Cerium compounds may be recognized by the red precipitate of ceric hydroxide, which is formed when sodium hypochlorite is added to a colourless cerous salt.
By the addition of caustic soda to cerous salts, a white precipitate of cerous hydroxide is formed.
By suspending the precipitated cerous hydroxide in water and passing chlorine through the solution, a hydrated form of the dioxide, 2CeO 2.3H 2 O, is obtained, which is readily soluble in nitric and sulphuric acids, forming ceric salts, and in hydrochloric acid, where it forms cerous chloride, with liberation of chlorine.
A hydrated chloride of composition 2CeC1 3.15H 2 O is also known, and is obtained when a solution of cerous oxide in hydrochloric acid is evaporated over sulphuric acid.
Double salts of cerous chloride with stannic chloride, mercuric chloride, and platinic chloride are also known.
A higher hydrated oxide, CeO 3 xH 2 O, is formed by the interaction of cerous sulphate with sodium acetate and hydrogen peroxide (Lecoq de Boisbaudran, Comptes rendus, 1885, loo, p. 605).
Cerous chloride, CeC1 3, is obtained when the metal is burned in chlorine; when a mixture of cerous oxide and carbon is heated in chlorine; or by rapid heating of the dioxide in a stream of carbon monoxide and chlorine.