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OSMOND 1887 proposed the estimation of P by causing the formation of phosphomolybdic acid and its subsequent reduction to a blue com'pound which could be measured colorimetrically. Of the many variants of this procedure, that of Fiske (2) proportionality between colour density and amount of P over a wide range; (3) relative freedom from interference by such substances as ammonium and iron salts, nitrates, nitrites, silicates and chlorides.
R. J. L. Allen (Sat,) studied this question.