Oxysulphides of Calcium

A mixture of calcium hydroxide and sulphide, regarded by Folkard as a molecular compound, 4Ca(OH)₂.3H₂S, is obtained by passing a dry mixture of hydrogen and sulphuretted hydrogen over calcium hydroxide. At 100° C. the composition may be expressed by the formula 2Ca(OH)₂.2Ca(OH)(SH), and at red heat in an inert gas, 2CaO.2CaS.H₂O. By further heating, calcium sulphate may be obtained. Orange-yellow prismatic crystals, to which several different formulae have been ascribed, CaO.CaS₂.7H₂O, 3CaO.CaS₄.12H₂O, 2CaO.CaS₃.10 or 11H₂O, CaS₃.3CaO.14 or 15H₂O, CaS₄.4CaO.18H₂O, and CaS₅.5CaO.20H₂O, can be obtained by boiling together calcium hydroxide, sulphur, and water, by treating a fused mixture of lime and sulphur with hydrochloric or acetic acid, or by evaporating a solution of the hydrosulphide. The crystals are monoclinic, gradually become colourless on exposure to air, and are decomposed by water but not by alcohol.