Note 11 — Chapter XII · SODIUM
George Kamensky translation
In solution (Berthelot) the acid salt in all probability decomposes most in the greatest mass of water. The specific gravity (according to the determinations of Marignac) of solutions at 15°/4° = 9,992 + 77·92p + 0·231p2 (see Note 7). From these figures, and from the specific gravities of sulphuric acid, it is evident that on mixing solutions of this acid and sodium sulphate expansion will always take place; for instance, H2SO4 + 25H2O with Na2SO4 + 25H2O increases from 483 volumes to 486. In addition to which, in weak solutions heat is absorbed, as shown in Chapter X., Note 27. Nevertheless, even more acid salts may be formed and obtained in a crystalline form. For instance, on cooling a solution of 1 part of sodium sulphate in 7 parts of sulphuric acid, crystals of the composition NaHSO4,H2SO4 are separated (Schultz, 1868). This compound fuses at about 100°; the ordinary acid salt, NaHSO4, at 149°.