For the best results the substance to be examined should be placed in the flask in a dry state and then 800 cubic centimeters of water added and shaken by means of the machine indicated for half an hour. Afterwards the flasks are filled up to the mark, well shaken, and filtered through double folded filters into ordinary flasks of about 400 cubic centimeters capacity. Before any of the filtrate is collected, the first that runs through should be well shaken in the receiving flasks and rejected. Fifty cubic centimeters of the filtrate thus collected, corresponding to one gram of the substance, should be used for the determination. (2) _Total Acid._—For total phosphoric acid, including the insoluble portions, the material is treated as follows: Five grams of the substance are placed in a 500 cubic centimeter flask with twenty cubic centimeters of nitric acid of 1.42 specific gravity, and fifty cubic centimeters of pure concentrated sulfuric acid, and boiled briskly for half an hour. With substances which contain much organic material, a little paraffin is added to avoid frothing. Such substances also require a larger quantity of nitric acid than that above specified. The flasks are allowed to cool, water added, again allowed to cool, and filled up to the mark at 17°.5. If hydrochloric instead of sulfuric acid be used in making the above solution, when the citrate method is employed, the results are always too high because the precipitate contains lime and alumina in such quantities as to render any compensation for them inaccurate. In addition to this the sulfuric has this great advantage over the hydrochloric acid; _viz._, in not separating silicic acid, inasmuch as the silicic acid is insoluble in boiling sulfuric acid.