Ammonium Phosphates

Ammonium phosphates. The normal phosphate, (NH₄)₃PO₄,is obtained as a crystalline powder, on mixing concentrated solutions of ammonia and phosphoric acid, or on the addition of excess of ammonia to the acid phosphate (NH₄)₂HPO₄. It is soluble in water, and the aqueous solution on boiling loses ammonia and the acid phosphate NH₄H₂PO₄ is formed. Diammonium hydrogen phosphate, (NH₄)₂HPO₄, is formed by evaporating a solution of phosphoric acid with excess of ammonia. It crystallizes in large transparent prisms, which melt on heating and decompose, leaving a residue of metaphosphoric acid, (HPO₃). Ammonium dihydrogen phosphate, NH₄H₂PO₄, is formed when a solution of phosphoric acid is added to ammonia until the solution is distinctly acid. It crystallizes in quadratic prisms.