SODIUM TETRAPHOSPHATE

Na6P4O13 ? H2O . Formula weight of the anhydrous salt is 469.85. The crystalline salt cannot be obtained. On standing for four weeks, the dried oil is partially transformed to Na3HP2O7 . H2O. Heating of this mixture to 200°C for two hours produces a quantitative yield of Na3HP2O7.

Hexasodium tetraphosphate is formed by careful hydrolysis of sodium tetrametaphosphate(method of Thilo and Ratz):

A solution of 4.8 g. of Na 4 P4 O 12 ? 4H2O in 85 ml. of hot water is prepared, and after cooling, a solution of 0.8 g. of NaOH in some water is added. The mixture is kept over H2SO4 in a vacuum desiccator, placed in an oven at 40°C. The rat e of evaporation should be such that after about 100 hours no less than 8 to 10 ml. remains. The solution is then diluted to 30 ml. and acetone is added. The colorless oil formed is dissolved in some water and reprecipitated with acetone.