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quantity of certain oils or other agents (the addition of oil being perhaps only 2 Ib. per ton of ore), and was then subjected to violent agitation, the copper minerals (if sulphides) would rise to the surface in the form of a froth, while the worthless gangue would settle to the bottom. Separation in this way was possible at rela- tively low cost and yielded a far higher percentage of the mineral than the older processes. The improvement might be general- ized by indicating an extraction of 90 %, compared with 65 to 75 % previously.

Metallurgy. Previous to 1910 the blast furnace and the rever- beratpry furnace were frequently competitive choices for the smelting of copper ore. At one time one would be in the lead and then improvements would cause preference to be given to the other. With the increasing fineness of the ore to be smelted, the leaning began to be definitely in favour of the reverberatory furnace, but with the advent of the Dwight-Lloyd sinterer, which enables fine ores to be agglomerated cheaply and efficiently, the blast furnace gained a new prestige. With the successful application of coal- dust firing, however, which was due especially to the work of David H. Browne at Copper Cliff, Ont., the reverberatory furnace ob- tained an unquestionable predominance, which it is likely to hold. The modern copper-smelting plant designed for the treatment of fine ore comprises roasting furnaces of the MacDugall type and rever- beratory smelting furnaces of very large size. Pr rvious to the in- troduction of coal-dust firing, a furnace at Anaconda, Mont., igx 1 12 ft., smelted 240 tons of charge with one ton of coal per 4i tons of charge. By the new method a furnace 25 x 144 ft. smelted 650 tons, and one ton of coal smelted seven tons of charge. For the smelting of coarse ore, and especially of heavy sulphide, the blast furnace operated on the pyritic or the semi-pyritic principle still held its place in 1920. These furnaces also were constructed of very large size. The Anaconda Co. attained dimensions of 72 x 1,044 in. at the tuyeres, but this was exceptional, the blast furnaces at most American works being something like 72 x 280 inches.

The converting of copper matte in a basic-lined vessel, which had long been a hope of copper metallurgists, was carried to success by W. H. Pierce and E. A. Cappelen-Smith at the works of the Balti- more Copper Smelting and Rolling Co., just previous to 1910, and early in 1910 the process was introduced in the works of the Garfield Smelting Co. in Utah. Subsequently it was found that the process was not limited to the Pierce-Smith horizontal converters, but could be applied to other forms of converters, both horizontal and upright. The main advantages of the basic over the acid converter are the decreased cost of lining (one basic lining for 2,500 tons of copper compared with one'acid lining for 10 tons), greater air efficiency, ability to convert low-grade matte with a mixture of silicious ore, reduction of intermediate products, neatness and cleanliness of plant, and decrease in danger from accidents. The basic converters are lined with magnesite. Their use became general. They reduced the cost of converting copper matte to less than 50 % of what it used to be with the converters lined with acid (silicious) material.

The existence of immense ore deposits of the porphyry type, but with the copper occurring as oxide or chloride, which rendered the ore unamenable to mechanical concentration, directed renewed attention to the hydrometallurgical extraction of the copper of such ore. At Chuquicamata, Chile, lies the world's greatest known de- posit of copper, its development being estimated at about 700,000,000 tons assaying about 2 % copper. Exploitation of this was under- taken by the Chile Copper Co., an American corporation. The cop- per occurs in the ore as brochantite contaminated with chlorides. E. A. Cappelen-Smith devised a process for the leaching of this ore with sulphuric acid, purification of the solution and deposition of the copper by electrolysis, using magnetite anodes, but in practice anodes of ferro-silicon have been substituted. The copper cathodes are melted and cast into bars of grade equivalent to standard

electrolytically refined copper. Production in 1920 was at the rate of 100,000,000 Ib. per annum. At Ajo, Ariz., the New Cornelia Copper Co. also produced electrolytic copper directly from ore, from which the copper was first leached by sulphuric acid. Hydrometal- lurgical extraction of copper was also applied on a large scale for the treatment of tailings, e.g.. by the Anaconda Copper Mining Co., and by the Calumet & Hecla Mining Co., the latter extracting the na- tive copper by means of ammonia, and precipitating the copper as oxide by distillation, with recovery of the ammonia. A similar process was employed for ore treatment at the Kennecott mine, in Alaska.

General Economic Conditions. A large part of the world's copper production was in 1920 derived from immense units. Thus in 1918 Anaconda produced 273,000,000 Ib. of copper. This, however, was derived from a group of mines. The Utah Cop- per Co. produced 12,500,000 tons of ore in 1917, yielding 196,- 000,000 Ib. of copper from a single mine. Previous to the World War about 15 cents per Ib. was regarded as a market price reason- ably to be expected on the average. The cost of production to the largest producers was about 10 cents per Ib. The immense demand for copper for military purposes that began in 1915 temporarily outran the ability of the producers to meet it, and the price ran up to about 32 cents per Ib. at the end of 1916 ; but the increased production began to show its effect in 1917 and the market declined materially during that year. In the latter part of 19 1 7 the American Government fixed the price at 235 cents. Min- ing, smelting and refining capacities were rapidly increased and in 1917 American electrolytic refiners attained a capacity for the production of 2,800,000,000 Ib. of copper per annum. With the termination of the war it was found that all of the Allied and Associated Powers had overbought their requirements, and pro- ducers were unable to curtail their scale of operations quickly. This led to the greatest accumulation of unsold copper in the history of the metal, and combined with the greatly increased cost of operation, a bad economic situation developed in the in- dustry which continued into 1921. At the end of 1920 the price for copper was about 125 cents per Ib. Statistics of the world's production of copper are given in the accompanying table.

Previous to the World War the world's production of copper had risen to an annual rate of about 1,000,000 metric tons. In 1916-8 there was an annual production of about 1,400,000 tons. In 1919 it was curtailed to slightly less than the pre-war rate. In April 1921 a general closing of copper mines became necessary on account of the economic situation, and the world's production was thus curtailed to about one-third of the pre-war rate. American interests control (1921) the major part of the copper production of Chile and Peru, and in fact control up- ward of 80% of the world's production. Outside of this control the production of Japan, Spain, Portugal, Australia and Africa is the most important, but of those countries Japan is the only one whose output has exceeded 100,000 tons per annum.

The best record of progress in the mining and metallurgy of copper, economic conditions, etc., is to be found in the file of the Engineering and Mining Journal, New York. Important technical

Country. United States. Mexico Canada Cuba Bolivia Chile Peru

Austria-Hungary Germany

Norway. . . Russia

Spain and Portugal Sweden Serbia Japan Australasia Africa Other countries

Totals

WORLD'S PRODUCTION OF COPPER In metric tons

1911

1912

1913

1914

1915

1916

1917

1918

1919

1920

491,600

563,300

557,400

525,529

646,212

881,237

872,065

879,026

548,677

576,450

61,900

73,7co

52,800

36,337

30,969

55,128

47,503

75,529

60,491

50,480

25,300

35-300

34,9oo

34-027

47,202

47,985

50,626

52,693

36,106

35,500

3,800

4,400

3,400

6,251

8,836

7,816

10,313

12,337

9,974

6,485

2,600

3,7oo

3,700

3,874

5,868

5-150

6,400

6,000

7,000

9,900

36,420

4!,647

42,263

44,665

52,341

71,288

102,527

96,565

63,930

94-531

27,735

26,969

27,776

27,090

34.727

43,078

45,176

44,4H

39.470

31,276

2,600

4.000

4,100

3,5oo

3,500

3,500

3,5oo

2,500

1,000

1,000

22,400

25,600

25,300

25,000

25,539

24,796

28,632

15,101

15,775

17,255

1,565

2,130

2,741

2,859

2,826

1,614

1,810

2,856

i, 800

1,400

25,700

33,500

33,900

31,938

25,881

20,887

16,000

51,800

59,9oo

54,700

37,099

46,200

42,000

42,000

41,000

40,000

25,000

3,221

3,957

4,215

4,692

4,56i

3,i8i

4,423

2,956

3,558

3.500

7,000

7,400

6,400

4-443

3,200

5,000

11,200

6,000

1,209

2,436

53,402

62,423

66,500

70,463

75,416

100,635

108,038

90,323

81 ,865

65,554

45,979

46,343

45,647

38,667

37,709

39,855

36,564

44-722

16,441

26,486

17-300

16,600

22,900

27,033

31,300

39,8i5

42,656

31,064

3 1.350

32,230

6,300

5,300

3,800

5,ooo

5,000

5,000

5,000

5.000

5,000

5,000

886,622 1,016,169 992442 928,467 1,087,287 1,397,965 1,434,433 1,408,086 963,646 984,483