134 ZINC. 



state, but chiefly as a sulphuret, constituting copper 

 pyrites; it is obtained from this ore by roasting, when 

 the sulphur is gradually driven off and an impure 

 oxide of copper left, which is subsequently strongly 

 heated with charcoal, to reduce it to the metallic 

 state. Copper has a considerable affinity for oxygen, 

 which it absorbs from the air at common tempera- 

 tures. Oxide of copper is a black substance, readily 

 obtained by heating copper in the air, or by decom- 

 posing any of its salts, such as the sulphate, by an 

 alkali. 



303. The salts of copper are mostly of a blue or 

 bluish-green color ; they are all decomposed by alka- 

 line solutions, a blue hydrated oxide of copper being 

 precipitated; if ammonia be employed, no precipitate 

 is obtained, or, if formed, easily dissolves, because the 

 oxide of copper is soluble in solution of caustic am- 

 monia, forming a very beautiful deep-blue liquid : this 

 property is useful in testing for the presence of 

 copper. 



304. Sulphate of copper, blue or Roman vitriol, 

 may be formed directly. It is manufactured on a 

 large scale, like the sulphate of iron (285); by ex- 

 posing the roasted sulphuret to the air, it absorbs 

 oxygen, and is converted into the sulphate. It is a 

 bright-blue salt, easily soluble in water, and used for 

 several purposes in the arts. It is frequently em- 

 ployed as a steep for seed-corn. 



305. Zinc is never found in the metallic state ; its 

 ores are calamine, which is a carbonate, and blende. 



