Sodium dithionate, Na₂S₂O₆

The dithionate is obtained by the action of sodium carbonate on barium dithionate. It is the principal product formed by boiling sodium silver sulphite with water:

2AgSO₃Na =Na₂S₂O₆+2Ag.

It is known in the forms of dihydrate and hexahydrate.

For the density of the dihydrate Topsoe gives 2.189. Thomsen found for the heat of formation of the anhydrous compound 398.8 Cal.; for its heat of solution – 5.37 Cal., and for that of the dihydrate -11.65 Cal., the heat of hydration being 6.28 Cal. The vapour-pressure and electric conductivity of solutions have also been studied.