Trisodium monoimidocyclotriphosphate dihydrate, Na3P3O8NH.2H(2)O, was made by hydrolysing triimidocyclotriphosphate in an aqueous acetic acid solution at 70 degrees C. The monoimidocyclotriphosphate was converted to cyclotriphosphate by heating in air according to the reaction Na3P3O8NH + H2O --> (NaPO3)(3) + NH3