc is a brittle metal, but when heated to between 120° and
150° C. it becomes both ductile and malleable. When the heat is in-
creased to about 210° it is again brittle, and may at this temperature be
readily pulverised in an iron mortar. Zinc fuses at about 412° C., and
when slowly cooled exhibits a highly lamellar and crystalline texture.
The zinc of commerce is not chemically pure, but is invariably contami-
nated with the presence of various other metals, such as lead, cadmium,
iron and copper. It may be obtained in a state nearly approaching to
purity by the following process:-A fragment of the purest commercial
zinc is dissolved in dilute sulphuric acid, and in the solution is placed a
slip of the same metal, which is allowed to remain for some hours. The
liquid is now filtered, carbonate of potassium added, and the precipitate,
after being well washed, heated with powdered charcoal in an earthen
retort. The zinc, which is volatile at a white beat, is thus distilled over
ZINC.
465
into a vessel of water placed beneath for its reception; care must be
taken that the neck of the retort be short and wide, as it will other-
wise be liable to become choked by an accumulation of the condensed
metal.
When a brilliant surface of clean and polished zinc is exposed to dry
air, it remains unchanged at common temperatures; in a damp atmosphere,
on the contrary, it is speedily tarnished and soon acquires a grey colour
from the formation of a superficial coating of oxide. When heated in
contact with air at a temperature above that of its point of fusion,
it takes fire, and burns with an extremely vivid white flame. The bril-
liancy of this flame is caused by the combustion of metallic zinc, which
gives rise to the formation of zinc oxide, the flores zinci, nil album, or lana
philosophica, of the early chemists, a body which may, practically, be con-
sidered as fixed at all temperatures; this becoming white-hot communi-
cates to the flame its peculiar intensity of colour. Oxide of zinc obtained
by this means is largely employed, when ground with oil, as a pigment, in
lieu of white lead; from its perfect whiteness, as well as from the cir-
cumstance of its not becoming blackened by sulphuretted hydrogen, it is
for many purposes to be preferred to the different preparations of the
former metal.
Zinc is soluble in hydrochloric and in dilute sulphuric acid, with evolu-
tion of hydrogen gas; the action of these acids is more energetic on ordi-
nary commercial zinc than on that which is chemically pure. This metal
decomposes water with the formation of zinc oxide and the evolution of
hydrogen; when zinc is in a state of fine division this reaction commences
at a temperature slightly exceeding 100° C. Zinc is also soluble, with
liberation of hydrogen, in boiling solutions of potash or soda.
If, at the same time that the zinc is inserted in the alkaline solution,
a slip of iron be placed in contact with it in the same liquid, the decom-
position of water may be effected at ordinary temperatures; in this case
the zinc alone is attacked, the iron merely serving as the negative
element of a voltaic couple, by the action of which the decomposition is
much facilitated.
ZINC ORES.
Zinc usually occurs in combination with either sulphur, oxygen, car-
bonic acid, sulphuric acid, or silica, and is also occasionally found asso-
ciated with alumina, as in a variety of the species spinel. Before the
blowpipe the ores of zinc are almost completely infusible, but when
strongly heated on a charcoal support, give off, with greater or less facility,
fumes of zinc, which becoming oxidised are deep yellow when hot, and are
deposited on the cooler parts of the charcoal as a white incrustation.
The zinc of commerce is chiefly obtained from the natural carbonates
and silicates of this metal, and from the native sulphide, or blende. The
ores of zinc occur either in veins traversing the older rocks, or in floors
and branches in more recent formations. The first mode of occurrence
is perhaps the most frequent, but the more recent deposits are generally
most productive.
2 H
466
ELEMENTS OF METALLURGY.
NATIVE ZINC.-A specimen is stated to have been found, near Mel-
bourne, in a cavity in basalt; but the occurrence of this metal in the
native state requires confirmation.
RED OXIDE OF ZINC; Zincite; Zinc oxydé ferrifère; Zinkoxyd. Hex-
agonal.-Red oxide of zinc, although rarely occurring in the crystalline
form, has sometimes been met with in crystals belonging to the hexagonal
system. It is found at Mine Hill and at Stirling Hill in New Jersey,
where it is associated with franklinite and calcite.
According to an analysis by Whitney, this mineral is composed of—
ZnO
Mn2O3
96.19
3.70
·
99.89
Its specific gravity varies from 5-4 to 5.5; lustre adamantine; affords
when scratched an orange-yellow streak; colour red, of various hues,
sometimes inclining to yellow. It possesses two distinct cleavages at an
angle of 120°; is brittle, and presents a conchoidal fracture.
Alone, before the blowpipe, this mineral is infusible, but with the
addition of borax a yellow transparent glass is obtained. Its surface
becomes dull, and ultimately white, by exposure.
A specimen of this mineral, of extreme purity, and weighing 16,400 lbs.,
was forwarded to the Great Exhibition of 1851.
SULPHIDE OF ZINO; Zinc sulfuré; Blende. Isometric.-This mineral
occurs either massive, or in dodecahedra, octahedra, and other allied
forms. It admits of six distinct cleavages parallel to the faces of the
dodecahedron; streak white to reddish-brown. Colour, resin-yellow to
dark-brown or black; specimens having a green or a red tint are occa-
sionally met with. Lustre waxy or resinous, and when recently broken
a brilliant and frequently submetallic surface is obtained. Specific gravity
4.0 to 4.1. Some specimens become electric by friction. This ore, par-
ticularly when of a dark colour, frequently contains sulphide of iron, and
the red variety is sometimes associated with from 1 to 2 per cent. of
sulphide of cadmium. When heated alone, or with the addition of borax,
before the blowpipe, it is infusible; when a charcoal support is employed,
it yields metallic fumes, resulting in a deposit of oxide of zinc.
Blende occurs in rocks of all ages, and is generally associated with the
ores of lead, as also, though less frequently, with those of iron, copper,
tin, and silver. The blende found in this country is, from the amount of
iron sulphide it contains, usually of a dark colour, and is hence called Black
Jack by English miners. This sulphide is found abundantly in Corn-
wall, Cumberland, and Derbyshire, as well as in Transylvania, Hungary,
the Hartz and elsewhere.
A transparent variety of a bright-yellow colour accompanies bourno-
nite and fahlerz at Kapnick in Transylvania; still more beautiful speci-
mens of an olive-green tint are procured from Schemnitz in Hungary;
transparent red blende occurs in Spain; whilst Sweden, Bohemia and
Saxony are famous for the brilliant brown and black crystals they afford.
ZINC.
467
The zinc and sulphur of which this mineral is composed are combined
in the proportion of 1:1, and its composition will consequently be
expressed by the formula ZnS.
Two analyses of this substance from different localities afforded
Arfwedson and Berthier, the following results :-
Sulphide of Zinc, Lamellar, from
in Crystals;
Arfwedson.
England;
Berthier.
Zn
66.34
61.5
Fe
S
·00
4.0
33.66
33.0
100.00
98.5
From the difficulties formerly experienced in its metallurgical treat-
ment, this mineral was until a comparatively recent date but sparingly
employed as an ore of zinc, although after careful roasting, it readily
yields, by distillation with carbonaceous matter, a large proportion of the
metal which it contains.
CARBONATE OF ZINO; Calamine;* Zinc carbonaté; Zinkspath. Rhombo-
hedral. This substance is found in crystals, in concretionary and compact
masses, and in pseudomorphic forms. When pure, its colour is yellowish-
white; but when much contaminated with iron, it is frequently brown or
reddish-brown.
Lustre vitreous, inclining to pearly; streak, white; cleavage parallel
to the faces of the rhombohedron. Specific gravity from 4.30 to 4·45.
Smithson, who analysed two specimens of this mineral from Derbyshire,
found them to contain-

1.
2.
ZnO
65.20
64.64
CO₂ ·
34.80
35.36
100.00
100.00
These numbers correspond to the composition represented by the
formula ZnO,CO2, or ZnCO3. It is soluble in acids with evolution
of carbonic anhydride; when strongly heated before the blowpipe, this
gas is eliminated and oxide of zinc remains. This is one of the most
important ores of zinc, and, together with the silicates with which it is
almost invariably associated, is extensively employed for the produc-
tion of that metal. A compact, fibrous, semi-transparent variety of this
* The Calamine of some writers is the Smithsonite of others, and vice versâ; this
causes great confusion. Dana and most of the continental mineralogists call the
silicate Calamine and the carbonate Smithsonite; thus reversing our use of the
terms.
:
2 H 2
468
ELEMENTS OF METALLURGY.
mineral, of a pale-yellow colour, and disposed in concentric laminæ,
occurs at Alston Moor in Cumberland, where it is found associated with
blende and galena in a calcareous rock. It is likewise abundant in
Derbyshire, as also in the Island of Sardinia, in Siberia, Hungary,
Silesia, Carinthia, and near Aix-la-Chapelle, as well as in many parts of
the United States of America.
SILICATE OF ZINC; Smithsonite; Zinc oxydé silicifère; Galmei. Ortho-
rhombic. This mineral was for a long time confounded with car-
bonate of zinc, although they differ materially from each other both in
their chemical and physical properties. It occurs in mammillated,
botryoidal, and fibrous forms; also massive, granular, and crystallised.
Its usual colour is white, sometimes with a bluish or greenish shade,
also yellowish to brown. Streak white. Transparent or opaque; vitreous
lustre and uneven fracture. Specific gravity 3.3 to 3.6. Crystals of this
mineral, when heated, become electric, and the same effect is sometimes
produced by friction.
Specimens of this mineral, analysed by Hermann and Schnabel, gave
the following results:-
From Nertschinsk. From Santander.
Hermann.
Schnabel.
SiO2
25.96
23.74
ZuO
65.66
66.25
H₂O
8.38
8.34
Fe₂03.
1.08
100.00
99.41
These results indicate that this mineral may be represented by the
formula 2ZnO,SiO,Aq, or Zn,SiO+H₂O. This is a valuable ore, and
is commonly associated with the carbonate in veins containing ores of
iron and lead, together with sulphide of zinc, or zinc blende. Considerable
quantities occur at Bleiberg and Raibel in Carinthia, as also at Fribourg
in Brisgau, at Rezbanya in Hungary, Tarnowitz in Silesia, and near Aix-
la-Chapelle. Concentric botryoidal masses are also found in the Mendip
Hills, and at Wanlockhead in Dumfriesshire; pseudomorphous crystals
of the same substance occur in some parts of Derbyshire, and at Schem-
nitz in Hungary. Before the blowpipe it decrepitates, intumesces, and
loses its transparency. When reduced to fine powder, it is soluble in
hydrochloric and sulphuric acids on the application of a gentle heat, and,
on cooling, silica is deposited in a gelatinous state.
WILLEMITE; Anhydrous Silicate of Zinc. Rhombohedral. This
mineral occurs in minute crystals, massive, disseminated in grains, and
sometimes fibrous. Lustre, vitreo-resinous. Colour, whitish- or greenish-
yellow, to green or brown, when impure; streak uncoloured; trans-
parent to opaque; specific gravity, 3.89-4.18; brittle, with conchoidal
fracture.
ZINC.
469
The following analyses of specimens, from Stirling, are by Vanuxem
and Keating, who, together, first described this mineral:—

1.
21.
SiO2
25.44
25.00
Mn2O3
2.66
6.50
·
• 67
Fe₂03
ZnO
68.06
71.33
100.00
99.66
From these results the formula 2ZnO,SiO2, or Zn2SiO4, may be
deduced. Willemite occurs at Vieille Montagne, near Moresnet, in
Belgium; at Stolberg, near Aix-la-Chapelle; at Raibel, in Carinthia ;
and also in Servia and in compact quartz in Greenland. In New Jersey,
at Franklin and Stirling, it occurs in such quantities as to constitute an
important ore of zinc. A variety known as Troostite is also found in the
last-named localities, in crystals of as much as 6 inches in length by
1 inch in diameter, imbedded in franklinite or in calcite. The following
minerals, although interesting to mineralogists, are not found in sufficient
quantities to be of any metallurgical importance :-
SULPHATE OF ZINC; Goslarite; White vitriol; Zinc sulfaté; Goslarit.
Orthorhombic. Its formula may be taken as ZnO,SO,+7H₂O, or ZnSO4
+7H20. It is a soluble salt of a white colour, and is usually associated
with blende, by the oxidation of which it is probably produced. It
occurs at Holywell in Wales, at Goslar in the Hartz, at Fahlun in Sweden,
and at Schemnitz in Hungary.
OXYSULPHIDE OF ZINC; Voltzite; Leberblende.-In implanted spheri-
cal globules; colour, dirty rose-red to yellow. Its composition may be
expressed by the formula 4ZnS,ZnO. Occurs at Rosières, near Pont-
gibaud in France; at the Elias Mine, near Joachimsthal in Bohemia;
and in Cornwall.
A hydrous phosphate and an anhydrous sulphate of zinc are also
stated to occur.
DISTRIBUTION OF ZINC ORES.
Of all the minerals containing zinc three only are of much importance
to the metallurgist; these are blende, calamine, and silicate of zinc.
These ores may be divided into two classes, according to their geological
position and mode of occurrence. First, those which occur in the older
formations in veins, generally associated with other metallic sulphides;
blende is the only important ore of this class. The second group, which
includes the most important ores, occurs chiefly in calcareous or dolo-
mitic rocks, often belonging to the Carboniferous system; the ores are
either intercalated with the strata, or occupy depressions in them. By
far the largest proportion of the zinc ore raised in Europe is obtained
મ
470
ELEMENTS OF METALLURGY.
from Germany, Belgium, Spain, and the Island of Sardinia; that pro-
duced by other countries being comparatively unimportant. The chief
deposits of Germany are situated in Upper Silesia, some also occurring in
the Rhenish provinces and in Westphalia. The most important Belgian
deposits are those of La Vieille Montagne, La Nouvelle Montagne, and
Corfalie. The production of zinc in Great Britain has been decreasing
for some years; the Mineral Statistics for 1872 show that the quantity of
zinc ores raised in the United Kingdom during that year amounted to
only 18,542 tons, equivalent to 5,191 tons of metallic zine; of this
quantity 4,292 tons were raised in England, chiefly in the counties of
Cornwall, Devon, Cumberland, and Salop; 10,493 tons were obtained
from Wales, chiefly from Denbighshire, Cardiganshire, Flintshire, and
Montgomeryshire. The Isle of Man during the same year produced
3,123 tons; Ireland, 634, and Scotland none. The principal zinc-
works in this country are situated at Swansea, and in the counties
of Cumberland, Durham, Denbigh, and Flint. The ores treated include
blende, chiefly obtained from various lead mines, together with calamine
and silicate of zinc. The two latter are, for the most part, the pro-
duce of foreign mines, considerable quantities of carbonate being im-
ported from Spain and Sardinia, whilst silicates are, to a small
extent, derived from the United States of America, where, according to
Prof. B. Silliman,* the annual production of zinc and zinc oxide is as
follows:-
Zinc (Spelter), the annual make is about.
Distributed as follows:-
Lehigh Zinc-works, Bethlehem, Pennsylvania
New Jersey Zinc Company, Newark, New Jersey
Missouri (two works)
Other Western companies, say
Zinc Oxide, the annual make is about
Distributed as follows:-
Lehigh Zinc-works, Pennsylvania
Tons.
4,500
Tons.
1,500
750
1,250
1,000
4,500
8,500
•
2,500
·
3,000
•
•
1,000
·
1,500
500
8,500
Passaic
""
New Jersey
Mercer
"
""
New Jersey
Page & Co., St. Louis, Missouri
•
•
•
Total product of metallic zinc and zinc oxide in United States, 1873 13,000
•
The New Jersey Zinc Company and other companies in New Jersey
work the remarkable deposit or vein of Sussex County, so familiar to
mineralogists, and which furnishes red oxide of zinc (zincite), wille-
mite, and franklinite, with a little blende and carbonate of zinc. These
ores are treated in muffle furnaces with anthracite-dust, and the oxide
produced is wafted by blowers to chambers, where it is collected in huge
bags of muslin. The residuum of manganiferous-iron is reduced in
* Private communication.
ZINC.
471
blast-furnaces to spiegeleisen, and the fume from the condensers, attached
to the tunnel heads of the blast-furnaces, is reduced to spelter in Belgian
retorts. This spelter is of remarkable purity, and commands a higher
price than European zinc for casting gas-fittings and other imitations of
bronze.
The Lehigh Zinc-Works use ores raised by them from a large deposit
of smithsonite and blende in the paleozoic limestones of the Saucon
Valley, Pennsylvania. The vein is extremely wet, requiring an engine
of 110-inch cylinder and 10-feet stroke, with two 36-inch pumps, to
keep down the water. This company use the Wetherill furnace- low
arched furnace, with a force-blast through the charge of crushed ore and
dust of anthracite, condensing the product by the American system.
Their spelter is made chiefly from massive blende, of which the quantity
is large. The Belgian system is used, and a large part of the product is
rolled at the works into sheet-zinc. This spelter is also exceptionally
pure.
The Missouri and other Western ores are chiefly "dry bone" (cala-
mine). But little zinc oxide is made as yet in the Western States.
The zinc-works at Elizabethport, New Jersey, are confined to reviving
the zinc from "galvanised iron," and hence their product is not exclu-
sively American.
The Bartlett Company reduces a considerable (but not declared)
quantity of zinciferous galena, from the Erie Lead Mines, to pigs of
“ zinc-lead,” which are all consumed by the company itself in producing
a kind of mixed lead and zinc paint known as "Bartlett lead," and said
to be a good pigment.
The make of zinc in the United States, and especially of zinc oxide,
is increasing. There are deposits of zinc in Tennessee, Wisconsin, and
elsewhere, which are stated to be in the course of development.
It appears from statistics kindly furnished by Mr. H. H. Vivian, who
himself works large quantities of this material, that the total annual
production of zinc ore in Sardinia is about 49,200 tons, representing
16,690 tons of spelter; this ore is chiefly exported to Germany, Belgium,
and to the United Kingdom.
Through the courtesy of M. St. Paul de Sinçay, Director of the
works of the celebrated Vieille Montagne Company, we are enabled to
give the following particulars relative to the present annual zinc-produc-
tion of Europe:-
Belgium
Germany
*Austria
*Great Britain
France
Spain
Tons.
45,745
-I
55,744
3,000
15,000
4,400
4,400
128,289
This, with 4,500 tons of spelter produced annually in the United
States, will make a total of 132,789 tons.
* Amouuts marked thus
*
are approximations only.
472
ELEMENTS OF METALLURGY.
1
ASSAY OF ZINC ORES, &c.
The zinc-yielding materials which are likely to come under the notice
of the metallurgist may be classified as follows:-
1. Ores of zinc in which the metal exists in the form of oxide, uncom-
bined with silica.
2. Ores in which zinc is present as oxide, but wholly or in part com-
bined with silica.
3. Ores in which this metal exists wholly, or in part, combined with
sulphur.
4. Alloys of zinc.
The estimation of the amount of zinc contained in an ore of that
metal may be effected either by dry, or fire assay, or by humid assay.
The determination by the former method is a somewhat troublesome
and uncertain process, since zinc, being oxidisable and volatile at high
temperatures, cannot be obtained in the form of a metallic button, as in
the case of the more fixed metals.
FIRE ASSAY. BY DISTILLATION.-Ores of the first class, being readily
reducible, only require to be mixed with carbonaceous matter and heated
to whiteness in a porcelain retort. The metal is by this means volatilised
and condenses in the neck of the retort, which, during the operation,
must be kept open by the occasional insertion of an iron rod, as other-
wise an explosion might ensue. When the operation is completed, which
is usually the case in about an hour, the retort is removed from the
fire and laid on its side to cool; it must then be broken, and the zinc
detached from the neck as completely as possible, together with any
globules which may have condensed in the dome; this separation is more
readily effected if the neck has been previously coated with plumbago.
Any zinc which cannot be thus mechanically detached must be removed
by immersing the fragments of the retort in hot nitric acid; the solution
thus obtained is evaporated to dryness, the residue, of nitrate of zinc,
being converted into oxide by ignition. This is weighed, and four-fifths
of its weight added to that already obtained by weighing the zinc
obtained in the metallic state.
Ores of the second class are also reducible by carbon, but it is found.
advisable to add some base, such as lime, which combines with the silica
set free on the reduction of the zinc oxide, and forms a fusible slag.
Ores of the third class must, previously to treatment by the same
process as those of class 1, be subjected to careful roasting to free them
completely from sulphur. To prevent clotting, the temperature must be
kept low during the first portion of the process, but must be considerably
raised towards the end, in order to insure decomposition of any sulphates
which may have been formed.
BY DIFFERENCE.—An approximation to the quantity of zinc contained
in an ore may be arrived at by calcining a given weight of the ground
material, re-weighing, and then mixing with carbon and fixed fluxes of
known weight. This mixture is placed in a brasqued crucible, and
kept at the temperature of an iron assay for half an hour. The residue
ZINC.
473
is weighed, and its weight subtracted from that of the original mineral
and fluxes (a correction being sometimes made for the ash left by the
charcoal used to effect reduction). The difference is the weight of zinc
oxide, four-fifths of which will represent the amount of zinc originally in
the sample. If much iron be present, the residue left in the crucible
consists of a button of slag containing globules of cast-iron. This is first
weighed intact; and is then crushed in an iron mortar, and the grains of
iron removed with a magnet and weighed, the weight of the slag being
readily ascertained by difference. The weight of oxygen lost by the iron
during reduction is now, by calculation, added, and on subtracting the
sum of these numbers from the amount of flux and mineral employed, we
obtain the weight of oxide of zinc present in the ore.
By deducting, on the other hand, the weight of fixed flux used from
that of slag obtained, the weight of the earthy matter and unreducible
oxides associated with the ore may be arrived at with tolerable precision.
These results have been expressed by Berthier in the following
manner:
Let W be the weight of crude ore, and w that of the ore after calcina-
tion; t, the weight of the flux added; f, the weight of the cast-iron
found; s, the weight of slag; o, the weight of the oxygen combined with
the iron; and z, the weight of the oxide of zinc sought.
Then we have-
W crude ore = calcined do w
Fixed fluxes added
Give-
Iron f Total ƒ + s
Slag's
Oxygen 0
t
w + t
f+s+o
Zinc oxide z = w + t − ƒ — 8 — 0
Flux added t
Earthy matter S t
If the ore of zinc be contaminated by any lead-mineral, this method
of assay is quite unreliable. Galena, if present, is during calcination
converted into oxide and sulphate of lead, which, when heated with
carbon, are respectively reduced to metallic lead and sulphide of lead,
and the latter, if iron be present, is reduced to the metallic state, iron
sulphide being formed. If lead be present as carbonate it is changed by
calcination to oxide, which is subsequently reduced to the metallic state
by the action of carbon. A considerable loss in weight also occurs by
the volatilisation of some of the reduced lead.
The methods of determining zinc by fire-assay, although formerly in
general use, have been entirely superseded by the more expeditious and
more accurate methods, which will be described under the head of
Humid Assay; they are now rarely used excepting in the absence of
liquid reagents.
HUMID ASSAY. BY DIFFERENCE.-This process is based on the solu-
•
474
ELEMENTS OF METALLURGY.
bility of zinc oxide in solutions of ammonia and ammonium carbonate,
and is not suitable for ores in which the zinc is present as silicate, upon
which the above-named re-agents have but little effect. On this account
the process may be found useful in determining, approximately, the
amount of zinc oxide present in an ore in which that metal also exists as
silicate. The process is conducted as follows:-A weighed quantity of
the ore is calcined in a muffle or over a gas-flame until all volatile
matters have been expelled. The calcined ore is then re-weighed,
placed in a beaker or flask, and digested for about twenty minutes with a
solution of ammonia and ammonium carbonate.
The insoluble residue is collected on a filter, thoroughly washed with
hot ammoniacal water, dried, ignited and weighed. This weight deducted
from that of the calcined ore employed gives, by loss, the weight of zinc
oxide; from which, by subtracting one-fifth for oxygen, we get the weight
of zinc present in the ore operated upon.
If the ore be in a state of fine division and tolerably pure, the zinc
oxide may be almost completely extracted by ammonia and ammonium
carbonate. If, however, much earthy matter or oxide of iron, more espe-
cially the latter, be present, some of the zinc oxide is retained in the
insoluble residue. To obviate this the process may be modified as
follows:----After calcination, the ore is treated with hydrochloric and a
little nitric acid; to the solution obtained ammonia and ammonium car-
bonate are added in excess. The insoluble residue, together with the
precipitate of ferric hydrate, &c., is collected on a filter, washed with hot
ammoniacal water, dried, ignited and weighed. The difference between
this weight and that of the calcined ore used, indicates the quantity of
zinc oxide dissolved. By this treatment, not only the zinc existing as
oxide, but also that present as silicate, is removed; silicate of zinc being
decomposed by the acids employed.
VOLUMETRIC ASSAY.-The volumetric estimation of zinc by a standard
solution of sodium sulphide is one of the quickest and most reliable
methods at present known, and is therefore commonly used for com-
mercial purposes. When sodium sulphide in solution is added to an
ammoniacal solution of zinc, the latter metal is thrown down as a white
precipitate. By using a standard solution of sodium sulphide, the quan-
tity of zinc present may be calculated from the amount of the standard
solution required for its precipitation. Various methods have been em-
ployed to determine when the whole of the zinc has been precipitated, the
following being most usually resorted to. The first of these will generally
be found most convenient.
Flakes of freshly-precipitated ferric hydrate may be added to the
ammoniacal solution of zinc; these will retain their colour until all the
zinc has been precipitated, but will become blackened directly the sodium
sulphide is in excess. A drop of the zinc solution may be transferred,
by means of a glass rod, to a piece of lead-paper, when the presence of
excess of sodium sulphide will be indicated by the blackening of the
paper. Instead of this a drop of a solution of pure nickel sulphate, or
lead acetate, may be placed on a white porcelain slab and touched with a
ZINC.
475
glass rod, which has previously been dipped into the zinc solution. If
there be any excess of sodium sulphide, a black precipitate will be formed;
if, on the contrary, a portion of the zinc still remains in solution no change
will occur.
The preparation of the necessary reagents is conducted as follows :—
Ferric Chloride Solution.-3 grammes of iron-wire are dissolved in
hydrochloric and a little nitric acid, and the solution diluted to one litre.
5 c.c. of this solution will contain about 0·015 gramme of metallic iron.
Standard Solution of Sodium Sulphide. About 100 grammes of crys-
tallised sodium monosulphide are dissolved in about 2½ litres of distilled
water. The solution should be either filtered or decanted, in order to
free it from any black precipitate which, in small quantities, may be
formed; it is then ready for use. Standardisation is effected by dissolving
two or three pieces of zinc, each weighing from 0·5 to 0·75 of a gramme,
in hydrochloric and a small quantity of nitric acid; each solution is put
into a separate flask and diluted with water to about half a litre; ammonia
in excess is then added. Into each flask 5 c.c. of ferric chloride solution,
to which ammonia has been previously added, are introduced. Solution
of sodium sulphide is now allowed to run slowly from a graduated burette
into the cold ammoniacal solution, which must be kept in constant mo-
tion, until the zinc is completely precipitated and the ferric hydrate is
blackened. The number of divisions of the liquid which have been run
into each flask is then read off, and the mean of the results taken as the
standard; from the quantity of this solution required to precipitate a
known weight of zinc, the weight of that metal which each c.c. of sul-
phide solution will precipitate is readily found by calculation.
When sodium monosulphide is unobtainable about 300 grammes of
caustic soda may be dissolved in 1 litre of water, and the solution divided
into two equal portions. Through one of these, sulphuretted hydrogen is
passed to saturation; the other portion of the solution is then added, and
a preliminary trial of the strength of the mixture is made. It may then
be diluted to approximately the required strength, and standardised in
the usual manner.
Estimation of the Zinc contained in an Ore.-From 0·5 to 2 grammes
of the pulverised ore are heated with hydrochloric and a little nitric
acid, a large excess of acid being avoided. When the decomposition is
complete, the solution is somewhat diluted, and ammonia and ammonium
carbonate added in excess; it is then kept at a gentle heat for twenty or
thirty minutes, filtered into a half-litre flask, and the residue on the filter
well washed with hot ammoniacal water. To the ammoniacal solution
5 c.c. of the ferric chloride solution should be added. It is, however, pre-
ferable first to add ammonia to the 5 c.c. of ferric chloride solution, and
then to pour the liquid containing precipitated ferric hydrate into the am-
moniacal zinc solution; this mode of procedure prevents the coagulation
which would be liable to occur if the ferric chloride were directly added.
When the solution is cold the sodium sulphide solution is gradually run
in from a burette, until the zinc is completely precipitated and the ferric
chloride is slightly blackened. The number of divisions of the solution
476
ELEMENTS OF METALLURGY.
run in is now read off, and the weight of zinc which that quantity of the
standard solution is capable of precipitating is determined by calcula-
tion; the result being the quantity of zinc contained in the weight of
ore employed. During the addition of the sodium sulphide solution the
contents of the flask must be kept in continual agitation, otherwise the
zinc may be entirely precipitated, in one portion of the solution, and
the ferric hydrate blackened, before the precipitation of the whole of the
zinc has been effected; should this occur, the results obtained would be
entirely unreliable.
The examination of an alloy of zinc usually involves a, more or less
complete, chemical analysis.
Orės of zinc are frequently contaminated by the presence of other
metals, which would vitiate the assay unless previously removed.
Iron.—When this metal is present in small quantities only, the assay
may be made without filtration; it is, however, preferable to filter off the
ferric hydrate from the solution of zinc in ammonia and ammonium
carbonate, and to add to the filtrate a definite amount of the ferric chloride
solution. When the quantity of iron is considerable the ferric hydrate is
liable to retain zinc oxide; in this case, after allowing the ferric hydrate
to subside, the ammoniacal solution is decanted, and the former again
treated with ammonia and ammonium carbonate before filtration.
Manganese is sometimes present in red zinc oxide, &c. On the addi-
tion of ammonium carbonate, the manganese is not completely separated;
but its complete precipitation may be effected by the application of heat
and the addition of a few drops of bromine to the ammoniacal solution.
Copper, if present in small quantities, cominunicates a blue colour to
the solution; it may be removed by the addition of a few drops of sodium
sulphide solution to the ammoniacal zinc solution, whilst hot, until the
blue colour is discharged. The precipitated copper must be separated by
rapid filtration, and the zinc estimated in the filtrate, after cooling, in
the usual manner.
If copper be present in large quantity, the ore must be treated with
dilute sulphuric acid, and the copper thrown down by immersing in the
solution a clean plate of iron.
The precipitated copper is thrown on to a filter, and, if necessary, may
be washed, dried and weighed; to the solution a small quantity of nitric
acid is added, to peroxidise the iron, and after adding ammonia and
ammonium carbonate the assay is proceeded with in the usual manner.
Lead and Cadmium do not interfere with the accuracy of the results,
since the former remains partly in the insoluble residue, as sulphate, and
the remainder is precipitated on the addition of ammonium carbonate,
whilst cadmium is insoluble in the ammoniacal solution.
Silver is rarely present in sufficient quantity to interfere with the
assay, but if necessary it may be separated by filtering the solution of
zinc oxide in hydrochloric acid, previously to adding ammonia; the
silver will thus be left with the insoluble residue on the filter, in the
form of chloride.
ZINC.
477
METALLURGY OF ZINC.
When calamine is the ore operated on, it is usually first submitted
to calcination, for the purpose of rendering it less compact and more.
readily acted on by the carbon used for its reduction; at the same
time carbonic anhydride and water are driven off. The latter, if present
during reduction, would lower the temperature of the retort and be liable
to carry off with it, mechanically, particles of undecomposed zinc oxide.
The loss by calcination is from 25 to 30 per cent. In some cases the
larger pieces of ore are roasted in kilns, the calamine being interstratified
with layers of fuel. A modified form of kiln having an independent
fire-place is used in southern Spain. An apparatus of this description
will yield from 5 to 8 tons of calcined calamine in twenty-four hours,
whilst one having two grates will calcine as much as 10 tons, with a con-
sumption of from 8 to 9 per cent. of coal. This, though possessing
fewer disadvantages than ordinary kilns, is apt to yield a product of
which the degree of calcination is not uniform.
It is, however, more usual to conduct the calcination in reverberatory
furnaces, but the ore must not be in large fragments, which would make
the charge difficult to turn and to thoroughly calcine. The furnaces
employed are of the ordinary reverberatory description, and may be
heated either by an independent fire-place or by the waste gases from the
distilling apparatus; when the latter are employed, considerable economy
of fuel is the result, but the draught and, consequently, the temperature
of the retorts nearest to the calciner are liable to be decreased, especially
after a charge of cold, and sometimes damp, ore has been thrown into it.
At Moresnet, near Aix-la-Chapelle, furnaces fired directly and furnished
with two hearths calcine about 8 tons of calamine in twenty-four hours,
with a consumption of 27 cubic feet of coal.
The silicates of zinc are not always calcined previously to being
treated for the metal they contain, but are frequently mixed with yari-
able quantities of slaked lime, in addition to the coke-dust used for their
reduction.
»
The process of roasting blende, which has for its object the conver-
sion of zinc sulphide into zinc oxide with the elimination of sulphurous
anhydride, is by no means so easily accomplished as the calcination of cala-
mine; when blende is roasted zinc sulphate is formed, and this can only
be decomposed by a strong red-heat. Kilns are not suitable for the roast-
ing of blende, the product obtained retaining too much sulphur to admit of
the subsequent separation of the metal by distillation; they are, however,
occasionally employed for preliminary roastings having for their object
the rendering of the blende friable. Roasting can only be satisfactorily
accomplished after the blende has been reduced to a uniform powder
capable of passing through a sieve of about thirty-six holes to the square
inch. The reverberatory furnaces employed are often divided by steps,
4 inches in height, into three separate beds. Their total length is gene-
rally about 36 feet, and the internal width 10 feet. The fire-bridge is 9
inches in height, and the grate 24 inches in width by 7 feet 9 inches in
1
478
ELEMENTS OF METALLURGY.
length, whilst the rise of the crown above the bed is about 25 inches.
The bed most remote from the fire-bridge is charged every eight hours
with 12 cwts. of raw ore, and the mineral is successively removed from
the different beds until it is ultimately drawn from that nearest the grate.
In this way the total length of time necessary to effect the calcination is
twenty-four hours, whilst the weight of ore in process of elaboration at
one time is 36 cwts.; during this process the ore is frequently stirred by
means of iron paddles. In some few cases the ore is roasted in muffle-
furnaces, in order that the sulphurous anhydride which is evolved may be
collected and utilised.
The calcined or roasted ore is usually reduced to powder in edge-
mills, a coarser powder being used for the Silesian than for the Belgian
process. In many cases roasted blende requires no further crushing,
having been ground sufficiently fine previously to roasting. The pul-
verised calcined ore is mixed with a proper proportion either of finely-
divided non-caking coal or a mixture of this with small coke, by which,
when strongly heated in earthen retorts, its conversion into metallic zinc
is determined. The reduction of the oxide is effected at the expense
of the carbon present, carbonic oxide is evolved, and the metallic zinc
liberated is condensed in proper receivers adapted to the retorts in which
the operation is conducted. The arrangement of the apparatus in which
these reactions take place is varied in different localities in accordance
with the qualities of the mineral treated and the nature of the fuel
employed.
ENGLISH PROCESS.
The process formerly in general use in this country for the reduc-
tion of zinc ores is called distillation per descensum, and is conducted
in a furnace in many respects similar to those used in glass-houses for
the fusion and preparation of glass. These furnaces were either square
or round in transverse section, but that represented in fig. 135, and which
was usually preferred, has the latter form. The fire-place, F, is raised to
a convenient height above the surface of the ground, and is situated in the
centre of the arrangement. Around this are disposed the crucibles, c,
which are charged with the mixture of ore and fine coal from which the
zinc is distilled. The conical hood is pierced with openings, d, corre-
sponding to each crucible, through which the charge is introduced. The
bottom of each pot is furnished with an orifice, which is stopped by a
plug of wood; this, being converted into charcoal during the process, is
rendered sufficiently porous to admit of the passage of the volatilised
metal, but at the same time prevents the escape of the small coal or
calcined mineral. Each crucible is covered by a lid secured in its place
by a lute of fire-clay; the volatilised zinc is condensed in a sheet-iron
tube fitted beneath the opening in the bottom of each crucible; these
tubes are frequently made in two portions, the shorter being funnel-
shaped and so arranged that it can be raised or lowered at will in order
to keep the flange at its upper end in close contact with the bottom
ZINC.
479
of the crucible. The longer piece of tube is fitted loosely on to the
shorter, but is not placed in position until the zinc begins to distil off.
The condensed metal falls, in the form of drops, into a sheet-iron vessel, r,
placed for its reception. As the tubes are liable to become choked by
the condensed metal, it is necessary to clear them from time to time by
the insertion of a long iron rod, since they might otherwise become
entirely closed, and give rise to explosions. The zinc collected in this
operation in the form of drops and very fine powder, mixed with a certain
proportion of oxide, is afterwards melted in a large iron pot, set in
brickwork, and heated by a fire beneath. The dross which collects
on the surface of the fused metal is skimmed off and returned to the

d
Fig. 135.-English Zinc Furnace; vertical section.
crucibles in a succeeding operation, whilst the zinc itself is cast into
rectangular slabs or ingots, in which state it is sent into the market.
Five distillations may be made by a furnace of this kind in fourteen
days, in the course of which 5 tons of calcined ore are treated, yielding
about 40 cwts. of metal. About 25 tons of a mixture of binding and
free-burning coal are employed in the extraction of 1 ton of metallic
zinc. The duration of each crucible may be calculated at about four
months; when unfit for further service, they are removed through
apertures made in the surrounding brickwork. New pots, before being
set, are heated to redness in a reverberatory furnace, and carried to their
places by a large pair of iron tongs slung in chains, and supported by a
kind of overhead railway, similar to that used for replacing ordinary
glass-house pots. When set in their places, the brickwork is repaired
and a cover fitted in the usual way. At the close of each operation,
the crucibles are discharged by removing the condensing pipe from the
bottom, and withdrawing the residue through the aperture, after breaking
with a rake the piece of charcoal by which it was closed during the
480
ELEMENTS OF METALLURGY.
process of distillation. Any cracks which may occur in the pots during
the process are stopped with fire-clay.
The consumption of fuel in this apparatus is too large in proportion
to the metal obtained to enable it to compete with the Belgian and
Silesian furnaces, and we are not aware that the English furnace is any-
where in use at the present time for the treatment of zinc ores.
BELGIAN PROCESS.
The minerals employed for the preparation of zinc at the works of
the Vieille Montagne Company, in the neighbourhood of Aix-la-Chapelle,
are the silicates and carbonate of zinc, which are either compact and
earthy, or crystalline and nearly pure.
The gangue of the local ores is almost exclusively composed of clay,
which occurs in the form of masses, occupying cavities in the middle
of the calamine. In order that this may become softened and be readily
removed, the mineral is left exposed to the air for several months before
it is employed, by which treatment the greater proportion of the im-
purities becomes detached and is carried away by the rains. When very
impure, the mineral is sometimes washed under a stream of water, by
which the clay is removed. At these establishments the ore is divided
into two classes, the white ore and the red, distinguished both by their
appearance and by their chemical composition. The second of these
contains a larger amount of iron than the first, and is less rich in zinc,
but is nevertheless more readily treated than the whiter variety.
The white ore contains, on an average, 46 per cent. of oxide of zinc,
and the red only 33. The peroxide of iron contained in these two ores
amounts respectively to 5 and 18 per cent.
The mineral, after it has been washed, is calcined in conical kilns
similar to those employed for burning lime. These kilns are heated by
two lateral fire-places, covered by an arch and are provided with a flue,
which is divided at a short distance from the hearth, and enters the
kiln by about twenty different apertures, arranged at regular intervals.
Each opening is 4 inches square, and is lined with fire-bricks. At
the bottom of the furnace are two rectangular openings, destined for the
removal of the roasted ore after having passed through the higher and
more intensely heated parts of the arrangement. Two slabs of cast-iron,
inclined at an angle of 45°, divide the descending column of ore, and
facilitate its removal through the doors. The ore is charged by the
mouth of the kiln, and the smaller and larger fragments are so mixed
together as to allow a sufficient passage for the heated air and flame
entering through the openings. By this treatment the mineral loses the
whole of its water and the larger proportion of its carbonic anhydride.
The loss experienced is 25 per cent.; the fuel employed is ordinary pit
coal. This operation is continuous, and, in proportion as the roasted
ores are removed from the lower part of the cone, fresh mineral is intro-
duced by the upper opening, around which is a platform, where a supply
is kept constantly in readiness.
ZINC.
481
The roasted ore, after. its removal from the kiln, is ground under
heavy edge-runners, sifted through sieves, and sent to the furnace, in
which its reduction is to be effected.
Four distinct furnaces are united in one mass of brickwork; each of
these has the form of an arched recess, A, fig. 136, whose greatest height
is about 8 feet 8 inches above the surface of the floor. The back of
this opening is composed of a brick wall, and is slightly inclined in
the direction a b, fig. 137; the face, c, d, is, on the contrary, left quite
open for the introduction of the retorts. The fire-place, F, is placed


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Fig. 136.-Belgian Zinc Furnace; front eleva-
tion, partly in section.
Fig. 137.-Belgian Zinc Furnace; transverse
section.
beneath the surface of the ground, and the flame and heated air enter the
interior of the furnace through four apertures, e, fig. 136. In the arch
are placed two separate flues, G, which terminate in a central chimney, C,
divided into four compartments, and closed by dampers, D, corresponding
to each division. In each of these furnaces are placed forty-eight or more
cylindrical retorts, r, closed at one of their extremities, and made of re-
fractory clay. Each retort is 3 feet 8 inches in length, and about 8 inches
in diameter on the inside. In the open end of each is introduced a
conical adapter of clay, o, 11 inches in length, and on this, which forms
the mouth of the condenser, is fitted a cone of wrought-iron, p, of which
2 I
482
ELEMENTS OF METALLURGY.
the smaller end does not exceed an inch in diameter.* The earthen
retorts are usually placed in the furnace in eight rows raised one above
the other, and with this view the back wall a b, fig. 137, is furnished
with as many successive steps or projections, on which are supported
the closed ends of each row of tubes. On the open face of the furnace,
cd, are arranged eight plates of cast-iron, protected on the inner side
by rebated fire-tiles; these are destined for the support of the outer ends
of the retorts, to which are attached the adapters already described.
The height of the steps at the back of the furnace and that of the
iron plates in front of the opening, is so arranged as to give to the
retorts a slight inclination downwards, by which the distillation of the
metal and the removal of the residual matters are much facilitated, and
any corrosive silicates which may be present flow forward into the cooler
portion of the retort, where their action is less destructive than in the
hotter portion. During two months the firing of a furnace of this de-
scription is kept up without intermission; but at the expiration of that
time it is commonly found necessary to allow it to go out, in order to
repair its internal lining.
When a new furnace, or one which has been recently repaired, is first
lighted, the open face of the arched cavity, A, is closely built up with
bricks or fragments of broken retorts, after which the temperature is very
gradually raised until a white-heat has been attained. At the end of four
days the furnace is considered, under ordinary circumstances, to be suf-
ficiently heated; the temporary stopping is gradually removed, and the
refractory tubes, previously heated to redness in a special oven, are sepa-
rately introduced into their respective places. The interstices existing
between the different tubes are now closed with fire-clay, so as to make
good the front of the furnace, and the adapters are secured in their
places by a luting of the same material.
When the retorts are thus arranged in the furnace, a small charge only
of powdered ore and carbonaceous matter is at first introduced; the charges
are successively increased until, at the expiration of three or four days,
the apparatus has got into a regular way of working. The mineral
mixed with fine coal, or with a mixture of coke and coal, slightly
moistened with water, is brought to the furnace in wooden boxes. The
charge of each consists of 1,100 lbs. of calcined calamine and 550 lbs. of
coal or of non-caking coal-dust and coke, which has been previously
reduced to the state of powder. These substances are intimately mixed
before being introduced into the retorts. Before charging the retorts, the
residue remaining from the preceding operation must be carefully with-
drawn, and the inside of each, as well as of the adapters, be thoroughly
cleaned with an iron scraper. The charging, which usually commences
at six o'clock in the morning, begins with the lower tubes. The mixture
* On the Continent the sheet-iron cones are sometimes fitted to the adapter in a
reversed position, the larger end being outwards. This is closed, with the exception
of a small hole left in the centre, which permits the uncondensible gases to escape.
The clay adapter and iron cone may in some cases be advantageously replaced by
the Stolberg condenser, which consists of a clay tube expanded in the middle, so as
to form a sort of well in which the condensed zinc is collected.
ZINC.
483
of ore and coal is introduced by the aid of a semi-cylindrical shovel
attached to an iron rod as a handle; and as soon as the charging is
terminated, the fire is increased by raising the damper on the top of the
chimney, and by the addition of a fresh supply of fuel. After a short
time, a large quantity of carbonic oxide gas is evolved, which burns
with a blue flame at the openings of the adapters. At the expiration
of a further period the brilliancy of the combustion is considerably
increased, and the flame at the same time assumes a greenish-white tint
and gives off copious white fumes. The distillation of the metal has
now begun, and the conical tube of wrought-iron is placed in position.
At this point great care is requisite, in order so to conduct the firing
that the heat of the tubes in every part of the furnace may be, as nearly
as possible, equal; in spite of every precaution, however, those in the
higher rows are invariably less heated than the others, and are con-
sequently only charged with such ores as are most easy of reduction.
With this view, the retorts in the higher rows are charged with ore
containing much iron, whilst the lower series is supplied with whiter
and more refractory kinds. At the expiration of two hours, the work-
man removes the wrought-iron adapter with suitable tongs, and strikes
it sharply above a vessel in which is collected the oxide of zinc or
cadmie, which is detached, and reserved to be added to the mixture
of ore and carbonaceous matter in a future operation. When this
has been done, an assistant holds a large iron ladle, called a poêlon,
under the beak of each retort, at the same time that the foreman draws
out into it with an iron scraper the distilled zinc, which accumulates
in the liquid state at the shoulder formed by the junction of the retort
and the adapter. He also detaches with his rake the metal which has
condensed in the form of drops on the inside of the clay cone.
liquid zinc thus collected in the poêlon is covered by a scum, prin-
cipally consisting of oxide of zinc, which is removed before pouring the
metal into moulds, where it receives the form of flat rectangular ingots,
weighing from 25 lbs. to 35 lbs. each. When these operations are com-
pleted, the cone is replaced, and, after firing continuously for a second
period of two hours, another tapping is made in the same way, and a
further supply of liquid zinc obtained. These manipulations are re-
peated at intervals of two hours until five o'clock in the evening, when
the distillation has commonly terminated.
The
The tubes are now cleaned out, and entirely freed from any earthy
residue, so as to be ready to receive the second charge, to which has
been added the oxide of zinc formed during the progress of the preceding
operation; in this way two charges are worked off in twenty-four hours.
Calamine, when thus treated, yields about 30 per cent. of metal, and
retains about 10 per cent. in the residue subsequently removed from the
retorts. The zinc which is retained in the residue exists in the form of
silicate of that metal, which is not easily reducible by the action of
carbon alone.
212
484
ELEMENTS OF METALLURGY.
SILESIAN PROCESS.
In Upper Silesia, where considerable quantities of zinc are annually
produced, the apparatus employed differs very materially from that used
for the Belgian process. Its form will be understood by reference to
figs. 138, 139, and 140,* which represent the furnace employed at Llan-
samlet, near Swansea; a furnace of similar construction, but without
a high chimney, is commonly employed in Silesia.
The bed is flat, horizontal, and very nearly square; on each side of it
rise six similar and equal arched recesses, a, fig. 140. In front is a vertical
wall, b, in which is the fire-hole, c, fig. 139; at the back there is a
similar wall, d, behind which rises the stack, e; the furnace is covered

S
ዘክ
S
9
A
7.
e
ས ་
Fig. 138.-Silesian Zinc Furnace, Llansamlet; longitudinal section.
by an arch, ƒ, extending from side to side. Below the fire-place is an
arched passage, g, which serves for the admission of air to the fire, and
allows the stoker to get ready access to the grate. The vertical partition
walls, h, are made of single large fire-tiles. A series of rectangular
niches, i, (fig. 140) correspond with the lateral arched recesses in the
upper part of the furnace; these are covered by cast-iron plates, with the
exception of a small rectangular orifice, through which the iron adapters
of the retorts pass into the lower niches. Flues, l, fig. 138, pass along
the top of the furnace at each side, and, at the back, to the stack. These
are covered with flat, movable tiles, and communicate with the interior of
the furnace by the smaller flues, m. The course taken by the gaseous
current in passing to the stack is indicated by the arrows.
* Copied from Percy's 'Metallurgy,' by permission of the author.
ZINC.
485
Most commonly the furnace is built of common brick and lined with
fire-brick, the whole being held together by iron bracings. In each arched
recess are placed two retorts, A (fig. 139), the open spaces around their
mouths being filled in with pieces of brick, and well plastered over with
clay, to prevent the admission of air. During the working of a charge, each
recess is closed by a movable sheet-iron plate, in which is a small peep-
hole closed by a slide; the temperature is thus kept sufficiently high to
prevent the solidification of zinc in the nozzles. The condensed zinc is
conveyed by iron adapters into the lower recesses, i, where it is received
in iron trays. The retorts, which are each about 3 feet in length, are

a
h
h
C
A A
h
h
d
α
a
α
|_ GU
e
Fig. 139.-Silesian Zinc Furnace, Llansamlet; horizontal section.
made of a mixture of equal parts of best Stourbridge clay and powder of
old glass-pots, from which the vitreous matter has been removed pre-
viously to grinding. This mixture, suitably moistened with water, is
well tempered by working with a heavy wooden rammer; and after being
allowed to stand for a few days may readily be formed into retorts by
means of wooden moulds, capable of being divided longitudinally into
two pieces. The walls are made thicker towards the end furthest from
the nozzle, as will be seen by reference to fig. 142, A. Each retort,
after being air-dried during about three months, is strongly fired in an
oven, heated either by a separate grate or by the waste heat from a dis-
tilling furnace, and is then ready for use. The opening, n, figs. 141, 142,
serves for the introduction and drawing of charges; while the furnace is
in operation it is kept closed by a tile. On each side of the mouth of the
retort is a small projection, o, supporting a bridge-piece, on which rests
486
ELEMENTS OF METALLURGY.
the clay nozzle, p, which is provided with an opening, q, closed during
the working of the apparatus by a luted clay door, through which an
iron rod may be introduced for the purpose of clearing the nozzle from
condensed zinc; to the clay nozzle, p, a cast-iron pipe, r, is fitted, and
to this is attached a wrought-iron adapter, s.

i
a
A
7
9
a
i
Fig. 140.-Silesian Zinc Furnace, Llansamlet; transverse section.
A new furnace requires first to be air-dried for several days, and then
to be heated by a gentle fire; after some time the muffles are placed in
position, their sides being protected from the flame by temporary brick
walls surrounding them. All openings are now closed and the heat is
gradually raised, until, after seven or eight days, the furnace has become

D
*
72.
CA
P
n
A
Fig. 141.
Fig. 142.
sufficiently hot for charging. The protecting walls are now removed, and
the spaces between the muffles and the openings in the front are closed
by pieces of brick plastered with fire-clay. Three or four light charges
are worked off before the retorts are in a condition to receive full ones;
new retorts always absorb a considerable quantity of zinc.
ZINC.
487
The ore treated in these furnaces is either blende or calamine; in
either case it is previously calcined. When the former is used, it is in
the state of a fine powder, whilst the latter is introduced into the retorts
in pieces of the size of peas. The charge for a furnace containing
twenty-four retorts consists of about 1,500 lbs. of calcined ore, together
with 100-150 lbs. of skimmings or dross, and about 7 cwts. of a mixture
of coal and the fine cinders, which fall through the bars of the grate.
This mixture is not equally distributed amongst the retorts, those
nearest to the grate receiving a somewhat larger amount than those
further removed from it. In charging a furnace which is in regular
work, the clay door, n, beneath the nozzle is removed, as also is that
closing the orifice, q; the spent charge is then raked out, and the nozzles
freed from any condensed zinc. The retorts are re-charged through the
orifice, n, by means of a sheet-iron scoop; the cleaning and re-charging
usually occupies from three to four hours, two men being employed in
the operation. Before and during the time of charging, the fire is allowed
to burn somewhat low, but afterwards the heat is gradually raised to
incipient whiteness. When a furnace has been charged and all leaks
have been stopped, one man only is required to look after it and attend to
the firing during the night; a uniformly-high temperature must be kept
up, and the condensers require frequent attention, since, should they get
too hot, the zinc in them would take fire; when this occurs, the doors
closing the recess must be taken down, and not replaced until the tem-
perature has become sufficiently lowered. On the other hand, should
the condensers get too cold the zinc in them solidifies, and must be
removed by the introduction of a heated iron rod. A considerable loss of
zinc is sometimes occasioned by cracks in the retorts; these must be
immediately stopped by brushing them over with a mop previously
dipped into a mixture of fire-clay and water.
The ore treated at Llansamlet is an argentiferous blende, which is
very finely ground, and subjected to a careful roasting during twenty-
four hours; the silver is extracted by a special process, and from the
residue zinc is distilled. Various opinions are entertained with regard
to the number of retorts which should be placed in each furnace to obtain
the maximum of economy, many holding that furnaces containing twenty
retorts give better results than those with a greater number. There are,
however, some furnaces of this description employed at the Vieille Mon-
tagne Co.'s Works containing as many as forty retorts each.
The loss experienced during the calcination of the ore and the
reduction of the zinc to the metallic state is equal to about 9 per cent.
of the metal present; the greater portion of this is retained in the
residues. At the Llansamlet works about 11½ tons of coal are neces-
sary for the production of 1 ton of zinc, at a cost for labour of about
2s. 8d. per cwt. of the metal obtained; this will however vary, since a
given weight of zinc can be more cheaply extracted, both as regards fuel
and labour, from a rich ore than from a poor one.
A furnace may be kept in continuous operation from twelve to thirteen
488
ELEMENTS OF METALLURGY.
months, at the expiration of which time it will require to be let out for
the purpose of repairs. Every four years the furnace must be taken
down as far as the grate, and rebuilt.
The zinc obtained by this process requires to be re-melted before it is
ready for the market; it is fused in an iron pot set in brickwork over a
properly-constructed fire-place; this pot usually contains about 8 cwts.
of metal, which is melted down in from half to three-quarters of an
hour, the surface being covered with a mixture of oxide of zinc and
finely divided metallic zinc; this is skimmed off and added to the next
charge to be subjected to distillation. The zinc obtained is toler-
ably free from impurities, with the exception of lead, which may to a
considerable extent be separated by allowing the fused metal to cool
nearly to its solidifying point before being laded into moulds; the lead,
on account of its higher specific gravity, thus falls to the bottom, and
the greater portion of it will be found in the last ingot. The ingots
containing lead are put aside until a sufficient number have accumu-
lated, when they are re-melted and the heavier metal allowed to settle
as before.
In Silesia the crude metal is melted in clay vessels, in order that it
may not be contaminated by contact with iron.
It would be somewhat difficult to institute a comparison between the
various processes employed for the extraction of zinc. It is, however,
certain that the consumption of fuel is greater in the English furnace
than in either the Belgian or the Silesian furnaces. Under similar con-
ditions the produce of zinc in the Belgian and Silesian processes is about
equal; the amount of labour required is greatest with the Belgian, and
least with the English process. The former, moreover, requires more
skill, and the labour is more severe, whilst the quantity of fuel expended
is less than in either of the others.
Ores containing much fusible gangue are most advantageously treated
by the Belgian method, since the retorts are more frequently cleaned out;
and moreover, from their inclination forwards, the corrosive slag flows
into the cooler end, where it does comparatively little damage. This
advantage is somewhat counterbalanced by the fact that a Silesian
furnace can be worked, continuously, longer, without being taken down
for repairs, than is possible with the Belgian furnace.
A large proportion of the zinc annually produced is employed in the
form of thin sheets. For this purpose it is necessary again to melt the
ingots, obtained by the treatment of the ores, as above described. This
is effected in a reverberatory furnace with an elliptical hearth, having
a slight inclination towards one side. At the lowest point of the hearth,
which is made of refractory clay, is placed a hemispherical reservoir,
in which the fused metal is collected; the ingots to be re-melted are
introduced through one of the doors and piled near the fire-bridge on
the highest part of the hearth. The fused zinc is dipped out of this
reservoir by means of iron ladles, and is poured into moulds which give
to it the form of plates convenient for the purpose of rolling into sheets.
MERCURY.
489
These plates are subsequently re-heated in a second furnace built in the
same mass of brickwork as the first, and which is heated by the waste
gases escaping from it. Here they are elevated to a temperature not
much exceeding 100° C., and are then passed through the rolling mill, by
which they are reduced to the form of sheets of different degrees of
thickness.
MICHIGAN
University
GENERAL LIBRA

MERCURY.
Mercury, or quicksilver, differs from other metals in being liquid
at ordinary temperatures. It has a silver-white colour, with a strong
metallic lustre, and is not, if quite pure, tarnished by exposure, in the
cold, to a moist atmosphere. If, however, it contains traces of other
metals the amalgam is rapidly oxidised, and the surface of the bath
quickly becomes covered by a grey powder. This metal is solid at a
temperature of -40° C., and is then both ductile and malleable. In polar
latitudes the cold is sometimes so intense as to cause the congelation of
mercury; a similar result may be obtained by a freezing mixture composed
of ether and solid carbonic anhydride. The same effect is also produced by
a mixture of pounded ice and crystallised chloride of calcium. If a rather
large quantity of mercury be placed in a platinum dish, and gradually ex-
posed to a proper refrigerating mixture, distinct octahedral crystals are
obtained. The mercury in this case becomes congealed around the sides of
the vessel, and, on pouring out the portion which still retains its liquidity,
brilliant crystals, belonging to the cubic system, are found coating its
sides. Considerable contraction takes place at the moment of congela-
tion; for while its density at 0° is 13-596, that of frozen mercury is
14.4. Mercury is distinctly volatile at all temperatures above 19° C.
That mercury is volatile at common temperatures is readily shown by
suspending a sheet of gold leaf in the upper part of a bottle in the
bottom of which a little of this metal has been placed. On removing
this arrangement to a cool place, and allowing it to remain a few days
without being disturbed, that part of the gold which is nearest to the
surface of the mercury will be found to have become whitened by its
vapour, whilst that portion of the sheet which is in the highest part of
the bottle remains unaltered. From the feeble volatility of this metal
at ordinary temperatures, its vapour merely forms a thin stratum im-
mediately over the surface of the metallic bath. Mercury boils at
350° C.
The mercury of commerce, when it comes directly from the furnace, is
in most instances nearly pure, but is sometimes contaminated by holding
small quantities of other metals in solution. With a view to the separation
of these impurities mercury is frequently distilled from an iron retort,
and again condensed in a vessel containing cold water. For this purpose
one of the wrought-iron bottles in which quicksilver is imported may be
490
ELEMENTS OF METALLURGY.
conveniently employed. One of these, after being about half filled with
the metal, should have attached to it a piece of iron gas-pipe bent nearly
at right angles, and furnished at its open extremity with a covering
formed of several layers of linen or cotton cloth, of which the end is
made to plunge into a basin containing cold water. The open extremity
of the iron pipe, together with the piece of linen hose attached, is
moistened by a constant stream of cold water, which is made to flow upon
them through a small stop-cock, and the iron bottle is heated in a fur-
nace until vapour of mercury begins to be plentifully given off. The
ebullition of the metal is often attended with explosions, and care must
be taken to so regulate the heat as to prevent the projection of any part
of the charge through the iron tube into the receiver. By operating in
this way, the greater portion of the foreign metals will be retained in the
retort, whilst the mercury passes over in a purified state into the vessel
containing cold water. A certain portion of the impurities is, however,
by this process carried over into the receiver; and consequently, when a
nearly pure specimen is required, their separation should be effected
by some other means. The best method of doing this is to treat the
mercury to be purified with nitric acid diluted with about twice its
volume of distilled water. The whole is then heated to about 50° C.,
and mercurous nitrate will be rapidly formed. This nitrate reacts on
the foreign metals present, which are removed in solution in the form of
salts. Any oxide of mercury present is also dissolved by the nitric acid,
with formation of nitrate. The action is continued during twenty-four
hours, and the mixture occasionally agitated.
Lastly, the water is separated by decantation, and the nitrate
obtained in a crystalline form by concentrating the solution. The
metallic mercury, after being washed with distilled water, is dried first
with bibulous paper, and subsequently by exposure under a bell-glass to
the desiccating influence of caustic lime.
When mercury is merely soiled by a slight admixture of oxide, it is
readily removed by brisk agitation in a glass bottle with a small quan-
tity of strong sulphuric acid. By this treatment the metal is divided
into extremely small globules, which expose a large surface to the action
of the acid. At the expiration of from three to four days the acid may
be poured off, and the purified mercury washed and dried.
Mercury is not attacked by strong hydrochloric acid, even when its
action is aided by ebullition. Dilute sulphuric acid likewise fails to
dissolve it; but if concentrated acid be employed, it is, with the aid of
heat, rapidly converted into mercuric sulphate, and sulphurous anhydride
is evolved. Nitric acid attacks this metal with great energy, even in the
cold, and when moderately diluted with water; nitric oxide is plentifully
evolved.
Mercury combines with great readiness with certain other metals, such
as gold, silver, zinc, tin, lead and bismuth, and forms, when in suitable
proportions, solutions of those metals. These mercurial alloys are
called amalgams; this property of the metal is extensively applied in
MERCURY.
491
;
extracting gold and silver from their ores, as well as in gilding, plating,
and the manufacture of looking-glasses. Mercury is, besides, the basis of
many powerful and valuable medicines, and is, on account of its great
density, and the regularity of its expansion and contraction under the
influence of increased and diminished temperature, preferred to all other
liquids for filling the tubes of thermometers and barometers. This metal,
when united with tin and zinc, forms the best excitor which can be
applied to the rubbers of electrical machines. Mercurous nitrate is some-
times employed as a wash for rabbit and hare skins, and gives to the fur
the property of readily felting.
MERCURY ORES.
NATIVE QUICKSILVER; Mercure natif; Gediegen Quecksilber. Isometric.
-In liquid globules, disseminated through the gangue; occurs in most of
the mines producing the different mercurial ores. It is usually much dis-
seminated through the rock, but sometimes becomes so accumulated in
cavities as to admit of being collected.
CINNABAR; SULPHIDE OF MERCURY; Mercure sulfuré; Zinnober.
Rhombohedral. This substance crystallises in rhombohedral prisms, but
most commonly occurs in the amorphous state. Sulphide of mercury is,
properly speaking, the only ore of that metal, and is distinguished by its
red colour and bright scarlet streak. Sp. gr. 8.998. Its lustre is, when
amorphous, semi-metallic, but when crystallised, adamantine. It is sectile,
and in most instances nearly opaque.
Two specimens of this mineral, analysed by Klaproth, yielded the
following results:-
Hg
S
Fe₂03
Cu
Bituminous matter
Gangue
From Japan. From Idria.
84.50
81.80
14.75
13.75
0.20
0.02
3.30
1.20
99.25
100.27
The composition of this mineral is therefore expressed by the for-
mula HgS. Cinnabar mostly occurs in connection with talcose and argil-
laceous schists, or in some other stratified rock; it is not found in large
quantities in crystalline or igneous rocks, although small specimens have
sometimes been observed disseminated through granite. When the ores
of mercury are met with in stratified rocks they are usually found in the
form of veins or lodes; but when, as is sometimes the case, the matrix is
492
ELEMENTS OF METALLURGY.
sandstone, they are commonly disseminated in minute grains throughout
the mass.
NATIVE CALOMEL; Mercure chloruré; Quecksilber-Hornerz. Tetra-
gonal. Colour white; lustre adamantine. Sp. gr. 6·48. Occurs at
Moschellandsberg, in the Palatinate, coating the cavities of a ferruginous
gangue, associated with cinnabar; also at the quicksilver mines of Idria
in Carniola, at Almaden in Spain, &c. Chlorine, 15-10; mercury,
84.90=100. Formula, HgCl.
Coccinite.-Found sparingly in Mexico; has been described as an
iodide of mercury. This mineral requires further examination.
Onofrite. A sulpho-selenide of mercury from San Onofre, Mexico.
Ammiolite.—Contains antimoniate (antimonate) of copper and sulphide
of mercury. A specimen from Chili, analysed by Rivot, contained 14.8
per cent of tellurium.
DISTRIBUTION OF MERCURY ORES.
The ores of mercury are very unequally distributed, being confined
to a comparatively small number of localities, in many of which they occur
in considerable abundance; nearly the whole of the metal furnished to
commerce is consequently supplied by a few mines. The geological
range of these ores is exceedingly wide, as they are found in the most
ancient as well as in the most modern formations. Some of the principal
mines of this metal are worked in rocks of the Silurian period, while
those inclosing the celebrated deposits of New Almaden in California
are of Cretaceous age. In proof of the very modern origin of certain
deposits of cinnabar, it may be stated that many of the fumaroles, at the
Sulphur Bank near Clear Lake, in California, are at the present time
depositing sulphide of mercury, together with various other minerals.
The vapours and gases issuing from the different crevices, appear to
be the agents by which the various mineral substances in course of
deposition are brought to the surface. Sulphur is being condensed on
the sides of many of the fissures, either in crystalline groups, as stalac-
tites, or as translucent amorphous masses. This substance is sometimes
intimately mixed with cinnabar, but more frequently with minute crys-
tals of iron pyrites, and with pulverulent silica, often blackened by
some tarry hydrocarbon. On the sides of many of the cavities gelati-
nous silica is deposited, coating chalcedony and opalescent silica in
various stages of formation, varying from a gelatinous state to that of
the hardest opal. This silica is sometimes colourless, but is more fre-
quently permeated by cinnabar and iron pyrites, or blackened by the
tarry matter before mentioned. When the bituminous matter occurs in
large quantity cinnabar is often replaced by minute globules of metallic
mercury. Some of the silica intermixed with specimens from this deposit
was, when first broken, so soft as to readily receive the impression of the
nail, but on reaching England, it had assumed the hardness and appear-
ance of ordinary chalcedony.
MERCURY.
493
An analysis (in duplicate), made in 1873, of a specimen of this
deposit, brought by the author from Clear Lake, in 1866, afforded the
following results :--
I.
II.
H₂O(combined *
{hygroscopic
11.85
11.82
7.13
7.12
Sio,t
38.71
38.53
A1203
CaSO
Fe
1.50
1.46
•
2.56
2.84
4
•
9.25
9.31
Hg
7.08
7.08
S
fcombined
\free.
10.21
10.39
11.71
11.42
100.00
100.00
Ores of mercury have been found in several localities in France, but
they do not occur in sufficient quantities to admit of being profitably
worked. The mercury mines of Rhenish Bavaria were formerly of con-
siderable importance, and up to the beginning of the seventeenth century
afforded from 150,000 to 180,000 lbs. per annum, but have now almost
ceased to be worked.
At Idria, in Carniola, mines of mercury have been in operation for
several centuries and are still of some importance; the ore, which is
chiefly cinnabar, associated with a little native metal, is disseminated in
shale and black compact limestone belonging to the Jurassic period.
The average yield of these mines from 1843 to 1847 was, according to
Professor Whitney, at the rate of 358,281 lbs. per annum.
Bohemia formerly produced mercury in small quantities, and Hungary
furnishes a small amount from cinnabar associated with copper ores.
The present annual production of Austria and Germany is estimated at
about 500,000 lbs.
The mercury mines of Spain are the most important in Europe; they
are situated in the province of La Mancha on the frontier of Estrama-
dura, the chief workings being in the neighbourhood of the town of
Almaden. Mercurial ores are, however, found over a wide belt extending
from the town of Chillon to that of Almadenejos, where mining opera-
tions on a considerable scale are being carried on. Pliny asserts that
the Greeks procured vermilion from the mines of this district 700 years
before the Christian era, and according to the same authority they annu-
ally yielded to the Romans 100,000 lbs. of cinnabar. The mines of
Almaden are opened upon three parallel beds belonging to the class of
contact deposits, and are situated at the junction of the Silurian slates
with a metamorphic rock locally called fraylesca, which forms a belt
between the stratified deposits and the eruptive rocks. The metalliferous
* By difference.
† Gives, with the combined water, the formula H₂O,SiO2.
Dissolved out by carbon disulphide.
494
ELEMENTS OF METALLURGY.
beds are from twenty to fifty feet in thickness and follow the flexures of
the stratification of the inclosing rock. These mines have now attained a
very considerable depth, and, according to Le Play, the main vein at the
bottom of the principal working is from forty to fifty feet wide, and
entirely unmixed with barren rock. The average yield of the ore is from
7 to 10 per cent., but, on account of the imperfect nature of the metal-
lurgical processes adopted, the loss of mercury is very large. The
present annual yield of the Spanish mercury mines appears to be
35,000 bottles, or about 2,695,000 lbs. Since the year 1645, they have
been worked solely on account of the government.
At Ripa, in Tuscany, mercury is obtained from several veins travers-
ing mica-slate; the quantity annually produced is, however, exceedingly
small.
Ores of this metal are found in numerous places in Peru, and were
known to the inhabitants long before the invasion of that country by
the Spaniards; the mines of the province of Huancavelica, both as
regards numbers and richness, are the most important. Those of Santa
Barbara have been worked since 1566; but although at one time very
productive, their annual yield is believed to have now fallen below
100,000 lbs. According to Humboldt, this mine yielded, from 1570 to
1782, 1,040,452 quintals,* or about 47,300 tons of metallic mercury;
the average annual yield was less than 6,000 quintals; but in the best
years it sometimes reached 10,500 quintals. From 1790 to 1845, the
total yield amounted only to about 66,000 quintals.
Various other mines of the ores of this metal are worked in different
parts of Peru, but they are of less importance and extent than those of
Huancavelica; the total yield of the country was, according to Whitney,
in 1854, about 203,000 lbs., of which one-half came from the mine of
Santa Barbara.
Although an immense quantity of mercury is consumed in Mexico for
the process of patio amalgamation, almost the whole of that employed is
imported from other countries. At the beginning of the present century
the annual consumption of mercury in Mexico amounted to 16,000 quintals.
This was furnished by the Spanish government, who retained the sole
right of supplying the metal, which was chiefly derived from the mines of
Almaden and Huancavelica. At the time of Humboldt's visit, about the
commencement of the present century, only two mines producing mercury
were being worked in the country; one called the Lomo del Toro, and the
other Nuestra Señora de los Dolores, yielding, together, only 70 to 80 lbs.
per week. A mercury mine was being wrought about the year 1844,
near Guadalajara, but the results having been unsatisfactory, it was ulti-
mately abandoned.
The existence of mercury in California was known, and works were
established for the treatment of its ores, considerably prior to the first
gold-discoveries in that country. In 1845, a company was formed to
work an extensive deposit of cinnabar at New Almaden, in one of the side-
valleys of San José; this has been a very productive and remunerative
* Each of about 1 cwt.
MERCURY.
495
mine. The only other mines which have been worked to any considerable
extent are the New Idria, the Redington, Guadalupe, and the San Juan
Bautista. With regard to the geological position of the cinnabar deposits.
of California, it may be remarked that although this mineral has been
found in formations of nearly every age, as far as is yet known, there
are no large and valuable deposits excepting in those belonging to the
Cretaceous period.
According to Mr. T. F. Cronise, the total yield of the New Almaden
mine, and the average percentage of metal obtained from July 1850 to
December 1867, were as follow:-

Dates.
Ore consumed;
Pounds.
Per-
centage.
Flasks.
Pounds.
July, 1850-to June, 1851
1851
1852
""
""
4,970,717
4,634,290
35.89 23,875
1,826,437
32.17
19,921
1,523,956
1852
1853
""
"}
4,839,520 27.94 18,035
1,379,677
1853
1854
""
7,488,000
""
1854
1855
""
""
26.49
9,109,300 26.23 31,860
26,325
2,013,862
2,437,290
>>
1855
1856
10,355,200
20.34
28,183
""
""
2,155,999
1856
1857
10,299,900
18.93
26,002
1,989,153
1857
"9
""
1858 10,997,170
20.05
29,347
1,245,045
1858
Oct., 1858
3,873,085
20.05 10,588
809,982
Nov., 1858
Feb., 1861
"
Jan., 1861*
1862
"5
13,323,200
18.21 34,765
2,659,522
1862
"
1863
15,218,400
19.27 40,391
""
""
3,089,911
""
1863 Aug, 1863
7,162,6€0
18.11
19,564
1,496,646
Nov., 1863 ,, Dec., 1864 | 25,646,100
16.40
46,216
3,535,524
Jan., 1865
1865 31,948,400
12.43
47,194
""
""
3,610,341
1866
1867
1866
26,885,300
11.62
""
""
35,150 2,688,975
""
""
>>
1867 26,023,933
7.05
21,461 1,871,266
Totals +
461,877 31,333,586
The total production of mercury in California in 1867 was 44,386
flasks, or about 3,400,000 lbs. ; the present annual production of this
metal in the world may be estimated at 6,670,000 lbs. avoirdupois.
ASSAY OF MERCURY ORES.
DISTILLATION WITH QUICKLIME IN AN ATMOSPHERE OF HYDROGEN.—All
ores containing mercury, whether in the metallic state, or as oxide, sul-
phide, selenide, chloride, or iodide, admit, after being reduced to a fine
powder, of being assayed with considerable accuracy by distillation with
caustic lime, in an atmosphere of hydrogen gas. This operation may be
conducted as follows:-A tube of hard glass, a b, of the diameter employed
for making organic analyses, is drawn out at one of its extremities, in the
way shown in fig. 143, and in this part a bulb, B, is so blown as to be be-
tween two parts of the narrowed tubing. The contraction at a is now
loosely plugged with asbestos, so as to allow of a free circulation of gas
* Mine closed by injunction.
† Ore on hand equivalent to 5,000 flasks.
496
ELEMENTS OF METALLURGY.
or air, while it prevents any solid matter from being drawn into the
smaller elongation between a and B.
Powdered quicklime is afterwards introduced into the tube, and
slightly consolidated by pressure with a piece of glass rod, care being
at the same time taken that the aperture be not hermetically closed; a
weighed quantity of the mercurial ore to be assayed is then mixed with
caustic lime and deposited at c. When the mixture has been placed in

a
Fig. 143.
the situation above indicated the remainder of the tube is filled with
lime, and its end closed with a perforated cork, into which a piece of
small glass tubing is accurately fitted. The prepared tube, after being
tapped on the table to form a small space above the material, is now
placed in an ordinary gas combustion furnace, and a current of dry
hydrogen is introduced by the extremity, b. The part of the tube between
b and c is first warmed, and the heat is progressively advanced in the
direction of a. The mercurial ore is by this treatment decomposed, and
the volatile metal being carried forwards by the current of dry hydrogen,
is condensed and collected in the bulb, B, which is kept cool for that
purpose. A small quantity of watery vapour is also condensed at the same
time, but by a continued evolution of dry hydrogen this is ultimately
carried off. At the close of the experiment, when the whole of the mer-
cury has been condensed and the watery vapour has all passed off, the
tube on either side of the bulb, B, is cut with a sharp file, and the bulb
itself weighed with the mercury it contains. The metal is then poured
out, and any portions which may still adhere to the glass removed by
washing, first with a little nitric acid and subsequently with distilled
water. After being thoroughly dried, the bulb is again weighed, and by
subtracting the weight of the empty glass from the result first obtained
the quantity of reduced mercury is ascertained. In conducting this
experiment, it is of importance that a large quantity of moisture should
not be contained in the substance operated on, since by its condensation
in the bulb, and subsequent evaporation, a sensible amount of mercury is
carried off.
DISTILLATION WITH QUICKLIME AND SODIUM BICARBONATE.-Instead of
operating in the way above described, the following process may be
adopted. An ordinary combustion-tube of about 18 inches in length, and
closed at the end before the blowpipe, is filled for a short distance with
sodium bicarbonate; this is pushed down to the closed end, so as to
occupy a length of about 2 inches, and a little quicklime subsequently
introduced. The ore to be assayed is intimately mixed with excess of
quicklime, and then introduced into the tube, where it should occupy
about 4 inches of the central portion; any particles which may have
adhered to the mortar are removed by the aid of quicklime, and the lime
which has been used for this purpose is likewise introduced into the
MERCURY.
497
tube. A layer of 6 inches of pure lime is placed upon this, and a loose
stopper of asbestos is then pushed a distance of 4 or 5 inches down the
tube; the anterior end of the tube being finally drawn out and bent at
a somewhat obtuse angle. A few gentle taps on the table will suffice to
shake together the contents of the tube in such a way as to leave a free
passage above them throughout its whole length.
The tube, thus prepared and arranged, is introduced into a combustion
furnace, and its point placed in a receiving flask half full of water; the
point is made to rest upon the surface of the water in the flask in such a
way that its aperture may be partially closed. The tube is now slowly
heated from the open to the closed end, as in the case of an organic
analysis, and the last traces of mercurial vapour are finally expelled by
heating the sodium bicarbonate, occupying a space of 2 inches, at its
closed extremity.
Whilst the tube still remains red-hot the neck is cut off and carefully
rinsed with a wash-bottle, transferring the rinsing-water to the receiving
flask; the small globules of mercury that have distilled over into the latter
are then united into one large globule by agitation, and after the lapse of
some time the perfectly-clear water is decanted or drawn off by a syphon,
and the mercury transferred to a weighed porcelain crucible, from which
any adhering water is removed by means of blotting-paper. The mercury
is finally dried over sulphuric acid under a bell jar, and the drying con-
tinued until its weight ceases to vary. This method, if carefully executed,
yields very accurate results; soda-lime may be employed in place of quick-
lime for mixing with the mercurial ore, but it does not appear to offer
any special advantage.
METHOD EMPLOYED AT IDRIA.—In establishments where many mercury
assays have to be made daily, a small reverberatory furnace is usually
employed. That used at Idria has, on one side, an iron plate with twenty-
six holes for the insertion of a corresponding number of assays. Eight
assays, each weighing four ounces, are taken from the charge of every
furnace; these are mixed with two or three spoonfuls of powdered quick-
lime, and the several assays are introduced into eight iron retorts, and
placed in the furnace above referred to. The receivers are then attached,
the space between the two carefully luted, and the assays heated to bright
redness; the distillation is finished when drops of mercury are no longer
deposited in the receivers.
The distillation must be performed with a slowly-increasing heat, and
care taken that a sufficient temperature is attained by every part of the
retort. Should the mercury obtained not flow well together, it is simply
boiled in water for a few seconds; the last remnant of adhering water is
removed by blotting-paper in the usual way, and after drying the mercury
at a temperature of about 40° C., it is transferred to a tared watch-glass
and weighed.
The assay is considered successful when the results of the various
duplicates closely agree, and no undecomposed cinnabar is deposited in
the receiver or in the neck of the retort. This method of assaying may
be conducted with a sufficient degree of accuracy to serve either to control
2 K
498
ELEMENTS OF METALLURGY.
the operation of reduction, or for determining approximately the value of
the ore; but the results obtained are in all cases somewhat below the
truth. The lower, however, is the amount of mercury contained in an
ore, the greater will be the difference between the true percentage and the
assay result; even with an ore containing 5 per cent. of mercury, the
quantity found by this method will be considerably lower than that which
it actually contains. Various methods have been proposed for the volu
metric assay of ores of mercury, but none of them admit of general use.
METALLURGY OF MERCURY.
2
2
The extraction of mercury from cinnabar, which may be considered,
practically, the only ore of this metal, is effected either by the oxidation
of the sulphur by atmospheric air, and the volatilisation of the liberated
metal, or by the use of fluxes, with which the sulphur enters into com-
bination, while at the same time the liberated mercury distils over, and
is subsequently condensed. When cinnabar is decomposed through the
oxidation of its sulphur, the reactions which take place are expressed by
the following equation: HgS+0₂ = SO₂+Hg. When lime is present
with cinnabar, and heat is applied, the following decompositions take
place: (HgS), + (CaO) -(CaS) + CaSO, +Hg. The choice of the
method adopted for the metallurgical treatment of mercurial ores is chiefly
influenced by their richness, quantity, the size of the fragments, and the
cost of fuel and materials. When the ores are rich and the quantities to
be treated small, the gallery furnace is frequently resorted to; but if
the quantities are large and the ores massive, kilns are more usually
employed. Condensation is often effected in large brickwork chambers,
which are found more efficient than the clay tubes formerly employed;
and the latter are now sometimes advantageously replaced by cast-iron
pipes kept cool by water.
4
3
The following are the principal methods employed for the extraction
of mercury from cinnabar :
1. Decomposition of the ore by roasting.
a. Roasting in mounds; applied in Hungary to the treatment of
cupreous ores containing mercury.
b. Roasting in kilns, carried on either by short intermittent opera-
tions or continuously; apparatus of various kinds are used for condensing
the metallic vapours.
c. Roasting in reverberatory furnaces, and condensing in iron pipes ;
this method is adopted for working schlich and other finely-divided ores.
2. Decomposition in close retorts by lime.
a. Process carried on by a series of distinct operations.
b. Operations continuous.
EXTRACTION OF MERCURY BY SUBJECTING CINNABAR TO A
PROCESS OF ROASTING.
This method of extracting mercury from its ores is cheaper, and
requires less time and fuel, than that by the use of fluxes in close
MERCURY.
499
vessels; on the other hand, mercury in the state of vapour becomes mixed
with the products of combustion of the fuel made use of, and, being
carried forward by the necessary draught, condensation becomes difficult,
and great loss of metal is the result.
At Idria, Almaden, New Almaden in California, and at Ripa in
Tuscany, large chambers, externally cooled by water, are employed as
condensers, while at some other establishments they are so constructed as
to allow jets of water to play into them. At the Pioneer Mine, in Cali-
fornia, the condensers are traversed by troughs, through which a stream of
water constantly flows. The porous masonry of large chambers is, how-
ever, found to imbibe a very considerable quantity of mercury; and they
have, consequently, been partially replaced at Idria by cast-iron pipes
cooled externally by water, and connected with condensers provided with
a suitable chimney. These tubes are, however, found to be acted upon
somewhat rapidly by the sulphurous vapours passing through them, and
have in consequence been, in some instances, replaced by wooden pipes.
Wooden pipes possess the advantage of being cheaper and more durable
than iron ones, and can, by means of small doors, be easily opened and
cleaned; the mercurial fume which collects in them is also free from
oxide of iron, and is consequently more readily removed and worked. It
is however probable, that, if tried, the ordinary towers used by alkali
manufacturers for the condensation of hydrochloric acid would be found
effective as condensers for mercury; they should, however, for this purpose.
be packed with open brickwork, in the way commonly adopted in copper-
works where that metal is extracted by the wet process.
The treatment of mercurial ores on a large scale is for the most part
conducted in kilns working intermittently, and which, after the exhaustion
of each charge, require to be allowed to cool before it can be withdrawn
and replaced by a fresh one. This circumstance not only causes con-
siderable loss of time, but, from the alternate heating and cooling of the
masonry, the walls are liable to become cracked, and thus allow of the
escape of an amount of mercurial vapour resulting in a serious loss of
that metal; at the same time most deleterious effects are produced on the
health of the workmen employed. The loss through this and other causes
is so great as, in some cases, to amount to above 40 per cent. of the
mercury contained in the ores operated on.
a. ROASTING IN MOUNDS.-In various parts of Hungary, as at Szlana,
Altwasser, &c., copper ores are found containing from 1 to 16 per cent. of
mercury, but probably averaging from 2 to 2 per cent. of that metal.
These ores are roasted in heaps preparatory to their fusion for copper
regulus, and during the operation a portion of the mercury is collected ;
the mounds are usually about 40 feet in length, 20 in breadth, and 3 feet
6 inches in height, and are provided with flues and chimneys similar to
those sometimes employed for the preparation of coke. Hot embers are
thrown into the vertical shafts, which are subsequently filled with small
coals; the decomposition of the sulphides very shortly commences, and
mercury condenses in drops on the outer and colder layers of ore. As
soon as the uppermost layer becomes so far heated that mercury is
2 K 2
500
ELEMENTS OF METALLURGY.
re-volatilised, it is covered by a fresh stratum, as are also all places where
any sinking of the outer covering has taken place. The process of
roasting is usually complete in about three weeks, and the upper layers
of the mound will then be found to contain mercury resulting from the
condensation of mercurial vapours expelled from the more central
portions of the pile. These upper layers are carefully removed, and
afterwards washed upon an iron sieve in a tub of water, in which the
mercury and fine ore accumulate; while the coarser portions which remain
on the sieve form the lower layers in the next mound prepared for cal-
cination. The fine ore is subsequently washed on very close sieves, which
allow the mercury to pass through them and to unite into large masses,
while the fine ore, to a large extent, remains behind; this is added to the
next mound for roasting. The upper layers are thus treated so long as
they continue to yield an appreciable amount of mercury, and the lower
ones, which have been completely roasted, are taken to the furnace in
which the first fusion for regulus is effected.
1
By this method of treatment ores are stated to yield 79 per cent. of
the mercury indicated by assay, and the collection of mercury from
copper ores containing only per cent. of that metal is said to be
attended with profit; in 1861, Hungary produced 31 tons of mercury
from the washing of copper ores of this description.
b. TREATMENT OF MERCURIAL ORES AT IDRIA. Old Process.-The ores
treated are here divided into two classes: the mineral in lumps varying
from the size of a nut to a cubic foot, and those fragments of which the
size ranges from that of a nut to the finest dust.
The first class comprises three subdivisions, namely, the poorest
kind, affording only 1 per cent. of mercury; the massive sulphide, con-
sisting of the richest selected fragments, often containing 80 per cent. of
metal; and lastly, the splinters arising from the breaking and sorting
of the different ores, which yield from 1 up to 40 per cent.
The second class is also subdivided into three varieties, and com-
prises the fragments extracted from the mine in small pieces, and which,
on an average, afford from 10 to 12 per cent. of metallic mercury; bits of
ore separated by washing on a sieve, and containing 30 per cent. of
metal; and lastly, the sand and schlich obtained by stamping and
washing the poorer ores; this generally affords a produce a little superior
to 8 per cent.
The metallurgical treatment of these several products consists in
subjecting them to a process of roasting in a large kiln-like apparatus,
in which the sulphur is converted into sulphurous anhydride, whilst
metallic mercury is set free and condensed in a series of chambers
arranged on either side of the furnace for that purpose.
This apparatus consists of a large roasting kiln, A, figs. 144, 145,
furnished on either side with a series of chambers, C, in which the
mercurial vapours are condensed.
The larger fragments of the mineral treated are closely piled on the
hollow arch, a, until the space between it and the next has been entirely
filled. On the second perforated arch, b, are placed fragments of smaller
MERCURY,
501
dimensions; and on the third, c, were formerly deposited, in earthen
vessels, the slimes arising from the mechanical treatment of the poorer
ores. This washed schlich is now formed into bricks, and charged
into the furnace, mixed with ordinary lump cinnabar.
When the furnace has been thus charged a fire is lighted on the
grate, and the heat is progressively raised until the decomposition of the
mineral begins to take place. The sulphide of mercury placed in imme-
diate contact with a current of heated air, which enters the furnace
through apertures opening into the spaces, G, H, is sublimed and rapidly
decomposed; the metal being conducted by proper channels into the
condensing chambers, C. The greater portion of this mercury becomes,
condensed in the first three chambers and is conducted by the gutters,

Ꮳ
ន
X
Fig. 144.- Furnace at Idria; longitudinal section.
Y
ER

Z
Z
y
Fig. 145.-Furnace at Idria; horizontal section.
x, y, z, to covered reservoirs prepared for its reception beneath the level
of the floor. In the last chambers of the series a considerable amount of
water, and but little mercury, is condensed. These products are, on
account of the impurities they contain, carried off by a separate set
of gutters, to a tank, in which they accumulate. The mercurial dust,
associated with the metal obtained from the last chambers, is subsequently
separated by filtration and mixed with some of the finer ores, to be again
treated in the furnace.
In order to condense, as far as possible, the last traces of mercury
passing through the apparatus, a stream of cold water is constantly made
to flow through the chambers, D, on inclined tables, extending from one
wall nearly to the other, and between these the vapours and gases are
obliged to circulate before escaping, through E, into the atmosphere.
The mercury is afterwards filtered through thick linen bags to separate
502
ELEMENTS OF METALLURGY.
solid impurities, and subsequently packed in wrought-iron bottles for
exportation.
This arrangement, which is perhaps the largest single metallurgical
erection in the world, is charged in three hours by the united labour of
forty men. The wood employed as fuel is usually beech, and the distil-
lation lasts from ten to twelve hours, during which time the whole
interior of the kiln is kept at a cherry-red heat. A complete charge for
the double apparatus is from 1,000 to 1,200 quintals of ore, which produce
from 80 to 90 quintals of mercury. The furnace requires, according to
the season of the year, from four to five days to cool; and therefore, when
the time necessary for charging and withdrawing the residue is included,
only one distillation can be made in the course of a week. This furnace
is 180 feet long and 30 feet in height; it was first erected at Idria in
the year 1794, before which time an aludel furnace, similar to that of
Almaden, was employed.
In the year 1812 the mines of Idria yielded 56,686 quintals of
mechanically-prepared ore, which afforded 4,832 quintals, or about
81 per cent., of metallic mercury.
Continuous Process.-The furnaces employed for this process were
constructed by Hähner, and have since 1850 been used with great advan-
tage for the treatment of all but the more finely-divided varieties of
ore; but even these can be advantageously treated if first mixed with
clay and afterwards made into bricks. The furnace is a cylindrical
kiln furnished at bottom with a movable grate constructed of iron bars,
each of which may be separately withdrawn, and beneath which a small
waggon can be placed for the purpose of removing the exhausted residues
after calcination. This cylindrical kiln is fed at top by means of a hopper
closed by a valve, and is connected, by a lateral flue immediately below
it, with a series of six condensing chambers, built of masonry, and exter-
nally covered with iron plates, kept cool by a continuous flow of cold
water. The chimney is built in tiers, each of which is cooled by water,
while the chambers, which communicate with one another alternately at
the bottom and top, have floors of clay, tightly rammed in on foundations
of masonry.
When this arrangement is lighted, a few pieces of broken brick are
placed on the bars so as to diminish the interstices between them, and on
these are laid some brushwood and charcoal, on which the first layer of
mercurial ore is charged. The kiln is now filled with ore and charcoal,
in alternate layers, to a height of about 12 feet; the wood upon the
grate is kindled, and the fire makes its way slowly upwards through the
Charges of 7 cwts. of ore, with from 3 to 4 per cent. of charcoal,
are let down through the hopper every forty-five minutes, whilst the ex-
hausted ore is from time to time withdrawn by removing some of the bars
at the bottom, and allowing it to fall into small iron waggons running on
a tramway. The ores remain twenty-two hours in the kiln, and those
containing 3.11 per cent. of mercury by assay yield 1.90 per cent. on the
large scale by this method of treatment.
mass.
Ure's furnaces, which were formerly employed at Ripa, in Tuscany,
MERCURY.
503
were afterwards superseded by those of Cossigny, and these, in their turn,
have been replaced by the Hähner furnace. At the works at Castellazara
the condensers attached to this apparatus are provided with hemispherical
cast-iron bottoms, with a pipe in the centre, through which the mercury
escapes into a vessel placed beneath for its reception. The ores operated
on in this establishment are extremely poor, but the cost of treatment
does not exceed 2s. 4d. per ton.
b. ALUDEL FURNACE OF ALMADEN.-This apparatus, figs. 146 and 117,

F
您
​b
Fig. 146.-Aludel Furnace; longitudinal section.
b
Fig. 147.-Aludel Furnace; sectional plan.
E


Fig. 148.—Aludels.
of which the first is a vertical section and the second a sectional plan,
was introduced in 1646 by Juan Alonzo Bustamente, from Huancavelica,
in Peru.
These furnaces, which are called buytrones, consist of a circular kiln,
A B, separated into two compartments by a brick arch, k, pierced with
numerous apertures. The ore is piled in the space, B, above the arched
diaphragm, the larger masses being placed first, and the smaller frag-
ments upon them. The top is then covered with bricks formed of clay,
kneaded with fine schlich. At the upper extremity of the cavity, B, is
arranged a system of openings, ƒ, which communicate with a series of
504
ELEMENTS OF METALLURGY.
earthen adapters, fitting into one another, and resting on the doubly-inclined
surface of the terrace, a, b, c. These earthen pipes, or aludels, fig. 148,
are merely thrust into one another, and luted with a little softened clay,
by which the leakage of the joint is partially obviated. The condensed
mercury partly remains in the aludels, but another and larger portion
flows through a hole pierced in the aludel placed at the lowest part of
the series, and is collected in the gutter, b, by which it is conducted
through wooden spouts into the receiving basins, r. The uncondensed
gases, mixed with mercurial vapours, pass through apertures, c, into the
chambers, C, where, passing under a diaphragm, e, a certain portion of
the metal is deposited in a vessel, i, filled with water. What still
remains uncondensed passes into the upper part of the chamber, whence
a considerable portion of it escapes into the atmosphere through a
chimney, E. The mercurial soot which accumulates on the sides of this
chamber is occasionally swept down, and, after being kneaded into bricks,
with the addition of softened clay, is again treated in a subsequent ope-
ration. The fuel employed is brushwood, which being ignited in the
space, A, beneath the arched diaphragm, affords the amount of heat
necessary for working the furnace. The aludels are placed in twelve
ranges of twenty-five in each; the fuel is introduced through the open-
ing, D, and the smoke and other products of combustion are principally
carried off by the chimney, F. a is a flight of steps for mounting on
the top of the furnace, and g a gutter by which rain-water is carried
off. The ore is introduced into the furnace through the door, h, and
opening, o, which are afterwards securely luted. The firing is continued
during twelve or thirteen hours, and the apparatus is then allowed to cool
for three or four days, at the expiration of which time it is cleaned out
and charged for another operation.
Furnaces similar to those used at Idria have been employed at
Almaden since 1860; their capacity is two and a half times greater than
that of the aludel furnace. About 13,500 tons of mercurial ore, yielding,
on an average, about 8 per cent. of mercury, are treated annually in two
Idrian and eight aludel furnaces.
b. New AlmadEN, CALIFORNIA.—The furnace here made use of is a
sort of brick-kiln of a rectangular form, furnished on one side with a
fire-place which is separated from it by a perforated partition wall. This
kiln is in communication with eight or nine, walled, condensing chambers,
terminating in a wooden tower, through which a continuous shower of
water is made to descend; the uncondensed vapours escape through a
wooden chimney at the end of the series. The fire is kept up during
sixty consecutive hours, and the apparatus requires forty-eight hours
for cooling, after each operation. The larger furnaces are capable of
receiving a charge of 100 tons of ore mixed with limestone, but the yield
of mercury is said not to exceed 62 per cent. of that which it contains.
Mr. F. Claudet found considerable quantities of mercuric sulphate in
the condensing chambers at New Idria.
c. EXTRACTION OF MERCURY IN REVERBERATORY FURNACES.—At Idria,
reverberatory furnaces are employed for the treatment of the smaller and
MERCURY.
505
poorer ores; the results obtained are said to be satisfactory. The ore is
introduced into the furnace by means of a hopper placed at the extremity.
nearest the chimney, and is divided into three charges, which are gradu-
ally worked towards the fire-bridge, while the exhausted matter is with-
drawn, through an opening, into an arched chamber beneath. Condensa-
tion is effected by means of cast-iron pipes, through which the volatilised
mercury, together with the products of combustion, first pass to a large
condensing chamber, and thence back again, through a considerable length
of similar pipes, to another chamber, near the furnaces, which is in com-
munication with a high chimney. These tubes are kept cool by a spray
of water constantly falling upon them from parallel wooden spouts,
pierced with holes, placed above them, and condense rather more than 95
per cent. of the total amount of mercury obtained. Two of these furnaces,
placed side by side so as to form one block of masonry, work 13 tons of
fine ore and 10 tons of schlich daily, with a loss of about 8 per cent. of the
mercury indicated by assay, and with a consumption of 50 cubic feet of
wood per cwt. of mercury obtained. This is about twice the quantity
of fuel required to treat the same amount of ore in the large kiln-
furnaces, but in them the loss of mercury is considerably greater.
DECOMPOSITION OF MERCURIAL ORES IN CLOSE VESSELS
BY LIME.
a. GALLERY OF THE PALATINATE. In the district of Zweibrücken,
where considerable quantities of mercury are extracted, a peculiar appa-
ratus called a gallery is employed. The mineral here treated consists
of a mixture of sulphide of mercury and calcite, which is heated in
earthen or cast-iron retorts or cucurbits, of which several are arranged in
one furnace, as shown in fig. 149.
The number of cucurbits, A, con-
tained in one gallery varies from
30 to 50, and to each of these is
adapted a stoneware receiver, B,
partially filled with water. Into

each of the retorts are introduced
from 56 to 70 lbs. of cinnabar and
from 15 to 18 lbs. of quicklime, a
mixture which should fill about
two-thirds of its capacity.
EF F F F F F F EERS
The sulphide of mercury is in
this case decomposed by the lime;
sulphide of calcium and sulphate
of calcium are formed, and the
liberated metal is condensed in the
stoneware bottles. The fuel employed, which is pit-coal, is burnt on
a grate situated at C. The dome is perforated with openings for the
purpose of creating a draught.
Fig. 149.—Gallery; transverse section.
b. RETORTS AT LANDSBERG.-With the view of obviating the incon-
506
ELEMENTS OF METALLURGY.
venience and loss experienced by the older methods of distilling mercury,
an apparatus was erected, in 1847, under the direction of the late Dr. Ure,
at Landsberg, near Obermoschel, in Bavaria. This arrangement consists
of a series of retorts, a, fig. 150. These are set in masonry, precisely in
the same way as those employed in the manufacture of coal gas, and are
fitted at one end with an eduction tube, b, and at the other with an air-
tight stopper, kept in its place by an iron screw. The eduction pipes
are each furnished with a nozzle, L, closed by a screw plug, through
which a large wire may be introduced to ascertain that the tube is clean
and free from any obstruction occasioned by adhering mercurial soot.
In connection with the pipes, b, is a large condenser, C, of cast-iron,
18 inches in diameter, and filled with water to p, a little above the level

he
k
a
ודי
VETEN
Fig. 150.-Retorts, Landsberg; elevation, partly section.
of the pipes. It is also furnished with a valve, g, by which any danger
from sudden expansion or condensation is obviated, and the tempera-
ture is further reduced by placing the condensing-pipe in a large wooden
trough, i, through which a current of cold water is constantly made
to flow. The cylinder, C, is likewise made slightly to incline towards D,
so that the condensed quicksilver may readily flow along its bottom, and
passing through the vertical pipe, be collected in the closed iron chest, E,
which may be secured by a lock at h. The tube D, is, from the commence-
ment, sealed at bottom, by terminating in a shallow iron chamber, filled
with mercury, and the progressive accumulation of quicksilver is indi-
cated by the position of the graduated iron float, k. These retorts, like
those employed in the manufacture of gas, are constantly maintained in
a uniform state of ignition, and any damage to the joints is thus obviated.
Each retort will contain a charge of ore weighing 5 cwts., which is mixed
with quicklime and from which the metal is expelled in the course of
about three hours.
At Ripa, in Tuscany, where this apparatus was introduced, it has
long since been superseded, and we are not aware whether at the present
time it is anywhere in use. Retorts on a somewhat similar plan have
been tried in some of the mercury mines of California, but they have not
been found economical. At the Enriquita mine, rotating retorts are
employed, and the results obtained are believed to be satisfactory.
BISMUTH.
507
BISMUTH.
Bismuth possesses a greyish-white colour, but at the same time presents
a distinctly-red tint when compared with zinc, antimony, or any of the
whiter metals. It is brittle, and consequently cannot be drawn out under
the hammer, and when broken presents a highly crystalline fracture.
Very beautiful crystals of this metal are readily obtained by fusing a con-
siderable quantity in an earthen crucible, and afterwards setting it aside
and allowing it to cool very gradually. For this purpose, the ladle or
crucible in which the fusion has been effected should be removed from the
fire to a sand-bath, and covered with a hot iron plate, on which are placed
a few pieces of ignited charcoal. At the expiration of a certain time, the
external crust of solidified metal is pierced by a hot iron, and the
interior portions, which still retain the liquid form, are rapidly poured
out. The upper crust is now removed, and beautiful crystals of bismuth
are found coating the sides of the vessel. These are really rhombohedra,
but having angles of nearly 90°, they have the appearance of cubes, and
from a slight covering of oxide, varying in its thickness, they frequently
assume very beautiful prismatic colours.
•
Commercial bismuth is never pure; but as the other metals with
which it is associated are commonly more oxidisable than itself, they may,
in a great degree, be separated from it by fusing the powdered alloy in
an earthen crucible, with one-tenth part of its weight of nitrate of potas-
sium. On heating this mixture until the nitre has been completely
decomposed, a portion of the bismuth, together with the major part of the
impurities, will have been oxidised and will remain with the slag, whilst
a button of purified bismuth collects in the bottom of the crucible.
To purify bismuth, dissolve the crude metal in nitric acid and con-
centrate by evaporation. Pour the clear concentrated solution into a
large quantity of distilled water, and wash the basic nitrate which is
precipitated by decantation. Boil with a very weak solution of caustic
potash to remove traces of arsenic, &c., wash, and dry. Mix the dried
basic nitrate with its own weight of black flux, and fuse it at a moderate
heat in an earthen crucible. On breaking the crucible, after cooling, a
button of nearly pure bismuth will be found at the bottom.
This metal fuses at a temperature of 259° C. It is volatile at a high
heat, and may be distilled. Bismuth is placed by Faraday at the head of
diamagnetic substances; it transmits heat less readily than most other
metals. At a white-heat bismuth boils, and is sublimed, and at this tem-
perature is stated by Regnault to decompose the vapour of water; it is
not affected by exposure to dry air, but when placed in a humid atmo-
sphere gradually becomes covered with a thin pellicle of oxide. When
strongly heated in air, bismuth burns with a bluish flame and gives off
fumes of a light yellow colour.
It is attacked with difficulty by concentrated hydrochloric acid. Sul-
phuric acid, unless concentrated and hot, does not attack it, and in this
case sulphurous anhydride is evolved. Nitric acid attacks it with great
facility, with the formation of a soluble nitrate of bismuth.
508
ELEMENTS OF METALLURGY.
BISMUTH ORES.
Bismuth occurs native, and also in combination with sulphur, oxygen
and tellurium. Its ores readily fuse before the blowpipe, and in the
oxidising flame afford an oxide by which the charcoal support is stained
of a brownish-yellow colour.
NATIVE BISMUTH; Bismuth natif; Gediegen Wismuth. Crystallises in
the rhombohedral system. Is found massive, granular, reticulated, and
arborescent. Colour greyish-white, inclining to red; lustre metallic, and
streak unchanged. Frequently contains small quantities of arsenic, and
is often associated with silver, and sometimes with iron.
Native bismuth accompanies various ores of silver, lead, zinc, cobalt
and nickel, and usually occurs in veins traversing either gneiss or clay-
slate. Its principal localities are the silver and cobalt mines of Saxony
and Bohemia, at Altenberg, Schneeberg, Annaberg, Joachimsthal, and
Johanngeorgenstadt; at Löling in Carinthia, and at Fahlun in Sweden.
Native bismuth also occurs at Huel Sparnon, near Redruth in Cornwall;
at Carrack Fell in Cumberland; at Alloa, near Stirling, Scotland; and
in Bolivia. Native bismuth supplies nearly the whole of this metal which
is employed in the arts; the greater portion was formerly derived from
the mines of Schneeberg, where it is found associated with ores of cobalt.
Bismuth is also found in combination with other bodies, but these
compounds are by no means of common occurrence.
Sulphide of Bismuth occurs in Cumberland, Cornwall, Saxony, Sweden,
and in South Australia. It is found both in the massive state and in the
form of acicular crystals; is composed of bismuth 81.3, sulphur 18-7.
This mineral is by no means plentiful, although its localities are com-
paratively numerous.
Bismuth Blende is a silicate of bismuth which occurs in minute do-
decahedral crystals of a dark hair-brown or wax-yellow colour. Its more
general appearance is that of implanted globules, which rarely exceed
the size of a pin's head. A specimen of this mineral, which occurs at
Schneeberg in Saxony, was found to be composed of oxide of bismuth,
58.8; silica, 23.8; arsenic anhydride, 2.2; gangue, 9.1; cobalt, copper
and iron, 5.9.
Acicular Bismuth is a sulphide of bismuth, copper, and lead, which
occurs in the mine of Klutscheffsky, near Beresof, in Siberia. It is found
in acicular crystals of a yellowish-white colour, and contains from 34 to
37 per cent. of bismuth.
Tetradymite is a compound of tellurium and bismuth, and occurs in
Sweden, Brazil, &c.
Oxide of Bismuth occurs as a pulverulent coating on some of the other
ores of this metal; it is found in Bohemia, in Siberia, at St. Agnes in
Cornwall, &c. It is of a yellowish-green colour, and contains 86 per cent.
of bismuth. A vein, containing ores of bismuth and wolfram, has been
recently worked near Meymac, Dep. of Corrèze, France. The bismuth
occurs as oxide, associated with native metal and sulphide.
BISMUTH.
509
Carbonate of Bismuth. This mineral occurs at St. Agnes, at Schnee-
berg, and at Johanngeorgenstadt.
The total annual production of bismuth, a considerable portion of
which comes from South America and South Australia, probably does
not much exceed 20 tons.
ASSAY OF BISMUTH ORES.
Assays of the ores of bismuth are conducted like those of the oxi-
dised ores of lead. When the substance operated on contains metallic
bismuth only, no reducing flux is, theoretically, required; but as there is,
in almost all cases, a portion of oxide present, a little powdered charcoal
should be added. On account of the volatility of this metal, it is of
importance that a readily-fusible slag should be obtained, and for this
purpose large quantities either of carbonate of sodium, of borax with
charcoal, or of borax with black flux, should be employed.
3
In the wet way, bismuth is usually precipitated from its solutions by
carbonate of ammonium, which when added in excess throws down the
whole as carbonate, provided the liquid be allowed to stand for several
hours in a warm place. The precipitate, after being washed and dried, is
separated from the filter and ignited in a porcelain crucible; the filter is
burnt separately, and the residue added to the ignited precipitate. This
consists of bismuthous oxide Bi₂O, containing 89.74 per cent. of metal.
When sulphuric or hydrochloric acid is present in the solution, carbonate
of ammonium must not be employed for precipitation, since the precipitate
would, in the former case, contain basic sulphate, and in the latter, oxy-
chloride of bismuth. In such cases bismuth must first be precipitated
by sulphuretted hydrogen, and the resulting sulphide attacked by nitric
acid. From the solution thus obtained the bismuth may be precipitated
by carbonate of ammonium.
METALLURGY OF BISMUTH.
SCHNEEBERG PROCESS.-The bismuth of commerce is chiefly obtained
from the native metal, of which a large proportion was formerly procured
from the mines of Schneeberg, in Saxony. The metallurgical treatment
of these ores is extremely simple, as it is sufficient to heat them in closed
vessels; by which treatment the metal becomes fused and flows out into
proper receivers, whilst the gangue and infusible impurities remain
behind.
At Schneeberg, liquation is effected in cast-iron retorts, a, b, fig. 151,
set in an inclined position in brickwork, A, and provided with a grate, g,
for the fuel employed. The ore treated is sorted by hand, broken into
pieces of the size of a hazel nut, and separated as much as possible from
associated gangue. The charge of each pipe consists of about 56 lbs. of
broken ore, which is introduced at a, and occupies three-fourths of its
length and rather more than one-half its diameter. A sheet-iron door at
the end, a, is now shut, and, when the whole of the tubes in the series have
been charged in the same way, heat is applied; the liquid metal soon
begins to flow through the apertures, b, left in the lower ends of the tubes,
510
ELEMENTS OF METALLURGY.
and falls into small pots, c, kept slightly heated by a few pieces of ignited
charcoal, introduced into a space left beneath them for that purpose.
Whenever the metal ceases to run freely, an iron rod is inserted through
the aperture, b, and the ore is moved about in the retort in order to remove
the obstruction. The fuel employed is wood, and each operation requires
about an hour for its completion.
As soon as the flow of metal has entirely ceased, the residuum is
scooped out with iron rakes into the water-trough, t, and a fresh charge
of ore is at once introduced into the retorts. The contents of the pots, c,
are dipped out with iron ladles, and cast into ingots varying from 25 to
50 lbs. in weight.
By this apparatus 20 cwts. of ore may be treated in eight hours,
with a consumption of 63 cubic feet of wood. The annual production

Fig. 151.-Bismuth Liquation Furnace; vertical section.
of bismuth at Schneeberg formerly amounted to about 5 tons, but it is
now considerably less.
JOACHIMSTHAL PROCESS. —At Joachimsthal, ores containing from 10 to
30 per cent. of bismuth are treated in large earthen crucibles. The ore
is ground and mixed with 28 per cent. of iron-turnings or other finely-
divided scrap-iron, 15 to 20 per cent. of carbonate of sodium, 5 per cent.
of lime, and 5 per cent. of fluor-spar. The crucibles employed are
23 inches in height and 16 in diameter at the mouth; they are filled with
the mixture above specified and its fusion is effected in a wind furnace.
When in a state of tranquil fusion the contents of the pots are laded out
into inverted conical iron moulds, in the bottom of which the bismuth col-
lects; this is covered by a speiss, which, in addition to cobalt and nickel,
contains about 2 per cent. of bismuth. The speiss is separated from the
bismuth for subsequent treatment, and the slag, which covers both, is
thrown away. The bismuth thus obtained contains a certain amount of
silver, which may be separated by subjecting the mixture to cupellation,
and subsequently reducing the oxide of bismuth produced. An alloy of
silver and bismuth works on the cupel quite as well as a mixture of silver
and lead.
PRODUCTION OF BISMUTH AT FREIBERG.-We are indebted for the
BISMUTH.
511
following description of the method employed at Freiberg (1870), for the
extraction of bismuth from argentiferous ores, to Mr. W. M. Hutchings,
who, when a pupil at the Royal Mining Academy, possessed the necessary
facilities for making himself acquainted with the process.
None of the Freiberg ores contain an appreciable amount of bismuth,
and indeed the quantity present in any of them is so small that it was
never detected by direct analysis. On an analysis being made, however,
of the hearth of the silver refinery in which a charge of Blicksilber from
the German cupelling furnace had been refined, it was found to be rich in
bismuth. Further analyses proved this to be always the case; some of
the hearths containing as much as 20 to 25 per cent. of bismuth, showing
that the small quantity originally present in the ores had become concen-
trated in the Blicksilber, and had finally passed into the refining hearth.
A process for its extraction was consequently introduced, and was carried
on at intervals, whenever a sufficient accumulation of material had been
collected. For this purpose the hearth was finely ground and passed
through a sieve, to remove all metallic shot. The fine powder was then
submitted to the extraction process about to be described.*
At a later period a class of ores from another part of the Erzgebirge,
and containing more bismuth, was sent to be smelted at the Freiberg works ;
these ores contained nickel and cobalt, which were concentrated into the
speiss produced in smelting. In order to obtain the bismuth from these
ores it was no longer sufficient to treat the refining hearth only by the
extraction process, since towards the close of a cupellation the litharge
produced was so rich in bismuth that it was found necessary to keep it
apart and to send it to the bismuth works. It was also found advan-
tageous not to complete cupellations in the cupel furnace, but to stop
the operation some time before the Blick, and to transfer the alloy to
the refining furnace, in which cupellation is completed and the silver
refined; both the litharge and the hearth being rich in bismuth. The
litharge is finely ground, like the hearth, and both are treated as
follows:
The powdered hearth or litharge is treated with hydrochloric acid in
glazed earthenware pots, 2 feet high, having an internal diameter of
1 foot 11 inches at bottom and 2 feet 8 inches at top. Twelve of these
pots are ranged upon a platform at one end of the room, with a water-pipe
placed above and parallel with them, so that water can be let into each as
required. A steam-pipe is also provided, in order that, when necessary,
steam may be blown into the several pots to heat their contents.
From 80 to 100 lbs. of hearth, or litharge, are placed in each pot, and
measured quantities of acid and water are introduced, in accordance with
the previously-determined richness in bismuth of the material operated
on. Thus, for example, 100 lbs. of hearth may receive 120 lbs. of acid
and 45 lbs of water. The acid used is common yellow hydrochloric. The
reaction is strong, and a considerable amount of heat is evolved; the mass
is actively stirred and is prevented from forming lumps. Stirring is
* A specimen of a cupel bottom brought from Freiberg by Mr. Hutchings was
found to contain 10 37 per cent. of bismuth.
512
ELEMENTS OF METALLURGY.
frequently repeated during seven or eight hours, after which more acid is
added, in quantity regulated by the amount of bismuth present, so that
the pot can be filled with water without any precipitation of bismuth
taking place.
The vessel, when so filled, is allowed to stand thirty-six hours, to let
the contents thoroughly settle. The clear liquid is then removed by
means of leaden syphons, and conveyed along wooden gutters to the pre-
cipitating tubs, which stand upon a platform on a lower level. These
tubs, made of pine-wood, are 4 feet 8 inches high, with an internal diameter
of 3 feet 7 inches, and sides 2 inches in thickness. Each tub has two
taps, one quite at the bottom and the other some 5 inches higher up. A
wooden gutter runs over all the tubs, and has a hole and plug corre-
sponding with each; the liquid syphoned out of the extraction pots is
conveyed to this main channel by short movable gutters, and, by means of
plugs, can be let into any one of the tubs in the series.
At the same
time that this liquid is run in, water is introduced, from the pipe extending
over all the tubs, in sufficient quantity to ensure the precipitation of the
bismuth as oxychloride; the whole is stirred and the precipitate is allowed
to settle.
The residues in the extraction pots are again treated with acid and
water, and the solution precipitated as before; this treatment is repeated
until the solution obtained is so weak that on adding a large quantity of
water no appreciable precipitate is formed. The residues are then
removed, strained, dried, and when a sufficient quantity has accumulated,
are passed through the blast-furnace.
When the oxychloride of bismuth has completely settled in the pre-
cipitating tubs, the clear liquid is lot off by the upper tap, and conveyed
along gutters into large wooden settling tanks, in order to catch any
small quantity of the precipitate which may be carried over. From these
the liquors are run off, leaving the precipitate in the bottom. Another
charge of liquid is now run into the precipitating tub and treated in the
same way; several precipitations thus take place in each tub, until the
precipitate nearly fills the space between the taps. After the clear liquid
has been run off by the upper tap, the precipitate is stirred, drawn off by
the lower one, and conveyed on to filters similar to those used in the
Ziervogel and Augustin silver processes. Each filter-tub is connected
with a safety-tub of the same size, into which the filtered liquid runs
before going to the settling tanks.
This first precipitate obtained upon the filters is not sufficiently pure
to be reduced at once to the metallic state. It is, therefore, taken from
them, treated with acid and water, and re-precipitated; for this purpose
there is a special set of three smaller pots and three separate precipitating
tubs.
The second precipitate is almost pure; this is dried, and afterwards
reduced by fusion in iron crucibles, heated in a wind furnace with 50 per
cent. of carbonate of sodium, 7 per cent. of charcoal-powder, and 3 per
cent. of powdered glass.
The bismuth thus obtained is refined by re-melting in iron crucibles,
LEAD.
513
and the removal of the scum which forms. The resulting bismuth is
commercially of good quality.
The most important alloy of bismuth is that known as "fusible
metal," which consists of one part of lead, one of tin, and two of bismuth.
This mixture melts at a temperature of 93.75° C, and expands in cooling.
On account of this property of expanding while still in a pasty condition,
it is employed for taking impressions from dies, &c., as even the faintest
lines are accurately reproduced.
LEAD.
Lead is a soft metal of a bluish-grey colour, and when recently cut
possesses a strong metallic lustre; on exposure to the air it becomes
rapidly tarnished, and acquires a superficial coating of plumbous
carbonate.
Lead is both malleable and ductile, possessing the former property
to a considerable degree; but its tenacity is inferior to that of nearly all
the other ductile metals. It is flexible and inelastic, and fuses at about
325° C. When slowly cooled, imperfect octahedral crystals are readily
obtained. At a red-heat, lead becomes sensibly volatile, but not to a
sufficient extent to admit of its distillation.
When kept in a state of fusion, in contact with the air, rapid oxida-
tion takes place. At first the surface of the metallic bath becomes
covered by an iridescent pellicle, which is quickly converted into a
powder of a reddish-yellow colour. At a red-heat this oxidation of the
metal proceeds with great rapidity; and it becomes necessary, in order
to continue the operation, that the oxide, which gradually melts, should
be removed for the purpose of exposing a fresh metallic surface.
Lead, exposed to the influence of a damp atmosphere, quickly absorbs
oxygen, and when acid vapours are present this action is much accele-
rated. Oxidation is induced by the presence of carbonic anhydride,
which gives rise to the formation of a white carbonate of lead. Even
distilled water determines the oxidation of the metal, and from this cause
leaden cisterns are rapidly corroded when used as reservoirs for pure water.
A bar of lead, placed in distilled water and exposed to the air, becomes
rapidly covered with a white coating of hydrated oxide, which is subse-
quently converted into a hydrated carbonate of lead, frequently forming
distinct nacreous scales on the surface of the metal. In such cases the
water is invariably found to hold a portion of lead in solution, which is
readily shown by its becoming brown on passing through it a current of
sulphuretted hydrogen.
From the tendency exhibited by lead to form soluble salts it ought
not to be used for the manufacture of tanks in which water for domestic
purposes is to be kept, since, from the poisonous nature of these com-
pounds, the most disastrous effects have not unfrequently resulted.
2 L
514
ELEMENTS OF METALLURGY.
The action of water on lead is, however, found to be much diminished
by the presence of small quantities of various salts, and particularly
sulphate of calcium, which has the property of preventing, to a great
extent, the oxidation and solution of this metal.
The lead of commerce often approaches to a state of chemical purity,
and is then extremely soft and malleable. When lead of still greater
purity is required, it may be procured by reducing, in a lined crucible,
oxide of lead obtained by the calcination of crystallised nitrate of lead.
Lead is somewhat feebly attacked by hydrochloric acid, even when con-
centrated and boiling. Weak sulphuric acid does not act on lead when air
is excluded; but if heated in very strong sulphuric acid, SO, is evolved
and sulphate of lead is slowly formed. The proper solvent for lead is
nitric acid, which forms with it a salt readily crystallising, on cooling, in
opaque octahedra.
LEAD ORES.
Lead is very rarely found in a native state, but usually in combination
with one of the non-metallic elements, particularly with sulphur. It also
occurs in combination with oxygen, selenium, arsenic, tellurium, and with
various acids. The ores of lead are fusible before the blowpipe, and
when fluxed with a little carbonate of sodium on a charcoal support
yield a globule of metallic lead. The metal thus obtained gives off
fumes, particularly when heated in the outer flame, and stains the charcoal
of a yellow colour.
NATIVE LEAD; Plomb natif; Gediegen Blei. Isometric.-The characters
of native lead are precisely similar to those of ordinary commercial lead.
It is a rare substance, of which specimens have been found, associated with
galena, in the county of Kerry, Ireland, and in an argillaceous rock near
Carthagena, in Spain. Native lead has also been procured at Alston
Moor, in Cumberland, where it occurs, disseminated with galena, in a
siliceous rock.
OXIDE OF LEAD; Massicot; Bleiglätte. Orthorhombic.-Is a pulveru-
lent mineral of a bright red colour, sometimes mixed with yellow, and
is a mixture of different oxides of lead, affording a metallic globule
when heated on a charcoal support before the blowpipe. It is some-
times a volcanic product, but usually occurs associated with galena, and
is found in small quantities in many lead mines.
From the compara-
tive rarity of this ore it is of but little practical importance to the
metallurgist.
CHLORIDE OF LEAD; Plomb chloruré; Salzsaures Blei. Orthorhombic.—
This rare mineral, known as Cotunnite, is found in the lavas of Vesuvius.
An oxychloride of lead, termed Mendipite, occurs in the Mendip Hills,
in the form of lamellar, shining masses, of a greyish-white colour,
deposited on a matrix of black oxide of manganese. It has a specific
gravity of 7·07. When treated before the blowpipe it decrepitates, and
fuses into a globule of a yellowish-white colour; if heated on a charcoal
support, metallic lead is obtained. Another oxychloride of lead, and a
chloro-carbonate of lead, occur in Derbyshire.
LEAD.
515
SULPHIDE OF LEAD; Galena; Galène; Bleiglanz. Isometric. This
mineral occurs both in the primitive and invariously-modified forms. Its
cleavage, which is cubical, is extremely perfect. It more rarely occurs in
a finely-granular state, and is sometimes found in fibrous masses. Com-
pact specimens, although occasionally met with, are of comparatively rare
occurrence. Its colour and streak are lead-grey; fragile; lustre metallic;
specific gravity from 7.5 to 7·7. When pure, it is composed of lead
86-55, and sulphur 13.45. Its composition is represented by the formula,
PbS. The lead in this mineral is invariably associated, to a greater or
When silver is present in considerable quantity,
the ore receives the name of argentiferous galena, and becomes a valuable
source of that metal.
less extent, with silver.
The analysis of an argentiferous galena from Schemnitz afforded
Beudant the following results:
Pb
Ag
Ꮪ
79.60
7:00
·
13.40
•
100.00
In addition to sulphide of silver, galena sometimes contains variable
quantities of sulphide of antimony. This substance appears to alter in a
certain degree the character of the mineral; those specimens of which
the lamina are curved, as well as those which present a bright steely
fracture, will often be found to contain antimony.
Galena occurs in granite, limestone, argillaceous and sandstone rocks,
and is frequently associated with ores of copper and zinc. The matrix
on which this ore has been deposited is, in the majority of cases, either
quartz, calcite, fluor-spar, or sulphate of barium. The rich lead mines of
the West of England occur in clay-slate; those of Derbyshire, and the
other northern districts, are principally in limestone, as are also the
extensive deposits of Bleiberg and the neighbouring districts of Carinthia.
In the Upper Hartz, and at Przibram, in Bohemia, the lead mines are
in clay-slate; at Freiberg, in Saxony, in gneiss; at Sala, in Sweden, in
crystalline limestone; and at Leadhills, in Scotland, in the older grits.
Valuable deposits of galena are worked in various parts of France, and
particularly at Huelgoët and Poullaouen, in Brittany; at Pontgibaud,
Puy-de-Dôme; and at Vialas, in the department of Lozère. In Spain,
sulphide of lead is found in Catalonia and Granada, in the granite hills
of Linares, province of Jaen, and elsewhere. Galena occurs in Belgium,
at Védrin, not far from Namur; in Savoy; in Bohemia, at Joachimsthal,
where the ore is principally worked for silver; and in Siberia, where
argentiferous galena occurs in limestone in the Daouria Mountains.
Extensive deposits of this ore are likewise found in America, particularly
in the States of Missouri, Illinois, Iowa and Wisconsin.
Cuproplumbite is a variety of galena containing 24.5 per cent. of
sulphide of copper. It is a rare mineral, obtained from Chili.
Dufrenoysite is an arsenical sulphide of lead of a dark steel-grey colour,
from the dolomite of St. Gothard.
2 L 2
516
ELEMENTS OF METALLURGY.
Selenide of Lead or Clausthalite, is a mineral of a lead-grey colour and
granular fracture. When heated before the blowpipe it gives off the odour
of horse-radish. It occurs in quantities too small to render it of any
practical value as an ore of lead.
CERUSSITE; Carbonate of Lead; Plomb carbonaté; Kohlensaures Blei.
Orthorhombic. This mineral generally possesses a white colour and an
adamantine lustre. It is found in acicular crystals, in radiated and
compact masses, in concretions, and in earthy deposits. All these
varieties, with the exception of that last-mentioned, possess the peculiar
lustre belonging to white lead. It sometimes happens that crystallised
specimens of this substance are nearly black: this arises from the pre-
sence of small quantities of sulphide, probably due to the action of sul-
phuretted hydrogen, resulting from the decomposition of galena, with
which carbonate of lead is generally found associated. It is an extremely
brittle mineral, and, when amorphous, exhibits a conchoidal fracture.
When treated with nitric acid, it dissolves, with evolution of CO₂; before
the blowpipe it decrepitates, but when heated on a charcoal support
affords a button of metallic lead. Its specific gravity varies from 6·46
to 6.48.
Two specimens of this mineral afforded on analysis the following
percentage results:-
Crystals, from
Leadhills.
By Klaproth.
Crystals, from
Teesdale.
By J. A. Phillips.
Pbo.
82
83.55
CO2.
16
16.52
98
100.07
2
These results indicate a carbonate of lead, having the formula
PbO,CO₂ or PbCO3. The amorphous and friable varieties are gene-
rally more or less contaminated with siliceous and earthy impurities.
This mineral is found in splendid crystals at Leadhills, at Wanlockhead,
in Derbyshire, and in some of the Cornish mines, as well as in many
other localities. When abundant, it forms a valuable ore of lead, some-
times yielding above 75 per cent. of that metal. From its dissimilarity
to the other ores of lead, it was for a long time considered by miners to
be of no value; large quantities, which had been formerly buried in
rubbish, were subsequently excavated and worked with great advantage
in many of the Spanish mines, as also at different points in the valley of
the Mississippi, United States of America.
The artificial white lead of commerce so extensively used as a pig-
ment, is a carbonate of lead containing variable quantities of the hydrated
oxide of that metal. For this purpose it is prepared artificially by
exposing metallic lead, cast into thin bars, to the united action of acetic
acid and CO2, by which means the subacetate at first formed is changed
LEAD.
517
into carbonate by the presence of a large excess of CO2. The acetic acid
employed is usually obtained by the destructive distillation of wood,
whilst a constant supply of CO2 is procured by the decomposition of
thick layers of spent bark from the tan-yard. The lead to be operated on
is laid over pots containing dilute acetic acid, and after being loosely
covered with boards is buried in tan to the depth of about 10 inches. On
this is again placed another series of pots containing acetic acid; these
are covered by a second layer of tan, and so on until eight or ten layers
have been placed in the stack, which, from the fermentation which is
rapidly set up, soon begins to evolve large quantities of CO2. This
action or working of the stack continues during from ten to twelve weeks,
and when it has nearly ceased, the layers of tan, lead, and pots are suc-
cessively removed, and the white lead formed is beaten from the surface
of the unattacked metal to which it adheres. The lead carbonate is now
ground in a mill with a due admixture of water, and when it has assumed
the form of an impalpable paste is run off into large reservoirs, where
it deposits in accordance with its density. The wet lead, after being
removed from these cisterns, is first dried in large stoves by steam-heat,
and subsequently ground in oil for the market.
ANGLESITE; Sulphate of Lead; Plomb sulfaté; Schwefelsaures Blei.
Orthorhombic. This substance crystallises in prisms, which have an im-
perfect lateral cleavage and are often slender and implanted. Specimens
of sulphate of lead in amorphous masses and in lamellar and granular
fragments, are also found. It is colourless, sometimes inclining to grey
or green. Lustre adamantine, vitreous, or resinous. May be either
opaque or perfectly transparent. When pure, it consists of 73 per cent.
of oxide of lead, and 27 of sulphuric anhydride. If heated with car-
bonate of sodium before the blowpipe it affords a globule of metallic
lead. Its composition is represented by the formula PbO,SO, or
PbSO4
This mineral is usually associated with galena, by the oxidation of
which it appears to be formed.
Fine specimens of this ore are found in the lead mines at Leadhills
and Wanlockhead, as well as at Huelgoët in France, at Monte Poni in
Sardinia, and in the States of Missouri and Wisconsin in America; it
does not, however, occur in sufficient quantities to be regarded as an
important ore of lead. Its density is about 6·3.
Linarite, or Cupreous Anglesite, is a blue hydrated double sulphate of
lead and copper, sparingly found at Leadhills and at Roughten Gill.
PYROMORPHITE; Phosphate of Lead; Plomb phosphate; Buntbleierz.
Hexagonal. This mineral occurs in hexagonal prisms, of a bright green
or brown colour. These crystals, which have a lateral cleavage, are
often nearly transparent, and have sometimes a fine orange-yellow
colour, derived from the presence of chromate of lead. Pyromorphite
has a specific gravity varying from 6.5 to 7.1, and affords a white
streak.
Besides being found in crystals, it sometimes occurs in mammillary
518
ELEMENTS OF METALLURGY.
and reniform masses, with a radiated structure. The composition of
two specimens of this substance examined by Karsten was as follows:-

From Bohemia. From Cornwall.
Pb3(PO4)2
89.268
89.110
РЬСІ,
9.918
10.074
Ca,(PO4)2
0.771
0.682
PbF2
0.137
0.130
100.094
99.996
This composition indicates the proportion of three atoms of phosphate
of lead to one of chloride of lead; formula 3(3 PbO,P2O5)+PbC12, or
Pb5(PO4)3Cl. Phosphate of lead is found in many of the lead mines
in this country, and particularly in those of Cornwall, Leadhills, and
Wanlockhead. The phosphate of lead from Huelgoët, in Brittany, con-
tains large quantities of alumina.
Arseniate of Lead much resembles in appearance the phosphate of
that metal, but when heated evolves the odour of garlic.
Chromate of Lead is a mineral of a bright red colour, which crystal-
lises in rhombic prisms, and blackens before the blowpipe; when heated
on a charcoal support it forms a shining slag containing numerous globules
of metallic lead. It has a specific gravity of about 6·0.
A specimen of chromate of lead, analysed by Berzelius, gave the
following results :-
РЬО
CrO3
•
68.50
31.50
It follows from the above numbers, that this mineral is a simple
chromate expressed by the formula PbO,CrO3, or PbCrO4. Chromate of
lead is the “chrome-yellow" of painters, but is for this purpose artificially
prepared by adding a solution of chromate of potassium to a soluble salt
of lead. Native chromate of lead occurs in small quantities only, and is
chiefly obtained from Brazil and from Beresof in Siberia. Melanochroite
is another chromate of lead, and Vauquelinite is a chromate of lead and
copper.
Plumbo-resinite is a rare ore of lead, obtained at Huelgoët, in Brit-
tany, and from the Missouri mines in the United States of America. A
specimen of this substance from Huelgoët, analysed by Berzelius, was
found to be constituted as follows:-Oxide of lead, 40·14; alumina,
37·00; water, 18.80; insoluble gangue, 2.60. This mineral has a yel-
lowish or reddish-brown colour, and possesses a lustre much resembling
that of gum arabic.
All the other minerals containing lead are more or less rare, and in
no instance occur in sufficient abundance to allow of being metallurgically
treated as ores of this metal.
LEAD.
519
DISTRIBUTION OF LEAD ORES.
The ores of lead are abundantly distributed through the geological
series, but appear to be most abundant in rocks of Silurian and Car-
boniferous age, and frequently occur in deposits which cannot be regarded
as true veins. Lead veins are often rich in one stratum of rock, and
become suddenly and entirely impoverished on entering another more or
less differing from it in composition. Galena always contains a certain
amount of silver, but lead ores are not, generally speaking, argentiferous
to any considerable extent, unless they occur in crystalline metamorphic
rocks. The more argentiferous ores are, for the most part, found in true
veins occurring in the older rocks, and these, although not so productive
for lead as deposits in limestone, are generally more persistent in depth.
The ores of lead found near the surface embrace various oxidised
combinations, resulting from the decomposition of galena; among these
carbonate, sulphate and phosphate of lead are the most common.
The lead-producing districts of the United Kingdom are scattered
over England, Wales, Scotland, and Ireland; but that of the north of
England is, from the quantity of ore raised, the most important. It lies
chiefly in the vicinity of Alston Moor, where the three counties of North-
umberland, Durham, and Cumberland meet, and where the ore is obtained
from veins inclosed in the Mountain or Carboniferous Limestone. A
nearly horizontal bed of eruptive rock, known to the miners as the
"whin-sill," is intercalated between the limestone in an irregular manner.
The principal workings are on rake-veins, or true lodes; but there are two
other classes of deposit, known respectively as pipe-veins and flat-veins.
The rake-veins commonly exhibit the usual characteristics of regular
veins, although they sometimes do not descend through the strata in an
uninterrupted course, but are arranged in zigzags, one portion having a
general parallelism with other parts of the same vein above or below it,
and being connected with it by horizontal prolongations.
The lead-region of Derbyshire is in many respects very similar to
that above described, but is more complicated in its details, being much
broken up by faults; and instead of one bed of whin-sill, as in Cumber-
land, there are three. The ordinary gangue of these veins is calcite,
fluor-spar and sulphate of barium.
The lead mines of Cornwall and Devon are worked on true veins, and
the ores raised contain a notable amount of silver, but the production has
of late years considerably fallen off. At the time Borlase wrote (1758)
only one lead mine was worked in Cornwall, and in 1839 the whole
produce of the county was somewhat below 180 tons. In the years from
1845 to 1850 over 10,000 tons were annually raised, from 3,000 to
4,000 tons of metallic lead being produced annually from East Huel Rose
alone. This mine has long since ceased to be productive, and according
to Mr. Hunt's statistics, the present annual production of Cornwall is
about 4,098 tons of lead, containing 207,700 ozs. of silver. In Devon-
shire the Combe Martin and Beer Alston Mines, which formerly yielded
ores containing from 80 to 140 ozs. of silver per ton, have long since
520
ELEMENTS OF METALLURGY.
ceased to be extensively worked; the most considerable lead mine now in
operation in that county is at Frank Mills, in the vicinity of Exeter. The
Snailbeach Mines in the county of Salop, the Grassington Mines in York-
shire, and the Minera Mines in Denbighshire, have long been celebrated
for their large production.
The lead-region of Cardiganshire and Montgomeryshire extends over
a length of about forty miles, and varies from five to twenty-two miles in
width. The usual strike of the lodes, which are inclosed in rocks of
Lower Silurian age, is east-northeast; the gangue chiefly consists of
fragments of slate cemented together by quartz and calcite.
The total quantity of lead ore raised and sold in the United Kingdom
during 1872, of lead and silver produced therefrom, and the value of each
respectively, were as follow:-
Lead ore
Lead
Silver
Weight.
Value.
""
83,968 tons £1,146, 165
60,455
628,920 ozs.
1,209,115
157,230
In Belgium, galena and other ores of lead are found, associated with
zinc, in limestone. The annual production of the country is probably
equivalent to from 800 to 1,000 tons of lead.
In Prussia, lead mines of some importance are worked in the Siegen
district. The veins of the Upper Hartz are concentrated in two groups,
the one near Clausthal, and the other in the vicinity of Andreasberg. In
the neighbourhood of Clausthal and Zellerfeld the veinstone is chiefly
made up of a breccia of "country rock" cemented together by calcite,
carbonate of iron, quartz and heavy spar. The principal ore is argen-
tiferous galena, with small quantities of copper ore and blende; in some
cases the ores widen out into a Stockwerk 300 feet in width, and from
such aggregations of narrow veins, rich returns of ore are not unfrequently
obtained. The system of veins in the neighbourhood of Andreasberg is
included within a space about a mile in length and two-thirds of a mile
in width; in addition to argentiferous galena, they yield silver ores proper,
including pyrargyrite and light-red silver ore.
Besides the mines of Andreasberg and Clausthal, there are in the
Hartz those of Rammelsberg, situated in the neighbourhood of Goslar.
Here the principal mass of ore dips in the direction of the inclosing
argillaceous slates, and, at a depth of about 40 feet, sends off a branch at
a considerably less angle. The length of this mass is about 1,800 feet,
and its greatest thickness 150 feet, but these dimensions gradually de-
crease in depth. This remarkable mass is almost entirely composed of
sulphides of iron, zinc, lead and copper, without any notable admixture
of gangue. There are also extensive workings in the great lead-bearing
sandstones of Mechernich, in Rhenish Prussia, where from rock yielding
only 1 to 2 per cent. nearly 20,000 tons of lead are produced annually.
LEAD.
521
The total annual production of lead in Prussia was, in 1871, about
49,500 tons.
In Nassau lead ores are raised from a group of veins extending from
Holzappel on the Lahn to Welmich and Werlau on the Rhine; about
thirty small mines are worked on these veins, and are estimated to yield
800 tons of lead annually.
The greater proportion of the lead produced in the Austrian Empire
is obtained from the celebrated mines of Bleiberg and Raibel in Carinthia.
The village of Bleiberg is situated near Villach, in the Carinthian Alps,
and the mines extend along the valley of the Nötsch from Bleiberg to
Kreuth, a distance of five miles. The ore, which is chiefly galena and
carbonate of lead, with a little blende and calamine, occurs in deposits in
a rock, believed to be of the age of the Muschelkalk, although this point
does not appear to have been satisfactorily determined.
Next in importance to the mines of Bleiberg are those of Przibram
in Bohemia, where the galena forms contact deposits on the sides of
dioritic veins occurring in rocks of Lower Silurian age. The metal-
liferous portions of these veins, which are generally too poor to repay the
expense of working until a depth of fifty fathoms has been attained,
consist of a mixture of galena, sulphide of antimony, blende, and iron
pyrites, with occasionally a little grey copper ore.
The total average
production of the Empire is estimated at about 10,000 tons of metallic
lead annually.
The annual production of lead in Russia, Sweden, and Norway is
small.
Spain has long been celebrated for her lead mines, which were de-
scribed by Strabo, Diodorus Siculus and Pliny, as exceedingly nume-
rous and extensive. Under the Moorish dominion, mining operations
were conducted with considerable activity, but upon the expulsion of the
Moors from the country the art appears to have rapidly fallen into
decay.
The discovery of America and of its mineral riches, which took place
shortly after the expulsion of the Moors, caused the mines of Spain to
be comparatively neglected; but after the loss of her American colonies
it was found necessary to make an effort for the development of her own
mines. By a decree of Ferdinand VII. the mines of Spain were, in
1825, laid open on tolerably liberal conditions to the enterprise of all,
whether natives or foreigners, and in 1849 this law was supplanted by a
new one, by which still further privileges were conferred.
One of the first points to which Spanish mining enterprise was
directed, after the promulgation of the ordinance of 1825, was the lead-
district of the Sierra de Gador, in the province of Almeria, where, in
1826, operations had been commenced on above three thousand different
grants. For a time the production of this region was almost fabulous in
quantity; in the year 1827, according to Whitney, these mines yielded
the enormous amount of 42,000 tons of lead, so reducing the price that
the miners entered into a mutual agreement to work during one-half
the year only. These deposits are not in veins, and are compared by
522
ELEMENTS OF METALLURGY.
Le Play to an immense amygdaloid, in which the paste is limestone and
the amygdules galena. The limestone is of Silurian age.
From the nature of the deposits, it is evident that so large a produc-
tion could not be continuously kept up; and from 1827, when it attained
its highest point, the falling-off was rapid; at the present time these
mines are considerably less productive than formerly.
At present the principal lead-producing districts in Spain are
Linares, in the province of Jaen, Carthagena, province of Murcia, and
various mining-fields in the province of Almeria.* Lead ore is also
produced in the provinces of Granada, Estremadura, Badajoz, and to a
small extent in some of the northern provinces. The Linares district
may be said to embrace the neighbouring districts of Bailen, Baños,
Vilches, La Carolina, and Santa Elena, an area of about 84 square miles;
but three-fourths of the production comes from Linares proper, an area
of not more than 12 square miles. The veins occur principally in
granite, but occasionally also in clay-slate, the Bailen mines being the
most important ones in the latter rock. The ore obtained, principally
galena, is dressed to a produce of 75 or 78 per cent., and contains from
6 to 10 ozs. of silver per ton of ore. So-called carbonates are also pro-
duced, which, although containing a certain amount of earthy carbonate
of lead, depend principally for their value on partially-decomposed
galena; they are chiefly obtained from the smaller mines insufficiently
supplied with washing apparatus, and contain from 35 to 60 per cent. of
lead. A certain amount of slag is also obtained from washing the
heaps left by the ancients; their tenure in lead, when sold, being from
30 to 50 per cent.
The production of the Linares district is not less than 60,000 tons of
galena per annum, to which may be added 10,000 tons of carbonates and
10,000 tons of slags. The carbonates and slags are nearly all smelted at
Carthagena.
The Carthagena district may be said to include Herrerias, Porman,
Aguilas, Cabo de Gato, Sierra Almagrera, and others. When Carthagena
stood at the head of the list of Spanish lead-producing districts slags
were the principal source of produce. Including what is received from
Linares, about 30,000 to 35,000 tons of pig-lead are now produced
annually, principally from earthy carbonates found in layers in the lime-
stone rock. Excluding imports from Linares, it is not probable that
more than 8,000 to 10,000 tons of galena are smelted. The carbonates
of, say, 20 per cent. produce, are reduced, partly in numberless little
smelt-mills scattered all over the district, and also at Escombrera, three
miles from Carthagena, as well as at Carthagena itself, where there are
large smelting establishments.
Almeria, including Motril, Guadix, Sierra de Baza, Solana, Berja, &c.,
has greatly diminished its production within the last ten years. It for-
merly produced nearly 80,000 tons of ore annually; its present production
may be 20,000 to 25,000 tons of galena, yielding about 78 per cent. of lead.
* We are indebted to Mr. T. Sopwith, jun., for our information relative to the
present production of pig-lead in Spain.
LEAD.
523
The three districts named are the only ones in which mines are
worked on a large scale; an additional 7,000 or 8,000 tons will cover all
the remaining production of Spain. The total production of the country
is believed to be nearly as follows:--
Linares, exclusive of slags and carbonates, 60,000)
Tons of Pig-lead.
tons at 76 per cent. (giving 70% nett), or say
Carthagena, including slags and carbonates from
42,000
Linares
Almeria
35,000
•
20,000
Other districts, 8,000 tons at 76 % (or 70% nett)
5,600
102,600
or say, on an average, 100,000 tons of pig-lead annually.
In the Piedmontese Alps, the mines of Pesey and Macot have been
worked during the last 150 years, and, together with that of Saint Jean
de Maurienne, produced, according to Burat in 1846, about 250 tons
of lead and 19,000 ozs. of silver annually. In the island of Sardinia
there are numerous mines, producing considerable quantities of lead
and silver. Thirty-nine different mines are at present in operation,
their annual production of lead being about 14,000 tons, containing
364,500 ozs. of silver; in addition to this, Sardinia annually affords
about 900 tons of lead and 15,000 ozs. of silver, obtained by smelting
Roman and other ancient slags.
The total annual produce of the kingdom of Italy is estimated at
15,500 tons of lead, containing 385,000 ounces of silver.
The most important mines of argentiferous galena in France are
those of Pontgibaud in the Puy-de-Dôme, which are worked under the
superintendence of Messrs. J. Taylor & Co., of London. The ore, which
is much mixed with silica, contains a large amount of silver, and is
smelted in blast-furnaces of peculiar construction, after having been sub-
jected to a preliminary roasting. The annual yield of the Pontgibaud
mines is about 1,500 tons of lead and 145,000 ounces of silver; the total
annual yield of lead in France is estimated at 2,500 tons, containing
185,000 ounces of silver.
The principal lead deposits of the United States of America are
situated in the Mississippi Valley, and are embraced in the States of
Wisconsin, Iowa, Illinois and Missouri.
Attention was first directed to the lead deposits of this region by the
famous expedition of Le Sueur, who, in his voyages up the Mississippi in
1700 and 1701, noticed many lead veins along its banks. The mines of
Missouri had, however, been worked for some time before any further
attention was given to the comparatively remote region of the Upper
Mississippi; but in the year 1788 a Frenchman named Julien Dubuque,
who had previously settled in the district, commenced mines on the
western bank of the river on a tract of land which includes the now
flourishing town of Dubuque. The principal mining centres are Galena,
in Illinois; Mineral Point, in Wisconsin; and Dubuque, in Iowa.
The lead is almost exclusively found in a certain portion of the Lower
524
ELEMENTS OF METALLURGY.
Silurian formation, and there are no deposits in the Valley of the
Mississippi which can be considered as coming under the head of true
veins.
In many localities lead ore, called "gravel mineral or "float mine-
ral," is obtained by washing the superficial detritus. The principal
deposits are, however, in vertical fissures, with dark red ferruginous clay,
in which loose masses of ore appear to be promiscuously scattered;
besides the clay and ore in these fissures there are often intermixed with
them fragments of veinstone and pieces of the inclosing rock.
The ore
is also often found in flat sheets or horizontal deposits, and as in such
cases it is accompanied by gangue and is unmixed with clay, this is
probably the original form in which the larger portion of the lead was
deposited.
The lead of this region is extremely poor in silver, seldom containing
much above one ounce to the ton.
Numerous true veins containing galena occur in the Eastern States of
North America; but although these afford ores which are richer in silver
than those of the deposits of the Mississippi Valley they are but little
worked, and their yield of lead is comparatively small.
The present annual production of lead in the United States is pro-
bably about 40,000 tons, and the total production of the world is estimated
at about 300,000 tons.
ASSAY OF LEAD ORES.
The ores of lead may, for the purposes of assay, be divided into two
classes.
The first class comprehends all ores of lead and other plumbiferous
substances which contain neither sulphur nor arsenic, or in which these
bodies are present in small proportion only.
The second class comprises sulphide of lead, or galena, together with
all lead ores containing either arsenic, phosphorus, or sulphur.
From the facility with which lead is sublimed when strongly heated
it is necessary to conduct the assay of its ores at a moderate temperature,
as a notable quantity of the reduced metal would otherwise be driven off
in the state of vapour.
The furnace best adapted for making lead assays is constructed
similarly to that used for the fusion of the ores of iron and copper, but
may be of somewhat smaller dimensions. For this purpose, the internal
cavity for the reception of fuel should be about 9 inches square, and the
height of the throat from the fire-bars about 13 inches.
A furnace of this kind should be connected with a chimney of at
least 20 feet in height, and requires to be supplied with good hard coke,
broken into pieces of about the size of eggs.
ASSAY OF ORES OF THE FIRST CLASS. -The assay of ores belonging to
this class is a very simple operation, care being only required that a suffi-
cient amount of carbonaceous matter be added in order to effect the com-
plete reduction of the metal, whilst such fluxes are supplied as will afford,
LEAD.
525
by combining with the siliceous and earthy matters present, a liquid and
readily-fusible slag. The mineral to be assayed is first pounded in an
iron mortar, and passed through a sieve of wire-gauze. Those portions.
which remain on the meshes are again crushed until the whole has been
passed through, since if this were not attended to, a fair sample of the
ore could not be obtained; as the more sterile portions, being usually the
hardest, are the last to become sufficiently reduced in size.
When the ore has been properly ground, 400 grains may be weighed
out and well mixed with 600 grains of dry carbonate of sodium, and
from 40 to 50 grains of powdered charcoal, according to the supposed
richness of the mineral.
This is now introduced into an earthen crucible of such a size as to
be not more than one-half filled by the mixture, and on the top of the
whole is placed a thin layer, either of carbonate of sodium or of common
salt. The crucible and its contents are then placed in the furnace and
gently heated, care being taken so to moderate the temperature that the
mixture of ore and flux, which soon begins to soften and enter into
ebullition, may not swell up and flow over the sides. If the effer-
vescence becomes too strong, it must be checked by partially removing
the crucible from the fire, and by a due regulation of the draught by
means of the damper.
When the boiling has subsided and gas is no longer given off, the
heat is again raised during a few minutes and the assay completed.
During the process of reducing the metallic oxide or carbonate the heat
should not exceed rather dull redness; but in order to complete the
operation and render the slags sufficiently liquid to admit of the accumu-
lation of the lead in one button at the bottom of the crucible the
temperature must subsequently be increased to bright redness.
To remove
When the contents of the pot have been reduced to a state of tranquil
fusion, it must, by the aid of proper tongs, be removed from the fire,
and the assay poured into an iron mould; or, after having been tapped
gently against some hard body, to collect the lead in a single globule, it
may be set aside to cool. When the operation has been successfully per-
formed, the cooled slag will present a smooth concave surface, with a
distinct vitreous lustre. As soon as the crucible has become sufficiently
cold it is broken, and the button of lead carefully extracted.
from the metal, obtained either from the mould or by breaking the crucible,
the particles of adhering slag, the button is hammered on an anvil, and
afterwards washed and rubbed with a hard brush. If any portions of the
slag adhere so firmly as not to admit of being readily removed by mechani-
cal means, it may, in most instances, be separated by placing the button
for a short time in a little dilute sulphuric acid, by which the slag is
dissolved, whilst the metallic button remains unaffected. When the ore
has been properly fluxed, and a liquid slag consequently obtained, the
whole of the metallic lead will have collected in one mass at the bottom
of the pot; when a sufficiently fluid slag has not been produced, it
must be broken down in an iron mortar, and any metallic lead it may
contain separated by washing.
526
ELEMENTS OF METALLURGY.
Instead of employing carbonate of sodium and powdered charcoal, the
substance to be assayed may be fused with twice its weight of black
flux, and the mixture slightly covered by a thin layer of borax. Very
good results are also obtained by mixing together—
400 grains of plumbiferous matter,
500
200
""
""
carbonate of sodium, and
crude tartar.
These ingredients, after being perfectly incorporated, are placed in an
earthen crucible and covered with a thin layer of borax.
The three foregoing methods yield equally good results, and afford
slags containing but a very small portion of lead.
The assay of very rich lead products belonging to this class may
be conducted without the use of any kind of flux, as, when heated to
redness in a lined crucible, they are readily and completely reduced. It
is, however, desirable in all cases to add about 10 per cent. of sodium
carbonate, by which the adherence of any metallic globules to the char-
coal lining is prevented. This method, although requiring a longer time
than those already described, does not, even when rich ores are operated
on, afford more satisfactory results.
When the substance operated on, in addition to lead, contains other
metals-such as copper, silver, tin, or antimony--the button obtained will
retain a greater or less proportion of these metals in the form of an alloy;
if zinc be present in the ore, traces only of that metal will be discovered
in the resulting button of lead. For commercial purposes the resulting
button of lead is seldom subjected to chemical examination, as the purity
of the metal is usually judged of in accordance with its colour and soft-
ness; but when a more accurate knowledge of its constituents is required,
it must be made to undergo the usual routine of analysis. The carbonates
of lead are the most important minerals belonging to this class.
ASSAY OF ORES OF THE SECOND CLASS.--This class not only com-
prehends galena, which is the most common and abundant ore of lead,
but also comprises the sulphides resulting from various metallurgical pro-
cesses, as well as the sulphates, phosphates, and arseniates of that metal.
Galena. The assay of this ore is variously conducted, but one
of the following methods is most commonly employed for commercial
purposes.
The ore to be examined, after having been properly crushed and sifted,
is fused, either—
1. With sodium carbonate or black flux;
2. With metallic iron;
3. With sodium carbonate or black flux and iron; or,
4. With a mixture of nitre and carbonate of sodium.
First Method: Fusion with an Alkaline Flux.—This operation is con-
ducted in an earthen crucible, which is to be left uncovered until its
contents have been reduced to a state of tranquil fusion.
The powdered ore, after being mixed with three times its weight of dry
sodium carbonate, is slowly and gradually heated in an ordinary assay
LEAD.
527
furnace until the mixture has become perfectly liquid, when the crucible
is removed from the fire, and, after having been gently tapped to collect
any globules of metal which may be in suspension in the slag, is set
aside to cool. When cold, the crucible may be broken, and a button of
metallic lead, which must be cleaned and weighed, will be found at the
bottom.
Instead of carbonate of sodium, either carbonate of potassium or
black flux may be used; but when the last-named substance is employed,
a little longer time is necessary for the complete fusion of the mixture.
Every 100 parts of pure galena will, by this method, afford from 75 to
77 parts of metallic lead, indicating a loss of from 7 to 9 per cent. on the
contents of the ore.
Some of the older assayers were in the habit of first expelling the
sulphur by roasting, and afterwards reducing the resulting oxide with
about its own weight of black flux.
This process, from the extreme fusibility of the sulphides and oxides
of lead, requires very careful manipulation, and, at best, the results
obtained are far from satisfactory. Pure galena, by this method, can
rarely be made to afford above 70 per cent. of metallic lead.
Second Method: Fusion with Metallic Iron.-This process depends on
the circumstance, that when galena is fused in contact with metallic
iron, that metal becomes converted into protosulphide, whilst the lead
originally combined with the sulphur is at the same time liberated.
The amount of iron actually required for the decomposition of pure
sulphide is about 22.5 per cent.; but it is advantageous, in practice, to add
a small excess of this metal, and 30 parts of iron to every 100 parts of
galena may therefore be employed.
The iron used should be either in the form of small nails or in that of
wire cut into short pieces. This mixture of ore and metallic iron is placed
in an earthen pot, of which it should not fill above two-thirds the capacity,
and is covered with a thin layer of either carbonate of sodium or borax.
The crucible and its contents are afterwards heated to full redness, by
which a well-fused and perfectly-liquid slag is produced. When the
contents of the pot are observed to be in a state of tranquil fusion, it is
removed from the furnace and allowed to cool. It is then broken, and
at the bottom will be found a button, which at first sight appears to have
throughout a uniform composition, but on being struck with a hammer
readily separates into two distinct parts. The upper portion consists of
a bronze-coloured sulphide of iron, which at once crumbles under the
hammer and is readily removed; whilst the lower part consists of a button
of malleable lead, which must be carefully cleaned and weighed. This
process affords, from pure galena, about 78 per cent. of metallic lead.
The loss appears to arise principally from the volatility of galena, which
begins to be driven off at a lower temperature than that required for its
decomposition by the iron.
In the mining districts of North Wales this method of assay is some-
times conducted in a manner somewhat different from that described.
Instead of adding finely-divided iron to the ore, the pounded mineral is
528
ELEMENTS OF METALLURGY.
itself heated, without the addition of any kind of flux, in a ladle made
of that metal. This ladle or dish is formed out of a thick piece of plate-
iron and is provided with a lip, by which the reduced metal is to be poured
off, and with four projecting corner-pieces, which afford a holdfast for the
tongs by which it is removed from the fire. The ore to be operated on is
first coarsely powdered and well mixed, so as to insure a fair sample.
Eight ounces are now weighed out and placed in the dish, which is covered
with a lid of thin sheet-iron, and gently heated in the fire of a smith's
forge until the ore ceases to decrepitate. The temperature is then raised
to full redness, and at the expiration of about five minutes the decom-
position of the sulphide will be completed. At this point the dish is
removed from the fire and the reduced lead poured out into a cast-iron
mould, whilst the slags and sulphide of iron formed are kept back in the
dish by a piece of wood held before the spout for that purpose. The
dish, together with the slags and iron sulphide, is afterwards again placed
on the fire and heated to bright redness during another five minutes, by
which the last portions of metallic lead adhering to the slags are
obtained. The contents of the dish are now thrown away, as not con-
taining any further amount of lead, whilst the metal which has been
run off is carefully weighed. This apparently rude method affords, in
experienced hands, remarkably good results, which are likewise con-
sidered to approach very nearly to the practical returns obtained during
the metallurgical treatment on the large scale. By this process, pure
galena yields from 79 to 83 per cent. of lead; but with the poorer
varieties of ore, such as those obtained from some of the Cornish mines,
satisfactory results could not be obtained, since, from the infusibility of
the associated gangue, &c., a considerable amount of lead would be re-
tained in the slag. The ladles used for this purpose are rudely made
of plate-iron, which, if about one-fourth of an inch in thickness, will last
during three or four separate trials.
Third Method: Fusion with Carbonate of Sodium or Black Flux and
Metallic Iron.—When galena and sodium carbonate are fused together out
of contact with the air, a large proportion of the lead is liberated in the
metallic form, but the slag still retains a certain amount of that metal
in the state of a double sulphide of lead and the alkali-metal.
If finely divided iron be now introduced, the sulphide of lead con-
tained in the slag will be decomposed; metallic lead is liberated, and
the slag contains a double sulphide, in which iron will have replaced the
lead formerly present. The earthy and siliceous matters constituting
the gangue are also dissolved in the slag without, to any great extent,
impairing its fluidity.
The quantity of black flux or sodium carbonate employed varies with
the richness of the ore operated on; but even for the poorest varieties
two parts of the alkaline reagent will usually be found sufficient. The
iron, which is merely used to separate that portion of the lead which
has been dissolved by the alkali in the state of sulphide, need not be
present in sufficient amount to effect the reduction of the whole of the lead
contained in the ore treated. Two parts of black flux or sodium car-
LEAD.
529
bonate, and from 10 to 15 per cent. of metallic iron, either in the state of
filings or in the form of small nails, will be found a convenient quantity
for this purpose.
When the fusion is made with black flux, and the iron is in the state
of filings, it will be proper not to add too large an excess, especially if
the assay be conducted at a high temperature, as in that case the result-
ing button of lead will contain a portion of iron. If, however, carbonate
of sodium be employed, the addition of a small excess of iron is attended
with advantage, as it ensures the complete desulphurisation of the galena
without affecting the purity of the resulting lead.
Iron filings, when employed for this purpose, are also liable to become
mechanically intermixed with the lead, and thereby, to a certain extent,
falsify the results. This inconvenience is obviated by the use of small
iron nails, which are corroded only on the outside, and, at the termination
of the assay, are found fixed in the upper surface of the button, from
which they can without much difficulty be separated. Pure galena, when
thus treated, yields from 75 to 78 per cent. of metallic lead.
Mitchell, in his 'Manual of Assaying,' recommends the following pro-
cess, which is a slight modification of that long employed at the École des
Mines of Paris. Two earthen crucibles are prepared by smearing their
insides with black-lead, such as that used for domestic purposes, and in
each of these are placed, with their heads downwards, three or four large
flooring nails. Mix the ore to be assayed with its own weight of sodium
carbonate, and, after having placed it in the pots, press it tightly down
about the nails. On the top of this, place about half an ounce of common
salt, and above it an amount of dried borax equivalent to the weight of
the ore operated on. The whole is now introduced into the furnace and
gradually heated to redness; at the expiration of ten minutes the tempera-
ture is increased to bright redness, at which it is kept for another ten
minutes, when the flux will be fused and will present a perfectly-smooth
surface. When this has taken place, the pot is removed from the fire, and
the nails are separately withdrawn by the use of a small pair of crucible
tongs, care being taken to well wash each in the fluid slag until perfectly
free from adhering lead. When the nails have all been withdrawn, the
pot is gently tapped, to collect the metal into one button, and then laid
aside to cool; after which it is broken, and the button of lead removed and
cleaned in the usual way. The result is then verified by a second assay,
made in the other pot.
When carefully conducted, this process is said to afford, from pure
galena, from 84 to 843 per cent. of metallic lead. It is, however, liable
to the objection, that the lead produced often contains fragments of
iron, arising from the nails being most energetically acted on at the
point of contact between the flux and the galena, which, when the slag
becomes fused, occupies the lower portion of the crucible; by this means
portions of iron become detached and frequently adhere firmly to the
button, from which there is sometimes considerable difficulty in removing
them. We have never obtained by this process above 82 per cent. of
metal from the purest specimens of galena, but notwithstanding it affords
2 M
530
ELEMENTS OF METALLURGY.
results sufficiently accurate for most commercial purposes. In all cases
where earthen crucibles are employed the assay may be poured into
an iron mould, instead of breaking the pot; the crucible can be thus
preserved and used for a second assay.
In place of adding metallic iron to the mixture of ore and flux intro-
duced into the crucible, it is much better that the pot itself should be
made of that metal.
For this purpose, a piece of half-inch plate-iron, of good quality, is
turned up in the form of a crucible and carefully welded at the edges;
the bottom is closed by a thick iron rivet, which is securely welded to
the sides, and the whole is then finished up with a light hammer on a
properly-formed mandrel. The crucible, when finished, should have the
form represented in fig. 152. To make an assay in a crucible
of this description it is first heated to dull redness, and
when sufficiently hot, the powdered ore, intimately mixed
with about its own weight of a mixture of one part of
sodium carbonate and two parts of dried borax, is intro-
Fig. 152.
duced by means of a long copper scoop of the form repre-
sented in fig. 153, and the crucible, which, for the introduction of the
mixture, has been removed from the fire, is immediately replaced. The
heat is now gradually raised to redness, during which time the contents

}
Fig. 153.
become liquid and give off large quantities of gas. At the expiration
of from ten to fifteen minutes the mixture will be observed to be in a
state of tranquil fusion, and the pot is partially removed from the fire
and its contents briskly stirred with a small iron rod;
any matters adhering to its sides are also scraped down
to the bottom of the pot, which, after being again
placed in a hot part of the furnace, is closed with an
earthen cover and heated during three or four minutes
to somewhat bright redness. The crucible is then

Fig. 154.
Fig. 155.
seized by strong bent tongs on that
part of the edge which is opposite the
projecting lip, a, (fig. 152) and, after
being removed from the fire, its con-
tents are rapidly poured into a cast-
iron mould, fig. 154. Another form
of mould is represented in fig. 155.
The sides of the pot are now care-
fully scraped down with a chisel-edged bar of iron, and the adhering
particles of slag and of metallic lead are added to the portion first

LEAD.
531
obtained, by sharply striking the edge of the pot, firmly held in the jaws.
of the tongs, against the top of the cast-iron mould. When sufficiently
cold the contents of the mould are readily removed, and the button of
lead, after having been separated from the adhering slag, is carefully
cleaned and weighed. By this process pure galena yields, on an average,
84 per cent. of metallic lead, free from iron and perfectly malleable.
This method of assaying is that which is in almost universal use in lead-
smelting establishments, and has the advantage of yielding good results
with all the ores belonging to the second class. A larger amount of lead
is, however, obtained by assay than can be produced from the same ores
in the large way; on this account the smelter always makes an allow-
ance in accordance with the nature of the ore treated.
Instead of using iron pots, or adding metallic iron to the ores, they
may be fused with a mixture of black flux and oxide of iron; this method,
however, does not afford satisfactory results, and is not so convenient as
the processes in which an iron pot is employed.
Fourth Method: Fusion with Carbonate of Sodium and Nitre.--When
galena is treated with nitrate of potassium, the whole of its sulphur is
converted into SO, before any portion of the lead is oxidised; and it
consequently follows, that if a suitable amount of nitre were employed
the desulphurisation of the metal would be completely effected, and the
whole of the lead obtained in the metallic state. To prevent any loss
which might arise from the deflagration which takes place, the ore is
mixed with twice its weight of sodium carbonate, and to this, in accord-
ance with the richness of the ore, is added from 30 to 35 per cent. of
nitrate of potassium. When too large a quantity of nitre is employed, a
portion of the metal will be oxidised and will remain in the slag, causing
a corresponding deficiency in the weight of the button obtained; there-
fore, as the proper amount can only be ascertained by repeated experi-
ments, this process is but ill adapted for the assay of ores for lead.
When, on the contrary, an ore contains silver, and that metal only is
to be estimated, regardless of the amount of lead present, this process
may sometimes be employed with considerable advantage, although it is
generally less to be recommended than fusion with borax and sodium
carbonate in a wrought-iron pot, as before described. The assay with
nitre is very easily conducted; the fusion takes place readily, and with-
out bubbling, and the slag, which is very liquid, contains no metallic
globules. In conducting this operation, the amount of nitre should,
if possible, be so arranged as to afford the largest quantity of metallic
lead; but it is of especial importance that enough to decompose the whole
of the sulphide should be employed, since if the slag retain any unoxi-
dised sulphur-compound a loss of silver may be experienced. When, on
the other hand, too large a proportion of nitre has been made use of,
the accuracy of the silver estimations will not be impaired, as lead alone
is oxidised, and the whole of the silver will be contained in the residual
metallic button.
ASSAY OF GALENA CONTAINING ANTIMONY.-Many of the ores of lead
contain a certain proportion of antimony, and from such minerals,
2 м 2
532
ELEMENTS OF METALLURGY.
according to Berthier, the assayer can obtain, at will, either pure lead, or
a mixture of the two metals in the form of an alloy.
To extract pure lead the ore may be fused in an open crucible,
with three times its weight of sodium carbonate, when the lead will be
liberated in the metallic form, whilst the antimony, becoming oxidised,
unites with the alkali and remains wholly in the slag. The presence
of antimony in the slag also prevents its retaining any portion of the
lead, and from this cause a tolerably exact separation of the two metals
is obtained.
When, in addition to lead and antimony, the ore contains silver, it
should be assayed by being heated with a mixture of sodium carbonate
and nitre, by which the antimony will be oxidised and retained in the
slag, while the lead and silver are obtained in the state of an alloy. In
this case it is only necessary to add a sufficient amount of nitre to effect
the total decomposition of the sulphides, as even when the whole of the
antimony and a portion of the lead have been oxidised no loss of silver
(which combines with the remaining lead) is experienced; but when, on
the contrary, the slags still contain undecomposed sulphide of antimony,
a small proportion of the silver is lost.
When it is required to reduce at the same time both the antimony and
lead, the ore may be fused with a mixture of borax and sodium carbonate
in an iron pot, in accordance with the process before described for assay-
ing lead.
Sulphate of lead is readily reduced by simple fusion with black flux
and sodium carbonate in an earthen crucible; but when phosphates and
arseniates are present in ores of this metal their assay should be con-
ducted in an iron pot, with a proper admixture of carbonate of sodium
and fused borax.
Various methods have been proposed for the estimation of lead by
means of standardised solutions, but none of them appear to have been
successfully applied to the assaying of lead ores.
ESTIMATION OF SILVER IN LEAD Ores.
From the amount of silver contained in many varieties of galena and
other ores of lead it becomes necessary, in order to determine their
commercial values, to ascertain with great exactitude their yield of this
valuable metal.
To ascertain this, the button of lead, obtained by any of the processes
already described, is subjected to cupellation in a furnace properly arranged
for that purpose. This process is founded on the circumstance that silver,
when exposed in a state of fusion to the action of the air, neither gives
off perceptible vapours nor is sensibly oxidised, even when a more
oxidisable metal than itself is not present.
In order, then, to extract the silver contained in the buttons obtained
by the assay of lead ores, it is only necessary to expose them, on some
absorbent medium, to such a temperature as will oxidise the lead, whilst
the silver itself is not so affected. The litharge produced is absorbed by
LEAD.
533
the porous mass on which the assay is supported, and nothing but a small
button of pure silver ultimately remains in the metallic state.
These supports, called cupels, figs. 156 and 157, the first of which is a
section, are made of bone-ash, slightly moistened with
water, and tightly consolidated by pressure in an iron
mould.
A convenient furnace for the purpose of cupellation is Fig. 156. Fig. 157.
represented in figs. 158 and 159, of which the first is an elevation and the
second a vertical section. The material of which this furnace is made is

m
d
a
Fig. 158.
Fig. 159.
wrought-iron, lined with fire-tiles, as shown in the drawing. The muffle,
m, is a small D-shaped retort of fire-clay, closed at one of its extremities
only, and sometimes furnished with holes
or perpendicular openings in the sides and
end, in order to allow of a free circulation
of air internally through it. Fig. 160 repre-
sents such a muffle before its introduction
into the furnace. When fixed, it is so ar-
ranged that whilst one of its extremities is
supported by a proper shelf the other cor-

Fig. 160.
responds with the opening d', to the sides of which it is luted by a little
moistened fire-clay. This position of the muffle allows of its being
534
ELEMENTS OF METALLURGY.
heated on every side by a supply of ignited fuel, whilst a current of
air from the opening, d', circulates through the interior. The cavity of
the muffle is in this way constantly traversed by a highly-oxidising
current of air, and the draught of the furnace is increased by the addi-
tion of a chimney of sheet-iron, c. To light this apparatus a little
ignited coke or charcoal is introduced through the opening, d; the fur-
nace is afterwards filled with the same fuel, and all the openings, excepting
the ash-pit, a, are closed by their proper slides. When the charcoal or coke
is properly ignited, and the muffle has become red-hot, six or eight cupels,
which have been warming on the ledge around the chimney, are taken by
the tongs, fig. 161, and placed on the floor of the muffle, which, to prevent
its becoming corroded, if any lead should be spilt upon it, is previously
covered by a thin layer of ground bone-ash.

Fig. 161.
The opening, d', is now closed by its door, so as to prevent the intro-
duction of cold air, and the cupels are raised to the temperature of the
muffle itself. When this is the case, the door is again removed, and into
each of the cupels is introduced, by a pair of slender steel tongs, a button
of the lead to be assayed. The door is now, a second time, closed during
a few minutes, to facilitate the fusion of the metal, and on its removal
each of the cupels is found to contain a bright convex metallic disc,
in which state the assays are said to be uncovered. The air thus admitted
rapidly converts the lead into litharge, which, as fast as it is produced, is
absorbed by the bone-ash of the cupel, and at the same time there arises
a white vapour, which partially fills the muffle, and either escapes at
the mouth, or is carried off through the openings in its sides. An annular
stain, which gradually extends, is at the same time formed around the
metal, and penetrates into the substance of the cupel, in proportion as the
metallic globule itself diminishes in size. When nearly the whole of
the lead has been thus converted into litharge, and has been absorbed, the
remaining bead of rich alloy appears to become agitated by a circular
movement, by which it seems to be made to revolve with great rapidity.
At this stage of the operation the agitation will be observed suddenly to
cease, and the button, after having for a moment emitted a bright flash of
light, becomes white and immovable.
This phenomenon is called the brightening of the assay, and a button
of pure silver now remains on the cupel.
If the cupel were at this period abruptly removed from the muffle
the metallic globule would be liable to sprout or vegetate, by which a
portion of it is not unfrequently thrown off and lost, while its surface is
covered by numerous arborescent asperities. To prevent this from taking
place, and to guard against the loss of metal which would be liable to
ensue, the cupel on which the button of silver has brightened may be
LEAD.
535
covered by another, kept red-hot for that purpose. The two are sub-
sequently withdrawn together, and allowed to remain on the ledge before
the muffle until the metal has become solidified, when the upper cupel
may be removed, and the globule of silver may be detached and weighed.
From the circumstance that silver is sensibly volatile at very elevated
temperatures, it becomes necessary to make cupellations for this metal
at the lowest heat by which the absorption of litharge can be readily
determined. If, however, the cupel be not sufficiently hot, an annular
incrustation of crystalline litharge will begin to accumulate around its
edges, and if, at this point, the fire be not immediately attended to the
deposit of oxide spreads over the whole surface of the metal, and its
further oxidation is entirely stopped.
The temperature best suited for this operation is obtained when the
muffle and the inclosed cupels are at a full blood-red heat, and the
vapours which arise from the alloy curl gradually away and are promptly
removed by the draught. When the muffle is heated almost to whiteness,
and the vapours rise to the crown of the arch, the temperature is too
high, and when, on the contrary, the fumes lie over the bottom, and the
sides of the openings in the muffle begin to blacken, more fuel must be
added through the door, f, and the heat gradually raised. When the
operation is conducted at the proper temperature, the cupel should be of
a full-red colour, and the fused alloy bright and convex.
At the com-
mencement of the operation the heat must be a little raised, for the
purpose of fusing and uncovering the button, and just before the globule
is about to brighten a slight elevation of temperature is again advan-
tageous, but if a good red-heat has been kept up during the working of
the assay, this is by no means necessary.
The success of the operation is likewise considerably influenced by
the force of the draught passing through the muffle. When the current
is too rapid, the cupel becomes cooled, and the lead is oxidised with
greater rapidity than it should be; in this case the litharge produced is
sometimes not absorbed by the test as fast as it is generated, and con-
sequently the surface of the alloy is covered by a layer of oxide of lead,
by which it may ultimately become protected from further oxidation.
When, on the contrary, the current is too feeble, the assay remains too
long in the muffle.
If an assay has been properly conducted, the button of silver is
round, bright, and smooth on its upper surface, and beneath should be
crystalline, and of a dead-white colour; it is easily detached from the
cupel, and readily freed from adhering litharge. This globule is now
removed and squeezed between the jaws of a pair of pliers, by which the
oxide of lead, which attaches itself to it, becomes pulverised, and is
easily removed by scratching with a small brush made of stiff hogs'
bristles. The cleaned metallic bead is afterwards weighed in a balance
capable of turning with Too of a grain.
1
1000
The fuel employed in the furnace above described, after it has
once got into steady action, consists of small pieces of hard coke. When,
in addition to silver, ores of lead likewise contain gold, the button
536
ELEMENTS OF METALLURGY.
remaining on the cupel will consist of an alloy of these metals, the
separation and estimation of which will be treated of under the head of
parting when describing the assay of gold ores.
In laboratories in which assays of gold and silver are constantly made,
the furnace above described, which has holes in two opposite sides closed
by stoppers, t, (and can consequently be used as a tube-furnace), is some-
times found inconvenient, on account of its small size, &c. For this
reason, either fire-clay furnaces bound with iron, or stationary furnaces,
forming part of the building of the laboratory, are frequently used.
For commercial purposes, the silver contained in any given ore is
estimated in ozs., dwts. and grains; one ton being, in all cases, taken as the
standard of unity.
TABLE SHOWING THE AMOUNT OF SILVER TO THE TON OF ORE, CORRESPONDING
TO THE WEIGHT OBTAINED FROM 400 GRAINS.
lf 400 Grains of
Ore give Fine
Metal
One Ton of Ore
will yield
If 400 Grains of
Ore give Fine
Metal
One Ton of Ore
will yield
gr.
oz. dwt. gr.
gr.
Oz.
dwt. gr.
·001
0 1 15
· 200
16
6 16
·002
0
·003
ون جهر
6
· 300
24
10 0
4 21
•
· 400
32
13 8
·001
6 12
⚫500
40 16
16
·005
8 4
· 600
49
0 0
·006
0 9 19
•700
57
3 8
·007
0
11 10
⚫800
65 6 16
·008
0 13
1
•900
73 10 0
·009
0 14 16
1.000
81 13 8
·010
0 16
8
2.000
163 6 16
⚫020
1 12
16
3.009
245 0 0
⚫030
2 9
0
4.000
326 13 8
·040
3 5
8
5.000
408 6 16
⚫050
4 1
16
6.000
490 0 0
⚫060
4 18
0
7.000
571 13
8
⚫070
5 14
8
8.000
653 6 16
·080
6 10
16
9.000
735 0 0
⚫090
7 7
0
10.000
816 13 8
•
· 100
8 3
8
The bone-ash employed for making cupels is first passed through a
sieve of wire gauze, and afterwards mixed with water until sufficiently
moistened to retain the mark of the fingers, when a handful is taken
up and
tightly squeezed. To cause the cupels when made to be sufficiently firm
and resistant, a little potassium carbonate is often added to the water
employed for moistening the bone-ash. The amount of alkaline carbonate
required for this purpose is exceedingly small, as a fragment of the size
of a nut will be sufficient to add to a pint of water. Instead of water,
some persons use sour beer, and in this case dispense with the use
of alkali. The mould in which the cupels are formed, fig. 162, usually
consists of a bevelled steel ring b, and a die, a, made of the same metal
and often fitted with a wooden handle. To make the cupel, this cavity is
nearly filled with the moistened bone-ash, which is first compressed
LEAD.
537
slightly by the hand and afterwards with the die, which is tightly driven
into the ring by the use of a wooden mallet, fig. 163. When sufficiently
consolidated the die is withdrawn, and, by
introducing a wooden cylinder exactly
filling the aperture, the cupel is without
difficulty removed. The use of the
wooden cylinder is sometimes liable to
crumble the edges of the cupel; and for
this reason a loose iron plate, c, exactly a
fitting the bottom of the mould, is often
introduced before the bone-ash is placed
in it. When this precaution is taken, b
the iron protects the bottom of the cupel,
and enables the operator to use consider- c
able force without injury to the edges of
the newly-made test. The iron plate has
obviously to be replaced at each operation, and, with the cupel before it,
is again forced out of the mould; in establishments in which a large
number of cupels are used they are frequently made by the aid of a screw-
press. When made, they are set aside to dry, and are then ready for
use; but it is better, if possible, to keep cupels at least three or four
weeks before using them.


Fig. 162.
METALLURGY OF LEAD.
Fig. 163.
By far the larger proportion, probably above nine-tenths of the lead
annually produced, is obtained from galena, which before coming into the
hands of the smelter is usually freed, by careful mechanical preparation,
from the principal part of the earthy and siliceous veinstone with which it
was originally associated. The metallurgical treatment of the ores of
lead may be effected by either of the following general processes :—
First. By what is known as the method of double decompositions, or,
as it is sometimes called, method by reactions. This is founded on the fact
that when PbS is roasted at a gentle heat, it is partially converted into
PbO and partly into PbSO4, and that on raising the temperature the fol-
lowing reactions are set up :
2PbO+PbS=3Pb+SO,
PbSO₁+PbS=2Pb+2SÖ₂.
Secondly. By roasting and subsequent reduction of the oxidised pro-
ducts, chiefly by carbonaceous matter.
Thirdly. By what is known as the precipitation process, in which
the desulphurisation of the lead is effected by metallic iron.
Two of these processes, and sometimes even all of them, may be
combined in the treatment of a lead ore.
Lead-smelting is conducted in three distinct varieties of apparatus,
which may be thus classified :
1. Reverberatory furnaces.
2. Blast-furnaces.
3. Shallow hearths.
538
ELEMENTS OF METALLURGY.
SMELTING IN REVERBERATORY FURNACES.
FLINTSHIRE PROCESS.-This, which is essentially a method by double
decompositions, comprehends the following distinct operations:-
a. Calcination at a low heat in order to produce a certain amount of
oxide and sulphate of lead.
b. So raising the temperature as to determine the fusion of the cal-
cined products, thereby causing the liberation of a large amount of lead
by the reaction of its oxide and sulphate upon the unchanged sulphide.
c. The incorporation of the residue with lime, and the reduction of
the unchanged sulphide, with formation of a larger amount of oxidised
lead-compounds than is required to effect the decomposition of the sulphide
of lead.
d. Tapping the reduced lead, and the subsequent removal of the pasty
grey slag by drawing.
The furnace employed for the reduction of lead ores by the Flint-
shire process varies somewhat in its construction and dimensions; the
length of the hearth is usually about 11 feet, and its width 9 feet, and
under this is an arched vault, extending the whole length of the bed to
the fire-bridge. The hearth is made of slags, moulded into the proper
form when in a plastic and semi-fused state, and has towards its
centre a depression in which the fused metal accumulates, and at the
bottom of which is situated the tap-hole. The fire-place is at one end,
and before reaching the cavity of the furnace the flame has to pass over
a fire-bridge, about 2 feet in width and from 12 to 14 inches below the
arch; at the opposite extremity of the hearth are openings communi-
cating with a flue in connection with a lofty chimney. The fuel is
supplied through a door at one end of the fire-place, in addition to
which the furnace is furnished with six working doors, usually about 9
by 12 inches, protected by heavy cast-iron frames built into the brick-
work, and closed by iron plates, which can be easily removed when
required. The slag bottom of this furnace is made nearly level with the
doors on one of the sides, but is inclined towards the other in such a way
as to be from 18 to 20 inches below the middle door, where it com-
municates with the tap-hole. A cast-iron tapping-pot is set in the ground
beneath the tapping-hole, and on the top of the furnace is a large hopper,
from which a fresh charge of ore is let down as soon as that which
is being worked is withdrawn.
The charge of such a furnace is usually, in North Wales, 21 cwts., but
as much as 24 cwts. are sometimes operated on at one time. In the
neighbourhood of Newcastle the charges are considerably smaller. As
soon as the lead from the preceding operation has been tapped off, and
the slags cleared out and removed, another charge of ore is dropped from
the hopper upon the hearth, which is at this time but barely red-hot.
This is spread in a tolerably even layer over the surface of the bed, care
being taken to prevent any portion of it from falling into the deep part
of the furnace or well. The charge is now frequently stirred during
two hours, the supply of air being regulated by the partial opening or
LEAD.
539
closing of the various doors, and the highest temperature, compatible
with keeping the charge free from clotting, is maintained. At the expi-
ration of this period the fire-bars are clinkered, and fresh fuel is thrown
upon the grate. The charge now begins to assume a pasty condition, and
any portions which may have run down towards the tap-hole are brought
back to the higher parts of the hearth. The doors are then opened for
the purpose of lowering the temperature, and as soon as the charge has
acquired the consistency of stiff mortar, it is spread before the fire-bridge
and upon the portions of the hearth furthest removed from the tapping-
hole.
This accomplished, the fire- and furnace-doors are again closed, the
charge is run down as quickly as possible into the well, and a couple
of shovelfuls of slaked lime are thrown upon its surface and incorporated
with the mass by stirring with a rake. By this means, the slags and
unreduced ores are rendered sufficiently pasty to allow of their being
again arranged or set-up on the sloping sides of the hearth, where they
are calcined for about half an hour, and again run down; during this
latter portion of the operation, a little coal-slack is sometimes thrown
upon the charge. When the whole of the charge has again collected in
the bottom, a further addition of slaked lime is made, and the slag is
pushed off from the surface of the metal upon the inclined sides of the
well, where it is allowed to drain; the lead is now tapped, and the grey
slag is withdrawn in pasty lumps through the doors at the back of the
furnace.*
The slags and matts which accumulate on the surface of the tapping-
pot contain a considerable amount of mechanically intermixed lead, to
separate which a paddle is inserted and the whole is well stirred.
Some coal-slack is now thrown in and well worked up with the contents
of the pot; this gives off a considerable amount of gas, which being
ignited affords sufficient heat to liberate the metallic lead. The surface
is then skimmed, the skimmings being at once thrown back into the
furnace, and the lead is laded out into cast-iron moulds; after this the
tap-hole is again opened, and the lead from the skimmings run out into
the pot, where it is allowed to remain until that resulting from the next
charge is withdrawn. The tap-hole is now closed, and another charge
let down into the furnace from the hopper placed above it.
The lead ores treated by this process in Flintshire generally contain
* The following analysis of grey slag from a Flintshire furnace was made in
Dr. Percy's laboratory by Mr. C. Tookey :—
PbS.
PbSO
РЬО.
ZnO
CaO
A1203
•
•
Fe2O3
Sio, (combined).
Insoluble residue
0.90
9.85
48.87
7.52
12.68
3.01
•
2.86
12.52
1.45
99.66
540
ELEMENTS OF METALLURGY.
from 75 to 80 per cent. of lead, and a charge of such ore may be worked
in from five and a half to six hours, yielding about 90 per cent. of the total
quantity of the lead obtained; the remaining 10 per cent. being sub-
sequently extracted from the slags and fume.
MODIFICATION OF THE FLINTSHIRE PROCESSES AT COUËRON.-Through
the kindness of Mr. W. Hutchison, manager of the Lead-Works, at
Couëron, Loire Inférieure, France, belonging to Messrs. P. Bontoux and
R. Taylor, we are enabled to give some particulars of the process of
smelting by double decompositions, as modified in that establishment.
The construction of this furnace will be readily understood by refer-
ence to the accompanying woodcuts. Fig. 164, is a longitudinal section;
fig. 165, a horizontal section on the line C D; and fig. 166, a transverse
section through the tapping-hole. The fire-place, A, is of the usual
3 2 2 2

-D
a
Ta
A
W.J.WELCH.SC
Fig. 164. Smelting Furnace, Couëron; longitudinal section.
dimensions, and the hearth, B, instead of being on an arch, as is com-
monly the case in North Wales, is supported on iron bars, on which is
laid a course of flat tiles. On these is placed a course of fire-bricks on
edge, on which is arranged the usual slag bottom. The furnace has the
ordinary number of working doors, a, with a fire-door, b, and tapping-
hole, c; there is a small fire-place below the pot, d, to prevent the too
rapid chilling of the lead during the process of lading into moulds.
Although similar in form and dimensions to the ordinary Welsh furnace,
it differs from it in one important particular, namely, in having the
tapping-pot placed near the flue end instead of under the middle door.
This arrangement gives a larger surface to the hearth for roasting the
charge, and permits of the lead being collected in the coolest part of the
furnace, where it is least exposed to loss from volatilisation.
The mode of working employed varies with the nature and composi-
LEAD.
541
tion of the ores treated. This variation depends principally on the length
of time required for roasting the ores before subjecting them to the
higher temperature of reactions. Pure ores, especially those containing a


a
a
a
a
b
Fig. 165.-Smelting Furnace, Couëron; horizontal section on C D.

a
B
d
Fig. 166.-Smelting Furnace, Couëron; transverse section through tapping-hole.
notable proportion of carbonate or sulphate of lead, require very little
previous roasting, whilst those containing blende, pyrites, &c., must be
calcined for a considerable time before smelting.
In general, the ores treated are derived from Sardinia, and contain,
542
ELEMENTS OF METALLURGY.
on an average, 81 per cent. of lead and but little silver. They are toler-
ably free from impurities, being composed of galena associated with car-
bonate and sulphate of lead, and a calcareous gangue, in which are
found small quantities of blende, calamine, ferric oxide and silica. The
cobbed ores, before delivery to the furnace, are ground between rollers,
and passed through sieves of eight holes to the linear inch; a charge
of ore weighs 27 cwts. Two men are employed at each furnace, one of
whom, the chief, works on the fore side, and takes a leading part in the
work to be done. In the treatment of rich ores, the ordinary method
of working consists in roasting them in such a manner that upwards
of one-half of the sulphide of lead present in the ore is converted into a
mixture of oxide and sulphate.
On raising the heat in the furnace to bright redness, the oxide and
sulphate, formed in roasting, react on the undecomposed sulphide in the
charge, and produce metallic lead, sulphurous anhydride, and a residue of
slag.
The process is thus divisible into two well-marked and distinct opera-
tions :-
a. Calcination or oxidation.
b. Smelting or reactions.
a. Calcination.—Supposing a charge to have been just worked off,
and the residual slags withdrawn, the furnace will be empty and at a red-
heat. The damper having been lowered, the charge of ore in the hopper, e,
is let down through the opening in the arch, and spread evenly over
the furnace bottom by means of rabbles.
This done, the working doors are closed, but the fire-door is left open
and the fire damped with cinders, in order so to moderate the heat that
the charge may become gradually red-hot without clotting. The charge
is thus left undisturbed for some time. During the first hour it is once
or twice lightly rabbled; at the expiration of that time, after being well
turned with the paddle, it will be found red-hot throughout. The damper
is then lowered so as to leave just sufficient draught for the free escape
of the gaseous products of calcination. The working doors are now left
partially open to admit the air necessary for the oxidation of the galena,
and under its oxidising action the charge soon acquires a high tempera-
ture. Care must however be taken to prevent the heat from so much
increasing as to cause softening of the ore.
When the heat is properly managed, a white crust consisting of a
mixture of oxide and sulphate of lead, in which the former predominates,
is rapidly formed on the surface of the charge, and no fumes are visible.
The surface is renewed from time to time, about every quarter of an
hour, either by rabbling or by paddling.
The requisite heat is maintained in the furnace during this process
by firing with cinders only, which are preferable to coal for that purpose;
not merely on account of their lower value, but also because they give a
steadier heat and do not yield gaseous hydrocarbons to interfere with
oxidation.
The alternate raking and paddling of the charge is continued at
LEAD.
543
regular intervals, until, on examination, it is thought to be sufficiently
desulphurised, which is generally the case at the end of from four to four
and a half hours.
The grate is then freed from clinker, coal is thrown on the fire, the
damper is opened, and a brisk fire is got up; in a few minutes the heat in
the furnace is thus raised so as to lead to a commencement of the period
of reactions.
b. Smelting.—As soon as the firing has commenced, the ore lying at the
back and extreme end of the furnace is raked towards the bridge. With the
increase of temperature which now takes place, the roasted ore soon begins
to soften and to give off white fumes, thus showing that the reactions
which result in the liberation of metallic lead have commenced. Great
care and attention on the part of the smelter are, however, necessary, in
order to prevent too great a loss of lead by volatilisation, during the
heating-up of the charge. The ore must on no account be allowed to
liquefy, and as often as it shows a tendency to fuse, some slaked lime in
powder is thrown on the charge, and well worked into it with a rake.
By this means, and by carefully regulating the draught, the charge can
be heated to the required temperature without fusion; lime must be fre-
quently added during the process, but in small quantities at a time. The
consumption of lime amounts, altogether, to about 2 per cent. of the ore
treated.
Shortly after reaction commences globules of lead may be seen on the
surface of the charge, and before an hour has elapsed a certain quantity
of lead has drained down the slope of the hearth into the well. The
charge, having in due time attained the temperature of bright redness,
must not be fired too hard; both the draught and the firing are so regu-
lated as to keep up the heat to the required degree without going
beyond it.
The reactions are much aided by frequently rabbling and turning the
ore; but as the working doors must remain open for this purpose, it
follows that a large quantity of air enters the furnace, thus oxidising the
sulphide in the ore, and so cooling the charge that the flow of lead
becomes interrupted. When the cooling is judged to have been carried
sufficiently far, the charge is rabbled, the doors closed, and the fire so
urged as to fill the furnace with flame during several minutes; on re-
opening the doors and paddling, the flow of lead re-commences as before.
At the expiration of from two and a half to three hours from the com-
mencement of the reactions, a considerable amount of lead will have accu-
mulated in the well. A first tapping is then made, the lead being received
in the tapping-pot, under which a small fire has been previously lighted in
order to warm it, and to maintain the lead in a melted condition; the tap-
hole is stopped with a plug of stiff clay.
The thick dross which rises to the surface of the lead, and which
contains a certain quantity of sulphide removed from the charge by the
hot lead, and again separated on cooling, is skimmed off with a shovel
and put back into the furnace. A little fine coal, together with some
burning cinders and lime, is now thrown on the lead, which is vigorously
544
ELEMENTS OF METALLURGY.
agitated with a small paddle and stirred until it is clean. It is then
skimmed, the skimmings being put on one side, and the clean lead laded
into moulds.
The firing, paddling, and cooling of the charge are repeated several
times, until at last the residue becomes dry, and gives out but little lead.
Thereupon the heat in the furnace is considerably increased, but not in a
degree to fuse or flow down the charge, and towards the close of the
operation the matters remaining on the hearth consist, to a great extent,
of oxides.
The pot-skimmings, composed of cinders and lead matt, are now thrown
into the furnace, and well paddled with the charge; the reaction of the
sulphide of lead and cinders on the oxide and sulphate producing a
further yield of lead.
When this has ceased, and it is seen that no more can be extracted
without a very high heat and the addition of coal to the charge, the grey
slag is raked out through the middle door at the back of the furnace, and
the second and last tapping is made.
The whole period of reactions occupies from five to five and a half
hours.
After the withdrawal of the slags, the bottom is examined, and if cor-
roded into holes, or in any way injured, it is repaired by putting into the
cavities a mixture of grey slag and lime, and beating it smooth with the
paddle. It is of great importance to maintain the bottom perfectly
smooth and with a good slope on all sides towards the tap-hole. A little
lime is now spread over the bottom, and a fresh charge is at once let down
into the furnace; the damper having been previously lowered to prevent
loss of fine ore by the draught. The weight of coal consumed is equal to
40 per cent. of the ore smelted. The produce of lead per charge of 1,350
kilos of ore at 81 per cent. is 15 pigs, weighing 901 kilos, and 290 kilos
of slags containing 50 per cent. of lead. Hence the total loss of lead in
the reverberatory furnace is 3-52 units by volatilisation, but of this a
certain proportion is recovered from the fume collected in the condensers
and flues. A larger percentage of lead in pigs might be obtained by
adding more coal to the charge, towards the end of the process, and firing
hard, in order to reduce part of the lead remaining in the slags. It is,
however, considered more economical to limit the produce in the rever-
beratory to about 80 per cent. of the lead contained, and to carry the
richer slags to the blast-furnace. This is especially the case when the
blast-furnace is connected with good condensers and long flues.
It will be seen from the foregoing description that the process of
reverberatory smelting adopted at Couëron differs principally from that
generally employed in England, in there being no melting or flowing-
down of the charge, as also in the long preliminary calcination of the ore
before the reactions are commenced. The position of the tap-hole near
the flue end of the furnace gives a longer slope to the hearth, and allows
of heavier charges being worked; at the same time the lead produced is
collected in the well at a greater distance from the fire.
CORNISH PROCESS.-This process is still employed at Par, near St.
LEAD.
545
Austell, where are situated the only lead-smelting works at present in
operation in Cornwall; it was also formerly in use at Point, near Truro,
as well as at the Falmouth Smelting Works; but smelting operations at
the last two establishments have been for some time abandoned. The
lead ores treated by this method consist principally of galena, usually
containing a considerable amount of silver, with blende and various sul-
phurised ores of copper, associated with a siliceous gangue; their average
yield of lead is between 60 and 70 per cent., and of silver about 35 ozs.
per ton.
This process comprehends two distinct operations, each conducted in
a separate furnace:
a. Calcination or roasting,
b. Flowing or smelting.
a. Calcination. The furnaces used for this purpose vary considerably
in size, some of them working charges of only 25 cwts., while others are
capable of taking charges of 3 tons; the average charge for such furnaces
may be taken at from 1 ton 18 cwts. to 2 tons. The Cornish calciner has
generally three working doors; two being in the longer sides and oppo-
site each other, whilst the third is at the extremity of the longer axis of
the hearth, in the immediate vicinity of the flue leading to the chimney.
The widest part of the hearth is that between the two lateral doors; at
the fire-place it has little more than one-third its maximum width, and
at the opposite extremity its dimensions are gradually contracted to the
width of the working door. Immediately within the two lateral doors
are rectangular holes in the bed, through which the calcined ore is raked
into an arched vault situated beneath. A passage through the fire-bridge,
of which one side is formed by a strong supporting bridge-plate of cast-
iron, admits of the free circulation of air; the charging is effected through
a hole in the roof, which is usually covered by a fire-tile. Externally
this furnace is built of ordinary rubble-work, but is internally provided
with a nine-inch lining of fire-brick; the working doors have either
strong cast-iron frames, or their sides are protected by large blocks of
granite; the calciner is usually worked by two men on each shift. Cal-
cination is effected at a high temperature, and the charge is turned over
once every hour; the operation is usually continued during from 15 to
18 hours, and a little lime added from time to time to prevent clotting;
about 6 cwts. of coal are consumed per ton of ore calcined.
b. Flowing. The furnace employed for this operation is very similar
to that used for the Flintshire process; the length of the hearth is about
14 feet, and its width 8 feet. This furnace has five working doors, two
on either side, and one in the end opposite the fire-bridge; the bottom,
like that of the Couëron furnace, is supported on iron bearers, and is
finished with slags.
The charge, which consists of 2 tons of calcined ore, is thrown in
through the back doors, and is spread evenly over the sloping bed; the
doors are then closed, luted with clay, and the heat raised. At the
expiration of from two to three hours the charge has run down into the
well, and, when rich ores are operated on, a first tapping is made at
;
2 N
516
ELEMENTS OF METALLURGY.
this period. The fused material is then dried up by being mixed with
lime and culm, and is again spread over the upper portions of the bed.
About 2 cwts. of scrap-iron are now thrown into that part of the well
nearest the tapping-hole, and a little fluor spar is sometimes scattered
over the surface of the charge. This done, the doors are again closed
and luted, the charge re-melted, and the furnace subsequently tapped;
this is accomplished by the use of a pointed iron bar, and the lead, which
first flows into the pot, is followed by regulus chiefly derived from the
action of the scrap-iron upon galena. This regulus, slurry, sometimes
together with a little of the lead, flows over the lip of the tapping-pot
into a small pit in the floor, and as soon as the slag begins to make its
appearance the tapping-hole is enlarged and the lip of the pot is closed
with ashes. The slag now flows out upon the surface of the metal in the
pot, which is almost surrounded, at top, by a strong iron hoop, and the
molten slag is thus directed into a gutter, through which it flows into a
pit outside the building.
From the time of charging to the final tapping-off of the slag the
operation commonly occupies about eight hours; two men are employed
in each shift, assisted by an attendant during the day shift. The con-
sumption of coals is from 8 to 9 cwts. per ton of calcined ore treated; and
the slags, which usually do not afford more than from one-half to one per
eent. of lead by dry assay, are sufficiently poor to admit of being thrown
away.
The principal portion of the copper contained in the ore becomes
concentrated in the slurry, which is re-smelted in order to extract the
lead and silver which it contains, and the resulting matt is then suf-
ficiently rich in copper to be sold to the copper-smelter. The lead
produced by this process is usually hard, and requires to be softened
by a process which will be described hereafter. When, however, two
tappings are made during the course of the operation, the lead obtained
from that which takes place after the first running-down of the charge is
much softer, and also more argentiferous, than that resulting from the
final tapping.
The flowing furnace is used in North Wales and in various other
localities, and is constructed and worked essentially in the same way as
in Cornwall. It is employed for the reduction of the rich grey slags
from the Flintshire furnace by the aid of scrap-iron and carbonaceous
matter, and is also used for smelting rich foreign silver ores and jewellers'
sweep.
In this process a large proportion of the lead is obtained by the
mutual decomposition of galena and of the oxidised products resulting
from calcination; the yield is, however, augmented by that reduced by
culm and by the decomposition of sulphide of lead by metallic iron.
It may therefore be regarded as a mixed process, comprehending the
whole of the various reactions upon which is based the metallurgical
treatment of lead ores.
SPANISH Furnace, or BOLICHE.-According to Pérès de Vargas, who
lived in Spain during the reign of Philip II. (1556), and who wrote on
LEAD.
547
the metallurgy of that date, the boliche had been known from time imme-
morial, having been used by the Romans when in occupation of that
country. Alonzo Barba, the celebrated priest of Potosi, states, on the
contrary, that it was an Indian invention, introduced from America
about the year 1640. M. Petitgand, the author of an excellent mono-
graph entitled 'Exploitation et traitement des Plombs dans le Midi de
l'Espagne,' * infers from this that it was first introduced from Spain into
America and subsequently re-imported into Spain, where its use and
method of construction had become forgotten. However this may have
been, there can be no doubt but that the boliche is an exceedingly ancient
form of furnace, and that for a very long period it was almost exclusively
employed in the south of Spain for the reduction of lead ores.
It is usually constructed of rubble-work cemented together with a
mortar formed either of clay or of vegetable soil, and is generally with-
out any support from iron bars, or binders. In place of these it is
provided with strong buttresses at the angles; these are frequently
carried upward, so as to form supports for the roof of the shed by which
it is covered. The interior is protected by a lining of fire-brick, the
hearth being composed either of laja or laguena, a description of clay
resulting from the decomposition of talcose schists, or of a nixture of
this clay with broken galena. The boliches employed by the various
English companies established in the neighbourhood of Linares are con-
structed entirely of sandstone, without any kind of lining, and are bound
together by ordinary iron braces.
This furnace essentially consists of two arched chambers, one of which
is employed for the reduction of the ore, while the only use of the second,
which is situated between it and the chimney, seems to be to moderate
the draught. These two chambers are separated by a fire-bridge, the
second being generally in connection with a chimney about 30 feet in
height. At Linares the boliches are worked in connection with the long
condensing flues of the establishment, which terminate in a single tall
chimney. The fire-place is without a grate, and is 2 feet 2 inches in
width and 5 feet 6 inches in length; the fuel, which consists of brush-
wood, such as cistus, broom, lavender, rosemary, juniper, &c., is supplied
through a door at the end of the fire-place. The smelting hearth inclines
towards the only working door, at the extremity of its longer axis, and
immediately within which is a receptacle in the floor for the collection of
the molten metal; this door, and that through which the fuel is intro-
duced, are the only openings in the furnace, with the exception of a
smaller one supplying air to the fuel, and through which the ashes are
withdrawn. The hearth, which is about 7 feet 6 inches in length by
6 feet 6 inches in width, has its angles rounded, and is sometimes made
nearly circular in form. The second chamber, serving to moderate the
draught, is lenticular in shape; its length, transversely to the chimney,
is 12 feet and its width 4 feet. At the extremity of its longer axis are
doors, which are usually bricked up, but which are from time to time
opened for the removal of fume and dust.
* 'Revue Universelle,' t. ix. 1861, p. 297.
2 N 2
518
ELEMENTS OF METALLURGY.
According to Dick, the smelting of a charge of lead ore in the
boliche at La Fortuna, Linares, occupies eight hours, and comprehends
three operations:-
a. Caldeo, or calcination, lasting from one to one and a half hour.
b. Blandeo. This is analogous to our sweating, and occupies from four
and a half to five hours.
c. Corrida. Analogous to our running down, and occupies the re-
mainder of an eight-hours' shift.
M. Petitgand, however, says that under favourable circumstances a
liga or charge may be smelted in from 4 to 5 hours. Mr. J. L. Thomas,
among other details furnished to Dr. Percy, states that a charge of ore,
weighing 60 arrobas, or 13 cwts. 1 qr. 16 lbs. English, and yielding by
assay 77.5 per cent. of lead, can be worked in from 5 to 6 hours. It is
evident, however, that the time necessary for working a charge will be
much influenced by the richness and fusibility of the ores treated.
The ore, which is thrown in through the working door by means of
a scoop with a handle on either side, is spread evenly over the bottom
and is stirred from time to time. When the operation of calcining is
considered to be sufficiently advanced, the temperature is increased and
the running-down of the charge commences. For drying up the slags
the ash and breeze falling into the ash-pit are alone employed. At the
close of the operation the lead is tapped off into a vessel, where it is
first stirred up with dry leaves, and from which it is subsequently laded
into moulds.
The yield of the boliche is about 80 per cent. of the contents of
the ore by assay; the grey slags, which are drawn in the usual way,
contain from 45 to 50 per cent. of lead, and amount to from 15 to
17 per cent. of the ore charged. They are reduced in a blast-furnace
blown by bellows worked either by treadles or by horse power. For
smelting, a charge of 60 arrobas of ore from 1,550 to 1,750 lbs. (avoir-
dupois) of brushwood are required.
From having been subjected to a less elevated temperature, the lead
smelted in the boliche is believed to be somewhat softer than that obtained
from the Flintshire furnace, but the difference in quality is by no means
marked. The reactions which take place in this apparatus are of pre-
cisely the same character as those which occur in the furnace employed in
North Wales, and the process is essentially one of double decompositions.
At Linares, boliches have been constructed with fire-places adapted for
the consumption of mineral fuel; but thus modified, it appears to offer
no advantages over the ordinary English reverberatory furnace; the
amount of ore worked in a given time is smaller, and the proportionate
consumption of fuel somewhat larger.
The boliche, although an ingenious contrivance for the reduction of
rich lead ores by means of brushwood, is nevertheless inferior to the
ordinary reverberatory furnace, when coal is to be obtained at a moderate
price.
BLEIBERG PROCESS. The galena treated at Bleiberg in Carinthia
occurs in Jurassic limestone, and is accompanied by blende, calamine,
LEAD.
549
willemite, cerussite, anglesite, and molybdate of lead. The ores of zinc,
removed as completely as practicable by a careful system of mechanical
treatment, are sold to zinc-works for reduction; while the lead ores are
delivered to the smelter, either in a somewhat rough state of division,
containing from 65 to 70 per cent. of lead, or as slimes, of which the
yield is usually about 5 per cent. less.
The furnace employed at Bleiberg differs essentially from those used
in this country, since the hearth, instead of being broad, with a well in
the middle and a tap-hole at the side, is long, and has a regular slope
towards the door, which is placed at the extremity of its longer axis.
The working bed is about 10 feet in length, and, at its widest part, 4 feet
10 inches in width; but it is gradually contracted towards the working
door, which is 1 foot square. Besides having a regular slope towards
this door, the hearth is hollowed from the two longer sides towards the
middle, so that the metal may flow from every part of the bed into a
receptacle in front of the working door. The fuel commonly employed
is wood, and the fire-place is parallel to the long axis of the bed; the
grate, which has a still greater inclination than the bed, is of stone,
traversed by openings for the admission of the air necessary for com-
bustion. These furnaces, which are usually constructed in pairs, are
mainly built of red sandstone, and the working bottom, which is 6 inches
in thickness, is made of a mixture of clay, old bottoms, poor slimes, and
dressed slags fritted together by heat.
Brown coal is sometimes used as fuel in place of wood, and in such
cases a grate consisting of iron bars is substituted for one of stone.
Furnaces with two hearths placed one above the other were for some
time employed at the Imperial Lead-Works, at Bleiberg, but although
the consumption of fuel was thereby considerably reduced, the frequency
of the repairs required and the uncertainty of the results obtained ulti-
mately caused them to be abandoned.
The process of smelting is conducted as follows:-As soon as the
hearth has become heated to dull redness the charge, weighing about
370 lbs. avoirdupois, is thrown in through the door, and, by means of a
rake, is spread evenly over every part of the bottom. The temperature is
now kept so low that calcination may be effected without softening or
agglomeration, and the ore is at short intervals turned over with a rake,
and fresh surfaces thus exposed to oxidising influences.
At the expira-
tion of from three to three and a half hours the roasting is generally
found sufficiently advanced, and the temperature is then so raised as to
determine the usual reactions between the unchanged galena and the
oxidised products resulting from calcination. The rabble is now worked
assiduously for the purpose of effecting a complete mixture of the charge,
thus facilitating the production of metallic lead through the mutual
decomposition of its sulphide and the oxidised products of roasting. This
operation generally lasts from three and a half to four hours, and the
lead, which is constantly liberated, flows down the inclined hollowed
surface of the bottom, into the receptacle placed in front of the working
door for that purpose; this lead, from its supposed purity, has received
550
ELEMENTS OF METALLURGY.
the name of " virgin lead,” Jungfernblei, and in order to indicate its source
of production was formerly sold in the form of irregular lumps as it fell
from the furnace. At the expiration of the period above stated from 125
to 150 lbs. of lead will have been collected, sulphide of lead will have
almost entirely disappeared, and the residual grey slag will contain lead
in an oxidised state only.
This slag is now dried up by the addition of ashes and breeze from
the ash-pit, and the mixture, after being well worked with the rabble, is
withdrawn from the furnace and laid aside to be treated with that result-
ing from the next operation. Another charge is introduced and the
process is conducted as before.
At the completion of the second stage the grey slag remaining on the
bottom of the furnace is in its turn mixed with breeze, while that result-
ing from the working of the previous charge is added through the working
door, the furnace thus containing the slags resulting from the treatment
of two distinct charges of ore. The temperature is now raised, small char-
coal is added when necessary, and the whole intimately mixed, with the
rabble, in order to effect the reduction of the various oxidised compounds
of lead. This reduction of the slag occupies from seven to eight hours, and
results in the production of from 150 to 220 lbs. of lead; it consequently
follows, that for the complete treatment of two charges, weighing together
about 740 lbs. avoirdupois, from twenty-one to twenty-three hours are re-
quired. The yield of lead is usually, when the ores are of average rich-
ness, about 23 per cent. less than that indicated by wet assay; the con-
sumption of wood is about 11 cubic feet per Austrian centner (123·460 lbs.
avoirdupois) of lead produced.
The workmen are paid at the rate of 1.80 florin per centner of lead
extracted, and are debited 6·40 florins per klafter for the wood consumed.
They also receive a bonus of 0·07 florin on each pound of lead produced
in excess of the prescribed quantity, and are fined the same amount for
every pound less than the amount allowed.
According to M. Landrin, the following allowances between the
assay-results and furnace-produce, were in force in 1857 :—
Assay result 82 per cent.: tolerated loss 2 per cent.
80
78
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The charge of the Bleiberg furnaces has recently been increased to
3 Austrian centners.
REDUCTION BY METALLIC Iron in ReverberaTORY FURNACES.—Silicate
of lead, as well as the sulphurised and oxidised compounds of that metal,
LEAD.
551
is reduced when strongly heated in contact with metallic iron; this
operation is usually conducted in a low blast-furnace, Krummofen, but
a reverberatory furnace has also occasionally been employed for the
purpose.
The treatment of somewhat siliceous ores by fusión in a reverberatory
furnace with either scrap-iron or cast-iron, was formerly carried on to a
limited extent in France, but was ultimately discontinued, on account of
the great cost, added to the unsatisfactory nature of the results obtained.
The furnace employed sloped from the fire-place to the chimney, placed at
the opposite extremity of the hearth, where there was a working door with
a tapping-hole beneath it, in front of which was situated the usual reservoir
for the reception of the reduced metal. The charge consisted of about
400 kilos of galena, containing nearly 80 per cent. of lead, mixed with
from 100 to 120 kilos of scrap- or cast-iron. When the temperature had
become sufficiently elevated the charge was stirred at frequent intervals,
and lead became reduced at the expense of the iron, which was converted
into sulphide.
From galena containing 80 per cent. of lead from 67 to 70 per cent.
of metal was extracted, the matt containing from 5 to 12 per cent. of
lead; 4 per cent. passed off by volatilisation, and the slags retained from
4 to 5 per cent.
The entire contents of the furnace were run off into the tapping-pot
which retained the lead, while the principal portion of the matt and slag
flowed over upon the floor. The last two products may be re-treated
in a blast-furnace for the lead which they contain, but the process of
smelting raw ores with iron in reverberatory furnaces is both wasteful
and expensive, and therefore, practically, unsatisfactory.
The processes employed in different localities for the reduction of lead
ores in reverberatory furnaces are exceedingly various, their adoption
being, in the majority of cases, determined by the nature of the ores, the
quality and price of fuel, and the nature of the fluxes available. The
methods described may, however, be considered as typical of those
employed in the principal lead-producing centres, although they are
sometimes more or less modified in order to suit the exigencies of local
circumstances.
SMELTING IN BLAST-FURNACES.
SLAG-HEARTH.-The various rich slags resulting from the different
operations of a lead-smelting establishment are either treated in the fur-
naces in which they are produced, as in the case of the Cornish and
Bleiberg processes, or they are reduced in a blast-furnace specially
employed for that purpose. In this country the slag-hearth is still fre-
quently used, although its application is no longer so universal as it
formerly was.
This is a deep hearth, or shallow rectangular furnace, blown by one
tuyer, made of fire-brick and cast-iron, incased, with the exception of the
front, in an exterior covering of ordinary brickwork, and bound by iron
552
ELEMENTS OF METALLURGY.
braces. The casing is extended upwards so as to form a sort of chimney,
which at the top is connected with the general system of flues for the con-
densation of lead fume with which every well-appointed establishment is
now provided. The depth of this furnace from the front to the tuyer is
usually about 30 inches, its width may be 22 inches, and its height a little
more than 3 feet. The bottom is composed of a thick cast-iron bed-plate,
laid with a slight inclination from the back towards the front of the furnace ;
on the bed-plate are placed cast-iron bearers, which carry the side walls of
the furnace. The front is partially closed by a plate of cast-iron, called the
fore-stone, and the back below the tuyer is formed of another thick plate
of the same metal; a space of from 5 to 7 inches is left between the
bottom of the fore-stone and the cast-iron plate forming the bottom of the
arrangement. In front stands the lead-trough, divided into two unequal
portions by a division forming part of the casting; the larger one corre-
sponds, in width, with the bed-plate under which its edge is introduced,
and at the bottom of the partition is a hole through which the molten
metal flows into the smaller division of the trough. The slags, escaping
from this furnace through an opening in the stopping of the breast,
pass over the edge of the larger division of the lead-pan and then flow
into a cistern sunk in the ground, through which flows a small stream of
cold water. This determines the disintegration of the slag, and allows
of the separation of any inclosed metallic shot. Before beginning
to work a furnace of this description, the bed-plate is covered with a
layer of well-burnt and coarsely-sifted ashes to within about an inch
below the level of the tuyer; and the ash bottom thus formed is made
to slope in the same direction as the plate itself. The space between
the bearers in front of the ash bottom is now closed with clay, &c.,
up to the lower edge of the fore-stone, and in this stopping, an opening
is subsequently made for the escape of the molten slag. The bottom
of spongy cinders, which is somewhat closely beaten-together, acts as
a filter, by which the metal is separated from the slags which flow
off over its surface, escaping by the opening in the breast; while the
heavier lead falls to the bottom of the hearth and, percolating through
the ash bottom, is conducted by the bed-plate into the lead-pot. The
larger division of this pot is likewise filled with cinders, which, as in the
former case, act as a filter, by means of which the molten lead is separated
from the less dense and somewhat more viscous slag. The fuel employed
is peat and coke, and the products obtained are slag-lead and a vitreous
black slag, which is sufficiently poor to be thrown away.
Blocks of peat are first piled upon the cinder bottom of the furnace,
and one of these is ignited and thrown before the tuyer. When the peat
has thus become fairly ignited, coke is thrown in; and as soon as this
appears to be properly lighted, grey slag, with some browse (partially-
reduced slags removed from the hearth at the termination of a previous
operation) and a little black slag, are introduced. From this time the
hearth is supplied with alternate charges of fuel and slag, and when a
sufficient quantity of the latter has been melted, which happens shortly
after the furnace has been set in operation, the smelter, with an iron bar,
LEAD.
553
makes a hole in the centre of the stopping, between the bed and the
lower edge of the fore-stone. Through this the molten slags make their
escape, and the furnace being now in its normal working condition, the
several operations are repeated, throughout the shift, without variation.
At the close of each shift, which often lasts about eight hours (six of
which will be employed in smelting and the other two in cleaning and
preparing the hearth for the next working period of similar duration),
the blast is continued for about half an hour without any further addition
of either fuel or slag.
As soon as the blast has been cut off, the clay stopping beneath the
fore-stone is removed, and the ash bed, with as much as possible of the
adhering slaggy matter, is taken out; this, under the name of slag-hearth
browse, is reserved for treatment during the course of the next shift.
Finally a few bucketfuls of water are thrown into the hearth, in order
to put out the fire and to cool it previously to the clearing or stubbing-out
necessary before commencing another shift.
The hearth is worked by two men-a smelter and his assistant. The
duration of a shift varies in different localities from eight to sixteen
hours, and the production of lead and consumption of fuel are greater or
less in accordance with the nature and richness of the materials treated.
According to H. L. Pattinson, the slag-hearth shift in the north of
England (1832) lasted from fourteen to sixteen hours, and produced from
10 to 21 cwts. of lead; from 15 to 18 cwts. of coke were required to
produce 21 cwts. of lead. From the nature of the material from which
it is obtained and the high temperature employed for its production,
slag-lead is invariably more or less hard, and requires softening before
it can be applied to the purposes for which ordinary lead is used; it is
laded out from the smaller division of the lead-pan and cast into pigs.
When grey slags are found to work with difficulty in the slag-hearth, the
addition of tap-cinder often proves advantageous. The material smelted
in the slag-hearth should not contain above 35 per cent. of lead, and
when richer than this must be mixed with black slag or some other poor
material.
The Spanish slag-hearth, which has been adopted at some of the lead-
works in this country, is circular, and blown by three water-tuyers.
Its general construction very closely resembles that of the Castilian
furnace, but it is without iron columns, and is connected with the main
flue by a sort of chimney. It is worked in the same way as the
Castilian furnace, but the slags are often run into water.
CASTILIAN FURNACE.-This furnace, which is circular, is usually about
3 feet in diameter, and is constructed of fire-bricks, so moulded as to fit
together and allow all the various joints to follow the radii of the circle
described by the brickwork. Its height is about 8 feet 6 inches, and the
thickness of the masonry is 9 inches. In this arrangement the breast is
formed by a semicircular iron pan, furnished with a lip for running off
the slags, and a longitudinal slot for the convenience of tapping. On the
top of this cylinder of brickwork a box-shaped covering of masonry is
supported by a cast-iron framing resting on four pillars, and in this is
551
ELEMENTS OF METALLURGY.
placed a door for the purpose of feeding, and the outlet by which the
various products of combustion, &c., escape into the flues. The lower
part of this hood is fitted closely to the body of the furnace, whilst its
top is closed by an arch of 4-inch brickwork laid in fire-clay. The
bottom consists of a mixture of fire-clay and coke-dust slightly moistened
and well beaten in to the height of the top of the breast-pan, which may
be about 3 feet above the level of the floor. Above the breast-pan an
arch is so turned that, when the breast has been built up, it may form a
niche 18 inches in width and rather more than 2 feet in height. When
the bottom has been properly beaten, up to the required height, it is so
hollowed out as to form an internal cavity communicating freely with
that of the breast-pan, which is likewise filled with brasque, and subse-
quently hollowed to the depth of the internal basin of the furnace. The
blast is applied by means of three water-tuyers, 3 inches in diameter at
the smaller end and 5½ inches at the other extremity, into which the
nozzles are introduced. The air is generally obtained by means of a fau,
and is conveyed to the tuyers through brick channels formed beneath the
floor of the shed in which the furnace is situated.
The ores or other plumbiferous matters treated in this apparatus
ought never to contain above 30 per cent. of lead, and if richer, should
be reduced to this tenure by the addition of a proper amount of poor
slags. In charging, it is of importance that the coke should be thrown
in the middle, whilst the matters to be treated are spread around next
the brickwork; by this means the furnace is prevented from becoming
too hot, and the bricks are consequently preserved for a much longer
period than they otherwise would be.
For the purpose of allowing the slags to escape into the breast-pan,
an arch is turned over the front at the height of the fore-hearth, which,
in order to prevent the cooling of the slag, is constantly kept covered
by a layer of coke-dust or cinders. From the breast pan the slags
flow continuously through a spout, provided for that purpose, into cast-
iron waggons, where they consolidate into masses, having the form of
inverted truncated pyramids, of which the larger base is about 2 feet
square. When a sufficient amount of lead has accumulated in the bottom
of the furnace, it is tapped into an iron pot by removing a plug of clay
from the tap-hole situated in a slot in the breast-plate, and, after being
properly skimmed, is laded into moulds.
The waggons into which the liquid slag is received run on a tramway,
by which, when one is removed, its place may be supplied by another.
When cold, the bodies of the waggons are turned over and the blocks of
slag removed. One of the advantages obtained by this method of work-
ing arises from the circumstance that, should the furnace at any time
run lead or matt, without its being observed by the smelter, the whole
of it will collect at the bottom of the waggon, where the block is cou-
siderably contracted, and from which any metal or regulus is removed
when the mass has become sufficiently cold.
These furnaces will smelt rich slags and other plumbiferous matters,
with an expenditure of about 10 per cent. of coke, whilst the slags
LEAD.
555
•
obtained from them should, in no instance, contain above 1 per cent. of
lead.
In working this furnace a little scrap-iron is generally used, and care
should be taken to prevent flame from appearing at the mouth; since,
provided the slags are liquid and flow readily off, the cooler the furnace
can be kept at top the less will be the loss of lead through volatilisation.
In addition to great attention being paid to the working of the furnace,
it is necessary, in order to obtain the best results, that the establishment
should be provided with capacious and extensive flues, in which con-
densation of the fume may take place before arriving at the stack through
which the more volatile matters make their escape. As an instance of
the economical working of these furnaces, it may be stated that slags
giving, by assay, 8 per cent. only of lead, with traces of silver of no com-
mercial value, have been treated with considerable advantage. In Derby-
shire, where large heaps of slag of the above percentage were treated, some
fifteen years ago, by the Castilian furnace, 3 per cent. only was directly
obtained in the metallic form, whilst 4 per cent. was obtained from the
flues in the state of fume, and subsequently reduced in a reverberatory
furnace; so that the results yielded in practice were nearly equal to
those indicated by assay.
When ores of lead are treated in the blast-furnace, they are usually
either smelted in the raw state with metallic iron, or first roasted and
subsequently fused with iron or some ferruginous flux.
SMELTING RAW ORES WITH METALLIC IRON.—This process was at one
time extensively employed at various places on the continent of Europe
for the reduction of siliceous lead ores. At Tarnowitz, in Silesia, where
it was long used, it has been replaced by reverberatory smelting, and in
the district of the Upper Hartz it has become superseded by a process in
which basic silicate of iron, in the form of finery-slags, has been sub-
stituted for metallic iron.
The reduction of lead ores, consisting principally of galena associated
with a siliceous gangue, was some years since conducted at Clausthal as
follows:-
The mixture treated consisted of 34 quintals of ground ore and schlich,
equivalent to 24 quintals of pure galena; 4 to 5 quintals of cupel bottoms
strongly impregnated with litharge; 1 quintal of Abstrich, or impure
litharge, formed on the surface of the German cupel; 39 quintals of slags,
derived either from the first fusion of the mineral treated, or from the re-
melting of matts; 4 quintals of granulated cast-iron.
The fusion of this mixture was conducted in a small blast-furnace of
from 20 to 25 feet in height, and about 3 feet square in the widest part.
The hearth of the furnace employed for this process is so arranged as to
extend beyond the breast into a small raised platform situated immediately
before it. The lining of the hearth consists of refractory fire-stone, and
the bottom is hollowed out of brasque in such a way as to afford a
gentle slope from the side of the tuyer to beyond the front wall. A
tapping-hole enters at the lowest part of this basin, and affords a means
of drawing off its contents when accumulated in sufficient quantity.
556
ELEMENTS OF METALLURGY.
This receiving basin, a, fig. 167, is placed on a level with the floor
and at some distance from the breast of the furnace, which is supplied
with a blast forced through two nozzles situated at t, fig. 168, which
represents a vertical section of the same furnace on a somewhat larger
scale. In charging the mineral, care is taken to direct it towards the side
of the tuyers, whilst the fuel is chiefly thrown towards the breast. The
cold air constantly entering through the tuyers rapidly cools the slag pro-
duced in their vicinity, and forms around the nozzles circular prolonga-
tions of six or seven inches in length, on the proper management of which
depends, in a great measure, the success of the operation. One of the
principal effects of these nozzles is to prevent the oxidation of the lead
the blast being by this means brought into immediate contact with the

d
d
Fig. 167.-Clausthal Furnace; front view.
fuel, without having to pass through the mineral charged at the back of
the furnace, cannot so readily give rise to the formation of fusible silicates
of lead.
With this view the smelter must bestow attention to the proper regu-
lation of the length of the slag-nozzles, as by them the economical
working of the furnace is materially affected. It is also necessary, by
regulating the supply of air and fuel, to so arrange the temperature
that the upper part of the shaft may not become too strongly heated,
as in that case considerable quantities of lead are driven off. With all
these precautions, there is, however, a constant loss from sublimation,
and therefore the whole of the gases passing from the tunnel-hole, T, are
LEAD.
557
made to pass through chambers, C, before escaping into the atmosphere.
by the chimney, D.
In these chambers large quantities of fume gradually accumulate;
this is occasionally removed through the doors, d, fig. 167, for the pur-
pose of being mixed with other lead products, and again treated in the
furnace.
During the whole time this arrangement is in action the slags flow
continuously into the fore-hearth, where, being solidified, they are seized
by a labourer with a stout iron hook, and dragged down the inclined
plane, p, to the foundry floor. When the basin, b, has become filled with
metallic lead, the plug is removed from the tapping-hole communicating
with the reservoir, a, into which the fused metal is rapidly drawn off.

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Fig. 168.-Clausthal Furnace: vertical section.
The products thus run off into the outer basin readily divide into two
parts: the lower portion is metallic lead, whilst the higher consists of
sulphide of lead, more or less mixed with sulphides of other metals
originally present in the ore, and particularly with sulphide of iron,
resulting from the decomposition of galena by that metal. This sub-
stance, which readily solidifies, is the first matt, and is removed from
the surface of the bath by an iron eye, around which a circular cake
is allowed to solidify, and is stowed in a proper situation for sub-
sequent treatment. The lead is afterwards laded into moulds. The
poorer slags are removed and thrown away, whilst those which contain
granules of metallic lead are added as flux in a future operation. When
558
ELEMENTS OF METALLURGY.
a sufficient quantity of rich slag is not to be procured, some of the poorer
slags are likewise used for this purpose; but this never takes place
excepting when a proper supply of the richer variety is not to be
obtained. The products resulting from a mixture having the composition
before given, consisted of 19 quintals of metallic lead and 8 quintals of
first matt, containing from 30 to 35 per cent. of lead.
When a considerable quantity of these first matts has accumulated in
the establishment, they are roasted in heaps, laid on a stratum of fuel,
and by this means large quantities of sulphur and sulphurous anhydride.
are disengaged.
This first roasting occupies from three to four weeks, at the expiration
of which time the heap is carefully picked over and the products divided.
into two classes; those portions which have been sufficiently roasted.
being again taken to the furnace and re-treated, whilst fragments which
still retain a considerable amount of sulphur must be subjected to a
second process of roasting. By this process four successive roastings
are necessary before the whole of the matt is obtained in a fit state for
smelting.
When sufficiently roasted, the matts are fused in a small blast-
furnace, after being mixed in the following proportions with various
other bodies:
32 quintals of roasted matt.
30
""
4 to 5
""
2
2
""
1
of rich slags obtained from the direct treatment of the ore.
of cupel bottoms.
of Abstrich.
of slags from the reducing furnace.
of granulated cast-iron.
The furnace in which this mixture is introduced is about 5 feet in
height, and is considerably contracted in the vicinity of the hearth, which,
as in the case of the larger apparatus, is provided with a sloping fore-
hearth, and a distinct tapping-basin for the reception of the metallic
products.
The fuel employed is coke, and the blast, supplied by a single tuyer,
is conducted into the furnace through a slag-nozzle of about 3 inches in
length. During the process of roasting, the larger proportion of the
sulphide of iron passes to the state of oxide, and during the subsequent
fusion, this oxide, which is partially reduced by the carbon of the fuel,
becomes protoxide, and unites with the siliceous matters present to form
a vitreous fusible slag; which, flowing through the aperture of the fore-
hearth, is continually removed. The sulphide of lead is at the same
time reduced through the agency of metallic iron, and new matts somewhat
analogous in their composition to the first are obtained.
These, when sufficiently solidified by cooling, are removed in the way
already described, after which the lead is taken out in iron ladles and
cast into pigs.
The treatment of 32 quintals of roasted matt, with its associated fluxes
and other products, afforded, at Clausthal, 12 quintals of metallic lead and
8 quintals of second matt.
LEAD.
559
The second matts are subjected to a treatment similar to that em-
ployed for those obtained by the direct treatment of the ores. They first
undergo one or more roastings, and are subsequently treated in the same
furnace and with the same additions as are employed in the case of first
matts. In this way a further amount of metallic lead and a third matt
are obtained; this is again roasted, fused with a proper addition of fluxes
and other matters, and metallic lead and a fourth matt are the result.
The copper, of which a small quantity only is contained in the original
ore, having a greater affinity for sulphur than is possessed by lead, con-
tinually accumulates in these matts, which, after the fourth roasting and
fusion, become rich in that metal. The sulphide last obtained, known by
the name of copper matt, is subsequently treated for coarse copper.
It has been already stated that the use of basic silicates of iron, such
as refinery-cinders, has lately, to a very great extent, superseded that of
metallic iron in the smelting works of the Hartz. Still more recently
highly ferruginous copper slags have been employed for the same pur-
pose in the Rachette furnace, and satisfactory results are stated to be
obtained.
TREATMENT OF LEAD ORES BY ROASTING AND SUBSEQUENT SMELTING
WITH METALLIC IRON.-The method of smelting employed at Pontgibaud *
affords an example of the treatment of highly siliceous ores by roasting
and subsequent fusion with scrap-iron in a blast-furnace.
The average
produce of the stuff, as extracted from the mines, is about 6 per cent.,
and consequently large quantities have to pass through the various pro-
cesses of crushing and washing, in order to obtain the large amount of
ore, containing on an average 50 per cent. of lead, and about 40 ozs. of
silver per ton, annually treated in the establishment. As much cobbed
ore as practicable is, however, selected, by hand picking, in order to avoid,
as far as possible, the loss incident to mechanical preparation. The
ores, which vary considerably in richness both as regards lead and silver,
are delivered to the works in a ground state; the gangue is always sili-
ceous, but blende, sulphate of barium, and arsenical and ordinary iron
pyrites are also present.
All assays are made in an iron crucible, and, when properly con-
ducted, yield results which are quite as high as those obtained by the
wet way; this is doubtless owing to the impurities in the button of lead
compensating for the loss by volatilisation.
The process employed at Pontgibaud for the treatment of argentiferous
galena comprehends two distinct operations, namely:-
a. Roasting in a reverberatory furnace.
b. Smelting the roasted ore with metallic iron in a blast-furnace.
a. Roasting.—Although the ores do not materially differ as regards
the nature of their gangue, they vary considerably in richness, and con-
sequently in the proportion of earthy matter which they contain. It has
therefore been found desirable, before commencing their treatment, to
* The mines and smelting works of Pontgibaud, Puy-de-Dôme, France, have, since
1853, been successfully carried on by an Anglo-French Company under the direction
of Messrs. John Taylor and Co., of London.
560
ELEMENTS OF METALLURGY.
prepare a uniform mixture from all the parcels of ore available. On this
greatly depends the regularity of the subsequent operations, and in a
great measure also their economical working.
As it would be difficult to thoroughly mix the whole of the various parcels
of ore, often amounting to several hundred tons, a lit de grillage of 20 tons,
or a little more than the quantity usually roasted per diem, is prepared.
This is done by weighing out and spreading in thin layers, one above
another, the exact proportion of 20 tons which each parcel bears to the
total quantity in stock. The bed being thus prepared, the charges are
obtained by cutting down, perpendicularly, with a shovel, the pile of
stratified ore, in such a way that every ton of the mixture removed shall
have the composition of the entire mass. To this mixture of ores
are added the calcined matts resulting from smelting in the blast-furnace;
these usually contain about 17 per cent. of lead and 14 ozs. of silver per
ton, and constitute about 10 per cent. of the charge. The object of
adding this to the lits de grillage is, that the oxide of iron may serve as
a flux at the close of the operation of roasting. As the ores are usually
very quartzose a little mill-cinder is generally added in addition to the
roasted matt.
This mixture is roasted in very large reverberatory furnaces, worked
from both sides, 40 feet in length, outside measure, and 15 feet in width
at the widest part. The exterior is built of cut lava, and the sides,
bottom, and roof are of fire-brick. This furnace is provided with twelve
working doors, and is, as before stated, furnished with a brick bottom.
Of the six doors on either side of the furnace, two correspond with each
charge, and enable the workmen to turn or advance the ore when re-
quired.
The different parts of the furnace occupied in succession by each
charge may be distinguished as follows:-
1st. Drying-bed immediately under the charging hoppers and furthest
removed from the fire place.
2nd. Desulphurising or oxidising bed, occupying the middle and
widest part of the furnace.
3rd. Agglomerating bed, next the fire-place.
The first two are on the same level, and the third about 6 inches
lower than the others.
At intervals of six hours, a charge of fused ore is withdrawn by tap-
ping, and the other charges in the furnace are advanced a stage in the
direction of the fire-place, while a fresh charge is let down from the
hoppers upon the drying bed beneath them. The time each charge re-
mains in the furnace is consequently eighteen hours; 8 tons (8,000 kilos)
are thus roasted in the course of twenty-four hours, with a consumption of
about 2 tons (2,000 kilos) of coal, and the addition of 6 per cent. of lime.
The amount of iron slag added is usually about 7 per cent.; but what-
ever the proportion of this flux or of lime may be, the weight of ore
charged remains constant. Four men are employed at each furnace per
shift of twelve hours, and the loss of lead during the operation is esti-
mated at from 2 to 3 per cent.
LEAD.
561
b. Smelting. The lits de fusion are usually composed as follows:-
Kilos.
Roasted ore
10,000
Scrap-iron.
1,000
Limestone
Fluor-spar
•
1,600
300
The above figures give the average quantities of flux in the furnace
mixtures; they are, however, modified with the nature of the ores, the
proportions of limestone and fluor-spar varying most considerably.
The fusion of the roasted ore and fluxes is effected in Castilian
furnaces constructed of blocks of cut lava, of which fig. 169 represents a

b
WELCH.SC
Fig. 169.-Blast-Furnace, Pontgibaud; elevation.
front elevation. Their height from the slag-overflow, a, to the charging
door at the back, is 5 feet, and their internal diameter is 35 inches; dia-
meter of tuyers, 3 inches; pressure of blast, 4 inches of water. The blast
is supplied by the nozzles, b, of which there are three in connection with
the mains, c; the tapping-hole is in the opening, d. Water-tuyers are not
employed.
The mode of charging is similar to that employed for other furnaces
of this kind, the ore being principally distributed around the sides, and
the coke kept in the middle and towards the breast. This furnace is
20
562
ELEMENTS OF METALLURGY.
maintained constantly full, and care is taken not to allow flame to appear
above the top of the charge; the breast-pan is large and will hold from
fifteen to twenty pigs of lead.
From 14 to 16 tons of roasted ore are smelted in the course of twenty-
four hours, with a consumption of 1 ton of coke; the quantity of lead
obtained during the same time is from 100 to 120 pigs, or from 5 to
6 tons. In addition to lead, the ores yield from 7 to 10 per cent.
of matt.
The slags formed under the most favourable circumstances contain
nearly 2 per cent. of lead; when they exceed 3 per cent. they are re-smelted.
It has been found, by assay, that the slags which are poorest in lead con-
tain at least 40 per cent. of ferrous oxide, but that this may be partially
replaced by lime, especially when fluor-spar is added to the charge. Slags
in which oxide of iron has been replaced by lime are, however, never so
poor in lead as those having the normal composition, while the amount of
that metal volatilised is considerably increased. The proportion of slags
produced is from 65 to 70 per cent. of the ore smelted, and as they flow
from the furnace they are received into cast-iron waggons, which when
full are drawn to the waste heaps and tipped.
The two cylinders of the blowing machine are each 52 inches in
diameter; length of stroke, 52 inches; number of strokes per minute, 12.
The lead obtained contains almost the whole of the silver originally
present in the ores smelted, excepting the small proportion either combined
with the matts or retained in the slags. The usual assay of the matts is from
15 to 20 per cent. of lead and from 12 to 16 ozs. of silver per ton; the
average amount of silver per ton of lead is 96½ ozs. The whole of the
silver in the matts, and a portion of that in the slags, is recovered during
subsequent operations, but traces of that metal are nevertheless unavoid-
ably lost. According to assay, this loss amounts to 6.12 dwts. per ton of
slag, or 0.568 per cent. of the total quantity contained in the ores. A
certain amount of silver is also volatilised with the lead, but how large a
proportion is lost from this cause cannot be accurately determined; that it
is, however, very small is probable, from the known properties of silver,
and from the amount found in the fumes collected from the flues and
condensers.
The proportion of silver thus carried off, and again recovered in all
the different processes, including cupellation, amounts to only 0.470 per
cent. of the total quantity contained in the ores.
The loss of lead in smelting ores in the blast-furnace amounts to 17
per cent. of the total quantity contained in them; 2 per cent. of this is,
however, subsequently recovered from slags by re-smelting, and about
3 per cent. from fumes. The actual loss, therefore, in the operation
is equal to 113 per cent. of the total quantity contained in the ores as
indicated by assay.
The fume obtained from the flues is subsequently mixed with sili-
ceous ores, and fused in a common calcining furnace; the fused mass
thus obtained is smelted in the blast-furnace like ordinary roasted
The fume and ore are mixed in the following proportions, and
ores.
LEAD.
563
are charged into the calcining furnace, through the working doors, upon
the middle bed.
Fume 60 parts, assay 62.7 per cent. lead.
Ore 40
40.0
""
Each charge weighs 2 tons, and five charges, or 12 tons, can be passed
through a furnace in twenty-four hours; the loss of weight experienced is
about 15 per cent. The same number of men are employed as for roasting
ore; the consumption of coal is 17 per cent. and of lime 3 per cent. of the
weight of stuff roasted.
The furnace mixtures, for fume and ore, are composed as follows:
Kilos.
Fume and ore
10,000
Iron.
1,200
Limestone
Fluor-spar.
3,500
300
15,000
The above quantity is smelted in twenty-four hours, with a con-
sumption of 9 per cent. of coke.
The quantity of fume annually collected is about 150 tons, averaging
57 per cent. of lead and 4 ozs. 5 dwts. of silver per ton. Its richness
varies considerably in different parts of the flue, but in general the per-
centage of lead increases, while the proportion of silver decreases with
the distance from the furnaces. The lead obtained from fume amounts
to 78.57 per cent. of the quantity contained in it, as indicated by assay; or
3.67 per cent. of the total weight contained in the ore.
The whole of the lead produced from the blast-furnace requires to
be purified before it can be desilverised by Pattinson's process. This is
effected by exposing it at a low red-heat to partial oxidation in a rever-
beratory furnace in the way shortly to be described.
Losses of Lead and Silver.-From 100 parts of lead contained in the
ores treated, 85.75 parts are obtained, either directly from them, or from
fumes and slags, namely—
""
From ores
fumes
slags
•
•
80.04 per cent.
3.67
""
2.04
85.75
In desilverising the lead thus obtained a loss of 3.25 per cent. is ex-
perienced, the total weight of poor lead produced for sale being 82.50
per cent. of the quantity contained in the ores. The loss in desilverising
is distributed as follows:—
Refining and reducing
Improving
1.25 per cent.
2.00
""
3.25
2 o 2
564
ELEMENTS OF METALLURGY.
The loss of lead in the three principal divisions of the Pontgibaud
process is therefore—
In roasting
,, smelting
desilverising
2.50 per cent.
11.75
3.25
17.50
The percentage losses on the total quantity of silver contained in the
ore, are-
In slags
market lead
0.568 per cent.
0.533
1·101*
By the process now employed, the annual production of silver is from
3 to 4 per cent. in excess of that indicated by assays of the ores treated.
Of 100 parts of silver produced
98.82 are obtained direct from the ores,
0.64
""
0.54
""
from the slags,
fumes.
""
The quantities of lead and silver produced at the Pontgibaud smelting
works (from local and purchased ores) for the year 1872, were as
follow :-
Lead
Silver
•
1,484 tons.
185,816 ozs.
C
The system of treating lead ores at Pontgibaud has undergone im-
portant changes since the publication, in 1851, of Rivot and Zeppenfeld's
Description des Gîtes Métallifères, &c., de Pontgibaud,' which appears.
to be still regarded by metallurgists as a description of what is actually
being done at the present time.
In confirmation of this statement, it may be observed that in a lengthy
paper on the metallurgy of lead, published in the 'Revue Universelle des
Mines,' in 1863, an engraving of the old roasting furnace is reproduced.
from Rivot and Zeppenfeld's work, and that in an elaborate, and usually
accurate, work on lead-smelting, published in this country in 1870, the
Pontgibaud process is given as it existed, before the abandonment of the
old and the introduction of the present method, in 1852.†
TREATMENT OF SILICEOUS ORES AT COUËRON.‡This treatment compre-
hends two distinct operations:-
a. Calcination in the reverberatory furnace.
b. Reduction in the blast-furnace, with lime and basic silicates of iron
as fluxes.
* Indicated by assay of slags, and market-lead; the actual production is in excess
of that found by the assay of ores.
† For a detailed description of this process as now conducted, see 'Mining and
Metallurgy of Gold and Silver,' by J. Arthur Phillips, p. 468. Spon.
The information relative to the treatment of siliceous ores at Couëron has been
kindly supplied by Mr. W. Hutchison, the manager of the works.
LEAD.
565
pur-
a. Calcination. The reverberatory furnace employed for this
pose is similar in form and dimensions to that represented in figs. 164,
165, 166, pages 540, 541; the only difference in the two being that the
one used for roasting has no tapping-pot, and has the bottom filled with
black slag, level with the working doors, so as to form a flat hearth on
which the charge may be uniformly spread and exposed to the fire. The
ores roasted in this furnace contain from 50 to 60 per cent. of lead with
variable proportions of silica; they are worked in charges of 1,400 kilos,
or about 28 cwts., each.
Each charge is placed ready in the hopper above the furnace in order
that it may be let down when required, without loss of time. Ores which
are not sufficiently divided are ground, and sifted through sieves with
meshes of an inch in diameter.
5
The interior of the furnace being red-hot, the charge is introduced,
and at once spread evenly over the hearth; the damper having been
previously run down to the lowest point so as to reduce the draught, and
thereby prevent mechanical loss of fine ore. The working doors are
now closed, and the charge is left undisturbed, until decrepitation has
entirely ceased and the ore has become partially red-hot. It is then
carefully rabbled, so as to expose the under part to the heat, and in a
few minutes afterwards is turned with paddles. In about an hour the
charge will have acquired a uniform dull-red heat. More air is then
admitted by partially opening the fire door, together with the two working
doors nearest the bridge. The damper is at the same time so adjusted as
to afford only sufficient draught for the free escape of the sulphurous
fumes. The charge is turned or rabbled at intervals of about a quarter
of an hour, so as to expose fresh surfaces to the oxidising action of the
air, and, by that means, to convert the sulphides into oxides and sulphates
with evolution of sulphurous anhydride.
The partial opening of the doors for the admission of air has the
effect of cooling the charge below the temperature requisite for oxidation,
and in order to maintain it at the proper dull red-heat, it is necessary
to close, from time to time, all the doors and to throw a few shovelfuls
of fuel on the fire. The fuel preferred at this stage of the process is
cinders, since they yield but little flame in burning; care must however
be taken not to raise the heat beyond the proper point, or it will cause
the ore to clot, thereby rendering its subsequent desulphurisation, within
a reasonable time, difficult if not impossible. Whenever it evinces a
tendency to soften, the doors are at once opened and the damper is
raised, until the charge has cooled to the proper temperature.
The alternate heating and cooling of the charge is repeated at frequent
intervals during the entire process, and in such a way, that, while furnished
with a plentiful supply of air, it is maintained without clotting, as nearly
as possible, at a dull red-heat. The ore is raked and turned at regularly-
recurring intervals, until at the end of six hours it contains a sufficient
amount of oxide and sulphate of lead to effect the decomposition of a
large portion of the remaining sulphide of lead during the subsequent
stage of agglomeration. Six hours are generally found to be sufficient to
566
ELEMENTS OF METALLURGY.
determine the necessary desulphurisation of ordinary ores. At the expira-
tion of that time the heat is considerably increased in order to effect the

L
10:
O
<
K
C
S d d
e
D
A
9
F
V.J. WELCH. Sc
Fig. 170.-Five-tuyer Furnace, Coueron; vertical section.
agglomeration of the charge and to give it the cohesion necessary for passing
through the blast-furnace. The grate is therefore cleaned from clinker,
LEAD,
567
the damper drawn up, and fresh coals put on until a good fire is obtained.
Under the influence of the increasing temperature the charge soon begins.
to soften, and at the same time it is constantly raked, turned with the
paddle, and advanced towards the bridge. In proportion as it melts it is
raked through one of the working doors upon the floor of the furnace-
house. At the expiration of about two hours the whole of the charge will
have been agglomerated, and is withdrawn. A fresh charge is now let
down from the hopper, spread evenly over the sole as before, and the
operation of roasting is again repeated. In this way three charges, of
1,400 kilos each, are worked in twenty-four hours; two men are employed
per shift of twelve hours, and the consumption of coal amounts to 22 per
cent. of the weight of the raw ore treated.
b. Reduction of Roasted Ores and Grey Slags.-The form and arrange-
ment of the blast-furnace now employed at Couëron will be understood
from the accompanying woodcuts, figs. 170 and 171; of which the first is
a vertical section through the fore-hearth, and the second a horizontal

O
O
O
D
Fig. 171.-Five-tuyer Furnace, Couëron; horizontal section.
section through the tuyers, but without the slag-lip, l. It is considerably
higher than the ordinary Castilian furnace, and is charged at the top; the
brickwork of the lower portion of the furnace, which is usually burnt
through very rapidly, being replaced, to a height of about 3 feet, by an
annular cylinder of cast-iron, A, kept cool by the circulation through it
of a constant stream of water. The whole of the upper part, B, is clad
with strong sheet-iron, well riveted together so as to prevent the escape
of fume.
The cast-iron body is made in one piece, with five tuyers, c, equi-
distant from each other, and converging towards the vertical axis of
the furnace. The number of tuyers, and their position, are matters of
considerable importance as affecting the working of the furnace. Were
fewer tuyers employed, and were they placed farther from the breast, as
is generally the case, the cooling effect of the water in front would be
prejudicial to the regular and prompt descent of the charge. In this
furnace as much as 25 to 30 tons of stuff are smelted in twenty-four hours,
the slags being reduced at the same time to a yield of toper cent, of
lead.
568
ELEMENTS OF METALLURGY.
In casting the hollow casing, A, it is important that the founder should
not only place the tuyers equidistant from one another and converging
towards the central axis of the furnace, but also that they should be
perfectly round, and have their axes placed horizontally. During the
working of this apparatus particular attention must be paid to keeping
up a regular supply of cold water.
The arrangement shown in dotted lines on the vertical section, fig. 170,
is the most convenient for the escape of the warm water, since it enables
the workman to see at a glance the quantity and temperature of the water
as it flows from the outlet-pipes, d, and falls into a funnel, e, placed beneath
and in connection with a drain. On the side opposite that from which the
warm water escapes an inlet-pipe is fixed, which conducts cold water to
the bottom of the casing; this is about 1½ inch in diameter, and is pro-
vided with a stop-cock to regulate the supply.
The sheet-iron hood, f, shown in fig. 170, is placed over the fore-
hearth, g, for the purpose of carrying off the fume which sometimes
escapes from the breast, and might injuriously affect the health of the
charger working on the top. This hood is so arranged as not to interfere
with the work at the fore-hearth, since, when necessary, it can be pulled
up on its hinges out of the way of the workmen by means of a chain, h,
and pulley, i; the cast-iron cylinder with five tuyers can be adapted to
the ordinary furnace charged at the side or back in the usual way. It
is nevertheless thought that this system of charging on the top through
the iron cylinder, C, closed by the cover, K, is to be preferred for lead
furnaces to the old plan, as preventing, to a great extent, the entrance of
atmospheric air into the flue. The products of combustion, &c., escape
by the flue, L, and the bottom of the furnace, D, is cut out of a mass of
brasque, E, in the usual way.
The adoption of the water-casing has led, at Couëron, to a consider-
able saving in repairs, bricks, clay, iron, and wages. The most important
economy, however, is in smelter's wages. Owing to the fact that the
time required at the old furnaces to patch up the sides is now entirely
employed in smelting, a proportionately larger quantity of stuff is
worked through. The greater regularity in the working of this furnace
has the effect of rendering the slags much poorer than formerly. There
is, therefore, not only a saving of lead from this source, but also a reduc-
tion of cost consequent on there being no rich slags to re-work.
The quantity of siliceous ores smelted at Couëron being relatively
small, it is more convenient and economical to mix them with grey slag,
fume, &c., than to treat them alone. The following is the usual compo-
sition of the mixture smelted :-
Kilos.
Grey slags from reverberatory furnaces. 10,000
Calcined ore
Agglomerated fume
Iron slags
•
2,000
2,000
3,000
17,000
On lighting the furnace the iron casing is filled with water by opening
LEAD.
}
569
the feed-cock at the back, and a small fire only is at first made, with wood
and coke, for the purpose of drying and heating the brasque bottom, E.
This fire is kept up until the bottom becomes perfectly dry and sufficiently
hot to prevent the first slags formed from setting and lessening the capacity
of the breast-pan. Coke is now charged at frequent intervals, until the
furnace contains a mass of burning fuel to a height of 3 feet above the
tuyers.
The natural draught is at first sufficient to carry on combustion, but
when the mass has become thoroughly ignited a light blast is introduced
through the tuyers. Before turning on the blast from the fan, however,
the fore-breast is cleaned out, and some burning coke is pulled forward to
the level of the lip, 7; this is covered with a shovelful of cinders, and
the opening closed by stiff clay. A hole is made with a pointed bar
between the cinders and the clay, so as to allow a jet of flame to escape
for the purpose of heating the fore-breast and preventing the first outflow
of slag from adhering to the front. After a few minutes this jet of flame
is stopped by putting a lump of coke before the hole, together with two
or three shovelfuls of cinders. Should these not suffice, some clay is
pressed down on the cinders to increase their cohesion. The tap-hole is
likewise left open for a short time after the blast has been put on, and
is afterwards closed with a plug of stiff clay.
The furnace is at first charged with slag only, until fused slag begins
to appear before the tuyer. The charging of the furnace mixture, alter-
nately with the requisite proportion of coke, is then begun and subse-
quently continued with but little interruption, until the furnace has
become filled to the height of the hopper, C, below which the charge must
not be allowed to sink. The mixture to be smelted is introduced equally
all round and against the sides in such a way that a depression is left in
the middle after each charge for the reception of coke. From the moment
the charge has attained a proper height in the furnace, the blast is increased
to its full force, the tuyers being worked with a very short nose of slag
and kept almost constantly bright.
During the heating-up of the furnace the water in the iron casing be-
comes boiling hot, and must be constantly renewed by the regular admis-
sion of cold water through the feed-tap. This supply is so adjusted that its
temperature at the outflow may be always under the boiling-point, or about
80° C.; but comparatively little water is required after the slag has come
down, since a portion of it adheres to the sides and interposes a layer of
non-conducting material between the iron and the fuel in the furnace.
The fused products in their descent collect in the cavity, D, in the
bottom of the furnace, formed of brasque, and arrange themselves ac-
cording to their respective specific gravities. Lead being the heavier,
sinks to the bottom, whilst the supernatant slag flows out through the
opening made with a bar in the stopping of the fore-breast, and thence
over the lip, l, into the conical cast-iron waggon, F. These waggons
are made to run on a small railway to a distance from the furnace, where,
on cooling, the slag is tipped out and examined for lead previously to
being thrown away.
570
ELEMENTS OF METALLURGY.
The flow of slag from the furnace now becomes continuous, or nearly
so, and is only checked by the gradual cooling of the stream as it runs
over the lip. The cooled slag is, however, from time to time detached
with a slice, and its flow maintained unchecked until it is found, by
sounding, that the lead in the breast-pan has risen to near the level of the
lip. A bar is then forced into the tap-hole for the purpose of breaking
the clay stopping and drawing off the lead into a tapping-pot sunk in
the floor; at the same time the slag-opening in the breast is temporarily
stopped with ashes or clay to prevent the blast from escaping on the
lowering of the slag-level, which follows the tapping of the lead.
As soon as slag makes its appearance the tap-hole is immediately
stopped, either by an iron bar driven into it, or by a plug of clay stuck
on the end of a pole and adroitly wedged into the aperture; the lead
collected in the pot, after having been cleaned and skimmed, is laded into
pig-moulds. For a short time after tapping, the wind is shut off, the fore-
breast is opened, and the bottom is cleaned from any lumps of slag, which,
if allowed to remain, would interfere with the proper working of the
furnace. This cleaning-out having been accomplished, in a few minutes
the breast is again closed with clay and cinders, and the blast is turned
on full as before. Shortly afterwards, as the slag rises above the level
of the outflow, a hole for its escape is again made in the breast by means
of an iron bar.
The furnace bottom is not generally cleaned out after every tapping;
unless they happen to be not very frequent, two or three cleanings
per shift are usually sufficient; but this depends on the working of the
furnace and the nature of the stuff smelted. It is observed that this
furnace generally works faster and better for some time after the with-
drawal of the unfused matters from the bottom. The number of lead
tappings per day depends very much on the size of the breast-pan and
the richness of the matters treated. Ordinarily, four or five tappings,
each of sixteen to twenty pigs, are made per shift of twelve hours.
The average quantity of stuff smelted in twenty-four hours is from 22
to 25 tons, which can be increased to 30 tons with free-running slags. A
smelting campaign lasts three months without any interruption, and
would probably last six, or even twelve months, were the supply of stuff
unlimited. Considerable attention and experience on the part of the
smelter are required in order to avoid mishaps, and to prevent a prema-
ture stoppage of the furnace. In any case, there is no necessity to stop
for ordinary repairs, as in the Castilian furnaces built entirely of bricks.
The consumption of gas-coke of inferior quality is 10 per cent. of the
furnace mixture. No iron is added, and no matt is obtained. A little
iron is reduced in the furnace from the iron slags employed as flux, and
perhaps this accounts for the poorness of the slags produced, which very
seldom exceed per cent. for lead. The slags are sometimes so highly
basic that it is necessary to add sand to the mixture in order to render
it sufficiently fusible, and to prevent the furnace from gobbing; the
most fusible slags contain about 30 per cent. of silica. The number
of men employed at this furnace is five, and the loss of lead, exclusive
LEAD.
571
of fume collected in the flues, is 6 per cent. This method may be
taken as an illustration of smelting by a process belonging to the second
class.
It may be mentioned that the furnace is connected with long flues
and condensers for the condensation of lead fumes.
HORNO DE GRAN TIRO, OR PAVO.-This furnace, which is used in
some parts of Spain, and particularly in the district of Carthagena, for
smelting poor carbonates of lead, is a cylindrical slag-hearth, which,
instead of being supplied with an artificially-produced blast, is worked
by a strong draught obtained by the aid of a chimney of about 45 feet in
height. This is connected with the furnace by an inclined flue at the top,
while the air enters through six horizontal tuyers, of refractory clay,
arranged radially around it a little above the level of the hearth, which
is formed of brasque in the usual way. Coke is the fuel employed, and
the ores treated commonly yield, by assay, about 12 per cent. of lead;
the average production of metal is from 8 to 9 per cent., and the con-
sumption of fuel from 30 to 32 cwts. per ton of lead obtained.
The methods of treating lead ores in the blast-furnace, and the form
and dimensions of the furnaces employed, vary in accordance with the
nature of the ores and the description of the fuel available, and admit of
almost endless modification. In this country, where the ores treated are
delivered to the smelter in a concentrated state, and where fuel is com-
paratively cheap, the blast-furnace is seldom employed, excepting for the
reduction of slags and other furnace products.
SMELTING IN SHALLOW HEARTHS.
BACKWOODS HEARTH.-The early settlers in Missouri, in the United
States of America, were in the habit of extracting lead from galena by
means of a rude hearth constructed of earth and rough stonework, but
without the aid of any sort of artificial blast. The front wall of this
hearth was about 8 feet in length and 6 feet in height, the internal cavity
was 8 feet long and 2 feet wide at bottom, but gradually widened towards
the top. This sloped regularly towards the front wall, in which, on the
prolongation of the longer axis, was an arch inclosing an aperture
through which the molten metal made its escape.
In the bottom of the cavity thus formed, a layer of heavy logs was
laid, longitudinally, and then followed a stratum of split billets; upon
these the galena was deposited, and the whole covered by a layer of
smaller branches chopped into short lengths. The fire was kindled
through the front arch, which, with the exception of a hole for the
escape of metal, was subsequently closed, and the reduced lead, flowing
continuously through it, was collected in a basin in front. The time
occupied by this operation was twenty-four hours, and nearly pure
galenas afforded one-half their weight of metal; the lead and slags re-
maining in the ashes were subsequently treated in a rough substitute for
the slag-hearth called an "ash-furnace." This very primitive method
of smelting, although of comparatively recent date, is now obsolete, but
572
ELEMENTS OF METALLURGY.
is probably very similar to some of the processes employed in remote
antiquity for the production of lead from its ores.
ORE-HEARTH, OR SCOTCH FURNACE.-In some parts of England, and
particularly in the counties of Durham, Cumberland, and Northumber-
land, the smelting of lead ores is often conducted in the ore-hearth or
Scotch furnace. This consists of a rectangular cavity of masonry, 22
inches square; its depth varies from 22 to 26 inches, and the whole of
its internal surface is lined with cast-iron. The bottom, which consists of
but one casting, is surrounded by a ledge; excepting, sometimes, on the
side facing the work-stone, a, fig. 172, which may be 2 feet 10 inches in
breadth, and about 1 foot 10 inches in the other direction.

黑
​0
Fig. 172.-Ore-Hearth.
This is provided with a narrow ledge, b, on each side, and is placed
with a fall of a few inches on its length; its higher side c, rests on the
ledge surrounding the hearth bottom, or in some instances is united
to it, and forms only one casting. When this is not the case, the joint
between the two is closed, and made lead-tight by a cement composed of
bone-ash moistened with water and well kneaded together. On the
back edge of the bottom is placed a prism of cast-iron called a back-
stone, about 6½ inches square and 28 inches in length; on this rests the
nozzle of the tuyer, over which is again placed another iron casting
called the pipe-stone, of the same length as the back-stone, and 10 inches
square. This has, at the centre, a cavity for the introduction of the
tuyer, and projects about 2 inches over the hearth; on it is again placed
another back-stone of the same dimensions as the first, which completes
this side of the hearth, and makes its total height from the bottom 25
inches. Along the lateral edges of the bottom are placed two prismatic
castings called bearers; these are each 26 inches in length and 5 inches
LEAD.
573
#
square, and consequently project slightly over the upper edge of the
work-stone. At the height of 5 inches above these bearers, and at a
distance of 13 inches from the back of the hearth, is supported another
bar of cast-iron, called the fore-stone, which has the same form and
dimensions as that on which rests the tuyer of the blowing apparatus.
The space at each end of the fore-stone is now closed by lumps of cast-
iron measuring 10 inches of a side, called key-stones.
Before the work-stone, a, and set in masonry inclosed in a circular
cast-iron jacket, G, is the lead-pot, E, into which the melted metal, as it
issues from the hearth, is conducted by the oblique channel, f, sunk
beneath the surface of the iron plate. In the woodcut this pot has not
been placed sufficiently near the furnace. To prevent the escape of
fumes into the smelting house, which might seriously injure the health
of the persons employed, the entire hearth is sometimes inclosed in a
hood of arched masonry, H, communicating with the chimney, and in
which is left a small door, I, for the introduction of the ore and fuel.
The iron plate, k, admits of being raised or depressed at pleasure, accord-
ing to the degree of draught required; and the blast communicating
with the tuyer is regulated by a valve placed in a pipe approached by the
arched opening, L, which is left for this purpose. The brickwork is con-
solidated and bound together by the iron straps, l, kept in their places
by screw-bolts passing through the masonry beneath the foundation of
the hearth.
Roasting. The ores smelted in the Scotch furnace were, to within a
comparatively recent period, merely subjected to a careful mechanical
preparation, previously to their direct metallurgical treatment. It has,
however, been sometimes found advantageous to roast them, so as to
effect their partial desulphurisation and oxidation, before treating them
for the metal they contain. The furnace employed for this purpose
varies considerably in its dimensions in order to suit local circum-
stances, but always consists of a flat hearth, covered by a low arch, and
is heated by a fire-place situated at one end; there are also, in most
cases, two doors, on either side, for the withdrawal and the working of
the ore treated. From 9 to 11 cwts. of galena, or other ore of lead,
usually constitute the charge of a furnace of this description, and require
from two and a half to three hours to become sufficiently roasted. The
mineral, which is introduced into the furnace without any kind of flux,
is first spread evenly over the surface of the bottom, and the fire is
afterwards so arranged as to keep it constantly at a temperature below
the melting-point of galena. Copious sulphurous fumes are presently
seen to escape from its surface, and if any portion should, from ap-
proaching too nearly the point of fusion, become softened, fresh surfaces
are presented to the air. In this way a certain proportion of the
sulphur is driven off, and the slimes and other friable substances are
so agglutinated as to resist the force of the blast without being liable to
be carried off into the flues in the form of dust.
Smelting. — At the termination of each shift a quantity of ore remains
on the hearth in a semi-reduced state, called browse, and is more or less
574
ELEMENTS OF METALLURGY.
mixed with fragments of coke and clinkers, from which it is afterwards
roughly separated.
To commence a new shift, the cavity of the furnace is filled with peat
cut into rectangular blocks: those at the back part of the hearth are
heaped up without any kind of order, but those placed towards the front
are arranged in the shape of a regular wall. The bellows are now set in
action, and an ignited peat is thrown immediately before the nozzle,
which quickly communicates the combustion to the whole mass. On the
top of this a few shovelfuls of coal are afterwards sprinkled, for the double
purpose of binding and consolidating the mass, and also to increase the
temperature. The browse resulting from the preceding operation is
then thrown on the surface of the ignited mass; and shortly after-
wards the larger portion of the material contained in the hearth is
stirred by the aid of a poker, and a portion of it drawn out on the work-
stone. The grey slag is now removed with a shovel, and is thrown aside
for subsequent treatment. The browse, cleaned from slag, is again thrown
back into the hearth, with the addition, if it be required, of a little small-
coal. If, as sometimes happens, the browse has not been properly freed
from slag, but becomes pasty and evinces a tendency to fuse, it must be
hardened by the addition of lime, which dries the mixture and facilitates
the subsequent extraction of the lead. When, on the contrary, the ore is
found too refractory, a small addition of lime is also made; but in this
case a less quantity is employed, as it is only intended as a flux for the
refractory matters present, and not, as in the other instance, to act as
a dryer of the too fusible scoriæ obtained. The lumps of slag which
are thus formed contain a considerable proportion of the lead originally
present in the ores, and are therefore collected for the purpose of being
afterwards treated in the slag-hearth.
When the whole of the browse has been thrown back into the hearth,
a few shovelfuls of ore are sparingly thrown on the top of it; before
doing this, however, it is necessary to remove the slags, and to place a
lump of peat before the tuyer, which not only prevents any of the mineral
from entering the nozzle, but likewise serves to spread the blast equally
through the different parts of the mass. After an interval of about twenty
minutes, the contents of the furnace are again partially drawn out on the
work-stone, and another portion of metallic lead is carried by the channel,
f, into the pot, E. The grey slag is removed by the use of the rake, and
another lump of peat is placed before the tuyer. The browse, together
with a proper quantity of coal and quicklime, is again thrown on to the
fire, and on the top of the whole is laid a fresh supply of raw or roasted
ore. Two men are employed on each shift, the operations being con-
tinued during from twelve to fourteen hours; at the expiration of that
time, a production, varying with the nature of the ore, of from 1 to 2
tons of metallic lead is obtained.
Towards the end of the shift no addition of ore is made, and, after
stopping the blast, all the browse is taken out, and separated from grey
slag. The bottom of the hearth is now filled with lead, which is laded
back from the receiving pot, and in this way the charge is constantly
LEAD.
575
kept floating on a bath of metallic lead. The bottom is thus protected
from the corrosive action of the slags.
The lead prepared by this process is said to be usually purer than
that produced in the ordinary smelting furnace; this may arise from the
circumstance that, being exposed to a less elevated temperature, the more
fusible constituents of the ore are alone obtained, while in the smelting
furnace the heat employed is often so great as to effect the reduction of
some of the foreign metals contained in it, which, by entering into com-
bination with the lead, tends to impair its quality. When ores, assaying
from 75 to 80 per cent., are operated on, from 1 to 2 cwts. of coal and
about four small cartloads of peat are required to produce a fodder
(21 cwts.) of lead. The cost of lead-smelting in the ore-hearth is, how-
ever, considerably in excess of that by the reverberatory furnace, and its
use is consequently gradually becoming more restricted.
2
2
THE AMERICAN HEARTH.-This hearth was first introduced at the
Rossie mines, in the State of New York, which are now abandoned; it
has a cast-iron bottom, 24 inches square, 12 inches deep, and 2 inches in
thickness. The work-stone, which is 32 inches wide and 22 inches from
front to back, is provided with raised sides, and has the usual diagonal
groove for directing the reduced metal into the receiving-pot. An air-
chest, 14 inches in height, of cast-iron, forms a wall on the sides and back
of this hearth; its outside width is 6 inches, and, as the thickness of the
metal is of an inch, a vacant space is consequently left within, a little
more than 12 inches in height and 4 inches in width. The blast passes
into this box on one side, and escapes at the other through a curved pipe
which conducts it to a tuyer occupying the usual position at the back of
the furnace; in this way the sides and back are kept cool, while the blast
is at the same time heated before entering the fire. The bottom is, like
that of the ordinary ore-hearth, kept full of molten lead, on which the
charge floats during the operations of smelting; the fuel employed is
exclusively wood, and the galena to be treated must be broken into
pieces, which should not be larger than of a cubic inch. This hearth
remains continuously in blast during six days of the week, and is worked
by four men, namely, two on each shift. About a quarter of a cord of
wood is consumed per ton of lead obtained, or the wood burnt reduces
a little more than 2 times its weight of metal. The daily consumption
of wood in a hearth of this description is three-quarters of a cord, and
the yield of lead is about 7,500 lbs.
8
An experimental ore-hearth on this principle was in operation at
Bleiberg, in Carinthia, during the years 1849, 1850 and 1851; the
average assay produce of the ores treated during those years was 71.16
per cent. of lead, and the average loss, exclusive of that in the slag, of
which a portion would be recovered, was 10.51 per cent. The average
consumption of wood was 3.36 cubic feet per centner of ore treated, or
5.26 cubic feet per centner of lead produced.*
According to more recent observations made by Plattner, 25 centners of
·
* Vicuna centner = 123 46 lbs. avoirdupois.
""
cubic foot = 1·075 English cubic foot.
576
ELEMENTS OF METALLURGY.
raw ore, containing by assay from 70 to 71 per cent. of lead, were treated
in twelve hours and yielded from 61 to 62 per cent. of lead, exclusive
of that contained in the slag. The richer parcels of ore, yielding by
assay 74 per cent. of metal, smelted more rapidly and afforded better
results; since 45 centners were treated in the course of twelve hours,
and yielded from 66 to 67 per cent. of lead, exclusive of that retained in
the slags.
At Przibram, in Bohemia (1856), the ore contained 74-88 per cent. of
lead, and the direct yield in the American hearth was 60.68 per cent.,
exclusive of that subsequently obtained by treating the slags. In the
course of twenty-four hours from 60 to 74 centners of ore were treated,
with a consumption of 53·4 cubic feet of wood and 50·1 cubic feet of
charcoal.
EXTRACTION OF SILVER FROM LEAD.
Before the discovery, by the late Hugh Lee Pattinson, of the process
by which the silver in argentiferous lead may be concentrated in a com-
paratively small amount of that metal, the whole of the lead obtained by
smelting was, when sufficiently rich, subjected to cupellation. When,
however, it contained less than about 8 ozs. of silver per ton it was
not considered to pay the expenses of the operation; whereas, by the
method of crystallisation, lead containing 2 ozs. only of silver per ton
may sometimes be desilverised at a profit. A considerable proportion of
the lead produced, both in this country and in others, contains a less
amount of silver than is necessary to pay the cost of its extraction by
direct cupellation, and consequently, until the discovery of the Pattinson
process, the whole of this silver was lost to commerce.
This process is founded on the circumstance, first noticed by Mr.
Pattinson in the year 1829, that when lead containing silver is melted in
a suitable vessel, and afterwards suffered slowly to cool, with constant
stirring, at a temperature near the melting-point of lead, small metallic
crystals begin to form within the liquid alloy, which, as rapidly as they
are produced, sink to the bottom, and on being removed are found to
contain less silver than the lead originally operated on; the still-fluid
alloy from which the crystals have been separated is at the same time
rendered proportionately richer in silver.
The work-lead obtained from the smelting furnace usually, however,
contains antimony, copper, and other oxidised impurities, and these are
sometimes present in sufficient amounts to materially interfere with the
concentration of silver by crystallisation; they are, therefore, previously
removed by a process known as improving or softening.
IMPROVING OR SOFTENING.-This operation consists of fusing the lead
in a reverberatory furnace of peculiar construction, and allowing it to
remain, when in a melted state, exposed for a more or less considerable
period to the oxidising influences of the air. By this treatment the anti-
mony and other metals, together with a portion of the lead, become gradu-
ally oxidised, and are removed from the surface of the bath by an iron
LEAD.
577
rake; thus constantly exposing a fresh surface to the action of the heated
gases, until the greater portion of the impurity is removed, and a pure,
or nearly pure, alloy of lead and silver obtained.
The hearth of the furnace in which this operation is conducted
often consists of a large cast-iron pan about 1 inch in thickness, which
may be 10 feet in length, 5 feet 6 inches in width, and about 10 inches in
depth. The fire-place, which is about 20 inches in width, has a length
equal to the width of the pan, from which it is separated by a low bridge
about 2 feet in width. The arch at the bridge end is 16 inches above
the edge of the pan, while at the other extremity its height from the same
point is only 8 inches. All the angles of the casting are carefully
rounded in order to prevent breakage from expansion or contraction, and
the softened lead is, when required, drawn off into a cast-iron pot by
means of a hole bored in the bottom near its outer edge. This, when
necessary, is stopped by a turned iron plug kept in its place by a weighted
lever.
The charge, which is about 11 tons, is first fused in an iron pot set
in brickwork at the side of the furnace, and is subsequently laded into
the pan through a sheet-iron gutter prepared for that purpose. When
the metal is in a fit state for tapping, a small portion taken out in a ladle,
and poured into an iron mould, will be observed on cooling to present on
the surface a peculiar flaky subcrystalline appearance, which, when once
seen, is easily again recognised. As soon as this appearance presents
itself the fire is lowered, the plug loosened, and the contents of the
pan are drawn off into a pot, from which they are afterwards laded into
moulds.
In some cases, as at Pontgibaud, much larger furnaces than that above
described are employed for the operation of softening. At that establish-
ment the improving pans are each 13 feet in length by 6 feet 6 inches in
width, and are capable of working charges of 20 tons.
The time necessary for softening hard lead necessarily depends on
the proportion of impurity it contains; consequently some varieties will
be sufficiently purified after the expiration of twelve hours, while in other
cases it becomes necessary to continue the operation during several days.
Ordinary hard lead from the Cornish flowing furnace, or from the Cas-
tilian blast-furnace, is usually softened in about thirty-six hours, with a
consumption of about 2 cwts. of coal per ton. In some smelting estab-
lishments the hard lead is softened in an ordinary reverberatory furnace,
provided with a slag bottom. When a furnace of this description is
employed, calcination takes place at a higher temperature, and the opera-
tion is conducted more rapidly than in iron pans; the consumption of
fuel is about the same, but the loss of lead by volatilisation is somewhat
greater.
The calcined dross, removed from the surface of the pan, is treated in
the reducing furnace, and the resulting cinder in the slag-hearth, or in
some other form of blast-furnace. The very hard lead thus obtained is
again subjected to a process of softening in the improving furnace; a cal-
cined dross is ultimately obtained affording a brittle alloy, which is
2 P
578
ELEMENTS OF METALLURGY.
usually sold to type-founders. The quantity of this very hard lead
annually produced, even in large establishments, amounts to only a few
tons.
DESILVERISATION.
PATTINSON'S PROCESS.-This operation is usually
conducted in a series of from nine to twelve cast-iron pots, which, if
worked by hand, contain 6 tons of metal each, but when cranes are em-
ployed 10-ton pots are more generally used; these are ordinarily 5 feet
4 inches in diameter and 2 feet 6 inches in depth. A pot at one end of
the series has generally a capacity equal to two-thirds only of that of
cach of the others, and is known as the market-pot.
Each pot is provided with a separate fire-place, and is heated by a cir-
cular flue passing round it, which can be closed when required by means
of a damper; the products of combustion finally escape into a flue below
the level of the floor, running parallel with the line of pots. In order
the more easily to follow the process, we will suppose the lead operated
on, which, according to its quality, may or may not have previously under-
gone the process of improving, to contain about 21 ozs. of silver per ton.
If the market-pot be called No. 1, this lead will be introduced into No. 6,
fig. 173;* when fused it is carefully skimmed with a perforated ladle, in
order to remove the covering of oxide or pot-dross, and the fire is at once
withdrawn. The cooling of the lead is now promoted by sprinkling
water on its surface, and while its temperature is being thus lowered it is
kept constantly stirred with a chisel-pointed iron bar called a slice. All
those portions, which become solidified and adhere to the sides of the
pot are also removed, and forced under the surface of the liquid metal,
where they again become melted. By this treatment crystals soon begin
to make their appearance; in proportion as these form and accumulate at
the bottom they are removed by a large perforated iron ladle, in which,
after having been well shaken, they are first allowed to drain into the pot
whence they have been removed, and afterwards carried over and depo-
sited in the next kettle (No. 5), in the direction of the market-pot. This
is continued until two-thirds of the lead in pot No. 6 has been transferred
in the form of crystals to pot No. 5, when the lead remaining in No. 6
will contain about 40 ozs. of silver per ton, while that transferred to
No. 5 yields only about 11 ozs. per ton.
The enriched lead in the bottom of No. 6 is now laded into No. 7,
next on the left, which eventually becomes filled with lead containing
40 ozs. of silver per ton. A fresh supply of lead of the same tenure
in silver is now introduced into pot No. 6, and the resulting crystals
passed in the direction of the market-pot, while the enriched lead, re-
maining in the bottom, is laded into the pot next to it on the other side.
Each pot in succession, as it becomes filled by crystals from the one side,
or by bottoms from the other, is in its turn crystallised.
* The system adopted in numbering the pots in different establishments is not
always the same. In many cases the numbers are made to commence with the kettle
next the market-pot, which is called No. 1; for the purpose of describing the pro-
cess it has, however, been considered more simple to begin with the market-pot, which
thus itself becomes No. 1.
LEAD.
579
"down the
In this way the crystals obtained from the pots as they go
house" towards the market-pot will become gradually poorer, while the
pot-bottoms passing "up the house" in a contrary direction are progres-
sively increasing in richness. The final result, consequently, will be
that at one end of the line of kettles the lead will contain but little
silver, while at the other it will have become very much enriched.
Any lead that may be on hand assaying about 40 ozs. of silver will
be introduced into pot No. 7, while lead containing 11 ozs. will be
melted in No. 5; the other pots in the series may, in the same way, from
time to time receive lead yielding the same amount, or a nearly similar
amount, of silver per ton as the metal which they severally contain.
When this system, which is known as the method of thirds, is strictly
adhered to, the lead in each pot will be, approximately, twice as rich in
silver as that which is next to it in the direction of the market-pot. If,
however, a different lead has been introduced into any of the pots, the
ratio of this progressive increase in silver may be more or less interfered
with. In the richer pots the separation of silver is less complete than in
the poorer ones, and consequently the progressive enrichment will not be
so rapid. In working the last pot the whole of the bottom is not always
laded out, as it is sometimes found advantageous to subject it to a treatment
by which the richness of the alloy is still further increased. When the
ordinary quantity of two-thirds of the lead has been transferred in the
form of crystals to the pot next to it down the house, the remaining one-
third will consist of a mixture of crystallised and uncrystallised alloy.
The latter being much richer than the former, is separated as completely
as possible, and this portion, only amounting to a little more than one-
half the bottom, is sent to the refining furnace. This separation is
effected by pressing the mixture with the curved side of one of the large
perforated ladles, when the still-liquid alloy enters the bowl and is.
removed by a small unperforated dipper; the lead thus obtained will
evidently be richer in silver than the portion remaining in the kettle in
the form of crystals.
The desilverised metal, or market-lead, should not contain above
10 dwts. of silver per ton, while the rich lead is usually concentrated
so as to contain from 400 to 600 ozs. per ton. During the whole of
these operations oxidation of lead is continuously going on, and it may
be estimated that lead assaying 20 ozs. of silver per ton will produce
25 per cent. of its weight of dross. At Pontgibaud, where the lead
usually operated on contains 96½ ozs. of silver per ton, nearly one-third
of the weight of the market-lead produced is skimmed off the various
pots and is passed to the reducing furnace.*
In an establishment in which the usual amount of silver in the lead
* Before skimming a pot a little sawdust or spent tan is usually scattered over
the surface of the metal, and well incorporated with the scum floating on the top.
This facilitates the separation of metallic lead, when the dross is removed in a small
perforated ladle, and also, to some extent, acts as a reducing agent during the sub-
sequent treatment of the oxides in the reverberatory furnace.
2 P 2
580
ELEMENTS OF METALLURGY.
operated on was about 21 ozs. per ton, assays of the several pots afforded
the following results:—
No. 1, market-pot
•
""
""
""
2345
6, charging-pot
784
""
9
•
Silver per Ton.
Oz. dwt. gr.
090 Market-lead.
0 18 6
2 0 0
4 5
5
0
11 4 0
21 9
41 1
79 8 0
129
Bottoms of No. 10 gave
10 .
219 16 0
·
358 ozs. 8 dwts. of
silver per ton.
At Pontgibaud, where the lead operated on is very rich, and a series
of twelve pots is employed, the assays of the various kettles were, in
1867, as follow :-
No. 1, market-pot
"
3
*
2
3
•
Silver per Ton.
Oz. dwt. gr.
0 9 15 Market-lead.
0 19 7
1 18 14
3 17 4
7 7 21
12 17 5
9
6717 UAWN
4
5
22 10 3
36 19 12
59 9 16
""
10, charging-pot
96 9 4
11
""
167 3 2
12
273 6 1
Bottom of No. 12 gave
514 ozs. 9 dwts. 18 grs.
per ton.
The ladle employed, when manual labour is made use of, is 16 inches
in diameter, 5 inches in depth, and is pierced with -inch holes. When
cranes are used, the ladles are 20 inches in diameter, 6 inches in depth,
and are picrced with -inch holes; thickness of iron, 2-inch; length of
handle, 9 feet 6 inches. The large baling-ladles used for turning back
the bottoms are 14 inches in diameter and 8 inches deep, having a
handle 7 feet long.
4
When, during the operation of fishing out the crystals, the ladle
becomes chilled and the holes partially closed, it is heated to the proper
temperature by being placed for a few seconds in the pot of hot lead, into
which they are turned over. It was formerly usual to provide small pots
for this purpose filled with lead, called heaters, in front of the larger pots,
but these are now generally dispensed with. Two crystallisers are em-
ployed in working each pot, and one fireman is required for each set;
the working of each pot occupies about two hours, and by the use of
cranes 10-ton pots can be worked as expeditiously as 6-ton pots by hand.
When the lead operated on contains about 24 ozs. of silver per ton,
the average expenditure of coal per ton of lead treated is 7.14 cwts.
At
LEAD.
581
Pontgibaud the desilverisation of the rich work-lead there produced is
attended with a consumption of about 9 cwts. of coal per ton.
Figs. 173 and 174 represent a plan and elevation of a set of Pattin-
son's pots as arranged for working with cranes. No. 1 is the market-pot,

10
d
B
7
d
d
4
B
Fig. 173.- Pattinson's Pots; plan.
having two-thirds the capacity of the others, which are working-pots; a
long ash-pit, A, extends the whole length of the set, and is partially
covered by the iron platform, B, supported on pillars; each of the fire-
places, a, is provided with an iron door.
In order to desilverise by the aid of this arrangement, the potman
sinks the ladle sideways to the bottom of the kettle; and having turned

WISON WK MA
Fig. 174.-Pattinson's Pots; elevation.
it over so as to become full of crystals, he attaches a hook to the cross-
handle, a', of the ladle, fig. 173, which is then withdrawn by the other
workman, who turns the winch. In doing this the iron shank slides
over a roller on the end of the crane, d, and as soon as it is withdrawn
from the metal, the first workman, who guides the handle during the
operation, slips it into one of the cheeks, c, at the back, where it becomes
securely fixed. The ladle, filled with crystals, is thus suspended over the
pot whence it was withdrawn, and after being allowed to drain for a short
time it receives a few shakes by smartly jerking the handle, which for
this purpose is released from the cheek at the back of the crane. This
is now swung round, the shank of the ladle slipped from under the catch,
and the crystals deposited in the pot next on the right. This is con-
tinued until the necessary amount of crystals has been withdrawn, when
the enriched lead, remaining in the bottom, is taken out by a ladle with-
out perforations, and is turned over in the next pot on the left.
Although the method by thirds is that usually adoped for the desilver-
isation of lead moderately rich in silver, no general rule can be laid
down with regard to the system of working to be employed, as this may
be more or less varied in accordance with the particular requirements of
582
ELEMENTS OF METALLURGY.
the case.
For the desilverisation of poor argentiferous lead a system
called the method by eighths is sometimes employed, when, instead of re-
moving two-thirds of the contents of each pot in the form of crystals,
seven eighths are taken out in that state. The treatment of poor argenti-
ferous lead may, however, be effected by a combination of the two systems;
beginning by the method of eighths, the enriched lead may be further
concentrated by the method of thirds.
MODIFICATIONS OF PATTINSON'S PROCESS.-A patent was granted to
Mr. P. J. Worsley, in 1860, for "Improvements in the Separation of
Silver and Lead," but although sundry experiments carried out at the
Rotherhithe Lead-Works sufficiently demonstrated the efficiency of the
process, it was ultimately abandoned, on the ground of the expensive
nature of the necessary alterations in the plant, and on account of the
time required for the workmen to acquire the requisite amount of
experience.
A very similar arrangement for effecting the same object has, how-
ever, been introduced at lead-works at Rouen and elsewhere, under the
name of the "système Laveissière." The arrangement employed for this
process essentially consists of two cast-iron vessels, the first of which is
called the melting-pot, and the other the crystallising-pot, which must be
placed at such a level that the metal from the melting-pot may be run
directly into it. Below the level of the crystallising-pot must be one or
more receivers for the reception of the enriched lead. The melting-pot
is provided, on the side next the crystalliser, with a discharge-pipe closed
by a slide valve.
The crystallising apparatus is a cast-iron pot, provided with a
vertical stirrer, which, at opposite sides of the bottom, has discharge-
pipes fitted with slide-valves. Each of these is heated by a fire to
prevent its becoming obstructed by the cooling of the metal within it,
and below are placed pots for the reception of the liquid alloy, which, on
opening the valves, drains from the crystals retained in the pot above.
The stirring apparatus consists of two vertical shafts of wrought-iron
working vertically in the centre of the pot; one of these is solid, and
stands on a step cast on the bottom, while the other, which incloses it, is
a tube, and is supported by a collar. Each axle has, at its upper extremity,
a mitre-wheel, and the outer one being shorter than the other, another
mitre-wheel is made to work horizontally between them in such a way as
to cause the two shafts to revolve in contrary directions. To the lower
extremity of each is attached an iron stirrer provided with knives, which
almost touch the sides of the pot, so as to protect them from any incrus-
tation of chilled lead. The object of this stirrer, which receives its
motion, by a belt, from a steam-engine or water-wheel, is to promote
throughout the mass the production of that uniformity of temperature
necessary for the crystallisation of the metal, and to so compress the
crystals formed as to cause them to separate readily from the liquid alloy.
With the formation of increasing quantities of crystals the resistance
to stirring becomes greater, and when a certain quantity has accumu-
lated, a considerable amount of power becomes necessary.
The appa-
LEAD.
583
ratus employed should therefore be provided with a tightening pulley, or
some similar contrivance, by which the belt is made to slip when the
desired accumulation of crystals has taken place. These conditions may
be so adjusted as to suit any system of working; but when the liquid
alloy is to be reduced to one-third the weight of the total contents of
the pot, the stirrer must be arrested as soon as two-thirds of the charge
have assumed the crystalline form. The pots are heated by separate fire-
places, and above those, into which the liquid alloy is run out, is a crane
by which the cnriched lead is lifted, by means of iron eyes cast into
the metal, and is brought back to the melting-pot, to be again treated.
In working with this apparatus, such a quantity of the lead to be
operated on must be melted as corresponds to the capacity of the crys-
tallising vessel, and as soon as it is fused it is run into the crystalliser,
and the operation of stirring commences.
The formation of crystals is effected in the usual way by gradually
lowering the temperature, and as soon as the required amount has been
formed the lateral valves are opened and the liquid alloy is run into the
receiving-pots. Lead, containing the same amount of silver as the
crystals remaining in the crystalliser, is now fused in the melting-pot in
such quantity as to make up with them another charge; this is tapped in
upon the crystals, and a second quantity of enriched alloy is obtained as
before. These operations are continued until rich alloy suited for cupel-
lation is obtained on the one hand, and poor lead ready for the market on
the other.
As soon as a sufficient amount of each class of lead has been accu-
mulated to make up a full charge, with the crystals remaining in the
crystalliser, the process may be continued with unbroken regularity. It
is stated that by this method the cost of labour is only one-half of that
by the ordinary process, and that, in addition, a considerable saving of
fuel is effected.
At the lead-works of MM. Luce & Rozan, at Marseilles, a process of
crystallising by steam has been introduced. The apparatus employed
is similar in form and arrangement to that employed by M. Laveissière,
at Rouen; but instead of using machinery for stirring the lead, the same
object is more simply and effectually accomplished by introducing a jet
of high-pressure steam into the molten metal. The agitation caused
by the ascent of the steam through the mass of lead is very great, and
necessitates that the sides of the pot should be much higher than usual
above the surface of the metal, and also that it should be provided with a
strong iron cover, having four segmental openings fitted with hinged flaps,
which the workmen open, one after the other, as required. To this
cover is fitted a large iron pipe, through which the escaping steam and
dust are carried into condensing chambers communicating with the
chimney. The steam is maintained at a uniform pressure of 45 lbs.
per square inch; experience having shown that a lower one is insuffi-
cient to overcome the resistance offered by the mass of crystals, and
that steam at a higher pressure acts too energetically as an oxidising
agent. Before turning on steam, care must be taken to let out any
584
ELEMENTS OF METALLURGY.
condensed water that may have collected in the steam-pipes, or otherwise
an explosion would ensue.
Mr. W. Hutchison, who visited the works of MM. Luce & Rozan
with a view to ascertaining the relative cost and efficiency of their method
as compared with the old system of working with cranes, is of opinion
that its adoption would, in the case of rich leads, result in an economy of
at least 30 per cent. on the old Pattinson process.
DESILVERISATION BY ZINC. PARKES'S PROCESS.-When lead and zinc
are melted together, and the fused mixture is allowed to cool slowly, the
zinc solidifies first, forming a layer on the surface of the metallic bath,
which may be readily removed in the form of a crust containing nearly
the whole of the silver present in the original lead. Patents for the
desilverisation of lead by this means were granted to Mr. Alexander
Parkes, of Birmingham, in the years 1850, 1851, and 1852; in 1859 this
process was in operation at the works of Messrs. Sins, Willyams,
Nevill and Co., of Llanelly. As it was there carried out, the process is
conducted as follows:-A charge of 7 tons of the lead to be desilverised
is fused in a large cast-iron pot, close to which is placed a smaller one for
the fusion of the necessary zinc. As soon as the whole of the lead has
become melted it is made to boil, by the insertion of a green pole, and
the oxides, which rise to the surface, are removed by a perforated skimmer.
The temperature of the metal is now raised to the melting-point of zinc,
and zinc is added in the fused state in the proportion of about 1½ lb. for
each ounce of silver contained in the lead operated on. The mixture is
now well stirred during about two hours, the fire subsequently withdrawn,
and the metal allowed gradually to cool; during the process of cooling,
any of the zinc alloy which may adhere, in the form of solid rings, to the
sides of the pot must be removed by means of a piece of wood, and as
soon as the surface has sufficiently hardened it is collected by skimming
with a perforated ladle. The alloy thus obtained is a mixture of lead
and zinc containing silver, and is subjected to a process of liquation in
an inclined iron retort, where it is heated somewhat above the melting-
point of lead. The eliquated lead thus obtained should assay about
10 ozs. of silver per ton, and the residual zinc will contain, in addition
to a considerable amount of silver, about 50 per cent. of lead. This
cliquated lead is allowed to accumulate until the quantity is sufficient to
form a charge for the melting-pot, when it is fused and skimmed in the
usual way, but without addition of zinc, as the proportion of that metal
present is sufficient for the removal of the silver. The zinc, after being
as far as possible freed from lead by liquation, is distilled in a Belgian
furnace, in admixture with lime and coal-dust; the residue in the retorts
consists of lead and pulverulent matter. The former is re-melted,
skimmed and cupelled; and the latter added to the charges, of an ordi-
nary lead furnace.
The lead which remains in the melting-pot, after the removal of the
argentiferous alloy from its surface, contains a certain amount of zinc
which must be removed by treatment in the ordinary softening furnace.
The furnace used for this purpose may be of the usual dimensions, and
LEAD.
585
the melted lead is maintained at a full red-heat for a period varying with
its quality. A calcination of from nine to twelve hours will generally
be found sufficient, but samples must be taken, from time to time, for the
purpose of testing the progress of the operation. The lead is skimmed
twice: once about three hours after charging, and a second time shortly
before tapping.
After a comparatively short trial, Parkes's process was abandoned at
the Llanelly works, as practical difficulties were experienced which
could not at the time be overcome. In 1851 this subject was carefully
investigated by Karsten and Lange at Friedrichshütte, near Tarnowitz;
but the process was finally abandoned on the following grounds: first,
that it was difficult to so completely separate the zinc from the desilver-
ised lead as to render it easily marketable; secondly, that the silver
could not be extracted from the zinc alloy without considerable loss;
and thirdly, that the separation of zinc from the lead was equally difficult
to accomplish.
MODIFICATIONS OF PARKES'S PROCESS IN Germany and ELSEWHERE.
The desilverisation of lead by means of zinc was again taken up in
Germany in 1866, since which date the process has been in operation
at the works of Messrs. Pirath & Co., of Commern, and at those of
Herbst & Co., near Call.
At the works above mentioned the process
is conducted as follows:-The lead is melted in a large iron pot, and is
sufficiently heated to fuse a piece of zinc when placed upon its surface.
The zinc is added in three successive portions: first, two-thirds of the
quantity required, then one-fourth, and lastly one-twelfth. After addi-
tion of the first portion, the two metals are intimately mixed by stirring
with a perforated ladle for about half an hour; during this period the
temperature is well maintained, and at the expiration of that time the fire is
damped down with wet fuel, and the pot allowed to cool. As soon as the
crust of zinc which accumulates on the surface has become sufficiently
solidified it is removed, and any portions that may adhere to the sides are
carefully detached; the skimming is continued until the lead begins to
crystallise and to set on the surfaces of the pot. The lead is now again
heated to the melting-point of zinc, the second portion of that metal is
added, and the stirring and skimming are conducted as before. Finally,
the third addition of zinc is made, and the contents of the pot are again
stirred and skimmed. On account of the richness in silver of the zinc
which now comes to the surface, it becomes necessary that in this case
the skimming should be performed with a more than usual amount of
The proportion of zinc added is regulated in accordance with the
amount of silver present in the original lead.
care.
For the complete desilverisation of argentiferous lead the following
proportions of zinc have, in practice, been found necessary :—
Lead containing 250 grammes of silver per 1,000 kilos requires 14 p. c. of zine.
500
1,000
"}}
""
""
""
11}{}
1/1
""
>>
17
1,500
""
>>
""
3,000
>>
""
>>
""
4,000
2
>>
""
586
ELEMENTS OF METALLURGY.
It will be observed that the quantity of zinc necessary is by no means
proportionate to the amount of silver contained in the lead. No reason
can at present be assigned for this, but the accuracy of the figures above
given has been confirmed by the results of a series of trials made at the
silver-works at Clausthal.
The argentiferous zinc removed from the mixing-pot retains a con-
siderable amount of lead, which is partially separated by liquation by
means of two iron pots, one placed at a higher level than the other; to
the bottom of the upper pot is cast a pipe, which can be opened or closed
as required. The zinc skimmings are strongly heated in this pot, and
the eliquated metal which collects in the bottom is tapped into the lower
vessel, while the argentiferous residue remains in the upper one in the
form of a pulverulent mass. The eliquated metal carries with it a little
silver and zinc, and after slowly cooling, it is skimmed, the skimmings.
being again subjected to liquation. The residual lead, which is now poor
in silver, is added to the original metal previously to the introduction of
the third portion of zinc. The argentiferous zinc residues are finally
melted in a small blast-furnace with an admixture of lead slags and tap-
cinder, and the lead obtained is cupelled in an English refining furnace.
At the works of Herbst & Co. the dezincification of the desilverised
lead is cffected by the aid of chloride of lead. For this purpose the poor
lead from which the zinc is to be removed is kept melted at a moderate
temperature, for about twenty-four hours, under a layer of chloride of
lead, when, by frequent stirring, the zinc is converted into zinc chloride
with the separation of a corresponding amount of metallic lead. The
chloride of lead used is prepared by treating fume from the flues with
hydrochloric acid, and is consequently by no means pure.
At the lead-works of Pirath and Co., at Commern, common salt has
been employed for the same purpose; and at the Imperial works at
Clausthal experiments have been made on the substitution of the natural
potassium salts of Stassfurt for chloride of sodium. These salts, which
contain chloride of magnesium, are by the aid of frequent stirring said
to have afforded results quite as satisfactory as those produced by the use
of chloride of lead, while a mixture of sulphate of lead and Stassfurt
salt is stated to have been more advantageous than either chloride of lead
or the salt alone. As, however, there is not the slightest difficulty in
removing, in the course of a few hours, the zine from desilverised lead in
an ordinary softening furnace by the aid of a moderate heat, it appears
very doubtful if any advantage is to be derived from the use of the
salts specified. It is believed that their use is now almost entirely
abandoned.
According to Illig the dezincification of desilverised lead may be
effected by passing it through a small blast-furnace with the addition of
sand and tap-cinder. There can be no doubt but that the zinc may be
thus removed, although a considerable loss of lead must necessarily
ensue, and the lead so treated would be more or less hardened; this
method of treatment is, in point of fact, a fusion in the slag-hearth.
In the year 1866, Clemens Fleming Flach, "of Call, in the kingdom
LEAD.
587
of Prussia," obtained letters patent in this country for " Improvements
in Extracting Silver from Lead." By the system described in the
specification of this patent the lead is first desilverised by two or more
successive additions of zinc in the usual way, and the resulting argenti-
ferous alloy is melted in a low blast-furnace with siliceous slags. The
zinc is removed from the desilverised lead by fusion with slags in a
blast-furnace, and by boiling the lead produced, when in a state of fusion,
by the introduction of green poles.
Several lead-smelters in this country, and among others the Par
Smelting Company, Cornwall, Messrs. Locke, Blackett and Co., New-
castle-on-Tyne, and Messrs. Glover and Robinson, Widnes, Lancashire,
are at present working under licenses from the representatives of the
late C. F. Flach.* This process has also been introduced into various
large Continental establishments, such as that belonging to the Mecher-
nich Company, near Duren, Prussia, and at the lead-works of Guillem
and Co., at Marseilles. As, however, might have been anticipated, the
process for separating zinc from the desilverised lead in the blast-furnace
has not been adopted.
This process in its modified form is exceedingly simple, and is con-
ducted in the following way: At a height of about 8 feet from the
level of the floor three cast-iron pots are placed in brick-work over sepa-
rate fire-places; the largest of these is of a capacity to contain a charge
of about 12 tons of lead, while the other two are much smaller, each
holding about 3 tons of metal.
The lead to be desilverised is melted in the larger pot, where the
usual quantity of zinc is added, in three successive portions, and the
argentiferous alloy is removed, in the way already described. This is
deposited in one of the smaller pots, in which a portion of the associated
lead is separated by liquation; this collects at the bottom, and the con-
centrated argentiferous alloy is skimmed from its surface by the aid of a
shallow perforated ladle. When one of the smaller pots has become filled
with skimmings from the large one it is subjected to liquation; the other
in the mean time serving for the reception of skimmings from the larger
pot.
The argentiferous alloy, from which as much as possible of the lead
has been previously separated, is smelted with an admixture of lead slag
and tap-cinder, in a blast-furnace, 2 feet square and 9 feet in height,
blown by three tuyers. The lead thus obtained is finally subjected to
cupellation. During the process of smelting in the blast-furnace the
zinc becomes volatilised, and is carried off by the flue in the form of
zinc oxide; the draught is accelerated by the introduction of a steam-jet
into the flue leading from the top of the blast-furnace to the chimney.
The lead eliquated in the smaller pots, from the skimmings removed
from the large one, is added to the next charge of original lead. That
remaining in the large pot, after the removal of the zinciferous crust, is
tapped into the pan of an improving-furnace, situated at a lower level,
where it is kept at a full red-heat during about twelve hours, and is occa-
* Flach died in 1868.
588
ELEMENTS OF METALLURGY.
sionally skimmed with an iron rake; at the cxpiration of this time it is
drawn off into a cast-iron pot and laded into moulds as market-lead.
At the Par Smelting Works, where this system has been in operation
for several years, a saving of nearly 40 per cent. has been effected over the
cost of desilverisation by Pattinson's process, and the excess of silver is
somewhat larger than is obtained by that method; the loss of lead is
stated to be slightly over 2 per cent. Guillem & Co., of Marseilles, state
that by this system their rich lead is concentrated so as to contain 9
per cent. of silver, and that they estimate the saving in cost, as compared
with the ordinary Pattinson process, at 45 per cent. Messrs. Glover and
Robinson have also entirely discarded the process of crystallisation,
and inform us that they find desilverisation by zinc considerably more
advantageous.
By Cordurie's process, for which a patent was obtained in this country
a few weeks prior to the date of Flach's, the dezincification of desilverised
lead is effected by the agency of steam. Superheated steam is passed
through the desilverised lead, heated to redness, until hydrogen gas ceases
to be evolved. By this means the zinc is oxidised by the oxygen of the
steam with an equivalent evolution of hydrogen, while the lead is but
slightly attacked; the zinc oxide which rises to the surface is subsc-
quently skimmed off. The argentiferous crust of zinciferous alloy is also
exposed to the action either of hot air or of superheated steam; the zine
is thus oxidised, together with a certain quantity of lead, and the mixed
oxides are separated from the residual argentiferous lead either by
liquation or by skimming. The rich lead resulting from this treatment
is cupelled.
A description of Cordurié's process, as conducted in the works of
Messrs. Rothschild, at Havre, has been published by M. Gruner,* who pre-
dicted that it would shortly supersede every other process of desilverisa-
tion. We, however, agree with Dr. Percy, that as zinc can be readily
removed from desilverised lead in the improving furnace, it is not probable
that superheated steam will ever be generally employed for that purpose.
In a pamphlet by Sièger on the comparative merits of the systems of
Flach and Cordurié, without date, but, we believe, published in 1870, it
is stated that several establishments which had made trial of Cordurié's
process had subsequently abandoned its use.
CUPELLING OR REFINING.-In this country the cupellation of argenti-
ferous lead is conducted on a hearth composed of bone-ash, which forms
the movable bottom of a reverberatory furnace. The cupel, or test, is
contained in an elliptical iron framing, seldom less than 5 or 6 inches
in depth, usually about 4 feet in its greater and 3 feet in its lesser
diameter. To support and strengthen the bottom of the test, this frame
is provided with four parallel cross-bars, 4 inches wide, and, like the
ring itself, half an inch in thickness. There are also two bars of wrought-
iron called "strap-bars," connecting the first transverse bar at the wider
end with the ring. This framing, or test-ring, is most frequently made of
wrought-iron, the cross bars being attached by rivets, but in some cases
* Annales des Mines,' 6 Sér. 13, p. 395. 1868.
*.
LEAD.
589
it is formed of cast-iron, and is then, including the bars across the bottom,
cast in one piece.
To prepare a test, the frame is filled with bone-ash well beaten in
layers, after having been previously moistened with a little water, holding
a small quantity of pearl-ash in solution; the presence of a minute pro-
portion of this substance has the effect of giving consistency to the cupel
when heated. After the framing has, in this way, been filled with slightly-
moistened bone-ash, solidly beaten down, a cavity is carefully scooped
in its upper surface, until the sides are left 2 inches in width at top,
measuring from the iron ring, and gradually widening to about 3 inches
at bottom; the thickness of the bottom itself may be about 1 inch.
At the front, or wider end of the test, three holes are usually bored

7
k
i
h
B
Fig. 175.-Refinery; front elevation.
through it; of these the central one is made to communicate, by means of
a channel, with the fluid litharge in the annular cavity, formed between
the test and the slightly-curved edge of the metallic bath. This allows
the fused oxide of lead to escape as rapidly as it is produced, and when
it becomes so much corroded by the action of litharge as to be no longer
serviceable, it is closed by a little moistened bone-ash, and a new channel
is opened in connection with one of the other holes.
The test thus prepared must be kept for some time in a warm place,
to become thoroughly dry, and may be then placed in the refining furnace,
of which it forms the bottom. Figs. 175, 176, 177, represent, respectively,
an elevation, a horizontal section, and a vertical section, through the
longer axis, of the refinery employed at the Couëron Lead-Works.
The size of the fire-place, A, varies with the other dimensions of the
furnace, but it is usually nearly square, and may measure about 2 feet by
2 feet 4 inches. This is separated from the body of the furnace by a
590
ELEMENTS OF METALLURGY.
bridge, from 14 to 18 inches in width, so that the products of combustion
pass from it directly over the surface of the test, and escape to the main
flue by two separate apertures, a. The test, B, is maintained in its
position, so as to form the furnace bottom, by being tightly jammed, by
means of the wedges, b, of which there are four, supported by two iron

C
a
B
Fig. 176.-Refinery; horizontal section.
bars, against the iron ring, c (fig. 177), firmly built into the masonry of the
furnace. The application of heat to the test must, at first, be regulated
with care, since if the temperature were too abruptly raised it would be
liable to crack and exfoliate. As soon as it has become properly annealed

-$2
k
a
.
B
Fig. 177.-Refinery; transverse section through tuyer.
it is heated to redness, and a charge of the lead to be operated on is intro-
duced. In the majority of cases this is previously fused in an iron pot, C,
set over a firc-place, and provided with a gutter, d, through which the
molten lead is laded into the cavity of the test. When first introduced into
the furnace, the liquid metal becomes covered by a greyish dross; but as
LEAD.
591
soon as it has acquired the full temperature of the test, the surface of the
bath uncovers, and fused litharge begins to make its appearance. The
blast is now turned on through the nozzle, e, and the melted litharge is
thus driven from the back of the test up towards the breast, whence it
escapes by a channel or gate, ƒ (fig. 176), in connection with the central
aperture, g, through which it falls into a shallow cast-iron pot, mounted
on wheels, and furnished with a long handle. When the channel, f, has
become so much acted upon by the litharge as to be no longer service-
able, a new one is made, as shown by the dotted lines, communicating
with one of the holes situated to the right or left of the longer axis of
the test. Fuel is supplied to the grate through the door, h, while that
marked i is used for the purpose of watching and regulating the opera-
tion; the fumes are carried off by the hood, k, and the iron chimney, l.
Sometimes, instead of feeding the test with rich lead in a fused state, the
metal is introduced into the furnace in the form of pigs. In such cases the
furnace is provided with one or more iron-lined openings, called pig-holes,
through which the metal is introduced at the back of the furnace, in the
vicinity of the blast-pipe. The blast, which is usually supplied by a fan,
not only furnishes the oxygen necessary for the formation of litharge, but
also sweeps the fused oxide along the surface of the metal towards the
breast. In some cases, a blast, produced by means of a jet of steam, is
employed, instead of a current of air from ordinary blowing machinery.
In proportion as the surface of the metal in the test becomes depressed,
through constant oxidation, and the continual removal of the resulting
litharge, additional lead is supplied, either from the melting-pot, C, or in
the form of pigs, so as to keep it nearly at the original level. In this
way the operation is continued until the lead has become so much enriched
as to render it desirable that it should be tapped. When the lead operated
on contains about 600 ozs. of silver per ton, this operation is generally
performed at intervals of eight hours; during this time about 32 cwts. of
lead will have been introduced, and from 4 to 6 cwts. of enriched alloy
will remain in the bottom of the cupel. The removal of the highly-con-
centrated argentiferous lead is generally effected by making a hole in the
bottom of the test by means of a drill contrived for that purpose, and
running it off into a cast-iron pot, on wheels, placed under the cupel for
its reception; in some cases, lading out the rich lead is resorted to
instead of tapping. When the concentrated rich lead has been thus
drawn off, the tapping-hole is closed, by a pellet of bone-ash, kept in
its place by an iron plate, and another charge is immediately introduced.
The reason for thus removing the enriched argentiferous lead from the
cupel is to avoid the carrying-off of too large an amount of silver in the
litharge, which would be the case if fresh lead were continuously added
to a constantly-increasing accumulation of silver. In works where the
concentration of silver is effected by the use of zinc, it is not customary
to tap the highly-enriched lead from the cupel; since it is found more
advantageous to carry on the operation without interruption, and to add
the metal resulting from the reduction of litharge to the original lead,
before the introduction of zinc. When tapping or lading out is resorted
3
592
ELEMENTS OF METALLURGY.
to, the whole of the lead operated on is thus further enriched, and the
resulting highly argentiferous alloy is finally subjected to cupellation,
either in the same test, or in another specially prepared for the purpose.
The appearance of the surface indicates the precise period at which
the operation is terminated; the blast is then turned off, and the fire
removed from the grate. The plate of silver is thus allowed to set, and
as soon as it has done so, the wedges, b, are removed from beneath the
test-frame, which, together with its contents, is lowered upon a small
iron bogie-waggon, and taken away to cool. The silver is subsequently
detached from the cupel, and any adhering particles of litharge, slag, or
bone-ash, are removed by scraping with a wire brush.
An ordinary refinery works off from 4 to 5 cwts. of lead per hour, and
consumes from 6 to 7 cwts. of coal per ton of lead oxidised. The plate
obtained may vary in weight from 5,000 to 10,000 ozs. and usually con-
tains from 997 to 998 parts of silver in a thousand.
The loss of lead experienced during the operation of cupelling is
about 7 per cent. of the weight worked; the process is conducted by
one refiner on each shift, occasionally assisted by a labourer. The test
bottoms, which are saturated with litharge, and contain a certain amount
of silver, are broken up and smelted, either in the blast-furnace or other-
wise. In smelting establishments in which the lead produced is first
Pattinsonised, and the silver afterwards obtained by cupellation upon the
English test, the annual surplus of that metal, in excess of the amount,
indicated by assay, of the ores, is seldom less than 2 per cent.
REDUCING.-The reduction to the metallic state of litharge from
the refinery, the pot-dross, and the dross from the calcining pans, is, in
this country, effected in a reverberatory furnace, somewhat resembling in
form that used for smelting; excepting that its dimensions are smaller,
and that the sole, instead of being lower beneath the middle door than at
any other part, gradually slopes from the fire-bridge to the flue at the
opposite extremity. Here there is a depression in which is the tap-hole;
this constantly remains partially open, and from it the reduced metal
continually flows into a small iron pot, placed on the side of the furnace.
Under this pot a fire is lighted, and the lead is subsequently laded from
the pot into moulds.
Before being thrown into the furnace, the litharge is mixed with
small-coal, and is then charged on that part of the hearth which lies
before the fire-bridge. To prevent the fused oxide from attacking the
bottom of the furnace, and also to afford a sort of hollow filter for the
liquid metal, the workman, before charging the oxide to be reduced,
covers the hearth with a layer, about two inches in thickness, of bituminous
coal. The heat of the furnace soon causes the ignition of this stratum,
and it quickly becomes burnt to the state of a spongy cinder upon which
the mixture of litharge and carbonaceous matter is charged. The small-
coal in the charge causes the reduction of the litharge, which, assuming
the metallic form, flows gradually through the interstices in the cinder,
and falls into the depression at the extremity of the hearth; whence it
gradually flows through an iron spout into the external pot in which it is
LEAD.
593
collected. The surface of the charge is, during its elaboration, frequently
stirred with an iron rake, for the double purpose of exposing new surfaces
to the action of the furnace, and also to allow the reduced lead to escape
more readily.
Additional quantities of the material operated on, mixed with coal,
are from time to time charged into the furnace; at the termination of the
shift, which commonly extends over twelve hours, the tap-hole is fully
opened, and, after the escape of the whole of the lead, the residual lead-
cinder is withdrawn. A new floor of cinders is then formed, and the
operation continued as before. A furnace with a bottom 8 feet in length
and 7 feet in width, will reduce 53 tons of lead from litharge, in the
course of twenty-four hours. About 3 cwts. of coal are required for the
reduction of each ton of litharge. No fresh material is charged for a
considerable time previously to the termination of a shift, and the lead-
cinder then withdrawn, is, in the majority of cases, smelted in the slag-
hearth or in some other form of blast-furnace.
GERMAN CUPELLATION.
The old German cupelling furnace, which is still in use in many Con-
tinental establishments, is represented in figs. 178, 179, of which the first
is an elevation, and the second a horizontal section.
This apparatus consists of a kind of reverberatory oven, having a cir-

i
L
Fig. 178.-German Cupelling Furnace; elevation.
cular hearth, A (fig. 179), and a lateral fire-place, B. The bottom, which is
regularly hollowed from the sides towards the middle, is composed of fire-
bricks closely set on edge upon a solid stratum of firmly-compressed slag,
2 Q
594
ELEMENTS OF METALLURGY.
1
and is again covered with a coating of marl, carefully beaten down by iron
rammers; this is always re-laid previously to the commencement of a
fresh operation. This layer of marl corresponds to the test employed by
English refiners, and is covered by a dome of iron plastered over with
marl, and capable of being either removed, or lifted into its place, by
means of chains attached to a lever supported by the movable crane, C.
In the sides of this furnace are five openings; by the largest of these, d,
the flame passes from the fire-place into the interior of the hearth; the
two openings, l, serve for the introduction of the tuyers, by which a blast

п
Fig. 179.-German Cupelling Furnace; horizontal section.
is thrown on the fused metal, for the purpose of assisting its oxidation and,
at the same time, forcing the litharge formed on its surface towards the
aperture, E, from which it escapes in a fused state; finally, F is the
opening, through which a portion of the lead to be operated on is inserted,
in the form of hemispherical pigs. At the commencement of the opera-
tion the opening, E, is partially closed by the marl of the cupel, but in
proportion as the operation advances channels or gateways are succes-
sively cut down by a serrated iron bar, to the level of the litharge con-
tained in the furnace. The litharge which escapes from this opening
flows down to the floor of the building, where it accumulates.
Before commencing a cupellation it is necessary to arrange the cupel,
and for this purpose, after having removed the dome, the old cupel
bottom, strongly impregnated with litharge, is broken up and carried
away to be treated for the lead which it contains. The brick bottom is
now moistened with water, and covered by a thick layer of marl, well
consolidated by the use of a heavy iron rammer, and the furnace is ready
for immediate use.
About 5 tons of ordinary lead are usually cupelled at one operation,
and of this a little less than three-fourths is introduced into the furnace
LEAD.
595
before lighting up; the remainder is added at successive intervals during
the progress of the cupellation. As soon as the marl cupel has been
completed, about 75 cwts. of lead are charged, in the form of small hemi-
spherical pigs, which are placed with their convex surfaces downwards,
so as not to injure the bottom. On the centre of the heap of lead thus
formed are placed some billets of wood; these are ignited by means of
a shovelful of burning charcoal, and the movable cover, after being care-
fully dropped into its place, is luted round with fire-clay. The blast is
then turned on, and a fire of billets is made upon the grate. From three to
five hours are required for the complete fusion of the mass, and when this
has been accomplished the surface of the molten lead is found to be
covered by a scum, to which the Germans give the name of Abzug. In
order to facilitate the removal of this, by skimming, and to render it as
liquid as possible, the temperature is now raised, and it is drawn through
the litharge-channel, E. This skimming occupies about an hour, during
which time fresh quantities of scum are continually rising to the surface.
The bath of lead gradually acquires a gentle circular movement, and
becomes bright and clear, but is quickly obscured by a pasty covering of
impure litharge, or Abstrich. This, which is removed through the litharge-
channel, ordinarily begins to flow about an hour and a half after the skim-
ming-off of the last Abzug, and continues to escape during about the
same length of time, after which pure litharge makes its appearance.
Litharge subsequently continues to flow from the furnace until the
Blick, or brightening of the residual silver, takes place; this generally
occurs in from thirty to thirty-three hours after first turning on the
blast.
As soon as the flow of Abstrich has ceased, two pigs of lead are in-
troduced through the opening, F, which, besides being used for this
purpose, serves as a passage for the escape of a large portion of the pro-
ducts of combustion. The lead thus added is placed on a part of the
upper border of the bottom, which is raised for that purpose slightly
above the ordinary level. In thus adding the second portion of the lead'
to be cupelled, a hard refractory mass of Abzug is left behind on the part
of the bottom where the fusion of the pig is effected; this is from time
to time loosened and removed.
Towards the close of the operation the temperature requires to be
considerably increased for the purpose of keeping the alloy, which is
then rich in silver, in a sufficiently liquid state. The nozzles of the
tuyers supplying air to the cupel are sometimes covered by small valves
called "butterflies," which, being hung before them, serve to spread
the blast over the surface of the metallic bath. The operation is thus
continued until the greater portion of the lead has been removed in the
form of litharge, and a plate of nearly pure silver remains.
Immediately after the brightening has taken place, the workmen throw
water over the surface of the metallic residue, and the Blicksilber, which
is not pure, but still contains a little lead, &c., is removed from the furnace
for the purpose of being refined. A depression is made in the furnace
bottom for the reception of this residual silver, which is consequently
2Q 2
596
ELEMENTS OF METALLURGY.
obtained in the form of a flattened cake, presenting, roughly, the shape of
the cavity made in the bottom of the cupel.
The average loss of lead during cupellation by the German process
estimated at 8 per cent.; but when, as was formerly the case, the bed was
formed of lixiviated wood-ashes mixed with a little lime, this loss is
stated to have been sometimes as high as 14 per cent. According to
Winkler (1837) about 250 cubic feet of cord-wood are required for the
cupellation of 5 tons of argentiferous lead in the state in which it is
obtained from the smelting furnace. At Freiberg (1860), where what is
called “refined lead" is operated on, about 18 tons are cupelled at one
operation ; of this, 63 tons are placed on the bottom at the beginning,
and the remainder added after the flow of litharge has commenced.
On account of the purity of this lead, the amount of Abzug formed
does not exceed 6 cwts., and there is no Abstrich; the amount of litharge
produced is about 17 tons, of which from one-quarter to one-sixth is
red litharge, which is sold as such, while the remainder is reduced to
the metallic state, and Pattinsonised. Each cupellation occupies about
eighty hours, and the quantity of wood consumed is from 162 to 165 cubic
feet; the loss of lead is said to be from 8 to 10 per cent.
The cupel
bottoms are subsequently taken to the lead furnaces to be smelted.
REFINING THE BLICKSILBER.-This operation, which is called Fein-
brennen, may be performed in various ways, all founded on the principle
of the separation of impurities by oxidation, at a temperature somewhat
above the melting-point of silver.
The most ancient process appears to be that of refining by means of
a blast on an open test, of which the general arrangement is somewhat
similar to that of the ordinary blacksmith's forge. This method of
refining is described by Agricola in his 'De Re Metallica' (1561), and
five illustrative woodcuts are given of the apparatus then employed; it
essentially consists of a large cupel beaten into an iron dish, and of double
bellows for supplying a constant blast. The test was formerly made of
a mixture of two-thirds lixiviated wood-ashes, and one-third bone-ash ;
subsequently a mixture of bone-ash and sulphate of barium was made use
of, but latterly marl similar to that used for the furnace bottom was
employed. A hollow is cut with a curved knife in the centre of this test,
which is placed in a cavity prepared for its reception in the top of
the hearth.
The Blicksilber is cut into pieces, and piled upon the test, which is
surrounded by a sheet-iron hoop filled with charcoal; ignited charcoal is
placed before the nozzle, and the blast is turned on. The fusion of the
silver is usually complete in the course of about half an hour, when the
iron hoop is taken away, and the charcoal removed from the surface of
the metal. Small billets of dry wood are now laid before the tuyer;
these are replaced by fresh ones as fast as they are consumed, and care is
taken to remove any ash that may fall upon the surface of the metallic
bath. During this operation the silver is occasionally stirred with an
iron rod, and, as soon as the pear-shaped drop of metal which adheres
to its extremity is observed to vegetate on cooling, the blast is stopped,
LEAD.
597
the fire removed, and the cake of fine silver cooled with water until
it is solidified. It is then removed from the test, and, after being
cleared from adhering particles of slag and litharge, is ready for the
market.
Instead of refining on an open test, the operation was sometimes con-
ducted under a muffle into which a blast was admitted; the refining of
Blicksilber is now usually conducted either in a movable test, like that
employed in the English process, or in a fixed cupel forming the bottom
of a reverberatory furnace.
LEAD FUME.
Lead, being to a considerable extent volatile at high temperatures, a
notable loss of that metal is experienced during the operations of smelt-
ing, refining, reducing, &c.; various means are consequently employed
for the purpose of collecting these fumes and for rendering them avail-
able as a source of lead. The most efficacious method of collecting
the lead carried off in the state of fume is by the use of long flues of con-
siderable transverse area. Numerous other contrivances, such as drawing
the fumes through water, passing them through condensing chambers,
the introduction of water in the form of spray, blowing steam into the
flues, &c., are sometimes resorted to, but usually with less satisfactory
results. The following are the respective lengths of the flues at the
various smelting works belonging to Mr. Beaumont, as furnished by Mr.
Sopwith to Dr. Percy:-
At Allen Smelt-Mill (one
the other
""
Allenheads Mill
Rookhope Mill
Yards.
4,451
4,338
•
3,424
2,548
14,761
The total length of the above flues is consequently about 8 miles;
their transverse area is not uniform, but their average height is 8 feet
and their width 6 feet. In one year 800 tons of lead have been extracted
from the fumes obtained from these flues. At Keld Head (1857) 96 tons
13 cwts. of lead were obtained from fume resulting from the production
of 1,374 tons, or in the ratio of 7·03 per cent. At Pontgibaud, where the
flues are 500 metres in length, and the ores are smelted in blast-furnaces,
3.67 per cent. of the lead which they contain is obtained from fume. At
the Wildberg Smelting Works, Germany, where the flues were 800 feet
in length, and smelting was conducted in the Castilian furnace, 1 per
cent. of the assay produce of lead was (1859) obtained from fume.
The lead contained in fume exists to a large extent in the form of
sulphate, and is obtained by roasting and smelting it either alone or
in admixture with lead ores. Fume-lead is considerably poorer in silver
than that derived directly from the ores from which it was produced.
The following are the results obtained by a series of assays of the
598
ELEMENTS OF METALLURGY.
lead fume at Wildberg, where the average assay for silver of the lead
produced was about 21½ ozs. per ton:
SAMPLES TAKEN FROM THE TOP OF MAIN FLUE AT DISTANCES OF 100 FEET APART.

Lead.
Silver.
Per cent.
Oz. dwt. gr.
No. 1, near blast-furnace
•
49
2 9 0
""
2, near reverberatory furnace
3, 100 ft. in advance of No. 2
20
3 5 8
70
3
4, 100
5, 100
""
""
6, 100
OOTH LO
3
44
3 5
4
48
2 17 0
47
3 5 8
""
7, 100
6
46
3
""
"J
8, 100
7
40
2
""
""
9, 100
က
8
42
3 5 8
""
""
10
Stop of chamber at throat)
49
22 17 8
""
of refinery
•
SAMPLES TAKEN FROM BOTTOM OF MAIN FLUE AT DISTANCES OF 100 FEET APART.

Lead.
Silver.
Per cent.
Oz. dwt. gr.
No. 1, near blast-furnace
53
2, near reverberatory furnace
59
29 0
290
""
3, 100 ft. in advance of No. 2
63
3 5 8
4, 100
3
61
29 0
99
5, 100
4
49
2 17
0
""
""
""
6, 100
5
64
2
5
""
""
7, 100
6
""
""
""
8, 100
7
""
""
""
9, 100
8
""
""
10
(bottom of chamber at foot)
9888
46
3 6
6
5
58
1 12 5
62
2 17 0
66
3 5 8
""
of chimney.
In the same way that, from the greater volatility of lead, the metal
obtained from fume contains a less proportion of silver than that directly
extracted from the ore, so also, on account of the greater oxidisability of
lead, is that obtained from slags less argentiferous than that reduced
from the corresponding ores.
SHEET-LEAD AND LEAD PIPE.
Lead is chiefly employed in the arts, either in the form of sheets
for covering houses, making gutters, &c., or for the manufacture of pipes
for the conveyance of water and other liquids. In order to make lead
into sheets, it is first moulded in a cast-iron frame into the form of a
plate; when this has sufficiently cooled it is lifted from its mould by a
crane, and placed on the machine by which it is to be rolled into sheets.
This consists of a long frame or bench (fig. 180), about 3 feet in height,
8 feet in width, and from 70 to 80 feet in length. At intervals of every
LEAD.
599
foot are placed the rollers, a, all on exactly the same level, and so
arranged that a heavy body may be pushed from one end to the other
with great facility. In the centre of this stage is the rolling machine,
consisting of two heavy rollers, of which only the upper one, A, is seen
in the woodcut, and which, by means of powerful machinery, are made to
revolve in contrary directions. Each of these cylinders is about 18 inches
in diameter, and is turned perfectly smooth and level on the surface. By
the screws, b, and the connected pinion-wheels, the distance between
these may be regulated with great accuracy on turning the hand-wheel, c,
which for this purpose is furnished with a graduated plate and pointer.
The motion of the rollers also admits of being readily reversed by a
simple mechanical arrangement. The plate of lead, prepared by casting,

a
Fig. 180.-Sheet-Lead Rolling Mill.
is afterwards brought between the rollers, by which it is strongly com-
pressed, and gradually drawn through to the other side, when the distance
between them is diminished, and, by reversing the motion of the mill, the
sheet is again drawn back to the part of the platform on which the
original plate was first laid. This process is repeated a greater or less.
number of times, the plate, B, first passing from the left to the right, and
then from right to left, until its thickness has been sufficiently reduced.
The motion of the leaden plate is much facilitated by the small wooden
rollers, a, and when the length obtained by the reduction of its thickness
becomes inconveniently great, it is divided into two parts, and each half
milled in a similar manner.
The lead is in this way sometimes passed between the rollers from
two to three hundred times; its thickness being diminished and its length
increased by each successive operation. The original plate is by this
treatment extended into a sheet, which, when intended for roofing pur-
poses, may be about 400 feet in length and 7 feet in breadth. This is
600
ELEMENTS OF METALLURGY.
afterwards cut up into convenient lengths, for the use of the plumber,
whose business it is to adapt it to the various purposes to which sheet-
lead is applied.
D
The manufacture of lead pipe by the ordinary method combines,
like that of sheet-lead, the
double process of casting
and elongation. What-
ever may be the dimensions
of the pipe required, it is
first cast in the form of a
short and thick cylinder,
which is afterwards reduced
to the proper size by being
forcibly drawn, when placed
on a mandrel of the exact
size of its proposed internal
diameter, through a succes-
sion of progressively-de-
creasing steel dies. By this
process, however, although
affording pipes of good
quality with regard to
soundness and finish,
lengths of from 20 to 30
feet only can be obtained,

B
02
MAIN| ||||||
A
V
P
B
יד
Τ
P
Fig. 181.-Lead-Pipe Machine; partly in section.
and, consequently, when very long pieces without a joint are required,
recourse is had to the hydraulic pipe-press (fig. 181). This machine
SILVER.
601
consists of a hydraulic press, T, connected with a double force-pump,
A, by which water is pumped beneath the piston, B, through the small
metallic pipe, p.
Above the top of the press, and on a level with the
floor of the workshop, is a heavy casting, supported by the stout iron pillars,
P, and containing the cylindrical reservoir, C, for the reception of the
lead, and an annular fire-place, F, charged with coal, and communicating
with a chimney for the escape of smoke. At the upper extremity of the
cavity, C, is secured a steel die, of the diameter of the outside of the
pipe to be made, whilst a inandrel, m, which passes directly through its
centre, has the dimensions of the inside of the pipe to be produced.
To use this apparatus, the piston, B, is brought into the position
shown in the woodcut, and the space, C, is filled with molten lead,
through the spout, S, which is immediately removed, and the aperture
firmly stopped by an iron plug, kept in its place by a strong key. The
pressure is now established by admitting water through the valve, v,
beneath the piston, B, which forces the other extremity, accurately fitting
the cylindrical cavity, C, gradually upwards, and causes the lead to
escape in the form of a perfectly-finished tube through the annular
space existing between the mandrel and the fixed collar. The pipe,
in proportion as it escapes from the press, is coiled around the drum,
D, from which it is afterwards removed, and cut into convenient lengths.
The pipe made by this machine is of good quality, and may be manufac-
tured of almost any required length.
On admitting the pressure above the piston by means of the valve, v′,
the plunger again descends to the bottom of the cavity.
Several alloys of lead with other metals are employed in the arts, but
the most important of these are type metal, and the various mixtures of
lead and tin, known by the name of " solders," already described.
SILVER.
On
SILVER is the whitest of the metals, and is capable of receiving a lustre
inferior only to that of polished steel. Its malleability and ductility are,
next to gold, greater than that of any other metal. Pure silver is harder
than gold and softer than copper; its specific gravity is 10-50; when
pure it enters into fusion at a full red-heat, corresponding to 1,023° C.
Fused in open vessels it absorbs oxygen in considerable quantity, some-
times amounting to twenty-two times the volume of the metal itself.
becoming solid, however, the whole of this gas is again expelled; this
circumstance is probably, in some degree, the cause of the metallic vege-
tation which takes place on the surface of silver buttons, when suddenly
cooled on the cupel. Heated very strongly in a blast-furnace this metal
gives off sensible metallic vapours, and between two charcoal electrodes in
connection with a powerful voltaic battery it is volatilised. By fusing a
large quantity of silver, and afterwards allowing it to cool very gradually,
602
ELEMENTS OF METALLURGY.
cubical and octahedral crystals may be obtained on piercing the solidi-
fied crust and running off the still-liquid metal. When solutions of
silver are decomposed by the action of feeble electric currents, the pre-
cipitated metal often assumes a crystalline form. Silver does not absorb
oxygen at ordinary temperatures, but speedily becomes blackened on ex-
posure to an atmosphere containing traces of sulphuretted hydrogen,
which is decomposed by it with great facility.
Heated to redness in contact with the caustic alkalies, it is not in the
least affected, and is for this reason employed for making crucibles, to be
used when attacking various substances by caustic potash. In the pre-
sence, however, of fused alkaline silicates, silver vessels become acted
on to a small extent, and the silicate is stained of a light yellow colour.
Oxide of silver is reduced by heat alone, and a globule of metal is
obtained.
Unless in a state of extreme division, silver is not attacked by hydro-
chloric acid, and even then it requires to be heated to the temperature of
ebullition, before decomposition of the acid is effected. By dilute sul-
phuric acid no effect is produced, but strong sulphuric acid, when heated,
is readily decomposed, with the formation of sulphate of silver and the
evolution of sulphurous anhydride. Nitric acid readily attacks silver,
even at ordinary temperatures; nitric oxide is evolved, and nitrate of
silver is produced. By chlorine, iodine, and bromine, silver is readily
attacked, even in the cold.
i
SILVER ORES.
Silver occurs not only in the native state, and alloyed with various
other metals, but also mineralised by non-metallic elements, such as,
sulphur, selenium, chlorine, bromine, or iodine; and, perhaps, in combina-
tion with certain acids.
NATIVE SILVER; Argent natif; Gediegen Silber. Isometric.-Native
silver is found accompanying all the ores of this metal, and more par-
ticularly the sulphides and chlorides; it is also frequently associated
with red silver ores, &c. It occurs either in a crystalline form, or in the
state of divergent branches, of which the extremities are often composed
of numerous minute crystals, similar to those observed in specimens of
native copper.
-
This metal likewise occurs in amorphous masses, in long filamentary
strings, and in the shape of compressed plates of greater or less extent.
One of the largest masses of metallic silver ever obtained in Europe was
procured from the mines of Kongsberg, in Norway: this specimen, which
is preserved in the museum of Copenhagen, weighs about 500 lbs.; others
of still larger size have been cited as coming from the same locality.
Crystals of native silver are seldom very distinctly defined, as they do not
usually occur in an isolated state and are generally more or less dis-
torted. The cube, the octahedron, and the dodecahedron, are among the
forms which it most commonly assumes. Native silver is often found
disseminated through ferruginous rocks, as at Huelgoët, in Brittany, and
SILVER.
603
in the mines of Chili, Peru, and Mexico, where these argentiferous iron
ores receive the names of "pacos" and "colorados." Native silver is also
found in the Hartz, Saxony, Hungary and Dauphiny; large quantities
are afforded by the mines of Peru and Mexico; and in the United States
of America beautiful specimens of native silver are found associated
with the copper procured from the district south of Lake Superior.
Native silver is often alloyed with gold, copper, or antimony.
NATIVE AMALGAM; Argent amalgamé; Natürlich Amalgam. Isometric.
-This mineral, which is of a silver-white colour and bright metallic
lustre, occurs both in distinct crystals and in irregular amorphous masses
it also not unfrequently assumes the form of thin compressed plates,
occupying fissures existing in the veinstone.
Its specific gravity is about 14; when heated before the blowpipe,
mercury is expelled, and a fused button of metallic silver remains. The
composition of this amalgam is, according to Klaproth—
Ag
Hg
08 08
36.00
64.00
100.00
This composition would appear to correspond with the formula AgHg,
although some other analyses indicate the presence of a larger percentage
of mercury.
This mineral is found in many localities, but the finest
specimens have been procured from Moschellandsberg in the Palatinate.
Arquerite, another variety of this substance, forms one of the sources
of silver in the rich mines of Arqueros, in the province of Coquimbo,
From its malleability and general appearance, this compound was
for a long time thought to be metallic silver. According to the analysis
of Domeyko, of the Mining School of Coquimbo, this amalgam consists
of-
Ag
AH
an an
Hg
•
86.50
13.50
1
•
100.00
From which it appears to be composed of silver and mercury in the pro-
portions represented by the formula Ag₁₂Hg.
12
ARGENTITE; VITREOUS SULPHIDE OF SILVER; Argent sulfuré; Silber-
glanz. Isometric.-Occurs massive, and crystallised in cubes and dodeca-
hedra. Its colour is a blackish lead-grey, and its streak, which is of the
same colour, is shining. The fracture of the massive varieties is slightly
conchoidal, sometimes approaching to vitreous. It is fusible even in the
flame of an ordinary candle, and before the blowpipe, on charcoal, gives off
sulphurous vapours, and yields a button of metallic silver. This mineral is
at the same time one of the richest and most abundant ores of silver, and
furnishes a large proportion of that annually produced by various foreign
mines. It occurs in those of Saxony, Bohemia, and Hungary, and is par-
ticularly abundant in the mines of Guanaxuato and Zacatecas in Mexico.
It occurs with stephanite, native gold, &c., in the Comstock lode, Nevada.
604
ELEMENTS OF METALLURGY.
The composition of argentite is, according to Klaproth :-
From
Himmesfürst.
From
Joachimsthal.
<
Ag
S
86.50
86.39
•
13.50
13.61
100.00
100.00
Formula Ag₂S.
STEPHANITE; BRITTLE SILVER ORE; Argent sulfuré fragile; Schwarz-
gültigerz. Orthorhombic.-This mineral is of an iron-grey colour, in-
clining to black, with a metallic lustre and unequal conchoidal fracture.
It has a specific gravity of 6-2, is extremely brittle, and when broken
yields a black powder.
Before the blowpipe, on charcoal, it affords a button of metallic silver,
after having given off sulphurous and antimonious fumes, in which the
peculiar odour of arsenic may frequently be detected. When crystallised,
it is found in small six-sided prisms.
This mineral, which occurs with other ores of silver at Freiberg,
Schneeberg, and Johanngeorgenstadt in Saxony, as well as in the mines of
Bohemia and Hungary, and in those of Chili, Peru, Mexico, and Nevada,
has, according to the investigations of Rose and Klaproth, the following
composition:-
From Freiberg;
!
From Schemnitz.;
By Klaproth.
By H. Rose.
Ag
66.50
68.54
Cu & As
0.50
0.64
Fe
5.00
Sb
10.00
14.68
S
12.00
16.42
94.00
100.28
Formula 5Ag₂S+Sb₂S₂, or Ag, S₁Sb.
5
POLYBASITE; Polybasite; Eugenglanz. Orthorhombic.-Crystals usu-
ally short tabular prisms, with the bases triangularly striated, parallel
to alternate edges; cleavage basal, imperfect. Also massive and dissemi-
nated. Colour, iron-black, excepting when in thin crystals, which appear
cherry-red by transmitted light; streak black. Specific gravity, 6·21.
Heated in an open tube it fuses, giving off sulphurous and antimonious
fumes; on charcoal, before the blowpipe, fuses into a globule with evolu-
tion of sulphur, and sometimes arsenic, coats the support with an anti-
monious deposit; it occurs in the mines of Guanaxuato and Guadalupe-y-
SILVER.
605
Calvo, in Mexico; at Trespuntas in Chili; at Freiberg in Saxony; and at
Przibram, &c. Also in Nevada, Idaho, and other localities in the United
States.
Two specimens of this mineral, analysed by H. Rose, afforded the
following results:-
From Mexico. From Schemnitz.
Ag
61.29
72.43
Sb
5.09
0.25
•
As
3.74
6.23
Cu
9.93
3.04
SZE
Fe
0.06
0.33
Zu
0.59
17·04
16.83
100 15
99.70
Its composition may be represented by the formula (Ag,Cu), (Sb,As)S..
DARK-RED SILVER ORE; PYRARGYRITE; Argent sulfuré antimonié;
Dunkles Rothgültigerz. Rhombohedral.-Colour black to cochineal-red;
streak red; transparent to opaque; fracture conchoidal. Specific gravity
5.7-5.9.
Two analyses of this mineral afforded the following percentage
results:-
From Mexico;
By Wöhler.
From Chili;
By Field.
Ag
60.02
59.01
Sb
21.80
23.16
S
18.00
17.45
99.82
99.62
The above figures indicate that the composition of pyrargyrite may be
represented by the formula 3Ag₂S+Sb₂S,, or Ag,SbS.. Fused with car-
bonate of sodium on charcoal, before the blowpipe, it affords a globule of
metallic silver.
Dark-red silver ore occurs with calcite, native arsenic, and galena, at
Andreasberg, in the Hartz; also in Hungary, Saxony, Norway, at Guadal-
canal in Spain, &c. It is extensively mined as a silver ore in Mexico.
Beautiful crystals of this substance are obtained in Chili from the mines
near Copiapo, and it also occurs in the Austin district, Nevada; in the
Poorman lode, Idaho, it is found in amorphous masses weighing several
pounds.
CHLORIDE OF SILVER; Argent corné; Hornsilber. Isometric.-This
mineral constitutes one of the richest and most abundant ores of Chili
and Peru, where it is frequently associated with native silver, apparently
606
ELEMENTS OF METALLURGY.
resulting from its decomposition. It also occurs in massive amorphous
fragments in connection with sulphide of silver, but still more frequently
disseminated in the ferruginous rock known in Peru under the name of
pacos, and in Mexico as colorados. The chloride of silver of Huelgoët is
also of this description, and is disseminated through a cavernous hydrated
oxide of iron, around the cavities of which it sometimes assumes the form
of small cubo-octahedral crystals, the largest of which do not exceed in
size the head of an ordinary pin.
The colour of this mineral is white or yellowish-white, which becomes
violet by exposure to light; the massive fraginents, when broken, pre-
sent a vitreous conchoidal fracture, the edges being transparent, or at
least translucent. Chloride of silver is extremely soft, and admits of
being cut with a knife or scratched by the nail with great facility. It
is fusible before the flame of the blowpipe, and, when supported on a
piece of charcoal, affords a pearl-like button, which, by continued exposure
to the reducing flame, yields a globule of metallic silver. On being
moistened with water, and afterwards rubbed with a piece of metallic zinc,
its surface becomes covered with a film of reduced silver. Chloride of
silver, when pure, consists of silver 75·3, chlorine 24·7; and its composi-
tion is therefore represented by the formula AgCl. Sp. gr. = 4·45.
Specimens of this mineral, although of comparatively rare occurrence
in European mines, are obtained from Norway, Siberia, Saxony, the Hartz,
Cornwall, and elsewhere.
In addition to the foregoing, the following combinations in which
silver occurs are known to mineralogists, although, from their rarity,
some of them are of but little commercial importance :-
Hessite: Telluride of silver; found in Siberia, Transylvania, &c.
Naumannite: Selenide of silver; occurs in the Hartz. Eucairite:
Selenide of copper and silver, found in Sweden and in Chili. Stromeyerite :
Sulphide of copper and silver, containing iron. Dyscrasite: Antimonial
silver. Sternbergite: Sulphide of silver and iron. Miargyrite: Sulphide
of silver and antimony, with a little copper and iron; very rare.
Proustite, or Light-Red Silver Ore: A combination of silver, arsenic, sul-
phur, &c., not uncommon in Mexico and Chili. Freieslebenite: Antimonial
sulphide of lead and silver, not uncommon in many silver mines on the
continent of Europe. Xanthoconite: Arsenio-sulphide of silver; occurs
in the Himmelsfürst mine near Freiberg. Embolite: Chloro-bromide of
silver, found in Chili. Iodide of Silver: Found in Mexico, Chili, Spain,
&c. Bromide of Silver: occurs in Mexico, Chili, &c. Selbite: regarded
as carbonate of silver, but probably merely a mechanical mixture of
certain carbonates with other minerals which are argentiferous.
DISTRIBUTION OF SILVER ORES.
The rocks inclosing veins yielding ores of silver differ very widely
both in composition and age. Silver ores often occur in lodes inclosed
in the older crystalline and metamorphic rocks, and many of these have
been worked to great depths without permanent change in character or
SILVER.
607
apparent diminution of productiveness. Some of the veins of Norway
and Saxony are remarkable examples of this mode of occurrence. In
South America a large proportion of the silver is obtained from veins in cal-
careous rocks; the silver-bearing strata of Peru and Bolivia are believed
to be of Carboniferous age; whilst the rocks, in which the famous silver
mines of Chañarcillo and Trespuntas, in Chili, are worked, are said to be
Lower Cretaceous. Those inclosing the celebrated Comstock vein at
Virginia City, in the State of Nevada, are eruptive and volcanic, belonging,
according to Richthofen, to the latter part of the Tertiary and beginning
of the Post-Tertiary periods.
Nearly the whole of the silver obtained in the United Kingdom is
extracted from argentiferous lead ores by processes which have been
described, when treating of the metallurgy of lead; the amount thus
annually produced is about 52,400 lbs. troy.
The celebrated Kongsberg mines, in Norway, were discovered in
1623, and have been worked with but little interruption up to the present
time; their yield of silver in 1864 was 7,365 lbs., but they were formerly
much more productive. Sweden also produces a certain amount of this
metal from the mines of Sala, in Westmannia, which annually produce
about 1,250 lbs. of silver. The total annual production of Scandinavia
is estimated at 15,000 lbs.
Hungary, Transylvania, and the Banat annually produce about
92,000 lbs. troy, while Saxony produces 80,000 lbs. annually; and of
this amount the mines of Freiberg alone yield 97 per cent. The
annual yield from the Hartz mines is about 27,500 lbs. troy. The total
production of silver in the German empire during the year 1871 was
about 178,000 lbs.* The annual production of Russia is estimated at
50,000 lbs. In France there are, at the present time, no mines in
operation on what can be regarded as silver veins, although those of
La Gardette and Chalanches, in the department of Isère, were formerly
worked for silver. Huclgoët, in Brittany, although strictly speaking
a mine of argentiferous galena, yields an ochreous clay containing
about 30 ozs. of silver, in the form of chloride, per ton of ore. The
mines of Pontgibaud, Puy-de-Dôme, produce large quantities of argenti-
ferous galena, very rich in silver, which is extracted by smelting in low
blast-furnaces, and subsequently subjecting the lead to crystallisation
and cupellation. The yearly production of silver in France is estimated
at 16,500 lbs. The annual yield of Italy, chiefly from the lead ores of
Sardinia, is about 32,000 lbs.
In Spain silver mines were formerly worked at Guadalcanal and Cazalla,
to the north of Seville. These occur in mica-slate, and were, at one time,
very productive, but they are now of little importance. The most impor-
tant silver mines of Spain are those of Hiendelaencina, in the province of
Guadalajara, about seventy miles north of Madrid. They were discovered
in 1843 by a native of the district, who had worked in the mines of
Mexico. This man, on his return to his native village, remarked the re-
semblance which a large stone on the road-side bore to some of the silver
* Some portion of this silver was probably produced from imported ores.
608
ELEMENTS OF METALLURGY.
ores he had seen in the mines of the New World. On being analysed it
was found to be a rich ore of silver, and the stone proved to be the out-
crop of a regular vein. The ore at Hiendelaencina is chiefly freies-
lebenite. The production of these mines from 1846, when they were first
worked, up to June, 1866, amounted to 631,544 lbs. troy, but their returns
since the year 1858 have materially diminished. The present annual
production of Spain is estimated at 100,000 lbs. troy.
The most important mines of North America are probably those of
Mexico, although of late very large amounts of silver bullion have been
produced by the states of Nevada and Idaho. Colorado also yields valu-
able silver ores, and in Utah argentiferous lead ores have recently been
discovered in large quantities and of unprecedented richness.
At the date of the publication of Humboldt's 'Essai Politique' (1825)
the mining districts of Mexico, arranged in accordance with the import-
ance of their several yields, followed each other in the subjoined order:
Guanaxuato,
Catorce
Zacatecas
Intendency of Guanaxuato
Real del Monte
Bolaños
>>
Guarisamey
Sombrerete
99
Tasco
>>
Batopilas
""
Zimapan
>>
Fresnillo
""
Ramos
Parral
""
San Luis Potosi
Zacatecas
Mexico
Guadalajara
Durango
Zacatecas
Mexico
Durango
Mexico
Zacatecas
San Luis Potosi
Durango
It is stated, by the same author, that the silver extracted from the
mines of Mexico from January 1st, 1785, to December 31st, 1789,
amounted to 7,314,344 lbs. troy. The War of Independence caused a
great falling-off in the annual production of the precious metal, which
between the years 1810 and 1845 probably did not average more than
800,000 lbs. of silver and a little over 400 lbs. of gold. Since 1850,
however, the mines of Mexico have partially regained their ancient pro-
sperity, and their present annual produce of silver may be estimated at
1,000,000 lbs.
Although the discovery of silver in Nevada only dates from the year
1859, its extraordinary production has already rendered its mines more
famous than those of many countries in which mining for this metal has
been continually carried on for ages. The mines on the great Comstock
vein in the immediate vicinity of Virginia City were the first extensively
worked, and have already produced bullion to the amount of not less than
£25,000,000, of which value about one-third is represented by gold. In
addition to those on the Comstock vein there are important silver mines
in the Austin district, at White Pine, and in other portions of the State.
The ores found on the Comstock chiefly consist of argentite and stephan-
ite, whilst many of the mines in the neighbourhood of Austin yield con-
siderable quantities of dark-red silver ore. At White Pine the ores are
chiefly chlorides. Idaho affords large quantities of massive pyrargyrite.
SILVER.
609
The silver of Colorado is chiefly derived from various mixed sulphides,
and the fine ores of Utah appear to be the result of the decomposition of
rich argentiferous galenas.
Native silver is also found associated with the native copper of Lake
Superior, and some mines are at present being worked for that metal on
its northern shore. The annual production of silver in the United States
and Territories is now probably not less than 1,400,000 lbs. troy.
Comparatively little is known of the geology of Central America,
excepting that the predominant rocks are granite, gneiss, and mica-slate,
and that the abundance of igneous rocks bears witness to extensive
volcanic action. Silver is found in various parts of that country, and
some years since mines, worked by an English company, in the mountain
of Alotepec, afforded, in the course of the eight years they were in opera-
tion, 53,000 lbs. of silver.
66
The silver mines of Peru, Bolivia and Chili, stand next in importance
to those of Mexico and of the United States of America. At the mines of
the Cerro de Pasco, the most celebrated in Peru, the principal ores worked
are of the description known as pacos," which are analogous to the
Gossans of the Cornish miner. These argentiferous gossans have been
found in such enormous quantities that at Pasco or Yauricocha they had
been worked since the commencement of the seventeenth century, and,
although during the last twenty years of the eighteenth century they had
produced above five million marks of silver, very few of the workings had
then penetrated to a depth of a hundred feet. In addition to the Cerro
de Pasco there are various other districts in Peru which have produced
large quantities of silver. Among the most important of these are
Caxamarca, Pataz, Huamanchuco and Hualgayoc. The total annual pro-
duction of the silver mines of Peru is estimated at about 200,000 lbs.
troy.
The mining district of Potosi, which was once included in the vice-
royalty of Buenos Ayres, now forms a portion of the Republic of Bolivia.
In this locality above thirty principal veins, besides others of less import-
auce, have been worked, and have at various times, since their first dis-
covery in 1545, yielded almost fabulous amounts of silver. Many of them
are situated in an isolated mountain called Hatun-Potocsi, the summit of
which reaches an elevation of 16,000 feet above the level of the sea;
the ores obtained, from the period of their discovery up to 1571, when the
process of amalgamation was first introduced, were treated exclusively by
fusion. The period of the greatest productiveness of the Potosi mines
was during the century immediately following their discovery, when the
average annual amount of the silver produced was about 600,000 lbs.
troy. Shortly after the commencement of the seventeenth century their
yield began to decline, and at its close, only amounted to an annual money
value of from six to eight hundred thousand pounds. Rich deposits of
silver ore have recently been discovered in the district of Caracoles ;
*
* The district of Caracoles is claimed by both Chili and Bolivia, but we have
included its annual production of silver in the Bolivian estimates.
2 R
610
ELEMENTS OF METALLURGY.
the quantity exported from Antofogasta and Mejillones de Bolivia (the
ports of Caracoles) from November, 1872, to July, 1873, was 10,115
tons, containing about 300,000 lbs. of silver. The present annual yield
of Bolivia is estimated at from 448,000 to 460,000 lbs. troy.
The most important silver mines of Chili are those situated in the
neighbourhood of Copiapo. The principal workings are in the vicini-
ties of Chañarcillo and Trespuntas, the first 16 leagues south, and the
second 30 to the north-east, of Copaipo. In Chili the development of the
mineral resources of the country has been of more recent date than in
the other South-American States; but its comparatively flourishing poli-
tical situation has enabled workings to be established on an extensive
scale, and within the last few years a considerable increase has taken
place in the amount of silver annually produced. Its present yield is
estimated at about 300,000 lbs.
The Santa Anna mines in the province of Mariquita, New Granada,
were formerly of some importance, producing from 11,000 to 12,000 lbs.
of silver annually, but their yield has much fallen off since the year 1869.
It has been estimated that the total annual production of the known
silver-producing countries of the world is about 4,100,000 lbs. troy, of an
approximate money value of £13,000,000.
ASSAY OF SIlver Ores.
BY FUSION WITH LITHARGE, &C.-In assaying silver orcs, the object
sought is to obtain the silver in the form of an alloy with lead, which
is afterwards passed to the muffle and cupelled in the ordinary way.
The method of assaying lead ores containing silver has been described
when treating of lead.
Argentiferous minerals containing copper may be assayed cither by
scorification, or by fusion with oxide of lead, as if silver alone were pre-
sent, since the resulting button of alloy admits of being readily cupelled
with a proper addition of metallic lead. In roasting such ores it is
generally necessary to employ a very low temperature, as, from their
great fusibility, they would otherwise be liable to agglutinate, by which
the further expulsion of sulphur would be rendered difficult.
Ores of silver in which the metals (after roasting or otherwise) exist
in the form of oxides are commonly fused with a mixture of litharge, or
red lead, and finely-powdered charcoal, by which an alloy with lead is ob-
tained, which is subsequently subjected to cupellation. The proportion
of litharge employed for this purpose must be varied according to circum-
stances, as the resulting button of alloy should not be too rich, since in
that case a portion of the silver might be lost in the slag; nor too poor,
as the cupellation would then occupy a long time, and a loss through sub-
limation and absorption by the cupel would be entailed. In ordinary
cases, if 400 grains of ore be the quantity operated on, a button of 200
grains will be a convenient amount for cupellation; and this may be ob-
tained by the addition of 500 grains of litharge, and from 12 to 15 grains
SILVER.
611
of finely-powdered charcoal or lamp-black. The whole is to be well
mixed with 200 grains of carbonate of sodium, on a sheet of glazed paper,
and afterwards introduced into an earthen crucible, of which it should
not fill more than three-fifths the capacity. This is covered with a thin
layer of borax, and fused in an ordinary assay furnace, care being taken
to withdraw it from the fire as soon as a liquid and perfectly-homogeneous.
slag has been obtained, since the unreduced litharge would otherwise
be liable to cut through the pot and thus spoil the results. When it has
sufficiently cooled, the crucible is broken, and the button of alloy ob-
tained is passed to the cupel.* In this and all similar experiments it is
necessary to ascertain by previous experiment the amount of silver con-
tained in the lead resulting from the reduction of litharge, in order to be
possessed of data from which to make the requisite deduction from the
result obtained. With poor litharge, however, the resulting lead contains
so small an amount of silver, that, for many commercial purposes, its
presence may be neglected.
When other minerals than oxides or carbonates are to be examined,
the addition of charcoal, or any similar reducing agent, becomes in some
instances unnecessary, as litharge readily attacks the sulphides, &c., and
oxidises nearly all their constituents, with the exception of silver, whilst
a proportionate quantity of metallic lead is set free. The slags formed
in this way contain the excess of litharge added, and the button of alloy
produced is subjected to cupellation in the usual manner.
The propor-
tion of oxide of lead added to ores of this description must vary in accord-
ance with the amount of oxidisable substances present; but it should in
all cases be in excess, since, if the slags retain traces of any undecom-
posed sulphide, the whole of the silver contained in the ore may not be
collected in the button of alloy obtained.
An objection to this method of assaying is to be found in the large
amounts of lead which are produced for cupellation; as one part of
pure iron pyrites affords 83 parts of this metal, whilst sulphide of anti-
mony and grey copper ore yield from 6 to 7 parts. This inconvenience
may be obviated by effecting the partial oxidation of the mineral either
by roasting or by the aid of nitre, by the skilful use of which a metallic
button of almost any required weight may be obtained.
When this reagent is employed in excess, it determines the oxida-
tion of all the oxidisable constituents of the ore. But when, on the con-
trary, the mixture contains a large amount of litharge, and nitre has not
been added in sufficient quantity to decompose the whole of the sulphides
present, reaction takes place between the undecomposed sulphides and
the oxide of lead. This gives rise to the liberation of metallic lead,
which, combining with the silver, affords a button of alloy, from which
the latter metal may be obtained by cupellation. The amount of nitre
to be employed for this purpose will depend on the composition of the
ores operated on, but it should be borne in mind that 24 parts of nitrate
* Instead of breaking the crucible its contents may be poured into a cast-iron
mould.
2 R 2
612
ELEMENTS OF METALLURGY.
3
of potassium are sufficient to completely oxidise 1 part of pure iron
pyrites, and that 1 and their respective weights are, in the case
of sulphide of antimony and galena, sufficient to produce the same
effect.
SCORIFICATION.-This is a simple and convenient process for assaying
silver ores, as well as some varieties of gold ores.
It consists in exposing the finely-ground ore, mixed with granulated
lead, and placed in a cup-shaped vessel or scorifier, to the action of a
bright-red heat, in an ordinary assay muffle.
Part of the lead is thus converted into litharge, and this, as fast as it
is produced, reacts on the various substances contained in the ore, form-
ing with them a clean slag, in which no appreciable amount of the precious
metals is met with; practically, the whole being found alloyed with the
lead remaining after the operation. The cup-shaped vessels or scorifiers,
employed for this process, should be of close-grained fire-clay and well
baked. It is important that they be compact in structure, so as to resist
the corrosive action of the fused litharge; they should also be capable
of bearing sudden changes of temperature without cracking.
A sufficient number of these scorifiers having been selected for the
assays to be made, 100 grains of the ore, ground to a fine powder, and
carefully dried to expel moisture, are taken and intimately mixed with a
certain quantity of granulated lead, and a small proportion of pounded
borax both being previously placed in the scorifiers, which are ar-
ranged in order on the assay table. The proportion of lead added
varies in accordance with the greater or less refractoriness of the ore;
namely, from five to eight times the weight of the mineral operated on.
In all cases, however, it is advisable to add a considerable excess of lead,
as the slags are thereby rendered more liquid.
The lead used should, if possible, be free from silver; but, in many
cases, such lead cannot be obtained, and it is consequently requisite to
estimate beforehand the amount of silver present and make a corre-
sponding deduction from the weights of the several buttons afforded by
assay.
The scorifiers being charged with a due proportion of ore, lead, and
flux, and the muffle brought to a full red-heat, they are removed to the
furnace, and as many are introduced as there may be room for in the
muffle. The introduction of the scorifiers at first greatly reduces the
temperature of the muffle, and, in consequence, some pieces of charcoal
may, with advantage, be placed in the entrance to assist in raising the
heat. The door of the muffle is now closed, and in a few minutes the
lead enters into fusion. White vapours are seen rising from the assay,
and the formation of litharge quickly takes place. As the borax melts,
and the quantity of litharge increases, the mass in the scorifier softens.
With increase of temperature, it becomes more liquid, and the lead is
seen to collect in a large globule in the centre.
When the assay is
thoroughly heated, which generally occurs in ten or fifteen minutes from
the commencement of the operation, the door of the muffle is removed;
SILVER.
613
atmospheric air now enters in greater quantity, and oxidation of the lead
proceeds more rapidly.
As the litharge accumulates, the slag, formed by its combination with
siliceous and other matters contained in the ore, is increased, and gra-
dually extends itself over the whole surface of the lead. The mouth
of the muffle is now allowed to remain open for ten or fifteen minutes;
after which period it is closed, and the temperature raised to bright
redness for about five minutes, in order to render the slags as liquid as
possible before pouring, and, at the same time, to facilitate the union of
any disseminated globules of alloy.
The scorifiers are now withdrawn from the muffle by means of
proper tongs, and their contents rapidly poured into suitable moulds.
When cold, the buttons of lead are readily separated from the adhering
slags, by a few blows with a hammer. The lead obtained should be soft
and ductile; if it be at all brittle, either an insufficient quantity of
lead has been added, or the scorification has not been carried suffi-
ciently far. When the operation has been successfully conducted, these
buttons contain what may be considered, practically, as the whole of the
precious metals present in the ore, and may be subsequently treated by
cupellation.
It is essential that the slags should be perfectly and uniformly liquid
at the time of pouring from the scorifier; if they be hard or contain pasty
lumps, part of the mineral may be left unacted upon, and small metallic
buttons may either be inclosed in the lumps, or remain attached to the
sides of the scorifier. If the slags should not appear perfectly liquid,
when a sufficiently high temperature is maintained in the muffle, and the
other conditions of the process have been attended to, it will be neces-
sary to add more borax, and, in some instances, even a little nitre. In a
few cases it may be requisite to stir the slags with an iron rod, in order
to divide the lumps which may have been formed, and to incorporate
them with the more liquid slags.
This method of assay is applicable to all kinds of argentiferous and
auriferous ores, without exception, when they are of moderate richness,
and from its convenience and the short time required, it is very generally
employed in establishments, where a great number of assays of silver ores
have to be made daily. When, however, poor ores have to be examined,
fusion with litharge is preferable; since, by that method, a greater
quantity of mineral can be operated on, and consequently more accurate
results obtained.
ASSAY OF SILVER BULLION.
FIRE ASSAY.-The assay of silver bullion, by the dry way, is con-
ducted as follows:-First, a fair sample of the alloy to be operated on is
accurately weighed in a delicate balance; secondly, this weighed portion
of the bar is cupelled with lead; and, thirdly, the button of silver
remaining on the cupel is weighed. The difference between the two
614
ELEMENTS OF METALLURGY.
weighings will represent the amount of impurity which has been removed.
The furnace employed for this purpose may either be of fire-clay bound
with hoop-iron, or may be constructed of a wrought-iron shell lined with
fire-tiles, figs. 158, 159; in either case, it must be provided with an
arrangement for easily regulating the draught.
In this country the quantity taken for examination is usually a repre-
sentative of the troy pound, which is subdivided into ounces and half-
pennyweights; that being the lowest denomination to which silver
bullion is reported. The assay pound may be represented by any actual
weight chosen by the assayer, but either 1 gramme, or half that weight,
is the quantity most frequently employed; the smaller weights are made
to correspond with ounces and half-pennyweights.* Assayers formerly
made their calculations in ounces, pennyweights, and grains, but it is
found more convenient to employ decimals, and, when commercial esti-
mations are required, to convert the decimal into trade expressions by
means of tables calculated for that purpose.
Pure silver is represented by unity divided into 1,000 parts, and
English standard silver, which contains, in the pound, 11 ozs. 2 dwts. of
that metal, with 18 dwts. of alloy, will be 925 thousandths. All excess
of alloy over the English standard is called "worseness," and Mexican
dollars, which consist of 10 ozs. 16 dwts. of silver, with 1 oz. 34 dwts.
of alloy, would be reported as worse" 5 dwts. Indian rupees, on the
other hand, are composed of 950 parts of silver united with 50 parts
of alloy. This is equal to 11 ozs. 8 dwts. of silver, combined with 12
dwts. of alloy; hence their trade report would be "better" 6 dwts.
In making an assay of silver bullion the first step to be taken is to
flatten out the cuttings taken from the several bars. The edges of these
are removed by the use of a pair of shears, and from each are prepared
two representative assay pounds, which are carefully put aside with one-
half the lead necessary for effecting their cupellation.
The amount of lead necessary to be added to an alloy of silver and
copper varies in accordance with the composition of the mixture to be
treated, and should be greater in proportion as the quantity of copper
becomes more considerable. In making this addition, it is necessary to
bear in mind that the lead must be present in such quantity that the
litharge formed may be enabled to dissolve the other oxides produced,
aud at the same time remain sufficiently liquid to be readily absorbed
by the cupel. If this necessary amount be not added the litharge
formed becomes pasty, and speedily covers the surface, whilst, if too
large a quantity be employed, the assays remain a long time in the fire,
and a loss of silver is experienced.
English standard silver requires about six times its weight of lead
for its cupellation. The affinity exercised by silver for copper renders it
necessary, in these operations, to add a larger amount of lead than would
be required if pure copper alone were to be dealt with.
*When the alloy to be examined is over 800 fine, 1 gramme is generally
employed; if under 800 half a gramme only is taken.
SILVER.
615
The following table shows the amounts of lead necessary to effect the
cupellation of various mixtures of silver and copper:-

Amount of Silver. Amount of Copper.
Quantity of Lead
required for one Part
of the Mixture.
1000
0
950
50
1
3
900
100
7
800
200
10
700
300
12
600
400
14
500
500)
400
600
300
700
16-17
200
800
100
900
Pure copper
1000)
The lead employed should be as free as possible from silver, and the
amount of that metal thus introduced into the assay must be deducted
from the results obtained. The duplicate weighed portions of the several
bars of bullion to be assayed must be wrapped in lead-foil, and arranged
in the compartments of a divided tray, having somewhat the dimensions
of the bottom of the muffle in which the cupellations are made, so that
the place of each may correspond with its position in the furnace.
When the muffle has attained a uniform bright red-heat, the cupels
are introduced, and its mouth is closed for a short time, either by a door
of fire-clay or by a large piece of charcoal, the latter being by prefer-
ence employed for this purpose when the temperature of the furnace has
been considerably lowered by the introduction of cold cupels. As soon
as they all present the proper bright-red colour, one-half of the lead
necessary for cupellation is introduced by the aid of suitable tongs, and,
when it has become fused, the assays, wrapped in the other half of the
lead required, are dropped into each cupel in the order in which they
stand in the divided tray. When all have been arranged in their proper
places, the assayer again closes the mouth of the muffle for a short time,
and shortly afterwards opens it to a greater or less degree, for the pur-
pose of admitting a current of air, by which the starting of the several
cupellations is effected. When this takes place the metallic bath becomes
uncovered, with the exception of some small patches of fused litharge,
which are observed to move rapidly from the centre towards the edges of
the cupel. As soon as the working is thus fairly begun, the draught
must be adjusted by means of the various openings in the furnace, which
are more or less completely closed, so as to maintain a uniform tempera-
ture in all parts of the muffle. When the furnace is working satisfac-
torily but little fume should be seen to arise from the assays, and the
litharge formed must be absorbed by the cupel as fast as produced. In
this way the metallic globule goes on steadily diminishing in size until,
616
ELEMENTS OF METALLURGY.
after the expiration of about twenty minutes, the whole of the lead and
of the base metals has become oxidised and absorbed by the cupel, and
the brightening of the silver takes place.
If the operation has been properly conducted, the "going-off" of the
assays will commence with the first row, and successively pass back from
row to row to the last. If, on the contrary, the working-off takes place
irregularly, or commences at the far end of the muffle, it is an indication
that the draught has not been skilfully regulated; and in such cases the
results obtained are usually less to be depended on than if the brighten-
ing of the buttons had taken place regularly from the mouth of the
mule towards its further extremity. The several assays, as soon as they
have gone off, are drawn to the mouth, and, after being allowed gradually
to cool, are removed into a divided iron tray in the same order in which
they were placed during the operation.
When the buttons thus obtained are rounded on top, or are only
slightly depressed in the centre, and can be easily removed from the
cupels, it is an evidence of the operation having been properly conducted.
If, on the contrary, they adhere firmly to the cupels, or throw out pro-
jections near the bottom, they are not fine. When they exhibit a flat-
tened appearance, it is an indication that they have been cupelled with
an insufficient amount of lead.
It now remains to clean and weigh the assays and to compare them
with a well-ascertained standard of comparison, consisting of weighed
quantities of silver, of which the degree of fineness has been previously
determined, and which have been cupelled under similar conditions, and
at the same time with the assays of which the composition is required.
It will be found that in all cases a certain amount of loss has been ex-
perienced; this is partly due to volatilisation and partly to absorption
by the cupel. The proofs which have been cupelled at the same time and
under similar conditions will, however, experience a corresponding loss,
and thus afford data for correcting the results indicated by the balance.
The other metals, besides lead and silver, present, usually afford indi-
cations from which it is easy to judge of their nature, and, roughly, also of
the amount in which they exist. Pure lead stains the cupel of a straw-
yellow colour, sometimes verging on orange. Copper gives a grey or dark-
brown tint, according to its quantity. Iron produces a black stain, which
is chiefly formed shortly after the commencement of the operation, and
gives rise to a dark ring around the sides of the cupel. Zinc leaves a
yellowish stain, and produces, during the process of cupellation, a lu-
minous white flame and abundant fumes of the same colour, which carry
off with them a notable amount of silver. Tin produces a grey slag, and
antimony leaves spongy yellow scoriæ, which cause the circumference
of the cupel to effloresce and to split off. The two last-named metals
render the cupellation of the mixtures in which they exist difficult, and
necessitate the employment of a large quantity of lead in order to carry
off the infusible oxides formed. When assays of alloys containing silver
have frequently to be made by cupellation, it will be found convenient to
keep in the laboratory a supply of lead-foil, ready weighed out into
SILVER.
617
pieces of 1 and 2 grammes, whilst poor milled lead is kept in pieces of
from 1 up to 6 grammes. Instead of weighing the larger pieces, they
may he prepared with sufficient accuracy by casting in small bullet-
moulds. By this means, the amount of silver in the lead being pre-
viously known, it becomes easy, by merely counting the number of pieces.
added, to know exactly what deduction is to be made for the silver in the
lead at the termination of the cupellation.
HUMID ASSAY.-On account of the difficulty experienced in obtaining
perfectly accurate results by the ordinary method (cupellation), a Com-
mission was appointed, in 1829, by the French Government for the pur-
pose of examining the different processes then employed in the Parisian
Mint for the assay of alloys containing gold and silver, and to report on
any modifications which it might be thought advantageous to introduce.
Gay-Lussac, who was one of the Commissioners to whom this question
was submitted, proposed the adoption of the humid method of assay now
generally employed, and published, in the name of the Commission, the
details of the various necessary operations. To this report, to Regnault's
more recent description of the methods and apparatus employed in the
French Mint, and to Mr. F. Claudet, assayer to the Bank of England, &c.,
we are indebted for many of the following particulars.
This process consists in determining the standard of the alloy
examined by means of a solution of chloride of sodium, of which the
strength has beforehand been accurately ascertained.
The solution of salt employed is so regulated that a decilitre is
capable of exactly precipitating 1 gramme of pure silver. To determine
the composition of an alloy, 1 gramme may be dissolved in 5 or 6 grammes
of nitric acid, and to this is carefully added the standard solution of
common salt from an accurately-graduated pipette until the introduction
of a fresh quantity ceases to be accompanied by a deposit of silver
chloride. Towards the end of the experiment, when the point of satura-
tion has been nearly arrived at, care must be taken to well shake the
bottle after the addition of each successive drop of the saline solution, as
by this means the liquor is rendered clear through the precipitation of
the chloride formed. When the whole of the silver has been thus
thrown down, the number of divisions of the burette which have been
employed in its precipitation are read off, and from the amount of chloride
of sodium used the percentage of silver present is ascertained.
When an accurate assay has to be made of an alloy of which the
composition is beforehand approximately known, as in the case of silver
coin or silver plate, the process is considerably simplified, and at the
same time affords results of the most exact description. For this purpose
two distinct solutions of common salt are employed: the first, or standard
solution, is of such a strength that one decilitre will precipitate 1 gramme
of pure silver; the second, called the decimal solution, is ten times weaker
than the first, and consequently contains in a litre of liquor the amount
of chloride necessary to effect the precipitation of 1 gramme of pure
silver.
The better to understand this process, let us suppose that an alloy
618
ELEMENTS OF METALLURGY.
intended for the French coinage is to be examined, which, in order to be
accepted, should contain at least 0.897 of silver. We will assume that
the alloy in question contains only 0.896 of silver, and consequently
that 1.116 gramme of the mixture will correspond to 1 gramme of pure
silver.* This quantity is cut off, and, after being accurately weighed, is
placed in a bottle, capable of being closed by a glass stopper, where it is
dissolved in from 5 to 6 grammes of pure nitric acid; and, as soon as the
solution has been completely effected, exactly 1 decilitre of the normal
solution of common salt is introduced.
It is evident that if, as was first supposed, the alloy really contains
0.896 of silver, the whole will be precipitated by the quantity of solution
added, and that the supernatant liquor will contain no trace of chloride of
sodium in excess. If, on the contrary, the proportion of silver is greater
than that assumed, there will still remain a portion of that metal in solu-
tion; whilst, if it be less, the whole will have been completely precipi-
tated, but the liquor will contain an excess of chloride of sodium. To
ascertain which of these results has been produced, the bottle is now
carefully closed with its glass stopper, and briskly shaken, until the pre-
cipitated chloride has subsided and the solution has become clear.
When this point has been attained, a cubic centimetre of the decimal
solution of common salt, capable of precipitating 0.001 gramme of silver,
is introduced. If any silver remain in solution, the liquor now becomes
cloudy, and after being again shaken, another centimetre of the decimal
solution is added. If, on the addition of this second centimetre of the
solution, the liquor again becomes turbid, it is, after being well shaken,
allowed to clear, and a third centimetre of the decimal solution poured
in, and so on, until no further turbidity is produced on the addition
of a fresh quantity of the decimal solution. If we suppose that five of
the cubic centimetres of the decimal solution, successively added, have
produced a precipitate in the liquor, whilst the addition of the sixth has
in no way affected its transparency, we may conclude that after the pre-
cipitation of 1 gramme of pure silver by the decilitre of the standard
solution, the liquor still contained at least 0.004 gramme of silver. From
the circumstance of the fifth cubic centimetre of decimal solution having
caused a turbidity, whilst the sixth produced no kind of effect on the
solution, it is also evident that the liquor at most did not contain more
than 0·005 gramme of silver; and therefore, in taking it at 4 thousandths
we arrive at the result to within 0.0005 of the truth.
The propor-
1,000+41
1.116
= 900
tion of silver in the alloy examined will therefore be
thousandths. When, on the contrary, the cubic centimetre of the decimal
solution gives no further precipitate in the solution of silver which has
already received the decilitre of the standard liquid, it is evident that
the silver in the alloy must be inferior to 0.896, and consequently the
mixture is below the legal standard. If in this case its exact com-
position be required, recourse must be had to a standard solution of nitrate
*When the amount of silver present is not known, a preliminary assay is first
made by cupellation, in order to ascertain the approximate fineness.
SILVER.
619
of silver, called the decimal solution of silver, so adjusted that one litre
of the liquor may contain exactly 1 gramme of silver.
To use this, a cubic centimetre of the decimal silver solution is first
dropped from a pipette into the bottle containing the assay, and removes
the chlorine contained in the same volume of the decimal solution of
common salt, which was added for the purpose of ascertaining whether
the whole of the silver had been precipitated. The liquor is now bright-
ened by agitation, and another cubic centimetre of the silver solution
added. If a turbidity is produced the bottle is again shaken, and a third
measure of the solution is introduced after the chloride formed has been
completely deposited. This is continued until the addition of the silver
solution ceases to cause a precipitate in the solution to be assayed. If,
in this case, the first five cubic centimetres of the silver solution (without
counting that used to neutralise the effect of the cubic centimetre of
decimal solution of common salt, first added to ascertain if any silver
remained in solution, after the addition of the decilitre of standard solu-
tion), gave rise to the formation of a precipitate, and on the introduction
of the sixth the liquor remained perfectly clear, it is probable that the
fifth cubic centimetre was not entirely decomposed. It is therefore
customary to admit that 4 cubic centimetres of the silver solution have
been sufficient to effect the decomposition of the excess of chloride of
sodium remaining in the liquid after the introduction of the decilitre of
standard solution.
It is consequently evident in this case, that it will be necessary to
subtract 4 thousandths, and that the correct composition will be ex-
1,000 - 41
pressed by
1.116
=892 thousandths.
In establishments where large numbers of assays of silver alloys
are made daily, the apparatus is so arranged as materially to facilitate
the performance of the various operations above described. In the French
Mint, where this method of assaying was first employed, the apparatus,
shown in figs. 182 and 183, has been adopted.
The standard solution of common salt is kept in a large vessel, V,
made either of stoneware, or of sheet copper tinned on the inside. This
reservoir, for the purpose of preventing evaporation, is covered by an
immovable lid, provided with a tube, a, by which the air enters the
chamber to supply the place of any portion of the solution that may
be drawn off. This vessel, which is supported on a shelf fixed near the
roof of the laboratory, is provided with a tube, b, c, d, bent at right
angles at c, which admits of being closed by a stop-cock, t. The pipette,
P, which contains exactly a decilitre of the liquid, is connected with the
tube, c, d, by means of the glass tube, d, e, which contains a thermometer
accurately graduated. The metallic connector by which the tube, d, e,
As chloride of silver is, to a certain extent, soluble even in weak solutions of
sodium chloride, it is, in practice, usual, when the whole of the silver has been pre-
cipitated by the decilitre of normal solution, to add a given number of cubic centi-
metres of the decimal silver solution, and subsequently to estimate the amount of
silver present, in solution, by the use of the decimal solution of common salt.
620
ELEMENTS OF METALLURGY.
the
is fastened to the pipette, P, is provided with two stop-cocks, t' and t",
of which the uses will be presently explained. In conducting an assay,
the operator closes the extremity of the pipette with the fore-finger of
the left hand, fig. 183, and, with the right, opens the taps, t' and t',
latter being opened first; by the first of these the solution enters the
pipette, whilst from the second the air escapes in proportion as it becomes
filled by the solution of chloride of sodium. When the pipette has become
filled by the liquor to a little beyond the mark m, the cocks t' and t' are
both closed, and the instrument remains charged with the solution.


p
FYINGINERENSINMASI
d
m
P
B
S
C
R
G
Fig. 182.
LETTRICED TREATIN
G
G
nu
P
Fig. 183.
On the table immediately beneath this apparatus is placed a sliding
support, W, in which is secured by means of a ring of copper, C, the
bottle, B, containing the solution, in nitric acid, of the alloy to be assayed,
whilst immediately in connection with it is a small stand, S, on which is
fastened a sponge, q, situated at the exact height of the beak, p, of the
pipette. The assayer now slides the plate, W, between the guides, G, in
such a way that the sponge may come in contact with the extremity of the
pipette, and by carefully admitting air through an aperture in the tap t'',
allows the liquid to descend until it exactly reaches the level of the line
m, marked on the glass by means of a scratching diamond. The sponge
removes the last drop of the solution, which would otherwise remain
attached to the beak of the instrument, and in proportion as it becomes
saturated with moisture, the liquid falls through the hollow support, S, into
the cup-shaped receiver, R, where it is collected. The operator now draws
SILVER.
621
the slide towards the right until it is stopped by a peg, which arrests it
when the neck of the bottle is immediately under the extremity of the
pipette, and by admitting air through the cock, t', he allows the solu-
tion to flow directly into it. The last drop of the liquor invariably
remains attached to the burette; but, as the instrument is gauged with
due attention to this circumstance, its addition is unnecessary, and would
in fact vitiate the result. As in most instances several assays are being
made at the same time, the weighed quantities of alloy are commonly
dissolved in numbered bottles, which are sometimes arranged in a metallic
frame somewhat similar to a cruet-stand, and which, after the introduction
of the acid, may be placed in a water-bath or on a sand-bath for the pur-
pose of facilitating their solution.
b
Que a
e
When the various samples have become completely dissolved, the
nitrous fumes are removed from the bottles by slightly blowing into
each, with bellows, through a glass tube, and a decilitre of the standard
solution is introduced into each by the method already described. The
bottles are subsequently placed in a metallic case, C, fig. 184, generally
made with a cover to keep the stoppers in their places, which, besides
being provided with compartments for each bottle, is suspended from the
extremity of a steel spring, a, b, and is steadied from below by the elastic
spiral, c, d. These bottles, after being carefully closed by their stoppers
and fastened in their several compartments, are well shaken by an assistant,
who takes hold of the handle, e, f, and briskly
agitates the whole apparatus during several minutes.
As soon as the liquors have in this way been ren-
dered sufficiently clear, the bottles are removed
from the frame, C, to a blackened table, fitted up
with divisions numbered to correspond with the num-
bers on the bottles themselves, care being taken that
each assay be placed in the compartment to which
it belongs. The decimal solution, which is contained
in a phial having a pipette passing through its cork,
is now employed for the purpose of determining
the exact amount of silver in the various assays.
This pipette is so marked, by a line drawn on its
surface, as to allow the operator to exactly measure
out one cubic centimetre of the liquid which it
contains. To do this, the point of the fore-finger is
applied to the upper extremity of the tube, which, whilst thus closed, is
raised above the surface of the liquid in the bottle, and is allowed to drop,
by the careful admission of air, until the liquid has fallen to the level of
the line marked on its surface. The opening is now closely stopped,
and the cubic centimetre of fluid is transferred to the first bottle of the
series, into which it is permitted to flow on removing the finger from
the upper extremity of the pipette.

Fig. 184.
www.www
The same quantity of solution is afterwards successively added to
each of the other assays. The assayer now examines each bottle in
succession, and makes a mark with chalk on the blackened table before
622
ELEMENTS OF METALLURGY.
those in which a precipitate has taken place. These are a second time
transferred to the shaking apparatus, in which they are briskly agitated
until the liquids have again become clear, when they are taken back to
their respective places on the blackened table, and another cubic centi-
metre of decimal solution is added to each in which a precipitate was
obtained by the last operation. By degrees the several bottles in which
no precipitate has taken place are thus eliminated, and on counting the
number of marks set before them the number of cubic centimetres of
the decimal solution which has been added to each assay is readily
ascertained. From this number must be deducted half a centimetre, as
only a portion of the last addition may be supposed to have suffered
decomposition.
The standard solution of sodium chloride employed is prepared at
15° C.; but as this, in common with all liquids, expands and contracts in
accordance with the temperature to which it is exposed, it was formerly
customary to construct a table of corrections, to be employed in cases
when the liquid is used at temperatures either above or below this point.
For this purpose the thermometer in the tube, de, was consulted, and
the correction read off from tables prepared for that purpose; it is now
generally preferred to make use of the following method, by which all
error arising from any alteration in the solution is at the same time
guarded against. With this object the assayer makes each morning experi-
ments on 1 gramme of pure silver, at the same time that he is conducting
his regular assays of the usual alloys, and from the result obtained by
these checks he is enabled to correct for any little irregularity in the
constitution of the solution employed.
The standard solution of chloride of sodium is made from common
salt, without any preliminary purification, and is usually prepared in
considerable quantities at a time. For this purpose 500 grammes of
common salt may be dissolved in four litres of water. The liquid is
filtered, and the amount of water that would be necessary to make a
solution of the requisite strength, supposing the chloride to be pure, is
added. By this means a solution roughly approximating only to the
composition of the normal liquor is obtained, and of which the exact
standard must be ascertained by adding a decilitre to a solution of one
gramme of pure silver in nitric acid. The liquor is clarified by agitation,
and by the addition of successive centimetres of the decimal solution,
either of nitrate of silver or of chloride of sodium, the exact amount of
silver or of chloride of sodium, as the case may be, remaining free after
the addition of a decilitre of the solution, is ascertained.
When this is known it becomes easy to calculate the quantity of water
or of sodium chloride which must be added in order to arrive at a correct
standard; and when this addition has been made, experiments of a
similar description are repeated, until satisfactory results are obtained.
The decimal solution of chloride of sodium is readily prepared by pouring
a decilitre of the standard solution into a bottle of the exact capacity of
a litre, and afterwards filling it with distilled water.
To prepare the decimal solution of silver, one gramme of pure silver is
SILVER.
623
dissolved in nitric acid, to which distilled water is afterwards added until
an exact litre of the liquid is obtained.
When the alloy operated on contains mercury, the results by humid
assay are no longer exact, as this metal, being precipitated at the same
time as the silver, decomposes a portion of the standard solution, by
which the experiment becomes vitiated. The presence of mercury in
the alloy examined is detected by exposing the bottles containing the
precipitated silver chloride to the action of light, since the presence of
a very minute trace of mercury prevents the usual darkening of that
salt. The assay of alloys containing mercury may, however, be made by
the humid process, if a solution of acetate of sodium be added to the
solution of silver previously to the introduction of the standard solution
of chloride of sodium, as this reagent has the property of preventing the
precipitation of mercurous chloride.
METALLURGY OF SILVER.
Galena and all other lead ores are argentiferous; and although in
some instances the amount of silver is so small as not to repay the
expenses of extraction, yet in the majority of cases it is present in such
proportions as to render its recovery a matter of commercial importance.
Whenever lead ores are treated for silver the lead is first obtained in the
metallic state by one of the processes described in the article on the
metallurgy of that metal, or by some modification of one or other of
them; the silver is afterwards separated from the alloy, either by cupel-
lation alone, or by concentration and the subsequent cupellation of the
enriched lead.
Argentiferous copper ores were formerly first treated for that metal,
and the black copper afterwards fused, with the addition of metallic
lead. This was subsequently removed by eliquation, and took along
with it a large proportion of the silver, from which it was finally sepa-
rated by cupellation in the ordinary way. In some instances, instead
of fusing black copper with metallic lead, the argentiferous copper
ores are smelted with the addition of galena or of some plumbiferous
metallurgical product, by which copper matts and metallic lead con-
taining the principal part of the silver are produced. The separation of
silver from copper ores may also be effected by the amalgamation of
matts obtained by their treatment for copper, either in blast or reverbe-
ratory furnaces; or such matts may be subjected to some process by which
the silver is removed in a state of solution.
Ores containing silver, associated with so small an amount of any
other useful metal that its extraction would not be attended with
remunerative results, are classed as dry silver ores, and may be smelted
either with the addition of an ore of lead, or with some metallurgical
product rich in that metal; on the other hand, they may be subjected to
treatment by amalgamation, or may be worked by one of the processes
for liquid extraction shortly to be described. All silver ores can be
treated by fusion with galena or with litharge, and the yield of silver thus
624
ELEMENTS OF METALLURGY.
obtained is generally in excess of that produced by amalgamation. In
smelting operations, however, the expenditure of fuel is necessarily
large, and consequently, in districts where this essential is scarce and
expensive some process of amalgamation is generally resorted to.
The amalgamation of silver ores is conducted in various ways; but
of the different processes employed the following are the most important :
Firstly, the Mexican process of amalgamation in heaps; secondly, the
barrel process, formerly employed at Freiberg, and still in use at Con-
stante in Spain, in the State of Nevada, and elsewhere; thirdly, the
Washoe process, by which unroasted ores are amalgamated in iron pans.
In the various processes adopted for the extraction of silver from its
ores by smelting, advantage is taken of the affinity possessed by lead,
when in a state of fusion, for this metal, which consequently performs,
when in that condition, a somewhat similar service to that which is
rendered by mercury at lower temperatures. The presence of gold in
an ore of silver in no way modifies its treatment in the furnace, since
the former metal invariably accompanies the latter in the lead produced,
and is ultimately separated from the alloy, obtained by cupellation, by the
process of "parting.'
As all silver ores may be treated by fusion with plumbiferous
materials, and the silver afterwards separated from the alloy obtained,
the various processes described for smelting lead ores are applicable to
those of silver. When, however, the extraction of silver is the chief
object in view, some form of blast-furnace is often employed, although
the flowing furnace, made use of for the treatment of refractory Cornish
ores, is likewise well adapted for the purpose. In all such cases the
primary result obtained is an alloy of lead and silver, which may be
either softened and concentrated before cupellation, or be passed directly
to the cupel. Where silver ores have to be worked in a district in which
fuel is moderately abundant, but ores of lead are with difficulty obtained,
it will generally be found advantageous to cupel the argentiferous alloy
without any preliminary concentration, and to employ the resulting
litharge in the next operation of smelting a fresh quantity of argen-
tiferous material. For this purpose the Continental system may be
employed if wood be abundant, but long flues must be constructed for
collecting the lead fumes, which can be used, mixed with litharge, for
the collection of silver.
When silver ores are treated by fusion with plumbiferous materials,
it will be necessary to arrange the several furnace mixtures nearly in
accordance with those indicated for smelting lead ores in the various
furnaces which have been described. The place of galena may be
supplied by litharge, &c.; and although the nature and quantity of the
fluxes required can be approximately ascertained by analysis, yet the
most suitable proportions to be employed can, in each case, only be exactly
determined after repeated and carefully-conducted trials. As the descrip-
tions of the furnaces and processes employed in lead-smelting are equally
applicable to those made use of for the treatment of silver ores, we shall
proceed to describe some of the methods adopted for the extraction of
SILVER.
625
silver by amalgamation. Before doing so, however, it may be necessary
to observe that when silver is found associated with large quantities of
iron pyrites or other sulphides, other than galena, the ores are frequently
fused for a coarse matt previously to fusion with litharge or other plumbi-
ferous material. The matt thus obtained is then either roasted and
subsequently smelted with some material capable of affording lead, or
is first concentrated by a second fusion, followed by another roasting.
Nearly the whole of the silver originally present in the ores treated will
thus be concentrated in the matts produced, and their subsequent metal-
lurgical treatment is, consequently, much simplified.
TREATMENT OF SILVER ORES BY AMALGAMATION.
MEXICAN OR PATIO PROCESS.--The ores treated by this process do
not ordinarily admit of being previously concentrated by mechanical
preparation, and even had the results obtained been more satisfactory
than they are generally found, the supply of water in the districts in
which they occur is, in most cases, so limited as to render washing
operations on an extensive scale impossible. This method of extracting
silver from its ores by the use of mercury and common salt, without
the assistance of artificial heat, was discovered in the year 1557 by Bar-
tolomé Medina, a native of the town of Pachuca, in Mexico, and has
been uninterruptedly employed from that period up to the present time,
without having undergone any material modification.
The silver in the ores operated on chiefly exists either in the metallic
state, or combined with sulphur, chlorine, iodine, or bromine. Arsenic
and antimony, which are present in certain classes of ore, not only
render their treatment difficult and expensive, but also materially aug-
ment the loss of both silver and mercury. When sufficiently rich,
such ores are frequently set aside for treatment by smelting, but they
are often so disseminated throughout the veinstone, and so intimately
mixed with it, as not to admit of separation by any system of hand pick-
ing. The gangue in which they are contained consists principally of
quartz, more or less associated with pyrites or with oxide of iron, and, in
addition to small quantities of other minerals, often contains from 5 to
10 per cent. of calcite or dolomite. Near the surface such veins are
generally much decomposed, and the ores then present the appearance
of a friable ferruginous quartz, in which a large proportion of the silver
occurs either in the native state or as chloride.
Although the loss of silver by the patio system of amalgamation is
very large, and much time is expended on the various necessary opera-
tions, it nevertheless possesses great advantages over all others, in the
barren and arid districts in which it is chicfly carried on, inasmuch as it
requires neither fuel nor a large amount of water; the only materials
necessary being salt, cupreous pyrites and mercury.
Rough stamping.-The ores to be treated by patio amalgamation are
first crushed dry in a molino or stamping mill, and are subsequently
ground with water in the arrastra (or arrastre) until reduced to the neces-
2 s
626
ELEMENTS OF METALLURGY.
sary state of fine division. The stamping mill generally consists, in
Mexico, of a series of wooden lifters or stems, shod with iron, and set in
motion by cams arranged round an axle, worked either by a water-wheel
or, more frequently, by a vertical shaft, carrying a beam, to which is
harnessed a team of four mules. The vertical shaft is provided with a
large wooden wheel, which communicates its motion to another, fixed on
the cam-shaft of the mill. Ore is supplied to this arrangement in pieces
of the size of the fist, which, when sufficiently reduced in size, fall
through sieves or screens, made either of metal or of dried hides per-
forated with numerous round holes, and which are fixed in an inclined
position before each battery. The particles of ore which pass through
these holes are removed for fine grinding in the arrastra, while the coarser
portions continue to be acted upon by the pestles, until sufficiently re-
duced in size to admit of their passing through the screens. In most
cases these mills are worked by relays of mules, which are driven at a
rapid rate, and frequently replaced by a fresh team.
Fine grinding. The arrastra, or tahona, consists of a circular pavement
of stone, about 12 feet in diameter, on which the ore is ground by means
of two or more stone mullers dragged continually over its surface by
mules attached to a horizontal arm. Around this circular pavement of
hard stone is constructed a kerbing, either of flat stones or of wood, form-
ing a kind of tub, about 2 feet in depth, in the centre of which a piece
of hard wood is firmly fitted between the blocks of which the flooring is
composed. Working on an iron pivot, in a step let into this central
post, is an upright wooden shaft, sccured at its upper extremity to a hori-
zontal beam by another journal; this is crossed at right angles by two
wooden bars forming four arms, of which one is sufficiently long to admit
of two mules being harnessed to it abreast. The voladoras, or mullers,
are generally made either of porphyry or of granite, although basalt is
sometimes employed for this purpose, and have a length of somewhat less
than the radius of the arrastra, with a thickness of about 16 inches.
each of them are bored two holes into which wooden pegs are driven for
attaching the chains, or thongs of raw hide, by which they are connected
with the arms traversing the central vertical shaft. These mullers are
so hung that their edges, in the direction of their motion, are raised about
an inch above the surface of the stone pavement, while the other side
trails heavily upon it. A sectional view of a Mexican arrastra is given in
fig. 185, in which A is the upright shaft, B, arms to which the mullers,
C (of which one only is shown), are attached, and D the central block of
hard wood in which the lower bearing works.
In
At Guanaxuato, where the ores are more finely ground than in any
other district of Mexico, and where in addition to silver they contain
a certain proportion of gold, from 6 to 11 quintals* of granza, or coarse
sand from the stamping mills, are charged into the arrastra with one
barrel, or about 10 gallons of water, at four o'clock in the morning;
at nine o'clock a second barrel is poured in, and a third at twelve;
at three o'clock three barrels, and at four, five barrels, of water are added.
* The Mexican quintal 100 lbs. avoirdupois, nearly.
SILVER.
627
At the expiration of twenty-four hours, when the grinding has been com-
pleted, the lama, or argentiferous mud, is baled out into barrels, in which it
is removed to reservoirs formed of masonry, where a portion of the water
is evaporated by exposure to the sun and air, and the mass is ultimately
left in a condition fit for subsequent treatment in the patio. In some es-
tablishments, instead of the lama being taken away in barrels it is baled
into wooden spouts, by which it is conducted to proper receptacles,
whilst in others it is tapped from a plug-hole at the bottom of each
arrastra, directly into properly-arranged spouts. The mules by which
the machines are worked are changed every six hours, and the arrastras
are generally arranged in rows in long sheds called galeras. At Zaca-
tecas, where the ores contain no gold, the grinding is not so long con-
tinued, and the lama is removed in a less finely-divided state. In this

О
A
Fig. 185.-Arrastra; partly in section.
district each arrastra grinds 10 quintals in the course of thirteen hours,
but the lama is much coarser than at Guanaxuato, and the results
obtained are less satisfactory.
Where, as at Guanaxuato, the ores contain, in addition to silver,
small quantities of gold, the arrastra is kept constantly charged either
with a certain amount of mercury or with an amalgam of silver or
copper. By this means the gold becomes concentrated in the amalgam
ultimately obtained, and highly profitable results are realised. In such
cases, care must be taken, in removing the lama daily obtained, not to
disturb the amalgam in the bottom of the arrastras, which is collected at
periods of from three to six months, and, after being strained and retorted,
is melted into bars which are afterwards subjected to the operation of
parting.
The yield of gold by this method is considerably less than the total
amount contained in the ores treated, the loss experienced generally
varying from 25 to 40 per cent. on the assay produce. A certain loss
of mercury also takes place during the process, which is apparently
caused by the decomposition of sulphide of silver with the formation of a
2 s 2
628
ELEMENTS OF METALLURGY.
proportionate amount of sulphide of mercury. The loss of this metal is
usually found to correspond very closely with the weight of silver taken
up by the amalgam during the progress of the operation.
The Patio. This is a large courtyard, generally paved with stone
slabs, the joints between which are carefully cemented in order to pre-
vent loss of mercury. A slight inclination is given to the surface of
the patio, in order that any water that may fall upon it may readily
flow away.
The ground ores are, as before stated, taken from the
tahonas to walled receivers (lameros), in which they become partially
dried, and where they are allowed to accumulate until there is a sufficient
quantity to form a heap, or torta, which, at Guanaxuato, usually consists
of 60 montones, about 96 tons.* When the necessary amount of lama
has been thus collected it is taken to a circular area on the patio, from
30 to 50 feet in diameter, according to the weight of ore operated on,
surrounded either by a low wall of stone or by a border of planks made
tight by filling all the crevices with clay or with mule dung. Into this
the lama is introduced until it forms a stratum of about a foot in thickness,
and is allowed to remain until, by the evaporation of the water, it has
assumed the consistence of a moderately thin mud. As soon as this con-
dition has been reached, the amalgamator proceeds to add from 3 to 5
per cent. of salt, and when this has been done the torta receives the first
treading (repaso), after which it is allowed to stand until the following
day. A larger amount of salt would, in many cases, expedite the working
of the torta, but on account of its high price this is seldom added.
In addition to common salt, imported from the coast, a large quantity
of impure chloride of sodium, obtained from various lagunes, was formerly
employed, but the cost of transporting considerable amounts of such an
impure material, added to the great increase in bulk of the tortas pro-
duced thereby, has caused its use, in a crude state, to be almost entirely
abandoned; this salt is, therefore, now concentrated and purified by
lixiviation and evaporation before being carried to the mines.
The day after salt has been thus mixed with the ore, addition of mer-
cury and magistral takes place. Magistral is prepared by slowly roasting,
in a reverberatory furnace, copper pyrites containing a considerable
admixture of iron pyrites, to which a small quantity of common salt
has been added. By this process, the minerals present in the raw
ore become oxidised with the formation of cupric and ferrous sulphates,
together with a small proportion of chlorides. The cupric sulphate
varies in amount from 20 to 40 per cent. of the whole, and is the chief
agent in the reduction of the ores, although the iron salt, which is present
in amounts varying from 6 to 12 per cent., also exercises a beneficial
influence on the results.
Before the addition of magistral, the torta is, if necessary, brought to
*The weight of the monton varies in different localities-
In Guanaxuato a monton usually contains
Real del Monte, Pachuca, and Tasco
Zacatecas and Sombrerete
Fresnillo
Bolaños
•
32 quintals
30
20
•
18
15
**
SILVER.
629
a proper consistence by the addition of water, and the roasted sulphides
are then thrown evenly over its surface by means of wooden shovels. The
proportion of this reagent added, is varied in accordance with the amount
of cupric sulphate it contains; but in the generality of cases, when magis-
tral of average strength is employed, something less than 1 per cent. is
found sufficient.
As soon as the magistral has been spread over the surface of the
torta, it is again trodden by mules for about an hour, when the mercury
necessary for the completion of the operation is added. Formerly, the
whole of the quicksilver required was not introduced at one time, but at
various periods during the progress of the operation. It is, however, now
more usual to add all the mercury immediately after the introduction of
magistral. This is done by straining it through a piece of canvas, by
which its particles are divided into minute globules, the quantity added
being from 3 to 4 lbs. for each mark* of silver supposed to be contained
in the heap. After the addition of mercury the torta is again trodden, to
effect its intimate mixture throughout the mass.
When magistral and mercury have been added to a torta, and it has
received its first treading, chemical action commences, and the amalga-
mator closely watches its operation by means of samples taken from all
parts of the heap. To make an assay or tentadura, a fair sample of about
8 ozs. of the ore is washed with water in a small bowl (jicara), and from
the results obtained the azoguero (amalgamator) is enabled to judge of
the progress of the operation. Shortly after the first treading of the torta
samples are taken, and a tentadura is made, and, after washing off the
earthy and lighter particles, the remaining polvillos, or metallic sulphides
and mercury, are carefully examined. At this stage the mercury con-
tains but little silver, and its colour and state of division afford the
only indications of the working of the torta. Should it be found divided
into small globules, or its natural colour be but slightly changed, it
indicates that the amount of magistral added is not sufficient. If, on
the contrary, the mercury has acquired a deep grey or leaden hue, the
quantity of magistral is too large, and the torta is said to be hot, in which
case the addition of a small quantity of lime may be necessary in order
to avoid an undue loss of quicksilver. When the heap is in good work-
ing order, the surface of the mercury presents a light-grey appearance,
and the aspect of the tentadura, taken the day after treading, will
have considerably changed. If now pressed by the thumb against the
side of the bowl, the mercury will be found to contain silver amalgam,
and what on the previous day was broken-up quicksilver (desecho), has
become limadura de plata, of a whitish colour and in the form of thin
scales. Three tentaduras are usually made daily on each torta: one in
the morning before commencing to tread, another after it has been trodden
for some time, and a third when the repaso has been completed. The
samples selected for this purpose must be taken from the middle of the
heap, as well as from the surface, since the top, from being exposed to
the action of the air and sun, is always in a more advanced condition
* Mark = 3,550·5 grains.
630
ELEMENTS OF METALLURGY.
than the interior. The treading, which must be repeated daily, or as
often as tentaduras indicate a necessity for doing so, has the effect of
stimulating the action of the magistral. When chemical action has
almost ceased, and nearly the whole of the silver which the process is
capable of extracting from the ore has been taken up by mercury, the
limadura becomes "weak," and on being rubbed by the thumb shows
but little solid amalgam. As soon as it is found to be free from amalgam,
and unites in globules at the bottom of the jicara, the operation is con-
sidered finished, and the torta is said to be rendido. For some years,
however, amalgamators have not entirely relied on the results obtained
by washing, but have also been assisted by fire assays made on average
samples taken from each torta; in this way its total content of silver is
readily ascertained. Another weighed sample is washed in the jicara,
and the mercury and amalgam carefully collected; the assay of these
afford data for calculating the proportion of silver which still remains.
unacted upon in the ores. The treading is generally performed by
mules, which are blindfolded and tied together four abreast; one mule
for every two montones of ore is, at Guanaxuato, required for the effectual
treading of a heap. A driver, who stands in the centre of the torta,
guides the animals with a long halter, causing them first to tread at the
outer edge, and gradually diminishing the radius of the circle described.
The time necessary for working a torta varies from fifteen to forty-five
days, according to circumstances.
Washing.—When the working of a heap has been completed, a quan-
tity of fresh mercury, called a baño, is sometimes added, but this practice.
is by no means universal. At Guanaxuato the washing apparatus (lava-
dero) consists of three circular tanks built closely together within an
inscribing circle; these are constructed of stone slabs with carefully-
cemented joints. The depth of each tank is 5 feet 4 inches, and its
diameter 9 feet 6 inches; they communicate with one another by means
of openings, of which one is at a height of 8 inches and the other at a
distance of 30 inches from the bottom. The last tank is provided with
two separate discharge holes; the first 6 inches from the bottom, and the
other, which is used only for cleaning up, is situated close to it.
In the centre of each tank is an upright shaft carrying agitating
arms; the whole being set in motion by a shaft provided with a spur-
wheel working in pinions on the shafts of the different washing vats.
The shaft carrying the spur-wheel passes through an upper flooring,
where motion is communicated to it by a team of mules attached to an
arm let into it at right angles; the pinions of the agitators in the second
and third tanks are a little larger than that working the stirrer in the
first, and their motion is consequently somewhat slower. The first tank
into which the metalliferous mud from the torta is charged is called the
tina cargadora, whilst the third, from which it runs off, after passing
through the second, is called the descargadora. Before being washed,
the torta is divided into several parcels, each of which is softened by
treading and the addition of water, and then taken to the washing house
in bateas, dusted on the inside with dried mule dung to prevent adherence.
SILVER.
631
About three montones of lama are now gradually introduced into the
first tank, water being at the same time run in, and the machinery is
made to revolve rapidly, by driving the mules at a gallop. When the
whole of the lama has been introduced, the speed of the agitator is
gradually slackened, until the mules move only at a gentle walk, and
samples of the slime are, from time to time, taken out and washed, in
order to ascertain if it still retains an appreciable amount of mercury.
When samples taken from the tinas afford only minute metallic traces,
the plug furthest from the bottom of the descargadora is removed, and, as
soon as the slimes have run off, they are replaced, and the operation is
continued until the whole of the torta has been washed. The bottom
plug is then removed with suitable precautions, and the whole of the
mercury and amalgam carefully collected.
At Guanaxuato, the heavier constituents of the torta, which remain
with the amalgam at the bottom of the tinas, are separated from the latter
by washing in bateas, and the resulting relaves are subsequently re-ground
in arrastras. By this treatment they are made to yield a certain amount
of auriferous amalgam, but they are not always again subjected to patio
amalgamation. In this district the slimes from the lavadero are now
sometimes concentrated by means of the round buddle.
At Zacatecas and Fresnillo the washing is conducted in a single cir-
cular cistern, and as soon as the azoguero considers that a torta is ready
he adds to it about 80 per cent. of the amount of mercury which it already
contains. At Guanaxuato, as has been already stated, the lama is taken
direct to the lavadero without any further addition of quicksilver. The
speed of the agitator is greater than in cases where three tinas are em-
ployed and about two and a half montones of lama are passed through
each cistern in the course of an hour. A considerable loss of amalgam is
the result of this system of washing, and in order to recover it, the heavy
residues collected in a cistern beneath the discharge-orifice of the tina
are re-washed on a planilla, or washing table. These, when sufficiently
rich, after being previously roasted in a reverberatory furnace, are re-
ground in an arrastra, and a second time treated by amalgamation in the
patio. In certain districts, and particularly in those situated nearest to
the city of Mexico, the washing of the tortas is conducted in a wooden
tank, of which one end is pierced with numerous holes at different heights,
which admit of being closed by plugs provided for that purpose. At
the opposite end a stream is admitted, and as soon as the cistern has
become nearly filled with water the lama to be washed is thrown in and
briskly stirred with shovels; when the ore is thus well incorporated with
water the plugs are successively removed, beginning with the upper one.
The lighter earthy matters are in this way first drawn off, and afterwards
the heavier metallic sulphides, until the amalgam, in a tolerably pure
state, alone remains in the bottom. After escaping from the tank, the
slimes are conducted through riffle-boxes for a distance of from 70 to 80
feet, in which a considerable portion of the amalgam and mercury, which
would be otherwise lost, is retained.
Filtration of Amalgam.—The amalgam obtained is first purified from
632
ELEMENTS OF METALLURGY.
1
adhering particles of mineral, and then filtered through a cone-shaped
bag (manga), of which the upper portion is cased with leather, while the
lower part consists of stout canvas only. This is hung, point downwards,
from a strong beam, and the mixture of mercury and amalgam introduced;
the former gradually passes through the meshes of the canvas, and is col-
lected in a vessel placed beneath for that purpose. The amalgam
remaining in the manga contains mercury to the extent of from four to
five and a half times the weight of silver present, and has a granular and
plastic consistency, which readily admits of its being moulded into bricks.
As soon as mercury has ceased to drop from the point of the manga it is
emptied on a table covered with leather, and the amalgam is beaten into
triangular bricks (bollos), from 3 to 4 inches in thickness, and so shaped,
that when six of them are placed together they form a circular cake,
having a hole in the centre for the escape of mercurial vapours, during
the subsequent process of distillation.
Retorting. The separation of mercury from the silver is effected by
distillation under a large cast-iron bell placed over the amalgam, and
around which is lighted a charcoal fire. A circular casting is let into
the floor of the retorting house, through which a current of cold water
constantly circulates, and on this is placed an iron support, on which the
bricks of amalgam are arranged. When thus prepared the bell (capellina)
is lowered over it, and the bottom carefully secured by a luting of clay.
Unburnt bricks (adobes) are now built around it in the form of a hollow
wall, so as to leave an annular space, 8 inches in width, between them and
the capellina; this is filled with ignited charcoal, and in proportion as
the mercury becomes volatilised, it is condensed by the action of the
current of water, and escapes through an iron pipe into a receptacle pre-
pared for that purpose. Instead of the wall of adobes an iron cage is some-
times placed around the bell, for the purpose of retaining the charcoal.
The resulting silver (plata piña) has a porous frosted appearance.
The spongy silver thus obtained is fused and cast into bars in the ordinary
way, and is generally above 990 fine.
Results obtained, &c.-The loss of silver experienced in patio amal-
gamation is always considerable, but varies in accordance with the nature
of the ores and the amount of skill brought to bear upon their treatment.
At Guanaxuato the average loss on docile ore is from 9 to 14 per cent.
on the assay produce; at Fresnillo the deficit is often 28 per cent., whilst,
according to Duport, the loss at Zacatecas, where the ores contain a large
proportion of antimonial sulphides, was, at the time he wrote (1843), from
35 to 40 per cent. of the yield indicated by assay. The loss of silver in
patio amalgamation at Real del Monte (1864-65), as furnished by Mr.
Buchan, was 9 per cent.
The loss of mercury experienced at the same period in that establish-
ment was 11 ozs. per mark of silver obtained; but this may be taken as
a favourable result, as the average expenditure of quicksilver may probably
be estimated at from 12 to 16 ozs. per mark of silver extracted.
The cost of patio amalgamation varies in different localities; at the
Hacien la Nueva, belonging to the Fresnillo Company, the cost of treatment
SILVER.
633
of a monton of 2,000 lbs. (1840-41) was $20.74, while at the Ophir Com-
pany's works, Nevada (1864), the cost of working the same weight of ore
was $23.25.
The chemical reactions which take place during the progress of patio
amalgamation are of a complicated nature, and the whole of them are not
yet thoroughly understood; the ore contains a mixture of native silver,
chloride of silver, and various sulphides, &c., containing silver. Common
salt is decomposed by cupric sulphate in the magistral, giving rise to
sodium sulphate and copper and iron chlorides. Cupric chloride in its
turn reacts on silver sulphide with the production of silver chloride,
which is dissolved in the excess of sodium chloride added to the torta,
and the silver is subsequently reduced to the metallic state by a portion
of the mercury, which is ultimately converted into calomel, whilst the
reduced silver forms an amalgam with unattacked mercury. The cuprous
chloride formed is dissolved in the excess of sodium chloride, and converts
another portion of silver sulphide into chloride, which is subsequently
reduced by mercury, and finally forms an amalgam with that metal.
The copper is, ultimately, chiefly converted into sulphide, and mercuric
sulphide is sometimes also found in the torta; this has been supposed to
be the result of the action of mercurous chloride on silver sulphide. It
has, however, been shown that this substance may be produced by the
direct decomposition of silver sulphide by metallic mercury, and it is
highly probable that this reaction takes place, to a certain extent, in the
torta. It has been contended, by persons practically acquainted with
patio amalgamation, that silver chloride is not necessarily formed during
the process; but the various phenomena brought forward in support of
this view appear to be capable of being otherwise explained.
STOVE AMALGAMATION.-In some of the colder and more humid
districts of Mexico a modification of patio amalgamation has been occa-
sionally resorted to. The ground ore from the arrastra is placed in a
shed where the salt, magistral, and mercury, are added, and the process
is conducted in the usual way. When the operation is about half com-
pleted it is removed to a stove (estufa), consisting of a chamber with flues,
so arranged beneath the floor as to communicate to the mixture the heat
of a fire-place with which they are connected. It is here exposed to a
gentle heat during from two to three days, and is then taken back to the
shed, where the operation is completed by the ordinary method of patio
amalgamation. In this way the time necessary for the reduction of the
ore is diminished, and the yield of silver somewhat augmented; the loss
of mercury is, on the other hand, more considerable.
HOT PROCESS.-In parts of South America where the ores contain a
large amount of native silver, or where that metal occurs in combination
with chlorine, iodine, or bromine, amalgamation is sometimes effected by
the aid of the cazo. This apparatus consists of a vessel formed either
of blocks of stone or of wooden staves, like those of a tub, the bottom
of which is made of a slab of copper 2 inches in thickness, but which
becomes gradually thinned by use. This metallic bottom is retained in
its place by a groove running round the interior of the vessel, in the
634
ELEMENTS OF METALLURGY.
same way that the head of a cask is secured, and all joints are carefully
luted with clay. The copper plate rests upon the walls of the hearth,
forming the roof of a fire-place, which has neither fire-bars nor chimney,
and which has but one opening for both the introduction of fuel and the
egress of smoke. After being roughly stamped, ores intended for cazo
amalgamation are ground in the arrastra; but as they are subsequently
subjected to a process of washing care is taken not to carry the operation
too far. The ordinary dimensions of the cazo are, diameter at top, 3 feet
3 inches; at bottom, 2 feet; depth, 18 inches. About 100 lbs. of con-
centrated ore forms the charge of a cazo, in which it is mixed with as
much water as will convert it into a liquid paste. When the contents of
the vessel have been made to boil, from 5 to 10 per cent. of salt is added,
and the workman, who squats by the side of the furnace and keeps the
mixture constantly agitated with a wooden stirrer, begins the addition of
mercury. More mercury is from time to time added, and numerous
samples are taken and washed in order to ascertain to what extent the
ores have become exhausted of their silver. The total amount of mercury
added is usually twice the weight of the silver supposed to be contained
in the charge, and the duration of the entire operation is six hours; the
liquid contents of the cazo, together with the slimes, are now dipped out
into reservoirs, whence they are subsequently removed for further treat-
ment by patio amalgamation. By this process the silver which exists.
in the ores in a native state, as well as that combined with chlorine,
iodine, or bromine, is readily made to unite with mercury, but silver
sulphide does not easily yield its metal to cazo amalgamation, and hence
the necessity of re-treating the residues in the torta. They do not, how-
ever, require the addition of magistral, since they contain a sufficient
amount of chloride of copper to convert the whole of the silver sulphide
into chloride.
In the district of Catorce the dimensions of the cazo are sometimes
much enlarged, and, under the name of fondon, this contrivance is some-
what extensively employed for the reduction of argentiferous ores. The
diameter of the copper bottom of the fondon is from 5 feet 6 inches to
7 feet 6 inches, and, instead of the necessary motion being imparted to
the charge by a wooden stirrer, worked by hand, it is obtained by blocks
of copper dragged over the bottom by an arrangement similar to the arms
of an arrastra. It may, therefore, be regarded as an arrastra in which
the stone paving and voladoras are replaced by a plate and blocks of
metallic copper, and to which a mule is harnessed in the ordinary way;
a fire-place is built below the bottom, which is provided with a plug-hole
for tapping off the slimes at the termination of each operation. The
charge varies from 1,200 to 1,500 lbs., and its treatment is completed in
six hours, as in the case of cazo amalgamation.
The loss of mercury
experienced during the treatment of silver ores in the cazo and fondon is
extremely small, not amounting to more than 2 to 3 per cent., since by
this process chloride of silver is finally reduced at the expense of the
copper bottom of the apparatus, instead of by the action of mercury,
as in the case of patio amalgamation.
SILVER.
635
AMALGAMATION IN BARRELS.-The amalgamation of silver ores by this
process was conducted with great skill and economy at Halsbrücke, near
Freiberg, from the year 1790 up to 1856.
This system was, however, abandoned in the course of the year last
named, on account of the expense of manipulation and of the unsatis-
factory results which it afforded when applied to certain classes of ore.
The changes of more than half a century had also so modified the rela-
tions originally existing between the prices of labour and fuel, that, at
the latter date, it was found advantageous to abandon the use of mercury,
and to smelt the argentiferous ores with others containing lead. The
usual constituents of the ores treated at Halsbrücke are sulphur, anti-
mony, arsenic, silver, copper, lead, iron, and zinc, which are more or
less mixed with various earthy minerals, besides sometimes containing
small quantities of bismuth, gold, nickel and cobalt. In the selection of
these ores they were so assorted as not to contain above 4 per cent. of
lead, or 1 per cent. of copper, as from combining with the mercury added,
these metals give to the amalgam a pasty consistency, and thereby render
the treatment both difficult and expensive.
The different ores selected for amalgamation varied in richness from
15 to 200 ozs. per ton. At one period the mixtures of these ores were
so arranged that the charges of the furnaces should always contain from
75 to 80 ozs. per ton. Latterly, however, it became usual to work the
poor and rich ores separately, since it was found that the total loss of
silver in the residues was thereby considerably diminished.
cess.
The mixtures of the poorer ores contained, on an average, from 30 to
40 ozs. per ton, whilst the amount of silver in those of the richer ores
varied from 90 to 130 ozs. per ton. It is essential that both mixtures
should contain a certain proportion of sulphide of iron, for the formation
of sulphate of iron, which is necessary to the success of the roasting pro-
The quantity of sulphide of iron present should not be less than
about 25 per cent. If the amount of iron pyrites, naturally occurring in
the ores, did not equal this proportion, addition was made either of that
mineral or of ferrous sulphate. Frequently, however, the ores at Freiberg
contained much more pyrites than was required, and in such cases a few
of the most sulphurous varieties were subjected to a previous roasting
without salt, in order to reduce the average amount in the whole to the
right proportion.
The ore when prepared was laid on a large floor, 40 feet in length
and 12 in width, and on the top of it was thrown 10 per cent. of common
salt, which was let drop from another room, through spouts placed in the
floor for that purpose. The heap, when it had been thus made up of
alternate strata of ore and common salt, was well mixed by being care-
fully turned over with a shovel, and then passed through a coarse sieve.
It was subsequently divided into small parcels, each weighing from
4 to 5 cwts. The salt annually employed for this purpose at the Hals-
brücke works amounted to 500 tons, and was supplied by the Prussian
salt mines.
The mixture of ore and salt was now roasted in reverberatory furnaces,
636
ELEMENTS OF METALLURGY.
provided with long flues, for the reception of the pulverulent matters
taken over by the draught.
The prepared charge was spread on the bottom of the hearth, where
it was at first gently heated, for the purpose of expelling the moisture,
which to a greater or less extent it invariably contained. During the
process of drying, which usually occupied from twenty to thirty minutes,
the charge was kept constantly stirred by a long iron rake. The lumps,
which were formed by this operation, were then broken down by means of
an iron beater, provided with a long handle. The heat was afterwards
raised, white fumes were given off, and, in about two hours from the
commencement, the whole mass had become red-hot. The charge was
occasionally turned, so that every particle of ore might be equally exposed
to the fire, and during the whole time the mass was diligently stirred
with the rake. The fire was now allowed to burn down, and the oxida-
tion of the sulphur aided by constant stirring. This went on without
intermission until the mass became quite dark, and a sample taken from
the furnace no longer evolved any odour of sulphurous anhydride. During
this period, the ore increased in volume, and the particles hung so
loosely together that the movement of the rake was scarcely at all
impeded. The heat was again raised for about three-quarters of an
hour; the iron sulphate, formed by the oxidation of pyrites, reacted on
the common salt, and caused the evolution of chlorine and hydrochloric
acid gases, which, coming in contact with various silver compounds, con-
verted them into chloride. Chlorides of the other metals present were at
the same time formed, together with sodium sulphate. When the roast-
ing was terminated, the charge was raked from the furnace into an iron
barrow, and thence removed to an adjoining floor. The ore was afterwards
raised to an upper story for the purpose of being passed through a set
of sieves, by which the finer powder was separated from the agglutinated
lumps. These were broken to a proper size, and a portion re-roasted by
adding a small quantity to each of the ordinary charges. The remainder
was mixed with 2 or 3 per cent. of salt, and calcined in the usual way.
The finer particles, which passed through the sieves, were, on the con-
trary, taken to heavy millstones, where they were reduced to the state of
an impalpable powder.
After roasting, the charge consisted chiefly of oxide of iron, basic
sulphate of iron, and protochlorides and perchlorides of iron and
copper; together with oxide and sulphate of copper, sulphate of lead,
oxide of antimony, and zinc, and a small quantity of metallic sulphides,
in addition to gangue, various earthy salts, sulphate of sodium, and the
excess of common salt employed. The compounds of silver, originally
present in the mineral, were converted into chloride, with the exception
of traces of metallic silver, and perhaps also of a minute quantity of
sulphide of silver, which remained in the residues. The charge in roast-
ing suffered a considerable diminution in weight, amounting to about
10 per cent.
This loss is due to the escape of sulphur, chlorine, particles of salt,
zinc, antimony, arsenic, chloride of iron, &c.
SILVER.
637
The amalgamation of the prepared ores was performed in twenty
wooden casks, arranged in four rows, each turning on cast-iron axles,
secured to their ends by means of bolts. These barrels, which were
internally 2 feet 8 inches in length, 2 feet
8 inches in diameter at the ends, and
2 feet 10 inches in the middle, were made
of pine, 3 inches in thickness, and were
strengthened by iron hoops and binders,
fig. 186. On one of the ends of each
barrel was a toothed-wheel, w, figs. 187,
188, communicating with a shaft, x, which
received its motion directly from a water-
wheel.

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230
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Fig. 186.-Amalgamating Barrel.
Above each of the barrels so arranged
was a wooden case, C, into which was
thrown the prepared mineral. To the
bottom of this case was fixed a wooden
spout, to which was attached a hose made of strong cloth, and terminated
by a short cylinder of tin-plate, for the purpose of introducing the
powdered ore into the different barrels, B. Each cask was furnished with
a circular opening, a (figs. 186, 187), 5 inches in diameter, fitted with a
wooden plug, through which had been bored a small hole, provided with a

h
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B
B
พ
3
Fig. 187.-Amalgamating Barrels; transverse section.
pin made of hard wood, for the purpose of running off the argentiferous
mercury at the termination of the process. Below the barrels, and a little
above the surface of the floor, were placed triangular troughs destined to
receive the residual matters at the close of the operation. At the com-
mencement of the process 3 cwts. of water were run into each barrel,
638
ELEMENTS OF METALLURGY.
after which 10 cwts. of the ground and finely-sifted ores were introduced
through the hose, h. Each cask contained from 80 to 100 lbs. of wrought-
iron, cut into fragments of about 1 inch square and 3 of an inch in
thickness, and which, in proportion as they became dissolved by the
action of the substances with which they were associated, were replaced
by fresh pieces.
As soon as the barrels were charged, and the plugs firmly secured in
their places by binding screws, the apparatus was thrown into gear
by means of a screw and sliding block, b (fig. 186), and made to rotate
with a rapidity of from twelve to fifteen revolutions per minute.
At the expiration of two hours the machinery was again stopped, for
the purpose of examining the state of the metalliferous paste. If the
charge was too firm a little water was added, but if, on the contrary, it was

B
B
W
{/ UNLIMIT
PE
Fig. 188-Amalgamating Barrels; plan, partly section.
found to be too soft, a small quantity of ore was thrown in. When this
had been attended to, 5 cwts. of mercury were poured into each cask,
and the barrel, after being securely closed, was again thrown into gear, and
kept constantly revolving for about sixteen hours, at the uniform rate of
thirteen turns per minute. During the first eight hours of this period
they were twice examined for the purpose of seeing whether the paste
which they contained was of the proper consistence, for if too thick
the mercury becomes too finely divided, and if too thin, it remains
at the bottom of the cask, and is not sufficiently mixed with the different
constituents of the charge. In the first case, it is necessary to add
a small quantity of water; and in the second, a little powdered ore.
After the introduction of the mercury the temperature of the casks
becomes considerably raised by the chemical changes constantly going
on within, so that even in winter it sometimes stands as high as 40° C.
At the expiration of eighteen hours the amalgamation was ordinarily
complete, and the casks were now entirely filled with water, and again
made to turn during from one and a half to two hours with a velocity of
only six or eight revolutions per minute. The mercury was by this
means separated from the slimy matters with which it was mixed, and
collected in one mass at the bottom of the barrels. When this union of
the globules of mercury had been accomplished, the different casks were
successively thrown out of gear and stopped with their apertures upper-
SILVER.
639
most. The small peg in the bung was now removed, and in its place was
inserted a hollow plug, to which was attached a small leathern hose, with
a screw and clasp for choking it when required. The cask was then
turned round so that the plug, a (fig. 187), was immediately over the
spout, o. The hose being put into the iron tube, p, the mercury was
allowed to run off into the gutter, v, by which it was conducted to a
receiver prepared for that purpose. The workman closely watched this
period of the operation, and the moment any of the earthy matters began
to flow from the orifice it was again tightly closed. The casks were
now turned with their apertures, a, upwards, the small hose-plug was
removed, and the bung loosened by a few taps with a mallet.
The bung-holes were then again turned downwards, the bungs with-
drawn, and the muddy residuum discharged into the trough situated
immediately under them, from which it flowed into large washing vats
placed on the ground floor below the barrels.
During the first two hours that the casks were in motion, and before
the introduction of mercury, the chlorides contained in the ore were
reduced to the state of protochlorides, the saline matters dissolved by
the water present, and the particles of silver chloride thereby exposed.
If, instead of this, the mercury were immediately introduced into the casks,
it would, by reacting on ferric chloride, &c., have become partially con-
verted into calomel, which, not being again reduced during the subse-
quent stages of the operation, would have resulted in a considerable loss
of that metal. This inconvenience is, however, avoided by the action of
metallic iron, as the resulting protochloride is without action on metallic
mercury.
The chloride of silver contained in the roasted ore is decomposed by
agitation with the metallic iron and quicksilver; the chlorine combines
with iron in the form of chloride of iron, whilst the silver is dissolved in
the liquid mercury. The chlorides of lead and copper which may be
present are also reduced at the same time as the chloride of silver, and
those metals enter into the composition of the amalgam produced.
The slimes, conducted to the washing vats before mentioned, were
mixed with an additional quantity of water, and kept constantly stirred
by rods attached to iron arms fixed to an upright shaft in the centre of
each vat, and turned by a small water-wheel. These vats were furnished
with openings at various distances from the bottom, by which the muddy
water was successively drawn off into tanks, where the solid matters were
allowed to settle. These, if they contained as much as 4½ ozs. of silver
to the ton, were removed to a drying floor, and subsequently re-roasted
with 15 or 16 per cent. of pyrites, and 5 or 6 per cent. of salt. The
calcined residues were afterwards sifted in the usual way, and then, with-
out being re-ground, subjected to amalgamation in barrels for a somewhat
shorter period than was customary in the case of ordinary ores.
The quicksilver collected in the bottom of the washing vats was
drawn off every five or six weeks, and, from the large proportion of
impurities it contained, was treated apart from the ordinary amalgam
obtained by tapping directly from the barrels. The mercury and amal-
640
ELEMENTS OF METALLURGY.
gam removed from the casks were afterwards filtered through canvas
bags, by which the liquid quicksilver was separated from the pasty
amalgam, which was retained by the closeness of the web, whilst the
mercury passed through into reservoirs prepared for that purpose.
The amalgam which was retained in the bags consisted of a mixture
of 6 parts of mercury and 1 of an alloy composed of about 80 per
cent. of silver and 20 of a mixture of copper, antimony, zinc, lead and
some other metals. The amalgam was subsequently heated in iron
retorts placed in suitable furnaces, and the mercury separated by distil-
lation from the non-volatile constituents which were obtained in the
solid form. The employment of retorts had latterly almost entirely
superseded the iron bells at one time used at Freiberg for this purpose.
It was, however, found necessary that the condensing tube of the retort
should be somewhat large, and of such a length that the vapours of
mercury might be condensed without the aid of water; explosions would
otherwise be liable to take place. Three retorts were employed, and
in cach were placed 450 lbs. of amalgam on iron dishes, which yielded
about 70 lbs of Teller-silber. The time required to complete the distil-
lation was generally about ten hours. The silver thus obtained was
alloyed with various other metals, which, with the exception of a certain
proportion of copper, were removed by a process of refining in a large
iron crucible, conducted in the following way :-
The crucible being placed in the furnace and made red-hot, the
lumps of silver alloy were successively introduced and brought to a state
of fusion. Powdered charcoal was then thrown on the fused metal, and
the crucible covered temporarily with a thin plate of iron. This, after
the lapse of a few minutes, was again removed, and the impurities which
had risen to the surface were, together with the unconsumed charcoal,
skimmed off by means of a perforated ladle. More charcoal was placed
on the liquid metal, and the scum subsequently removed as before. These
operations were repeated, with occasional stirring of the metallic bath,
until the metal had become perfectly cleaned. The process generally
occupied from six to eight hours, and, when completed, the metal should
be malleable and dissolve completely in nitric acid, to which solution the
addition of an excess of ammonia should impart a clear blue colour only.
The silver was now cast into ingots, and in this state was sent to the
Saxon Mint. The dust obtained from the flues was from to time removed,
and, after having been sifted, was mixed with and treated as ordinary
ore. The slags, sweepings, &c., from the melting operations, were
crushed, and afterwards fused with carbonate of potassium and nitre, by
which means the silver which they contained was obtained in the form of a
metallic button. The supernatant liquor, run off from the tanks in which
the schlich from the barrels was allowed to settle, chiefly consisted of a
solution of sodium sulphate and common salt, together with small quan-
tities of iron sulphates and various other soluble salts.
The loss of silver by this process was from 5 to 9 per cent. of the
amount contained in the ore, and the mercury expended varied from one-
fifth to one-fourth of the weight of fine silver produced. According to
SILVER.
611
Winkler, the average loss of mercury at Freiberg during seven years
was about 3 ozs. per lb. troy of silver produced. At Constante, Spain,
the loss of quicksilver was (1856) 8.9 ozs. per lb. of silver, and the loss
of the latter metal, on the assay produce, 12 per cent. At Real del
Monte, Mexico (1864-65), the loss of mercury was 7.6 ozs. per lb. of
silver obtained, and the loss of silver 13 per cent. The loss of mercury
at the Ophir Company's Works, Nevada (1867), was 2.96 ozs. per lb.
of bullion, and that of silver 10 per cent. on the assay produce.
The cost of barrel amalgamation necessarily varies in accordance with
the nature of the ores treated and with the locality in which the works
are situated. At Constante the total cost of treating one ton of ore,
containing on an average 100 ozs. of silver, was (1855) £2 5s. 6d., while
at Real del Monte (1864–65) it amounted to about £3 10s. per ton. The
cost of treatment by barrel amalgamation at the Ophir Works, Nevada
(1867), was $20.14 per ton of 2,000 lbs.
Amalgamation of Copper Matts. In the copper-works of Mansfeld,
silver was formerly extracted from the last matts by a process of amal-
gamation in many respects similar to that employed for the direct
treatment of argentiferous ores, but they are now treated by Ziervogel's
process of extraction by means of hot water. The matt operated on by
this method is first stamped and sifted, and afterwards reduced between
millstones to the state of powder. This fine powder, after being slightly
wetted with water, is roasted in a reverberatory furnace, provided with
condensing chambers, for the purpose of retaining the fume and finely-
divided ore which may be carried over by the draught. The matt to be
roasted is first heated very gently, whilst the calcination of a preceding
charge is being completed on the hotter portion of the bed, which, from
being the nearest to the fire, is the most strongly heated. Each charge
of powdered matt weighs 4 cwts., and is evenly spread over the surface
of the floor, and kept constantly agitated by an iron rake, with the view
of exposing fresh surfaces to the oxidising influence of the air. At the
expiration of three hours this roasting is sufficiently advanced, and the
ore is then raked out, through a door in the side of the furnace, into a bin,
where it is allowed to cool. The ore thus prepared is now mixed with 10
per cent. of common salt and the same weight of finely-powdered carbonate
of calcium. To this mixture water is added, and the whole is worked into
a paste, which is subsequently dried in properly-arranged stoves. The
dried mass is then ground in a mill to the state of an impalpable powder,
and is subjected to a second roasting at a much higher temperature than
the first. The carbonate of calcium added in this case is for the purpose
of effecting the decomposition of the sulphates of iron and copper, which
would otherwise be produced in such large quantities as to give rise to con-
siderable loss of mercury during the subsequent amalgamation. In order
to ascertain if the roasting is sufficiently advanced, the workman with-
draws, from time to time, a small sample from the furnace, and intimately
mixes it, in a wooden bowl, with water and with a certain proportion of
mercury. This pasty mixture is subsequently washed in a larger quantity
of water, by which the lighter earthy particles are removed, whilst the
2 T
642
ELEMENTS OF METALLURGY.
:
heavier amalgam is collected at the bottom, and from the aspect of this
it may be judged whether the operation is progressing favourably or not.
When the appearances thus observed are not satisfactory, addition is made
either of salt, lime, or roasted matts, in the proportions which may be
judged necessary.
This second roasting occupies from one and a half to two hours, at
the expiration of which time the charge is withdrawn from the furnace,
and amalgamated in casks similar to those employed for the same purpose
when silver ores are treated. Each barrel is charged with 5 cwts. of
roasted ore, 75 gallons of warm water, and 80 lbs. of scrap-iron. The
tubs are now made to turn for a sufficient time to effect the decomposition
of perchlorides, and 3 cwts. of mercury are introduced. The apparatus
is then kept in motion during fourteen hours, at the expiration of which
time the barrels are filled with water, and kept slowly turning for about
two hours, to determine the separation of the liquid amalgam from the
carthy matters with which it is mixed. The tubs are afterwards emptied
by the same process as that formerly employed at Freiberg, and the
copper schlich obtained is afterwards mixed with 15 per cent. of plastic
clay, and moulded into cakes, which, after being dried at a gentle heat,
may be treated in a blast-furnace for the copper they contain.
The silver remaining in the distillatory apparatus after the expulsion
of the mercury, is fused in large black-lead crucibles, which are filled
with the metal to within 2 inches of the top, and the silver is briskly
agitated with an iron rod whilst in a fused state. The liquid metal soon
begins to give off fumes, and throws up a dark-coloured scum, which is
skimmed off, and a fresh coating of charcoal thrown on its surface. The
crucible is afterwards covered, and again briskly heated; any fresh slag
which may have been thrown up is skimmed off, and the operation is
repeated as long as any slag continues to be formed. The silver, which
is still contaminated by from 15 to 18 per cent. of copper, is cast into
ingots, which are afterwards refined by cupellation.
WASHOE PROCESS OF AMALGAMATION. Shortly after the discovery of
rich silver mines at Virginia City, in the State of Nevada (1859), it became
evident that on account of the prevailing high prices of labour, fuel,
forage and all other necessaries, none of the processes employed in other
localities for the treatment of silver ores could, in that district, afford
profitable results, if applied to material assaying from $30 to $60 per
ton, of which the Great Comstock lode was capable of yielding vast
quantities. Under these circumstances it was most important that some
means should be devised for extracting the silver from such ores, without
the preliminary roasting required for the barrel process on the one hand,
and without the great expenditure of mercury, time and labour necessary
for patio amalgamation on the other. In addition to the expense and
other disadvantages of the latter process, it was found, after numerous
trials conducted on a large scale, that the climate of Nevada materially
interfered, during a large portion of the year, with the chemical reactions
of the torta. The experiments undertaken with a view of overcoming
these various difficulties, finally resulted in a system of amalgamation
SILVER.
643
in iron pans, which, from having been first introduced in the Washoe
district, is generally known as the "Washoe process."
The applicability of this method to the treatment of argentiferous
ores depends, to a very great extent, on their composition, as well as on
the nature of the various minerals with which they may be associated.
The veinstone obtained from the Comstock mines chiefly consists of
crumbling white quartz, with which is mixed a certain amount of clay
and country rock; a closer inspection generally shows the presence of
iron and copper pyrites, and a still more careful search, particularly if
aided by the use of a hand-lens, reveals the presence of blende, galena
and argentite; more rarely stephanite and polybasite may also be dis-
tinguished among the ores. Specimens may be found in which many,
or all, of these minerals may be distinctly recognised. Gold occurs in
the ores from the Comstock vein to the amount of nearly one-third of
their total value.
For the purpose of metallurgical treatment they were formerly, and
still are, to a certain extent, divided into three classes. The first class
embraces those ores whose assay value is above $150 per ton of 2,000 lbs.
the second class includes ores whose assay value ranges from $90 to
$150 per ton; and the third class comprehends all workable ores of lower
value than the foregoing, the average assay value varying considerably
in different mines. The silver of ores of the first class is so intimately
associated with lead, antimony, arsenic, iron and other base metals, as to
render its extraction difficult, and they consequently cannot be profitably
treated by the simple processes to which the more docile ores, of the
second and third classes, are subjected. Ores of the first class are crushed
dry, roasted with common salt in reverberatory furnaces, and then amal-
gamated in barrels. The ores of the second and third classes are treated
by the Washoe or pan process; the chief difference, where any exists, in
the details of treatment of the two classes consists in the time required
for amalgamation, and the amount of quicksilver and "chemicals
employed.
وو
The ore treated by the Washoe process is drawn from the mines in
fragments of various dimensions, and before being subjected to amalgama-
tion requires to be brought to a state of minute division. Blake's me-
chanical stone-breakers, or sledge-hammers, are employed for reducing
them to a suitable size for feeding into stamping mills, in which they are
crushed wet to the state of fine sand, and thence pass off, in suspension
in water, through iron screens perforated with small holes, and are col-
lected in suitable reservoirs, from which they are subsequently removed
for the purpose of being ground in cast-iron pans or amalgamators with
hot water and mercury, with or without the addition of certain chemicals.
The amalgam thus obtained is separated from redundant quicksilver by
straining in the usual way, and is afterwards retorted, and the residual
alloy melted into bars.
Stamping Mill.—The stamping mill consists of a series of heavy iron
pestles, which are successively lifted to a height, varying from 9 to 15
inches, and allowed to fall with their full weight on the ore beneath
2 T 2
644
ELEMENTS OF METALLURGY.
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Fig. 189. Stamping Mill; front elevation.
SILVER.
645

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Fig. 190.-Stamping Mill; section on A B.
646
ELEMENTS OF METALLURGY.
them. These stampers are inclosed in a mortar or battery-box of cast-
iron, which is kept constantly supplied with the ore to be crushed, and
from which it can only escape by passing through screens, the degree of
fineness of the apertures in which regulates its state of division. The
mortars are rectangular in form, and usually contain five stampers, forming
what is called a "battery "; they are supported on a solid wooden founda-
tion, and the whole machine is established within a substantial framework
of timber. Motion is given to the stampers by means of a series of cams
keyed on a cam-shaft placed immediately in front of the battery, which
is made to revolve, either by water or steam power.
Fig. 189 is a front elevation of two five-stamp batteries, and fig. 190 a
transverse section of the same machine, on the line A B. These draw-
ings have been reduced from the magnificent work, published by the
United States Government, on the 'Mining Industry of the Fortieth
Parallel,'* under the direction of Mr. Clarence King. The stampers
move vertically between guides of hard wood, G, g, forming part of the
battery-frame. The foundation for the battery consists of heavy tim-
bers, F, standing vertically, placed close to one another, and firmly
bolted together; the side timbers, T, and the battery-posts, C, are securely
fastened to the foundation, being strengthened by the iron bars, R, and
stays D. The mortars, M (fig. 189), are placed directly on the founda-
tion of vertical mortar-blocks, and are secured by bolts, as shown in the
figures. The mortar most generally employed for wet crushing is a cast-
iron box, from 4 to 5 feet in length, 3 feet 6 inches in depth, and about
12 inches in width, inside measure, cast in one piece. The feed-opening, l,
through which the ore to be crushed is introduced, is about 4 inches in
width and nearly as long as the mortar. On the opposite side is the dis-
charge aperture, furnished with a screen, i, through which the crushed ore
is made to pass; this opening also is nearly of the same length as the
mortar; the lower edge being raised from 2 to 3 inches above the tops of
the dies, d, fig. 190. The screen is attached to a wooden frame, j, which
is secured in grooves cast in each end of the mortar, and by two lugs, o,
cast in front of the discharge opening; it is firmly held in its place by
means of the wedges, w. Screens are sometimes placed vertically, but
they are more frequently inclined as shown in fig. 190; they may be made
of fine brass wire-cloth, having from forty to sixty meshes to the lineal
inch; but for wet crushing, Russian sheet iron, perforated with holes
varying from to of an inch in diameter, is generally preferred. A
piece of canvas is usually hung loosely before the screens, to prevent
splashing.
1
24
1
40
The mortar is furnished with dies, d, which are so fixed in the bottom
as to receive the blows of the stampers, and to sustain the wear which in
its absence would be experienced by the bottom of the mortar. This
die is a cylindrical block, corresponding in diameter with the shoe of the
stamper, which falls upon it and is about 6 inches in height. In order
to keep it in its place the lower end is cast with a square flange, which
'Mining Industry of the Fortieth Parallel,' by James D. Hague, with geo-
logical contributions by Clarence King.
SILVER.
647
fits into the bottom of the mortar and prevents it from moving. Some-
times, also, those parts of the mortar which are exposed to constant wear,
have a lining of iron plates, which, like the dies, can be taken out and
replaced when necessary. The top of the mortar is covered with planks, q,
resting on flanges cast on the inside, which, meeting in the middle, have
semicircular notches in each, so as to form holes, through which the stems
of the stampers work.
Each stamper consists of a stem or lifter, s, a head, h, attached to the
lower end of the stem, and a shoe, e, which sustains the wear of the
operation, and can be readily changed when required; it is also pro-
vided with a collar or tappet, t, by which the revolving cam, c, lifts the
stamper previously to its fall. The stem is a turned bar of wrought-
iron, about 3 inches in diameter and from 10 to 12 feet in length.
The stamp-head is a cylindrical piece of cast-iron, 8 inches in dia-
meter and 15 inches in length, hooped at either end with wrought-iron;
this hoop is shrunk into a recess, so that it does not project beyond the
general surface of the cylinder. In its upper end is a slightly-conical
socket corresponding with the axis of the cylinder, in which the stem is
secured by thin wooden wedges. In the lower end of the head is another
similar socket, into which is secured, in the same way, the shank of the
shoe, which is a cylinder of hard cast-iron of the same diameter as the
head, and 6 inches in length; this is provided with a tapering shank
5 inches long. At the bottom of the sockets in the head, for the reception
both of the end of the stem and shank of the shoe, an oblong hole is
generally cast across the diameter, for the purpose of drifting them out
when necessary.
The collar or tappet, t, is a piece of cast-iron of a cylindrical form,
8 inches in length, and bored out so as to closely fit the stem, to which
it is tightly secured, either by a gib and keys or by means of a steel-
pointed binding-screw.
The rotatory motion imparted to the stamper by the friction of the
cam against the tappet is one of the advantages afforded by the use of
round stems and shoes, and has not only the effect of increasing the
grinding power of the machine, but also causes both the shoe and die to
wear more evenly than when the stamper falls without such a circular
motion. The cams, c, are curved arms keyed to a shaft, K, (fig. 189) so
placed in front of the battery that by its revolution they are successively
brought in contact with the tappets on the different stampers, causing
them to be raised to a height determined by the length of the cam, and
falling at the moment of release of contact. In the silver districts of
Nevada the cams are generally double-armed, as shown in the woodcuts,
although single-armed cams are also sometimes employed. The form of a
single-armed cam will be seen on reference to the elevation of a stamping
mill illustrating the method employed for the treatment of gold quartz.
Motion is communicated to the cam-shaft by means of the pulley, P,
keyed upon one end of it, from which a broad belt, made of alternate layers
of canvas and india-rubber, passes over another pulley, p, on the driving-
shaft, k; this belt is tightened by the pulley, m. The order in which the
648
ELEMENTS OF METALLURGY.
stampers are made to fall is not always the same in different mills; in a
five-stamp battery, however, a common arrangement is first to let fall the
middle stamper, then the end one on the right, then the second on the
left, afterwards the second stamper on the right, and, finally, that on
the extreme left. When it becomes necessary to hang a stamper, so
that the cam may revolve without reaching the tappet, it is supported by
the articulated prop or stud, n, of which there is one for each stamper,
arranged on a small iron shaft placed across the battery and passing
through the uprights, to which it is secured. Each stud is of such a
length as to support the stamper, when placed under the tappet, at a
height of about an inch above the highest throw of the cam. In order
to bring the stud in this position the workman lays a smooth stick, about
1½ inch in thickness, on the face of the cam as it rises towards the tappet,
and holds it there while the stamper is being lifted. By this means it
is raised sufficiently high to allow of the support being dropped into its
place, which being done, the tappet is hung above the reach of the cam.
When it is desired to again set the stamper in motion the operation is
repeated, the stud being withdrawn at the moment when the stick placed
on the face of the cam has lifted the tappet clear of its support.
The weight of the stampers in most general use is from 600 to
700 lbs.; their usual speed is from 60 to 90 blows per minute, and their
ordinary drop from 9 to 12 inches. The higher the speed of the stampers
the smaller is the amount of drop given to them. A mill of this descrip-
tion, discharging through screens of the usual degree of fineness, will, on
an average, pulverise two tons of ordinary ore from the Comstock lode,
per stamper, in the course of twenty-four hours.
The amount of water required in the battery varies with the character
of the ore and with the degree of fineness to which it is to be reduced.
The usual consumption in the Washoe district is from 250 to 300 cubic
feet per ton of rock treated; but this includes the water used in the
pans, which does not pass through the batteries. In California and
throughout the gold regions of the Pacific coast the stamping mill
employed for the reduction of auriferous quartz is similar, in all essential
particulars, to that above described, and it will consequently require no
further description when the treatment of gold ores has to be considered.
The ore to be stamped is usually supplied to the mill by a shovel through
the aperture, l, but some machines are constructed in such a way as to be
self-feeding.
Settling Tanks. The stuff discharged from the battery is conveyed,
in suspension, by the water escaping through the screens, by means of
troughs, to settling tanks, of which there is a series arranged in front
of the stamping mill. These tanks, which are generally constructed of
planks, are 6 or 7 feet square and from 3 to 4 feet in depth; they are so
disposed as to communicate with each other, near the top, in such a way
that the stream carrying the crushed ore in suspension, having entered
one tank, flows into the next, and so on from one to another. A deposit
of the solid material thus takes place in each tank, until the water flowing
from the last in the series escapes in a tolerably clear state. The number
SILVER.
649
of tanks must be sufficient to allow of some of them being emptied,
whilst others are collecting the crushed ore, and the troughs in con-
nection with them are provided with gates, by which a certain number
can be shut off from the others when required. In this way the larger
proportion of the solid matter is deposited in the tanks; but the water
which escapes is still charged with slimes, consisting of ore which has
been reduced to a state of impalpable division, and which can only
be obtained by a process of settling extended over a considerable time.
For this purpose the stream is conducted either through another series of
large settling tanks or into a large pond outside the mill. The slimes
thus collected form an important but variable proportion of the total
amount of ore crushed, and in some instances represent as much as
10 per cent. of the material operated on; but although they afford, by
assay, a considerable yield of silver, they have been only recently treated
with profitable results. As soon as one of the tanks has become filled
with finely-divided ore, the stream is diverted thence into others which
have space for receiving a further supply, and the full tanks are cleaned
out. The crushed ore taken from the settling tanks is now subjected to
the process of pan amalgamation.
Pans. The pans employed for this purpose vary considerably in the
details of construction, but all essentially consist of a round tub, of which
the bottom is of cast-iron, but of which the sides are sometimes of wood.
A hollow pillar is cast in the centre, within which is a vertical shaft
projecting above its top, and to which motion is communicated by gearing
situated below the pan bottom. To the top of this shaft is keyed a yoke
or driver, by which the muller, or upper grinding surface, is made to
revolve. On the inside of the pan is fixed a false bottom of iron, cast
either in sections, called "dies," or in one piece which has a diameter
somewhat less than that of the pan; this is provided with an aperture
through which rises the central pillar. The false bottom furnishes the
lower grinding surface of the machine. The muller, forming the upper
grinding surface, is a circular plate of cast-iron, corresponding in size
with the false bottom, and having a flat, conical, or conchoidal surface,
according to the shape of the pan bottom.
There are various contrivances for raising or lowering the muller, in
order that it may rest its whole weight on the bottom, so as to produce
the greatest grinding effect, or be maintained at any desired distance
from it, when less friction or more agitation is required. Numerous
devices have also been adopted for communicating a proper motion to the
pulp, so that when the muller is in action the material may be constantly
kept in circulation, passing between the grinding surfaces and coming in
contact with the mercury with which the pan is charged. Some pans are
cast with a shallow chamber in the bottom for the admission of steam
for the purpose of heating the pulp, whilst in others "loose steam" only
is employed, which is conducted directly into the pulp through an iron
pipe.
The flat-bottomed pans of Varney and Wheeler, and that of Hepburn
and Peterson, with a conical bottom, have been long employed with satis-
650
ELEMENTS OF METALLURGY.
factory results, although within the last two or three years other makers
have introduced new pans, of which the characteristic features are
increase of size and great simplicity of construction. Among these the
large flat-bottomed pans of McCone, Horn, and Fountain are worthy of
notice, as combining economy in first cost and a capacity which enables
them to treat in the same time a much larger quantity of ore than could
be worked in the pans formerly employed.
Varney's pan, which is very extensively used, is represented in figs.
191, 192, 193, of which the first is an elevation, the second a vertical sec-

CHORODAT
A
E
B
A
H
CARZUARY
Fig. 191.-Varney's Pan; elevation.
tion, and the third a view from above. The body of the amalgamator con-
sists of a tub, A, 4 feet 4 inches in diameter and 18 inches deep, with a
cover, B, in which is an opening for the introduction of the crushed ore
to be ground and amalgamated. The pan is supported on suitable frame-
work, and from its centre, extending from the bottom, to which it is cast,
some distance above the cover, is the tube, D (fig. 192), through the inte-
rior of which is a hole passing vertically through the pan, in order that
the shaft, C, may work within it. On the bottom of the pan, and secured
to it by the bolts, e, is fixed the lower muller, a, consisting of a circular
cast-iron plate, having a round hole in the centre considerably larger than
the base of the tube, D. This die or false bottom may, if desirable, be
cast in sections. That portion of the aperture through the lower muller
not occupied by the tube, D, is filled with wood, d, so as to present a flat
SILVER.
651
surface from the tube to the circumference.
The diameter of the muller
is somewhat less than that of the interior of the pan, by which means a
space, a', is left, to be filled with quicksilver. Above the lower muller is
the upper one, b, of similar general form and size, having twelve shoes, c,
the form and relative position of which will be understood by supposing
a plate, of the diameter and thickness of the lower muller, attached to
the under side of the upper one, and sawn into twelve equal parts on lines
drawn from the circumference of the plates to the outside of the tube, D.
The saw must also be supposed to be inclined at an angle of about

-
A
7'
Z
C
E
A
p
X X X X \
Fig. 192.-Varney's Pan; vertical section.
forty-five degrees, thus producing grooves from the central opening to the
periphery.
Each shoe is fastened to the upper muller either by a bolt f, or by a
wrought-iron rivet cast into the shoe and riveted into a counter-sink
in the upper side of the muller, as seen in fig. 192; the bosses and
recesses, j, keep the die firmly secured in its place.
In the lower muller are radial slots, similar to those in the upper
one. These slots may be either inclined or made vertically, and are
filled with wood, set with the grain perpendicular to the plate; this wears
slightly in advance of the surface of the die, thus forming cavities for
the admission of pulp, by which the grinding capacity of the machine is
materially increased.
Over and around the tube, D, but not in contact with it, is placed
652
ELEMENTS OF METALLURGY.
the larger tube, E, exactly perpendicular to the lower face of the upper
muller, and having around its lower extremity the flange, V, upon which
rests the ring, h, which forms part of the upper muller. This is con-
nected with the muller by means of six curved arms, i, two pairs of which
are nearer together than the others, and the space between them is filled
by a projection from the periphery of the flange, V, for the purpose of
carrying with it the upper muller when the flange makes a revolution.
With the shaft, C, the larger tube, E, is connected by the key, k, and the
set-screws, 1, in the boss, G. The shaft, C, passes through a babbet-
metal bearing at m, and through the boss, F, of the driving-wheel, in
which is a feather sliding vertically in the shaft. This shaft is stepped

་
"
fecd hole
$
C
2
Fig. 193. Varney's Pan; as seen from above.
into the vertical sliding-box, H, which is itself held in the box, O. The
step-box rests upon an iron bar, one end of which is supported by the
bolt, u, fig. 193, and the other is connected with a screw and hand-wheel,
x, by which it can be either raised or lowered, raising or lowering the
upper muller at the same time.
Within the body of the pan are suspended three curved plates, r, ex-
tending from near the surface of the upper muller upwards, and stretching
in length from the inner side of the pan around to a point near the out-
side of the larger boss, opposite to that from which they started. The
lower edges of these round plates are bent inwards, as shown at s,
forming flanges, and the inner ends are secured to the ring, q, which is
of sufficient diameter to surround the tube, E, without touching it. The
whole is suspended by iron rods attached to each plate, which, passing
SILVER.
653
through the cover, can be adjusted by means of the hand-wheels, J. The
outer ends of the curved plates slide vertically in grooves in the projec-
tions, t, fig. 193, cast upon the inner side of the pan.
The operation of this apparatus is as follows:-The space, a', around
the periphery of the lower muller, is charged with quicksilver, and the
pan is nearly filled with a mixture of water and stamped ore, in such pro-
portions as to form an easily-flowing paste; the upper muller is now made
to rotate at a speed of from sixty to eighty revolutions per minute. By
means of the centrifugal force thus developed the pulp between the
mullers is made to pass out through the radial channels left by the dies,
as well as betwixt the grinding surfaces of the mullers themselves, and
coming continually in contact with the mercury, with which the machine is
charged, amalgamation is effected. This outward motion of the pulp pre-
vents the mercury from coming into contact with the grinding surfaces,
by which it would be broken, and a considerable loss be the result.
The rotation of the upper muller causes the pulp in the pan to revolve
with it, and this current, being met by the curved plates, r, is directed
towards the aperture in the centre of the upper muller. The radial
slots between the shoes allow considerable currents to pass, with a suffi-
cient velocity, to produce a partial vacuum, by which the pulp in the
bottom of the pan is set in motion, causing a rapid and abundant flow
downwards at the centre and upwards around the inner surface of the
pan. In this way the pulp is ground, and made to circulate, until the
pulverisation of the ore and amalgamation of the precious metals have
been satisfactorily effected.
Hepburn and Peterson's pan has a capacity about equal to that of
the Varney pan, but the form of the bottom is that of an inverted cone.
This bottom is lined with four conical dies, secured in their places in the
usual way, and is never made with a steam-chamber, steam being always
introduced directly into the pulp through a piece of gas-pipe. In the
centre is a hollow pillar, through which passes the driving-shaft; the form
of the upper muller corresponds with that of the bottom, and it has, in the
centre, a hollow vertical cone by which it is connected with the driver.
Its under side is furnished with shoes, between which are left radial
passages for the circulation of the pulp. There are also radial grooves
between the shoes, cast in the muller itself, so that when they have been
reduced in thickness by use there may still be a sufficient channel for the
passage of pulp. A similar passage is left between the dies lining
the interior of the bottom. The movable inverted cone, to which the
shoes are attached, is raised or lowered by a screw and hand-wheel,
the bottom of the screw resting on the top of the driving-shaft, with
which the boss of the bottom pillar is connected by a sliding-key. In
this apparatus circulation of the pulp is effected without the use of
the wings or guides employed for that purpose in some other pans.
When this pan is in action the pulp, passing between the grinding sur-
faces from the centre to the circumference, is made to descend towards
the centre; this movement being promoted by the shape of the pan and
the motion of the muller-plate. The muller is usually worked at the rate
654
ELEMENTS OF METALLURGY.
of from sixty to seventy revolutions per minute. The pans of McCone,
Horn, and Fountain are flat-bottomed, and of larger dimensions than
those above described; they are sometimes provided with steam-chambers
beneath the bottom. The ordinary charge of the pans most generally in
use is from 1,200 to 1,500 lbs., but those of McCone and Fountain, which
are 5 feet in diameter and about 25 inches in depth, will work charges of
from 4,000 to 5,000 lbs.
In charging a pan the upper muller is raised a short distance from the
bottom one, water is supplied by a hose-pipe, and ore, from the settling
pits, is at the same time thrown in with a shovel. The mixture is now
heated, either by blowing steam into it or by means of a steam-chamber.
In the latter case it is somewhat difficult to obtain the most desirable
temperature (85° C.); but on the other hand, when loose steam is blown
directly into the pan, considerable attention is necessary, in order to pre-
vent the charge from becoming too liquid, through the accumulation of
condensed water. To avoid this, in many mills, the temperature of each
charge, after being first raised by the admission of loose steam, is sub-
sequently maintained by means of a steam-jacket. The muller is gradu-
ally lowered, and, in the course of about two hours, the ore will have
attained the state of a finely-divided pulp. When this has been accom-
plished, or, in some mills, at the beginning of the operation, the mercury
is introduced; this is done by pressing it through a piece of canvas, by
which it becomes equally spread over the surface of the pulp in the
form of minutely-divided globules. The usual amount of quicksilver
thus added is from 60 to 70 lbs. to an ordinary charge of from 1,200
to 1,500 lbs. of ore. The muller is now raised, so as to act rather as
an agitator than as a grinder, and its action is continued during two
hours.
With the view of promoting amalgamation, it is usual to add to the
charge, either at the time of its introduction into the pan or shortly
afterwards, various materials generally known as "chemicals," and which
usually consist of cupric sulphate and common salt; the quantity of each
employed in different establishments varies considerably, but is usually
from 1 to 3 lbs. to each charge of ore. The action of these substances,
however, is but imperfectly understood, and their efficiency is open to
considerable doubt, since in many mills in which both cupric sulphate
and common salt were formerly employed the use of either one or the
other has been discontinued, without in any way affecting the results.
In other cases the employment of chemicals has been altogether aban-
doned, and yet, under all these varying circumstances, an equally good
production of silver has been realised.
After two hours have been devoted to grinding, and from two to three
more hours have been employed in amalgamation, the operation is usually
regarded as complete, and the contents of the pan are run off into a sepa-
rator or settler. The discharge of the pan is facilitated by the addition
of water, supplied under pressure, through a flexible hose, which, at the
same time, dilutes the pulp and allows it to flow more readily into the
separator. After having been emptied and roughly washed out by a
SILVER.
655
stream of water, the pan is again supplied with a fresh charge of ore,
and the operation of grinding at once resumed.
At stated times, or whenever it is desired to ascertain the exact yield
of a parcel of ore which has been under treatment, the pans, settlers, and
all other apparatus containing amalgam, are thoroughly cleaned up. For
this purpose the mullers must be raised, the shoes and dies removed, and
all the parts scraped with a knife, in order to remove the hard amalgam
adhering to the surfaces. In many cases, above one-fourth of the total
amount of bullion yielded by the ore is obtained in this way.
Separators. Separators or settlers, figs. 194, 195, like pans, differ to a
certain extent in the minor details of construction, but are generally
round tubs, of either wood or iron, with cast-iron bottoms, and resemble
pans in many of their general features, although they are of considerably
greater diameter. A hollow cone, C, fig. 195, is cast on the centre of the
bottom, through which passes the vertical shaft, S, which is connected
with gearing below the tub. To its upper extremity is attached the yoke
or driver, D, which gives motion to arms, A, extending from the centre
nearly to the circumference. These armis carry a number of ploughs
or stirrers, P, usually made of hard wood, which rest lightly on the
bottom, and which, when in motion, communicate to the pulp the amount
of agitation necessary for facilitating the separation of any mercury or
amalgam with which it may be mixed; this stirring apparatus makes
from twelve to fifteen revolutions per minute.
The separator is placed immediately in front of the pans, but at a
lower level, so that the latter may be readily discharged into it. In some
establishments two pans are discharged at the same time into one settler,
in which case the operation occupies the same length of time as the
grinding and amalgamation of a charge in the pan, or from four to five
hours. In other mills only about two hours are allowed for settling,
and the two pans connected with each settler are discharged into it
alternately.
The water employed in discharging the pan considerably dilutes the
consistency of the pulp, and this dilution is often further increased by the
addition of fresh quantities during the progress of the operation. The
degree of fluidity of the pulp, and the speed of the stirrers, materially
affect the results obtained, since if the paste be too thick the amalgam
and quicksilver will remain in suspension, and if, on the contrary, it be
too thin, sand will settle with them on the bottom of the vessel. It is
evident that a too rapid, or a too sluggish, motion of the revolving arms
would also produce similar effects. The degree of dilution yielding
the most satisfactory results with a given speed of the agitator, can only
be determined by experience. A discharge-hole, near the top of the
tub, allows the lighter portions of the pulp to run off, and at successive
intervals the point of discharge is lowered by withdrawing a lower plug
from a series of holes, h, in the side of the settler. In this way the
whole of the materials, with the exception of amalgam and quicksilver,
are finally removed; the latter are subsequently collected by the
aid of various devices. There is generally for this purpose a groove
656
ELEMENTS OF METALLURGY.
in the bottom of the separator, leading to the bowl, B, from which the
fluid amalgam may be dipped; or it may be drawn off by removing
the plug, p, from the end of the outlet-pipe. The quicksilver, charged
with amalgam, is cleaned by repeated washings with water, and by care-
fully removing from its surface any particles of sand, pyrites, &c., that may
adhere to it. In some mills the cleaning of the quicksilver and amalgam
is effected in a small iron pan, resembling a settler in its construction,
in which it is washed by slow agitation with plenty of clean water.
When sufficiently cleansed the amalgam is separated from the redundant
mercury by straining through a canvas bag, of the form and dimensions

a
-A
ローロ
​h
a
-0-0-
B
·A-
P
Fig. 194.-Separator; as seen from above.
of that employed in Mexico for a similar purpose, which has been de-
scribed when treating of patio amalgamation.
Agitator.—After leaving the separators the pulp is generally passed
into wooden tubs, varying from 6 to 12 feet in diameter, and from 2 to
6 feet in depth, in which are collected small portions of mercury and
amalgam, as well as heavy particles of undecomposed ore, which have
been carried off in the pulp discharged from the separators. A simple
stirring apparatus, somewhat resembling that of the separator, keeps the
material in a state of gentle agitation; the revolving shaft carries four
arms, and makes from ten to fifteen revolutions per minute.
In some
establishments there are several agitators, but in most cases only one,
whilst in others they are entirely dispensed with; the stuff that accumu-
lates on the bottom is shovelled out, at intervals of three or four days,
SILVER.
657
and is again worked over in the pans. Beyond the agitators are blanket-
sluices and various other contrivances for concentrating and collecting
the more valuable portion of the tailings.
Retorting and Melting.—The amalgam having been strained in bags,
and pressed, in order to expel as much as possible of the fluid quick-
silver, is subjected to a process of distillation, by which the remaining
mercury is separated from the gold and silver. The cast-iron retort
employed for this purpose is from 2 to 3 feet in length, and from 9 to
12 inches in diameter, the casting being about 1 inch in thickness.
This rests either on two heavy cast-iron bearers, the ends of which are
built into the brickwork, or on an arch of fire-bricks, and is placed beneath
another arch, from the crown of which the products of combustion are

D
oh
Oh
A
Ок
Oh
B
Fig. 195. Separator; vertical section.
carried off to a chimney, through rectangular apertures in communi-
cation with a flue. The open end is fitted with a cover like that of
a coal-gas retort, and from the other end an iron tube carries off the
volatilised mercury.
This is screwed to a downcast pipe, and is so
arranged that, by means of screw stoppers, every facility is afforded for
cleaning the pipes. The vertical tube is inclosed within another, so
as to form a Liebig condenser, through which a current of cold water is
constantly passed, the heated water escaping at the top.
The downcast pipe opens into a small chamber without a bottom,
immersed sufficiently low in a vessel of water to keep it air-tight, but
still to so small an extent as to prevent the occurrence of accidents from
the passage of water up into the heated retort.
This retort is provided with cast-iron semi-cylindrical trays, which
2 U
658
ELEMENTS OF METALLURGY.
are easily slid into their places, and are generally divided into two parts
by a transverse partition. In some cases the amalgam is introduced
directly into the retort, the use of trays being dispensed with.
Before the amalgam is placed in the retort or trays, the interior is
coated with a thin wash of clay or of milk of lime, or a lining of paper
may be employed instead; by this precaution the retorted amalgam is
prevented from adhering to the iron, and much trouble avoided. The
amalgam, having been placed in the retort, the cover is luted either with
a little clay or with a mixture of clay and wood ashes, and is fastened in
its place by a screw-clamp, or otherwise. A fire is now lighted, and the
heat slowly and gradually raised, until the retort assumes a bright

d
C
C
C
h
Ꮽ
C
h
Ъ
α
a
a
a
B
A
C
Fig. 196. Retort and Setting; longitudinal section.
cherry-red colour, and is so maintained until mercury ceases to distil
over; this usually occurs at the expiration of eight hours, and the charge
of amalgam operated on, at one time, may vary from 800 to 1,200 lbs.
The retort is now allowed to cool gradually, and, when sufficiently cold,
the crude bullion is withdrawn; this amounts to about one-sixth the
weight of the original charge.
A form of retort frequently employed in the vicinity of Virginia City
for the distillation of amalgam is represented, in longitudinal section, in
fig. 196. The ash-pit, A, is beneath the fire-place, B, which communi-
cates, by means of the flues, a, with the chamber, b, inclosing the retort, C,
from which the products of combustion are conveyed by the flues, c,
through the cavity, d, to the chimney. Dampers in the flues, c, may
SILVER.
659
be regulated so as to heat the retort to the same temperature throughout
its length. The tube, D, conducts the mercurial vapours to the vertical
pipe, E, where they are condensed by the current of cold water flowing
through F. The condensed mercury collects in the reservoir, G, from
which it is drawn off through an iron pipe. Any mercurial vapours that
may escape through leakage, or the removal of the door, are collected
by the hood, e, and conveyed into the flues. The arrangement for secur-
ing the cover, g, is similar to that employed for gas-retorts; the trays, h,
are used for holding amalgam, and the iron braces for binding the
brickwork are indicated by the letter, f.
The retorted amalgam is broken up, melted, and cast into ingots; the
fusion being most commonly effected, with the addition of a little borax,
in an ordinary plumbago crucible. The loss in weight experienced in
melting retorted amalgam is between 2 and 3 per cent. The ingots thus
obtained are chipped and assayed in the usual way, and commonly con-
tain, in 1,000 parts, 24 parts of gold and 840 of silver, the remaining
136 thousandths consisting chiefly of copper.
Tailings.*—The pulp, after issuing from the settlers, in which it has
been, as far as possible, separated from amalgam and mercury, is variously
treated in different mills. In some the whole mass is passed through
agitators, for the purpose of collecting a portion of the amalgam, mercury,
and undecomposed sulphides carried off from the separators; in others
concentrators of various kinds are employed with a similar object, by
the use of which a certain amount of undecomposed sulphides is
obtained in a concentrated form. In cases where there is a sufficient
supply of water, and the inclination of the surface admits of such an
arrangement, blanket-sluices are laid down, over which the stream of
tailings is allowed to flow; the heavier and more valuable particles
being arrested by the blankets. Dams are also constructed at convenient
points for the accumulation of tailings, which, after exposure to the
weather for several months, are again worked at a profit.
The ordinary result obtained by pan amalgamation varies between
65 and 70 per cent. of the assay value, and this, by the subsequent
treatment of slimes and tailings, is sometimes increased to 85 or 90
per cent. In the Washoe district the cost of treatment, where water
power is employed, is from $5 to $5.50, and in steam-mills from $6 to
$6.75 per ton. The tailings, &c., collected in the various reservoirs
established for that purpose, contain, on an average, by assay, gold
and silver of the value of $15 per ton, from which $9.75 are extracted,
by re-treatment, at an expense, in steam-mills, of about $5.50 per ton.
General Arrangement of Reduction Works.-The batteries are commonly
arranged in one straight line, behind which, on the feed side, is the
breaking-floor, where the ore is reduced to a suitable size for the stamping
* The term "tailings" is applied to the pulpy and sandy residues which escape
from the separator or agitator after the treatment of ores by pan amalgamation.
By "slimes"
is generally understood those portions of the ore which have been
reduced in the battery to such an impalpable state as to be carried through the
settling tanks in suspension in water; the more pulpy portions of tailings are some-
times called “pan-slimes.”
2 U2
660
ELEMENTS OF METALLURGY.
mill, either by a mechanical stone-breaker or by hammers. When
the slope of the ground permits such an arrangement, large bins are
frequently constructed behind the breaker, and at a higher level, into
which are tipped the contents of the waggons bringing ore out of the
mines. The stamping mills discharge the crushed ore into troughs, which
convey it to settling tanks standing immediately in front of the batteries,
and a platform is provided for the reception of the ore shovelled out of
the tanks.
In the majority of cases the pans are arranged in a straight line,
parallel to that of the batteries, while the separators stand in another line
parallel to the pans, and on a sufficiently lower level to admit of the
contents of the pans being tapped directly into them. Below the sepa-
rators are the agitators, or other contrivances for preventing the escape
of gold, silver, and amalgam. Power is communicated from a steam-
engine or water-wheel, either by gearing or by belting, to a shaft in front
of, and parallel with, the batteries. On this shaft are pulleys opposite to
those on the several cam-shafts, to which motion is communicated by
suitable belting. The same shaft imparts motion, through a counter-shaft
and belting, to the stone-breaker and pans. For the purpose of working
the latter a line of shafting is arranged under them, from which the
various separators and agitators are also driven by means of belting and
pulleys.
The power required for each stamper of ordinary weight is about
11-horse, whilst that necessary for each pan varies from 3- to 6-horse
power, according to its size and construction. The expenditure per ton
of ore stamped, ground and amalgamated, varies according to the size
of the mill and the degree of perfection of its arrangements, but may be
taken on an average at 2-horse power.
Chemical Reactions of the Washoe Process.—Mr. James D. Hague, who
has carefully investigated this subject, has arrived at the following
conclusions:— *
That the ores chiefly consist of native gold, native silver and sulphides
of silver, associated with varying proportions of blende and galena.
The action of sodium chloride and cupric sulphate produces in the
pan cupric chloride.
The presence of metallic iron causes the formation of cuprous
chloride.
Both cupric and cuprous chlorides assist in the reduction of the
ore, by the chlorination of silver sulphide, and by decomposing blende
and galena.
Cupric sulphate augments the amalgamating energy of mercury by
the formation of small quantities of copper amalgam, and also tends to
remove lead from the quicksilver.
Notwithstanding the action of these reagents, as above indicated, the
quantities usually added in the Washoe mills are too small to produce
any very beneficial results.
Mercury and iron, under the influence of heat and friction, are the
* ‘Mining Industry of the Fortieth Parallel,' p. 293.
SILVER.
661
chief agents in the extraction of the precious metals by the Washoe
process.
It is an essential condition that the mercury be kept perfectly bright
and pure, in order to effect direct contact of that metal with silver
sulphide and metallic iron.
In the Washoe process the consumption of mercury is chiefly
mechanical, the loss through chemical action being comparatively small.
THE STETEFELDT FURNACE.
The most expensive item in the cost of working first-class ores in the
Washoe district, by barrel amalgamation, is roasting or chlorination,
which alone is generally estimated at $15 per ton. Within the last five
years a furnace has been invented by Mr. Stetefeldt, of Austin, which
promises to effect a considerable saving in the expense of this operation.
Its action essentially consists in allowing very finely pulverised ore,
mixed with common salt, to fall against a current of heated air rising
through a shaft, by which means the particles of the various metallic
sulphides are transformed into oxides, whilst sulphurous anhydride is
evolved. By the action of this and watery vapour on common salt,
hydrochloric acid is generated, and by the reaction of this acid on the
oxides formed, metallic chlorides are ultimately obtained.
The chemical action of this apparatus is very similar to that of the
ordinary reverberatory furnace; but, as the ore is made to fall in a
shower of finely-divided particles, it is more thoroughly exposed during
its descent to oxidising and chlorinising influences. In consequence of
this its effects are stated to be more rapid and complete, whilst the
expenditure of labour is exceedingly small.
This furnace consists of a shaft, about 20 feet in height and from
3 to 4 feet square at the base; at two opposite sides are fire-places, from
which short flues communicate with the main shaft. At the top is the feed-
ing apparatus, which supplies, in a continuous shower, the ore in a state
of extreme division. At a short distance below the top of the shaft is a
flue, through which the gases escape and by which they are conducted to
a series of chambers, where any portions of the ore which may have.
been carried over by the heated current are deposited. An auxiliary fire-
place, in communication with the flue, serves the double purpose of keeping
up the temperature and of extending the region of active chemical action.
A discharging door is left at the bottom of the main shaft, whence
the principal portion of the ore treated is withdrawn. Similar doors are
arranged at convenient points along the main flue, and communicate with
the several chambers. The chimney for the final escape of the gases
is at the end of the dust-chambers, and is about 40 feet in height.
The ore is first mixed with salt on a drying floor, and is then crushed
by dry stamping; it is afterwards raised by an elevator to the hopper of
the feeding apparatus at the top of the furnace, whence it is supplied
continuously to the chlorinising column. The temperature of this is
maintained as uniformly as possible, the heat employed being sufficient
662
ELEMENTS OF METALLURGY.
to keep the ore, which accumulates at the bottom, constantly red-hot. Mr.
Stetefeldt states that the results of the actual working experience of one
of his furnaces, erected at Reno, near Virginia City, go to show that it gets
through a larger amount of work with a smaller expense for labour, fuel
and salt, than any apparatus previously employed for the same purpose.
It is further stated that about 90 per cent. of the silver present in the
ore is converted into chloride. One of these furnaces, worked by eight
men, is said to accomplish the chlorination of as much ore as ten rever-
beratory furnaces requiring the labour of thirty-six men. The fuel con-
sumed in the Reno furnace averages about two cords of wood in twenty-
four hours, and it will treat an amount of ore per day, which, in
ordinary calciners, would require the consumption of ten cords. From
3 to 6 per cent. of salt is required, according to the richness of the ore;
whilst in the reverberatory furnace at least twice that quantity would be
necessary. It is also maintained that the bullion produced from ores
roasted in this furnace contains less impurity than that from those treated
in the ordinary way, and consequently that it is well adapted for working
ores containing a large amount of "base metal." The expense of
roasting 1 ton of ore with salt in the Reno furnace was, in 1870, between
$6 and $7; but it was expected that the cost would be materially
reduced by the application of certain improvements then projected.
The woodcuts, figs. 197, 198, will afford a correct idea of the con-
struction of the furnace at Reno. Shaft through which the ore falls, a;
b, top of shaft, on which the feeding apparatus is arranged; c, damper,
inserted when the screens of the feeding machinery are exchanged;
d, door through which the roasted ore is discharged upon the cooling
floor; e, fire-places; f, flue through which the gases escape; g, triangu-
lar flue-bridges of cast-iron; h, cast-iron plates, forming the bottom of
the flue, and which allow the dust, which settles in this part of the
apparatus, to fall into the chamber, i; k, discharging door; 7, fire-place,
which heats the lower portion of the flue, ƒ; m, flue connected with the
dust-chamber, o; n, discharging doors.
The principal dust-chamber at Reno is 24 feet long, 8 feet wide, and
10 feet high; from this the gases pass under the floor of a kiln, on which
the ore and salt are dried, 39 feet in length and 7 feet in width. A flue,
3 feet 4 inches wide, 4 feet 6 inches high, and about 180 feet in length,
leads from the drying-kiln to an iron chimney, 2 feet 6 inches in dia-
meter, situated on the hill-side. The top of this chimney rises 40 feet
above that of the furnace. The fire-places and arches are built of fire-
bricks, but the other parts of the apparatus with common bricks. The
walls are built double, with spaces between them, and the furnace is
bound with iron rails and 3-inch rods.
At first much difficulty was experienced in providing suitable feeding
apparatus. Gerstenhöfer's feeder, consisting of fluted rollers, which force
the ore through slits in the top of the furnace, was not found to answer,
as it caused the one to fall in lumps, which arrived at the bottom of the
shaft in an almost unaltered state. This is caused by the tendency pos-
sessed by the particles of all finely-pulverised minerals to adhere to each
SILVER.
663
other if a slightly-compressed mass be allowed to fall through the air.
After various trials, the machine adopted for this purpose was arranged
as follows:-
A hollow cast-iron frame, kept cool by a small stream of water, rests
on top of the furnace. In this frame is a cast-iron grating, covered by a
3

A
α
k
B...
m
n
n
n
Fig. 197.-Stetefeldt Furnace; vertical section.
screen of finely-punched sheet-iron, similar to those ordinarily employed
for wet crushing. Immediately above the punched screen is another,
made of coarse wire-cloth, which is fastened to a movable frame. This
is provided with flanges resting on adjustable rollers on the outside of
the hopper, and receives a reciprocating motion from a crank. The

7
d
f
m
a
Fig. 198.-Stetefeldt Furnace; section on A B.
course of this is 13 inch, and in order to avoid the motion of a stratum
of pulverised ore with the coarse sieve, a number of thin iron blades are
so arranged across the hopper that their lower edges almost touch the
upper surface of this sieve. These blades serve to keep the finely-divided
ore from being displaced when the crank is set in motion, whilst the
meshes of the iron screen cut through it and cause its particles to fall
664
ELEMENTS OF METALLURGY.
through the apertures of the punched screen beneath. The number of
revolutions of the crank-shaft varies from thirty to seventy per minute,
and by this means the ore is regularly and continuously introduced into
the furnace.
The principal changes contemplated in this apparatus are the con-
struction of larger dust-chambers, the employment of gaseous fuel
obtained from gas-producers of the ordinary construction, and the sup-
pression of the chamber, i, whilst the flue, f, will be brought down on
the side, r, of the furnace, seen in the section on A B.
PROCESSES FOR EXTRACTING SILVER BY THE WET WAY.
The processes by which silver is extracted from ores and metallur-
gical products by the various wet methods are all comparatively modern,
and belong to that recent period during which the practical metallurgist
has availed himself of the assistance to be derived from chemical research.
In many instances these methods have now supplanted the older processes
of liquation and amalgamation, and may often be advantageously employed
for the treatment of argentiferous materials, particularly of those in
which the amount of copper is large and that of lead comparatively
small. Under favourable circumstances the methods of silver-extraction
by the wet way possess advantages over smelting and amalgamation; but,
in the case of some of them, in order to obtain satisfactory results it is
necessary that the material operated on should not contain any consider-
able amount of either lead, zinc, antimony, or arsenic. Ores containing
these metals in large quantities are not adapted for treatment by the wet
processes, and the fact of these metals being frequently associated with
silver ores has tended to prevent their more extensive application.
AUGUSTIN'S PROCESS.-When ordinary argentiferous ores, or sulphurous
metallurgical products containing silver, are roasted with common salt,
chloride of silver is formed, which is soluble in a heated and concentrated
solution of salt. From this solution the silver may be precipitated by
metallic copper, which can in its turn be thrown down by iron; the
residual liquors, until by repeated use they become too much contaminated
with sodium sulphate, may be employed for dissolving fresh quantities of
silver chloride. The solubility of chloride of silver in a solution of
common salt is a fact long known to chemists, but was first taken practi-
cal advantage of (1849) by Augustin, one of the officers of the Mansfeld
Mining Company, as the foundation of a process for the extraction of
silver from its ores. This process is less applicable to the direct treat-
ment of ores than to such products as speiss and matt, since raw ores
frequently contain substances which interfere with the complete chlorina-
tion of the silver.
Copper matts, yielding from 50 to 70 per cent. of copper, but free
from metallic granules, and containing no lead, zinc, antimony, or arsenic,
afford the best results when treated by Augustin's process.
The presence of an excess of copper sulphides is favourable to the
production of residues poor in silver, but a mixture of metallic copper, in
SILVER.
665
the form of shot, results in a loss of that metal. It is often found advan-
tageous to submit copper matts to a process of concentration before sub-
jecting them to treatment for silver by this process. When lead is
present, it should be transformed into chloride and subsequently removed
by hot water, previously to the treatment of the roasted matts by salt
water.
The desilverisation of copper matt is effected by the following series
of manipulations:-
First Roasting. The matt is first finely ground and sifted, and then
roasted at a low red-heat on the upper hearth of a double reverberatory
furnace; this operation is completed in about five hours, the ordinary
charge being 4 cwts. The ore is then transferred to the lower hearth,
where it is roasted during two hours at a moderate temperature; the
heat is then raised, and the roasting continued during three additional
hours. By this treatment the silver contained in the matt will, for the
most part, be transformed into sulphate, while the iron and copper will
have become converted into oxides mixed with basic sulphates of these
metals. A sample drawn from the roasted charge should, when treated
with hot water, afford a solution of a faintly blue colour, in which the
addition of a drop of solution of common salt should produce a precipitate
of silver chloride.
Roasting with Salt.-As soon as a sample taken from the furnace
affords the above-described results, the charge is withdrawn, and after
being allowed to cool, is ground between millstones. The ground ore
is then passed through a bolting-sieve, and placed, in charges of 3 cwts.,
in the same furnace in which it was previously treated, where it is mixed
with from 3 to 5 per cent. of common salt. It is now roasted at a low
temperature, by which the chloride of sodium is decomposed by the sul-
phuric acid of the sulphates; chlorine unites with silver, and nearly the
whole of that metal is transformed into the state of chloride. This
second roasting usually occupies from two to three hours, and the mix-
ture, after being withdrawn from the furnace and allowed, to a certain
extent, to cool, is taken to the lixiviating house.
Lixiviation and Precipitation.—A lofty shed is generally devoted to
the lixiviation of the chlorinised ores. At Freiberg, where Augustin's
process was employed from the year 1849 to 1862, but finally abandoned
in favour of a process for the treatment of roasted matts by sulphuric
acid, the operations were effected by means of a plant of which fig. 199
represents a side elevation.
The lixiviating tubs, a, arranged in a straight line on
a floor
considerably above the ground-level, were each provided with a false
bottom supporting a filter. On the bottom of the tub was laid a wooden
cross, upon which rested a disc made of planks perforated with large
holes; this was covered by a uniform layer of twigs; a linen cloth was
stretched over these twigs and made tight against the sides of the vessel
by a wooden hoop. These tubs, provided with wheels, were each charged
with about 8 cwts. of roasted matt, and could be transported by the
waggon, b, running on the tramway, c, and were finally arranged in their
666
ELEMENTS OF METALLURGY.
respective places by means of cross-rails on the platform, d. Hot brine
was conducted to the several tubs from the reservoir, e, supplied from
the larger tank, f, through the trough, g; the solution of salt employed
for this purpose was heated to the necessary temperature by the aid of
properly-arranged steam-pipes. The heated brine, on coming in contact.
with silver chloride, dissolved it, and flowed off through the filters into a
trough, by which it was conducted into a tank above the level of a series
of tubs. From this reservoir the fluid was conducted into four tubs, in
which the silver was precipitated by cement-copper. The copper used
for this purpose was placed on filters similar to those arranged on the
bottom of the lixiviating tubs. From these tubs the liquors flowed into
three tubs, h, charged in the same way as the upper ones with precipitated
copper, and where the last traces of silver were thrown down. The cu-
preous liquors now falling successively into the series of tubs, i and k,

MB
d
ہم
f
9
Fig. 199.-Augustin's Process; side elevation of apparatus.
charged with metallic iron, deposited the greater portion of their copper,
and were finally conducted into a tank, l, where any traces of copper still
retained in solution were precipitated by coming into contact with an
additional amount of iron. The brine, thus freed from its silver and
copper, was pumped back again into the reservoir, f, to be re-heated and
again used.
When the tubs, a, had been exhausted of silver, they were taken on
the waggon, b, and placed on a line of rails at right angles to the tram-
way, c, where they were washed, first with liquors resulting from previous
washings, and finally with water. The washing waters, when sufficiently
concentrated by repeated use, were treated as silver solutions. After the
third lixiviation, for which pure water was employed, the tub was taken
to the tipping platform, m, where it was turned over and its contents dis-
charged into a suitable drainer, n.
SILVER.
667
The process of lixiviation may be divided into two periods: the first,
during which the ore is treated with concentrated solutions of common
salt, occupying about twenty hours. The first period was considered as
terminated when a piece of bright copper held in the escaping liquor was
no longer whitened by a deposit of silver, and the tubs were then removed
upon the waggon, b, for the purpose of receiving the second washing;
first with weak liquors, and subsequently with water, as above described.
The products obtained were-Firstly residues in tubs, containing
from 40 to 65 per cent. of copper, with more or less considerable traces
of silver. When found to contain more than 0.03 per cent. of silver
they were put aside to be again operated on; when affording less than
that quantity they were passed to the smelting department for the
production of copper.
:
:
Secondly cement silver, in a finely-divided state, which, after being
washed with dilute hydrochloric acid, and subsequently with water, was
pressed into balls, thoroughly dried, and taken to the refinery.
Thirdly: cement copper, employed for the precipitation of silver
during succeeding operations.
Fourthly liquors freed from silver and copper, from which a portion.
of the iron precipitates as a basic salt; these may be employed in lieu of
fresh brine, but require to be occasionally freed from sodium sulphate by
crystallisation.
The expense of treating copper matt by this process must necessarily
vary in accordance with the cost of salt, fuel and labour, in the locality
in which the works are situated. The loss of silver is usually from 8 to
12 per cent. Speiss yields its silver to this process with more difficulty
than copper matt.
Augustin's process was, in the year 1857, replaced at Mansfeld by the
cheaper and more effective method of Ziervogel, which, from the great
purity of the matts there produced, has been found peculiarly adapted for
their treatment.
ZIERVOGEL'S PROCESS.-Augustin's process for the extraction of silver
by hot brine had not long replaced the old method of amalgamation
at Mansfeld, before it was, in its turn, superseded by the simpler and
cheaper plan introduced by another officer of the Company, Hütten-
meister Ziervogel.
This method is founded on the circumstance, that when a mixture of
copper and iron sulphides, containing silver, is roasted in a state of fine
division, in a reverberatory furnace, with certain precautions, ferrous sul-
phate is first formed; this by further roasting, becomes ferric sulphate,
which is finally decomposed into ferric oxide. At this period sulphide of
copper is transformed into cupric sulphate, and on the temperature being
further increased, cupric oxide is produced and sulphuric acid expelled.
Finally, silver sulphide is converted into sulphate of silver; a salt readily
dissolved in water, while nearly all the other ingredients of the roasted
matt are insoluble in that menstruum. If the roasted material be now
lixiviated with hot water, the silver will be obtained in a solution, from
which it may be readily precipitated in the metallic form.
668
ELEMENTS OF METALLURGY.
Ziervogel's process, although admirably adapted for the desilverisation
of the pure copper matts of Mansfeld, is not generally applicable to the
treatment of silver ores contaminated by arsenic, antimony, lead, or zinc.
The quantity of silver in the refined copper produced at Mansfeld,
from residues partially resulting from amalgamation, and partly from
treatment with hot brine, was (1846-1849) from 0.0388 to 0.0631 per
cent.; whilst in 1861, that resulting from Ziervogel's process only
contained 0·0215 per cent.
The copper matt operated on at Mansfeld is first concentrated and
granulated, and afterwards reduced to the state of an impalpable powder
between granite millstones, driven by water-power. Its average compo-
sition is as follows:-
Cu₂S
79.9
·
FeS
11.0
•
PbS
2.0
•
ZnS
5.0
·
•
MnS
0.2
Nis
0.5
CoS
1.0
Ag₂S
0.4
•
100.0
The matt, after being ground, is bolted through cylindrical sieves,
having from 1,400 to 1,500 apertures per square inch; and all the particles
which are too coarse to pass through the meshes of this apparatus, escape
at the lower end of the cylinder, and are returned to the mill for the
purpose of being re-ground.
Roasting. This operation is conducted in a furnace provided with
two distinct hearths, 10 feet in length and 8 feet in width, placed imme-
diately over each other; the upper one is heated from below by the flame
and gases passing from the fire-place, through that beneath it, whilst from
above it receives its heat from the same gases which are conducted over
its arch in zigzag flues, answering the purpose of condensing chambers.
These flues are covered by cast-iron plates, forming a floor on which the
discharged residues are dried previously to being smelted for copper. The
gases are finally conducted into a chimney, 154 feet in height, which is
in communication with seven similar furnaces. In order to regulate the
admission of air beneath the grate the ash-pit is closed, but is in connec-
tion with an arched channel running below all the furnaces, and com-
municating finally with the atmosphere. The amount of air admitted
into the ash-pit through this passage is easily regulated by means of an
opening, which can be more or less completely closed by a sheet-iron
door, attached to a regulating bar. There is also an opening in the bottom
of the upper hearth, through which the partially-roasted charge may be
transferred to the lower one. During the process of roasting this is closed
by an iron plate.
It is evident from the foregoing description that this apparatus, in
point of fact, consists of two distinct furnace-hearths, placed one over the
other. The lower one is open, and through it the gases from the fire-place
SILVER.
669
pass freely on their way to the chimney. The upper is, on the contrary,
a close furnace or muffle, which is heated on its under side by the gases
passing through the lower one, whilst, from above, it receives its heat
from a series of flues, through which the products of combustion are finally
conducted. Each hearth is provided with a working door, and a small
flue, for the escape of moisture and fumes, connects the upper hearth with
the condensing chambers.
Each charge for this furnace consists of 5 cwts. of finely-divided
copper matt, 70 lbs. of imperfectly-desilverised residues from a pre-
ceding operation, and 25 lbs. of lixiviated lumps, which have become
caked during the process of roasting.
According to Steinbeck, this mixture, without taking into considera-
tion the amount of oxygen present, has the following composition:---
S
Cu
Fe
Pb
Ag
Zn
Mn
Ni
Co
Insoluble residue
19.32
58.00
9.18
2.48
0.28
4.31
0.15
0.44
•
0.84
1.08
The roasting may be divided into three periods:
The materials are first properly mixed and then spread on the upper
hearth, still hot from the previous charge, and are allowed to remain
without stirring for about half an hour, in order that they may become
perfectly dried; about 5 lbs. of dry and finely-powdered brown coal are
now added, and the whole is well worked, with the rake, for about one
hour.
As the air, entering by the working door, passes directly to the flue,
the roasting in that portion of the furnace progresses more rapidly than
towards the opposite end; consequently at the expiration of a certain time
it becomes necessary to change the position of the charge. The material
between the working door and the flue is now turned back toward the
further extremity of the hearth, whilst that which originally occupied
the space between the door and the back of the furnace is spread on
the hearth between the door and the flue. The mass is then raked for
another hour, subsequently again turned, and afterwards raked during
two hours and a quarter, by the two workmen in charge of the furnace,
alternately. At this period of the operation 25 lbs. of powdered brown
coal are added to the charge, with which it is well mixed, and the whole,
in a brightly-glowing state, is raked through the aperture in the bottom
of the first hearth on to the bed beneath. The first stage of the operation
of roasting occupies about five and a half hours.
No fuel is thrown on the grate during the second period; the partially-
roasted charge is evenly spread over the surface of the red-hot lower hearth,
where it is continuously raked during about an hour, in order to prevent
its caking. The flue between the furnace and condensing chambers is also
670
ELEMENTS OF METALLURGY.
closed by a damper, in order to prevent a further rise of temperature by
the rapid oxidation of sulphur, and the combustion of the brown coal
which has been added. In the course of half an hour the brown coal has
become almost entirely consumed, and, after being continuously raked
during an hour, the position of the different portions of the charge in
the furnace is changed. The damper is now withdrawn and oxidation is
accelerated by the admission of air during one hour and a half; from this
period the temperature of the mass gradually diminishes, and the charge
ultimately assumes a dark colour.
In order to determine the progress of the operation, and to ascertain
whether this period should be further prolonged, a sample is now taken
from different parts of the hearth; this is cooled on a tile, and any lumps
which it may contain are carefully picked out. The more finely divided
portions are spread on the surface of an ordinary white plate, and a suf-
ficient amount of water is added to moisten it thoroughly throughout. If
the resulting solution be of a blue colour, and the addition of common
salt produces a white precipitate, it indicates that the formation of silver
sulphate has commenced, and that the second roasting period may be con-
sidered finished. Should the washing of the sample yield a greenish
solution, indicating the presence of salts of iron, the operation must be
further continued. The second period of roasting usually occupies two
hours and a quarter.
The fuel employed during the third roasting period should be oak,
beech, birch, or some other hard wood; but fir must be avoided, since it
produces a smoky flame, which exercises a reducing action unfavourable
to the progress of the operation. The flame rises from the grate to the
arch of the furnace, and does not come into direct contact with the
charge lying upon the hearth; the draught is regulated by dampers
in accordance with the state of the weather and the direction of the
wind.
The roasting mixture is now thoroughly and continuously worked
over by the rake; at the expiration of an hour it has acquired a dull red-
heat, which is afterwards increased to full redness. But few lumps
or clots should be formed during the progress of roasting, and these
are not broken down but become more compact in proportion as the
temperature increases. At the expiration of an hour and a half, that
portion of the charge lying nearest the fire-bridge is, under ordinary cir-
cumstances, sufficiently roasted; this is determined by lixiviating a
sample, which should afford a solution of a light blue colour and yield a
dense precipitate of chloride of silver on the addition of common salt. The
charge is now turned over, and that portion which was originally furthest
from the fire-place is brought to the bridge end of the hearth; the whole
is constantly stirred, until a second sample, taken from different parts
of the mass, shows that it is ready for drawing. If too much heat is
applied during this operation, silver sulphate becomes decomposed, in
which case the liquid resulting from washing a sample will be quite free
from cupric sulphate, and entirely without colour. The third period of
roasting usually occupies five hours and a half, thus making the total
SILVER.
671
period necessary for the complete elaboration of a charge, on the two
hearths, thirteen hours and a quarter.
The loss of silver experienced during the operation of roasting
amounts to 7.06 per cent.; 91.736 per cent. of the silver originally
present is in the form of sulphate in the roasted ore, and 1.20 per cent.
is insoluble. The fume resulting from the treatment of matts in the
roasting furnace is collected from the flues and condensing chambers,
and smelted, for matt, in cupola furnaces; these matts are rich in
silver.
Lixiviation and Precipitation.—On being withdrawn from the furnace
the roasted material is cooled to 87° C., and placed, in charges, each of 5
cwts., in the tubs, A, fig. 200, of which there is a series of ten.
These are
provided with false bottoms, and with filters constructed in a similar way to
those employed for the extraction of chloride of silver by means of hot

A
E
F
N
H
M
Fig. 200.-Ziervogel's Process; transverse section of apparatus.
brine. A leaden tube, b, 2 inches in diameter, conveys from 2 to 3
cubic feet of water heated to 87° C. upon the top of the charge, which is
covered with oakum for its better distribution over the surface. As
soon as the liquors begin to flow from the tap, c, inserted beneath the
false bottom, the tap on the pipe, b, is closed, and another, communi-
cating with the pipe, a, of larger diameter, is opened, by means of which
about 5 cubic feet per hour of water, heated to the temperature before
indicated, and slightly acidulated with sulphuric acid, are supplied to
the lixiviating tub.
This is continued until the addition of common salt to a sample of
the liquors flowing off no longer produces a precipitate of silver chloride.
The solution of sulphate of silver flows from c, into the first compartment,
B, of a tank 30 feet long, 2 feet wide, and 1½ foot high. From B the
liquors enter the compartment, C, by flowing over a division which does
not quite reach the top of the vessel, and are then distributed, by means
of an equal number of taps, into ten precipitating tubs, D, provided with
672
ELEMENTS OF METALLURGY.
false bottoms. This clarifying box, as well as all the other reservoirs
employed, is provided with a float, d, indicating the height of the liquid.
Upon the filters of the tubs, D, are placed layers of cement-copper
about 3 inches in thickness, above which are laid about twenty copper
bars 14 inches long, 5 inches broad, and 1 inch thick. The greater
portion of the silver is precipitated in these tubs, and the liquors, on
leaving them, are received in the lead-lined trough, E, 15 inches in
width and 6 inches in depth, on the bottom of which is a layer of small
pieces of sheet-copper. They then flow into the tubs, F, which have
false bottoms, and contain a little granular copper and a few bars of the
same metal. The desilverised liquors, which have now a temperature
of about 56° C., are conducted by the gutter, g, into a leaden reservoir,
whence they are pumped into a leaden pan, capable of containing about
70 cubic feet, where they are heated to 87° C., and again employed for
lixiviation. Half a pound of sulphuric acid is added to each charge of
the leaden pan, and has the effect not only of facilitating the solution of
silver sulphate, but also of preventing the separation of basic salts. The
precipitated silver is removed from the tubs, D, every twenty-four hours,
and the filters are taken out and cleaned once a week.
The precipitated silver is chiefly contaminated by the presence of
copper and gypsum; it is reduced to powder by being pounded with
wooden pestles, and the lumps of copper are separated by washing. It
is subsequently lixiviated for seven days with sulphuric acid, diluted
with eight times its volume of water, in nine tubs, H, in order to remove
as much as possible of the remaining copper salts and gypsum, and is
finally washed with hot water. The liquors resulting from washing rise
through L, and are conducted, by the trough, M, first over metallic
copper, and afterwards into tanks containing scrap-iron; the water from
the final washing is run off at N, and conducted, by the gutter beneath,
to a lead-lined tank.
The washed silver, about 0·865 fine, is moulded into blocks dried in
a kiln, and refined in a reverberatory furnace. When the residues are
found by assay to contain less than 0.03 per cent. of silver, they are
removed, to be treated for black copper; but if they yield a larger amount
of this metal they are again roasted and lixiviated.
The desilverised liquors are from time to time purified, by throwing
down the copper by metallic iron, and the precipitated copper, obtained
in the ordinary course of working, is divided into two classes by washing
and decantation. The more granular portion is employed for the preci-
pitation of silver, whilst the other, which is contaminated by basic salts,
is treated directly for the production of copper.
Dr. Lamborn, in his 'Metallurgy of Silver and Lead,' (p. 191), gives
the following table, showing the cost and results of various methods of
extracting silver from cupreous products at Mansfeld :-
Amount of Silver
left in Copper.
0.100 per cent.
0.059
Extracting the silver by—
Cost.
£ s. d.
Liquation
from 1 cwt. of copper 1 10
0
Amalgamation
0 16
6
•
""
""
Augustin's method
0 13 6
0.059
•
>>
Ziervogel's method
0 7
6
. 0.029
>>
>>
""
SILVER.
673
This process can be only successfully carried out where the material
treated is of a pure and unvarying character, as in the case of the products
obtained from the Kupferschiefer of Mansfeld. Considerable care and
experience are also required on the part of the workmen employed, since
the preliminary roasting, on which the success of this method chiefly
depends, is an exceedingly delicate operation.
VON PATERA'S PROCESS.-The extraction of silver from its ores by
this process comprehends the following manipulations:-1st. Roasting
with common salt, until the silver present has been converted into chloride.
2nd. Dissolving out the silver chloride by means of a cold dilute solu-
tion of hyposulphite of sodium. 3rd. Precipitating the silver in the form
of sulphide, from its solution in sodium hyposulphite, by the addition
of sodium sulphide. 4th. The sulphide of silver thus obtained is reduced
to the metallic state by exposure in a muffle at an elevated temperature.
Dr. Percy, in a paper published in 1848, first suggested the extraction
of silver from argentiferous ores by its conversion into chloride and sub-
sequent solution in sodium hyposulphite; this paper, which ultimately fell
into the hands of Von Patera, resulted, in 1858, in the introduction, at
Joachimsthal, of the process which now bears his name. The ores from
that district are remarkable for the diversity of their constituents, and in
addition to silver, frequently contain copper, lead, bismuth, iron, nickel
and cobalt, associated with sulphur, arsenic and antimony. Mining
operations in the vicinity of Joachimsthal, although less productive than
formerly, still yield a certain amount of argentiferous ores of extraor-
dinary richness; those treated by the process now under consideration
contain, on an average, between 2 and 3 per cent. of silver, and small
parcels are sometimes operated on which yield as high as 15 per cent. of
that metal. The only fuel to be obtained at a moderate price in the
district is lignite, but labour is abundant and moderately cheap.
Roasting.—The ores, on arriving at the works, if not sufficiently
reduced in size, are coarsely ground, and then roasted in a furnace, into
which steam is introduced during the progress of the operation.
This apparatus, instead of having the usual long narrow hearth,
broad fire-bridge, and short wide fire-place, has a bearth 9 feet 6 inches.
in width, and measuring but 6 feet from the bridge end to the take-up of
the flue leading to the chimney.
The grate, which is only 9 inches in width, is four-fifths the length of
the longer axis of the hearth, from which it is divided by a fire-bridge
consisting of an iron tube, protected with clay, and pierced with a
number of small holes on the side furthest removed from the grate.
A charge of 400 lbs. of the ore to be operated on is spread on the
hearth of this furnace, and the heat is gradually and cautiously raised, in
order to avoid agglomeration. No steam is admitted during the first
stage of the operation, but as soon as the charge has attained a red-heat
as much is turned on as can be introduced without materially affecting
the temperature of the furnace. At the expiration of four hours from
the time of charging, the ore is withdrawn, and, after being allowed to
cool, it is ground in a mill to the state of a fine powder, with the addition
2 x
674
ELEMENTS OF METALLURGY.
of from 6 to 12 per cent. of common salt, and from 2 to 3 per cent. of
sulphate of iron.
A charge of this mixture, weighing 300 lbs., is introduced into a
furnace similar to that employed for the first roasting, and the second
roasting is commenced. The mixture is evenly spread over the surface
of the hearth, and as soon as a red-heat has been obtained steam is
admitted as before, care being taken, by constant stirring, to prevent
agglomeration; the temperature is gradually increased, and at the ex-
piration of from ten to sixteen hours, according to the richness and
composition of the ores, the operation is complete.
The addition of ferrous sulphate to the partially-desulphurised ore is
for the purpose of effecting the necessary decomposition of common salt
in case a sufficient amount of other metallic sulphates should not be
produced. The introduction of aqueous vapour is thought to facilitate
the chemical decompositions going on in the furnace, and to assist in the
condensation of fumes in the flues and chambers prepared for that
purpose.
The roasted and finely-divided ore, containing silver in the state of
chloride, is now taken to the lixiviating room.
Lixiviation with Water.—In addition to chloride of silver, which is in-
soluble in water, the roasted ores contain variable quantities of copper,
zinc, iron, nickel, and cobalt, which, being present chiefly in the form of
chlorides and sulphates, are readily dissolved by washing. In each of
a row of tubs are placed 400 lbs. of roasted ore, and hot water is allowed
to percolate through the several charges during a period of six hours.
By this means all the soluble salts are removed, and the liquors passing
through the filters are conveyed by a trough, b (fig. 201), into a tank,
where the metallic oxides are precipitated by lime-water; the precipi-
tate thus obtained is subsequently fused with a mixture of residues and
poor ores in a blast-furnace.
The liquors draining into the trough are from time to time tested by
sodium sulphide, and as soon as a precipitate is no longer obtained on the
addition of a drop of this reagent, the operation is considered finished,
and cold water is allowed to pass through the tubs for the purpose of
lowering the temperature of the residues.
Lixiviation with Sodium Hyposulphite.—The residues remaining in
the several tubs, A, after the removal of the various salts soluble in
hot water, are transferred to the tubs, B, which are also provided with
filters and false bottoms. At Joachimsthal seven of these are employed,
and are placed on a level with the tubs, A (of which there are several),
between which and the vessels, B, is a tramway, on which is the waggon,
c; the tubs, B, stand on trucks, c', which can be run on to the waggon, c,
and then made to traverse, either backwards or forwards, immediately in
front of the row of tubs, A. The vessel, B, after receiving a charge of
200 lbs. from the tub, A, is removed to its position on the other side of
the tramway, where it is treated with the solution by which the removal
of the silver is to be effected.
This consists of a cold solution of hyposulphite of sodium, 1 cubic foot
SILVER.
675
of which is capable of dissolving 0-753 lb. of silver, which is brought by
the trough, b', and allowed to filter slowly through the mass. In this
way the silver chloride is gradually taken up in the form of a double
salt, which, passing beneath the false bottom into the trough, d, is conveyed
to the precipitating tubs.
The duration of this operation is, to a considerable extent, influenced
by the richness and composition of the ores, as well as by their state of
mechanical division. Parcels containing 15 per cent. of silver are not
sufficiently impoverished by lixiviation in less than forty-eight hours,
whilst ores containing 1 per cent. can be treated in about twelve hours.
Ores which do not contain above 7 per cent. of silver require but one
chlorination and lixiviation, but when richer samples are operated on two
successive roastings and lixiviations become necessary; during the second
roasting addition is again made of salt and ferrous sulphate. The lixi-
viation is considered complete when the liquors dropping from the tubs

HA
e
-m
B
Fig. 201.-Von Patera's Process; transverse section of apparatus.
no longer afford any traces of a precipitate on the addition of a drop
of sodium sulphide; the residues are dried and fused in a blast-furnace
with addition of pyrites, &c.
Precipitation of Silver.-The liquors passing through the filters at
the bottom of the tubs, B, are conducted by the trough, d, into the
vessels, E, F, of which there are ten; six holding 40 gallons each, and
four of the capacity of 80 gallons. The precipitant employed is prepared
by fusing soda-ash with sulphur, and subsequently boiling the product
dissolved in water with excess of sulphur. The solution thus obtained,
which contains sodium pentasulphide, together with a small amount of
hyposulphite of sodium, is conveyed to the precipitating vessels in large
stoneware jars, and is poured into the argentiferous solutions so long as
a precipitate is thrown down on the addition of a further quantity.
The contents of the tubs are first well stirred, and then allowed to
settle, and a sample of the clear liquid having been taken in a test tube,
a few drops of the precipitating solution are added. If a dark-coloured
precipitate is the result it shows that a certain amount of silver still
2 x 2
676
ELEMENTS OF METALLURGY.
remains in solution, and a further addition of the precipitant is necessary.
If, on the contrary, no precipitate takes place, it becomes probable that
too large an amount of sodium pentasulphide may have been added. In
order to determine this point, some fresh liquor, holding the double salt
of silver in solution, is added to a sample taken from the tub under
treatment. Should a precipitate be thus obtained, argentiferous liquor
must be cautiously added to the tub until no further reaction takes place.
When this point has been attained all doubt as to whether the whole of
the silver has been precipitated, on the one hand, and no excess of the
precipitant has been employed, on the other, is removed by taking two
samples of the supernatant liquors, to one of which a few drops of a
weak solution of common salt are added, whilst into the other a small
quantity of solution of acetate of lead is introduced. If the addition of
common salt produces no precipitate of silver chloride, it shows that the
whole of that metal has been removed, and should no discolouration
take place on the addition of the solution of the lead salt, it indicates
that the precipitant has not been added in excess.
The exact neutrality of the residual liquid is necessary in order to
obtain the most satisfactory results, since the liquors from which the
silver has been precipitated are employed in the next operation. The
presence of sodium sulphide would evidently convert a portion of the
silver into insoluble sulphide, whilst the addition of too small a quantity
of this precipitant would leave a certain amount of chloride of silver in
solution, and thereby diminish the solvent powers of the liquors for that
salt.
Six hours after the addition of the precipitating solution the flocculent
precipitate has sufficiently settled to admit of the supernatant liquor
being syphoned off into a tank, situated below the level of the floor; it
is thence pumped to the level of the trough, b', to be again used in the
process of dissolving. The slimy sulphide of silver is drawn off by the
taps, e, f, and is placed in a filter-bag of canvas to drain.
Instead of any loss of sodium hyposulphite being experienced during
the working of this process, a gradual increase of that salt is the result;
this arises from the action of the air on the precipitating liquors, and
consequently the solutions employed for dissolving chloride of silver
require to be occasionally diluted by the addition of water. The yield
by this process amounts to 88 per cent. of the silver present in the ores
treated; from 1 to 2 per cent. is lost, and the remainder is found in
intermediate products. The cost of materials and labour amounted, in
1862, to about 8s. 6d. per cwt. of ore operated on, or 4s. 4d. per lb. of
silver produced.
Treatment of Silver Sulphide.-The sulphide of silver, removed from
the tubs, E and F, is placed in conical canvas bags, G, supported on
wooden frames, and allowed to drain. After standing about half an hour
the bags, with their contents, are placed under a screw-press, and as
much as possible of the remaining moisture is carefully expressed. The
precipitate is now removed from the bags, dried in a warm room, and
afterwards replaced in similar filters and washed with warm water. The
SILVER.
677
silver sulphide, thus freed from soluble salts, is again dried and sub-
sequently heated to redness in a muffle to which atmospheric air has free
access. In this way the greater portion of the sulphur is burnt off,
leaving a residue which contains from 60 to 80 per cent. of silver.
This residue is fused in large graphite crucibles, and any sulphur
which it may still retain is removed by the addition of metallic iron; the
ferruginous sulphide thus produced is skimmed off, and added to the
roasting mixture, instead of ferrous sulphate. The surface of the metal
is finally cleaned by adding a small quantity of a mixture of bone-ash
and wood-ashes, which, on being carefully scraped off, leaves metallic
silver of from 0·940 to 0.960 fine; this is refined.
Residues. The residues, containing nickel and cobalt, together with
the precipitate by lime-water, and ores poor in silver, are smelted with
addition of 10 per cent. of pyrites, 12 per cent. of slags, and a variable
amount of lime.
This, if the spent ores contain 0.23 per cent. of silver and 3-4 per
cent. of nickel and cobalt, affords a matt yielding about 1.25 per cent. of
silver and 17 per cert. of nickel and cobalt. The matt thus obtained is
re-smelted with addition of sodium sulphate, moistened, allowed to fall
into powder by exposure to the atmosphere, and subsequently lixiviated to
remove soluble salts. The residue, which contains from 1 to 2 per cent.
of silver, is fused with arsenical pyrites for the production of speiss and
copper matt. The former is purified by re-smelting, and the copper matt
is treated for silver and copper.
EXTRACTION OF SILVER AND GOLD BY SULPHURIC ACID. This process
consists in treating argentiferous copper matts or black copper with hot
dilute sulphuric acid, by which the copper, in the form of cupric sulphate,
is dissolved, whilst a large proportion of the silver and nearly the whole
of the gold remain in the residues. The products treated by this
method should be as free as possible from iron, which, if present, would,
to a certain extent, pass into the sulphate of copper produced, and dimi-
nish its commercial value. The residues are afterwards smelted either
with lead ores or plumbiferous products, and the silver is extracted in
the usual way.
This method is chiefly applicable to the treatment of
products containing such impurities as lead, antimony, and arsenic, and
yields a large proportion of the assay value of the gold when that
metal is present. It is generally found more advantageous in this
process to treat black copper than copper matt, since the former simply
requires to be so far refined, previously to treatment, as to be freed
from iron, whilst the latter requires sundry preliminary roastings and
fusions.
We are indebted to Professor F. Ulrich, formerly of the Imperial
Smelting Works at Oker, Lower Hartz, for the following description of
the method of conducting this operation in that establishment.
The copper produced at Oker is of two kinds; that which is of good
quality is poor in silver, while that of an inferior description contains, in
addition to silver and gold, various substances exercising a prejudicial
influence on the copper. The first variety is converted into rosette
678
ELEMENTS OF METALLURGY.
copper, and is sold in the metallic state. Up to 1858, the copper contain-
ing silver was treated by liquation. At that date a better process was
introduced, by which the copper is obtained in the form of a nearly
pure sulphate, and the silver and gold as a muddy residue, mixed with
various other substances constituting the impurities of the original
copper.
The metal is first finely granulated, by being poured in a fused state
into water, and then moistened with warm dilute sulphuric acid, and
exposed to the air. Oxidation of the copper rapidly takes place, and the
granules become covered by a dark film. A fresh supply of warm dilute
sulphuric acid is now added, by which the sulphate thus formed is dis-
solved. The acid solution of sulphate of copper obtained is made to
pass through a long leaden gutter, in which, as it cools, imperfectly-
formed crystals of sulphate of copper are deposited; after cooling, this
liquor contains only a small quantity of copper, but a large amount of free
sulphuric acid. This liquor is collected in a reservoir, and, after being
re-warmed, is again run into the vessels containing the granulated copper.
This process is continuously repeated, the sulphate of copper being dis-
solved in weak sulphuric acid, and the strongly-acid mother liquors
again run over the granulated copper. The silver and gold are carried
off in suspension in the acid liquors, and deposited, with the crystals
of sulphate of copper, in the leaden gutter; these are from time to time
removed for re-crystallisation, when the inclosed metallic mud is
liberated, and obtained in a separate form. This mud is afterwards
smelted with litharge, and yields lead containing about 2 per cent.
of silver; the clear liquors deposit crystals of almost pure sulphate of
copper.
The copper treated by this process at Oker contains, on an average,
0·16 per cent. of silver, and, after granulation, is placed in large wooden
tanks lined with thick sheet-lead. On the bottom of these tanks is first
laid a layer, 6 inches in thickness, of large fragments of copper, and
upon these is placed the granulated metal to a depth of 3 feet 6 inches.
From a hole in the bottom, the liquors run into a slightly-inclined lead-
lined gutter, of which the length must be such that the liquors in running
through it may become sufficiently cooled to deposit nearly the whole of
the sulphate of copper which they contain. The strongly-acid mother
liquors are blown by an injector into a lead-lined cistern, where they are
re-heated by steam, and from which they are run, as required, through a
syphon, upon the granulated copper; their density is 30° Baumé, and
they are heated to from 87° to 100° C. Each time the liquors are run
off the copper is exposed, during fifteen minutes, for the purpose of oxi-
dation, and sulphuric acid is run on until the copper has again regained
its metallic appearance.
When the crystallised deposit in the gutter has attained a thickness
of about 3 inches, it is removed and thrown upon an inclined plane, from
which the adhering liquors drop back into the gutter. This crude sul-
phate of copper is taken to leaden boiling pans, 12 feet in length, 11 feet
in width and 23 feet in depth, where it is dissolved, either in water or in
SILVER.
679
weak acid liquors. The quantity of liquid is so regulated that a solution
is obtained which, at 87° C., has a density of 30° Baumé.
This solution is allowed to settle during twelve hours, care being
taken to avoid, as far as possible, any decrease of temperature; at the
expiration of this time the liquor, which is perfectly clear, is run into
crystallising pans, 10 feet long, 5 feet wide and 4 feet deep, in which
are hung numerous strips of lead. On these, in the course of from twelve
to fourteen days, are formed beautiful crystals of sulphate of copper,
which are subsequently removed and packed for the market.
The mud, containing the silver and gold, which settles in the boiling
pans, is taken out and mixed with litharge. This mixture is smelted for
lead, and the quantity of litharge is so regulated that the resulting alloy
shall contain about 2 per cent. of silver. The lead thus obtained is
passed to the cupelling furnace, and affords silver containing from 1.5 to
1.7 per cent. of gold.
In the year 1870, 402,600 lbs. of copper were dissolved at the Oker
Works during 350 working days, in 873,152 lbs. of sulphuric acid, of
50° Baumé. Three dissolving pans were employed, and the resulting
crude sulphate of copper was dissolved in four boiling pans, having an
aggregate capacity of 800 cubic feet. It was re-crystallised in forty-
eight crystallising tanks, having a total capacity of 9,600 cubic feet, and
the sulphate of copper obtained weighed 1,531,877 lbs. The consumption
of coal was 10,433 ctrs.
The mud containing the silver and gold was treated for the precious
metals with a loss of 8.4 per cent. of the lead employed, and the silver
obtained slightly exceeded the amount indicated by assay.
CLAUDET'S PROCESS.-The object of this process is the recovery of
the silver which, in the form of chloride, is dissolved in the liquors
resulting from the treatment of cupreous pyrites by the wet method of
extraction. These contain a large amount of undecomposed common salt,
which dissolves the silver chloride, and from which, until recently, it
was found impossible to precipitate the silver in a concentrated form.
It has long been known to those engaged in copper-extraction that
the copper-precipitate produced from Spanish and Portuguese ores con-
tains not only a notable quantity of silver, but also distinct traces of gold.
No successful attempt to separate the precious metals and to turn them
to profitable account had, however, been made up to the commence-
ment of the year 1870, when Mr. F. Claudet patented a process for their
separation from ordinary copper-liquors by the addition of a soluble
iodide.
The amount of silver present in burnt ore seldom exceeds 18 dwts.
per ton; but as the whole of this is never obtained in solution, it follows
that, in order to obtain satisfactory commercial results, in dealing with
such minute quantities, the process employed should be both cheap and
expeditious.
The vats in which burnt ore, which has been roasted with salt, is
lixiviated, generally receive some eight or nine successive washings,
either with water, with weak liquors, or with water acidulated by hydro-
680
ELEMENTS OF METALLURGY.
chloric acid; and of these the first three only contain a sufficient amount
of silver to be worth working.
For the purpose of removing the soluble salts from the ground and
roasted ore hot water is first employed; and, as a large proportion of
the sodium chloride used remains undecomposed, it acts as a solvent for
the silver chloride produced during the process of furnacing.
The analysis of a first washing from a copper tank, gave Mr. Claudet
the following results :-
ANALYSIS OF STRONG LIQUORS.
Sp. Gr. 1.240.
Contents per Gallon.
Grains.
Na₂SO
NaCl
4
Cl (combined with metals)
Cu
Zn
Pb
Fe
•
Ca
Ag
•
10,092
4,474
4,630
3,700*
480
•
•
40
·
32
52
個
​3.06
·
7,347-12, 106 NaCl
5,686 2,274 sulphur.
As, Sb, Bi, &c., not estimated.
Total Cl
""
SO3
Proportion of Cu to Ag=10,000 : 8.2.
The respective amounts of copper, chlorine, sulphur and silver con-
tained per gallon in nine successive washings of one tank of ore, are
given in the following table:-
LIQUORS RESULTING FROM NINE WASHINGS OF ONE TANK OF ORE.
No. of
Washing.
No. of Grains per Gallon.
Sp. Gr.

Cu.
CI.
S.
Ag.
1st
1.285
5,230
10,798
1,324
4.06
2nd
1.250
4,600
9,079
1,455
3.25
3rd
1.175
1,935
3,215
1,881
1.05
4th
1.080
646
717 1,255
0.19
5th
1.095
666
643
1,436
0.12
6th
1.070
692
544
1,588
0.06
7th
1.060
342
217
938
0.03
8th
1.030
200
434
0.06
9th
1.020
117
294
0.04
Washings 1 and 2 contain
"}
82.50 per cent. of total silver.
1, 2, and 3 contain 94.30
""
The several operations for the extraction of silver are conducted in
the following manner; and as the first three washings contain nearly 95
* 405 grs. of this copper existed in the state of cuprous chloride.
SILVER.
681
per cent. of the total amount of that metal dissolved, these alone are
treated.
The liquors are first run into suitable wooden cisterns, each having a
capacity of about 2,700 gallons, where they are allowed to settle.
Estimation of Silver in the Liquors.—The yield of silver per gallon is
now ascertained by taking a measured quantity, to which are added hydro-
chloric acid, potassium iodide, and a solution of acetate of lead. The
precipitate thus obtained is thrown upon a filter, and, after being dried,
is fused with a flux consisting of a mixture of sodium carbonate, borax,
and lamp-black. The resulting argentiferous lead is passed to the cupel,
and, from the weight of the button of silver obtained, the amount of that
metal in a gallon of the liquid is estimated.
Precipitation of Silver.-The liquor from the settling vat is allowed
to flow into another of slightly larger capacity, whilst at the same time
the exact amount of some soluble iodide (a solution of kelp may be
employed for this purpose), necessary to precipitate the silver present, is
run into it from a graduated tank, together with a quantity of water
equal to about one-tenth of the volume of the copper solution. During
the filling of the second tank its contents are constantly stirred, and,
when filled, it is allowed to settle during forty-eight hours.
The supernatant liquors are, after being assayed, run off, and the tank
is again filled; the precipitate collected at the bottom is, about once a
fortnight, washed into a vessel prepared for its reception.
This precipitate is chiefly composed of a mixture of lead sulphate,
lead chloride, silver iodide, and subsalts of copper, from which the latter
are readily removed by washing with water acidulated by hydrochloric
acid. Thus freed from copper salts, the precipitate is decomposed by
metallio zinc, which completely reduces the silver iodide, and also the
lead chloride. The results of this decomposition are-
First, a precipitate rich in silver, and containing a certain amount of
gold.
Second, zinc iodide, which, after being standardised, is employed in
subsequent operations to precipitate further quantities of silver.
The more important constituents contained in a sample of the pre-
cipitate were estimated, with the following results:-
ANALYSIS OF DRIED SAMPLE.
Moisture 25 per Cent.
Oz.
dwt. gr.
4.455 per cent. =1,455 6
cent.=1,455 6 0 per ton.
Ag
Au.
0.0595
•
Zn
15.440
•
Pb
56.400
Cu
0.600
CaO
1.10
Fe.
0.70
6.68
7.60
= 19 8 12
""
SO 3
Insoluble.
The results obtained by this process at the Widnes Metal Works
show, that 0·65 oz. of silver and 3 grains of gold may be extracted from
;
682
ELEMENTS OF METALLURGY.
each ton of ordinary Spanish pyrites; at a total cost, including labour,
loss of iodide, &c., of 8d. per tou, or 12.3 pence per oz. of silver produced.
If from this amount be deducted the value of the gold, the expense of
working a ton of ore is reduced to 2d.; thus leaving a profit of about 3s.
on each ton of ore treated.
GOLD.
Gold is possessed of a characteristic yellow colour, and is the most
malleable of the metals. One grain of pure gold may be beaten into
a leaf having a superficies of 56 square inches, and which, from this
measurement, and the known specific gravity of the metal, is calculated
to have a thickness of only one two-hundred-thousandth of an inch.
When in extremely thin leaves, gold is, to a certain extent, trans-
parent, and, on being held between the observer and the light, appears of
a greenish colour; on rendering the film non-lustrous by heat the colour
becomes ruby-red. When large quantities of gold have been fused, and
allowed slowly to cool, cubes more or less modified on their edges and
angles are frequently obtained. Native gold likewise affords numerous
well-defined crystals belonging to the cubic system, but of these the
greater number are affected by the faces of the regular octahedron, or
the rhombic dodecahedron. The specific gravity of gold is 19.50.
Gold fuses at a temperature of 1,102° C., and when still more strongly
heated, affords sensible metallic vapours. If a powerful electric dis-
charge be passed through a fine gold wire, it becomes entirely dissipated,
and a sheet of white paper held beneath, becomes stained with a purple
line caused by a deposit of minutely-divided metallic gold. If, instead
of a sheet of white paper, a plate of polished silver be employed, it is
traversed by a brightly-gilded line, which is firmly attached to its surface.
A globule of gold, exposed between two charcoal electrodes to the action
of a powerful voltaic battery, enters almost immediately into fusion,
and gives off abundant metallic fumes, by which its weight is rapidly
diminished.
When precipitated from its solutions, gold assumes a dark brown
colour, but on being rubbed by a piece of polished steel, or other hard
body, it readily assumes its ordinary colour and metallic aspect. If pre-
cipitated gold in this form be strongly heated, and, when in that state,
struck repeatedly with a hammer, its particles readily become welded and
united into a solid mass, without their having undergone actual fusion.
The gold used in the manufacture of jewelry, as well as that em-
ployed for being coined into money, is invariably alloyed with some other
metal, such as copper, and is therefore never absolutely pure. Pure gold
may be indefinitely exposed to the action of air and moisture without
becoming in the least degree tarnished, nor is it oxidised by being kept
in a state of fusion in open vessels. Neither sulphuric, hydrochloric, nor
nitric acids attack gold, even when in a fincly-divided state; but by aqua
GOLD.
683
Gold
regia it is readily attacked, and dissolved in the form of chloride.
may also be dissolved by hydrochloric acid, to which some substance
capable of liberating chlorine has been added; among these may be men-
tioned chromic acid and peroxide of manganese.
Bromine, even in the cold, attacks this metal, although by iodine it is
but sparingly acted on, even by the aid of heat. Gold is not directly
attacked by sulphur at any temperature; but when fused with the alkaline
sulphides, it is rapidly acted on with the formation of double sulphides.
It is also soluble in aqueous cyanide of potassium in open vessels.
Gold probably always occurs in the metallic state, alloyed with more or
less silver, and frequently with minute quantities of copper and iron. It
is also occasionally found in combination with the rare metals palla-
dium, rhodium and tellurium, as well as with mercury forming a native
amalgam. These compounds are, however, mineralogical curiosities
only, and are of little commercial importance.
Native gold generally presents the characteristic yellow colour pecu-
liar to this body when in a state of purity, but its natural surfaces some-
times require to be rubbed with some hard substance before they assume
the ordinary appearance of manufactured gold. The hardness of gold is
less than that of iron, copper, or silver, but greater than that of either
lead or tin. When broken by repeated bendings it presents a matted
silk-like structure, which is more or less fine, in accordance with the
purity of the specimen. Native gold occurs crystallised, in branches, in
filaments and plates, in disseminated grains, and in pepitas mixed with,
and forming part of, various alluvial deposits. The greater portion of
this metal is procured in the latter form; but as these sands are them-
selves the product of the destruction of auriferous rocks, the metal which
they contain must be regarded as the débris partially resulting from the
disintegration of the matrix in which it was originally inclosed. Crystal-
line specimens are likewise numerous, the cube being in all cases the
primitive form. Crystals seldom occur isolated, but are more frequently
grouped together in the form of irregular branches. Their faces are
often dull, and sometimes slightly rounded, even in specimens directly
extracted from the vein, which, consequently, cannot have been exposed
to attrition.
The small branches of gold which sometimes occur in auriferous veins,
when closely examined appear to consist of a series of minute octahedra,
implanted one upon another, so as to form a sort of chain.
The grains and fragments found in alluvial deposits vary considerably
in size, but are generally small. When of the size of a nut and upwards
they receive the name of "nuggets"; and in some localities such pieces
are not of unfrequent occurrence.
A nugget was once discovered in Cabarrus county, North Carolina,
weighing 37 lbs. troy. In Paraguay, masses of gold varying from 1 to
50 lbs. in weight were some years since obtained at the foot of one of the
highest mountains. Various lumps varying from 16 to 17 lbs., and one
weighing 27 lbs., have been found in the Ural district; and in the valley
Taschku Targanka a fragment was met with, in 1842, which weighed
684
ELEMENTS OF METALLURGY.
nearly 100 lbs. This specimen has been deposited in the Museum of
Mining Engineers at St. Petersburg. Some very large specimens of gold
have been obtained from California, and masses weighing considerably
above 1 cwt. have also been procured from the Australian diggings.
The composition of various specimens of gold, obtained from different
localities, is given in the following table :-
Locality.
Au.
Ag.
Fe.
Cu.
Analyst.
Transylvania, Vöröspatak
Barbara
60.49 38.74
Rose.
84.80
Beresof
91.88
14.68 0.13 0.04
8.03
97
>>
Siränovski, Altai
60.98 38.38
0.33
""
Brazil
94.00
5.85
Darcet.
Bolivia, Ancota
""
Tipuani
94.73 5.23 0.04
91.96 7.47 trace
Forbes.
N. Grenada, Bogota
92.00 8.00
Bouss.
Trinidad
82.40
17.60
""
Peru, Carabaya
97.46
2.54
Forbes.
·
..
""
Yungas
79.89
20.11
Nova Scotia, Tangier
98.13
1.76
trace 0.05 Marsh.
California
90.70
8.80 0.38
Rivot.
90.96
9.04
Oswald.
""
Canada, Chaudière
89.24
10.76
S. Hunt.
Australia
99.28 0.44 0.20 0.07 Northcote.
Bathurst
95.68 3.92 0.16
:)
Henry.
Mitta Mitta
89.57
10.43
Ward.
•
Tasmania, Giandara
92.77
7.23
""
Black Boy Flat 94.95 4.66 0.08
""
DISTRIBUTION OF GOLD.
Gold appears to be as generally distributed as the other metals, but
it usually occurs in such exceedingly minute quantities as either to
escape observation or not to repay the cost of extraction.
Native gold, in situ, is most frequently met with in quartz veins in-
tersecting metamorphic rocks, and is, almost invariably, associated with
iron pyrites and other metallic sulphides, such as galena, blende, &c. It
is, however, sometimes found in combination with bismuth, tellurium,
palladium and rhodium, and also with mercury in the form of native
amalgam. The metamorphic rocks inclosing gold veins are mostly chlo-
ritic, talcose, and argillaceous slates, and, less frequently, they are met
with in mica schist, hornblendic slates, gneiss, diorite, or porphyry. Auri-
ferous veins also occur in granite. A laminated talcose quartzite, called
itacolumite, is common in some gold regions, as in Brazil and North
Carolina, and schists containing specular iron or granular magnetite
sometimes inclose gold.
The gold of quartz veins occurs in the form of plates, strings, and
thin scales, as well as in crystalline grains of greater or less dimensions
these are frequently apparent to the eye, but rock showing no visible
traces of gold is often sufficiently rich to admit of being treated with
profitable results.
GOLD.
685
Native gold invariably contains a certain amount of silver, and often
traces of copper and iron. According to Dana, the average proportion
of gold in the native gold of California is 880 thousandths. Australian
gold is usually purer than Californian, and averages from 900 to 960
thousandths of pure metal. The gold of Canada contains from 10 to 15
per cent. of silver, whilst that from Nova Scotia is often very pure.
It is not however from the treatment of auriferous quartz that the
principal portion of the gold of commerce is derived; a very large pro-
portion of it being obtained from alluvial diggings, in which gold is
separated from associated sands and gravels by various systems of
washing.
}..
In these deposits nature has, on a vast scale, performed the operations
of crushing and washing, and has finally deposited the precious metal in
positions from which it can be cheaply and conveniently extracted. To
this circumstance are mainly attributable the sudden fluctuations which
have, from time to time, taken place in the gold-production of the world.
On the discovery of a new and extensive gold-region a large amount of
unskilled labour is at once applied to the extraction of gold from alluvial
diggings, whilst to obtain the same weight of metal from quartz veins
would necessitate the application of skilled labour and the expenditure
of a large amount of time and money. Indeed, had not this natural dis-
integration and concentration taken place, the larger portion of the gold
annually collected could not have been advantageously brought into the
market. In California the auriferous gravel-beds are of vast extent, and
have sometimes a thickness of 250 feet.
Alluvial gold occurs in the form of flattened grains or scales of dif-
ferent degrees of fineness, the size depending partly on its original form
of occurrence, and partly on the distance to which it has been transported
by the agency of water. As before stated, gold is widely distributed
over the surface of the globe; it occurs in rocks of various ages, from the
oldest up to the Cretaceous. But although this metal occurs in many
regions of metamorphosed and crystalline slates, it is in comparatively few
localities that it exists in sufficient quantities to render its extraction
remunerative.
In Cornwall and Devon the tin-streams afford occasional specimens
of gold, but not in sufficient quantities to make its collection a matter of
commercial importance. The older slaty rocks of North Wales, and par-
ticularly those of Merionethshire, have long been known to inclose veins
which are more or less auriferous. This gold-bearing district would
appear, however, to be confined to an area of about twenty-five square
miles, principally lying on the north of the road leading from Dolgelly
to Barmouth.
It has been ascertained that many of the quartz veins occurring in
this neighbourhood contain gold, but the amount found has, in all cases,
proved insufficient to pay working expenses. In 1861, nearly 3,000 ozs.
were obtained from the Vigra and Clogau mines alone; and this result,
having become widely known, caused considerable local excitement, which
led to the extensive exploration of nearly all the quartz veins of the
686
ELEMENTS OF METALLURGY.
district. These operations were carried on, with gradually-declining acti-
vity, during some four or five years, at the end of which period those
embarked in the enterprise had generally become satisfied that gold
mining in Wales was not likely to be remunerative. The total quantity
of gold raised from the commencement of operations in North Wales up
to the 1st of April, 1866, amounted to 12,800 ozs., of which the Vigra
and Clogau produced 11,778 ozs. The chief portion of the gold in these
mines was met with in the form of a short deposit, which soon became
exhausted, and the undertaking is now abandoned.
In Scotland, gold occurs at Leadhills in Lanarkshire, and at Glen
Coich in Perthshire, but in very small quantities only, although in the
time of Elizabeth extensive washings for gold were carried on in the
alluviums of Leadhills. More recently gold has been discovered in
Sutherlandshire, and three or four years since numerous articles appeared
in the newspapers with regard to the alleged richness of these diggings.
Such reports attracted to the district numerous returned Australian and
Californian miners; but their labours were comparatively unproductive,
and the so-called "Sutherlandshire gold-fields" are no longer heard of.
Towards the close of the last century, a considerable quantity of
gold was discovered in the county of Wicklow, disseminated in a quartzose
and ferruginous sand. This gold was found chiefly in the form of
nuggets of considerable size, and one was obtained weighing 22 ozs.
For a short time this gold was collected on a comparatively large scale
by the peasantry of the neighbourhood, who, in the course of two months
gathered an amount for which £10,000 sterling was paid. The working
of the deposit was subsequently undertaken by Government, but the
supply soon became exhausted, and, after having been about two years in
operation, with unprofitable results, the works were abandoned.
France possesses no gold mines, but the sands of some of her rivers
are, to a small extent, auriferous. The only quartz vein which has been
known to contain gold is that of La Gardette, in the Department of
Isère, which was discovered in 1700, and on which workings were in-
termittently carried on up to the year 1841; but the production was ex-
ceedingly small. The Rhine has, for centuries, produced small quantities
of gold, its sands having been more or less extensively worked in the
neighbourhood of Strasburg, &c. In 1846, M. Daubrée made a report
to the Academy of Sciences, in which he states that the most productive
gravels were those deposited below sandbanks or gravel islands, which
had become eroded by the action of the river, and that gold was found
in a somewhat concentrated state only in the coarser gravels, from
which the finer sands had been removed by running water. The yield
of the year 1846 was estimated by M. Daubrée at £1,800, the washers
earning, on an average, from one and a half to two francs per diem.
The Rhone and several other French rivers have produced small quantities
of gold, and the Ariège is said to have derived its name from the amount
of auriferous sands it formerly deposited.
Gold mines were successively worked in Spain by the Phoenicians,
Romans, and Moors, and, although the amount now obtained from that
GOLD.
687
country is insignificant, it is stated to have, at one period, produced large
quantities of the precious metal. The present small yield is derived
from washing the sands of rivers and streams, and the total annual value
obtained may be estimated at £1,500.
A great number of localities in Italy were known to the ancients as
producing gold, and at one period this metal was worked so extensively,
that the quantity produced is said to have caused a reduction of one-third
in its price throughout the country. At present, the only gold mines of
any importance are in the north of Piedmont. The chief amalgamation
works are situated on various small streams near the foot of Monte Rosa,
where a considerable amount of gold is found in the valleys of Anzasca,
Toppa, and Antrona. The principal mines are those of Vallanzasca, Val
Toppa, and Pestarena, which are being worked by English capitalists, and
where the ores consist of a compact auriferous pyrites. The aggregate
produce of these mines during the year 1866 amounted to 5,952 ozs. of
the total value of £19,150 9s. 8d. Their production has since very
materially declined.
The amount of gold annually produced in Germany is small, although
in some localities washing and mining operations in pursuit of this metal
have been interruptedly carried on from remote antiquity.
In Tyrol and Salzburg a little gold has been long obtained by the
treatment of exceedingly poor ores. At Zell, in 1847, the average yield
of the vein-stuff treated was 21 dwts. per ton. The annual production
of the mines of Tyrol and Salzburg may be estimated at 65 lbs. troy.
The most important gold mines of Europe are those of Hungary and
Transylvania, where gold is found in veins of auriferous pyrites asso-
ciated with galena and sulphides of silver. The mines of Hungary have
been worked since the eighth century, and all the operations are con-
ducted with much skill and economy. In those of Königsberg gold is
disseminated with ores of sulphide of silver, which occur in veins inclosed
in a decomposed feldspathic rock. At Schemnitz, Kremnitz, Neusohl,
and Libethen, the ores afford both silver and gold, together with a suffi-
cient amount of galena to materially assist in their metallurgical treat-
ment. In Transylvania some of the mines afford a rare combination of
gold and tellurium. The production of gold from the mines of the
Austrian Empire amounted in 1865 to 4,900 lbs. troy.
In Sweden there is a mine at Edelfors, in Småland, where gold occurs
in auriferous pyrites, but the produce of the country is totally insig-
nificant.
The gold mines of the Russian Empire are situated partly on the
eastern flanks of the Urals and partly in the districts of Perm, Tomsk,
and Yenisseisk, &c., in the interior of Siberia. The auriferous detritus of
the Russian possessions is, however, poor in comparison with deposits
which have been found more recently in California and Australia; for
although some considerable masses have occasionally been met with,
much of the auriferous ground now profitably worked in Russia, where
labour is cheap and water abundant, would, if situated in California or
Australia, be totally valueless.
688
ELEMENTS OF METALLURGY.
The produce of the Russian washings from 1850 to 1860 amounted
to 687,025 lbs. troy.
Gold is found in the rivers of Syria and other parts of Asia Minor,
and the Pactolus, a river of Lydia, was anciently celebrated for its
golden sands. Gold mines are also known to be worked in Thibet,
where this metal is found in quartz veins traversing a crumbling granite,
of a reddish colour. It is also met with in Hindostan, as well as in the
islands of the Eastern Archipelago. Gold-washing is likewise carried
on in China and Japan, both of which countries are believed to afford
a considerable annual yield; comparatively recent advices from China
state that new gold-fields have been opened up in Shangtung, Chufoo
district.
Africa was probably the source of a large proportion of the gold pos-
sessed by the ancients; and nearly all modern travellers who have pene-
trated into the interior of that continent agree in their accounts of its
wealth. The whole of the gold which Africa now supplies is in the
form of dust and water-worn grains, evidently obtained from alluvial
washings.
The gold of Sennaar and Southern Abyssinia occurs in quartz inclosed
in granite, and is associated with hæmatite and iron pyrites; gold is also
found in alluvial deposits of an ochreous character.
A considerable amount of interest was recently excited by a report
of the discovery of gold-fields at the Cape of Good Hope, adjoining the
frontier of the Transvaal Republic. No practical results, on an exten-
sive scale, appear, however, to have been hitherto obtained, and we must
consequently await the further development of this region before arriving
at any conclusion with regard to its extent and importance.
The annual amount of gold now annually furnished by Africa is esti-
mated at about 3,800 lbs. troy.
The gold-fields of the United States of America may be divided
into two great geographical sections, viz., those of the Atlantic slope,
or the Appalachian gold-region, which has been worked to some extent
for the last fifty years, and that of the Pacific States, of which California
may be considered the most important, which, within six years after
its discovery, in 1848, had produced more than twelve times the total
amount of gold which had, up to that period, been obtained from the
region on the Atlantic shores.
The Appalachian gold-fields are included within the States of Vir-
ginia, North Carolina, South Carolina, Georgia, Tennessee, and Alabama,
although some others have occasionally afforded specimens of the precious
metal. The first notice of the discovery of gold occurs in Jefferson's
• Notes on Virginia;' Drayton, in his View of South Carolina' (1802),
also mentions the finding of a small piece of this metal on Paris
Mountain.
The first United States gold was coined in 1825, and from that time
up to 1830 four-fifths of the gold coinage of the country was of American
gold. From 1804 to 1827 North Carolina furnished the whole of the
gold produced in the United States, amounting to $110,000; but in
GOLD.
689
1829 Virginia contributed $2,500, and in the same year South Carolina
yielded $3,500. In 1830 Georgia made its first deposit at the Mint,
amounting to no less than $212,000. Previously to 1825, all the gold
of North Carolina had been procured from washings, but in that year
auriferous veins were discovered. This turned attention from the
deposit mines" to "vein mines," and led to the discovery of gold veins
in various localities in that and the adjoining States.
CC
In 1852-53, the discoveries which had then been recently made in
California, produced great excitement with regard to gold mining gene-
rally, and attention was, as a natural consequence, directed to the auri-
ferous districts of the southern States. Many English and American
companies were formed for the purpose of working the mines of the
Atlantic coast, and for a time mining operations were actively prosecuted.
In this case, however, as on a former occasion, wild speculation was
carried on to a greater extent than legitimate mining, and although
many of the undertakings might perhaps have afforded satisfactory
returns if judiciously carried out, the results were, a second time, gene-
rally disastrous, and the southern gold-region, after a short period of
spasmodic activity, again subsided into comparative disrepute.
Although it had long been known that gold had occasionally been
found in California, yet until the acquisition of that region by the
United States of America but little was known either of the country or
of its productions. The first practical discovery of this metal was made
either late in February, or early in March, 1848.
Colonel Sutter had contracted with a Mr. Marshall for the supply of a
large amount of lumber, and in order to execute this contract a saw-mill
was erected on the south fork of the American River, at a place now called
Coloma. When this was set to work, the water, rushing rapidly through the
tail-race, exposed certain bright metallic particles, which were recognised
as gold. It was at first sought to keep this discovery secret, but this
was soon found impossible, and the news shortly after reaching San
Francisco caused an excitement which quickly emptied it of its inhabit-
ants, amounting then to only a few hundreds in number. From this
time the rush to the diggings became so great, that when the governor of
the State visited the district in the following July, he found that 4,000
people were already employed in washing on the American River and its
tributaries, and were extracting gold of the value of from $30,000 to
$40,000 daily.
The fame of these extraordinary discoveries became widely spread
during the latter months of 1848 and the spring of 1849, and a rapid
influx of immigration commenced, which has, with more or less activity,
continued to the present time, and has already resulted in an addition of
at least 3,500,000 lbs. troy of gold, value £175,000,000, to the available
bullion of the world.
The great sedimentary auriferous belt of California lies on the western
slope of the Sierra Nevada, beginning in the vicinity of the Téjon Pass,
and extending through the State to its most northern limit. The prin-
cipal gold-producing region may, however, be said to occupy the western
2 Y
690
ELEMENTS OF METALLURGY.
portions of the counties of Mariposa, Tuolumne, Calaveras, Amador, El
Dorado, Placer, Nevada, Sierra, and Plumas, with portions of the eastern
sides of Yuba and Butte counties.
The slates of the auriferous belt are principally Jurassic, although
the presence of Triassic fossils indicates that a certain portion of them
belong to that age.
The gold of California and Australia is derived from the three fol-
lowing sources :—
1st. From auriferous veins, most frequently inclosed in metamorphic
slates.
2nd. From deposits of alluvial gold occupying ancient river-
courses.
3rd. From deposits in which the gold of ancient river-systems has
been re-distributed by modern streams.
Auriferous veins, like all others, are exceedingly variable, not only in
their dimensions, but also in their productiveness. It is, however,
generally observed that the widest veins are not usually the richest, and
that some of the quartzose bands running parallel with the inclosing
walls are uniformly more productive than others. As a general rule those
veins are most auriferous which contain a considerable amount of various
metallic sulphides, more particularly iron pyrites, and but few which do
not afford a notable percentage of this mineral are found permanently
remunerative.
Contrary to an opinion very generally entertained a few years since,
gold veins are not found to be more liable to impoverishment in depth
than other metalliferous lodes, some of those on the Pacific coast having
been worked, on their inclination, to a depth of more than 1,400 feet
without experiencing any perceptible diminution in yield.
In many localities, and particularly between the south and middle
forks of the Yuba River, the auriferous gravels belonging to the second
class have, under ordinary circumstances, a thickness of 120 feet; and
when, as is sometimes the case, these ancient river-beds have been pro-
tected by a capping of basalt, their thickness not unfrequently exceeds
250 feet. These deposits are principally worked by a process known as
hydraulic mining, and yield one-half of the gold annually produced in
the country.
These ancient river-beds, or deep placers, are believed to be of Pliocene
age, and frequently inclose trunks of large trees which have become
entirely silicified.
The attention of the first miners was exclusively directed to deposits
of the third class, or shallow placers, in which gold lay near the surface
and within the reach of those who, without capital, were only in possession
of ordinary mining tools. These shallow diggings, however, gradually
became exhausted, and at the expiration of some five or six years attention
was generally directed to deeper deposits.
The greatest exportation of gold from California took place in the
year 1852-53, when the amount was estimated at about 240,000 lbs. troy ;
from that period the export of gold bullion has been gradually diminish-
GOLD.
691
ing, and the present annual production of the State is probably not above
80,000 lbs.
It must not be forgotten, however, that California is by no means the
only gold-producing State or Territory west of the Rocky Mountains.
Nevada, Colorado, Idaho, Utah, Oregon, and Washington, all produce
gold; and it is believed that the total annual yield of this metal in the
United States cannot now be far short of 180,000 lbs. troy.
Although the most productive known gold-fields of North America
are comprehended within the limits of the United States, several of the
British possessions on that continent annually afford a certain amount of
gold.
The existence of this metal in Canada first attracted attention in
1847, although it is stated that a French Canadian had found specimens
of some value long before that date. In 1850 gold was discovered in the
alluviums of the Chaudière and various neighbouring streams; and at
the Great Exhibition of 1851 specimens were exhibited by Sir William
Logan, the Government Geologist, and by the then recently-formed
Chaudière Gold-Mining Company.
Up to the present time the results obtained, both from the alluvial
washings and from quartz-mining operations, have been unsatisfactory,
and the gold production of Canada still remains exceedingly small.
Mr. Douglas, the governor of Vancouver's Island in 1856, reported
the discovery of gold in British territory north of latitude 49°, but
stated that in consequence of the hostile attitude assumed by Indians
the number of diggers was small. In 1858, however, the stream of
immigration set in with sufficient force to overcome the opposition of the
natives, and from that period British Columbia has become permanently
recognised as a gold-producing country.
It has, however, been found, that although the country is unquestion-
ably rich in gold, the winters are so exceedingly severe as to preclude
the possibility of continuous mining during the colder months, and,
consequently the miner has to expend in winter a large portion of the
money which he had economised during the summer months. This
severity of the climate has caused British Columbia to be somewhat un-
popular among gold miners, and their number has consequently decreased
within the last four years. Nearly the whole of the gold produced now
finds its way to San Francisco; but as a large proportion reaches that
city through private hands it is impossible to obtain exact statistics. The
total annual yield of British Columbia is, however, probably between
12,000 and 15,000 lbs. troy.
A few years since attention was called to the Province of Nova Scotia
by an article published in 'Blackwood's Magazine,' in which it was stated
that gold would be found in the hills south of Annapolis; and a compari-
son was instituted between that locality and the valley of the Sacramento.
Many persons were induced, by this article, to leave their ordinary occupa-
tions to seek for gold, but their researches in all cases proved unsuccessful,
and the explorations were finally abandoned. So long ago also as 1855 Dr.
Dawson, in his Acadian Geology,' when describing some of the meta-
2 x 2
692
ELEMENTS OF METALLURGY.
morphic rocks of the country, observes: "Quartz veins, however, occur
abundantly in some parts of this district, and it would not be wonderful
if some of them should be found to be auriferous."
In the month of March, 1861, a man who was stooping to drink at a
rivulet observed a piece of gold among the pebbles at the bottom. During
the course of the following June gold was discovered in quartz veins in
the cliff near Lunenburg, and subsequently, in the sands on the beach
beneath the headland, in which auriferous veinstone had been previously
met with. Gold-discoveries now followed each other in rapid succession
at Lawrencetown, Dartmouth, Sheet Harbour, Isaacs Harbour, Sherbrooke,
Waverley, Oldham, and elsewhere.
Auriferous drift occurs in Nova Scotia only in patches of very limited
extent, and almost the whole of the gold hitherto obtained has been the
produce of the treatment of gold quartz. The veins are, generally speak-
ing, small, but tolerably rich in gold. The present annual production of
gold in this Province is about 1,200 lbs. troy.
Mexico, although rich in silver, yields comparatively little gold,
almost the whole of the latter metal being separated from argentiferous
ores.
Little is known respecting the auriferous districts of Central America
except that Costa Rica and some other States annually produce a certain
amount of this metal, and that an English company is engaged, with
somewhat doubtful prospects of ultimate success, in gold mining in
Nicaragua.
The most important gold country of South America is Brazil, where
the principal mines are situated in the province of Minas Geraes, and
are chiefly wrought on extensive veins and deposits of auriferous pyrites.
The Morro Velho mine, belonging to the St. John d'El Rey Company,
was, up to within the last seven years, the largest and most prosperous
gold mine in Brazil, having, since 1839, produced a net profit to the pro-
prietors of over a million sterling. This undertaking is, however, at
present suffering from the effects of a disastrous fire, probably caused
by the heat resulting from the oxidation of pyrites, producing combustion
of the timber-work; and it, unfortunately, cannot be re-established in
its former highly satisfactory condition without the expenditure of a large
amount of time and capital.
Brazil afforded its largest yield of gold about the middle of the
eighteenth century, before the comparative exhaustion of its rich alluvial
deposits, when the amount on which the royal fifth was annually paid
varied from 17,000 to 21,500 lbs. The production of Minas Geraes, by
far the most productive mining district of the country, was estimated in
1866 at 6,000 lbs. troy per annum.
The first authenticated discovery of gold in Australia was made in
1839, by Count Strzelecki, who communicated the fact to Sir George
Gipps, then governor of the colony of New South Wales. The presence
of the precious metal was again specially noticed in 1841 by the Rev.
W. B. Clarke, of Sydney. The attention of the colonial public was not,
however, seriously directed to this subject until the existence of an
GOLD.
693
extensive gold-field, almost throughout Australia, was announced in 1851
by Mr. E. H. Hargreaves, a returned Californian miner.
It would appear from the investigations of Mr. A. R. C. Selwyn that
the age of the gold-bearing strata of Victoria is much greater than that of
the auriferous rocks of California, and further, that they most frequently
belong to the Silurian epoch.
With regard to the occurrence of the precious metal in Victoria, Mr.
R. B. Smyth, Secretary of Mines for the Colony, remarks (Intercolonial
Exhibition, 1861'): "Gold is now found to occur not only in quartz veins
and the alluvial deposits derived from these and the surrounding rocks,
but also in the claystone itself; and, contrary to expectation, flat bands of
auriferous quartz have been discovered in dykes of diorite, which inter-
sects the Upper Silurian or Lower Devonian rocks. Quartz of extraor-
dinary richness has been obtained from these bands, and the new
experience of the miner is leading him to look for gold in places hitherto
entirely neglected. It is probable that some time may be lost, and that
his labours may not always be well directed or successful, but it is com-
mendable that he should not be deterred from explorations by warnings
and remonstrances founded on surmises often baseless. If he had closely
followed the older precepts we should, at this moment, have been de-
pendent for our yield of gold on the shallower alluviums and the surface
only of the veins of quartz."
In Australia, as in California, the gold first obtained was entirely
derived from washing the more recent gravels; but ancient river-beds,
often covered by a thick capping of basalt, have since proved highly pro-
ductive. As in California, quartz veins are now advantageously worked to
very considerable depths below the surface.
The largest gold-yield of Victoria was in the year 1856, when the total
produce was 249,000 lbs. troy; its annual production is, at the present
time, about 130,000 lbs. troy, worth £6,500,000. The total amount of
gold produced in the colony, from 1851 to the present time, is estimated
at about 3,000,000 lbs. troy; worth, approximately, £150,000,000.
The produce of the gold-fields of New South Wales, since their dis-
covery in 1851, is estimated at some 400,000 lbs. only, representing a
value of £20,000,000.
South Australia and Tasmania both produce annually a certain amount
of gold, but the quantity is comparatively small, since from 1851 to the
close of 1860 the total weight exported, including that coming from New
Zealand, was only valued at £374,000. Queensland also yields a certain
quantity of gold.
Gold was first discovered in New Zealand in 1842, and the principal
portion of that which has been since exported from the colony has been
the produce of the South Island. In 1864 the gold exported from the
North Island amounted to 280 lbs., whilst the South Island furnished
1,400 lbs. troy. Various important mining districts have, however, been
discovered since that period, and quartz crushing is now being actively
prosecuted. The annual yield of this colony is therefore believed to be,
at present, in excess of the above amount.
694
ELEMENTS OF METALLURGY.
Various other localities annually afford small amounts of this metal,
either from alluvial washings or from regular mining. The total yield of
such operations is, however, comparatively so small that any special
mention of them would be superfluous. The total annual yield of the
world is believed to be, now, about 460,000 lbs. troy, representing an
approximate value of £23,000,000.
ASSAY OF AURIFEROUS MINERALS.
Minerals containing gold are assayed in precisely the same way as
ores of silver, but as the former usually contain a very small propor-
tion of the precious metal, it becomes necessary to operate on a larger
quantity of the substance to be examined. When these compounds con-
tain lead they may be conveniently fused with a proper quantity of black
flux; if, instead of containing lead, they consist of oxidised bodies, but
are free from that metal, the assay may be advantageously conducted by
the addition of a mixture of litharge and powdered charcoal or black
flux; when chiefly composed of siliceous and earthy matters mixed with
oxidisable substances, such as mispickel, or iron or copper pyrites, their
fusion may be effected by the use of litharge only; and lastly, when
these substances so preponderate as to yield too large a button of lead
for convenient cupellation, a mixture of litharge and nitre may be used
with advantage. It is, however, necessary to remember, that when any
of these compounds contain sulphur it is of importance that the whole
of it should be either removed or oxidised during the process of assaying,
as otherwise, and particularly in presence of alkaline sulphides, a portion
of the gold might enter into combination with the slags in such a way
as not to be separated by lead.
CUPELLATION. The buttons of alloy thus obtained are cupelled, with
the precautions enumerated when treating of the assay of alloys of silver,
although, when gold is the metal sought, the process is in a slight
degree varied.
When the resulting button consists merely of an alloy of lead, silver
and gold, together with a small admixture of one or more oxidisable
metals, its cupellation presents even less difficulty than in the case of
alloys of lead and silver only, because in the first place gold is less
volatile than silver, and consequently may be exposed to a greater heat,
and in the second place less loss is experienced at high temperatures by
absorption into the cupel.
When, in addition to gold, silver, and lead, the button obtained by
assay likewise contains copper, it must be cupelled like the similar
alloys of silver; but as copper possesses a much greater affinity for gold
than it has for silver, a large addition of lead must be made in order to
insure the production of a pure button.
PARTING.—When, as is almost universally the case, the button
obtained by the fusion of the ore contains, in addition to lead and gold,
a notable proportion of silver, it must be cupelled at a moderate temper-
ature, and, if necessary, an additional quantity of silver added. By
T
GOLD.
695
operating in this way, the button obtained on the cupel consists of an
alloy of silver and gold, which is afterwards treated with an excess of
nitric acid; this effects the solution of the silver, and leaves the gold
untouched in the form of a brown powder, in the bottom of the flask in
which the experiment has been conducted. In order, however, to obtain
exact results, it is necessary that a certain relation should exist between
the amount of the two metals of which the alloy is composed, since if
the silver be not present in sufficient quantity the mixture is not com-
pletely attacked by the nitric acid; whilst on the other hand, when
too large a proportion of this metal is added, the gold remains in a
pulverulent form, which renders its collection for the purpose of weighing
somewhat difficult.
The above-described operation, which has received the name of
"parting," succeeds best when the alloy contains a little less than three
parts of silver to one of gold; and therefore, in all cases, the addition
of silver must be so managed as to agree as closely as possible with
this proportion. If the alloy contain less than two and a half parts of
silver to one of gold, the solution of the silver cannot be completely
effected, since in this case some of its particles are so enveloped in gold as
to resist the action of the acid.
The operation of adding the proper amount of silver to an alloy to
reduce it to the right standard for the process of parting is called " inquar-
tation." The quantity of silver necessary for this purpose is estimated
in accordance with the approximative composition of the alloy produced
by direct cupellation of the button obtained by assay, which may be
judged of, in many instances, by a simple inspection of its colour and
hardness.
The inquartated button, when obtained, should be carefully flattened
with a polished hammer on a steel anvil, and afterwards attacked in a
small flask or large test tube by nitric acid of specific gravity 1·18.
After having been boiled for about ten minutes with acid of this
strength, the liquid is carefully poured off, and the residue heated to
ebullition, during a few minutes, in acid of the specific gravity 1·28.
The acid is now carefully decanted, and the residual gold, after being
completely washed with distilled water, is transferred to a thin porcelain
capsule, from which the water is partially removed, and the remainder
evaporated by exposure in a water-bath. When perfectly freed from
moisture, the pulverulent gold may either be weighed directly in the
capsule in which it has been dried, or be folded in a little poor lead-foil
and again passed to the cupel, so as to obtain it in the form of a metallic
globule.
ASSAY OF GOLD QUARTZ, ETC.—To make an assay of auriferous quartz,
the sample to be operated on must be finely pulverised, and may be sub-
sequently mixed with red lead or litharge, together with a little carbonate
of sodium, borax, and an amount of pounded charcoal, sufficient for the
production of a button of lead of a convenient size for cupellation.
In the case of very poor ores, the silver derived from the oxide of
lead will frequently be sufficient for the purpose of inquartation; whilst,
696
ELEMENTS OF METALLURGY.
for the examination of richer ores, the addition of a little pure silver, at
the time of placing the button on the cupel, becomes necessary.
If, besides gold, the ore contains iron pyrites, or any other sul-
phurised mineral, the addition of a reducing agent, such as charcoal, may
sometimes be dispensed with, and the fusion may be made either with
oxide of lead alone or with oxide of lead and a little borax.
When pyrites, or any other metallic sulphide, is present in large
quantities, the sample should be first roasted until all traces of sulphur
have ceased to be evolved, and then treated as in the case of substances
not containing that body, but with the addition of a larger proportion of
charcoal and borax. It must, however, be borne in mind, that when any
compound containing sulphur is to be assayed for gold, all the sulphur
should be either expelled by a preliminary roasting, or be oxidised during
the operation; it may otherwise give rise to the formation of alkaline
and other sulphides, which are liable to cause a portion of the gold to
enter into combination with the slags.
It may be here remarked, that although it is easy to estimate with a
considerable degree of accuracy the amount of gold contained in a given
quantity of ore, it is much more difficult to obtain a fair average sample
of the total produce of a vein. When the metal is in a state of fine
division, and uniformly disseminated throughout the matrix, this presents
comparatively little difficulty; but when, on the contrary, it is granular,
and occurs in irregular deposits, much care is necessary in order to insure
trustworthy assays.
It is therefore of importance, that whenever ores are to be assayed
for gold, great care should be taken in procuring the samples on which
the experiment is to be conducted. With this view, the heaps should be
well cut through, and 2 or 3 tons taken out of each. The ore thus ob-
tained must be reduced to fragments of the size of beans, which, when
proper crushing machinery is not at hand, may be accomplished by
breaking with a hammer on an iron plate.
The ore thus prepared must now be thoroughly mixed, made into a
heap, and again cut through, taking out of it this time 3 or 4 cwts.,
which are reduced to the state of a fine powder, either in a crushing mill,
in a large mortar, or on an iron plate. After being again mixed, the
powdered ore is cut through, and about 20 lbs. weight taken for the
purpose of being still further reduced in size; this must be passed
through a sieve of fine wire-gauze. On the sample thus prepared, five or
six different assays are to be made, and the mean of the results is taken
as the produce of the ore examined. By operating as above described,
great accuracy may be insured; but when a less degree of exactitude is
sufficient, the quantities of ore crushed may be somewhat reduced, and
the number of assays fewer.
Fusion with Litharge, Carbonate of Soda, &c.—When the quartz con-
tains traces only of iron pyrites, or of any other sulphide, 1,000 grains of
finely-divided ore, may be carefully mixed with three times its weight of
litharge, or red lead, 200 grains of carbonate of sodium, 200 grains of
borax, and from 15 to 20 grains of pulverised charcoal. This mixture
GOLD.
697
must be introduced into an earthen crucible, of which it should not
occupy more than one-half the capacity, and after being thoroughly fused
in an assay furnace, the pot and its contents are removed by the use of
proper tongs, and allowed to cool. When sufficiently cold, the crucible is
broken, and the button of lead removed for the purpose of being cupelled.
If, in the first experiment, the button obtained weighs less than 100 grains,
a little more charcoal ought to have been added. Instead of breaking
the pot, the crucible, on being removed from the fire, may be held between
the bent jaws of a pair of tongs, and its contents poured into a conical
cast-iron mould.
Fusion with Red Lead or Litharge only.-In cases where the sample of
quartz to be operated on contains a sufficient amount of pyrites to reduce
a convenient quantity of lead for cupellation, the assay may be effected
by fusion with litharge, or red lead alone. When this method is em-
ployed, the oxide of lead must be used in large excess, and 1,000 grains
of the ore may be fused with from four to five times its weight of red
lead or litharge. If the button obtained in this way be not sufficiently
large, its size may be increased, to any desired extent, by the judicious
addition of lamp-black or powdered charcoal.
Auriferous Pyrites.—In order to determine the amount of gold con-
tained in auriferous pyrites, the sample should be first pulverised and
then roasted, until all odour of sulphur has ceased to be evolved. Mix
the roasted ore with half its weight of dry carbonate of sodium, twice its
weight of red lead or litharge, a proper amount of charcoal and some
fused borax; in other respects treat as before. The cupellation of
buttons thus obtained is to be conducted as described under the head
of "Estimation of Silver in Lead Ores.”
·
Inquartation.—It has already been stated that in order effectually to
dissolve out silver from an alloy of gold and of that metal, it is necessary
that the weight of the silver should be nearly three times greater than
that of the gold present. When, therefore, the amount of gold contained
in the leaden button is approximately known, the piece of silver added
should be of such a weight as to satisfy, as nearly as possible, this
condition. The only inconvenience, however, attending the addition of
too large an amount of silver, is that the gold obtained by the subse-
quent action of acid is thereby rendered flocculent.
Parting.—The button remaining on the test after cupellation is,
when sufficiently cold, flattened, and carefully cleaned with a hard
scratch-brush. After being examined by the aid of a lens, to satisfy
the assayer that it is free from extraneous matter, the flattened button is
taken between the jaws of a pair of forceps, and dropped into a long-
necked flask of about 2 ozs. capacity, containing pure and somewhat-
dilute nitric acid.
The flask and its contents are now heated until all action on the
alloy has ceased, and the liquid is carefully decanted. A little more
nitric acid is now poured on the assay, and again made to boil; water
is added, and the liquid poured off as before. The residual gold is then
carefully washed by decantation, and finally turned out, by a little care-
698
ELEMENTS OF METALLURGY.
ful manipulation, into a small porcelain capsule, in which it is slowly
dried, by being placed in a water-bath; it is finally heated to redness,
and subsequently weighed.
If, in addition to gold, the mineral also contains silver, and it be
desirable to ascertain its amount, it is necessary to first cupel the button
of lead without the addition of silver; the alloy thus obtained is weighed,
and its weight noted, deduction being made for the amount of silver
derived from the reduced oxide of lead, which must be ascertained by
experiment. It is also necessary to examine the red lead, or litharge, in
order to ascertain if it contain traces of gold, and in case of that metal
being likewise present, due allowance for the amount found must be made
on the produce obtained. If the silver be not sufficient for the purposes
of parting, more is added, by folding the bead, together with a bit of
pure silver, in a piece of lead free from the precious metals, and again
cupelling. Lastly, the alloy obtained is treated with nitric acid, and
the amount of gold present determined by weighing.
The weight of silver contained in the ore will evidently be represented
by that of the button of alloy from the first cupellation, less the united
weights of the gold in the ore, and of the silver and gold (if any) afforded
by the reduced oxide of lead.
In conclusion, it may be observed, that when proper precautions are
taken to obtain a fair average sample, and the mean of a sufficient number
of assays is taken, there is no difficulty in ascertaining, with a considerable
degree of accuracy, the yield of auriferous quartz.
ASSAY OF GOLD BULLION.
For the purpose of coinage and for the manufacture of jewelry, gold
is never employed in a pure state, but is almost universally alloyed with
a certain proportion of copper; this has the effect of hardening it, and
thus preventing excessive loss of weight through handling, or friction
against other bodies, whilst its colour and general appearance are not
sensibly affected. In this country the proportion of gold present in an
alloy is often estimated in carats. Unity is thus supposed to be divided
into 24 carats, whilst each carat is itself subdivided into 32 thirty-
secondths; so that unity may be considered as being actually made up of
768 thirty-secondths of a carat. In this way the gold coinage of the
United Kingdom is said to have a fineness of 22 carats, or, in other
words, every 24 parts of an English gold coin consist of 22 parts of pure
gold and two parts of copper. Estimated decimally, the British standard
for gold coin is 916.66 parts of fine gold in 1,000. The standard made
use of for the gold currency of France and of the United States of
America, is 900 thousandths.
The usual standard of good English jewelry is 18 carats, and articles
made of this alloy have generally the hall mark of the Goldsmiths' Ccm-
pany impressed upon them. A large proportion of the commoner kinds
of jewelry however, is made of from 12- to 9-carat gold.
In order to ascertain the value of a given weight of gold bullion, it
GOLD.
699
is necessary that it should be accurately assayed, and consequently a
piece is carefully cut from each bar and forwarded to a recognised assayer,
who determines the exact amount of the precious metal present.
For this purpose half a gramme of the alloy is carefully weighed
and subjected to cupellation with a proper quantity of lead, together with
an amount of pure silver equal to two and a half or three times the
weight of the gold supposed to be present.
The button removed from the cupel is squeezed, laterally, between the
jaws of a pair of strong pliers to loosen any adhering litharge, which is re-
moved by the aid of a stiff brush, and is afterwards flattened, by a smooth-
faced hammer on a polished anvil, into an elongated disc about 2 of an
inch in length. This, after being annealed, is passed repeatedly through a
flatting mill until it has assumed the form of a thin strip from 2 to 3 inches
in length, which is again annealed, and coiled upon itself by rolling between
the finger and thumb. The cornet is now introduced into a long-necked
flask containing about an ounce of pure nitric acid of 22° Baumé = 1∙18
sp. gr., and boiled until red fumes have ceased to be given off. This acid
is carefully poured off, and the cornet again twice boiled, each time for
about ten minutes, in acid of 32° Baumé = 1.28 sp. gr. In the last two
boilings a piece of charcoal, consisting of half of a charred pea, is intro-
duced for the purpose of preventing ebullition from taking place irregu-
larly, and with explosions, by which either the cornet might be broken, or
a portion of the liquid projected out of the flask. The acid is now poured
off, and, after the third attack, the cornet is twice washed with distilled
water. The flask is now filled with water and reversed into a small
crucible of fine clay covering its neck; by this means the cornet is
deposited gently, and without breaking, in the bottom of the crucible, and
the water which covers it is poured off. The crucible and its contents
are heated to redness in the muffle, care being taken to avoid the
fusion of the gold. From the weight of the cornet obtained, the fineness
of the alloy is calculated, but in all cases where great accuracy is
required at least two separate assays are made of each bar.
After boiling in nitric acid, the cornet is of a brownish-yellow colour,
of a spongy texture, and exceedingly fragile, so that it could not be
touched by the fingers without breaking; it is therefore transferred to the
crucible, together with a portion of the water contained in the flask. By
heating it in the way described, it acquires an amount of cohesion which
admits of its being readily handled without danger of breaking, and at
the same time it assumes a decidedly metallic aspect; its volume is also
considerably diminished.
In establishments in which large numbers of assays of gold bullion
are habitually made, the use of glass flasks for the attack of the cornets
by nitric acid, is now frequently dispensed with, and instead, an apparatus
made of platinum is employed. This consists of a shallow dish, furnished
with a rack, in which are inserted a number of small vessels, also of
platinum, having nearly the shape of an ordinary thimble, with apertures
which admit of the free entrance of the acid contained in the dish in
which they are inclosed.
Into these the cornets are inserted, and nitric
700
ELEMENTS OF METALLURGY.
acid of the required strength is poured into the outer dish, which is
heated, either over a sand-bath or a gas-burner. As this acid serves for the
attack of all the cornets inclosed in the several small platinum cullenders,
a considerable economy of time is effected, since by one operation the
acid is charged on the whole of them. While the attack is being made
the apparatus is covered by a funnel-shaped dome of glass, communi-
cating, by means of a glass tube, with a condenser in connection with the
chimney of the laboratory. In this way a considerable amount of the
acid is recovered, and all unpleasant fumes are avoided.
CC
Formerly the return was made to the Bank to the one-eighth of a
carat, "better" or worse" than standard, and tables were used for readily
converting one form of return to the other; but returns are now made in
thousandths and thirds of thousandths. The amount of lead necessary
for passing an alloy of gold on the cupel depends on the quantity of
copper which may be present. The following are the proportions
which, after careful experiment, have been generally adopted:
Amount of Gold in Alloy.
Amount of Lead necessary
for Cupellation.
1 part
10 parts
1,000
900
800
•
•
16
"
700
22
600
24
500
26
400
300
34
200
100
In the case of ordinary gold bars, in which the proportion of copper is
invariably small, the half gramme employed for assay is passed to the
cupel with two grammes only of lead. A piece of copper wire weighing
15 milligrammes is also often added, to render the button malleable, and
prevent it from cracking when flattened under the rolls. However care-
fully and skilfully the parting of the resulting button may be conducted,
the cornet of gold will frequently be found to retain minute traces of
silver, by which its weight will be, to a small extent, increased. This
increase of weight or surcharge is most observed in cornets obtained
from bars containing a very small quantity only of copper, since when the
proportion of that metal is considerable, and a large amount of lead has
consequently to be employed during its cupellation, a loss of gold takes
place by absorption into the pores of the cupel. In the assay of bars of
bullion of an intermediate composition, the loss of gold during cupella-
tion, and the surcharge of silver remaining after parting, not unfrequently
counterbalance each other, and the true fineness of the alloy is directly
obtained with a sufficient degree of accuracy. It is however necessary,
in order to ascertain the amount of surcharge, to have check assays or
proofs made of pure gold and copper, according to the supposed quality
of the alloys.
The following results of numerous experiments made in the Paris
GOLD.
701
Mint upon mixtures of fine gold and copper in the proportions indicated
in the Table, afford data for calculating the necessary corrections:-

Copper. Gold.
Result obtained. Difference.
·
100
900
900·25
+0.25
200
800
800.50
+0.50
300
700
700.00
0.00
400
600
600.00
0.00
500
500
499.50)
600
400
399 50
•
700
300
299.50
-0.50
800
200
199·50
900
100
99.50)
The last traces of silver may be removed by heating the cornet before
it has been exposed to the annealing action of the muffle, with fused acid
sulphate of potassium in a small clay or porcelain crucible. When
sufficiently cooled the whole is treated with water containing a little
sulphuric acid, and the cornet subsequently dried and ignited.
Determination by the Touchstone, &c.-The method of assay already
described, although perfectly adapted for the determination of the value
of bullion and other unmanufactured products, cannot be conveniently
applied to the examination of jewelry, since it would be necessary to
destroy the object in order to ascertain its composition; a method is,
therefore, employed by which its standard is readily determined to
within 1 per cent. of the truth, whilst the most delicately-chased article
is in no way disfigured by the trial. This process essentially consists
in rubbing some convenient part of the object to be examined on a hard
siliceous stone of a black colour, on which it thus leaves distinct metallic
traces; from the aspect of these marks, and from their behaviour when
treated with nitric acid or with a weak solution of aqua regia, the assayer
judges of the purity of the gold subjected to examination. The material
employed for this purpose, which is generally known by the name of
touchstone, is a fine-grained, dark-coloured variety of quartzite, said to
have been anciently brought from Lydia, although stones of equally
good quality are obtained in Saxony, Bohemia, and numerous other
localities.
In order to be enabled to judge of the value of an alloy from the
nature of the mark left by it on the surface of the stone, the assayer is
furnished with a series of small bars, or touch-needles, formed of alloys
of copper and gold, of which the composition has been accurately
determined.
The trace left on the stone by the alloy to be examined, is successively
compared, both before and after the action of an acid, with the different
marks obtained from these several needles, and it is supposed to possess a
similar composition to that of the needle whose mark agrees most closely
with it under both these circumstances. The acid most commonly
702
ELEMENTS OF METALLURGY.
employed for this purpose is nitric acid of sp. gr. 1·28, to which about 2 per
cent. of hydrochloric acid is sometimes added. In making these assays,
the first streak obtained on the stone cannot be employed to ascertain
the composition of the object examined, as the surface of jewelry is
rendered, by the process of "colouring," of a higher standard than that
of the alloy of which it is throughout composed. For this reason, there-
fore, the object must be passed once or twice over the surface of the
stone, in order to remove the superficial coating of richer alloy, before
making the streak from the comparison of which with those of the needles
the commercial value of the mixture is to be determined. This method,
although affording much less accurate results than those obtained by
inquartation and parting, is nevertheless for many purposes sufficiently
exact.
The colouring, as it is called, of jewelry, is effected by externally
dissolving out the copper with which it is alloyed, and thereby exposing
a superficial facing of fine gold. To produce this effect, the object to be
coloured is first heated in a gas jet or spirit lamp, and then plunged into
a weak solution of nitric acid, by which the copper on its surface is
removed. The same effect is also produced by placing, for a few minutes,
the object to be coloured in a paste composed of a mixture of alum,
common salt and saltpetre.
The gilding of metallic ornaments is either performed by rubbing
their surfaces, rendered perfectly clean by immersion in dilute nitric or
sulphuric acid, with an amalgam of gold and mercury, and then expelling
the latter metal by heat, and subsequently burnishing down the deposited
gold; or, when the object to be gilt is entirely composed of copper, it
may be made to receive a covering of gold by being first cleaned and
amalgamated by being dipped into a solution of nitrate of mercury, and
then, after being carefully washed, placed in a vessel containing a boiling
solution of chloride of gold in carbonate of potassium. The objects gilt
by this method are afterwards coloured by dipping them into water con-
taining a mixture of nitre, sulphate of zinc, and green vitriol; they are
then dried, and subsequently washed in clean water. These, and all the
other processes by which gilding was formerly effected, have, however,
within a few years, become in a great measure superseded by the various
processes of electro-gilding, which consists in depositing, from its solu-
tions, by electric agency, a layer of gold of any desired thickness.
The solution most commonly employed for this purpose is cyanide
of potassium, containing cyanide of gold; the object to be gilt is
attached by a wire to the negative pole of the arrangement, whilst in con-
nection with the positive is a piece of pure gold, which is dissolved in
proportion as the metal is deposited on the object to be gilt. By this
means, therefore, the thickness of the coating is not only entirely under
the command of the operator, but the strength of the solution is also
constantly kept up at the expense of the ingot of gold in communication
with the positive pole.
GOLD.
703
MECHANICAL AND METALLURGICAL TREATMENT OF GOLD.
The mining and metallurgy of gold are so intimately connected, and
the metal is so frequently converted into bars on the mines and diggings
where it is separated from the siliceous and other materials with which
it is associated, that it would be difficult to treat intelligibly of the one
without also giving a concise description of the other. From the great
difference existing between the density of gold and that of siliceous
alluvial gravels, it is easily separated from them by washing; the methods
employed for this purpose, however, vary not only with the localities in
which the operation is carried on but also in accordance with the nature
of the minerals with which the gold is associated.
Gold is obtained by two distinct processes, viz., placer mining and
vein mining. In placer mines the metal is found imbedded in strata of
clay, sand and gravel; while in vein mines it forms one of the con-
stituents of mineral veins or lodes. In placer mining the auriferous
earthy material, usually called "pay-dirt," is exposed to the action of
water, by which the clay is carried off in suspension, and the sand and
gravel removed by the force of the current; the gold, on account of its
high specific gravity, either remains behind in the apparatus employed,
or is caught and amalgamated with mercury.
In quartz mining the gold-bearing veinstone is ground to a fine
powder, and the gold is either caught on the rough surface of blankets
or skins, over which the finely-divided material is borne by a stream of
water, or it is amalgamated by bringing it in contact with metallic
mercury.
PLACER MINING.
Water is the great agent employed by the placer miner, and its
abundance or deficiency is to a great extent the measure of the work to
be performed and of the profits to be realised. Placer mines may be
divided into two classes, deep and shallow. In the former the pay-dirt
lies at considerable depths, whilst in the latter it is found near the sur-
face. Many deep diggings are worked on what have evidently been
ancient river-beds, and are sometimes covered to a considerable thickness
by flows of basalt or lava. Shallow diggings, which are chiefly found
in the beds of gullies and ravines, as well as on the bars of rivers, often
owe their richness to the re-distribution, by modern streams, of the gold
of ancient river-systems constituting deep placers.
The appliances made use of by the placer miner are usually exceed-
ingly simple, but at the same time often singularly ingenious and
effective.
PAN. This is the simplest of all contrivances for washing auriferous
materials. It is used in all branches of gold mining, either for washing,
or as a receptacle for gold, amalgam, or for rich dirt. The pan is made
either of stiff tin-plate or of sheet-iron, with a flat bottom about 12 inches
in diameter, and has sides from 5 to 6 inches in height, sloping outwards
704
ELEMENTS OF METALLURGY.
at an angle of 45°. Sheet-iron is to be preferred to tin-plate, because it
is usually stronger and does not amalgamate with mercury. The process
of washing is conducted in the following way :-After being about three-
fourths filled with dirt the pan is placed in water, which should not be
more than a foot in depth, so that it may rest on the bottom, while the
miner inserts his fingers in and under the mass, in order to lift and stir
it, in such a way that it may become thoroughly wetted throughout. The
pan is then held by the two sides, that portion of it which is towards the
body being raised, and the opposite edge lowered. He now commences
shaking it from side to side, taking care that the whole of the dirt is
under water, and that a little of it can escape over the outer edge.
Assisted by the shaking, and by the rolling of the gravel from side to side,
the clayey portion of the dirt rapidly becomes suspended in water and
forms a thin mud which escapes over the side, whilst clean water is con-
tinually flowing into the pan. The light sand follows the mud, while the
larger stones and lumps of tough clay remain. The stones and pebbles
collect on the top of the clay, and are scraped together with the fingers,
and thrown out. This process is continued, care being taken to gradually
lower the outer edge of the pan until all the clayey matter has been
swept away by the water, and until gold and a certain amount of black
magnetic iron-sand alone remain.
To get rid of this black sand, the contents of the pan are dried, and
a small quantity is placed in a "blower," consisting of a shallow tin scoop
open at one end. The miner holds this with the open end from him, and
gently blows out the sand, leaving the particles of gold behind. During
this operation the blower must be occasionally shaken, so as to bring all
the particles of black sand within range of the current of air.
The pan is also constantly employed for separating amalgam from
sand or pyrites, and for cleaning up rich dirt collected in the cradle, long
tom, or sluice.
CRADLE. The cradle, or rocker, is, after the pan, the cheapest and
most simple apparatus employed for gold-washing. It rests on two
rockers, and its general appearance is not unlike that of a child's wooden
cradle. The cradle-box is 40 inches in length, 20 in breadth, and is
at one end from 18 inches to 2 feet in depth, whilst at the other it is
sloped off to about 4 inches only. On the deeper end of the cradle
stands a hopper or riddle-box, 20 inches square, with sides from 4 to
6 inches high. The bottom of the riddle is of sheet-iron, perforated
with holes half an inch in diameter, and the box itself is so constructed
that it can be either slipped into its place or lifted off without difficulty.
Under the riddle is placed an apron of wood or cloth, attached to the
sides of the cradle and sloping towards the upper end of the arrange-
ment. Across the bottom of the cradle-box are nailed two riffle-bars,
each about an inch square, one near the riddle and the other at the
shallow end.
The dirt to be washed is shovelled into the hopper, and the cradler
sits beside his machine; with one hand he pours water, dipped with a
ladle from a pool at his side, upon the dirt, and with the other he
GOLD.
705
imparts to it a rocking motion. By means of the water, aided by the
rocking, the dirt is disintegrated and carried through the riddle, falling
on the apron, by which it is carried to the head of the box, whence, as
the bottom has an inclination towards the shallow end, it runs downwards
and escapes, leaving the gold, black sand, and heavier particles of gravel
behind the riffle-bars.
The pay-dirt contains many large stones, and such as give a too con-
siderable shock to the cradle, by rolling from side to side, are picked out
by hand, and, after being examined to see that no particles of gold are
adhering to them, are thrown away. All the smaller ones are allowed to
remain until a hopperful has been washed, so that nothing but clean
stones remain, and then the cradler, rising from his seat, removes his
hopper, and, with a jerk, throws out all its contents. The whole process
of washing with this arrangement is merely a repetition of the manipu-
lations described. The hopper is about one-third filled with pay-dirt,
and water is poured in by means of a ladle held in one hand, whilst with
the other the cradle is rocked. The cleaning-up is done by removing
the hopper, taking out the apron, scraping all the dirt from the bottom
of the cradle with an iron spoon, putting it into a pan, and washing off
the impurities as already described. Mercury is sometimes, but not
generally, used in the cradle.
TOм.—The tom, or long tom, was formerly much used by Californian
miners, but is now seldom employed by them, having become generally
superseded by the sluice. It consists of a wooden trough about 12 feet
in length, 18 inches in width at its upper end, and gradually widening to
30 inches at the lower. Its sides are 8 or 9 inches high, and at the
lower end, its bottom is of sheet-iron perforated with holes half an inch
in diameter. This sheet-iron is turned up, so that the water cannot flow
over it, but passes down through the perforated riddle into a riffle-box
furnished with transverse bars.
The tom itself is arranged at a considerable angle, and a stream of
water is admitted at the higher end. The pay-dirt is thrown in at the
head, and kept constantly well stirred with a shovel, care being taken to
throw back to the upper part of the trough such pieces of clay as are not
sufficiently disintegrated.
The tom can be most advantageously employed where the amount of
stuff to be washed is not large and the gold is coarse. The riffle-box is
charged with mercury, and, as its contents are constantly kept in motion
by the falling into it of the water from the riddle above, a considerable
proportion of the gold is caught, although there is always a notable loss
of the finer particles.
PUDDLING BOX.-The puddling box ordinarily consists of a rough
wooden box about 18 inches in depth and 6 or 8 feet square, and is
employed for the disintegration of very tough clay.
Into this box the pay-dirt is thrown, a certain amount of water being
at the same time introduced, and the miner stirs up the mixture with a
hoe until all the finer earthy particles are in a state of complete sus-
pension. He then removes the plug from an auger-hole about 4 inches
2 z
706
·
ELEMENTS OF METALLURGY.
i
from the bottom, and allows the thin mud to run off, whilst the heavier
materials, including the gold, remain at the bottom. The plug is after-
wards again introduced into the hole, and the operation is continued until
a sufficient amount of auriferous sand and gravel has been accumulated,
when it is cleaned up, either by the aid of the pan or of the cradle. This
.contrivance is only employed in claims worked on a very limited scale,
and is never resorted to where the sluice has been introduced.
SLUICE. The sluice is now the great washing apparatus of California,
and washes nearly all the pay-dirt and produces the greater portion of
the placer gold of that country. It is generally a long wooden trough,
through which a stream of water constantly flows, and into which the
auriferous material is continuously shovelled. Its length is always
several hundred feet, and sluices more than a thousand feet long are not
unfrequently employed. The width is often about eighteen inches, but is
sometimes as much as six feet. It is made of rough pine-planks, 1½ inch
thick, in sections or boxes, from 12 to 14 feet in length, the bottom plank
being sawn 4 inches wider at one end than at the other. By this means
the narrow end of one box is made to fit into the broad end of the next,
and the sluice is composed of a long succession of boxes fitting each
other by spigot and faucet joints, but not otherwise fastened. These
boxes stand on trestles, and have a descent or grade" varying from
8 to 18 inches in 12 feet. The amount of inclination given to them is
necessarily varied in accordance with the nature of the stuff to be
washed. The dirt often contains numerous large stones and boulders,
all of which must be carried off through the sluice by the action of the
water rushing down its channel. When much clay is present the sluice
should have a considerable grade, and as a rapid current is more liable
to carry off fine particles of gold than a slower one, the length of the
arrangement should be proportionately extended. Economy and facility
of working require that the sluice should not be much above the surface
of the ground, and the inclination is therefore, to a certain extent, modi-
fied in order to conform to local circumstances. Sometimes the upper
portion of a sluice has a steep grade for the purpose of more readily
disintegrating the dirt, whilst the lower end has a less inclination given
to it with the view of more effectually collecting the gold. The clay of
ordinary pay-dirt is completely disintegrated in the first 200 feet of a
sluice with a low grade, and its prolongation beyond that point is only of
use for collecting the liberated gold. In certain cases, however, the
clay met with is so exceedingly tenacious that it will roll in large balls.
through a quarter of a mile of a high-grade sluice with a large head of
water, and be scarcely diminished in size.
The bottom of the sluice is provided with riffle-bars for the purpose
of retaining the gold, which would readily pass off the surface of the
boards, and these would themselves be rapidly worn out, unless thus
protected. Most commonly the false bottom is composed of longitudinal
riffle-bars, from 2 to 4 inches in thickness, from 3 to 4 inches wide, and
about 5 feet 6 inches in length. Two sets of bars are fitted into each
box, and are wedged in, from 1 to 2 inches apart, with a transverse bar
GOLD.
707
of the same width and thickness, placed between each set of riffles.
The bottom of the sluice is therefore divided into parallelograms about
5 feet 6 inches in length, from 1 to 2 inches wide, and from 2 to
4 inches in depth. In these spaces the gold, amalgam, and quicksilver
are retained. The larger pieces of gold would be readily caught with-
out the aid of mercury, but its use is now almost universal, and its
employment becomes the more necessary in proportion as the grains of
gold contained in the dirt are more minute.
Instead of riffle-bars sawn longitudinally with the grain of the wood,
"block-riffles," cut across the tree and standing in the sluice with the
grain upwards, are often employed. These are found to be much more
durable than those of the ordinary kind, but require a somewhat different
arrangement in the boxes. In some sluices, and particularly those em-
ployed for hydraulic mining, the block-riffles are placed transversely in
the box, and kept at a distance of about 2 inches apart by means of
strips of wood interposed between them at the bottom, but of consider-
ably less depth than the blocks themselves.
In small sluices the riffles are sometimes placed in zigzag on the
bottom of the boxes, but not touching the side at one of their extremi-
tics. These are set at an angle of 45° with the axis of the sluice,
and just below the open space left between the first riffle and the side of
the box, another bar starts at right angles to the first, and an open space
is again left at the lower end of this bar. This is continued down
to within a short distance from the end of the sluice, where ordinary
riffle-bars are commonly inserted. In sluices thus constructed, much of
the water and light mud flows directly over the riffle-bars, whilst the
heavier materials are obliged, from falling to the bottom, to assume
a zigzag course. A vessel containing mercury placed near the head of
the sluice allows it to fall drop by drop into the trough, and this, follow-
ing the course of the riffle-bars, overtakes the gold, which takes the same
direction. These zigzag riffles are retained in their places by being
nailed to the bottom of the box.
The height of the sides of sluice-boxes varies from 9 inches to 2 feet,
and the stream of water employed has never a less depth than 2 inches
over the bottom. In most instances the sluice extends throughout the
length of the claim in which it is situated, and the auriferous dirt is
thrown in with shovels, of which from four to twenty are constantly
at work.
In nearly all sluices quicksilver is put in above the riffle-bars, at
various places along the boxes, and mercury that has been before used is
considered better for gold-catching than that fresh from the flask. Oil
and grease tend to prevent amalgamation, and must therefore be care-
fully avoided.
The most usual method of arresting very fine gold is to cover the
surface of a copper plate with quicksilver, and to allow the dirt and
water to pass slowly over it, with a depth of not more than a quarter of
an inch. The amalgamation of a copper plate is effected by adding a few
drops of nitric acid to water, covering a little mercury in the bottom of
2 z 2
708
ELEMENTS OF METALLURGY.
a saucer, and then rubbing the product with a rag over the surface of the
metal. Decomposition of the nitrate of mercury formed quickly covers
the surface of the copper with a bright coating, to which the metallic
mercury readily adheres.
A plate which has been once thus amalgamated does not again require
similar treatment, but a little additional quicksilver must from time to
time be sprinkled upon it, as the gold will gradually collect and form a
solid amalgam. The plate employed, which is often about 3 feet wide,
and 6 feet in length, is set nearly level. In very large sluices the stream
is divided, so as to flow over several distinct plates, in order to secure a
slow and shallow current. It is evident that with a rapid current, or with
deep water, many particles of light gold would pass off without coming
in contact with the surface of the amalgamated plate.
When the surface of a plate has become covered by auriferous amalgam
it is believed to act more efficiently than a new one, and at the time of
cleaning up it is sometimes coated with a hard brittle mass to a thickness
of an inch. To remove this the plate is warmed until the hand cannot
long remain in contact with it, by which treatment the amalgam becomes
softened, and is then readily scraped off. The plate, after being sprinkled
with mercury, is again ready for use. The mixture of mud and water is
admitted to the copper plate through a riddle made by piercing a thin
iron plate with holes about of an inch in diameter. This is often
placed above the copper plate, and prevents its surface from being swept
by the gravel and coarser materials which pass along it.
ΤΟ
Shortly after the water and dirt have begun to pass through the
sluice all the space between the different riffle-bars becomes filled with
sand and gravel, which is, however, in a constant state of agitation, and
presents irregularities in which the principal portion of the gold is
caught.
The coarser grains are arrested near the head of the sluice, whilst
the finer particles are carried to more considerable distances. In sluices
where the dirt operated on contains much coarse gold, the mercury
is often introduced from 40 to 60 yards below the head, as the coarse
metal, by virtue of its greater density, becomes readily separated from
the earthy matters with which it is mixed.
The separation of the gold, amalgam, and mercury from the sand and
gravel in the bottom of the sluice is called "cleaning up," and the period
which elapses between one cleaning-up and the following is called a
"run." A run ordinarily extends over eight or ten days, but in most
instances the work is only carried on during daylight, although in some
cases it is continued both day and night. When the period fixed on for
cleaning up arrives the throwing-in of dirt ceases, and the water is allowed
to run until it becomes perfectly free from turbidity. Five or six sets of
riffle-bars at the head of the sluice are now taken out, and the dirt, which
has accumulated between them, is washed away, whilst the gold and
amalgam are arrested by the first of the remaining sets of riffles, whence
they are removed by the aid of a spoon or scoop, and are placed in
a washing pan. More riffle-bars are now removed, and the gold and
GOLD.
709
amalgam are again collected; this is repeated until all has been taken out,
and the whole of the gold and amalgam is transferred to the iron pan.
The quicksilver and amalgam taken from the sluice are put into a
buckskin or piece of canvas, and pressed in such a way that the liquid
metal passes through, while the amalgam is retained. This amalgam,
from which the mercury has been carefully pressed out, contains about
one-third of its weight of gold. The amalgam is then heated to drive off
the mercury, and the gold, which remains after the operation, is in the
form of a spongy mass of a light yellow colour.
The removal of the mercury may be effected either in a close retort or
in an open iron pan. In the first case the quicksilver is recovered for
subsequent use, whilst in the second, it is volatilised and lost. The pan
is, however, generally preferred by placer miners.
Large sluices are not unfrequently paved with stones, which make a
more durable bottom than wood, and also one that catches fine gold
more effectually. On the other hand, cleaning up is more difficult, as is
likewise the re-laying of the bottom afterwards. The stones used are
water-worn pebbles, of a somewhat flattened form, of which the greatest
diameter is from 6 to 8 inches.
The ordinary sluice, as already described, mainly consists of a series.
of wooden boxes, but, in some cases, these are dispensed with, and the
arrangement is then called a "ground-sluice." This contrivance is
chiefly employed for washing dirt in localities where water is abun-
dant for a few weeks only after heavy rains, and where it, consequently,
would not pay to erect large wooden sluices.
To prepare a ground-sluice a stream is first directed through a small
channel, which the miners, aided by the current, endeavour constantly to
enlarge, and when it has become sufficiently deep they detach, by means
of crow-bars, the high banks, so that the pay-dirt falls into the ditch,
where it becomes rapidly disintegrated. A few large pebbles should be
introduced at intervals into the bed of the ground-sluice, for the purpose
of arresting the gold, since, if the bottom were smooth, and without
irregularities, the chief portion of the precious metal would be carried
away by the current. No mercury is employed in the ground-sluice, but
the concentrated dirt collected is finally cleaned up in a wooden sluice,
or long tom.
HYDRAULIC MINING.-Hydraulic mining is resorted to only in situa-
tions where the pay-dirt is of great thickness and where water is abun-
dant; it may be regarded as the highest branch of placer mining, since
by it a larger amount of dirt is washed in a given time, and at a less
expense, than by any other process. Hydraulic claims are usually
situated in hilly districts, as it is not only necessary to be provided
with a column of water of considerable height, but also to find in the
valleys below the sluices a receptacle for the enormous amount of débris
resulting from the operation. Whatever may be the depth of the auri-
ferous deposit, the whole of it should be removed, to the bed-rock. This is,
as far as possible, effected by the action of water issuing at a high pressure
from metallic nozzles, and directed against the more or less indurated
710
ELEMENTS OF METALLURGY.
alluviums to be operated on. This disintegration of the auriferous
material goes on simultaneously with the washing of the resulting gravel,
and is effected by the same supply of water.
In California, the water employed in hydraulic claims is generally
purchased from one of the large public companies formed for supplying
the gold-diggings with this essential requirement of the miner. Its cost
is from 10 c. to 20 c. per miner's inch per working day, and the con-
sumption of each mining claim, worked on a tolerably extensive scale,
may be taken at about 300 miner's inches. A miner's inch is the
quantity of water which will flow during ten hours through an aperture
1 inch square, under a mean head of 6 inches; and 300 miner's inches
are equal to 284,210 cubic feet, or about 1,772,000 imperial gallons.*
Under ordinary circumstances, from 3,000 to 3,500 cubic yards of gravel
and soft conglomerate may be removed and washed daily by this expen-
diture of water.
The installation of a hydraulic washing is commenced by bringing in
a stream, by means of a flume" or aqueduct, to the head of the mining
ground at a height of from 120 to 150 feet above the level of the bed-rock,
where it is conducted through a wooden trough or tank, into which it
constantly flows. This is provided with a suitable valve, and from it the
water is most commonly conveyed to the bottom of the claim through
wrought-iron pipes from 8 to 12 inches in diameter. These terminate at
their lower extremity in a strong cast-iron box, in which are apertures
provided with slide-valves and union joints, to which are attached flexible
hose, fitted with gun-metal nozzles, 2 to 2 inches in diameter. The
flexible hose are made of strongly-sewn canvas, which will, without any
external support, withstand the pressure of a column of water 50 feet in
height. As however, the pressure employed is usually much greater than
this, they require to be strengthened, either by iron rings or by a net-
work of cordage. When metallic bands are used they are placed over
the hose at intervals of from 3 to 4 inches, and are connected with
each other by longitudinal cords, dividing the circumference into four
equal parts. These tubes, which are called "crinoline hose," are very
flexible, and will sustain, without danger of bursting, the pressure of
a column of water 180 feet in height. When a netting is employed as a
means of strengthening the hose, it is made of rope, half an inch in
diameter, and forms meshes about 3 inches square. In some cases, the
cast-iron boxes at the bottom of the columns are dispensed with, each
nozzle being in direct and independent communication with the cistern
or tank at the head of the claim; sometimes also, the hose are directly
connected with the iron piping by the use of T-pieces. The amount of
manual labour necessary for carrying on the operations of a hydraulic
claim, is exceedingly small in proportion to the amount of work done,
since, in addition to the men engaged in directing the various nozzles,
only one person is usually employed in attending to the sluice, so as
to remove obstructions, and prevent its becoming choked by the dirt and
*Mining and Metallurgy of Gold and Silver,' by J. Arthur Phillips, p. 61.
Spon, 1867.
GOLD.
711
boulders washed from the face of the stope. In order to render evidenț
the enormous advantages possessed by this method of working over every
other system of placer mining, it may be stated that it has been estimated
that, taking a miner's wage at $4 per day, the cost of treating a cubic
yard of gravel by the various processes which have been described will
be approximately as follows:
By, the pan
cradle.
$20.00
5.00
""
""
""
long tom
1.00
sluice
0.33
""
•
hydraulic process
0.05
The quantity of dirt, however, that can be washed by a hydraulic pipe
in a given time, depends on various circumstances, such as the supply of
water, the height of the column, the tenacity of the material, and the
amount of moisture it may happen to contain. More work can usually be
done in winter than in summer, since, from the greater dampness of the
stuff during that season, it becomes more easily disintegrated.
In some
hydraulic claims, in which the pay-dirt is cemented into a kind of friable
conglomerate, blasting is resorted to as a means of facilitating its
removal by the subsequent action of water. For this purpose a tunnel
is driven along the upper surface of the bed-rock into the hill, which
may be 150 feet in height, and a number of kegs of powder (frequently
above a hundred) are introduced. The tunnel is now re-filled with earth,
and the powder is exploded by the use of a properly-arranged slow-burn-
ing fuse.
The explosion, which often makes comparatively little noise,
loosens and shatters thousands of cubic yards of the surrounding hill, and
materially facilitates its subsequent removal by the water thrown against
it through the various nozzles.
In order to avoid the danger that would result to workmen from land-
slips on an extensive scale, the pay-dirt, when above 100 feet in thick-
ness, is often worked in two or more terraces or steps, the upper one
being first operated on.* In hydraulic claims, generally, all the alluvium
is removed to the bed-rock, but in some cases working has to be sus-
pended long before this point is reached, from the circumstance of the
conformation of the country not allowing of an outlet for the water at that
depth. The cheapness and expedition of this process admit of very poor
alluviums being treated with advantage; and in some cases, claims in
*Mr. G. Attwood informs us that since the date of our last visit to California
(1866) the height of the columns and the diameter of the nozzles employed for
hydraulic mining have been considerably increased, and that it is now not uncommon
to work with jets five inches in diameter, under a pressure of four hundred feet.
When such powerful apparatus is resorted to, the lower pipes, which sustain the
greatest pressure, are made of thick, double-riveted, sheet-iron; to these the nozzles
are attached by ball-and-socket joints, and are worked by pinions and toothed seg-
ments. The amount of work daily accomplished by such an arrangement is described
as enormous. while, from the distance at which the men are enabled to stand from
the face of the pay-dirt, banks of a great height can be worked without danger from
land-slips. The pressure employed is also so great that gunpowder is not required,
excepting in the case of the hardest cements.
712
ELEMENTS OF METALLURGY.
which the dirt only affords gold to the value of 3 c. per ton of 15 cubic
feet, have been worked with satisfactory results.
The accompanying woodcut (fig. 202), from a photograph of the Palm
claim, Timbuctoo, Yuba county, California, will afford a good idea of the
general appearance of an extensive hydraulic washing.

>.....
Fig. 202.-Hydraulic Mining; Timbuctoo, California.
In the majority of cases a larger amount of water is required for
piping down the bank than for washing the dirt removed, and conse-
quently, when the sand and gravel are strongly cemented together, the
sluice cannot always be kept properly supplied without the aid of gun-
powder.
EXTRACTION OF GOLD FROM AURIFEROUS VEINSTONE.
The methods employed for the extraction of gold quartz from the
mine differ in no respect from ordinary mining operations applied to the
systematic working of mineral veins. After the quartz has been obtained
by the operations of mining, it is necessary that it should be reduced to
a state of fine division before the separation of the gold it contains can be
effected. Various contrivances are employed for this purpose, and one
of the simplest and most primitive is the arrastra.
ARRASTRA. — This apparatus, as constructed for the treatment of
auriferous ores, consists of a circular bed of stone, from 10 to 12 feet in
diameter, on which the mineral operated on is reduced to an impalpable
state of division, by means of one or more large stone mullers, dragged
continually over its surface by horse or mule power. The rudest form
of arrastra is commonly employed, and is made of a pavement of unhewn
flat stones, usually laid in clay. In the centre of this circular bed is an
GOLD.
713
upright wooden shaft, which turns on a pivot working in a step cut
in the central stone, and, at its upper extremity, is supported by a beam,
to which is attached the other bearing. Through this post horizontal
bars are passed, projecting on three sides to the outer circumference of
the pavement only, whilst on the other there is a sufficient projection
beyond this line to admit of one or more mules being harnessed to it.
(See fig. 185, p. 627.)
On each arm of this bar is attached, either by chains or strips of raw
hide, a flat stone, weighing from 300 to 500 lbs. These are so hung that
the side in the direction of the line of rotation hangs about an inch
above the bed, whilst the other drags upon the surface of the pavement.
The periphery of the arrastra is formed by a stone wall, 12 inches in
height, which serves to keep the mineral operated on constantly within
the area traversed by the mullers.
*
The charge of such an arrastra is about 4 cwts. of quartz, previously
broken into fragments of the size of beans, and requires to be ground
during from four to five hours, in order to reduce it to a sufficiently-fine
state of division. Water is now added and the mill again started, in
order that the ground ore may become thoroughly incorporated with it.
Care is, however, taken that the resulting mud be not too liquid, as
in that case the mercury, when added, would fall to the bottom, and a
large proportion of the gold thus escape amalgamation. The paste having
assumed the consistency of thick cream, quicksilver is scattered over its
surface, by being squeezed through a piece of canvas, in the proportion
of about an ounce and a half of that metal to every ounce of gold sup-
posed to be contained in the quartz. The grinding is now continued for
a further period of two hours, by which the quicksilver becomes divided
into minute globules, which are disseminated throughout the mass, and
by which the amalgamation of gold is effected. When the amalga-
mation is supposed to be complete, more water is let in on the surface
of the paste, and the mullers are again set slowly in motion. By this
treatment the lighter earthy particles become suspended in water, while
the heavier amalgam gradually collects at the bottom. This result is
supposed to have been obtained at the end of about half an hour, and
the mud is then run off, leaving the gold and mercury at the bottom.
Another charge is now introduced, and the operation repeated as before,
with similar precautions.
The run with a rude arrastra of this description generally extends over
a week, but sometimes over a considerably longer period. For the pur-
pose of cleaning up, the paving-stones of the bed require to be taken up,
in order to collect the amalgam which settles between them, and the
whole of the mud must be removed and carefully washed.
In some cases a more expensively-constructed arrastra, similar to
those described when treating of the amalgamation of silver ores in
Mexico, is employed; in such cases, the cleaning-up is much less trouble-
some, and is therefore more frequently repeated.
The amount of work performed by this machine is exceedingly small
in comparison with the power expended; but the proportion of gold
714
ELEMENTS OF METALLURGY.
extracted is generally larger than is obtained with more expeditious and
more complicated apparatus. The arrastra is, therefore, not unfrequently
employed as a means of making a practical trial of the value of gold
quartz, before proceeding to erect expensive machinery for its treatment
on a large scale. In California this extremely-primitive contrivance for
working auriferous quartz has now almost entirely disappeared. Those,
however, who travelled through that country about the year 1854 will
remember not unfrequently falling in with a family of Mexicans, who, in
some secluded valley, with a couple of miserable mules harnessed to a
rude arrastra, managed to pick up a scanty living by working the outcrop
of some quartz vein.
CHILIAN MILL. In the early days of quartz mining, the Chilian mill
was much employed for grinding auriferous ores, but this machine has
now even more completely disappeared than the arrastra. It consists of
a paved circular floor, of considerably smaller diameter than that of the
arrastra, on which two large runners of hard stone revolve on their edges.
In the centre of the bed is an upright post, on the top of which is
a pivot for the axle on which both the stone rollers turn. One end of
this axle is prolonged beyond the periphery of the bed, and to this
is harnessed a mule, which walks continually round. The method of
amalgamation in the Chilian mill is very similar to that employed in the
arrastra, but the results are less satisfactory than those obtained with the
last-named machine.
..
STAMPING MILL.-Nineteen-twentieths of the quartz crushed for the
purpose of extracting the gold it contains is pulverised in the stamping
mill. In fact, this may be said to be the only machine now extensively
employed in any part of the world for the reduction of auriferous vein-
stone. It essentially consists of a series of heavy pestles inclosed in a
rectangular mortar; each of these is successively lifted by means of a
cam, and then allowed to fall with its full weight on the ore to be operated
on. A constant supply of mineral is kept up in the mortar, while that
which has become sufficiently reduced in size is gradually removed, by
suspension in water, through the apertures of properly-arranged sieves or
screens. In some cases the stems or lifters are made of wood, as in
the old German and Cornish stamping mills, but the modern machine,
figs. 189, 190 (pp. 644, 645), is now more frequently employed. The size
of the apertures in the screens is varied in accordance with the dimen-
sions of the particles of gold in the rock under treatment, but it is evident
that with very small apertures the amount of rock crushed, all other con-
ditions being equal, will be less than when a coarser grating is employed.
Screens are commonly made of thin sheet-iron, in which are punched, at
regular intervals, holes of the diameter of a rather large sewing needle.
The auriferous material having become reduced to the state of finely-
divided sand, it becomes necessary to find means for the concentration
and separation of the gold. This may be effected either with the aid of
mercury or without it.
Amalgamation in Battery.-When quicksilver is used the batterics are
often furnished with amalgamated copper plates of about 5 inches in width,
GOLD.
715
extending the whole length of the battery-box or mortar. One of these is
placed on the feed side, and the other on the side of the discharge, the
former being protected by the iron lining of the feed-hopper, and each
having an inclination of about forty-five degrees. When these are not em-
ployed, the auriferous amalgam accumulates in the spaces between the
dies, as well as between the dies and the sides of the box. The quartz,
previously broken to a convenient size, is supplied by the feed aperture.
A small stream of water flows into the battery-box through a gas-pipe, and
a little quicksilver is sprinkled into it, by the feeder, at intervals of about
an hour, and in quantities varying with the estimated richness of the rock
which is being worked. One ounce of gold requires for its collection an
ounce of mercury, but when the gold is in a finely-divided state the ad-
dition of a small excess of mercury is considered advantageous. The
proper proportion is, however, readily arrived at by closely watching the
discharge. When any particles which may pass through the screens are
observed to be dry and brittle more quicksilver must be added; if, on
the contrary, they appear soft and pasty, or globules of mercury pass off,
the supply of that metal in the battery-box requires to be diminished.
The amalgamation of gold is satisfactorily effected when the proportion
has been properly adjusted, excepting in cases where the gold is coated
by minerals which interfere with its combination with mercury. When
the rock contains coarse gold, and a proper supply of quicksilver has
been regularly introduced, from 60 to 80 per cent. of the precious metal
is caught in the battery-box. When, as is sometimes the case, the gold
is in a very finely-divided state, and is associated with ores of silver or
other sulphides, less satisfactory results are obtained. In some instances,
when such ores are under treatment, the alloy obtained, after the removal
of mercury by distillation, only yields about one-third of its weight of
gold, and the amalgam produced is spongy and of a dark colour, con-
sisting of an aggregation of minutely-divided particles. Amalgam of
this description is exceedingly light, and is therefore difficult to collect,
either by riffles, amalgamated copper plates, by blankets, or by any of the
other appliances usually employed for that purpose. When, therefore,
the rock operated on is of such a nature as to yield an amalgam of this
description, amalgamation in the battery is not to be recommended, since
this spongy product is more difficult to catch than the most finely-
divided gold, and is liable to float off, in spite of all the precautions that
may be taken to arrest its progress. For the purpose of collecting the
particles of gold and amalgam which escape through the screens, various
contrivances are resorted to. As, however, these differ but little in
detail, whether quicksilver be added in the battery-box or otherwise, it
will be sufficient to describe the system most commonly employed in a
well-conducted modern quartz mill.
Blankets. In many of the most efficient quartz-crushing establish-
ments of California the sand and water, escaping through the screens, are
conducted over the surface of blankets forming the lining of shallow
troughs or sluices, inclined at an angle of from three to four degrees
with the horizon. Beyond the blankets are amalgamated copper plates,
716
ELEMENTS OF METALLURGY.

W.J.WELCH.SC
B
Fig. 203.-Stamping Mill, with Blanket-Sluices and Riffles; longitudinal section.
GOLD.
717

VIRUM
D
E
Fig. 204.-Stamping Mill, with Blanket-Sluices and Riffles; plan.
W.J.WEL.CH.SC
718
ELEMENTS OF METALLURGY.
which are again followed by some contrivance for collecting the auri-
ferous materials which may not have been arrested in the upper por-
tion of the apparatus. Finally, there is generally a long tail-sluice for
collecting any auriferous sulphides which might otherwise escape and be
lost. The troughs in which the blankets are placed are from sixteen to
eighteen inches in width, with a regular longitudinal slope, care being
taken to lay them perfectly level in a transverse direction, so that
an equal depth of water may flow over every part of the bottom.
The blankets used for this purpose are generally woven from long
grey wool, and are of such a width that when wetted and fitted closely to
the bottom and sides of the trough they extend about an inch beyond the
latter. In laying them in the sluices they are so placed as to overlap
each other like the slates or tiles on a roof, in such a way that the water
flowing from the upper one may run directly over the next in the series,
without any of the sand finding its way between the bottom of the sluice
and its covering of blankets. The troughs are made in two or more
lengths, and are so disposed that the sand and water flowing from the
first, fall upon the second from a height of three or four inches. The
arrangement of the batteries and sluices will be understood by refer-
ence to the woodeuts, figs. 203, 204, of which the first is a longitudinal
section, and the second a plan of the apparatus. In front of the battery-
box, A (fig. 203), is a water-tight trough, B, of the same length, and
which has an opening, b, communicating with the sluice, C. There
is also a second aperture, b', at the end, which, like the first, can be closed,
either by a wooden plug or by one of wet blanketing. Before each battery
is a sluice, C, and between each pair is a third, C' (fig. 204), which is used
when either of those on each side of it is thrown out of action in order to
remove the blankets. When the batteries are in their ordinary course of
working, the water, carrying the crushed ore in suspension, passes through
the troughs, C, and, flowing over the blankets with which they are lined, a
large proportion of the gold and heavier minerals with which it is asso-
ciated becomes entangled with the fibres of the wool, whilst the lighter
particles of quartz are carried off by the current, and escape from the lower
end of the arrangement. After the expiration of a certain time the fibres
of the blankets become so charged with the heavier particles of crushed
ore as to cease to act, and to obviate this, they are frequently washed,
and subsequently replaced in their respective troughs. The blankets at
the upper end of the sluices are generally removed and washed every
fifteen or twenty minutes, and in order to do this the orifice, b, communi-
cating with one of the sluices, C, is closed, and the aperture, b', in con-
nection with the central sluice, C', standing between the two batteries, is
opened. By this means the water is turned off from the sluice, C, whilst
the discharge from the battery is directed through the central trough, C'.
As many of the blankets in the first trough, C, as may require it, are now
taken up, and while doing so, are so folded as to prevent the loss of any
of the adhering matter. They are then taken to a cistern or tank pre-
pared for that purpose, and, after being carefully washed, are again laid
in the trough, from which they were removed. The discharge from the
GOLD.
719
battery is now cut off from the sluice, C', and again admitted into its ori-
ginal channel, the same operation being repeated whenever it is found
necessary to wash up the blankets on the sluices, C, belonging to the same
or to other batteries. When it is found requisite to remove the blankets
from the intermediate trough, C', it is done during the time that those on
either side of it are in operation. Instead of the arrangement described,
two sluices are sometimes connected with each battery, and, in such cases,
one is being cleaned up while the other is in use. The blankets in the
upper sluices only are removed so frequently as above stated, and those
on the lower ones, D, D', often remain some hours without being washed.
The gold retained in the battery, added to that collected on the blankets,
will, in the majority of cases, amount to at least eight-tenths of the total
produce from the rock operated on. A valuable proportion, how-
ever, of the precious metal escapes over the blankets, and means have to
be adopted to arrest the largest possible percentage of this light gold.
For this purpose amalgamated copper plates are generally employed.
Amalgamated Plates. In the majority of cases, the water and sand
escaping through the screens, after flowing over two blanket-sluices at
an angle of about three and a half degrees, are conducted through
troughs, E E', laid somewhat more horizontally, and lined at bottom
with amalgamated copper plates. From these the current passes through
another set of troughs, F, F', set at a still less inclination, also lined at
bottom with amalgamated plates, whilst at the end are reservoirs for the
collection of tailings. The riffle-plates in the troughs, E, E', are made
to slide easily in and out of their places, for the purpose of being cleaned
or re-amalgamated, and are usually from eight to ten inches in length.
Those in the troughs, F, F', are also movable, but are commonly made
considerably longer than those in the first sluice furnished with an
amalgamated lining.
Cleaning up.—The stamping mill is usually kept continually at work
day and night, and the frequency with which the battery-boxes are
cleaned up is to a great extent regulated by the richness of the rock
which is being operated on. When mercury is introduced into the
battery the boxes are cleaned up every three or four days, but, in estab-
lishments where no quicksilver is used in the mill, this operation is
generally put off until the end of the week. In the former case a very
large proportion of the gold is taken from the battery in the form of
amalgam, and, even when quicksilver is not introduced, the cleaning-up
of the battery-box furnishes a considerable percentage of the produce,
which accumulates in the spaces between the dies, as well as in those
formed between the dies and the sides of the box itself. When it has
been determined to clean up a battery the props are placed under the
tappets, so as to keep the stamp-heads raised to their full height; the
screens are now removed, and the dies taken out. The whole of the sand
and other auriferous material is then carefully collected in a pan by the
aid of an iron scoop, and, after everything that may be adhering to
the dies has been washed off into the same pan, they are again intro-
duced into their respective places. When quicksilver has been employed
720
ELEMENTS OF METALLURGY.
in the battery, in addition to removing the dies and collecting the sand
and amalgam, the copper plates, if any have been used, require to be
scraped and re-amalgamated. When this has been done the screens are
fastened in their places, and the props taken from under the different
tappets, when the cam, belonging to each stem, is in such a position as
to facilitate its withdrawal. The coarser the gold is in the rock treated,
the larger will be the percentage of the total produce retained in the
battery. In order to separate the gold and amalgam from the sand and
pyrites with which they are mixed in the battery the materials resulting
from a cleaning-up are generally washed by panning. This is often done
in the cistern used for washing the blankets, since by this means any-
thing of value that may pass over the edge of the pan is collected for
subsequent treatment.
Amalgamation of Blanket Washings.-The amalgamation and separa-
tion of the gold from pyrites and other matters caught on the blankets,
and subsequently collected in the washing tank, are effected in various
ways. In some cases they are ground with water and mercury in a
Chilian mill or in an arrastra, of which the bottom is an iron pan, to
which motion is imparted from the shafting connected with the stamping
mill. Sometimes one of the pans previously described, when treating of
the processes employed in Nevada for the amalgamation of silver ore, is
used; but, in the Grass Valley district, and in some other localities in
California, a very simple contrivance is employed.
This apparatus consists of two wooden rollers, eight inches in
diameter and about two feet in length, furnished with numerous flat
pieces of iron arranged radially on their circumference, with the thin
edges at right angles to the axes of the cylinders.
These rollers are, by means of belts, made to revolve in a shallow
cistern of mercury, in a direction contrary to that of the current of water
flowing through the machine, and above them is placed a hopper, in
which is introduced the sand, &c., to be washed. Below the cylinders is
a riffle-board, with an inclination of seven degrees, generally covered
with removable plates of amalgamated copper, but, if copper plates are
not used, the steps of the riffles are reversed and filled with mercury.
The auriferous sand and pyrites, taken from the cisterns in which the
blankets have been washed, are placed in the hopper, and a stream of
slightly-warm water is allowed to fall into it in such a way as to gradu-
ally wash it under the rollers, and thence over the surface of the riffle-
board, which is either covered with amalgamated plates or charged with
quicksilver.
The material operated on being always highly concentrated, great
care is taken to insure its equal flow over the bottom of the sluice-
board, and a person is constantly in attendance for the purpose of skim-
ming off any oxide or other impurity that may accumulate on the surface
of the plates or on the mercury of the riffles. These skimmings are,
with other auriferous materials, subsequently treated in a pan, or in a
small arrastra with a cast-iron bottom.
The sulphides, such as galena and iron pyrites, which pass off over
GOLD.
721
the riffle-board, are collected in a receiver at its extremity, and are
treated for the gold which they inclose, either by grinding in a pan, by
smelting, or by chlorination.
At Schemnitz, and in some other localities, where gold is extracted
from auriferous iron pyrites, the Hungarian mill, represented in fig. 205,
is employed as an amalgamator. A number of these machines are so
arranged one above another that the products escaping from the first
may flow into the second, and so on throughout the whole length of the
series. The pyrites to be treated is first reduced by stamping mills to
the state of a fine powder, and while held in suspension by a stream of
water is conducted into the upper mill by the spout, S, and, flowing
through it, passes by the spout, S', into the second, from which it may
S
y
d
b Ś g
C
Մ
w
TERMOSI
.

Fig. 205.-Hungarian Mill; elevation, partly section.
be subsequently conducted into other similar mills by the spout S'.
The fixed part of these mills consists of a cast-iron basin, a, b, c, d,
fastened by screws to the top of a strong wooden table, A. The centre
of this casting is furnished with a tubulature traversed by the rotat-
ing axis, x, and set in motion by the toothed wheel, w.
The upper
and movable part of the arrangement, ƒ (shown in section in the right-
hand figure), is composed of hard wood, and is attached to the upright
spindle by the iron collar, g. This movable part of the apparatus has
externally the same form as the internal cavity of the fixed iron casting,
from the surfaces of which it works, at a distance of about half an inch;
it is also furnished with several raised iron ribs fastened to its under
side, and which come almost in contact with the bottom of the pan.
The upper surface of this wooden muller is hollowed into the form
of a funnel, into which is conducted the liquid slime, which penetrates
into the space remaining between the surfaces of the upper and lower
parts, and then flows over the side of the basin by the spout placed
there for that purpose. On the bottom of the iron pan is about 56 lbs.
of mercury, which forms a stratum of rather more than half an inch
in thickness, and with which, when the machine is set in motion, the
pounded mineral is constantly agitated by means of the projections.
attached to the bottom of the revolving wooden block. The spangles
3 A
722
ELEMENTS OF METALLURGY.
!
of gold are thus dissolved by contact with mercury, and those which
escape combination in the first amalgamator are arrested by the others
following in the series. After this apparatus has been at work during
four or five consecutive weeks, the mercury is drawn off, for the purpose
of obtaining the gold which it contains.
Tailings, &c.-The tailings which escape over the blankets and other
contrivances employed for arresting gold, are collected in settling pits,
and are carefully washed for the purpose of concentrating the auriferous
sulphides. This may be effected by the use of tyes, buddles, rockers,
shaking-tables, &c., and a valuable amount of gold, that would otherwise
be lost, is thus recovered. In many instances the use of settling pits
and reservoirs is dispensed with, the concentrating appliances being so
arranged that the tailings to be treated pass directly into them from the
mercury-sluices or riffles.
The addition of a minute quantity of metallic sodium, or of a little
sodium amalgam, to the mercury employed for the collection of gold has
been recommended, and at least two distinct patents have been taken out
for the use of sodium amalgam. Dr. Wurtz, of New York, applied for
an American patent in November, 1864, and Mr. Crookes made a similar
application in this country in February, 1865; it may, therefore, be
assumed that both were experimenting on its properties at the same time,
and each without any knowledge of what was being done by the other.
Shortly after the publication of these patents, the employment of
sodium amalgam was extensively tried both in Australia and California,
but the evidence obtained with regard to its efficiency has been of a
somewhat conflicting nature, and its adoption by those employed in the
treatment of gold quartz has consequently been far less general than
was at first anticipated. It is, however, believed that the addition of a
very minute amount of sodium amalgam to the quicksilver used for
separating gold from auriferous pyrites, as well as from pyritous sands,
such as those collected on the blankets, is sometimes attended with
beneficial results.
Retorting, and FUSION INTO INGOTS.—The amalgam collected during
the various operations for the treatment of auriferous products is first
filtered, either through canvas or buckskin, as in the case of that
obtained from placer sluices, and afterwards retorted, and the gold melted
into bars.
Generally, the redundant mercury is first separated by filtration
through a prepared skin, in which the pasty amalgam remaining is wrung,
until it assumes the form of a somewhat granular mass, having the con-
sistency of moderately hard putty. This contains about 35 per cent. of
gold, and before being introduced into the retort is moulded into lumps
of the size of oranges. The retort employed is of cast-iron; it has the
form of an ordinary black-lead crucible, and varies in size in accordance
with the quantity of amalgam to be treated at each operation. The top
is turned flat, and is provided with a well-fitting cover, secured in its
place, either by a screw-clamp or by iron cotters; into this is screwed
an inch gas-pipe with an ordinary bend at right angles, and, at a distance
GOLD.
723
of about three feet, this is again bent downwards, so as to form another
nearly right angle.
Before introducing the balls of amalgam into the retort its interior
surface is slightly covered by a thin coating, either of clay made into a
thin paste with water, or with a mixture of water and wood-ashes; this
is done in order to prevent the adhesion of the gold, in case of its being
accidentally too strongly heated. The cover should also be luted with a
little clay, before being fastened in its place. When the balls of amal-
gam have been put in, and the cover has been fixed in its place, the ves-
sel, with its contents, is introduced into an ordinary wind furnace, like
that employed for the assay of iron ores, and a fire of coke or charcoal
is made around it. The open end of the pipe will now be within a
short distance only of the floor, and beneath it is placed a pan of water,
into which a piece of canvas, bound around it so as to form a sort of
hose, is allowed to dip to the depth of about an inch. In order to
prevent accidents from the ascent of water into the retort, the level of
that in the pan must be carefully kept below the end of the metallic
pipe, and the descending limb of the apparatus is cooled by being
bound with wetted cloths. Instead of cloths cooled by the constant
application of water, a Liebig condenser is sometimes employed; this
has the advantage both of being neater, and also of requiring less
attention on the part of the person in charge of the operation. When
the apparatus has been thus arranged the fire is lighted, and the heat
gradually increased, until the vessel has acquired a dull-red colour, care
being at the same time taken to insure perfect condensation of the mer-
cury. In this way the heat is kept up for several hours, but when the
pipe begins to cool, and drops of quicksilver are no longer observed to
fall from its extremity, the operation is considered finished; the fire may
now be withdrawn, and the retort removed from the furnace. The cover
should not, however, be removed until the retort has become nearly cold,
since mercurial vapours, if inhaled, would be highly injurious. When
very large quantities of auriferous amalgam have to be dealt with, a fixed
retort, similar to that employed for the treatment of silver amalgam,
may be used with advantage.
Retorted gold is generally fused, for the purpose of being cast into
ingots, in the furnace used for heating the retort during the distillation
of amalgam. Either coke or charcoal may be employed as fuel, and the
black-lead pots in which the melting is effected should be well annealed,
by being gradually heated, before being exposed to the full heat of the
fire. The spongy gold, which at the commencement of the operation
filled the pot, gradually becomes fused, and, in that state, occupies much
less space than it did before; so that as soon as the first charge has
become melted, the cover may be taken off, and a further addition of re-
torted gold made. A little borax is added with each charge, and when
the crucible has become sufficiently full of fused metal, it is withdrawn
by the aid of a pair of stout tongs, and its contents poured into open
cast-iron moulds.
The cost of extracting the gold from a ton of auriferous quartz by
3 A 2
724
ELEMENTS OF METALLURGY.
stamping, &c., will vary materially according to the cost of labour,
fuel, and other circumstances. In 1861, Mr. Ashburner calculated the
average expense of treating one ton (of 2,000 lbs.) of gold quartz, in
California, as follows:
In water mills, water free
""
:)
""
purchased
•
$1.22
1.60
2.14
steam
The cost, both of labour and materials, has however been reduced
since the date of this estimate, and, consequently, at the present time,
it may be regarded as being somewhat too high.
CHLORINATION PROCESS.
This method, usually known as Plattner's process, is based on the fact
that chlorine gas transforms metallic gold into a soluble chloride, without
materially attacking the metallic oxides with which it may be associated.
From the solution of chloride of gold in water, thus obtained, gold may
be precipitated, in the metallic form, either by metallic iron or copper, or
by a solution of ferrous sulphate, &c.; or it may be obtained in the state of
sulphide by sulphuretted hydrogen. No metallic sulphides or arsenides.
must, however, be present, as these substances would be transformed into
chlorides, causing an unnecessary expenditure of chlorine. The presence
of sulphur is also injurious from giving rise to the production of chloride
of sulphur, which, in the presence of water, becomes transformed into
hydrochloric and sulphurous acids, and a certain amount of the metallic
oxides is consequently dissolved. The whole of the sulphur must, there-
fore, be expelled by careful roasting, while the iron is, at the same time,
converted into peroxide; the chlorine employed should also be freed
from hydrochloric acid.
In California, the extraction of gold from auriferous pyrites by the
chlorination process is thus conducted :
The concentrated tailings are first roasted in a reverberatory furnace,
heated by a wood fire, until no further smell of sulphur is perceptible; a
little charcoal is sometimes introduced towards the close of the operation
for the purpose of decomposing any sulphates or arsenical salts that may
have been produced. This roasting is effected at a low temperature in
order to avoid agglomeration of the ore, and, at the expiration of from
six to eight hours, the charge is withdrawn and spread evenly on the floor
to cool. When sufficiently cold it is repeatedly turned and sprinkled
with water, so that it may become sufficiently and regularly moistened
throughout. The success of the subsequent operations depends, in no
small degree, on the amount of water thus added, and the uniformity of
its mixture with the ore. After having been properly moistened, the
roasted pyrites is charged into large wooden tubs, 7 feet in diameter and
2 feet 6 inches in depth. These are provided with perforated false
bottoms, beneath which the chlorine is introduced, and thence ascends
through the damp and finely-divided auriferous oxide of iron, which ulti-
mately becomes permeated by the gas. The chlorine is produced from a
GOLD.
725
mixture of common salt, peroxide of manganese, and sulphuric acid, con-
tained in a leaden generator, which communicates with the space beneath
the false bottom by means of a lead pipe. There is also a plug-hole in
the bottom of each tub for the purpose of draining off the auriferous
solution obtained. After being charged with moistened ore each tub is
closely covered by a wooden lid, and chlorine is introduced beneath the
false bottom. At the expiration of some hours, the whole mass has
become strongly penetrated by chlorine, which, as a greenish gas, lies
heavily above the tailings. In this condition the tub and its contents are
allowed to remain from ten to fifteen hours, at the expiration of which
period, the cover is removed and clean water introduced. As soon as the
water has risen to the surface of the charge, the plug-hole at the bottom
is opened, and the water containing the dissolved chloride of gold is run
off into glass carboys. The gold is subsequently precipitated in the
metallic form by the addition of ferrous sulphate, and forms a brownish-
black deposit on the bottom of the carboys; this reaction is expressed by
the following equation:
2AuCl₂+6FeSO¸ = Au¿+Fe¿Cl¸+2Fe2(SO4)3⋅
3
The precipitated gold thus obtained is collected on filters, dried, and
afterwards fused with borax in black-lead crucibles; the ingots of gold
prepared in this way are usually 995 fine. When the gold is in a
finely-divided state this process affords satisfactory results; but the
larger particles of metal not being completely dissolved in the time
necessary for the solution of the smaller ones, a loss must necessarily
result unless the time during which the ores are exposed to the action of
chlorine is sufficiently prolonged to effect the solution of the largest
fragment of gold present.
It therefore follows that the chlorination process is most advantage-
ously applied to ores in which the precious metal is uniformly and finely
divided. Any silver that may have been present in the original sulphides
treated, as well as that constantly alloyed with the gold, is by this
process converted into chloride of silver, which is insoluble in the auri-
ferous solution, and therefore remains with the residues in the tubs.
At Reichenstein, in Upper Silesia, this process was formerly em-
ployed for the extraction of small quantities of gold from the residues
remaining after preparing arsenical products from pyrites by roasting. In
this establishment 0·045 oz. of gold was obtained per cwt. of the material
treated by chlorination, whereas only 0-026 oz. was, at a former period,
afforded by the processes of smelting and cupellation employed when the
ores were treated for lead. The roasted ore operated on was introduced
into clay pots, in which it was subjected to the action of chlorine, in
charges of 14 cwt., and the gold afterwards precipitated from the resulting
solutions by sulphuretted hydrogen. At Reichenstein, this process is
at present abandoned, as the old residues have all been worked up, and
the arsenic-works no longer produce a sufficient amount of roasted
material to render its treatment profitable. At Schemnitz, auriferous
matts have been treated for silver by Ziervogel's method, and the gold
726
ELEMENTS OF METALLURGY.
afterwards extracted from the residues by Plattner's process; but we are
not aware whether this system of working is still in operation.
PARTING BY SULPHURIC ACID.
When the separation of gold from silver is conducted on an extensive
scale, the use of nitric acid would be attended with great expense, and
should therefore only be resorted to when the proportion of the more
valuable metal is considerable. This difficulty is entirely obviated by
the employment of sulphuric acid, although it is necessary, in order that
the alloy be completely attacked, that it should not contain more than
about 25 per cent. of gold, and from the slight solubility of sulphate of
copper in strong sulphuric acid, it is also of importance that it should
not contain much beyond 10 per cent. of copper.*
The alloy, after the additions necessary to bring it to the proper
standard have been made, is fused either in large crucibles or in a small
reverberatory furnace, and granulated by being poured, while in a liquid
state, into vessels containing cold water. The granulated mixture is
now placed in large cast-iron boilers, into which are thrown 24 times
its weight of strong sulphuric acid of sp. gr. 1-840, and the whole is at
once heated to ebullition by a fire placed beneath the pans. The quan-
tity of alloy treated in each vessel varies from 5 to 10 cwts., and to pre-
vent the evolution of noxious gases into the laboratory, a leaden dome,
connected with a well-drawing chimney, is placed over them during the
time the attack is being made. The strong sulphuric acid under these
circumstances is rapidly decomposed, sulphate of silver is formed, while
sulphurous anhydride is evolved; this, for the sake of economy, is fre-
quently conducted into a sulphuric-acid chamber, where it again becomes
oxidised, and is fitted to be employed in a repetition of the same process.
At the expiration of four hours the attack is completed, and at this
stage of the operation a certain quantity of sulphuric acid is added
of the sp. gr. 1-69, obtained by the concentration of the acid mother
liquors remaining after the crystallisation of the sulphate of copper
produced during the precipitation of metallic silver, as will presently
be described.
The liquors are now made to boil during a few minutes, when the fire
is withdrawn from beneath the pans, and the liquors are diluted and
allowed to stand, in order that the finely-divided gold may be deposited
on the bottom. When this has taken place, and the supernatant liquor
has become clear, it is drawn off by a syphon, while still hot, into leaden
evaporators partially filled with the mother liquors remaining from the
crystallisation of sulphate of copper. These are heated by a series of
steam-pipes until the whole of the sulphate of silver which begins to fall,
on cooling, is re-dissolved, when a further deposit of gold is obtained, and
the liquor is again syphoned into another series of evaporators, in which
* When gold bullion is to be refined, it is first alloyed with the requisite amount
of silver, and is then granulated and treated in the same way as bars of silver con-
taining gold.
GOLD.
727
are suspended a number of copper bars, by which silver is rapidly pre-
cipitated in the form of a crystalline powder. In the course of a few
hours the last traces of silver are by this means completely removed, and
the metallic deposit, after being carefully washed, is compressed, by a
powerful hydraulic ram, into the form of solid rectangular bricks.
These, when dry, are fused in large earthen crucibles, and cast into
ingots. The silver thus obtained contains from 3 to 5 thousandths of
copper.
·
The pulverulent gold obtained by this first attack still contains a
considerable quantity of silver, and is therefore usually subjected to the
action of strong sulphuric acid in platinum vessels heated from a fire
placed beneath.
The solution of sulphate of copper produced during the precipitation
of the silver by copper bars is evaporated in a shallow cistern lined with
lead, and heated by a series of steam-pipes laid in zigzag across the
bottom. When the liquors have in this way been concentrated, they are
syphoned off into large tubs lined with lead and bound with copper or
wooden hoops, as, from the readiness with which sulphate of copper acts
on iron, bands of this metal would be rapidly attacked by any of the
liquor accidentally spilt over the sides of the vessels. After having
been filled, these tubs are closely covered to prevent their too rapid
cooling, and, after the expiration of about ten days, the mother liquors
are drawn off, and the crystals of sulphate of copper adhering to the
sides carefully removed. These mother liquors, when again concen-
trated, yield a further supply of crystallised salt, after which they are
set aside, to be employed in place of sulphuric acid in the second stage of
the operation, as already described.
When sulphate of copper of very superior quality is required, the
crystals first obtained are sometimes subjected to a second crystallisation,
but in the majority of cases they are merely washed on a wicker sieve,
and, after being allowed to drain in a large leaden cullender, are packed
in strong casks for the market. From the great economy with which
this process is conducted, and the comparatively low price of sulphuric
acid, it sometimes admits of being advantageously applied to the refining
of silver containing 0·0005 only of gold.
When an alloy consists chiefly of copper, and contains at most from
twenty to thirty per cent. of the precious metals, the parting is not
attempted until a portion of the copper has been oxidised by roasting in
a reverberatory furnace. The granulated alloy, after having been thus
treated, is acted on by weak sulphuric acid, by which oxide of copper is
alone dissolved; and when the mixture has in this way been enriched,
until it contains the requisite proportion of silver, it is subjected to the
usual process of refining by strong sulphuric acid. This method of
enriching the alloy by the oxidation of its copper was first employed at
Belleville, near Paris, where it has been for many years employed with
great success; it was also for some time practised at Freiberg for the
purpose of separating copper from the silver obtained by amalgamation;
but as the alloy there treated contained small quantities of several other
น
728
ELEMENTS OF METALLURGY.
metals besides copper, the fine silver obtained was found to be rather
brittle, and for this reason the process was ultimately abandoned.
During the time it was employed, the metal to be refined was subjected
to three successive roastings and attacks, and in this way silver contain-
ing only 4 thousandths of impurity was obtained.
Platinum vessels were at one time extensively employed for parting
alloys of silver and gold by means of sulphuric acid, and porcelain has
likewise been used for the same purpose; but as cast-iron resists the
action of concentrated sulphuric acid sufficiently for all practical uses,
and also possesses the advantage of cheapness, it has now almost entirely
superseded all other materials for the construction of such vessels.
The parting of gold and silver may also be effected by the use of nitric
acid, but this process can seldom be employed when the resulting nitrate
of silver cannot be advantageously utilised. Gold bullion has also
sometimes been refined by attacking with aqua regia and subsequently
precipitating the gold from the solution, by the use of ferrous sulphate
or otherwise, but cases in which such a method can be now employed arc
altogether exceptional.
REFINING BY CHLORINE GAS.*
The process of refining by chlorine gas was invented by Mr. F. B.
Miller, assayer in the Sydney Branch of the Royal Mint, and is applied
with great advantage to the treatment of bars obtained from melting
down placer gold, of those resulting from working auriferous quartz, or
whenever the proportion of silver present is not materially in excess of
10 per cent. This method of refining consists simply in passing a current
of chlorine gas through the gold while in a melted state, which is easily
done by thrusting into the molten metal a small clay tube connected with
a stoneware vessel in which chlorine is generated.
The chlorine, on coming in contact with the silver in the molten alloy,
at once combines with it, forming chloride of silver, which, being of less
specific gravity, rises to the surface of the melted gold, while this latter
remains in a purified condition beneath.
Chloride of silver has always been considered a somewhat volatile
substance, but, in practice, it is found that its volatility is not nearly so
great as might have been anticipated, and that, if its surface is coated
with a layer of fused borax, it may be kept melted at a high temperature
without very material loss.
The furnace required for the operation is the ordinary 12-inch square
gold-melting furnace, the principal points to attend to in its construction
being that the flue should be as near the top as possible, so as to allow of
the crucible standing high up in it without being cooled by the draught,
and that the furnace itself should not be too deep, so that, when the pot
is placed in the fire, the bottom of it may not be more than 3 inches above
the bars.
*The following description is an abstract of a paper read by Mr. Miller before
the Royal Society of Victoria.
GOLD.
729
The covering of the furnace should consist of two fire-tiles, 7½ inches
wide and 15 inches long, one of which should have a long slot or hole
in its centre, for the clay chlorine-pipes to pass through. An iron
cover will not answer, as it soon becomes much too hot for convenient
working.
The crucibles in which the refining is performed should be French
white fluxing-pots; ordinary black-lead pots will not answer, owing to
the reducing action they exert on the compounds formed. To prevent
the infiltration of the very fluid chloride of silver into the pores of the
clay pots they are prepared by filling them with a boiling saturated solu-
tion of borax in water, which is allowed to stand for ten minutes, and is
then poured off, the crucibles being afterwards set aside to dry; the
borax forms a glaze on the inner surface of the crucibles when they
become hot in the furnace.
1
2
When used for refining, these French clay crucibles are placed within
black-lead pots, as a precaution against loss, should the former crack,
which, however, seldom happens. The crucibles are covered with loosely-
fitting lids, with the requisite holes bored through them for the passage
of the clay chlorine-pipes, &c. A pipe, inch in diameter, 22 inches
long, and of-inch bore, has been found to answer all requirements.
The chlorine generators should consist of the best glazed stoneware acid-
jars, each capable of holding from 10 to 15 gallons, and furnished with
two necks. One of these openings should be stopped with a sound cork,
or vulcanised india-rubber plug, through which should pass tightly two
glass tubes, the eduction-tube and the safety- or pressure-tube; the length
of the former being a few inches, and the latter 8 or 10 feet. The other
opening, intended for introducing the oxide of manganese, &c., should be
closed with a leaden plug, covered with a short piece of india-rubber tube,
and well secured.
Each generator should be charged with a layer of small quartz
pebbles, down nearly to the bottom of which the pressure-tube should
extend. On this layer should be placed from 70 to 100 lbs. weight of
binoxide of manganese, in grains about -inch cube, sifted from powder;
this quantity will be sufficient to effect many refining operations, and will
obviate the necessity of repeated dismantling of the apparatus.
Each generator should be suspended to about half its height in a
galvanised-iron water-bath. The chlorine gas is produced, when required,
by pouring common hydrochloric acid down the safety-tube, the apparatus
being warmed by means of gas-burners beneath the water-baths. The
gas is conveyed from the generators by means of a leaden pipe fitted with
branches to supply the several furnaces, all intermediate connections
being formed by means of vulcanised india-rubber tubing, which, if
screened from direct radiation from the fire, stands the heat well, even
immediately over the furnaces.
Screw compression-clamps on the india-rubber tubes give the means
of regulating the supply of gas as required, and enable the operator to
shut it entirely off as soon as the refining is over. The chlorine then,
having no means of escape, accumulates in the generator, and soon forces
730
ELEMENTS OF METALLURGY.
t
all the acid up the safety-tube into a vessel placed above to receive it,
and, the acid no longer acting on the oxide of manganese, the supply of
gas ceases.
Two such generators, and three ordinary gold-melting furnaces, are
capable of refining about 2,000 ounces of gold containing about 10 per
cent. of silver, between 9 A.M. and 2 P.M.
As soon as the gold is melted, from 2 to 3 ozs. of borax in a state
of fusion are poured upon its surface. If the borax is added sooner,
it acts too much on the pot; and, if thrown in cold, is apt to chill
the gold.
The clay pipe which is to convey the chlorine to the bottom
of the melted gold is now introduced. At the moment of its entering
the melted gold, the screw compression-clamp is slightly loosened, so as
to allow a small quantity of gas to pass through it, and thus prevent any
metal rising and setting in the pipe, which is then gradually lowered to
the bottom of the molten gold, where it is kept by means of weights
attached to the top. The compression-tap is now relaxed, and the gas
is heard bubbling through the melted metal, sufficient hydrochloric acid
being, from time to time, added to the generators to keep up a rapid
evolution of chlorine.
The column of liquid in the safety-tube, acting, as it does, like a
barometer, affords a ready means of knowing the pressure in the genera-
tor, and of judging of the rate of production of the gas, as well as at
once showing, by its fall, if anything irregular has occurred--such as a
leak or a crack of the chlorine-pipe or pot. From 16 to 18 inches in the
safety-tube correspond to and balance 1 inch of gold in the refining-
crucible. When the chlorine is first introduced into the melted gold,
fumes are seen to pass up from the holes in the crucible lid; these are
not chloride of silver, but the volatile chlorides of some of the baser
metals, and they are especially dense when much lead is present in the
alloy under treatment, forming a white deposit on any cold substance
presented to them. After a time, longer or shorter, according to the
nature of the impurities in the gold, these fumes cease.
So long as any
decided quantity of silver is present in the molten gold, the whole, or
nearly the whole, of the chlorine is absorbed; little, if any, appearing
to escape.
As soon as the operation is nearly over, fumes of a darker colour
than those observed at the commencement make their appearance; and
the end of the operation is indicated by a peculiar flame or luminous
vapour of a brownish-yellow colour, occasioned by the escape of free,
and now waste, chlorine. This, however, is not a sufficient indication:
the process is not complete until this flame imparts to a piece of white
tobacco-pipe, when held in it for a moment, a peculiar reddish or
brownish-yellow stain.
When these appearances are observed, usually in about an hour and a
half from the introduction of the chlorine, the gas is shut off, and the pots
are removed from the fire; the white crucible is lifted out of the black
one, and, together with its contents, is allowed to stand several minutes,
until the gold becomes cold enough to solidify. The chloride of silver,
GOLD.
731
which remains liquid much longer, is then poured off into iron moulds.
The crucible is now inverted on an iron table, when the still red-hot
gold falls out in the shape of a cone; this is slightly scraped, and then
thrown, hissing, into a concentrated solution of common salt, to free it
from any adherent chloride of silver.
An alloy containing originally 89 per cent. of gold, 10 per cent. of
silver, and 1 per cent. of base metals, will yield, on an average, a cake of
chloride weighing, with a little adherent borax, 16 ozs. for every 100 ozs.
operated on.
The gold is now fine, and simply requires casting into ingots.
As before stated, it is found that all these operations can readily be
performed, and about 2,000 ozs. refined per day in three common melting
furnaces, in about five hours; 98 per cent. of the gold originally con-
tained in the alloy operated on is then ready for delivery.
The other 2 per cent. remains with the chloride of silver, partly in
the metallic state, and partly in a state of combination with chlorine,
and probably with silver.
1
8
To free the chloride of silver from this combined gold (that mechani-
cally mixed being eliminated at the same time), it is melted in a boraxed
white pot, with the addition of from 8 to 10 per cent. of metallic silver,
rolled to about inch thick. The chloride of gold is, by this means,
reduced at the expense of the metallic silver, chloride of silver being
formed; while the liberated gold sinks, and, together with the excess of
silver, melts into a button at the bottom of the pot. As soon as the
whole is thoroughly melted, the pot is removed from the furnace, and
allowed to stand about ten minutes; the still-liquid chloride of silver is
then poured into large iron moulds, so as to form slabs of a convenient
thickness for the next operation, namely, its reduction to the metallic
state.
The fineness of the gold produced by this process varies from 991 to
997 in 1,000 parts, the average being 993·5. The remaining 63 thousandths
are silver; this compares favourably with any of the previously-known
practical processes, none of which leave less silver in the resulting
fine gold.
If the refined gold be subjected to a re-refinage by chlorine, the
amount of silver left in it can be reduced to 0.2 per cent., just as in
refinage by the ordinary sulphuric acid process the same result can be ob-
tained by subjecting the refined gold to a further refinage with bisulphate
of potassium. For practical working, however, this would probably never
be attempted.
The silver resulting from this method of refining is tough, but its
quality varies somewhat according, to the gold originally operated on;
if the alloy treated contains much copper, the greater part of this
remains with the resulting silver, but the other metals are nearly all
eliminated.
The fineness of the silver hitherto obtained has varied from 918.2 to
992-0 in 1,000 parts, the average being 965.6.
An analysis of the silver resulting from refining gold, known
732
ELEMENTS OF METALLURGY.
originally to have contained, among the base metals in the alloy, copper,
lead, antimony, arsenic, and iron, gave the following results:-
Ag
Cu
972.3
25.0
Au
2.7
Zn and Fe.
traces
1,000.0
Miller's process for the purification of gold, by means of chlorine
gas, has been successfully introduced into the Royal Mint by Mr. W.
Chandler Roberts.
A
PLATINUM.
It
In its pure state, and especially when refined by the process of
Deville and Debray, platinum is nearly as white as silver; it is capable
of receiving a high polish, has neither taste nor smell, and is very
ductile and malleable. Platinum is softer than silver, but its hardness
is much increased by the presence of small quantities of iridium.
resists the strongest heat of a wind furnace, but may be fused by the
electric current or by the oxyhydrogen blowpipe, before which it is dis-
persed with scintillation. According to Deville and Debray, it absorbs
oxygen in the fused state, and when melted in considerable masses
spirts like silver on cooling. Platinum, which has a specific gravity of
about 21.50, is the heaviest of all known substances, excepting osmium
and iridium, of which the density is equally high, or even higher. Pla-
tinum is not oxidised by the air at any temperature, and is not attacked
by any of the simple acids; by aqua regia it is dissolved with formation
of platinic chloride, PtC14. Platinum is attacked by the caustic alkalies,
and by the alkaline earths, at a red-heat, particularly by the hydrate of
lithium or of barium; but it is not affected by the alkaline carbonates,
even when exposed to their action at very elevated temperatures. A
mixture of nitre and caustic potash produces this effect with greater
rapidity than the alkali alone; and laminated platinum, when heated in
presence of arsenic, sulphur, or phosphorus, loses its malleability and
ductility. When these bodies are brought, at a high temperature, in
contact with platinum in a fine state of division, combination readily
takes place, and brittle fusible compounds are the result. Platinum is
also attacked at high temperatures by acid sulphate of potassium. A
mixture of silica and charcoal attacks platinum at high temperatures,
producing silicide of that metal, and for this reason platinum crucibles,
which have been frequently ignited in an open fire, become rough on
the exterior, and lose their flexibility. Platinum vessels should never
be exposed to the direct action of a furnace, but should be inclosed in an
earthen crucible containing a little magnesia, or caustic lime.
PLATINUM.
733
Platinum alloyed with silver is soluble in nitric acid, and consequently,
gold containing small quantities of this metal may be assayed by inquar-
tation with silver, and the subsequent removal of silver and platinum by
boiling in nitric acid.
Platinum possesses the remarkable property of causing the combina-
tion of oxygen with hydrogen, and with other inflammable gases. This
property is exhibited even by clean surfaces of platinum, in a greater
degree by platinum in a spongy state, and still more by that metal in the
extremely-divided form known as platinum-black. Spongy platinum is
obtained by the ignition of ammonio-platinic chloride.
Platinum-black may be prepared in various ways. A common method
is by boiling a solution of platinic chloride, PtCl, with carbonate of
sodium and sugar. In this case, formation of chloride of sodium takes
place, platinum is precipitated in the metallic state, a portion of the
sugar is decomposed, and carbonic anhydride escapes during ebullition.
It may also be made by dissolving platinous chloride, PtCl2, in boiling
caustic potash, and gradually adding small portions of alcohol to the
solution. Rapid evolution of carbonic anhydride takes place, and the
metal is precipitated in a state of extreme division. The same result is
obtained by decomposing platinum sulphate by heat and strong alcohol.
Platinum-black prepared by one of the foregoing processes is some-
times employed in eudiometrical experiments.
This substance, when dried, resembles lamp-black, and soils the
fingers in the same way; it may be heated to full redness without any
change of its appearance or properties, but at a white-heat it assumes a
metallic aspect. Platinum in this state, like charcoal, absorbs and con-
denses gases within its pores. Platinum works well under the hammer,
forging and welding like iron.
DISTRIBUTION OF PLATINUM.-This metal is found in a native state,
and occurs alloyed with various others in alluvial deposits similar to
those from which gold, its frequent associate, is obtained; the sands
producing platinum lie principally in valleys traversing serpentine.
Native platinum generally presents the appearance of small flattened
grains, of a greyish-white colour, approaching to that of tarnished steel.
These grains are commonly flattened, and appear to have been polished by
friction against other hard bodies. Their size usually varies from that of
linseed to that of hempseed, but a few fragments of much larger dimen-
sions have occasionally been discovered. One piece brought from Choco,
in Peru, by Humboldt, and presented to the Berlin Museum, weighs 1,088
grains, or above two ounces avoirdupois. The Madrid Museum pos-
sesses a specimen found in 1822, in the gold mine of Condoto, in South
America, which is as large as a turkey's egg, and weighs 11,641 grains.
A specimen of this metal was found, in the year 1827, in the Ural
Mountains, near the Demidoff mines, which weighed 11.57 lbs. troy.
The largest specimen yet discovered weighs 21 lbs. troy, and is in the
cabinet of Count Demidoff.
The grains of native platinum are far from pure, the metal being
usually combined with osmium, iridium, palladium, rhodium, and ruthe-
734
ELEMENTS OF METALLURGY.
nium, besides gold, silver, iron, and copper; they are also frequently
associated with various heavy minerals, such as magnetite, titaniferous
iron, chrome iron ore, and iron pyrites.
Four specimens of native platinum afforded, on analysis, the following
results:
1.
2.
3.
4.
Pt
80.87
$2.60
85.50
80.00
Au
0.20
0.80
1.50

Fe
10.92
10.67
6.75
7.20
Ir
0.06
0.66
1.05
1.55
Rh
4·44
1.00
2.50
Pd
1.30
0.60
1·00
Cu
2.30
0.13
1.40
0.65
Os
Iridosmine
0.11
3.80
1.10
1.40
Sand
2.95
4.35
•
100.00
98.06
101.15
100.15
1. Ural, by Osann; 2. Borneo, by Böcking; 3. California, by Deville
and Debray; 4. Choco, by Deville and Debray.
Platinum was first discovered (1735) by Ulloa, a Spanish traveller,
in the alluvial deposits of the river Pinto, in the district of Choco, South
America. It has since been found in the Ural mountains, in the island
of Borneo, in the sands of the Rhine, in those of the Jacky in St. Do-
mingo, and in the gold-regions of Brazil, California, &c.
The gold-washings in Peru furnishing the largest quantity of pla-
tinum are those situated between the second and sixth degrees of south
latitude. Among these may be mentioned the mines of Condoto in the
province of Novita; those of Santa Rita or Viroviro; of Santa Lucia,
and the ravine of Iro, and at Apoto between Novita and Taddo. The
deposit of platinum here occurs in the alluvial gravel, at a depth of
about 20 feet from the surface.
The grains of platinum are separated from gold by amalgamation.
From an apprehension that platinum might be employed for the purpose
of debasing gold, it is said to have been formerly thrown into the rivers
with a view of preventing fraud, and that through this practice, large
quantities of this valuable metal have been lost. The grains of platinum
which are found in the sands of the river Jacky, near the mountains of
Sibao in St. Domingo, are extremely brilliant, and are intermixed with
a siliceous sand, which is frequently ferruginous.
The largest proportion of the platinum at present produced is ob-
tained in the Ural districts from the auriferous sands of Kuschwa,
Nischne Tagilsk, and Goroblagodat.
Russia annually affords about 35 cwts. of this metal, which is about
five times the amount of the united products of Brazil, Borneo, St. Do-
mingo, and the United States of Columbia.
PLATINUM.
735
The production of Borneo is estimated at about 500 lbs. per annum.
ESTIMATION OF PLATINUM.-This metal is, for the purposes of analysis,
weighed either in the metallic state, or in the form of ammonio-platinic
chloride, 2NHCl,PtC1, which is collected on a tared filter, and dried at
a temperature of 100° C.
When platinum exists in a solution in the form of chloride, the liquor
is first concentrated by evaporation, and subsequently mixed with about
twice its volume of pure alcohol. Solution of chloride of ammonium is
now added in excess, and the liquor again concentrated by evaporation.
in a water-bath; by this means ammonio-platinic chloride is precipi-
tated, and after being carefully washed, first with dilute solution of sal-
ammoniac, and afterwards with a mixture of alcohol and ether, is dried
in a water-bath. From the weight of the double salt obtained, the per-
centage of platinum is readily deduced, as every 100 parts of the former
correspond to 44-30 parts of metallic platinum. Instead of deducing by
calculation the weight of platinum from that of the double salt obtained,
its amount may be at once determined by decomposing the ammonio-salt
by ignition, and weighing the metallic spongy platinum which remains.
For this purpose the double chloride should be exposed to a full red
heat in a closed porcelain crucible, protected from direct action of the
fire by being inclosed in an ordinary earthen pot: the decomposition of
this salt may likewise be effected in a gas-furnace, in which case the ex-
ternal crucible of fire-clay may be dispensed with. This decomposition
of the salt by heat requires to be conducted with great care, since if the
evolution of ammonium chloride be too rapid, a notable amount of metallic
platinum will be carried off. Instead of using chloride of ammonium
for the precipitation, chloride of potassium may be employed; the
potassium salt, 2KCl,PtC14, which is in this case produced is either dried
and weighed, as when chloride of ammonium has been employed, or is
decomposed, by heating to redness, into metallic platinum and potassium
chloride. The latter is separated by solution in hot water, and the for-
mer dried and weighed in the metallic state.
The separation of platinum from other metals is often effected by
taking advantage of the insolubility of its double chloride, deposited on
the addition of either chloride of ammonium, or chloride of potassium,
to solutions containing chloride of platinum. The insolubility of this
metal in all the acids, excepting nitro-hydrochloric, is another property
which frequently affords a ready means of separating platinum from other
bodies. When platinum is alloyed with a considerable proportion of any
metal soluble in nitric acid, it becomes itself attacked by that reagent,
and consequently, although pure platinum is untouched when thus
treated, many of its alloys are completely soluble in this menstruum.
Native platinum cannot be assayed in the dry way, and its complete
analysis is a long and difficult operation, which can only be success-
fully undertaken by an experienced chemist.*
The commercial assay
*The first somewhat complete examination of platinum ore was made by
Dr. Wollaston; both Berzelius and Vauquelain have added much to our knowledge
of the chemistry of platinum. The processes employed by the former for the analysis
736
ELEMENTS OF METALLURGY.
of platinum is conducted by performing, on a small scale, one of the
various processes now to be described.
METALLURGY OF PLATINUM.
WOLLASTON'S PROCESS. The platiniferous grains subjected to metal-
lurgical treatment, besides containing the principal metal sought, also
yield variable quantities of the constantly-associated metals, palladium,
osmium, iridium, rhodium, and ruthenium; they also frequently contain,
in addition to these, gold, silver, iron and copper, together with various
heavy minerals, such as titaniferous and chrome iron ores.
When gold is present in sufficient quantity, the ore is first subjected
to amalgamation for the purpose of its extraction, and the residue, after
a careful mechanical preparation, and washing, first with nitric acid
and subsequently with hydrochloric acid, is treated for platinum. The
concentrated ore is attacked by aqua regia, containing an excess of hydro-
chloric acid, either in large glass carboys or in stoneware vessels, heated
on a sand-bath placed under a chimney, by which the evolved fumes
are carried off. The aqua regia by which the attack is made is always
diluted with water, as by this means a smaller quantity of iridium is
dissolved than when the acids are employed in an undiluted state, and
when this metal is present even in small quantity the platinum produced
is rendered hard and its tenacity impaired. The aqua regia is several
times renewed before the solution of the ore is completed, and care is
taken to avoid the inhalation of the escaping fumes, which, from the
presence of osmium compounds, are extremely prejudicial to the work-
men. The solution thus obtained is now set aside, in order that it may
brighten by subsidence, and the clear liquid, after being drawn off by a
glass syphon, is treated with solution of sal-ammoniac as long as a yellow
precipitate is deposited. The mother liquors from this precipitate still
contain a considerable amount of platinum, together with variable quan-
tities of the other metals originally present; these are precipitated by
bars of zinc, by which a deposit of a dark colour is produced, from
which a certain amount of platinum is obtained. With this view the
dark-coloured deposit is first washed clean with hot water, and the
residue subsequently re-attacked by aqua regia containing a large quantity
of hydrochloric acid; the excess of hydrochloric acid prevents the precipi-
tation of any palladium or lead contained in the solution. Sal-ammoniac
is now added to the clear solution, and a second precipitate of ammonio-
platinic chloride obtained.
The double chloride thus obtained is heated to redness in large black-
of platinum ores will be found described in Gmelin's 'Handbook,' vol. vi. p. 259.
Claus, in 1854 (Beiträge zur Geschichte der Platinmetalle), proposed a simpler and
in some respects more accurate method. More recently another method has been
devised by Deville and Debray (Ann. Ch. Phys. (3) lvi. p. 385). Abstracts of the
two processes last referred to are given in Watts's 'Dictionary of Chemistry,' Art.
'Platinum.'
PLATINUM.
737
lead crucibles, and by this means chlorine and sal-ammoniac are expelled
while metallic platinum, in a spongy state, remains.
This spongy platinum is next finely pulverised, by being rubbed
between the hands, and afterwards intimately mixed with water, so as to
form a dense black slime. This is carefully passed through sieves of
fine wire-gauze, and the coarser particles, which remain on the meshes,
again crushed, and ultimately made to pass through.
In conducting this operation, it is of importance to avoid the use of
any hard body, by which a commencement of aggregation between the
particles of metal might be produced; scrupulous cleanliness on the part
of the workmen is also necessary, to prevent the introduction of any ex-
traneous matter into the finely-divided mass, which might be sufficient to
cause a serious imperfection in the forged platinum produced. To avoid
this, the metallic powder is repeatedly washed, by decantation, previously
to its consolidation into one mass.
The platinum paste is now introduced into an apparatus consisting of
a gun-metal cylinder, accurately fitted with a steel piston, and inclosed
at the lower end in a steel foot-piece, by which the escape of the pasty
mass is prevented. Care is taken that the mass to be compressed be
entirely free from air-bubbles, and, after first ramming with a wooden
pestle, the steel piston is applied. The water is thus separated from the
metallic particles, and their closer compression is afterwards effected by a
hydraulic or powerful screw-press. The discs of platinum thus formed
are subsequently heated to whiteness, and then hammered on an anvil,
until a perfectly homogeneous mass has been obtained.
MODIFICATION OF WOLLASTON'S PROCESS.-A considerable proportion
of the platinum of commerce is prepared by the direct addition of sal-
ammoniac to the solution obtained from the ore, but when greater purity
is required the process is thus modified. The solution, which is gene-
rally deep-red, and evolves chlorine from the presence of tetrachloride of
palladium, is boiled; whereupon chlorine, is expelled, and the palladium
present reduced to the state of dichloride.
Chloride of potassium is now added to the solution, which precipitates
the platinum as sparingly-soluble double chloride of platinum and potas-
sium, leaving the palladium in solution. This precipitate, which, when
pure, has a yellow colour, but is red when iridium is present, is collected
on a filter, and washed with a dilute solution of chloride of potassium.
The double salt of platinum is ignited with twice its weight of carbonate
of potassium, and the platinum thus reduced to the metallic state while
a portion of the iridium remains as trioxide. The soluble potassium
salts are subsequently removed by washing with hot water, and the
platinum dissolved by nitro-hydrochloric acid, which leaves the trioxide
of iridium undissolved. In order to effect the complete separation of
iridium, it may be necessary to repeat the precipitation by chloride of
potassium and the re-solution of the platinum several times. The pla-
tinum solution thus freed from iridium is mixed with sal-ammoniac, and
the metal thrown down as double chloride of platinum and ammonium.
3 B
738
ELEMENTS OF METALLURGY.
This is ignited, and the resulting spongy platinum treated as before
described.
When platinum ore is attacked by aqua regia, a portion consisting of
grains of iridosmine, besides various foreign substances which have not
been entirely removed by washing, always remains undissolved.
DEVILLE AND DEBRAY'S PROCESSES.-Platinum prepared as above de-
scribed is never quite pure, but contains small quantities of osmium,
silicon, &c. In order to remove these impurities, and at the same time
to render it more compact and freer from cavities, it is fused in a furnace
composed of blocks of well-burnt lime, by means of a hydrogen or coal-
gas flame supplied with a current of oxygen.
In a furnace of this description, Deville and Debray succeeded, with a
consumption of about 43 cubic feet of oxygen, in melting and refining
25.4 lbs of platinum in the course of forty-two minutes; very much
larger masses have since been melted by this method.
During the operation of fusion, the osmium is expelled in the form of
tetroxide, while silicon is removed in the state of silicate of calcium,
which, forming a fusible slag, is ultimately absorbed by the walls of the
furnace.
Lime is so bad a conductor of heat that a basin of this substance
less than an inch in thickness may be filled with melted platinum without
the temperature of the exterior being raised much beyond 150° C.
Deville and Debray have likewise introduced the following process
for the treatment of platinum ores in the dry way. A small reverbera-
tory furnace, of which the bottom consists of a hemispherical cavity of
fire-brick lined with refractory clay, is, after being heated to full redness,
charged with a mixture consisting of 2 cwts. of platinum ore and the same
weight of galena. The charging occupies some time, as small quantities
only are introduced in succession, and the whole is kept constantly
stirred until a fusible matt has been produced. A small quantity of
powdered glass is used as a flux, and by degrees a weight of litharge,
equal to that of the galena employed, is thrown in; the reaction which
takes place between the galena and litharge results in the expulsion of
sulphur and the reduction of the lead to the metallic state. The reduced
lead forms with the platinum a readily-fusible alloy, which is allowed to
remain for some time undisturbed in a melted state; in this way the
iridosmine, which has not been attacked, and of which the specific
gravity is very high, collects at the bottom of the metallic bath. The
upper portion of the platiniferous alloy is now drawn off into ingot-
moulds, while the residue, containing iridosmine, is added to the next
charge. The platiniferous lead is subsequently subjected to cupellation
in the ordinary way, and the crude platinum obtained is refined on a bed
of lime, by the heat evolved during the combustion of a mixture of coal-
gas and oxygen. The platinum thus prepared is nearly pure, is very
ductile and malleable, and works well under the hammer.
The inalterability of platinum at high temperatures, together with its
power of resisting the action of a great number of the most powerful
PLATINUM.
739
chemical agents, renders it a useful material for the manufacture of
crucibles, evaporating dishes, &c., for laboratory use. Large platinum
stills are also sometimes employed for the concentration of sulphuric
acid; vessels employed for this purpose are strongly gilt on the inside, as
unless thus protected, platinum prepared by Wollaston's 'process soon
becomes sufficiently porous to admit of the transudation of the acid. An
attempt was made some years since, in Russia, to introduce a platinum
coinage, but not having been found convenient, the coins were ultimately
withdrawn from circulation.
3 B 2
(741)
INDEX.
ABEL.
A.
ABEL on state of carbon in chill-castings,
&c., 114
Abstrich, 595
Abzug, 595
Acicular bismuth, 505
Acids, effects of, on grey and white iron,
114
Agitator, Washoe process, 656
Agricola, ancient process of cupellation,
596
Air-dried peat, water in, 35
wood, 29
Alloys, 13
use of, in blast-furnaces, 242
, specific gravities of, 14
action of acids on, 15
action of air on, 15
of iron, 120
of aluminium, 364
of copper, 435
of tin, 455
of antimony, 462
of bismuth, 513
Alluvial gold deposits, 685
Almaden, aludel furnace of, 503
>
, arrangement of aludels at, 504
annual production of mercury at, 504
Alston Moor, lead ores at, 519
Altenberg, roasting kilns at, 186
, preparation of metallic arsenic at, 463
Aludel furnace of Almaden, 503
Aluminium, properties of, 362
minerals yielding, 362
estimation of, 362
metallurgy of, 363
discovery of, 363
alloys of, 364
preparation of, from cryolite, 364
Amalgam, native, 603
filtration of, 631
bricks of, 632
retorting of, 632
condensation of the mercury evolved
in retorting, 723
Amalgamation, methods of, 624
Mexican or patio process, 625
stove, 633
hot process of, 633
in barrels, 635
ANTHRACITE.
Amalgamation of copper matts, 641
Washoe process of, 642
America, charging of charcoal furnaces in, 231
American bloomery, 168
economising waste heat from, 169
daily production of iron in, 169
hearth, 575
at Bleiberg, 575
observations by Plattner on, 575
at Przibram, 576
Ammiolite, 492
Ammonia, attempted collection of, from
coke-ovens, 88
Analysis of fuel, 24
estimation of ash, 24
of hygrometric moisture, 25
of sulphur, 25
of carbon and hydrogen, 26
of nitrogen and oxygen, 26
of iron ores, 156
estimation of water, 156
attack by hydrochloric acid, 156
estimation of insoluble matter, 157
of lime and magnesia, 157
of sulphur, 158
[158
of phosphoric anhydride,,
of carbonic anhydride, 158
of titanic oxide, 159
of insoluble residue, 159
Anchor coke-oven, 79
-, cooling of coke from, 79
Ancient mines on borders of Ural Moun-
tains, 2
tools found in, 2
smelting in Siberia, 3
distinction between argentum vivum
and hydrargyrus, 3
alloys of copper, 5
zinc-brass coins, analyses of, 6
steels, 7
use of sulphide of antimony, 8
Anglesite, 517
-, cupreous, 517
Annealing, 10
Anthracite, 48
composition of, 48
formation of, 48
use of, in blast-furnaces, 242
objections to use of, 259
furnaces, 259
•
dimensions of, 259
charges for, 259
742
INDEX.
ANTHRACITE.
Anthracite furnaces, spiegeleisen made in, 260`
for spiegeleisen, dimensions of, 260
Antimonial nickel, 359
Antimonious oxide, 457
Antimony known to the ancients in the
metallic state, 8
properties of, 456
ores, 457
sulphide of, 457
tetroxide of, 458
ochre, 458
blende, 458
AUSTRIA.
Assay of iron ores, crucibles, brasquing of, 150
-, regulation of temperature
in, 150
testing buttons produced, 151
conclusions deduced from
colour of slag, 151
Swedish process for, 152
wet, 152
Marguerite's process, 152
Penny's process, 154
of
copper ores, dry, 378
>
Cornish method, 378
"
annual production of, 458
reduction of sulphide of, by iron, 459
by iron, 460
metallurgy of, 460
eliquation of the sulphide of, 460
reduction of, to the metallic state, 460
English method of smelting, 461
>
singling, 461
doubling, 461
melting for star metal, 461
alloys of, 462
slags from smelting, 462
ores, assay of, 458
class I. containing oxides, 458
class II. sulphides, 459
Aphanesite, 373
Armour-plates, 308
Argentite, 603
Arquerite, 603
hammered, 308
Arrastra, 626, 712
Arsenic, properties of, 462
white, manufacture of, 463
metallic, preparation of, 463
at Altenberg, preparation of, 463
at Reichenstein, preparation of, 464
Arsenical ores, assay of, 462
Arsenious oxide, condensation of, 450
, production in Devon and Cornwall, 450
Artificial fuels, preparation of, 50
Ashburner, on cost of extracting gold from
gold quartz, 724
Ashes of woods, 32
of peat, 35
of American peat, 37
of lignite, 42
of coal, 46, 47
of Boghead cannel, 47
Assay furnace, 144
of iron ores, dry, 144
fluxes, 146
-, apparatus necessary for, 144
preliminary operations and
classification of ores, 146
classification and proportion
of fluxes, 148
proportion of fluxes in Ger-
man iron-works, 149
assay, 149
method of conducting
crucibles used for, 150
German, 383
, wet, 385
,
precipitation by zinc, &c., 385
Pelouze's process, 387
by cyanide of potassium, 388
of tin ores, 444
of antimony ores, 458
of arsenical ores, 462
of zinc ores, dry, 472
?
of mercury ores, 495
, wet, 473
volumetric, 474
distillation with quicklime
[496
with sodium bicarbonate,
method employed at Idria,
in current of hydrogen, 495
of bismuth ores, 509
of lead ores, 524
[491
[flux, 526
by fusion with alkaline
with metallic iron, 527
with carbonate of sodium
and metallic iron, 528
nitre, 531
of silver ores, 610
of silver bullion, dry, 613
wet, 617
of auriferous minerals, 694
,
cupellation, 694
parting, 694
of gold quartz, 695
bullion, 698
Atacamite, 373
Aubel on fusion of nickel, 361
Augustin's process for extraction of silver, 664
"
first roasting, 665
roasting with salt, 665
lixiviation and precipitation, 665
, arrangement of apparatus, 665
,
precipitation of silver and copper, 666
products obtained by, 667
, expense of, 667
Auriferous minerals, assay of, 694
veinstone, extraction of gold from, 712
the arrastra, 712
Chilian mill, 712
stamping mill, 714
Australia, discovery of gold in, 692
,
yield of gold in, 693
tin ores in
Austria, Bessemer process in, 335
blowing engines in, 215
INDEX.
743
AYRESOME.
Ayresome Iron-Works, furnace hoist at, 237
>
kiln hoist at, 238
empty waggon drop at, 241
Azurite, 370
weekly production of iron at, 256
B.
BALLING or re-heating, 302
Bankart's process for extraction of copper, 423
Barrel amalgamation, 635
640
?
at Halsbrücke, 635
roasting the ore with salt, 635
reactions during roasting, 636
of roasted ores, 637
loss of silver by, 640
, arrangement of barrels, 637
wrought-iron used in, 638
addition of mercury, 638
discharging the barrels, 639
reactions in, 639
treatment of slimes, 639
filtration of amalgam, 640
, retorting, 640
fusion of silver alloy, 640
treatment of flue-dust, slags, &c.,
loss of mercury at Freiberg, 641
at Constante, 641
Real del Monte, 641
in Nevada, 641
Barrow-in-Furness, method of collecting
waste gases at, 231
materials used in the production of one
ton of iron at, 257
Bessemer converters at, 338
Bath metal, 435
Baudrimont's table of tenacity of metals, 11
Bauerman on composition of cast-iron and
steel, 116
Bauxite, analysis of, 191
Beechwood charcoal, composition of, 61
Belfast, iron ore from, 191
Belgian process for extraction of zinc, 480
naces, 482
>
minerals employed in, 480
precaution in lighting new fur-
charging the retorts, 482
tapping the condensed zinc, 483
cleaning the tubes, 483
loss of zinc in, 483
Bell, I. L., on heat absorbed in blast-furnace,
261
observations of, on dissociation of car-
bonic oxide, 197
Bell-metal, 435, 456
Bérard's process for manufacture of steel, 339
Berthier's process for estimating calorific
power of fuel, 19
inaccuracy caused by pre-
sence of hydrogen, 20
for extraction of nickel, 360
BLANKET.
Berthier on composition of Mansfeld schist, 407
Bessemer's process, pressure of blast in, 327
formation of burnt iron by, 327
modifications of, 327
method of conducting, 332
, pig-iron free from phosphorus
required for, 333
-, analysis of slags from, 334
action of silicon in, 335
action of manganese in, 335
analyses of metal at various
stages of, 336
in Austria, 335
converter, 328
-, lining of, 328
,
description of, 329
list of works using, 338
plant, 330
at Neuberg, 333
pig-iron, 247
steel, classification in Sweden of, 334
analyses of, 337
rails, preparation of, 337
appliances for manufacture
of, at L. & N. W. R. works, Crewe, 337
loss of weight in converting
pig-iron into, 338
Best-selected copper, 401
401
principles involved in making,
Birmingham, nickel-works of, 360
Bismuth, properties of, 507
commercial, 507
purification of, 507
action of acids on, 507
ores, 508
-, native, 508
sulphide, 508
blende, 508
acicular, 508
and tellurium, 508
oxide of, 508
carbonate of, 508
annual production of, 509
ores, assay of, 509
metallurgy of, 509
extraction of, Schneeberg process, 509
2
Joachimsthal process, 510
production of, at Freiberg, 510
occurrence of, in refinery hearths, 511
, alloys of, 513
Bituminous coal, 45
Blackband ironstone, 140
-, analysis of, 141
Black Brush ore, 134
Black plates, 310
Black tin, assay of, 445
in brasqued or black-lead
crucibles, 445
nide, 446
Cornish method, 446
fusion with potassium cya-
Blankets, use of, in collection of gold, 715
744
INDEX.
BLANKET.
Blanket-washings, amalgamation of, 720
Blast cylinder at Dowlais, 211
212
reservoir in connection with,
Blast, hot, history of, 216
Blast-furnace and accessories, 196
"
reactions in, 197
primitive form of, 198
stack or body of, 198
boshes, 198
throat, 198
belly, 199
hearth, 199
tymp, 199
dam-stone, 199
dam-plate, 199
fore-hearth, 200
}
tymp-arch, 200
•
?
tuyer-holes, 199
cinder-notch, 200
cinder-tub, 200
cinder-fall, 200
roughing-hole, 200
tap-hole, 200
at Oldbury, 201
at Stockton Iron-Works, 201
at Ditton Brook, 201
obstruction of hearth of, 246
fuel used in, 241
coke suitable for use in, 242
use of raw coal in, 242
of anthracite in, 242
of turf in, 242
of air-dried wood in, 242
weight of air thrown into, 242
blowing-in of, 243
proportion of charge for, 243
-, number of workmen employed about,
243
descent of charges in, 243
mixing of charges for, 244
distribution of materials in, 244
tapping of, 245
" effects of various methods of charg-
ing, 244
261
coal suited for use in, 259
heat absorbed for work done in,
slags, 192
analyses of, 192
from treatment of spathic ores,
analyses of, 193
height of, 205
dimensions of, 206
in the Cleveland district, 210
-, capacity and production of, 250
-, modern, increased
production of,
251
, pipes and nozzles, 227
connections for cold-blast, 227
-, hot-blast, 227
Blauöfen, 251
Bleiberg process of lead-smelting, 545
BRICKS.
Bleiberg process, fuel employed in, 549
method of conducting operation, 549
, payment of wages,
wages, 550
ore-hearth at, 575
Blende, zinc, 466
-, roasting, 477
bismuth, 508
Blicksilber, 595
refining of, 596
Blister-copper, 399
Blister-steel, 115, 316
Bloomery, American, 168
169
>
economising waste heat from,
daily production of iron in, 169
high or Stückofen, 170
in Carniola, 171
fuel required for, 171
Blowing engine at Dowlais Iron-Works, 212
air discharged by, 212
dimensions of beam, 213
, fly-wheel, 213
boilers for, 215
Slate's, 215
Thomas and Laurent's, 215
Fosseys', 215
Austrian, 215
in Rhenish Prussia, 216
engines in the north of England, 214
at Creuzot, 214
high-speed, 215
power, reserve of, 216
in of a blast-furnace, 243
out of blast-furnaces, 246
Blowing machinery, 210
Blue billy, 281
Boghead cannel coal, composition of ash of, 47
Bog iron ores, analyses of, 138
Boliche or Spanish furnace, 546
history of, 547
dimensions of, 547
caldeo, 548
blandeo, 548
corrida, 548
at La Fortuna, Linares, 548
,
yield of lead from, 548
Brass, 436
436
composition of different varieties of,
calamine, manufacture of, 437
direct preparation of, 438
solder, 435
Breckon and Dixon's coke-oven, 76
nature of improvements in, 77
quality of, and quantity of coke
made in, 79
Bricks, fire, 104
additions made to clay in manu-
facture of, 104
manufacture of, 105
composition of, 105
labour and fuel required in
manufacture of, 105
INDEX.
745
BRICKS.
blue, 106
Bricks, fire, Dinas, composition of, 106
Britannia metal, 456
British coals, composition of, 45
British Columbia, occurrence of gold in, 691
Bronze, 14, 456
Brown coal, charring of, 89
iron ores (older), 134
analyses of, 134
-, newer, 135
from Oolite, analyses of, 136
Brunton's calciner, 647
Bull-dog, 195, 281
slag, 196
Bullion, silver, fire assay of, 613
calculation of results, 614
>
, quantity of lead required for cu-
pellation, 614
alloyed with copper, lead required
for cupellation, 615
618
humid assay, 617
standard solution, 617
decimal solution, 617
method of conducting an assay,
, apparatus employed, 618
correction for temperature of
standard solution, 623
-, preparation of standard solution, 623
, gold, assay of, 698
Burden, effects of, on character of slag, 194
Burnt cupreous pyrites, treatment of, 428
-, grinding and sifting, 429
calcination, 430
lixiviation, 432
process, 434
, precipitation of copper, 433
modifications of ordinary
recovery of sodium sul-
phate from waste liquors, 434
, composition of, 429
, proportion of salt and sul-
phur required for roasting, 429
, assay for determining when
completely calcined, 432
tals from, 679
iron, 310
cess, 327
extraction of precious me-
formation of, by Bessemer's pro-
Cadmia, 6
Cake-copper, 401
Caking coal, 43
C.
effects of different methods of
treatment on, 44
effect of exposure to air on, 44
effects of inorganic matter on,
44
unsuitable for metallurgical pro-
cesses, 45
Calamine, 467
CAST-IRON,
Calamine, calcination of, 477
brass, manufacture of, 437
Calcination and roasting, distinction between,
391
Calcining kilns of Cleveland district, coal used
in, 256
California, gold-fields of, 689
Californian coal, 42
Calomel native, 492
Calorific intensity, definition of, 16
of fuel, 23
Calorific power, definition of, 16
of fuel, 16
of carbon, 18
of carbonic oxide, 19
of hydrogen, 19
o fuel, Berthier's method of esti-
mating, 19
of coal, 22
determination of, by means of
litharge, 27
Calorific powers, table of, 21
Calorimetric experiments of Rumford, 17
Canada, gold raised in, 691
Cannel coal, 47
Capacity and production of blast-furnaces,
250
Carbon, products of combustion of, 19
calorific power of, 18
>
state of, in steel, 114
percentage of, in cast-iron, 115
state of, in cast-iron, 262
graphitic, estimation of, in iron and
steel, 348
combined, estimation of, in iron and
steel, 349
determination of, in iron and steel,
Eggertz's process, 351
Carbonic oxide, calorific-power of, 19
Carbonisation of coal in heaps, 66
construction of heaps, 66
regulation of combustion, 67
Carinthia, refinery process in, 268
puddling in gas-furnaces in, 284
Carinthian process for making steel, 321
Caron on state of carbon in steel, 114
Case-hardening, 115, 319
Cassiterite, 440
Castilian furnace, 553
ores suitable for, 554
removal of slag from, 554
-, expenditure of coke in, 554
use of scrap-iron in, 555
in Derbyshire, 534
Cast-iron, nitrogen in, 116
Bauerman on composition of, 116
state of silicon in, 117
effects of silicon on, 118
strength of, 250
state of carbon in, 262
silicon in, 262
partial decarburisation of, by cementa-
tion, 343
746
INDEX.
CAST-STEEL.
CLAYS.
Cast-steel, 344
manufacture of, 345
time occupied in melting, 346
fuel consumed in making, 346
Catalan process, for direct reduction of iron
ores, 163
168
description of furnace, 163
-, hearth, 164
blowing-machine, or trompe, 165
regulation of air supply, 166
hammer employed in, 166
method of working, 166
, massouquettes from, 167
greillade, 167
reactions in, 167
, massoques, 168
time employed in working charge,
weight of ore treated, 168
character of metal obtained, 168
Cementation, 115, 313
315
converting furnace for, 314
—, charging of, 314
time required for, 315
trial-bars, 315
preparation of charcoal for use in, 315
iron from Swedish ores, suited for,
increase of weight experienced by iron
during, 316
physical properties of bars before and
after, 316
of cast-iron, 343
Cerussite, 516
Cervantite, 458
Charcoal, 50
relative advantages of quick and slow
charring, 51
60
determination of yield of, 51
quantity of, yielded by different woods,
, quantity of, produced by various
methods of burning, 60
absorption of gases and water by, 61
peat, 61
from beech wood, composition of, 61
and coke manufacture of, by Mr. E.
Rogers, 70
from brown coal, 89
piles, irregular contraction of, 53
-, yield of, per acre of forest-land, 241
Charcoal-burning in piles, 51
?
, disadvantage of, 57
in rectangular heaps, 55
collection of pyroligneous acid, 57
in long piles, 57
lation, 57
collection of products of distil-
in China, 57
Charcoal hearth, methods of manufacturing
iron in, 276
Charcoal kilns, varieties of, 58
grates of, 58
Charcoal kilns, for saving both tar and char-
coal, 59
uncondensible gases evolved from,
used as fuel, 60
253
furnace, Swedish, 206
utilisation of waste gases from, 206
furnaces, iron, 251
Styrian, ores treated in, 251
Von Fischer's, 252
Von Fridau's, 252
of Sweden, 252
>
temperature of blast, 253
weekly production of, 253
consumption of charcoal in,
Charring of wood, loss of bulk occasioned by, 56
in furnaces or kilns, 57
of peat in ovens, 63
of brown coal, 89
Chenot's process for direct reduction of iron,
172, 317
>
construction of furnace, 172
cooling reduced metal, 173
charge of furnace, 172
balling of sponge, 173
Chili and Bolivia, copper supplied by, 377
Chilian mill, 713
Chill-casting, effect of, on carbon in iron, 114
China, charcoal-burning in, 57
Chlorination process for extraction of gold, 724
method of conducting, in Cali-
fornia, 724
?
precipitation of the gold, 725
at Reichenstein, 725
at Schemnitz, 725
Chodnew, analysis of Obuchow's steel, 341
Chrysocolla, 372
Cinder-pig, 118, 195
Cinnabar, 491
modern deposits of, 492
Circular hot-blast stove, 219
-, passage of air through, 220
Claudet's process for the extraction of silver
from burnt pyrites, 433, 679
681
analysis of strong liquors, 680
estimation of silver in the liquors,
precipitation of silver, 681
analysis of silver precipitate, 681
Clausthal, reduction of lead ores at, 555
use of slag-nozzles, 556
collection of fume, 556
first matt, 557
, roasting first matts, 558
second matt, 558
third and fourth matt, 559
, copper matt, 559
Clausthalite, 516
Clay ironstones, 139
-, analyses of, 140
Clay's process for direct reduction of iron
from cres, 171
Clays, fire, 101
INDEX.
747
CLAYS.
Clays, fire, composition of British, 102
foreign, 103
effect of impurities on, 104
Cleveland ironstone, 141
district, roasting kiln in, 190
in, 231
in, 256
blast-furnaces in, 210
modifications of cup and cone used
furnaces of, 253
ore smelted in, 256
-, average production of a furnace
Cloez, method of extracting nickel, 360
Close-regulus, analysis of, 403
Coal, calorific power of, 22
-, composition and origin of, 38
occurrence of, 38
formation of, from woody tissue, 38
, nitrogen in, 39
sulphur in, 39
inorganic matter in, 39
red and white ash, 39
occurrence of minerals in, 39
brown, or lignite, 39
occurrence of, 40
Californian, 42
free-burning, 43
-, caking, 43
cretaceous, composition of, 43
bituminous, 43
effect of heat on the caking property
of, 44
ashes, composition of, 46
cannel, 47
best suited for blast-furnace, 259
Coals, British, composition of, 45
, foreign, composition of, 46
Coarse-metal, granulation of, 379
Cobalt, 354
,
ores of, 355
bloom, 355
glance, 355
and nickel, estimation of, 355
-, preparations of, 356
>
separation of, from nickel, 356
oxide of, 356
blue, 358
Coccinite, 492
Cogging mills, Ramsbottom's, 337
Coke, 65
first employment of, 65
good quality, properties of, 66
influence of mode of preparation on, 66
making at St. Etienne, 74
produced in ovens, properties of, 76
composition and properties of, 88
, power of absorbing water, 88
suited for use in blast-furnaces, 242
furnaces, iron, 254
in Siegen district, 254
Coke-oven, 71
without fire-place, Rive-de-Gier, 74
lining of, 75
COPPER.
Coke-oven, construction of, 74
charging of, 75
>
,
regulation of draught in, 75
charge, amount of, 75
continuous operation of, 76
duration of process, 76
Breckon and Dixon's, 77
nature of improvement, 77
quality and quantity of coke made
in, 79
>
, anchor, 79
cooling of coke from, 79
Pauwel's and Dubochet's, 81
use of, at St. Etienne, 82
Pernolet's, 82
products obtained by, 82
chief features of, 83
charge of, 83
condenser applied to, 86
washers, 86
time occupied in working charge, 87
treatment of impure coal in, 87
Coke-ovens, charge of, 72
drawing charges of, 72
near Newcastle, 73
cooling of, 73
collection of tar from, 80
Silesian, 80
-, charge of, 81
-, regulation of combustion, 18
coal used in, 81
waste heat from, 88
collection of ammonia from, 88
Coking in mounds, 67
70
dimensions of mound, 68
lighting of mounds, 68
in rectangular kilns, 68
, charging the kilns, 68
, airways left in, 69
-, regulation of draught, 69
time occupied by the process,
yield of coke, 70
in ovens, 71
regulation of draught, 72
time taken in working a charge, 72
Cold-short iron, 310
Colour of metals, 8
Colouring of jewelry, 702
Combustion, products of, 16
Condensation of arsenious oxide, 400
Condie's steam hammer, 294
Condurrite, 373
Converter, Bessemer, 328
"2 number of charges of steel worked
daily in, 338
Converters at Barrow-in-Furness, 338
Copper, importance of, in ancient manufac-
tures, 4
ancient alloys of, 5
-, occurrence of, in peat, 37
nickel, 359
preparation of chemically-pure, 365
748
INDEX.
COPPER.
COWPER.
Copper, properties of, 365
ร
>
effects of acids on, 365
met with in commerce, impurity of, 365
blue carbonate of, 370
sulphate of, 373
selenide of, 373
annual production of, in the world, 377
supplied from Chili and Bolivia, 377
available supplies of, since 1865, 377
estimation of, by potassium cyanide, 388
-, principles involved in metallurgy of,
391
refining of, 399
best-selected," 400
overpoled, 400
dry, 400, 404
tough-pitch, 404
cakes, 404
tiles, 401, 404
ingots, 404
precipitated from mine waters, 420
alloys of, 435
Copper-smelting, roasting the fine- or white-
metal, 399
refining and toughening, 399
, making of "best selected," 400
modifications of English method, 402
Napier's method, 404
Rivot and Phillips's method, 406
Continental method, 407
in blast-furnace, Mansfeld, 410
Copper-extraction, wet processes for, 419
Cordurie's process, dezincification of lead,
588
Cornish assay of copper ores, 378
379
379
alloyed with manganese, &c., 436
matt obtained in lead smelting, 559
383
mica, 373
?
native copper, 366
cuprite, 366
melaconite, 367
redruthite, 367
copper pyrites, 368
erubescite, 369
tetrahedrite, 370
blue carbonate of copper, 370
green carbonate of copper, 371
chrysocolla, 372
ores, 366
iron, 385
"
distribution of, 374
dry assay of, 378
wet assay of, 385
by precipitation by zinc or
Pelouze's process, 387
by cyanide of potassium, 388
Copper-extraction, wet, German hydrochloric-
acid process, 420
process, 421
rites, 428
at Twiste, 420
>
Henderson's hydrochloric-acid
Longmaid's processes, 422
Bankart's process, 423
Linz processes, 423
Sinding's process, 425
Henderson's process, 427
treatment of burnt cupreous py-
Copper-smelting, English method of, 392
calcination of mixed ores, 393
fusion of calcined ores with raw
ores, slags, &c., 396
calcination of granulated or
crushed coarse-metal, 398
fusion of calcined coarse-metal
with ores, slags, &c., 398
>
>
, apparatus employed, 378
preliminary examination,
method of conducting assay,
fusion for regulus, 379
calcination of the regulus,381
fusion for coarse copper, 382
refining, 382
treatment of slags for copper,
method of assaying tin
ores, 446
, process of lead-smelting, 544
>
calcination, 545
flowing, 545
time occupied by, 546
Cornwall and Devon, lead ores in, 519
Coronarium, 5
Corsican process for direct reduction of iron
ores, 169
up, 170
2
[169
roasting, reduction and fusion in,
forging massé into bloom, 170
duration of roasting and working
, expense of production by, 170)
fuel used for, 170; yield, 170
Cost of blast-furnaces at Newport, 260
Cotunnite, 514
Couëron, lead-smelting at, 540
ores smelted at, 541
calcination of lead ores at, 542
smelting at, 543
repairing of furnace bottom at, 544
coal consumed at, 544
weight of charges, &c., 544
treatment of siliceous lead ores at, 564
calcination, 565
-, five-tuyer furnace, 566
reduction of roasted ores and
grey slags, 567
568
,
>
water-casing of furnace, 568
composition of smelting mixture,
lighting the furnace, 568
, management of furnace at, 569
quantity of material smelted, 570
loss of lead, &c., 571
silver refinery at, 589
Couplings of rolling mills, 300
Cowper's hot-blast stove, 222
INDEX.
749
COWPER.
Cowper's hot-blast stove, action of, 223
temperature of blast from, 224
arrangement for prevention of
choking, 224
Crace-Calvert, F., on estimation of sulphur
in coal and coke, 26
Cradle, gold-washing in, 704
Cretaceous coal, composition of, 43
Creuzot, blowing engines at, 214
Crucibles, 106
, properties required in, 106
highly refractory, mixture for, 107
action of metallic oxides on, 107
and refractory materials, testing fusibil-
ity of, 108
burnt and unburnt, 108
London, 108
,
Cornish, 108
Hessian, 109
>
French, 109
•
plumbago, 109
for making cast-steel, 345
Crucible tongs, 145
Cryolite, preparation of aluminium from, 364
Crystallisation, 9
Cuprite, 366
D.
Damascening, 347
Danks's rotative puddling furnace, 288
, description of, 289
supply of air to, 289
, separation of silicon and phos-
phorus from iron in, 289
—, weight of ball from, 290
Dannemora iron ores, composition of, 129
Darlaston, method of collecting waste gases.
at, 229
Davy, discovery of aluminium by, 363
Derbyshire, lead ores in, 519
by zinc, 584
FERROUS.
Drying of peat, 34
Dry wood, elementary composition of, 31
distillation, 48
puddling, 278
method of conducting the opera-
tion of, 283
copper, 400
Ductility of metals, Table, 11
Dufrenoysite, 515
Dumas's table of hardness of metals, 9
Duplex hammer, 295
E.
EASTWOOD'S mechanical stirrer, 286
Eggertz's processes for analysis of iron and
steel, 351
Eggertz on carbon in Swedish iron and steel,
352
Ekman's re-heating furnace, 305
Elasticity, 12
Electrum, 2
Elementary composition of dry wood, 31, 32
of dry peat, 35
Elevated temperatures, measurement of, 23
Elutia, 4
Embolite, 606
English method of copper-smelting, 392
ores treated by, 392
conditions to be observed in
making mixtures, 392
393
calcination of mixed ores,
fusion of calcined ores with
raw ores, slag, &c., 396
calcination of granulated or
crushed coarse-metal, 398
fusion of calcined coarse-
metal with ores and slags, 398
metal, 399
Desilverisation of lead, 578
Detroit, composition of charges at, 254
Deville, Sainte-Claire, manufacture of alumi-
nium by, 363
478
Deville and Debray's processes for treatment
of platinum, 738
Dinas fire-brick, composition of, 106
Direct and indirect production of iron, appa-
ratus for, 197
Dissociation of carbonic acid in blast-furnace,
197
Distillation, dry, 48
Distribution of iron ores, 127
Ditton Brook Iron-Works, 201
working of new furnace at, 257
Double shear-steel, 317
decompositions, lead-smelting by, 537
Dowlais, roasting kilns at, 187
capacity of furnace at, 258
blast cylinder at, 211
blowing engine at, 212
refinery at, 263
, roasting the fine- or white-
refining and toughening, 399
modifications of, 402
process for the reduction of zinc ores,
"
fuel employed in, 479
duration of crucibles, 479
introduction of new pots, 479
, compared with other pro-
magnetic iron ores, 130
cesses, 480
Erinite, 373
Errors in analysis of coal, Dr. Percy on, 26
Erubescite, 369
Erzgebirge tin-smelting in the blast-furnace,
455
Eucairite, 606
Euchroite, 373
Expansion of metals by heat, 13
FAHLERZ, 370
Ferrous silicates, 117
F.
750
INDEX.
FETTLING.
Fettling, materials used for, 281
effect of, on iron produced, 282
of Danks's rotative furnace, 288
Finishing rolls, 299
Finspong, composition of charges at, 253
Fire-bricks, 104
qualities required in, 104
manufacture of, 105
composition of, 105
labour and fuel required in manu-
facture of, 105
-, blue, analysis of, 106
Fire-clays, properties and occurrence of, 104
Flach's process for extracting silver from
lead, 587
method of conducting, 587
>
, advantages of, 588
Flatting mill, 10
Flintshire process of lead-smelting, 538
543
"
charge of furnace, 538
, grey slag from, 539
ores treated by, 539
modifications
of, at Couëron,
Flowing furnace, lead-smelting in, 546
Flue-cinder and tap-cinder, 304
Fluxes, effects of, on fusibility of slags and
condition of iron in blast-furnace, 193
and slags in smelting iron ores, 190
Foreign coals, composition of, 46
metals in iron and steel 350
Forge- and mill-cinders, 195
-, sulphur and phosphorus in, 195
Forge-cinders, preparation of, for the blast-
furnace, 196
Forge machinery and operations, 290
hammers, 291
tilt hammer, 291
helve hammer, 291
foundation for, 291
weights of castings for, 292
Forges, open, particulars of, 320
Forging press, Haswell's hydraulic, 297
Formall, 5
Fossey, blowing engine of, 265
Franklinite, 123
Free-burning coal, 43
Freiberg, production of bismuth at, 510
-, reduction of oxychloride of bismuth
at, 511
refining of bismuth at, 512
-, cupellation at, 596
Freieslebenite, 606
Frémy on the composition of steel, 312
Fresenius, analysis of spiegeleisen, 549
Fuel, definition of, 15
constituents of, available as source of
heat, 15
•
calorific power of, 16
calorific intensity of, 23
Fume, lead, 597
?
GALENA.
treatment of, at Pontgibaud, 562
Furnace, regenerative, 96
-, temperature of gases escaping
from, 97
for, 97
>
-, economy of fuel in, 97
accumulation of heat in, 97
material used in construction of, 9
surface of brickwork required
re-heating, description of, 98, 303
, assay, 144
blast, Plymouth Iron-Works, 198
Oldbury, 202
Stockton, 203
Ditton Brook, 204
Swedish charcoal, 206
the Rachette, 207
top at Darlaston, 229
at Grosmont, 232
hoist, Newport, 234
-, Ayresome, 236
-, Styrian charcoal, 251
anthracite, 259
-, puddling, 278
at Neustadt, 285
, converting, 314
calcining, copper, 394
-, melting, 396
"
rectangular, Mansfeld, 410
six-tuyer, Mansfeld, 412
roasting, 430
, tin, 452
, antimony liquation, 461
English zinc, 479
Belgian zinc, 481
Silesian zinc, 485
, mercury, at Idria, 501
aludel, 503
bismuth liquation, 510
cupelling, 533
lead-smelting, Couëron, 540
, Clausthal, 556
blast, lead, Pontgibaud, 561
five-tuyer, Couëron, 566
silver refinery, 589
German cupelling, 593
Stetefeldt, 663
97
Furnaces and crucibles, refractory materials
for, 100
Fusibility of metals, 11
of refractory materials, testing of, 108
Fusible metal, 513
GALENA, 515
"
G.
containing sulphide of antimony, 515
occurrence of, 515
assay of, 526
, gaseous, 90
Fuels, artificial, preparation of, 50
Fume in copper calciner flues, 433
526
by fusion with sodium carbonate,
by fusion with metallic iron, 527
INDEX.
751
GALENA.
Galena, assay of, by fusion with carbonate
of sodium and metallic iron, 528
in iron pots, 530
fusion with carbonate of sodium
and nitre, 531
containing antimony, 531
Gallery of the Palatinate, 505
Gases, absorption of, by charcoal, 61
from peat, 91
Gas-furnaces, puddling in, 284
Gas-producer of Siemens, 92
fuel employed in, 92
reactions in, 92
temperature of gases from, 93
, composition of gases from, 95
analyses of gases from, 96
of copper ores, 383
German assay
roasting, calcining, 384
melting for coarse copper, 384
refining, 384
cupellation, 593
GOLD.
Gold, discovery of, in California, 689
occurrence of, in California and Aus-
tralia, 690
in Canada, 691
in British Columbia, 691
in Nova Scotia, 691
in Mexico, 692
in Brazil, 692
in Australia, 692
total annual yield of the world, 694
employment of, by the Romans, 2
quartz, assay of, 695
fusion with litharge, carbo-
nate of sodium, &c., 696
litharge only, 697
fusion with red lead or
auriferous pyrites, 697
inquartation, 697
parting, 697
bullion, assay of, 698
lead necessary for cupelling, 700
surcharge, 700
effect of copper in various pro-
portions, 701
determination by the touchstone, 701
quality used for jewelry and coinage,
silver, 435
-, composition of different varieties,
436
refinery, 267
, weight of charge, 267
time occupied in working charge,
698
267
mechanical and metallurgical treatment
loss of metal in, 267
of, 703
change produced in, 268
German or Walloon forge, 271
Gerstenhöfer's feeder, 662
Gibbs's process for recovery of sulphate of
sodium from spent copper-liquors, 434
Gilding, 702
Gjer's calcining kiln, 189
Gleiwitz and Königshütte, refinery at, 267
Göthite, 124
Gold, properties of, 682
•
fusion of, 682
precipitated, 682
action of acids on, 682
occurrence of, 683
native, 683
crystals of, 683
nuggets, 683
native, composition of, 684
distribution of, 684
in quartz veins, 684
712
placer mining, 703
, pan, 703
cradle, 704
tom, 705
puddling box, 705
sluice, 706
hydraulic mining, 709
extraction of, from auriferous veinstone,
ings, 720
722
[685
721
the arrastra, 712
Chilian mill, 714
stamping mill, 714
amalgamation in battery, 714
blankets, 715
·, amalgamated plates, 719
cleaning up, 719
amalgamation of blanket-wash-
treatment of tailings, &c., 722
retorting and fusion into ingots,
by chlorination, 724
from pyrites in Hungarian mill,
use of sodium amalgam in, 722
amalgam, retorting and fusion, 722
cost of extracting from auriferous
quartz, 723
extraction by the chlorination process
at Reichenstein, 725
parting by sulphuric acid, 726
refining by chlorine gas, 728
-, analysis of silver resulting from the
refining of, 732
native, quantity of silver in, 685
alluvial, 685
occurrence of, in Devon and Cornwall,
in Wales, 685
in Scotland, 686
in Ireland, 686
in France, 686
in Spain, 687
in Italy, 687
in Germany, 687
[687
in Hungary and Transylvania,
in Sweden, 687
in Russia, 687
[687
in Africa and other countries,
"
752
INDEX.
•
GOSLARITE.
IRON.
Goslarite, 469
Grain-tin, preparation of, 455
Granulation of coarse-metal, 397
Grecanic, 5
Gregory, T. F., discoveries of tin in Queens-
land, 443
Grey pig-iron, 247
cast-iron, conversion of, into white, 262
Grosmont, method of collecting waste gases
at, 231
Guanaxuato, patio process at, 627
roasting apparatus at, 630
Guide train, 306
Guillotine shears, 302
Gun-metal, 14, 435, 456
Hæmatite, 123
H.
Hammer used in German refinery, 274
-, steam, 292
Hammered iron, advantages of, 306
Hard wood, 30
head, 453
composition of, 454
Hardness of metals, 9
Hassenfratz on steel-making in 1812, 341
Haswell's hydraulic forging press, 297
-,.compressive power of, 297
Hawkins's process for making steel, 313
Heat, capacity of metals for, 13
pyrometric degree or intensity of, 16
unit of, 17
effect of, on the caking properties of
coal, 44
261
effects of, on fuels, 48
waste, from coke-ovens, 88
objections to utilisation of, 88
absorbed for work done in blast-furnaces,
Heath, Mr. J. M., on manufacture of Wootz,
317
Heaton's process, 268
,
analysis of products from, 269
removal of silicon by, 269
Henderson's process for production of iron, 269
for the extraction of copper, 421,
427.
Henry, Mr. T. H., on cause of blisters in
blister-steel, 316
on composition of wootz, 317.
Hepburn and Peterson's pan, 653
Hessite, 606
High temperatures, terms used to express, 24
Hindoo process for manufacture of steel, 317
History of metallurgy, 1
Hoists or lifts, 235
Hollow fire, 277
Homogeneous metal, 318
Horno de Gran tiro or Pavo, 571
Hot-blast, history of, 216
Hot-blast, temperature of, 217
stove, common, 217
modifications of, 218
222
circular, 219
-, passage of air through, 220
pistol-pipe, 221
at Neustadt, 221
use of waste gases for heating,
Cowper's, 222
Whitwell's, 225
Hot process of amalgamation, 633
the
cazo, 634
at Catorce, 634
Hungarian mill, 721
Huntsman, introduction of cast-steel by, 345
Hydraulic mining, 709
water required for, 710
work accomplished by, 710
cost compared with other
methods, 711
2 ,
use of gunpowder in, 711
Hydrogen, calorific power of, 19
I.
Idria, mercury ores at, 493
>
treatment of mercurial ores at, 500
, apparatus used at, 500
charging the apparatus at, 500
condensation of last traces of mercury
at, 501
fuel employed at, 502
-, weight of charges at, 502
,
,
production of mines, 502
continuous
process,
502
extraction of mercury in reverberatory
furnaces at, 504
Ilmenite, 123.
Improving of lead, 576
hard lead, 577
pans, 577
Inorganic matter in coal, 39
Inquartation, 695
Iron, employment of, in early times, 7
, properties of, 109
-, impurities in, 109
-, pure, preparation of, 110
electro-deposited, property of occluding
hydrogen, 111
111
"
employment in the arts in three forms,
black oxide of, 112
, wrought, texture of, 111
fusibility of, 112
magnetism of, 112
rust, &c., of, 112
solution of, in acids, 113
and carbon, 113
state of carbon in, 113
, grey, white, and mottled, 114
INDEX.
753
IRON.
Iron, cast, per cent. of carbon in, 115
effect of sulphur on, 115
silicon in, 115
and silicon, 117
and sulphur, 118
and phosphorus, 118
and nitrogen, 119
and manganese, 119
influence of other metals on, 120
alloys of, 120
sands, titaniferous, 130
metallurgy of, 159
reduction of ores to metallic state, 160
for tin-plates, 276
merchant, labour bestowed on the manu-
facture of, 305
advantages of hammering, 306
plates and sheets, classification of,309,368
red-short, 310
168
cold-short, 310
burnt, 310
malleable, direct production of, 161
in India and Borneo, 161
in Africa, 161
in Catalan forge, 163
in American bloomery, 168
high bloomery or Stückofen,
Corsican process for, 169
Clay's process for, 171
Chenot's process for, 172
Yates's process for, 173
Siemens's process for, 174
indirect method of obtaining, 176
, preparation of, by reverberatory pro-
cess, 277
native, 121
meteoric, 121
ores, 121
>
analyses of, 122
magnetic, 122
Franklinite, 123
titaniferous, or ilmenite, 123
KERMESITE.
Iron ores, Berthier's process for the estimation
of lime and magnesia in, 147
146
fluxes, 148
dry assay of, 146
preliminary operations and fluxes,
classification of, 146
classification and proportion of
—, proportion of fluxes in German
iron-works, 149
for, 150
"
method of conducting assay, 149
crucibles used for assay of, 150
, dry assay of, brasquing crucibles
-, regulation of temperature, 150
>
testing of button produced, 151
conclusions deduced from colour
>
of slag, 151
152
Swedish process, 152
wet assay of, by Marguerite's process,
Penny's process, 154
-, advantages of, 155
dry and wet methods of assaying
compared, 155
shire, 181
, analysis of, 156
estimation of water, 156
attack by hydrochloric acid, 156
estimation of sulphur, 158
-, phosphoric anhydride, 158
carbonic anhydride, 158
titanic oxide, 159
insoluble residue, 159
reduction of, 160
mechanical preparation of, 176
weathering of, 178
roasting or calcination of, 179
in open heaps, 179
at Königshütte, 180
in S. Wales and Stafford-
between walls, 181
in furnaces or kilns, 182
removal of sulphates from, after
specular, iron hæmatite, 123
Göthite, 124
roasting, 186
brown, 124
red, 125
iron pyrites, 125
carbonate of iron, siderite, 126
distribution of, 127
red, distribution of, 131
Dannemora, 129
analyses of, 133
older brown, 134
from Belfast, analysis of, 191
Ironstone, clay, 139
blackband, 140
Cleveland, analyses of, 142
J.
newer brown, 135
, Spanish, 135
tertiary and post-tertiary, 137
bog, 138
of Cleveland, 141
quantities of, raised in the United
Kingdom in 1871,142
2
Berthier's process for the estima-
tion of water in, 147
JEWELRY, colouring of, 702
Joachimsthal, process for extraction of bis-
muth at, 510
Von Patera's process at, 673
Jungfernblei, 550
K.
KARSTEN, analyses of slags from spathic
ores by, 193
Kermesite, 458
3 c
751
INDEX.
KERMES.
Kermes mineral, 462
Kilu hoist, Ayresome Iron-Works, 238
Kilns, charring in, 57
for charcoal-making, varieties of, 58
in which portion of the wood acts
as fuel, 59
ployed, 59
in which independent fuel is em-
Klaproth, analyses of cinnabar by, 491
Krupp, casting of steel, 344
Kupfergaarherd, 416
slags from, 417
Kupfernickel, 359
Kupferschiefer, 407
Lake Ores, 137
L.
Lake Superior, furnaces and fuel for iron.
smelting at, 258
Lancashire and Cumberland, weekly produc-
tion of iron per furnace in, 257
Landsberg, retorts for mercury extraction at,
505
Langen's apparatus for collection of waste
gases, 230
modification used at Hörde, 230
Lang's process for preparation of forge-cinder
for use in blast-furnaces, 196
Lead, properties of, 513
•
action of air and water on, 513
purity of commercial, 514
-, preparation of pure, 514
action of acids on, 514
ores, 514
, native, 514
oxide, 514
chloride, 514
sulphide, 515
and copper sulphides, 515
arsenical sulphide, 515
selenide, 516
"
carbonate, 516
sulphate, 517
phosphate, 517
arseniate, 518
chromate, 518
ores, distribution of, 519-
production of, in the United States, 520,
524
"
in Belgium, 520
in Great Britain, 520
529
in Prussia, 521
in Austria, 521
in Spain, 523
in Italy, 523
in France, 523
assay of ores of, 524
assaying, method given by Mitchell,
assay in iron pots, 530
sulphate, assay of, 532
LINZ.
Lead, estimation of silver in ores of, 532
extraction of silver from, 576
improving or softening, 576
Pattinson's process for desilverisation
of, 578
modifications of, 582
Parkes' process for desilverisation of,
by zinc, 584
modifications of, 585
extraction of silver from, by cupelling
or refining, 588
592
reduction of litharge from refinery,
fume, 597
length of flues for collecting, 597
condition of lead in, 597
sheet, 598
pipe, 598
silver in, 598
alloys of, 601
metallurgy of, 537
Lead-smelting by method of double decom-
positions, 537
by method by reactions, 537
in reverberatory furnaces, 538
Flintshire process, 538
at Couëron, 540
Cornish process, 544
in the flowing furnace, 546
in the Spanish furnace or boliche, 546
Bleiberg process, 548
with metallic iron in reverberatory
furnace, 551
in blast-furnace, 551
slag-hearth, 551
-, Spanish slag-hearth, 553
>
Castilian furnace, 553
at Clausthal, 555
at Pontgibaud, 559
, roasting of ores and subsequent smelt-
ing with metallic iron, 559
at Couëron, 564
in the Horno de Gran Tiro or Pavo, 571
in shallow hearths, 571
in the Backwoods hearth, 571
in the ore-hearth or Scotch furnace, 572
in the American hearth, 575
Libethenite, 373
Lifts or hoists, 235
at Newport 235
prevention of overwinding, 236
Lignite or brown coal, 39
occurrence of, 40
composition of, 41
ashes, composition of, 42
Lime, use of as flux in blast-furnaces instead
of limestone, 191
Linarite, 517
Linz, processes employed at, for copper-ex-
traction, 423
424
treatment of poor sulphides at, 423
, poor oxides and carbonates at,
INDEX.
755
LITHARGE.
Litharge, determination of calorific power
by means of, 27
from refinery, reduction of, 592
Longmaid's processes for the extraction of
copper, 422
Lucas's patent for manufacture of steel, 313
for cementation of cast-iron, 344
Luce and Rozan's modification of Pattinson's
process, 583
MAGISTRAL, 628
M.
Magnetic iron ores, distribution of, 128
English, composition of, 130
Magnetite, 122
Malachite, 371
Malleability of metals, 10
Malleable iron, direct preparation of, 161
in India and Borneo, 161
in Africa, 162
cess, 163
168
>
by Catalan or French pro-
in the American bloomery,
Corsican process, 169
in the Stückofen, 170
Clay's process for, 171
Chenot's process, 172
Yates's
process, 173
Siemens's process, 174
Manganese and iron, 119
in Bessemer steel, 335
estimation of, in iron and steel, 349
alloyed with copper, &c., 436
Mannheim gold, 435
Mansfeld district, composition
of, 407
copper schists
treatment of copper schists of, 407
fuel employed in, 408
blast-furnace used in, 410
burning the schist, 409
>
stein, 410
smelting for production of Roh-
circular furnaces in, 413
, roasting the coarse-metal, 414
smelting for "Spurstem" or
fine-metal, 414
415
&c, 415
>
grinding granulated fine-metal,
roasting ground fine-metal, 415
dissolving out sulphate of silver,
fusion for black copper, 415
refining, 416
obsolete processes at, 417
liquation at, 417
amalgamation of copper matts at, 641
Ziervogel's process at, 668
-, composition of copper matts at, 668
comparative cost of silver extracted by
various processes, 672
Marguerite's process for the estimation of
iron, 152
METALLURGY.
Marguerite's process for the estimation of
iron, reactions in, 152
ing, 152
, operations necessary for conduct-
-, preparation of standard solution,
in, 153
solution of the ore, 153
determination of the iron, 154
Market lead, 579
Massicot, 514
Massoques, 168
Massouquettes, 167
McCone, Horn, and Fountain's
Mechanical rabbles, 286
Melaconite, 367
Melanochroite, 518
Melting-house, 345
Mendipite, 514
pans, 654
Menelaus, experiments on mechanical pud-
dling by, 287
Merchant iron, labour bestowed on manufac-
ture of, 305
"
best best, 305
treble best, 305
coal consumed in making, 305
Mercury, first mention of, 3
-, properties of, 489
commercial, 489
purification of by distillation, 489
by nitric acid, 490
alloys of, 490
uses of, 491
native quicksilver, 491
sulphide, 491
native calomel, 492
coccinite, 492
onofrite, 492
ammiolite, 492
ores, 491
>
distribution of, 492
at Idria, 493
in Bohemia, 493
in Spain, 493
in Tuscany, 494
in Peru, 494
discovery of, in California, 494
annual production of, 495
, assay of, 495
extraction, from cinnabar, 498
principal methods of, 498
by roasting cinnabar, 498
, condensers, 499
by roasting in mounds, 499
at Idria, 500
filtration of mercury, 501
at New Almaden, 504
in reverberatory furnace, 504
ores, decomposition in close vessels, 505
Metallic oxides, action of, on crucibles, 107
Metallurgy, history of, 1
of iron, 159
of copper, 391
of tin, 451
3 c 2
756
INDEX.
METALLURGY.
Metallurgy of antimony, 460
of zinc, 477
of mercury, 498
of bismuth, 509
of lead, 537
of silver, 623
of platinum, 736
Metals known to the ancients, 1
-, physical properties of, 8
colour of, 8
lustre and opacity of, 8
-, crystallisation of, 9
-, specific gravity of, 9
hardness of, 9
precipitation of, from solution, 10
malleability of, 10
fusibility of, 11
elasticity and sonorousness of, 12
odour and taste of, 12
, power of conducting heat of, 13
capacity of, for heat, 13
expansion of, by heat, 13
volatility of, 13
effect of alloying, 14
Miargyrite, 606
Mill for rolling sheet-lead, 599
Mills and forges at work in Great Britain,
311
Mill-piles, 301
Mill rolls, 229, 305
-, three-high train, 306
Millerite, 359
Miller, F. B., process for refining gold, 728
, generation of chlorine, 729
results afforded by process, 731
separation of gold from silver chloride,
731
fineness of gold and silver resulting
from, 731
Minary and Soudry process for preparation of
forge-cinders, 196
Mine-pig, 118
Mispickel, cobalt in, 355
Mosaic gold, 435
Mottled pig-iron, 247
Muntz's metal, 438
Müsen district, spiegeleisen made in, 255
Mushet's steel, 313, 318
N.
NAIL-rods, rolling of, 310
Napier's method of copper-smelting, 404
Native iron, 121
copper, 366
antimony, 457
zinc, 466
mercury, 491
bismuth, 508
lead, 514
silver, 602
gold, 683
ORES.
Native platinum, 733
Naumannite, 606
Neuberg, Bessemer plant at, 333
carbon in Bessemer steel at, 335
Neustadt, hot-blast stove at, 221
waste gases used in, 222
gas puddling furnace, 285
New Almaden, California, extraction of mer-
cury at, 504
Newport, lift at, 235
New South Wales, tin discoveries in, 444
Newton, process for making steel, 313
Nickel, 358
and cobalt, estimation of, 355
ores, 358
glance, 359
metallurgy of, 360
use of, in the arts, 361
fusion of, 361
oxide, reduction of, 361
Nitrogen in coal, 39
in cast-iron, 116
Noad, analysis of metal and slag from Parry's
refinery, 267
North of England, blowing engines in, 214
Nova Scotia, gold in, 692
O.
OBUCHOW's steel process, 321
-, analysis of, 341
Occlusion of hydrogen by electro-deposited
iron, 111
Oersted's method of preparing aluminium
from its chlorides, 363
Oker, extraction of silver and gold from
Cõpper at, $77
678
granulation of the metal, 678
crystallisation of sulphate of copper,
treatment of "mud" containing silver
and gold, 679
-, quantities worked at, 679
Oldbury, blast-furnace at, 201
Ollaria, 5
Onofrite, 492
Oolites, analysis of brown iron ores from the,
136
Ore-furnace slag, 396
Ore-hearth, lead-smelting in, 572
roasting, 573
smelting, 573
browse, 573
quality of lead produced in, 575
cost of melting in, 575
Ores of iron, 121
cobalt, 355
nickel, 358
copper, 366
tin, 440
antimony, 457
zinc, 465
INDEX.
757
ORES.
PIG-IRON.
Ores of mercury, 491
lead, 514
silver, 602
Orichalcum, 5
Oven, coke, description of, 71
Overpoled copper, 400
Oxland and Hocking's calciner, 447
Oxland's process for separation of tungsten
from tin ores, 450
Packfong, 435
P.
Palatinate, gallery of, 505
Pan, gold washing in the, 704
Pans, Washoe process, 649
Varney's, 650
Hepburn & Peterson's, 653
McCone, Horn, & Fountain's, 654
charging of, 654
, heating, 654
addition of mercury, 654
>
,
use of chemicals, 654
Parkes's process for desilverisation of lead, 584
585
at Llanelly, 584, 585
modifications of, 585
-, proportion of zinc required for,
dezincification of the lead, 586
Flach's improvements on, 587
Parry's refinery, 266
result of one week's working at
Ebbw Vale, 266
267.
analyses of metal and slag from,
Parting of silver from gold, 694
by sulphuric acid, 726
treatment of the separated gold, 727
, precipitation of the silver, 727
recovery of sulphate of copper, 727
of alloys containing large quantities of
copper, 727
nse of platinum vessels for, 728
use of cast-iron vessels for, 728
by means of nitric acid, 728
Patio process for extraction of silver, 625
-, rough stamping, 625
2
fine grinding, 625
at Guanaxuato, 626
at Zacatecas, 627
yield of gold by, 627
the patio, 628
addition of magistral and mercury
to the torta, 629
-, assay or tentadura, 629
treading of the torta, 630
washing, 630
filtration of amalgam, 631
-, retorting of amalgam, 632
results obtained by, 632
chemical reactions of, 633
Pattinson's process for extraction of silver
from lead, 576
Pattinson's process for extraction of silver
from lead, method of thirds, 579
at Pontgibaud, 580
by manual labour, 580
by use of cranes, 581
method by eighths, 582
modifications of, 582
-, système Laveissière, 582
crystallising by steam, 583
Pauwels & Dubochet's coke-oven, 81
Pea iron ore, 125
Peat, origin of, 33
and turf, distinction between, 34
cutting of, 34
dredging of, 34
ashes, 35
dry, elementary composition of, 35
air-dried, water in, 35
2
composition of, 36
obstacles to the use of, 36
, processes for improvement of, 36
occurrence of iron pyrites in, 37
of organic salts of calcium in, 37
of copper in, 37
, gases from, 91
, charring of, in heaps, 62
in ovens, 63
-, apparatus used for, at Crouy-sur-
Ourcq, 63
-, by superheated steam, 64
Peat-charcoal or coke, 61
unsuitability of, for metallurgical
purposes, 61
Pelouze's process for estimation of copper, 387
Penny's process for volumetric estimation of
iron, 154
Pentlandite, 359
Percy, Dr., on errors in analysis of coal, 26
Pernolet's coke-oven, 82
chief features of, 83
charge of, 83
condenser applied to, 86
washers, 86
time occupied in working a
charge in, 87
87
, precautions necessary in working,
treatment of impure coal in, 87
difference between Pauwels & Du-
bochet's and, 88
Peters, on composition of spathic ore at Müsen,
250
Pewter, 456
Phosphorus in iron, 118
effect of, on iron, 119
estimation of, in iron and steel, 349
Physical properties of metals, 8
Pig-boiling, 278
Pig-iron, amount produced by various coun-
tries, 143
, white, 247
,
grey, 247
mottled, 247
758
INDEX.
PIG-IRON.
Pig-iron from Franklinite, 247
?
composition of, 248
Swedish, sulphur in, 253
Piles for heavy plates, 309
for boiler-plates, 309
for large sheets, 309
Pimple-copper, 404
Pinchbeck, 435
Pipe, lead, 598
Pistol-pipe stove, 221
Placer mining, 703
pan, 703
cradle, 704
Tom or long Tom, 705
"
puddling box, 705
sluice, 706
Placers, 690
amalgamated copper plates, 708
ground-sluice, 709
hydraulic mining, 709
Plates and sheets, rolling of, 308
Platinum, properties of, 732
black, 733
distribution of, 733
, occurrence of, 733
, native, impurity of, 733
}
analyses of, 734
amount yielded by various countries, 734
estimation of, 735
>
metallurgy of, 736
uses of, 738
Plattner's process for extraction of gold, 724
Pliny's description of properties of mercury,
3
of occurrence of gold, 1
of iron, 7
Plumbo-resinite, 518
nigrum, 1
Plumbum candidum, 4
Plymouth, blast-furnaces at, 198
Polybasite, 604
Pontgibaud, lead-smelting at, 559
?
roasting, 559
lit de grillage, 560
reverberatory furnaces, 560
smelting, 561
lit de fusion, 561
loss of silver and lead, 562
treatment of fume, 562
Pattinson's process at, 580
Precipitation of metals from solution, 10
Precipitate, copper, percentage of copper in,434
Price & Nicholson's process, 342
Prince's metal, 435
Printers' blue, 358
type, 14
Products of combustion, 16
of carbon, 19
Proustite, 606
Prussia, charcoal furnaces in, 254
Przibram, ore-hearth at, 576
Pseudo-malachite, 373
Puddling of iron, 277
varieties of fuel used for, 277
PYROMORPHITE.
Puddling, reactions of, 277
•
wet, 278
dry, 278
, operations included in, 282
282
286
method of conducting the operation,
melting the charge, 282
mixing the iron and slag, 282
elimination of the carbon, 283
balling, 283
in gas-furnaces, 284
in Carinthia, in gas-furnaces, 284
at Neustadt, 285
in Siemens's regenerative gas-furnace,
tools employed jn, 286
mechanical, 286
of steel, consumption of fuel in, 324
Puddling furnace, 278
"
lining of, 281
charge of, 284
coal consumed in, 284
Danks's rotative, 287
Spencer's, 290
Puddling rolls, 299
speed of, 301
box, 705
Puddled iron, yield of, 302
302
bar, 300
conversion of, into merchant iron,
Puddled steel, 321
323
unon,
323
iron most suitable for, 322
furnace used for manufacture of,
fluxes used in manufacture of, 323
action of highly-oxidised slags
charge, 323
324
deductions from appearance of
stirring of, 323
-, balling of, 324
shingling of, 324
time occupied in working a heat,
at Lohe, 325
at Geisweide, 325
at Zorge, 325
treatment of balls, 325
reaction in manufacture of, 326
slags from, 326
Purple ore, 281, 433
Pyrargyrite, 605
Pyrites, copper, 368
iron, 125
from Elba, 126
from Spain and Portugal, 126
, cupreous, composition of, 429
Pyrometric degree or intensity of heat, 16
Pyrometer, Wilson's, 23
Siemens's electric, 24
Schinz's, 24
Pyromorphite, 517
INDEX.
759
QUEENSLAND.
Q.
Queensland, tin-discoveries in, 443
Quicksilver, native, 491
R.
Rabbles, mechanical, 286
Rachette furnace, 207
description of, 209
-, arrangement of tuyers, 209
Rails, removal of rough ends from, 302
Rail-piles, 305
ingots, 337
Ramsbottom's duplex hammer, 295
cogging mill, 337
Raw steel, 319
Reactions in blast-furnace, 197
lead-smelting by, 537
Réaumur on manufacture of steel, 340
Rectangular heaps, charcoal-burning in, 55
kilns, coking in, 68
coking kilns, regulation of draught, 69
yield of coke, 70
Red iron ores, 131
Redruthite, 367
Red-short iron, 310
analyses of, 133
Reduction works, general arrangement of,
659
Refining of iron, 262
at Dowlais, 263
crude pig-iron, method of conducting
operations, 264
Refinery, melting-down, 264
, running-in, 264
?
charge worked in, 265
action of slag in, 265
time occupied in working charge, 265
"
blast required for, 266
,
weekly production of, 266
fluxes used in, 266
Parry's, 266
German, 267
Refinery process in Carinthia, 268
Heaton's, 268
-, Henderson's, 269
Refinery-slag, 399
Refining copper, in Cornish assay, 382
of gold by chlorine gas, 728
Refractory materials, testing fusibility of,
108
•
for furnaces and crucibles, 100
fire-stones, 100
siliceous sand, 101
fire-clays, 101
plastic property of, 101
, British, composition of,
fire-clays, foreign, composition
of, 103
Regenerative furnace, 96
ROUGHING ROLLS.
Regenerative furnace, temperature of gases
escaping from, 96
-, economy of fuel in, 97
accumulation of heat in materials
used in construction of, 97
97
for, 91
Regulare, 5
surface of brickwork required in,
Siemens's, advantages claimed
Regulus, fusion for, in Cornish assay, 381
Re-heating furnace, description of, 98, 99,
302
304
"
time occupied in working a heat,
weight of piles for, 304
Ekman's, 305
Reichenstein, preparation of metallic arsenic
at, 464
Retort at Virginia City, 658
Retorting of amalgam, 657
and fusion of auriferous amalgam,
722
Retorts at Landsberg for extraction of mer-
cury, 505
Reverberatory furnaces, use of, in English
method of copper-smelting, 393
Reversing rolls, 300
Rhenish Prussia, blowing engines in, 216
Rich lead, 579
Riepe's process, specification of, 321
Riley on iron and steel, 289
Rinmann's green,
358
Rive-de-Gier, coke-ovens at, 74
Rivot and Phillips's method of copper-smelting,
406
Roaster-slag, 399
Roasting and calcination, distinction between,
391
Roasting or calcination of iron ores, 179
Roasting kiln, in Styria, 182
ว
Altenberg, 186
Dowlais, S. Wales, 187
of Gjers, 189
at Cleveland, 189
Rogers on manufacture of charcoal and coke,
70
Rolling metal, 10
Rolling mill, Wagner's, 306
Ramsbottom's, 307
size and speed of, 308
of armour-plates, 308
Rolls, communication of motion to, 299
roughing, 299
finishing, 299
-, couplings of, 300
reversing, 300
three-high train of, 301
puddling, speed of, 301
Rotative puddling furnaces, 287
Tooth's, 287
Danks's, 288
Roughing rolls, 299
760
INDEX.
RUMFORD.
Rumford's calorimeter, data required for, 18
table of calorific powers of woods, 21
Rust, formation of, accelerated by presence of
carbonic acid, 112
by electric action, 112
Sand bed, 246
S.
Sardinia, zinc ore raised in, 471
Schemnitz, Hungarian mill at, 721
Schilling on reactions in puddling for steel, 325
Schinz's pyrometer,
Schneeberg, process for extraction of bismuth
at, 509
Scorification, 612
Scotch blast-furnaces, produce of, 258
Selbite, 606
Selenide of copper, 373
Senarmonite, 458
Separators, Washoe process, 655
Settling tanks, Washoe process, 648
Shallow hearth, lead-smelting in, 571
Shears, 301
guillotine, 302
Shear-steel, 316
Sheet-lead, 598
zinc, 488
Sherman, refining of iron by iodine or iodides,
270
Siberia, ancient smelting in, 3
remains of furnaces found in, 131
Siderite, 126, 138
Siegen district, steel-making in, 321
Siemens's electric pyrometer, 24
regenerative furnace, advantages claimed
for, 91
gas-producer, 92
remarks on cooling of gaseous current
from producer, 93
296
gas-producer, fuel used in, 92
reactions in, 92
temperature of gases from, 93
regenerative gas-furnace, puddling in,
, process for direct reduction of iron
oles, 174
175
176
-, description of apparatus, 174
working of apparatus, 174
bauxite used in, 174
time occupied in working charge,
making cast-steel in, 175
addition of spiegeleisen, 165
ferro-manganese, 175
compared with indirect methods,
theoretical quantity of iron pro-
ducible in, 176
Siemens-Martin process for the manufacture
of steel, 342
-, assays of metal from, 343
SILVER.
Siemens-Martin process, mixtures employed
by M. Martin, 343
Silesian process of extracting zine, 484
description of furnace, 484
manufacture of retorts, 485
, precautions in starting new fur-
nace, 486
ores treated by, 487
charging the retorts, 487
ore treated at Llansamlet, 487
loss in calcination, 487
duration of furnace, 487
re-melting the zinc, 488
Silicates, ferrous, 117
Silicon in cast-iron, 115, 262
353
state of, in cast-iron, 117
effects of, on cast-iron, 118
in Bessemer process, 335
estimation of, in iron and steel, 348,
Silver, estimation of, in ores of lead, 532
volatility of, 535
536
"
per ton of ore, table for calculating,
cupelling or refining, 568
absorption of oxygen by, 601
action of caustic alkalies on, 602
action of acids on, 602
annual production of, in the United
Kingdom, 607
Norway and Sweden, 607
France, 607
, Germany, 607
, Spain, 607
Italy, 607
North America, 608
Peru, 609
Bolivia, 610
Chili, 610
Silver bullion, fire assay of, 613
humid assay of, 617
metallurgy of, 623
extraction by patio process, 625
, by stove amalgamation, 632
by hot process, 633
by amalgamation in barrels, 635
by Washoe process, 542
, by Augustin's process, 664
by Ziervogel's
666
by Von Patera's
673
""
679
""
by Claudet's
and gold, extraction by sulphuric acid,
native amalgam, 603
677
native, 602
arquerite, 603
"
argentite, 603
stephanite, 604
, polybasite, 604
, pyrargyrite, 605
chloride, 605
iodide, 606
bromide, 606
INDEX.
761
81
Silver ores, 602
"
607
SILVER.
distribution of, 606
production of various countries,
discovery of, in Spain, 607
in Nevada, 608
, assay of, 610
by fusion with litharge, 610
by
""
by scorification, 612
ST. ETIENNE.
Spencer's revolving puddling machine, 290
Spiegeleisen, 114, 247
-, analysis of, by Fresenius, 249
composition of charges for production
of, 255
treatment of, in the open hearth, 321
use of, in Bessemer process, 327
Sponge-iron, use of, for precipitating copper,
434
-, preparation of, 434
nitre, 611
treatment by fusion with plumbi-
Squeezers, 295
ferous materials, 624
Sinding's process for precipitation of copper,
425
Single shear-steel, 317
Sireuil, Siemens-Martin process at, 342
Six-tuyer furnace, Mansfeld, 413
temperature of blast in, 413
Slags, blast-furnace, composition of, 192
"
analyses of, 192
fiom treatment of spathic ores, analysis
of, 193
effects of burden on, 194
found in refinery, 265
from puddled steel, 326
from Bessemer process, analysis of, 334
Slag-hearth, 551
men employed in working, 553
use of tap-cinder in, 553
Spanish, 553
Slate's engine, 215
Slimes, collection of, 649
Sluices, 706
riffles in, 706
use of mercury in, 707
amalgamated copper plates in, 707
cleaning up, 708
treatment of amalgam from, 709
ground, 709
Smalt, preparation of, 357
Smaltine, 355
Smithsonite, 468
Smyth, R. B., on occurrence of gold in Vic-
toria, 693
Snelus on stages of the charge in Bessemer
process, 336
-, report on Danks's furnace, 289
Soft wood, 30
Solder, fine, 456
plumber's, 456
, tin, 456
South Staffordshire, iron made in, 255
ores used in, 255
"
flux,
coal,
255
""
255
""
Spain, mercury mines of, 493
Spanish iron ores, 135
Spathic iron ore, 138
at Müsen, 250
Specific gravity of metals, 9
of alloys, 14
of woods, 30
of charcoal, 60
Spring-steel, 316
reciprocating, 295
, rotary, 295
single and double, 296
Squeezer used in Danks's process, 298
Stamping mill, gold and silver, 645, 714
-, general arrangement of, 718
Steam hammers, 292
"
single and double acting, 293
advantage of, 293
weight of, 293
small, 293
Condie's, 294
foundations for, 294
foundation for Krupp's, 294
at Woolwich arsenal, 295
Steel, ancient, 7
,
composition of, 111
state of carbon in, 114
properties of, 312
methods of production of, 312
making, by addition of carbon to
malleable iron, 313
312
317
by direct reduction of iron ores,
spring, 316
shear, 316
Hindoo process for the manufacture of,
Mushet's, 318
production by partial decarburisation
of cast-iron, 319
in open hearths, 319
-, puddled, 321
334
loss in making, 324
Bessemer, classification of, in Sweden,
analyses of, 337
treatment of, at Crewe, 337
manufacture of, by fusion, of a mixture
of cast- and wrought-iron, 340
by fusion, of cast-iron with ferric
oxide, 340
manufacture in England, A.D. 1812,
341
Obuchow's process for making, 341
-, cast, 344
hardening and tempering of, 346
analysis of, 347
Bessemer, carbon in, 335
and iron, carbon in, 352
St. Etienne, coke-making at, 73
762
INDEX.
Stephanite, 604
STEPHANITE.
Stetefeldt furnace, 661
Stetefeldt furnace, preparation of the ore, 661
>
advantages of, 662
feeding-apparatus for, 662
Stibium, 8
Stockton Iron-Works, 201
Stove amalgamation, 633
Stromeyerite, 606
Stückofen, or high bloomery furnace, 170
in Carniola, 171
fuel used in the, 171
Styria, charcoal furnaces of, 251
Styrian kilns, 182
process for making steel, 321
steel, copper in, 336
Sulphide of antimony, ancient use of, 8
Sulphur, F. Crace-Calvert, on estimation of,
26
in coal, 39.
effects of, on cast-iron, 115
estimation of, in iron and steel, 348
>
Eggertz's process for, 352
Sulphuric acid, extraction of gold and silver
by, 677
Swansea, anthracite furnaces in neighbour-
hood of, 258
Sweden, manufacture of iron in charcoal
hearth in, 276
Swedish charcoal furnace, 206
TAILINGS, 659
T.
treatment of, 729
Tap- and flue-cinder, 304
Tapping of blast-furnace, 245
Tar, &c., collection of, from coke-ovens, 80
Temperature of hot-blast, 217
Tempering of steel, 246
Tenacity of metals, alterations of, by change
of temperature, 11
Tertiary and post-tertiary iron ores, 137
Test, preparation of, for refining, 589
Tetrahedrite, 370
Tetradymite, 508
Thenard's blue, 358
Thin sheets, rolling of, 310 ·
Thomas and Laurent's blowing engine, 215
Three-high mill train, 306
Tile-copper, 401
Tilt hammer, 274
at Finspong, 177
Tin, alloys of, 455
physical properties of, 439
preparation of pure, 440
action of acids on, 440
ores, 440
cassiterite, oxide of tin, 440
pyrites, 441
distribution of, 442
mode of occurrence, 442
VARIATION.
Tin ores, assay of, 444
447
-, roasting of, 446
in reverberatory furnaces, 446
Oxland and Hocking's calciner,
advantages of, 449
separation of tungsten from, 450
metallurgy of, 451
ores, treatment of, 452
smelting, 452
refining, 453
Tin-plates, iron for, 276
Tin, refined, 453
Tin-smelting, treatment of slags and residues,
454
>
in blast-furnaces, 454
fuel employed, 455
in the Erzgebirge, 455
, quantity of fuel used in, 455
poling, 453
tossing, 454
, consumption of fuel in, 454
Tom or long tom, 705
Tongs, crucible, 145
Tools employed in puddling, 286
Tooth's mechanical puddling furnace, 287
Touchstone for testing gold, 701
Tough-pitch copper, 400, 404
Trompe, 165
Tungstate of soda, uses of, 451
Tungsten, separation of, from tin ores, 450
Tunnel head, 201
Turf, 33
Turf and peat, distinction between, 34
Turf, use of, in blast-furnaces, 242
Tuyers, 201
209
arrangement of, in Rachette furnace,
number of, in different furnaces, 227
Twiste, copper extraction-works at, 420
Type, printers, 14, 456
U.
Uchatius's process, 340
Ulrich, G. H. F., tin ore discoveries in N.S.
Wales, 444
Unit of heat, 17
United Kingdom, production of iron ore in,
during 1871, 142
United States of America, gold-fields of, 688
?
annual zinc-production of, 470
Ural mountains, ancient mines on borders
of, 2
Ure, Dr., apparatus at Landsberg for mercury-
extraction, 506
Utilisation of waste gases, 227
Valentinite, 458
Vanning, 445
V.
Variation in pressure of blast, 216
INDEX.
763
Varney's pan, 650
VARNEY.
-, operation of, 653
Vauquelinite, 518
steel, 318
Vickers, W., patent for production of cast-
Victoria, occurrence of gold in, 693
Vieille Montagne, zinc ores used at, 480
calcination of ores at, 480
washing of ores at, 480
furnaces at, 481
Vignoles's patent for charring of peat by
super-heated steam, 64
Voltzite, 469
Von Patera's process for silver extraction, 673
2
roasting, 673
lixiviation with water, 674
lixiviation with sodium hypo-
sulphite, 674
time occupied in lixiviation, 675
precipitation of the silver, 675
preparation of the precipitant, 675
silver obtained by, 676
cost of, &c., 676
treatment of silver sulphide, 676
residues, 677
W.
Waggon drop, pneumatic, 241
Wagner's rolling mill, 306
Walloon forge, 271
>
cess, 273
"
"
charge for, 273
manner of conducting the pro-
cooling the hearth, 274
treatment of slags from, 274
hammering the bloom, 274
hammer employed, 274
tilt hammer, 275
weight of bloom from, 276
Washoe process of amalgamation, 642
classification of ores for, 643
breaking of ores for, 643
stamping mill, 643
settling tanks, 648
collection of slimes, 649
, pans, 649
, separators, 655
, agitator, 656
retorting and melting, 657
, tailings, 659
general arrangement of reduction
works, 659
results obtained by, 659
chemical reactions of, 660
Waste gases, utilisation of, 227
>
first attempts for utilisation of
sensible heat of, 228
228
improvement by James P. Budd,
inflammable, utilisation of, 228
from charcoal furnaces, 228
WOOTZ.
Waste gases, method of collecting, at Darlas
ton, 229
of, 230
230
2
coal, 233
Langen's apparatus for collection
collection of, by cup and cone,
in Cleveland, 230
at Grosmont, 231
at Barrow-in-Furness, 231
composition of, 232
from furnaces working with raw
from blast-furnaces, solid matter
carried over by, 235
collection of, at Mansfeld, 413
Water, absorption of, by charcoal, 61
-, coke, 88
Water-tuyers, material used in construction
of, 227
balance, 237
Weathering of iron ores, 178
Welsh blast-furnaces, ores employed in, 257
Wet puddling, 278
assay of copper ores, 384
extraction of copper, 419
White cast-iron, advantages of, for manufac-
ture of malleable iron in open fires, 270
, production of, 263
nickel, 359
lead, manufacture of, 516
arsenic, manufacture of, 463
annual production of, 463
White-metal, 399
Whitwell's hot-blast stove, 225
dimensions of, 225
225
at Consett works, 225
❤
material used in construction of,
hot-blast and gas-valves for, 225
, arrangements for cleaning, 226
time occupied in cleaning, 226
, economy of, 227
Willemite, 468
Wilson's pyrometer, 23
Winslow's squeezer, 298
Wire, manufacture of, 11
Wöhler's method of obtaining aluminium, 363
Wollaston's process for treatment of plati-
num, 736
modification of, 737
Wood, calorific power of, 21
composition of, 29
proportion of water in, 29
air-drying of, 29
dried at 136° C., 30
hard, 30
soft, 30
ash of, 32
, quantity of charcoal yielded by deter-
mination of, 51
Woods, various, quantities of charcoal yielded
by, 60
Wootz, 317
764
INDEX.
WROUGHT IRON.
Wrought or malleable iron, 111
texture of, 111
fusibility of, 112
magnetism of, 112
rust, &c., on, 112
production of, from cast-iron in
open fires, 270
shire, 284
superior quality made in York-
, analysis of, 347
X.
XANTHOCONITE, 606
YATES's process, 173
Yellow-metal, 438
Y.
ZINCITE.
Zinc, metallic, first mention of, 7
history and properties of, 464
, preparation of pure, 454
combustion of, 465
oxide of, as a pigment, 465
ores, 465
native, 466
red oxide of, 466
sulphide of, 466
carbonate of, 467
silicate of, 468
anhydrous silicate of, 468
sulphate of, 469
oxysulphide, 469
ores, distribution of, 469
annual production of, in U.S.A., 470
ores raised in Sardinia, 471
annual production of, in Europe, 471
ores, assay of, 472
fire assay of, by distillation, 472
-, by difference, 472
humid assay of, by difference, 473
volumetric assay of, 474
contained in an ore, estimation of,
Z.
ZACATECAS, patio process at, 627
washing apparatus at, 631
475
Zaffres, 357
assay of, interference of foreign metals,
Zaratite, 359
476
Zechstein, 407
"
Ziervogel's process for the extraction of
silver, 667
materials suitable for treatment
by, 668
, roasting, 668
672
, composition of charges. 669
testing roasted ore, 670
use of oak as fuel, 670
loss of silver in roasting, 671
lixiviation and precipitation, 671
treatment of precipitated silver,
480
metallurgy of, 477
roasting ores of, 477
grinding calcined ore, 478
English process for extraction of, 478
Belgian process for extracting, 480
ores, loss experienced in calcination,
furnaces at Vieille Montagne, 481
, arrangement of retorts, 482
Silesian process of extraction, 484
re-melting of, 488
comparison of the different methods of
extracting, 488
per, 672
employment of precipitated cop-
sheet, 488
Zincite, 466
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