Arsenic Phosphate, AsPO₄

Arsenic Phosphate, AsPO₄, has been prepared by heating pyrophosphoric acid at 230° to 245° C., adding arsenious oxide in small portions, and further heating the mixture at 280° C. until it solidified as a hard mass of white microscopic needles. It is hygroscopic and, when exposed to moist air, arsenious oxide separates. Using an excess of pyrophosphoric acid, a compound of composition 4AsPO₄.3H₄P₂O₇ was similarly prepared. It formed a hygroscopic mass of white microscopic needles which melted above 400° C.