Cupric arsenate, Cu₃(AsO₄)₂

The Cupric arsenate, Cu₃(AsO₄)₂, occurs as pentahydrate under the name trichalcite. The tetrahydrate is produced by heating cupric nitrate with calcium arsenate, or copper with a solution of arsenic acid, and also by the interaction of cupric chloride and silver arsenate. Concentration at 70° C. of a solution of cupric carbonate in excess of arsenic acid yields pale-blue leaflets of the formula CuHAsO₄,H₂O. Other acidic salts, and also basic salts, are known.