Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/381

C O P P E 11 351 tanks by means of metallic iron in the same way that cementation copper is obtained from solutions of the sulphate. The solution is run into the tanks, in which there are miscellaneous heaps of old malleable iron ; the chlorine combined with the copper unites with the iron, and metallic copper in a state of fine division is thrown down. The completion of the precipitation is ascertained by dipping a bright steel knife into the solution in the tank, and when no deposit of copper covers the steel the liquor is run off and a new charge conveyed into the tank. The tanks are drained periodically for removing the precipitate, which is first roughly separated from small pieces of iron, after which it is more thoroughly freed from iron, &c., by washing in water in a rocking sieve apparatus. The precipitate so obtained should contain 80 per cent, of metallic copper, which is either smelted directly for blister c-opper, or may be fused with the white metal of the ordinary smelting process, and subsequently roasted. It has been found possible to extract in this process with profit the small proportions of lead, silver, and gold which Spanish pyrites is known to contain. Two processes are in operation for this purposes one devised by Mr F. Claudet and the other by Mr W. Henderson, the original patentee of the wet process. The liquors from the first three washings contain practically all these metals, and they alone are treated. Mr Claudet precipitates them from the solution by means of iodide of potassium. Mr Henderson dilutes his solutions to from 20 to 25 Twaddell, and adds a very weak solution of a lead salt, such as the acetate, by which he obtains a cream-coloured precipitate containing about 53 per cent, of lead, 5 or 6 per cent, of silver, and 3 oz. of gold to each ton of the precipitate. The importance of the wet process may be estimated from the fact that although it originated only in 18GO, already 14,000 tons of copper are annually produced by it in Great Britain alone, out of an annual production for the whole world estimated at from 126,000 to 130,000 tons. ALLOYS OP COPPER. Copper unites with facility with almost all other metals, and a large number of its com pounds are of the highest importance in the arts. Indeed copper is much more important and valuable as a con stituent element in numerous alloys than it is as pure metal. The principal alloys in which it forms a leading ingredient are 1st, brass ; 2d, bronze ; and 3d, German or nickel silver ; and under these several heads their respective applications and qualities will be found. These alloys are each much diversified as regards the relative proportions of the various metals which enter into their constitution, and these differences similarly modify the appearance and physical properties of the compounds. In this way for practical purposes they may be regarded as a great number of separate metals, each possessed of distinct qualities which fit it for special industrial uses. The following tables, compiled from various authorities, represent the analysis of typical examples of the several alloys: TABLE A. Composition of Brass or Copper and Zinc Alloys. Copper. Zinc. Tin. Iron. Lead. Roman coin Titus 96-06 2-71 0-85 Tombac or Talmi gold Statue of Minerva in Paris English brass 86-40 83-00 70-29 12-20 14-00 29-26 1-10 2-00 0-17 0-30 i-oo 28 Aich metal 60-20 38-10 1 60 Rosthorn s sterro-metal .... Ship-nails, bad 54-00 52-73 40-50 41-18 5-50 4-72 , i good 62 62 24-64 2 64 8 69 Muntz s metal, or yellow sheathing, consists of 60 parts of copper and 40 of zinc, but the copper may vary from 50 to 63 per cent, and the zinc from 50 down to 37. TABLE B. Composition of Bronzes. Copper. Tin. Zinc. Lead. Iron. Roman Coin Domitian 98-92 1-08 ,, Diocletian ,, Maxentius ,, Justinian .... 95-84 88-72 84 53 2-23 5-85 6 "82 1-93 5 43 8 "65 Ancient arrowhead 70-30 24-53 5 20 Common bell metal 79 90 20-03 . . . Bronze statue, Thonvaldsen s ) shepherd . ( 88-77 9-25 1-28 0-71 Bell of 12tli century 76-10 22-30 1 60 1 60 Chinese gong 80-50 19-50 Japanese bell metal 60-50 18 15 6 10 12 20 3 05 Locomotive bearings , 73-60 9 50 9 00 7 00 42 ,, piston 89-00 2-40 9 00 Speculum 65-13 32 78 Aluminium bronzes are composed of pure copper with from 2^ up to 10 per cent, of aluminium. Phosphor bronze, according to the purposes for which it is intended, contains from 3 to 15 per cent, of tin and from ^ to 2| per cent, of phosphorus. Small proportions of other metals, among which are silver, nickel, cobalt, antimony, and bismuth, with sulphur, frequently enter into the composi tion of bronzes. TABLE C. Composition of Nickel Silver. a, P< o 1 e o E C N C H Cadmium. Chinese Packfong 40-40 31-60 2 60 25-40 Parisian metal for ) spoons, forks, &c English nickel silver for i plating 69-80 63-34 19-80 19-17 trace 5-50 17-01 4-7 English nickel silver for j plating (another kind) J 62-63 10-85 trace 26-05 SALTS OF COPPER. Several salts of copper possess con siderable industrial value, chiefly for the formation of blue and green pigments, in dyeing and calico-printing, and for the deposition of metallic copper by electro-metallurgy, &c. The principal salts of copper are the acetate, the carbonate, and the sulphate. Acetate of Copper or Verdigris. This salt is found in commerce in the two forms of basic and neutral acetate. The principal seat of the manufacture of the basic acetate is Montpellier in France, where the marc and other refinse of grapes, after the expression of the juice for wine-making, is employed as a source of the acetic acid necessary. Sheets of copper are placed among this refuse, and these soon become coated with a deposit of verdigris, which has only to be scraped off, kneaded up with water, and pressed into cakes. The neutral salt is prepared from basic acetate by dissolving it in pyroligneous acid (wood vinegar) and evaporating the solution to the crystallizing point. It is also formed by the double decomposition of the acetates of lead and calcium with sulphate of copper. Verdigris is much used as a pigmeut both in oil and water-colour paint ing and in dyeing, and as a basis of compound pigments. Carbonate of Copper in an impure condition forma a valuable series of pigments called verditer, Bremen blue, or Bremen green, possessing various shades of mingled green and blue according to the nature of the compounds with which the carbonate is mixed. The basis of these pigments is prepared by an elaborate and tedious process from the oxychloride of copper. Sulphate of Copper, CuS0 4 , 5H 2 O, called also blue stone, or Roman vitriol, is, on the large scale, prepared direct from, the cementation water from pyrites mines by evaporation

to the crystallizing point. It is also prepared by the