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Cupric sulphide, CuS

By adopting special experimental precautions, it is possible to prepare Cupric sulphide, CuS, free from cuprous sulphide and sulphur by precipitating a solution of cupric sulphate or chloride with hydrogen sulphide, although if no precautions are taken the precipitate is likely to be contaminated with these substances. At 180° C. concentrated sulphuric acid converts copper into a mixture of cupric sulphide and sulphur, from which the sulphur can be removed by heating at 160° C. in a rapid current of hydrogen.

A crystalline variety of cupric sulphide is produced by heating cupric sulphate with ammonium thiocyanate above 180° C. The amorphous form can also be rendered crystalline by heating in a sealed tube with ammonium hydrogen sulphide at 150° to 200° C., the product consisting of lustrous, violet, hexagonal leaflets.

Cupric sulphide occurs in nature as covellite or indigo-copper, indigo-blue, hexagonal plates, density 4.59 to 4.64, and hardness 1.5 to 2. The dark-green, amorphous variety has the density 4.16, and is a good conductor of electricity. It is decomposed in vacuum at 400° C. into cuprous sulphide and sulphur. Its oxidation by air in ammoniacal, neutral, and acidic suspensions is similar to that of cuprous sulphide, but more energetic. Its heat of formation from its elements is 11.6 Cal. It dissolves readily in hot, dilute nitric acid, and in solutions of sodium polysulphides.
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