188 METALS AND THEIR COMBINATIONS. 



The commonest copper-ore is Copper pyrites, a double sulphide of 

 copper and iron, Cu 2 FeS 2 or Cu 2 S.Fe 2 S 3 , having the color and lustre 

 of brass or gold. Other ores are : Copper glance, cuprous sulphide, 

 having a dark-gray color and the composition Cu 2 S ; malachite, a 

 beautiful green mineral, being a carbonate and hydroxide of copper, 

 CuCO 3 .Cu(OH) 2 . Cuprous and cupric oxide also are found occasion- 

 ally. Copper is obtained from the oxide by reducing it with coke ; 

 sulphides previously are converted into oxide by roasting. 



Copper is the only metal showing a distinct red color ; it is so 

 malleable that, of the metals in common use, only gold and silver 

 surpass it in that respect ; it is one of the best conductors of heat and 

 electricity, it does not change in dry air, but becomes covered with a 

 film of green subcarbonate when exposed to moist air. 



Copper frequently is used in the manufacture of alloys, of which 

 the more important are : 



Copper. Zinc. Tin. Nickel. 



Brass 64 36 



German silver ... 51 31 ... 18 



Bell-metal .... 78 22 



Bronze .... 80 16 4 



Gun-metal .... 90 10 



Copper frequently is alloyed with gold and silver. 



Copper is a bivalent element, forming two oxides and two series of 

 salts, distinguished as cuprous and cupric compounds ; the cuprous 

 salts are here but of little interest. 



Cupric oxide, CuO (Black oxide or monoxide of copper). Heated 

 to redness, copper becomes covered with a black scale, which is cupric 

 oxide ; it is obtained also by heating cupric nitrate or carbonate, both 

 compounds being decomposed with formation of the oxide ; finally, 

 it may be made by adding sodium or potassium hydroxide to the 

 solution of a cupric salt, when a bulky, pale-blue precipitate of cupric 

 hydroxide, Cu(OH) 2 , is formed, which, upon boiling, is decomposed into 

 water and cupric oxide, a heavy dark-brown powder (Plate III., 2) : 



CuSO, + 2KOH == K 2 SO 4 + Cu(OH) 2 ; 

 Cu(OH) 2 = H 2 O + CuO. 



Cuprous oxide, Cu 2 O ( Red oxide or suboxide of copper). When 

 cupric oxide is heated with metallic copper, charcoal, or organic 

 matter, the cupric oxide is decomposed, and cuprous oxide is formed. 

 (Excess of carbon or organic matter reduces the oxide to metallic 



copper.) 



CuO + Cu = Cu 2 O; 

 2CuO + C = Cu 2 -f CO. 



