Cobaltous Sulphite, CoSO₃

Cobaltous Sulphite, CoSO₃, is obtained in the hydrated condition as rose-coloured crystals by dissolving cobaltous hydroxide in sulphurous acid and concentrating at a low temperature. Muspratt found the crystals to contain five molecules of water, and Rammelsberg three. Rohrig some years later proved that both hydrates exist. The salt is but sparingly soluble in water, yielding a readily oxidisable solution. With alkali sulphites double salts are obtained. Thus Potassium Cobalt Sulphite, K₂SO₃.CoSO₃, is obtained as a pale red precipitate on warming mixed solutions of a soluble cobalt salt and potassium sulphite. Ammonium Cobalt Sulphite, (NH₄)₂SO₃.CoSO₃, is prepared in a similar manner. A sodium salt and basic sulphites have been described.