Rare Earth Metals Arsenates

Only a few of these compounds have been prepared, and those described below have not been fully investigated, so that their composition, and even their existence, need confirmation.

Cerous Monohydrogen Orthoarsenate, Ce₂(HAsO₄)₃, is obtained as a white powder, insoluble in water, by digesting cerous oxide with aqueous arsenic acid. It dissolves in excess of the latter and, if the solution is evaporated, a gelatinous mass, probably cerous dihydrogen orthoarsenate, Ce(H₂AsO₄)₃, is obtained.

4H₂O.Ceric Dihydrogen Orthoarsenate, Ce(H₂AsO₄)₄.4H₂O, may be prepared by heating cerous nitrate (1 g.-mol.) and arsenic acid (4 g.-mols.) with concentrated nitric acid for several hours, distilling off most of the nitric acid, and allowing the liquid to crystallise. The salt separates as white needles. When it is dissolved in the minimum quantity of concentrated nitric acid and the cold solution diluted with water, a white crystalline precipitate of eerie monohydrogen orthoarsenate, Ce(HAsO₄)₂.6H₂O, is formed.

Transparent and opalescent jellies of ceric arsenate have been described.

A gelatinous precipitate of lanthanum monohydrogen orthoarsenate, La₂(HAsO₄)₃.xH₂O, is formed when sodium monohydrogen orthoarsenate is added to a solution of lanthanum sulphate. A similar product has been obtained with didymium sulphate.

Yttrium Orthoarsenate, YAsO₄.nH₂O, is formed as a white gelatinous precipitate when sodium monohydrogen orthoarsenate is added to a solution of an yttrium salt, or when yttrium hydrogen arsenate is treated with ammonia. When dried, the precipitate forms a yellow horny mass which dissolves in nitric acid. Yttrium monohydrogen orthoarsenate,, Y₂(HAsO₄)₃.xH₂O, is obtained in solution by dissolving yttria in aqueous arsenic acid. When the solution is heated, arsenic acid is precipitated. Yttrium dihydrogen orthoarsenate, Y(H₂AsO₄)₃.xH₂O, is obtained as a white precipitate by adding an excess of sodium monohydrogen orthoarsenate to a solution of an yttrium salt. The product dissolves in nitric acid.