Ammonium Zinc Orthophosphate, NH₄.ZnPO₄

The dihydrate, NH₄.Zn.PO₄.2H₂O, is precipitated from solutions of zinc salts by ammonium phosphate or by ordinary sodium phosphate in the presence of ammonium salts or ammonia. The anhydrous salt precipitates if the temperature is 80° C. or over. In cold solutions the precipitate is flocculent, but it becomes crystalline on heating.

When the precipitate is dried at 100°-105° C. for several hours it has the composition NH₄.Zn.PO₄, and it suffers no loss by prolonged heating at this temperature. It is quantitatively converted into pyrophosphate of zinc by gradual heating in an open crucible.3 It does not decompose at 130° C., but decomposition begins at 150° C., and ammonia is freely evolved at 200° C.

One hundred c.c. of water at 17.5° C. dissolve 0.00145 grm. of NH₄.Zn.PO₄ (Zn = 0.00053 grm.) and 0.00224 grm. at boiling-point (Zn = 0.00082 grm.).

The salt is completely hydrolysed by prolonged boiling with water into the normal phosphates of zinc and ammonium, and it is converted into zinc chloride by boiling with ammonium chloride.