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. |