Any compound of either divalent or trivalent cobalt and the sulfate group; anhydrous cobaltous sulfate, CoSO₄, contains divalent cobalt, has a melting point of 96.8_C, is soluble in methanol, and is utilized to prepare pigments and cobalt salts; cobaltic sulfate, Co₂(SO₄)₃_18H₂O, contains trivalent cobalt, is soluble in sulfuric acid, and functions as an oxidizing agent.