COPPEB, SILVEB, AND GOLD 407 



Cupric chloride, CuCl 2 , when ignited, gives cuprous chloride, CuCl 

 i.e. the. salt corresponding with sub.oxide of copper and therefore 

 cuprous chloride is always formed when copper enters into reaction 

 with chlorine at a high temperature. Thus, for example, when copper 

 is calcined with mercuric chloride, jt forms cuprous chloride arid vapours 

 of mercury. The same substance is obtained on heating metallic 

 Copper in hydrochloric acid, hydrogen being dis.engaged ; but this reac- 

 tion only proceeds with finely-divided copper, as hydrochloric acid acts 

 very feebly on compact masses of copper, and, in the presence of air, 

 gives cupric chloride. The green solution of cupric chloride is decolo- 

 rised by metallic copper, cuprous chloride being formed ; but this 

 reaction is only accomplished with ease when the solution is very con- 

 centrated and in the presence of an excess of hydrochloric acid to 

 dissolve the cuprous chloride. The' addition of water to the solu- 

 tion precipitates the cuprous chloride, because it is less soluble ia 

 dilute than in strong hydrochloric acid. Many reducing agents which 

 'are able to take up half the oxygen from cupric oxide are able, in the 

 presence of hydrochloric acid, to form cuprous chloride. Stannous 

 salts, sulphurous anhydride, alkali sulphites, phosphorous- and hypo- 

 phosphorous acids, and many similar reducing agents, act in this 

 manner. The usual method of preparing cuprous chloride consists in 

 passing sulphurous anhydride into a very strong solution of cupric 

 chloride : 2CuCl 2 + S0 2 + 2H 2 = 2CuCl + 2HC1 + H^SO^ Cuprous 

 chloride forms colourless cubic crystals which are insoluble in water. 

 It is easily fusible, and even -volatile. Under the action of oxidising 

 agents, it passes into the cupric salt, and it absorbs oxygen from moist 

 air, forming cupric oxychloride, Cu-jC^O. Aqueous ammonia easily 

 (dissolves, cuprous chloride as well as cuprous oxide ; the solution also 

 turns blue on exposure to the air. Thus an ammoniacal solution of 

 cuprous chloride serves as an excellent absorbent for oxygen ; but this 

 solution absorbs not only oxygen, but also certain other gases for 

 example, carbonic oxide and acetylene. 8 



to the formation of cupric oxide, which colours glass blue. This may even be taken 

 fwlvantage of in testing for copper under the blow-pipe by heating the copper compound 

 with borax in the flame of a blow-pipe ; a red glass is obtained in the reducing flame, 

 and a blue glass in the oxidising flame, owing to the conversion of the cuprous into cuprio 

 oxide. 



Etard (1882), by passing sulphurous anhydride into a .solution of cupric acetate, ob 

 tained a white precipitate of cuprous sulphite, Cu 2 SO3,H 2 O, whilst he obtained the same 

 salt, of a red colour, from the double salt of sodium and copper ; but there are not any 

 convincing proofs of isomerism in this case. 



8 The solubility of cuprous chloride in ammonia is due to the formation of compounds 

 between the ammonia and the chloride. In a warm solution the compound NH 3 ^CuCl. 

 is formed, and at the ordinary- temperature CuCl,NH 3 . This salt is soluble in hydro, 

 chloric acid, and then forms a corresponding double salt of cuprous chloride and ammo* 



