Barium Pyroarsenate, Ba₂As₂O₇

Barium Pyroarsenate, Ba₂As₂O₇, is obtained by fusing barium oxide with potassium or sodium metarsenate and extracting with anhydrous glycerol. In contact with cold water the hexahydrate, Ba₂As₂O₇.6H₂O, is formed.The same crystals are obtained by precipitation from barium chloride and sodium arsenate solutions. With boiling water, barium orthoarsenate is left as a solid, and the solution, on evaporation and calcination, gives barium metarsenate, Ba(AsO₃)₂.