Characters. - Deep green, prismatic crystals, yielding a bright green powder, efflorescent on exposure to air, odourless, having a nauseating metallic taste and an acid reaction.

Tests. - If the aqueous solution of the salt be treated with hydrosulphuric acid until all the copper is precipitated, the filtrate should leave no residue on evaporation (alkalis, alkaline earths, or iron). If the aqueous solution be heated to boiling with solution of soda in excess, it will yield a filtrate which should not be clouded by hydrosulphuric acid (absence of lead and zinc).

Uses. - Like sulphate of copper. Not used internally.