Arsenites of Rare Earth Metals

When cerium dioxide is heated with arsenious oxide some oxidation of the latter occurs, but the product appears to be a mixture of oxides. Didymium hydrogen orthoarsenite, Di₂(HNaO₃)₃, has been obtained as a white, granular, insoluble powder by boiling didymium hydroxide with an aqueous solution of arsenious oxide. Lanthanum hydrogen orthoarsenite, La₂(HNaO₃)₃, has been prepared in a similar manner. The existence of these compounds needs confirmation, however.