Silver sulphite, Ag₂SO₃

The Silver sulphite, Ag₂SO₃, is prepared by precipitating Silver nitrate with the theoretical proportion of sulphurous acid or sodium sulphite, the salt being decomposed by excess of the acid, and dissolved by excess of the sulphite. It is a white substance, its colour changing under the influence of light to purple and then to black. Its solubility in water is less than 1:20000. When boiled with water, it decomposes in accordance with the equation

2Ag₂SO₃ = Ag₂SO₄ + 2Ag + SO₂.

When heated alone, 10 per cent, decomposes as indicated, and the remainder is converted into silver dithionate and metallic silver:

2Ag₂SO₃ = Ag₂S₂O₆ + 2Ag.