Barium Pyrophosphate, Ba₂P₂O₇

Barium Pyrophosphate, Ba₂P₂O₇, may be obtained in orthorhombic prisms of density 3.9 by fusing barium oxide, phosphate, or sulphate, with potassium pyro- or meta-phosphate, or as a white precipitate by mixing sodium pyrophosphate and barium chloride solutions, or neutralising pyrophosphoric acid with barium hydroxide solution. It crystallises from solution with 2 molecules of water. It is only slightly soluble in water, but is attacked by mineral acids. If heated in hydrogen, phosphoretted hydrogen and other phosphorus compounds are evolved, and barium phosphate is left.

Several acid pyrophosphates have been separated, all infusible at red heat.