Acid Calcium Hypophosphate, CaH₂P₂O₆

Acid Calcium Hypophosphate, CaH₂P₂O₆, may be prepared by mixing freshly precipitated lime and hypophosphoric acid in exactly equivalent proportions and evaporating in the cold. Heating the solution gives the neutral salt. A solution of the acid salt may also be obtained by dissolving the neutral salt in hypophosphoric acid, or by digesting with water a mixture of acid barium hypophosphate and calcium sulphate in molecular proportions.

It forms monoclinic crystals of composition CaH₂P₂O₆.6H₂O, which easily lose 4 molecules of water at the ordinary temperature. The remaining two are removed at 150° C. with partial decomposition. One part of the salt dissolves in 60 of water.