The relation between composition and conductivity in solutions of meta- and orthophosphoric acids

When P₂O₅ is thrown into excess of water at room temperature, about 75 per cent. of the total dissolved acid is HPO₃ and the rest H₃PO₄. There is no evidence of the formation of H₄P₂O₇. This HPO₃ exists as complex and simple molecules, and the proportions of the two may vary widely from one solution to another of the same total concentration. Two changes then take place, a depolymerisation of the (HPO₃)_n and a hydration of HPO₃, of which the former is probably the quickest. The latter change (hydration) does not, as in the reaction studied by Sabatier, follow exactly the same exponential law until all the acid is changed. The two changes are seen most clearly in the G, K curves, Fig. 3, and from these it also appears that the conductivity of HPO₃ is considerably greater than that of H₃PO₄.