Barium Metaphosphate, BaPO₃

Barium Metaphosphate, BaPO₃, may be obtained by dissolving barium carbonate in excess of phosphoric acid, evaporating, and heating. It forms a white powder, which is unchanged by dilute acids and by water, but is decomposed by concentrated sulphuric acid.

Polymerised compounds have also been obtained, for example barium hexametaphosphate, Ba₃P₆O₁₈, similar to the calcium and strontium hexametaphosphates, and possibly others.

Several double phosphates of the alkalies with barium are known: barium potassium orthophosphate, Ba₂K₂(PO₄)₂, or with 20H₂O, and barium sodium orthophosphate, Ba₂Na₂(PO₄)₂. 18H₂O or 20H₂O; barium sodium pyrophosphate, 6Ba₂P₂O₇.Na₄P₂O₇.6H₂O; and also the metaphosphates, NaBaP₃O₉. 4H₂O, NH₄BaP₂O₉.H₂O, and KBaP₃O₉.H₂O, and Na₄Ba(PO₃)₆.8H₂O. Uranium barium metaphosphate, Ba(UO₂)(PO₃)₂, in thin green hexagonal plates, has been isolated. There is also a mineral, uranocircite, BaO.2U₂O₃. P₂O₅.8H₂O.