(3) _Citrate-Soluble Acid._—Two grams of the sample are digested with 100 cubic centimeters of citrate solution, 1.09 specific gravity, for half an hour at 50° in a beaker. Afterwards the soluble matter is separated by filtration with the aid of a filter-pump and the residue washed with a solution of one part water and one part citrate solution until all the dissolved phosphoric acid is removed from the filter. Generally three or four washings are sufficient. The residue on the filter is dried, ignited, and dissolved in a mixture of two cubic centimeters of nitric and twenty cubic centimeters of sulfuric acid, the solution made up to a volume of 200 cubic centimeters, filtered, and 100 cubic centimeters of the filtrate taken for the determination. The acid in the filtrate is nearly neutralized and fifty cubic centimeters of citrate solution are added, and afterwards twenty-five cubic centimeters of magnesia mixture and twenty cubic centimeters of twenty-four per cent ammonia. After standing for forty-eight hours, the precipitate is separated by filtration, ignited, and weighed in the usual way. The difference between the total phosphoric acid and that in the insoluble residue, after treatment with ammonium citrate, as above, gives the quantity of phosphoric acid soluble in the citrate solution. The difference between the total citrate-soluble and the water-soluble gives the quantity of the reverted phosphoric acid. The ammonium citrate solution used for the digestion is made as follows: Two hundred and fifty grams of crystallized citric acid are dissolved in half a liter of hot water, diluted with 550 cubic centimeters of water, 276 cubic centimeters of twenty-four per cent ammonia added, and finally, exactly neutralized by adding, little by little, fifty per cent citric acid solution. The Halle methods of separating the water and citrate-soluble acids appear to be less complete and reliable than those in use by the Official Agricultural Chemists of this country. The precipitation of basic phosphates, when large quantities of water are used at once in separating soluble acid, must tend to diminish the quantity obtained, while the lack of care in assuring the neutrality of the citrate solution might lead to varying results.