464 



COPPER 



Copper in any liquid is easily discovered by 

 placing in it a plate of polished iron, when it will 

 be observed coating the metal with its well-known 

 reddish tint, making its appearance over the part of 

 the plate immersed in the fluid. If the quantity of 

 copper is very small, the liquid should be concen- 

 trated till it half fills a watch-glass, and a bright 

 steel needle used in place of an iron plate. Solu- 

 tions of cupric salts have a blue or greenish-blue 

 colour, but this on addition of ammonia in excess 

 becomes an intense purplish blue. 



Native Copper, although frequently met with 

 wherever copper ores occur, is yet rarely discovered 

 in sufficient quantity to admit of its being system- 

 atically worked. It is found crystallised in cubes 

 and in modifications of this form ; also in arbores- 

 cent pieces, in thin lamin;e, and in irregular lumps 

 or masses. Sometimes it forms a nucleus with first 

 a layer of red oxide and then a second layer of car- 

 bonate of copper around it. The largest masses of 

 native copper are obtained from mines in Russia 

 and from copper-bearing strata in the neighbour- 

 hood of Lake Superior. One mass was mined at 

 Minnesota in 1859, weighing 500 tons, which 

 required the work of forty men for a year to extract 

 it. The largest yet obtained was got in 1866 at 

 the Central mines, Lake Superior, and weighed 

 SOO tons. 



The ores of copper are numerous. Cuprite, ruby 

 copper, cuprous oxide, or red oxide of copper, is the 

 richest ore. It contains, when pure, nearly 90 per 

 cent, of copper. Malachite ( q. v. ), or green carbonate 

 of copper, consists, when pure, of 57 per cent, of the 

 metal. This ore occurs largely in Russia, South 

 Australia, and in some localities in South America. 

 Chessylite, azurite, or blue carbonate of copper, in a 

 pure state contains 55 per cent, of copper. Chal- 

 copyrite, copper pyrites, or yellow copper ore, a sul- 

 phide of copper and iron, is, from its abundance, 

 the most important of copper ores. Although 

 containing, when pure, 35 per cent, of copper, 

 yet on account of impurities, what is mined in 

 England does not yield, on an average, more than 

 8 per cent, of the metal. Some of the auriferous 

 copper pyrites of the western states of America 

 and elsewhere is worked as an ore of gold (see 

 GOLD ). Erubescite, or purple copper ore, is also a 

 sulphide of copper in which the proportion of the 

 metal varies from 60 to 70 per cent. Tetrahedrite, 

 or gray copper ore, is a sulph-antimonite of copper 

 of very variable composition, but often containing 

 from 30 to 40 per cent, of copper, &c. Atacamite 

 (q.v.) is an oxychloride of copper mined in Chili, 

 and found in other countries. Melaconite, or black 

 oxide of copper, and Chrysocolla, a silicate of 

 copper, are sometimes smelted as ores of the 

 metal. 



COPPER-SMELTING. In practice, the process of 

 smelting copper from ore ( copper pyrites ) like the 

 Cornish is somewhat complicated, but in theory it 

 is comparatively simple. The main impurities of 

 the ore are quartz, iron, sulphur, and very com- 

 monly arsenic. The process is conducted with the 

 view of separating the iron and quartz as a fusible 

 slag, and of dissipating the sulphur and arsenic, by 

 converting them into sulphurous and arsenious 

 acids, through oxidation in the furnace. At Swan- 

 sea, which is the chief seat of copper-smelting in 

 this country, leverberatory furnaces are used, and 

 these are of two kinds, called respectively calciners 

 and melting furnaces. Gas, along with Siemens' 

 regenerative apparatus, is now to some extent used 

 in different parts of the world for supplying heat 

 to copper furnaces, but at some places it has been 

 given up, after a short trial, owing to the costly 

 repairs which it causes. There are never fewer 

 than six operations in the Welsh process of 

 copper-smelting, and when so limited, a favourable 



admixture of ores, such as copper pyrites and 

 copper carbonates, is necessary. In the first, the 

 ore is calcined in a furnace for at least twelve 

 hours, by which time the greater part of the sul- 

 phide of iron is decomposed, and much sulphurous 

 and other acids have formed and escaped in fumes 

 i.e. a partial oxidation of the iron and sulphur 



Fig. 1. Section of a Reverberatory Copper-melting 



Furnace : 

 A, fireplace ; B, fire-bridge ; C, bed of sand ; D, melted copper. 



takes place. In the second, the calcined ore is 

 melted along with siliceous slags obtained in later 

 stages of the process. Here a fusible slag, consisting 

 in great part of silicate of iron, is formed, and the 

 sulphides of iron and copper are run off as a regulus, 

 termed coarse metal, and granulated in water. A 

 section of a melting furnace is given in fig. 1. In 

 the third, the coarse metal is calcined again for 

 twenty-four hours, during which time most of the 

 sulphide of iron is converted into oxide. In the 

 fourth, the calcined coarse metal is melted with 

 slags rich in oxide of copper, and also with rich ores, 

 as oxide and carbonate. These oxidise any sulphide 

 of iron remaining, and a regulus called white metal 

 is formed, consisting almost entirely of sulphide of 

 copper, and containing about 75 per cent, of the 

 metal. In the fifth, called ' roasting,' the regulus 

 is very slowly melted, so as to allow of the gradual 

 and thorough reduction of the sulphide by heated 

 atmospheric air through the formation of oxide of 

 copper. When oxide and sulphide of copper are 

 heated together, they decompose each other, the 

 sulphur escapes as sulphurous acid, and impure 

 metallic copper, called blister copper, is produced, 

 while other foreign bodies are for the most part 

 removed in the slag. In the sixth, the copper from 

 the previous operation is refined. To effect this, it 

 is melted in a furnace, and exposed to the oxidising 

 influence of the air for from fifteen to twenty hours, 

 by which time it is full of dioxide, and this is in 

 turn reduced by throwing pure coal on the surface 

 of the molten metal, and then stirring it with a 

 pole of green birch-wood. 



At those smelting works where the sulphurous 

 acid produced in the calcining or roasting of copper 

 pyrites is saved for the manufacture of sulphuric 

 acid, peculiar furnaces, such as Gerstenhofer's, 

 Hasenclever and Helbig's, and Maletra's, are used 

 for roasting the ore. Shaft or cupola furnaces, 

 instead of those of a reverberatory kind, are used 

 in some countries, for smelting copper ores where 

 these are highly ferruginous, or oxidised, or com- 

 paratively poor. Coke, anthracite, or charcoal is 

 used as fuel in cupola furnaces, which require a 

 blast of air at a moderate pressure. 



Wet Copper Extraction Process. Soon after iron 

 pyrites ( sulphide of iron ) began to be used about 

 thirty years ago as the source of sulphur for the 

 manufacture of sulphuric acid, it was thought 

 desirable to recover the copper, amounting to a 

 small per cent, of the pyrites used. The burnt 

 pyrites, consisting chiefly of oxide of iron, along 



