COPPER. 167 



Tin. Nickel. 



18 

 22 

 16 

 10 



Copper is also frequently 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 of but little interest. 



Cupric oxide, CuO ( Oxide or monoxide of copper}. Heated to red- 

 ness, copper becomes covered with a black scale, which is cupric 

 oxide; it is also obtained 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 hydrate 

 to the solution of a cupric salt, when a bulky, pale blue pre- 

 cipitate of cupric hydrate, Cu2HO, is formed, which, upon boiling, 

 is decomposed into water and cupric oxide, a heavy dark brown 

 powder : 



CuSO 4 + 2KHO = K 2 SO 4 + Cu2HO; 

 Cu2HO = H 2 4 CuO. 



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

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

 matter containing this element, the cupric oxide is decomposed, 

 and cuprous oxide is formed. (Excess of carbon or organic 

 matter reduces the oxide to metallic copper.) 



CuO 4 Cu = Cu 2 O; 

 2CuO + C = Cu 2 O 4 CO. 



Some organic substances, especially grape-sugar, decompose 

 strong alkaline solutions of cupric sulphate with precipitation 

 of cuprous oxide, which is a red, insoluble powder. 



Cupric sulphate, Cupri sulphas, CuS0 4 .5H 2 = 249.2 (Sulphate of 

 copper, Slue vitriol, Blue-stone}. This is the most important com- 

 pound of copper. It is manufactured on a large scale, either 

 from copper pyrites, or by dissolving copper in sulphuric acid, 

 evaporating and crystallizing the solution: 



Cu + 2H 2 SO 4 = CuSO< -f 2H 2 O + S0 2 . 



