Barium Pyroarsenite, Ba₂AsO₅.2H₂O

Barium Pyroarsenite, Ba₂AsO₅.2H₂O, is prepared by precipitation from solutions of arsenious acid and barium hydroxide. The precipitate is dried at 100° C. If air-dried, the compound contains 8 molecules of water, according to Stavenhagen, and 4 according to Stein. When the salt is strongly heated, arsenic sublimes and barium arsenate is left. Precipitation of barium chloride solution with potassium pyroarsenite also gives the pyroarsenite.m.atomistry.com/">Ba(AsO₂)₂, may be obtained by warming barium chloride with a solution of ammonium arsenite to which acetic acid has been added until arsenious acid is on the point of precipitation. The precipitate is then dried at 100° C. It is a white powder easily soluble in water, but it can also be obtained as a gelatinous precipitate when a mixture of barium chloride and acid potassium arsenite in solution is left to stand a few hours.