Abstract
1. The colorimetric determination of phosphoric acid in hydrochloric and citric acid extracts of soils by a method involving the evaporation of the extract, ignition and acid extraction of the residuewith either the Denigès and Fiske-Subbarow methods of colour development was satisfactory only with light soils. Clay soils gave low results owing to the presence of larger amounts of iron.2. A method is given in which the organic matter and iron are removed by treatment with sodium permanganate and potassium ferrocyanide. The results are in good agreement with the gravimetric method.

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