If the solution of the mineral phosphate employed contain any notable quantity of organic material, it must be destroyed by boiling with bromin or some other oxidation agent, before the precipitation by the acetate method is commenced. The presence of silicic acid need not be taken into special consideration since this can be detected and determined in the phosphate precipitates after they have been ignited and weighed. While the determinations of the phosphoric acid in Hess’ method were made by precipitation in the presence of citrate, he found that they agree perfectly with the previous precipitations with molybdic solution. =35. Method of Glaser.=—The principle on which this method rests depends on the preliminary removal of the lime by conversion into calcium sulfate and its precipitation in the presence of strong alcohol.[25] It is conducted as follows: Five grams of the phosphate are dissolved in a mixture of twenty-five cubic centimeters of nitric acid of 1.2 specific gravity and about 12.5 cubic centimeters of hydrochloric acid of 1.12 specific gravity, and made up to a volume of half a liter, and filtered. One hundred cubic centimeters of the filtrate, equivalent to one gram of the substance, are placed in a quarter liter flask and twenty-five cubic centimeters of sulfuric acid of 1.84 specific gravity added. The flask is allowed to stand for about five minutes and meanwhile shaken a few times. About 100 cubic centimeters of alcohol of ninety-five per cent are then added and the flask filled with alcohol to the mark and well shaken. A certain degree of concentration takes place and this is compensated for by lifting the stopper and filling again with alcohol to the mark and shaking a second time. After allowing to stand for half an hour the contents of the flask are filtered, 100 cubic centimeters of the filtrate being equal to four-tenths gram of the substance. This volume, filtered, is evaporated in a platinum dish until the alcohol is driven off. The alcohol-free residue is heated to boiling in a beaker with about fifty cubic centimeters of water. Ammonia is added to alkaline reaction, but in order to avoid strong effervescence it is not added during the boiling. The excess of ammonia is evaporated, the flask allowed to cool, the contents filtered, precipitate and filter washed with warm water, ignited, and the phosphates of iron and alumina weighed. Half of the weight of the precipitate represents the weight of Fe₂O₃ + Al₂O₃. The estimation, as before indicated, should be carried on without delay, the whole time required not exceeding from one and a half to two hours.