_Cerous nitride_, CeN, has been prepared by Moissan[203] by the action of ammonia on the heated carbide; it can also be obtained by heating the hydride in a stream of nitrogen.[204] Muthmann and Kraft also state[205] that it can be prepared by heating metallic cerium in the gas, the metal burning with the liberation of much energy in the form of heat and light; but Dafert and Miklanz[206] deny that it can be obtained in this way. Cerium nitride is a lustrous, brass yellow to bronze coloured solid, stable in dry air, but at once attacked by moist air, with evolution of ammonia, and formation of the dioxide. When moistened in air with a few drops of water, the substance reacts violently, becoming heated to redness. Alkalies and acids decompose it, with formation of cerous compounds. [203] _Compt. rend._ 1900, ~131~, 865. [204] Dafert and Miklanz, _Monats._ 1912, ~33~, 911. [205] _Annalen_, 1902, ~325~, 261. [206] _Loc. cit._ The _sulphide_, Ce₂S₃, has been prepared by Biltz[207] by heating the sulphate to a red heat in a current of sulphuretted hydrogen; he describes it as a red powder. The _chloride_, CeCl₃, combines with ammonia with evolution of heat even at a temperature of -80°. Five additive compounds are described;[208] they are white powders, decomposed by water. [207] _Ber._ 1908, ~41~, 3341. [208] Barre, _Compt. rend._ 1913, ~156~, 1017. The solubility curve of the various _sulphate hydrates_ has already been given (see p. 125). Various _double sulphates_ with ammonium sulphate, and the sulphates of sodium, potassium, thallium and cadmium are known. The cadmium double compound has the composition Ce₂(SO₄)₃,CdSO₄,6H₂O, and is prepared by mixing solutions of the simple salts in presence of sulphuric acid. Many _double nitrates_ have been prepared; these are for the most part stable, highly crystalline compounds, easily soluble in water and alcohol. With the nitrates of the common divalent metals, cerous nitrate forms a series of double salts of the general formula 2Ce(NO₃)₃,3R(NO₃)₂,24H₂O, where R = Mg, Mn, Co, Ni, or Zn; these form an isomorphous series, crystallising in the hexagonal system. The _acetylacetone compound_ melts at 131°-132°. In the presence of hydrogen peroxide in the cold, ammonia throws down from solutions of cerous salts a reddish-brown peroxyhydrate, Ce(OOH)(OH)₃,[209] which on heating loses oxygen, and yields ceric hydroxide. The reaction is very delicate, and may be used as a test for cerium. If the precipitate be treated with acids in the cold, ceric salts are first obtained, but these are at once reduced, in the acid solution, by the hydrogen peroxide formed, so that cerous salts remain; ceric salts may be obtained by first boiling the suspension of the peroxyhydrate and treating the ceric hydroxide so obtained with acids. [209] Pissarjewski, _Zeitsch. anorg. Chem._ 1902, ~31~, 359. THE CERIC COMPOUNDS