Com. crude 80% H3PO4 contg. ca. 2% SO4 was desultated with CaHPO4.2H(2)O (Ca/SO4 = 1) to 0.04%. A com. soln. of Na phosphates, Na/P = 1.67, was evapd. and calcined at 350, 400, 450. 500, or 550 degrees C to prep. Na tripolyphosphate. Phases I and It were identified by x-rays. With the crude acid, impurities (esp. SO4) caused the high-temp. phase (Na5P3O10-1) to form at > 500 degrees C. With the desulfated acid, phase I appeared at 350 degrees C with no Na5P3O10-11 as an intermediate. The no-waste method caused the resulting Na5P3O10 to contain impurities in proportions identical with those in the starting acid, SO4 0.04, Fe 0.3-0.5%.