Ammonium ferri-diorthophosphate, NH₄.H₂[Fe(PO₄)₂]

Ammonium ferri-diorthophosphate, NH₄.H₂[Fe(PO₄)₂], was first obtained by Danziger by addition of a large excess of di-ammonium hydrogen phosphate to a strongly acid solution of ferric chloride. It is then formed as a white precipitate. If obtained in an analogous manner to the preceding salt, it yields pink, microscopic, hexagonal crystals. In the absence of a sufficient quantity of ammonia the acid salt, [Fe(PO₄)₂.H₂]NH₃.7H₂O, is obtained.