LEAD COPPER BISMUTH. 323 



C When a charcoal reduction test (for which see directions in test 

 3 for sulphates) is made on any dry lead compound, a globule of 

 metallic lead is obtained, which is recognized by its softness and 

 malleability. Try its solubility in dilute hydrochloric, sulphuric, and 

 nitric acids. 



Tests 1, 2, and 4 are sufficient for recognition of a lead compound. 

 Lead salts are mostly colorless. Lead nitrate has an acid reaction, 

 due to hydrolysis in water. 



Copper, Cu u = 63.1 (Cuprum). Found in nature sometimes in the 

 metallic state generally, however, combined with sulphur or oxygen. 

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

 copper and iron, CuFeS 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. Antimony. 



Brass .... 64 36 



German silver ... 51 31 ... 18 



Bell-metal ... 78 ... 22 



Bronze .... 80 16 4 



Gun-metal ... 90 ... 10 



Babbit-metal ... 43 ... 43 ... 14 



Copper frequently is alloyed with gold and silver. 



Copper forms two oxides, and corresponding to these are two series 

 of salts, known as cuprous and cupr/c compounds. Cuprous salts of 

 oxygen acids do not exist. The principal cuprous compounds are 

 Cu 2 O, CuCl, CuBr, Cul, Cu(CN), Cu 2 S. All these, except Cu 2 Oand 

 Cu 2 S, are white and insoluble in water. Cupric iodide, (CuI 2 ), and 

 cyanide, (Cu(CN) 2 ), cannot be obtained, as they decompose into the 

 cuprous salt and free iodine or cyanogen, CuI 2 = Cul + I. These are 

 obtained when potassium iodide or cyanide solution is added to solu- 

 tion of cupric sulphate : 



CuS0 4 -f 2KI = Cul + I + K 2 SO 4 , 



