calcium sulphate

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A white solid compound, CaSO4; r.d. 2.96; 1450°C. It occurs naturally as the mineral anhydrite, which has a rhombic structure, transforming to a monoclinic form at 200°C. More commonly, it is found as the dihydrate, gypsum, CaSO4.2H2O (monoclinic; r.d. 2.32). When heated, gypsum loses water at 128°C to give the hemihydrate, 2CaSO4.H2O, better known as plaster of Paris. Calcium sulphate is sparingly soluble in water and is a cause of permanent hardness of water. It is used in the manufacture of certain paints, ceramics, and paper. The naturally occurring forms are used in the manufacture of sulphuric acid.

Subjects: Chemistry.

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