Modern copper smelting

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Preface

TO THE SEVENTH EDITION.

Since the last thorough revision of this work, the metallurgy of copper has been greatly modified by the success and general intro¬ duction of Automatic Calcining Furnaces; by the rapid and extraordinary development of the Copper Bessemer process; by the important and far-reaching improvements in Blast Furnaces and Reverberatories; and perhaps, above all, by the gradual dawning of the idea that, because Copper is worth fifteen times as much as Iron, it is not absolutely necessary to expend fifteen times as much money in handling and treating its ores.

The fusion of sulphide ores by the heat generated from their own oxidation (Pyritic Smelting) has also, lately, become an accomplished fact in several different localities — though how im¬ portant it is to be as a process pure and simple can scarcely yet be foretold.

The electrolytic refining of pig copper has become such an important feature in many American and European works, that it has been thought proper to include a chapter on this method. I have been most fortunate in securing the assistance of Mr. Maurice Barnett of Philadelphia, whose standing and long prac¬ tical experience well qualify him to write with authority upon this subject.

All these radical changes have made it necessary to re-write this work, and, also, to add very considerably to its size. Taking advantage of the break caused by a professional trip to Australasia, I have spent months in studying European copper practice, in order to glean what might be useful in our own work. The preparation of this edition, with its numerous elaborate working drawings and plates, has occupied considerably more than a year, and even then would have been impossible

Vlll

PKEFACE.

without the hearty co-operation of most of the copper smelters of the United States, and the direct assistance of several metallur¬ gists who have written for me on special subjects.

Thus, Mr. Robert Sticht, of Montana, has contributed an ex¬ haustive and valuable paper on Pyritic Smelting. Mr. A. H. Low, of Denver, has furnished much valuable original material in relation to the assaying of copper. Mr. H. A. Keller, Superin¬ tendent of the Parrot Silver & Copper Company of Butte, has collaborated with me in writing the chapter on bessemerizing, and has furnished me with material that can only be supplied by a specialist in that department, and that will be appreciated by every copper smelter in this country and in Europe. Mr. I. H. Glutton, of the Messrs. Elliott’s Metal Company, Lim., South Wales, has kindly furnished me with a detailed description of the Iodide Copper assay, as practised in Great Britain.

It is impossible for me to even enumerate the names of gentle¬ men in Europe, Australasia, and America, who have given me assistance in preparing this edition, and in gathering the material for the same. I must, however* particularly thank Mr. Christo¬ pher James, of Swansea, Mr. Bichard Pearce, of Argo, Colorado, and Mr. C. M. Allen, of Butte, Montana.

I also gratefully acknowledge courtesy and assistance from Messrs, N. I5. Hill, W. L. Austin, H. A. Vezin and M. I. lies, of Denver, Colorado, and wish to thank the Directors of the Boston & Colorado Smelting works, and the Globe Smelter. Also Messrs. E. P. Matthewson, A. S. Dwight, Carl Eilers, and A. Raht, of Pueblo, Colorado, and the Directors of The Pueblo Smelting Company, The Colorado Smelting Company, and The Philadel¬ phia Smelting and Refining Company. Also Mr. Franklin Ballou, of Leadville, Colorado, and the Directors of the LaPlata Smelter and the Arkansas Valley Smelter. Also, Mr. Otto Stalman, of Salt Lake, Utah; and Messrs. W. A. Clark, F. A. Heinze, R. G. Brown, A. H. Wethey, H. Williams, H. C. Bellinger, Captain Palmer, C. W. Parsons and 0. Szontagh, of Butte, Montana, and the Directors of The Colorado Smelting & Mining Company, The Parrot Silver & Copper Company, The Butte & Boston Mining & Smelting Company, and The Montana Ore Purchasing Com¬ pany. Messrs. Frank Klejietko, G. M. Hyams, and the Directors of The Boston & Montana Consolidated Mining & Smelting Com¬ pany, of Great Falls, Montana. Messrs. H. Thofebrn, V. Ray, and the Directors of The Anaconda Mining Company of

PREFACE.

IX

Anaconda, Montana. Mr. A. R. Meyer, President of The Kansas City Consolidated Smelting & Refining Company, of Kansas City, Missouri. The Matthiessen & Hegeler Zinc Company, of LaSalle, Illinois. Mr. H. F. Brown, of Chicago. Mr. Titus Ulke, of Wash¬ ington. Mr. James Douglas, of New York, President of the Copper Queen Mining Company. Also the late Lord Swansea, and Messrs. T. D. Nicholls and William Terrill, of Swansea, and Mr. Gerard B. Elkington, of Pembrey, Wales. My best thanks are due to the Directors of the Rio Tinto and the Tharsis Com¬ panies for their unbounded hospitality at their Spanish mines, and to their local superintendents and other officials. Also to M. Carnot, of the Ecole des Mines, and to MM. Martin and Fenelais, of Paris. Also to the late Professor Stelzner, to Professors Richter and Weisbach, and to the Royal Bureau of Mines at Frei¬ berg. Also to Herren Bergmeister Schroeder, Hiittenmeister Steinbeck, and the Directors of the Mansfelder Gewerkschaft. To the Humboldt Machine Company, o f Kalk-on-the-Rhine. Also to Messrs. Bowes Kelly, Win. Knox, H. H. Sticht, and the Di¬ rectors of the Broken Hill Mining Company, of New South Wales. To the Hon. John Henry and Mr. G. F. Beardsley, of Tasmania; and many others.

It is only fitting that I should acknowledge my especial indebt¬ edness to Messrs. Fraser & Chalmers, of Chicago, whose knowledge of, and intimate relations with, almost every important mining district in the world, has enabled them to afford me assistance and information that has been of the greatest value.

E. D. P., Jr.

Dorchester, Mass., August, 1895.

Contents

PREFACE .

CHAPTER I. — Copper and its Ores

Properties of Copper, 1. Effect of Impurities, 2. Tempered Cop¬ per, 3. Compounds of Copper and their Reactions, 6. Ores of Copper, Native Copper, Cuprite, 7. Melaconite, 8. Malachite, Azurite, 9. Clialcopyrite, 10. Chalcocite, 11. Bornite, Tetrahedrite, 12.

CHAPTER II. — Distribution of the Ores of Copper . „

The Atlantic Coast Beds, 14. The Lake Superior Deposits, 16. The Deposits of the Rocky Mountains, and Sierra Nevadas, 17. The Butte Mines, 18. The Arizona Copper Mines, 20. The Clifton District, 21. The Bisbee District, 24. The Globe District, 25. The Black Range Copper District, 27.

CHAPTER III. — The Sampling and Assaying of Copper

Sampling Ores, 28. Automatic Samplers, 29. Losses in Ship¬ ment, 38. English Weights and Samples, 39. The Assaying of Copper, 41. The Electrolytic Assay, 43. The Cyanide Assay, 52. Low’s Modified Cyanide Assay, 56. The Iodide Assay, 59. Tli6 Colorimetric Assay, 65. The Lake Superior Fire Assay, 65. The Determination of Gold and Silver in Copper Furnace-material, 67. A Method for Determining Sulphur in Roasted Ores, 71.

CHAPTER IV. — The Chemistry of the Calcining Process

Varieties of Roasting, 76. Behavior of Sulphide Ores during Roasting, 76. Degree of Roasting, 81. Matte Assay, 82. Calcu¬ lation of Roasted Ore for Smelting Mixture, 82. Chemical Reac¬ tions, 84. Capacity of Calcining Furnaces, 85. Loss of Copper during Roasting, 86.

CHAPTER V.— The Preparation of Ores for Roasting

Classification of Roasting Appliances, 87. Best Size to Break Ores, 88. Production of Fines, 89. Cost of Breaking Ores by Machinery, 92. The Breaking of Ore by Hand, 93. Cost of Breaking Ore by Hand, 95. Granulation of Mattes by Water, 97. Crushing

PAGET.

1-13

14-27

28-74

75-86

87-103

CONTENTS.

Xll

PAGE.

Machinery, 98. Machines for Preparatory Crushing, Jaw-crushers,

99. Machines for Fine Crushing; Stamps, Ball Pulverizers,

Chilian Mills, Multiple-jaw Crushers, 100. Cornish Rolls, 101. Elevators, 108.

CHAPTER VI. — The Roasting of Ores in Lump Form . 104-170

Heap-roasting, 104. Injurious Effects of Heap-roasting, 105.

Remedies, 106. Selection of Site for Roast-yard, 107. Preparation of Roast-yard, 108. Elevated Track for Roast-yard, 110. Size of Roast-heaps, 113. Construction of Roast-heaps, 115. Proper Use of Fuel in Heap-roasting, 117. Firing the Roast-heap, 119. Man¬ agement of Roast-heaps, 120. Loss of Copper by Leaching, 123. Removing of the Roasted Heap, 126. Heap Matte, 128. Costs of Heap-roasting, 132. Results of Heap-roasting, 133. V-method of Heap-roasting, 136. The Heap-roasting of Matte, 137. Costs of Heap-roasting Matte, 140. Stall -roasting, 140. Open Stalls, 141. Manufacture of Slag-brick, 142. Arrangement of Stalls, 150. Management of Roast stalls, 153. Results of Stall-roasting, 156.

Cost of Erecting Roast-stalls, 158. The Stall-roasting of Matte,

163. The Roasting of Lump Ores in Kilns, 166.

CHAPTER VII. — The Roasting of Ores in Pulverized Condi¬ tion . 171-199

Classification of Roasting Furnaces, Shaft-furnaces, 171. The Gerstenhofer Furnace, the Hasenclever Furnace, the Maletra Fur¬ nace, 172. The Stetefeldt Furnace, Pelatan’s Stall, 173. Hand Reverberatory Calciners, with Open Hearth, 174. Construction of Calciners, 177. Calciner Stacks, 186. Cost of Calcining Furnaces,

192. Cost of Calcining in Hand-reverberatories, 193. Muffle Cal¬ ciners, Revolving Cylinders, 194. Cylinders with Continuous Discharge, 195. Cylinders with Intermittent Discharge, 196.

CHAPTER VIII. — Automatic Reverberatory Calciners... . 200-223 Classification of Automatic Calciners, the O’Harra Furnace, 200

The Allen-O’Harras at Butte, 201. The Pearce Turret Furnace,

205. The Improved Spence Calciner, 214. The Brown Horseshoe Calciner, 218. The Spence Automatic Desulphurizer, 220. The Matthiessen & Hegeler Company’s Calciner, 222. Calciners with Movable Hearth, Blake's Calciner, 223.

CHAPTER IX. — The Smelting of Copper . 224-235

The Object of Smelting, Advantage of High Rate of Concentration,

224. Products of Smelting, Blister Copper, 226. Copper Bottoms,

227. Matte, 228. Speiss, 231. Slags, 232. Flue-dust, 234. Classification of Smelting Methods, 235.

CONTENTS.

xm

PAGE.

CHAPTER X. — The Chemistry of the Blast-furnace . ...236-249

Distinctive Features of the Blast-furnace, 236. Reactions in the Blast-furnace, 237. Example of Calculating a Blast-furnace Charge, 240.

CHAPTER XI. — Blast-furnace Smelting (with Carbonaceous

Modern American Copper Blast-furnace, 251. Advantages of Water-jacket Furnaces, 253. Heat Abstracted by Jacket- water,

258. Water-jacket Blast-furnaces, Cast-iron Jackets, 260. Wrought iron Jackets, 263. Herreshoff Furnace, 266. Verde Water-jacket Furnace, 270. Furnace Bottoms, 271. Blowing-in Water-jackets,

275. Forehearths, 281. Mansfeld Process, 282. Great Falls Foreheartli, 285. Herreshoff Forehearth, 287. Orford Siphon-tap,

294. Mathewson’s Matte-trap, 297. Reverberatory Forehearths,

298. Size and Shape of Blast-furnaces, 303. Blast-furnaces Simply for Resmelting, 303. Suggestion for Butte Practice, 306. Blast-furnaces for Partial Oxidation, 307. The Charging of the Blast-furnace, 309. The Handling of Blast furnace Products, 310.

Keller on Slag-pots, "'313. Mechanical Pan-conveyers for Slag,

Granulation of Slag by Water, 317.

CHAPTER XII. — Blast-furnaces Constructed of Brick . 320-342

The Orford Raschette Furnace, 320. Smelting-in Bottom, 326. Irregularities in Running, 327. Intermittent Running of Blast¬ furnaces, 333. Repairs of Furnaces, 338. Estimate of Cost of Large Brick Blast-furnace, 341.

CHAPTER XIII.— General Remarks on Blast-furnace Smelting. 343-371

Capacity of Blast-furnaces, 343. Use of Wood in Blast-furnaces,

345. Use of Bituminous Coal in Blast-furnaces, 346. Size of Orecharges, 350. Treatment of Fine Ore in Blast-furnaces, 353.

Effect of Fine Ore in Diminishing Capacity of Blast-furnaces, 358.

Blowers and Accessory Blast Apparatus, 363. Results at Butte Smelters, 366. Cost of Smelting in Water- jacketed Blast¬ furnaces, 368.

CHAPTER XIV. — Pyretic Smelting . 372-395

Definition of Pyritic Smelting, 372. Cost of Coke per Ton Ore Smelted in Ordinary Smelting, 374. Advantages of Pyritic Smelt¬ ing, 376. Effect of Shape of Furnace on Pyritic Smelting, 379.

Pyritic Smelting with Column Charging, 382. Pyritic Smelting with Layer Charging, 386. Comparison of Chemical Reactions in Ordinary Smelting and in Pyritic Smelting, 390. Summary for Pyritic Smelting, 393.

XIV

CONTENTS.

PAGE.

CHAPTER XV. — Pyritic Smelting — Its History, Principles, Scope, Apparatus, and Practical Results . 396-441

Distinction between true “ Pyritic Smelting ” and mere Concentra¬ tion of the Gold and Silver by the Use of Pyritic Ores, 396. His¬ tory of Pyritic Smelting, 400. Hollway’s Experiments, 401.

Pyritic Smelting at Toston, Montana, 411. Austin’s Patents, 412.

Boulder Pyritic Smelter, Bi metallic Pyritic Smelter, 415. Table of Pyritic Furnaces in the United States, Literature of the Process.

416. Apparatus, and Principal Scope of the Process, 417. Recov¬ eries of Values in Pyritic Smelting, 427. The Cost of Pyritic Smelting, 435. Cost of Works for Pyritic Smelting, 438.

CHAPTER XVI. — Reverberatory Furnaces . 442-527

The Chemistry of Reverberatory Smelting, 442. The Evolution of the Modern Reverberatory, 445. Reverberatory Practice at Butte, Montana, 451. Anaconda Hot-air Reverberatory, 454. The Butte Reverberatories, 457. Modern Reverberatories, 458. Brick Bottoms, 466. Hot Air in Reverberatory Practice, Depth of Bottom below Skimming Doors, 467. Handling Slag and Matte, 471.

Labor on Reverberatories, 474. Dust-chambers, 475. Construc¬ tion of Reverberatory Smelting-furnaces, 476. Chimneys, 481. Reverberatory Hearths, 484. Management of Furnace, 487. Cost of Running a Reverberatory Furnace, 490. Cost of Erecting a Modern Reverberatory Furnace, 492. Smelting for White Metal,

493. The Making of Blister Copper, 495. Copper Refining, 499.

Cost of Copper Refining, 509. Refining Copper with Gas, 509.

The Blister Process at Atvidaberg, 510. The Refining Process at Atvidaberg, Gas Furnaces in America, 518. The “Direct Method” of Copper Refining, 519.

CHAPTER XVII. — The Bessemerizing of Copper Mattes . 528-575

Table of American Converters, 529. Peculiarities of Copper Bes¬ semerizing, 534. Materials Suitable for Bessemerizing, 538, Description of a Converter Plant, 540. Cost of a Three- converter Plant, 548. Converter Practice, 549. Results of Bessemerizing Mattes, 551. Remelting Cupola, 553. Converter Reactions, 557. Indications Furnished by Converter Flame, 558. Time Required for Converting Matte, 563. Labor Required at Converters, 564. Silver and Gold in Copper Bars, 565. Metallurgical Losses in Bessemer¬ izing, 566. Cost of Converting Copper Matte, 569. Converter Linings, 570.

CHAPTER XVIII. — The Electrolytic Refining of Copper . 576-606

Refining by “ Multiple Arc,” and by “ Series ” Methods, 577. Com¬ parison of Costs in these Two Methods, 581. Boilers and Engines for

CONTENTS.

XV

PAGE.

Electrolytic Work, 583. Generators, 584. Anodes, Cathodes, and Tanks, 586. Conductors, Electrolyte, etc., 594. Current Required, 596. Treatment of the Gold and Silver-slimes, 602.

Cost of Treating Slimes, 604. Cost of Electrolytic Refinery, 606.

CHAPTER XIX. — Selection of Process and Arrangement of

The Three Groups of Ores to be Treated. Native Copper Mines, 607. Oxidized Ores, 608. Sulphide Ores, 610. Choice of Location and Site of Smelter, 618. Railway Tracks, 620. Handling Slag and Matte, 621 . Foundations and General Construction of Works, 622. Transportation of Material in the Works, Water Supply, 624. Supplies, 627. Management of Workmen, 628.

Unless otherwise specified, the “short ton ” of 2,000 pounds (907.2 kilos) is used in this work.

One pound (avoirdupois) . . . 0.4536 kilos.

One foot = 12 inches . 0.3048 metres.

One gallon . 3.7854 litres.

One ounce (Troy weight, as used for precious metals) 31.1 grams.

To reduce “ ounces per ton of 2,000 pounds” to per cent., multiply by 0.00343. Example : What is the value, expressed in per cent., of an ore con¬ taining 155 ounces silver per ton ?

To change per cent, into ounces per ton of 2,000 pounds, multiply by 292. Example : An ore contains 0.01543 per cent, of gold, how much is this per ton of 2,000 pounds when expressed in ounces?

Answer — 0.01543 X 292 =- 4.5 ounces per ton.

The common measure of wood (fuel) in the United States is the “ cord ” of 128 cubic feet.

An American dollar contains one hundred cents, and is equal to about

4 shillings 2 pence . . . English, or

4 marks 16 pfennige . German, or

5 francs 21 centimes . French.

The value of certain foreign coins in American money has been determined by the United States Treasury Department as follows:

Country.

Title of Coin.

Value in U. S.

Money.

Bolivia .

Boliviano . . .

$0.72.7

0.54.6

0.91.2

0.92.6

0.19.3

0.23.8

4.86.65

0.34.6

0.19.3

0.99.7

0.78.4

0.79

1.01.4

0.26.8

0.72.7

1.08

0.58.2

0.19.3

0.26.8

Brazil .

Milreis .

Chili .

Peso .

Cuba . .

Peso .

France .

Franc .

Germany .

Mark . ...

Great Britain .

Pound .

India .

Rupee .

Italy .

Lira .

Japan .

Yen (gold) . .

Yen (silver) .

Mexico .

Dollar .

Newfoundland .

Dollar .

Norway .

Crown .

Peru . . .

Portugal .

Milreis .

Russia .

Rouble .

Spain .

Peseta .

Sweden .

Crown .

MODERN COPPER SMELTING.

Chapter I. Copper And Its Ores

Copper is a red metal, having, when pure and non-porous, a specific gravity of 8.945 in vaeno and at the freezing point of water.*

The slight porosity of ordinary commercial copper reduces this figure to 8.15 — 8.6.

The capacity of copper for conducting heat stands very high, being 898 when gold is called 1000.

Its electrical conductivity is 931, silver being 1000.

When copper is heated to within 200 or 300 degrees of its melt¬ ing point, it becomes brittle and friable, and may be actually pulverized.

The melting points of substances that are not easily fusible have not been determined with exactness. As an approximation, copper may be assumed to melt at 2000 degrees Fahr. (1093 degrees Cent.).

When fused it possesses a sea-green color. It is volatile when exposed to our highest attainable temperatures, such as the electric arc, or the oxy-hydrogen flame.

Molten copper has the property of absorbing certain gases, such as hydrogen, carbonic oxide, sulphurous acid, etc., which it sets free again on solidifying. This causes serious difficulties in mak¬ ing copper castings, and requires the employment of special pre¬ cautions to prevent porosity.

The malleability, ductility, softness, and strength of copper

* W. Hampe, Zeitschrift fur Berg - Hutten- und Salinenwesen, 1873, p. 218

MO DEUX COPPER SMELTING.

i*v are extraordinarily affected by the presence of minute quantities of certain other substances.

Cuprous oxide dissolves rapidly and homogeneously in metallic copper, and, according to Hampe’s researches, produces absolutely no effect until present to the extent of 0.5 per cent. Even 1 per cent, of this substance produces but a very slight diminution in toughness. In greater quantities, it lowers the ductility of the metal, but may be present up to 8 per cent, to 18 per cent, without rendering the copper unfit for most purposes.

/row, when present, is generally distributed through the copper with much regularity. Reliable data as to the effect of this sub¬ stance on the tensile strength and electrical conductivity of copper are not to be had. But the weight of evidence seems to show that the minute proportion of iron so frequently present in refined cop¬ per has no appreciable effect on any of its useful qualities, except, possibly, its electrical conductivity.

Zinc forms an alloy with copper in every proportion, and slightly lowers its ductility at high temperatures. But until the zinc reaches at least 18 per cent., the tenacity of the alloy at ordinary temperatures does not seem to be lessened.

Lead , while a useful addition to copper that is to be employed for certain mechanical purposes, and assisting in procuring solid castings, has a decidedly injurious effect if present in too large quantities. One-third of one per cent, is sufficient to make the metal both red -short and cold-short, while 0.75 per cent, will ruin copper for any ordinary purpose.

Tin also alloys with copper in all proportions, and begins to injure its ductility when present in quantities of 1 per cent.

Nickel is frequently present in commercial copper, and up to 0.3 per cent, seems to produce no injurious results.

Bismuth is, perhaps, the worst enemy of the copper refiner; for, in spite of its oxidizability, it clings to copper with much tenacity, and affects its properties in the most surprising manner. Hampe finds that merely 0.02 per cent, is sufficient to make the metal distinctly red-short, and cold-shortness begins with 0.05 per gent. bismuth.

Arsenic is not so injurious to copper as is often supposed. Hampe cannot find that 0.5 per cent, of this substance has any bad effect on copper, except to diminish its electrical conductivity; and copper containing 0.8 per cent, arsenic was drawn by him into the finest wire.

COPPER AND ITS ORES.

Antimony np to 0.5 per cent, acts very much like arsenic, and the lowering of the metal’s electrical conductivity does not seem to be accompanied with a loss of either strength or ductility. So Hampe decides after a long series of most careful researches. When present in quantities greater than 0.5 per cent., antimony is much more injurious than arsenic.

lellurium , which is by no means a rare constituent of copper in certain districts, produces red-shortness, even though present in very small amounts. But Mouchel claims that at ordinary tem¬ peratures, the addition of 0.1 percent, of tellurium largely increases the tensile strength of copper without materially lessening its conductivity.

Silicon has been very thoroughly studied by Hampe as to its effect on copper.*

The addition of 0.5 per cent, of this metal causes a distinct low¬ ering of electrical conductivity. But copper may contain 3 per cent, of silicon before its toughness or malleability is affected. Six per cent, makes copper brittle, increasing as the silicon is increased, until at 11.7 per cent, the alloy is as brittle as glass.

Sulphur in quantities of 0.25 per cent, lowers the malleability of copper. One-half of percent, prod Lices cold-shortness, though curiously enough such copper is not red-short.

Phosphorus in small quantities seems to produce no injurious effect. At 0.4 per cent, red-shortness is developed.

Carhon is not at all taken up by molten copper, according to Hampe’s late researches, though not long ago it was believed to be absorbed in considerable quantities, and to affect the copper most seriously. Too long-continued poling was thought to bring about this result, but it seems to be now conclusively established that the evil effect of ‘‘overpoling” copper in the refining furnace is due to the reduction of certain metallic compounds, which, when present in the copper in an oxidized condition, produce no visible effect. Such compounds are arsenates and antimonates of lead and bismuth, mixtures of oxides of lead and copper, etc. The gases arising from poliug, such as carbonic oxide, hydrogen, etc., may also be absorbed by the copper, and affect it injuriously.

Tempered copper has been put upon the market by the Eureka Tempered Copper Company, samples of which were examined at the V ' ersuchsanstalt fiir Bau-und Maschinen Material with the following results, the investigation having been made by P. Kirsch:

*Chemiker Zeitung , 1892, No. 42.

MODERN COPPER SMELTING.

I. — CHEMICAL COMPOSITION.

Ordinary Copper.

Per cent.

Tempered Copper.

Per cent.

Silver .

0.026

0 . 025

Copper . . .

Tin .

99.930

99.981

Zinc .

I ron .

0.082

0.088

Aluminum .

Arsenic .

0.046

0.042

Phosphorus .

0.017

0.018

Total .

100.101

100.154

As will be seen from the foregoing analyses, the difference of tempered copper from copper of ordinary commercial quality, as far as its composition is concerned, is but slight.

The coppers of which the analyses are given above were mechan¬ ically tested, with the following results:

II. — MECHANICAL PROPERTIES,

Strength in kgs.* per sq. mm.

Elastic Limit in kgs. per sq. mm.

Extension.

Per cent.

Contraction in Area.

Per cent.

Tension, tempered .

18.14

8.05

18.0

26.7

Tension, tempered .

19.58

7.67

23.5

36.6

Tension, untempered .

16.30

7.13

21.0

36.6

Tension, untempered.. ..

17.17

7.08

22.5

35.7

Compression, tempered.. .

39.38

0.42

28.0

Compression, tempered. ..

37.20

9.93

26.8

Compression, untempered

33.12

9.62

27.4

Compression, untempered

36.21

11.20

27.6

* 1 kg. per square mm. = 1,425.45 pounds per square inch.

The tests and analyses quoted above were carried out in America, and are quoted for the sake of comparison with those performed at the Versuchsanstalt, which were as follows:

(«) Modulus of Elasticity. — The modulus of elasticity deter¬ mined on a specimen tested in tension was 10,000 kilos per square mm. The modulus determined by compression tests was 2,930 kilos per square mm., with a load of 2.5 kilos per square mm., and 1,020 kilos per square mm. with a load of 7.2 kilos per square mm.

(b) Tensile Strength. — Test pieces used: Sheet, 0.11 mm. in thickness, 50.2 kilos per square mm.; sheet, 0.13 mm. in thick-

COPPER AND ITS ORES.

ness, 67.9; sheev., 0.55 mm. in thickness, 56.8; sheet, 0.64 mm. in thickness, 53.4; sheet, 1.19 mm. in thickness, 52.3; wire, 0.50 mm. in diameter, 31.8; wire, 0.80 mm. in diameter, 72.0; wire, 1.65 mm. in diameter, 52.0; wire, 2.60 mm. in diameter, 50.0; wire, 4.20 mm. in diameter, 47.6; rod, 87 mm. in diameter, 19.0.

The last named specimen had an elastic limit of 8.1 kilos per square mm. A compression test was made in which deformation began when the load had reached 8.1 kilos per square mm. The load could be increased to 219 kilos per square mm. without pro¬ ducing cracks, although the test piece, which was originally 30 mm. in height, had been shortened to 7.8 mm.

(c) Ductililty. — The extension given by the sheet varied between 0.2 — 2.0 per cent., while that of the wire was 0.1 — 0.2 per cent, and that of the rod 13.1 per cent., while the contraction of area at the point of fracture of the latter was 33 per cent. From these tests, as well as by winding tests with the wire, it appears that the material possesses great ductility.

The foregoing series of tests shows that tempered copper possesses properties that distinguish it from the ordinary material, its strength in pieces of small section being noticeably high, although that of larger test pieces is by no means remarkable, as it shows the tensile strength of only 19 kilos per square mm., while ordi¬ nary commercial copper gives 20 — 25 kilos per square mm. Cast¬ ings made of it are of good quality, and its electrical conductivity is high.*

Copper is easily soluble in nitric acid, in aqua regia, and in strong boiling sulphuric acid.

In dilute sulphuric and muriatic acids, with admission of air, it dissolves slowly.

The metallurgical processes for obtaining copper from the greater proportion of its ores are based upon its strong affinity for sulphur, wherein it exceeds every other metal.

If an impure plate of copper be used as an anode in an acid solution of sulphate of copp r, and another plate be taken as cathode, a properly regulated electric current will precipitate chemically pure copper upon the cathode, the anode dissolving in the same ratio, while the impurities contained in the latter (in¬ cluding often gold and silver), remain as a residual mud. This is

* Mittheil. Techn. G ewerbe- Museums, 1891, 261-267, through Journal of the Society of Chemical Industry for February, 1892.

G

MODERN COPPER SMELTING.

the basis of the modern electrolytic refining of copper, first made a technical and commercial success by the Messrs. Elkingtou of England.

Compounds of Copper Most Important to Metallurgists,

AND THEIR REACTIONS.

Copper has two oxides.

Cuprous oxide melts at a red heat without decomposition. It is freely dissolved in molten metallic copper. In a pulverized condition it can easily be changed into the higher oxide by gently heating it in air. It is easily reducible to metallic copper, and forms a fusible slag with silica.

Melted with subsulphide of copper in proper proportions, the copper in both substances is reduced entirely to the metallic state, while the sulphur of the matte combines with the oxygen of the cuprous oxide, and forms sulphurous acid gas. This reaction, and a few analogous ones that follow, are the main basis of our treat¬ ment of most ores of copper.

Subjected to the same treatment with sulphide of iron, the copper combines with sulphur to form a subsulphide, which, to¬ gether with a portion of the undecomposed sulphide of iron, forms a matte, while the iron that has been changed to a protoxide by the oxygen of the cuprous oxide, combines with silica, that should also be present to form slag. The matte being heavier sinks to the bottom and can easily be separated from the supernatant slag, and the first step in the fusion of copper ores has been accomplished.

Cupric oxide is infusible. It is easily reduced to metal by hydrogen or carbonic oxide gases.

It will not combine with silica to form a slag at ordinary metal¬ lurgical temperatures unless there be such conditions present that it is mostly reduced to cuprous oxide.

Its reactions with sulphide of iron and silica lead to the same result as in the case of cuprous oxide. That is, we obtain a matte, containing the copper as a subsulphide together with indeterminate sulphides of iron, and a silicate of the ferrous oxide that has been formed, as already explained.

Both of these oxides are soluble in ammonia.

Silicate of copper, in the presence of a strong base, such as fer¬ rous oxide or lime, is reduced by carbon to the metallic state.

When heated with sulphide of iron we obtain sulphide of copper and silicate of iron.

COPPER AND ITS ORES.

When heated with metallic iron we obtain silicate of iron and metallic copper.

Sulphides of copper.— W e know two sulphides of copper: CuS and Cu2S. Only the latter is of importance metallurgically, as the CuS loses one-half its sulphur at a comparatively low temperature.

This Cu2S, or subsulphide of copper (cuprous sulphide), melts at a low temperature, and fuses together with sulphide of iron to form an apparently homogeneous substance called matte. This is the object of the first smelting operation with ordinary ores. Much of the sulphide of iron contained in the ore, as well as the sulphides of copper, has been changed into oxides by a preceding calcination at a low temperature. The reactions described above having taken place, we obtain a matte containing all of the copper as a subsulphide with much sulphide of iron, while the alkaline earths and the protoxide of iron combine to a worthless slag.

Under favorable circumstances, and with low-grade ores, we may thus sometimes diminish our material to be treated by 90 per cent, or more in this single fusion, and thus obtain practically all of the copper (as well as any gold or silver present), in a very small quantity of matte, on which we can afford to put considera¬ ble expense.

The Ores of Copper.

Although the copper-bearing minerals are numerous, yet those of commercial importance are few in number, and, for the most part, quite simple in chemical composition. The following min¬ erals may be properly considered ores of copper, and are found in the United States in the localities enumerated.

Native Metallic Copper.

Aside from the extensive occurrence of this metal in the Lake Superior region and, more sparingly, at Santa Rita, New Mexico, it is found very frequently as a product of decomposition, though seldom in sufficient quantities to render it of any commercial importance. It is usually remarkable for its purity.

Cuprite, or Red Oxide of Coppeh. Cu20; 88.8 Cu, 11.2 0.