Thorium Sulphite, Th(SO₃)₂.H₂O

Thorium Sulphite, Th(SO₃)₂.H₂O, was obtained by Cleve as a white precipitate by dissolving the sulphate in sulphurous acid and warming the solution. The solubility of this salt in sodium sulphite solution, with the formation of a complex salt, furnishes a means of roughly separating thorium from cerium, lanthanum, and didymium; for when a neutral solution of the mixed salts is poured into excess of a saturated solution of sodium sulphite nearly the whole of the thorium remains in solution, while the other metals are precipitated. The complex sulphites, Th₂(OH)₂(SO₃)₃.2Na₂SO₃.22H₂O and Th(OH)₂SO₃.2K₂SO₃.10H₂O have been isolated.