Bismuth Arsenate, BiAsO₄

Bismuth Arsenate probably occurs naturally in the minerals atelestite, rhagite, walpurgite and mixite. It may be obtained as a white crystalline substance by the action of arsenic acid or alkali arsenate upon a nitric acid solution of bismuth nitrate. The hemihydrate, BiAsO₄.½H₂O, which loses water only when heated strongly, forms microscopic monoclinic prisms, density (at 15° C.) 7.142; it is tasteless and melts only with difficulty. A basic arsenate, 2BiAsO₄.3Bi₂O₃, has also been prepared by the action of sodium arsenate upon an ammoniacal solution of bismuth citrate. It forms a gelatinous precipitate, which resembles the corresponding phosphate in its chemical properties.