Chromous Sulphate, CrSO₄

Chromous Sulphate, CrSO₄.7H₂O, is produced by dissolving chromous acetate in dilute sulphuric acid, or by interaction of chromium and sulphuric acid. It forms blue crystals, isomorphous with those of FeSO₄.7H₂O, and is soluble in water, though not in alcohol. It is readily oxidised by the oxygen of the air. Moissan describes a hydrate, CrSO₄.H₂O, as a white powder, which with water regenerates the heptahydrate.

Several double sulphates of divalent chromium exist: sodium chromous sulphate, Na₂SO₄.CrSO₄.4H₂O, is prepared by the action of chromous acetate upon a mixture of sodium sulphate and sulphuric acid. The potassium salt, K₂SO₄.CrSO₄.6H₂O, is obtained by alcoholic precipitation of a mixture of chromous chloride and potassium sulphate in solution in absence of air. An ammonium salt, (NH₄)₂SO₄.CrSO₄.6H₂O, has also been prepared.