The mercuric sulfate which is produced by the Kjeldahl method is not precipitated in the presence of ammoniacal solution of ammonium citrate, but there may be small quantities of mercurous salts present or some finely divided metallic mercury which may contaminate mechanically the phosphate precipitate. These disturbing influences may be removed by previous treatment with sodium chlorid. If from fifty to sixty cubic centimeters of sulfuric acid have been used for the solution and oxidation and this be made up to half a liter, it will be sufficiently dilute to permit an almost quantitative separation of the mercurous chlorid produced by treatment with sodium chlorid. Neubauer, who has proposed this method, finds that when sodium chlorid is used previous to the precipitation of the phosphoric acid, a precipitate of ordinary size contains, at most, only one milligram of mercury, while without the use of sodium chlorid as much as four milligrams may be found. The details of the method employed by Neubauer are as follows: Ten grams of the fertilizing material are placed in a half liter flask with from fifty to sixty cubic centimeters of strong sulfuric acid, two grams of mercury, and a little paraffin to prevent foaming. The oxidation is carried on as usual in the Kjeldahl method. The liquid, after cooling, is diluted with water and one cubic centimeter of a citrate solution of sodium chlorid added, cooled, filled to the mark, filtered, and fifty cubic centimeters taken for the determination of the phosphoric acid, according to the citrate method and the same quantity for the determination of the ammonia by distillation. THE CITRATE METHOD. =63. General Principles.=—It has been seen that in the molybdic method there is introduced a process at considerable cost, both of reagents and time, having for its object the separation of the phosphoric acid from all the other acids and bases which may have been present in the original sample. The phosphorus is thus obtained in composition with molybdenum and ammonium in a form easily soluble in ammonia, from which it can be accurately separated by means of a soluble salt of magnesia. The citrate method has for its object the suppression of this intermediate step and the determination of the phosphoric acid by direct precipitation in presence of iron, lime, and alumina. The principle on which it is based rests on the well-known power of an alkaline ammonium citrate to hold in solution the salts of iron, alumina, and lime, while at the same time it permits of the separation of phosphoric acid, as ammonium magnesium phosphate. In no case can the citrate method be regarded as an exact analytical process, but large experience has shown that the errors of the method are compensatory and that it affords a good and ready method for fertilizer control.