Strontium Orthophosphates

Tristrontium Phosphate, Sr₃P₂O₈, is obtained by the precipitation of strontium chloride with sodium phosphate in ammoniacal solution. It first separates in the colloidal state with absorption of heat, but it then slowly crystallises with the evolution of heat. When dried at 100° C. it forms a hard vitreous substance. It is insoluble in water and is decomposed by boiling water, but it is soluble in phosphoric acid forming monostrontium orthophosphate.

Halogen compounds of tristrontium phosphate, of the type 3Sr₃P₂O₈.SrF₂, corresponding to the calcium apatites, are known.

Distrontium Phosphate, SrHPO₄, is formed as a gelatinous precipitate by adding a slightly acid solution of strontium chloride to disodium hydrogen phosphate below 50° C. It gradually crystallises with 2 molecules of water. It is insoluble in water but soluble in acids and in some salt solutions. There is also an anhydrous salt, strontium monetite, of density 3.544.

Monostrontium Phosphate, SrH₄(PO₄)₂.2H₂O, is obtained by the action of dilute phosphoric acid on strontium hydroxide, or on distrontium phosphate, under suitable temperature conditions.

With regard to the study of the solubility of the three strontium orthophosphates, owing to their decomposition by water, the same difficulties arise as in the case of the calcium compounds.