Potassium sulphite, K₂SO₃

The Potassium sulphite, K₂SO₃ can be prepared by passing sulphur dioxide into a solution of potassium carbonate till evolution of carbon dioxide ceases; or by dissolving a known weight of potassium hydroxide in water, saturating with sulphur dioxide, and adding an equal weight of the hydroxide. Evaporation of the solution yields the rhombic dihydrate, which is transformed into the anhydrous salt at 120° C., a white solid with heat of formation 272.6 Cal. A monohydrate is also known.