Barium Hydrophosphite, 2BaHPO₃.H₂O or H₄Ba₂P₂O₇

Barium Hydrophosphite, 2BaHPO₃.H₂O or H₄Ba₂P₂O₇, is formed by precipitation of barium chloride with ammonium phosphite. It loses water between 150° C. and 200° C. At higher temperatures it is decomposed, giving hydrogen, phosphorus, and barium pyrophosphate. A dihydrophosphite, BaH₂(HPO₃)₂.H₂O, 2H₂O, or 3H₂O, which loses 1 molecule of water of crystallisation on being dried, is known. Other crystalline acid salts of varying composition are also obtained by evaporating solutions of the ordinary phosphite with phosphorous acid. Barium Pyrophosphite, BaH₂P₂O₅, is obtained by the dehydration of the acid phosphite at 120°-160° C.