Sodium hydrogen sulphate, NaHSO₄

The primary sulphate is formed by the interaction of equimolecular proportions of sodium chloride and sulphuric acid, or by crystallizing the normal salt from solution in sulphuric acid. At ordinary temperature monoclinic crystals of the monohydrate are deposited, at 50° C. triclinic crystals of the anhydrous substance.

Sodium hydrogen sulphate is a white salt, of density 2.435 at 13° C. Its heat of formation from the elements is given by Thomsen as 267.4 Cal., and by Berthelot as 269.1 Cal.; from sulphuric acid and sodium hydroxide it is 14.75 Cal. The heat of solution is given by Thomsen as 1.19 Cal., but by Berthelot as -0.8 Cal.

Other investigations concern the molecular volume; and such properties of the solution as viscosity, density, and electric conductivity.

Various sulphates of sodium and hydrogen have been prepared. With absolute sulphuric acid sodium sulphate reacts, forming a complex crystalline derivative10 melting at 40° C., and having the formula Na₂SO₄,8H₂SO₄. d'Ans has prepared another example with the composition Na₂SO₄,NaHSO₄. Kendall and Landon have described 2Na₂SO₄,9H₂SO₄, an unstable substance at its melting-point, 60° C. (by extrapolation); Na₂SO₄,2H₂SO₄, unstable at its melting-point; and Na₂SO₄,H₂SO₄, melting at 186° C. Other compounds of similar type have been prepared.