Cuprous sulphite, Cu₂SO₃

Sulphur dioxide reacts with a solution of cupric acetate in acetic acid to form colourless, hexagonal leaflets of Cuprous sulphite, Cu₂SO₃,½H₂O. In aqueous solution sulphur dioxide converts this substance into a red, prismatic form, Cu₂SO₃,H₂O, also formed by the action of this gas on alkali cuprous sulphites in presence of water. The sulphite is capable of forming complex ammonium derivatives of the type Cu₂SO₃,(NH₄)₂SO₃.