Sodium hydrogen sulphite, NaHSO₃

The primary sulphite can be isolated by precipitating with alcohol a solution of sodium carbonate saturated with sulphur dioxide:

Na₂CO₃+2SO₂+H₂O = 2NaHSO₃+CO₂.

Besides the anhydrous salt, there is a trihydrate, and also a tetrahydrate. Barth has investigated the electric conductivity.