is helpful to describe the chemistry of phosphoric acids and strong phosphoric acids or polyphosphoric acids as follows as used herein the term u201c phosphoric acid s u201d means commercial phosphoric acid s containing 85 u2013 86 h 3 po 4 the strong phosphoric acids or polyphosphoric acids referred to as ppa polyphosphoric acid are members of a continuous series of amorphous condensed phosphoric acid mixtures given by the formula where the value of n depends on the molar ratio of water to phosphorus pentoxide present in its most general definition polyphosphoric acid composition can range from distributions where the average value of n is less than unity giving rise to a mobile liquid to high values of n where the polyphosphoric acid is a glass at normal temperatures because the species of polyphosphoric acid are in a mobile equilibrium a given equilibrium composition can be prepared in many ways for instance the same distribution or polyphosphoric acid composition could be prepared by either starting with concentrated orthophosphoric acid h 3 po 4 n 1 and driving off water or by starting with phosphorus pentoxide p 2 o 5 and adding an appropriate amount of water all polyphosphoric acid compositions can be described as a ratio of p 2 o 5 and water by reducing the various species present on paper to p 2 o 5 and water we will.