COPPEK, SILVER, AND GOLD 401 



of these compounds. There are many such localities in the Perm and 

 other Governments bounding the Urals. Blue carbonate of copper, or 

 azurite, is also often met with in the same localities ; it contains the 

 same ingredients as malachite, but in a different proportion, its com- 

 position being CuH 2 O 2 ,2CuCO 3 . Both these substances may be ob 

 tained artificially by the action of the alkali carbonates on solutions 

 of cupric salts at various temperatures. These native carbonates are 

 often used for the extraction of copper, all the more as they very 

 readily give metallic copper, evolving water and carbonic anhydride 

 when ignited, and leaving the easily-reducible cupric oxide. Copper 

 is, however, still more often met with in the form of the sulphides. 

 The sulphides of copper generally occur in chemical combination 

 with the sulphides of iron. 3 These copper-sulphur compounds (copper 

 pyrites CuFeS 2 , variegated copper ore Cu 3 FeS 3 , &c.) generally occur in 

 veins in a rock gangue. 



The extraction of copper from its oxide ores does not present any 

 difficulty, because the copper, when ignited with charcoal and melted;, 

 is reduced from the impurities which accompany it. This mode of 

 smelting copper ores is carried on in cupola- or cylindrical furnaces, 

 fluxes forming a slag being added to the mixture of ore and charcoal. 



8 Iron pyrites, PeS 2 , very often contain a small quantity of copper sulphide (see 

 Chapter XXII., Note 2 bis), and on burning the iron pyrites for sulphurous anhydride the 

 copper oxide remains in the residue, from which the copper is often extracted with profit, 

 For this purpose the whole of the sulphur is not burnt off from the iron pyrites, but a 

 portion is left behind in the ore, which is then slowly ignited (roasted) with access of air. 

 Cupric sulphate is then formed, and is extracted by water ; or what is better and more 

 frequently done, the residue from the roasting of the pyrites is roasted with common 

 salt, and the solution of cuprio chloride obtained by lixiviating is precipitated with iron, 

 A far greater amount of copper ia obtained from other sulphuretted ores. Among these 

 copper glance, Cu 2 S, is more rarely met with. It has a metallic lustre, is grey, generally 

 crystalline, and is obtained in admixture with organic matter ; so that there is no doubt 

 that its origin is due to the reducing action of the latter on solutions of cupric sulphate. 

 Variegated copper ore, which crystallises in octahedra, not infrequently forms art 

 admixture in copper glance ; it has a metallic lustre, and is reddish-brown ; it has a 

 superficial play of colours, due to oxidation proceeding on its surface. Its composition is 

 CusFeSj. But the most common and widely-distributed copper ore is copper pyrites^ 

 which crystallises in regular octahedra ; it has a metallic lustre, a sp. gr. of 4'0, and 

 yellow colour. Its composition is CuFeS 2 . It must be remarked that the sulphurous 

 ores of copper are oxidised in the presence, of water containing oxygen in solution, 

 and form cupric sulphate, blue vitriol, which is easily soluble in water. If this water 

 contains calcium carbonate, gypsum and cupric carbonate are formed by double 

 decomposition: CuSC^ + CaCOs = CuCO 5 + CaS0 4 . Hence copper sulphide in the form 

 of different ores must be considered as the primary product, and the many other copper 

 ores as secondary products, formed by water. This is confirmed by the fact that at the 

 present time the water extracted from many copper mines contains cupric sulphate in 

 eolution. From this liquid it is easy to extract cupric oxide by* the action of organic 

 matter and various impurities of water. Hence metallic copper is sometimes found in 

 natural products of the modification of copper sulphide and is probably deposited by 

 the action of organic matter present in the water. 



