Sodium metaphosphate, NaPO₃

The Sodium metaphosphate, NaPO₃, is prepared by the interaction of sodium nitrate and phosphoric acid at 330° C. It is a white, vitreous mass, almost insoluble in water, and melting at 617±2° C. It is sometimes called " Maddrell's salt," after its discoverer. The semihydrate, NaPO₃,½₂O, is formed by heating sodium arfimonium hydrogen phosphate at 160° to 170° C., and subsequently raising the temperature to 320° C. Tammann has proved the existence of a number of poiymeric forms, the di-, tri-, tetra-, and hexa-meta-phosphates having been described. The metaphosphate can also exist in metameric forms. In the crystalline state it is unimolecular, and in the glacial condition at least termolecular.