| By cooling, or by precipitation with hot water of saturated solutions of calcium sulphate in hot concentrated sulphuric acid, several different acid sulphates may be obtained, CaSO4.H2SO4, CaSO4.3H2SO4, and 2CaSO4.H2SO4. Kendall and Davidson, on studying the solubility curve of calcium sulphate in anhydrous sulphuric acid, found two modifications of the compound CaSO4.3H2SO4. Only one of them was stable over the range of temperature of the experiment, namely 0°-63° C. These compounds are all decomposed by water or by moist air. The compound CaSO4.H2SO4 has been obtained in the gelatinous state. D'Ans separated an acid double sulphate of calcium and sodium, but it was probably an isomorphous mixture. |