The precipitation of the copper from the solution, in which it is present as sulphate, or as cuprous and cupric chlorides, is generally effected by metallic iron.
Copper dioxide, CuO 2 H 2 O, is obtained as a yellowish-brown powder, by treating cupric hydrate with hydrogen peroxide.
Copper sulphide may be converted either into the sulphate, which is soluble in water; the oxide, soluble in sulphuric or hydrochloric acid; cupric chloride, soluble in water; or cuprous chloride, which is soluble in solutions of metallic chlorides.
Oils which contain sulphur-compounds are subjected to a special process of refining in which cupric oxide or litharge is employed as a desulphurizing agent.
It reduces many metallic oxides, such as lead monoxide and cupric oxide, and decomposes water at a red heat.
Normal cupric carbonate, CuCO 3, has not been definitely obtained, basic hydrated forms being formed when an alkaline carbonate is added to a cupric salt.
Cu2S5, Cu 2 S 6, Cu4S5, Cu 2 S 3, have been described; they are all unstable, decomposing into cupric sulphide and sulphur.
Cupric hydroxide, Cu(OH) 2, is obtained as a greenish-blue flocculent precipitate by mixing cold solutions of potash and a cupric salt.
Cuprous oxide is reduced by hydrogen, carbon monoxide, charcoal, or iron, to the metal; it dissolves in hydrochloric acid forming cuprous chloride, and in other mineral acids to form cupric salts, with the separation of copper.
A neutral solution of an arsenite gives a yellow precipitate of silver arsenite, Ag3AsO3, with silver nitrate solution, and a yellowish-green precipitate (Scheele's green) of cupric hydrogen arsenite, CuHAsO3, with copper sulphate solution.