Determined directly by the citrate method, the following data were obtained: Allowing to stand thirty hours after adding magnesia mixture, 1.08 and 1.53 per cent in duplicates. Allowing to stand seventy-two hours after adding magnesia mixture, 2.17 and 2.30 per cent in duplicates. In each case fifty cubic centimeters of the solution were taken, representing half a gram of the sample. In another series of determinations twenty-five cubic centimeters of the sample were mixed with an equal volume of a mineral phosphate solution, the value of which had been previously determined by both the molybdic and citrate methods. The fifty cubic centimeters thus obtained represented a quarter of a gram each of the cake-meal and mineral phosphates. The filtration followed eighteen hours after adding the magnesia mixture. The following data show the results of the determinations: Per cent Per cent Per cent Per cent P₂O₅ in P₂O₅ in P₂O₅ P₂O₅ in mineral organic found in organic phosphate. sample. mixture × 2. sample. 1 15.37 2.52 17.90 2.53 2 29.16 2.52 31.68 2.52 3 31.37 2.52 33.83 2.45 4 31.58 2.52 34.20 2.62 ---- Mean content of P₂O₅ in organic sample 2.53 It is thus demonstrated that the citrate method can be applied with safety even to the determination of the phosphoric acid in organic compounds where the quantity present is less than three per cent. It is further shown that solutions of mineral phosphates varying in content of phosphoric acid from fifteen to thirty-two per cent may be safely used for increasing the content of that acid to the proper degree for complete precipitation. In cases where organic matters are present they should be destroyed by moist combustion with sulfuric acid as in the determination of nitrogen to be described in the next part.