May be prepd by heating H3PO4 with sufficient phosphoric anhydride to give the resulting product an 82-85% P2O5 content: Bell, Ind. Eng. Chem. 40, 1464 (1949); Van Wazer, Holst, J. Am. Chem. Soc. 72, 639 (1950); Kennard, Org. Chem. Bull. 29, no. 1 (1957). Consists of about 55% tripolyphosphoric acid, the remainder being H3PO4 and other polyphosphoric acids. Typical analysis: 83.0% P2O5; ortho equivalent 115.0%.