Sodium selenite, Na₂SeO₃

The Sodium selenite is formed by heating a mixture of selenious acid and sodium chloride. At ordinary temperature the aqueous solution deposits the pentahydrate, above 60° C. the anhydrous salt. For the heat of formation from its elements in aqueous solution Thomsen gives 238.4 Cal.

Berzelius mentions a salt which was either sodium hydrogen selenite, NaHSeO₃, or pyroselenite, Na₂Se₂O₅.