Metathorium Oxide

Metathorium Oxide is a peculiar, isomeric modification of the oxide, obtained by igniting the oxalate, or the hydroxide precipitated from dilute solution at low temperature. When hydrochloric or nitric acid is evaporated with this oxide a syrupy residue is obtained which dissolves in water, forming an opalescent liquid. These solutions contain salts of metathorium oxide, which are reprecipitated by the addition of the corresponding acids, in which they are insoluble. These phenomena were first observed by Berlin, Bahr, and Cleve; and it was thought by Bahr that they were due to the oxide of a new metal, whilst Locke considered that the thoria had been reduced to Th₃O₅. The subject has been further investigated by Wyrouboff and Verneuil and by Stevens. According to Wyrouboff and Verneuil the product of the careful ignition of thorium oxalate, nitrate, chloride, or hydroxide is a mixture of two polymerides of thoria, which on account of polymerisation can combine additively with nitric acid to form salts of the empirical composition (ThO₂)₆.HNO₃ and (ThO₂)₅.2HNO₃. From analogy with corresponding cerium salts these nitrates are believed to have the molecular composition

(ThO₂)₂₄.4HNO₃ and (ThO₂)₁₀.4HNO₃.

Stevens believes that metathorium oxide is not Th₃O₅, but has the same composition as ordinary thoria. When prepared from the oxalate and containing some water it combines with dry hydrogen chloride, forming metathorium oxychloride, which is represented by the formula ThO₂.xThCl₄, and dissolves in water, forming a solution which is clear if 9-10 per cent, of chlorine is present, and is opalescent when more basic. It resembles metastannic chloride in properties, and does not give a precipitate with silver nitrate. Metathorium hydroxide is obtained by precipitating the chloride with ammonia; Stevens regards it as metathoric acid and as analogous to metastannic acid.

It would appear from the work of Ruer on colloidal zirconium hydroxide that the reason silver nitrate does not precipitate chloride from metathorium chloride solution is that the latter is colloidal and has the power also of retaining silver chloride in the colloidal form.