The monohydrate also results as a white precipitate when concentrated sulphuric acid is added to a saturated solution of ferrous sulphate.
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.
Since the development of the contact processes the fuming acid has become so cheap that it is now exclusively used for the preparation of the acids approaching the composition of "monohydrate."
Real "monohydrate" or acid approaching loo% can be made by Lunge's process of cooling strong O.V.