On exposure, it loses water and gives the monohydrate, Na2C03 H20, a white powder sold as "crystal carbonate"; this substance, which is also formed on heating the decahydrate to 34°, crystallizes in the rhombic system.
Van Deventer, ibid., 1906, 3, p. 515.) It crystallizes with five molecules of water as large blue triclinic prisms. When heated to Poo°, it loses four molecules of water and forms the bluish-white monohydrate, which, on further heating to 250°-260°, is converted into the white CuSO 4.
Real "monohydrate" or acid approaching loo% can be made by Lunge's process of cooling strong O.V.
The monohydrate also results as a white precipitate when concentrated sulphuric acid is added to a saturated solution of ferrous sulphate.