Zinc Sulphite, ZnSO₃

Zinc Sulphite, ZnSO₃, is obtained in small, slightly soluble crystals by dissolving zinc, zinc carbonate, zinc oxide, or zinc sulphide in aqueous sulphurous acid. Excess of acid converts the sparingly soluble normal sulphite into the readily soluble acid sulphite (from which solution the normal sulphite is precipitated on warming), and if zinc sulphide is slowly added to the excess of acid, zinc thiosulphate is the principal product. Zinc sulphite also separates slowly in the cold from mixed 25 per cent, solutions of sodium sulphite and zinc sulphate (acidified with acetic acid).

The crystals are either ZnSO₃.2H₂O or ZnSO₃.2iH₂O, and either monoclinic or orthorhombic.

The basic salt, 5ZnSO₃.8Zn(OH)₂, is said to be produced by boiling the normal or acid sulphite with water, and 8ZnSO₃.7Zn(OH)₂.7H₂O by mixing boiling normal solutions of zinc sulphate and sodium sulphite. The double salts, Na₂SO₃.3ZnSO₃.7iH₂O, K₂SO₃.3ZnSO₃.7½H₂O, and (NH₄)₂SO₃.ZnSO₃, have been reported.