Cuprous ferric sulphide

Cuprous ferric sulphide, Cu2S.FeaS3, occurs in nature as copper pyrites, cholcopyrite, or towcmite, and is one of the commonest ores of copper (see p. 23). It is tetragonal, possessed of a brass-yellow colour, and exhibits a conchoidal fracture. It is decomposed by nitric acid, and tarnishes upon exposure to air, frequently yielding beautiful iridescent surfaces, a blue colour predominating. Masses of such tarnished ore are found in Cornwall, and arc known as peacock ore. The blue colour is probably due to the formation of a surface layer of cupric sulphide or covellite, CuS. 

Copper pyrites may be obtained in the laboratory in the wet way by shaking a weakly ammoniacal solution of cuprous chloride with potassium ferric sulphide until the solution no longer contains copper —6... 

By the action of chlorine and chlorine compounds on the sulphides of arsenic. By passing chlorine over the dry sulphides, realgar or orpiment, at 130° to 140° ., theoretical yields of arsenic trichloride and of sulphur dichloride are obtained.5 The trisulphide reacts with hydrogen chloride in the cold, but chlorination by means of hydrochloric acid is difficult, only a small quantity of the chloride being volatilised.7 The reaction is facilitated by the presence of ferric chloride,8 cuprous chloride or potassium antimonyl tartrate.9 Other chlorinating agents, effective with the sulphides, are sulphur mono-chloride,10 a mixture of ammonium chloride and nitrate,11 and mercuric chloride.12... 

When arsenic trisulphide is exposed to dry hydrogen chloride or hydrogen bromide, it liquefies at the ordinary temperature and on heating complete volatilisation occurs.9 It is not readily attacked by halogen acids. When boiled with concentrated hydrochloric acid it is decomposed, but with great difficulty, and the hydrogen sulphide and arsenious chloride evolved reproduce arsenious sulphide in the receiver.10 A similar reaction occurs when heated with a chloride in the presence of concentrated sulphuric acid, but the decomposition is incomplete.11 The reaction is facilitated by the presence of cuprous chloride or ferric chloride. Only a slight reaction is observed with dilute acid,12 and the... 

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