_Manipulation._—In all cases the solution is first made slightly alkaline with ammonia and then acid by a few drops of acetic, so that no free mineral acid may be present. (1) _With liquids free from iron_: If, on the addition of ammonium or sodium acetate, no turbidity be produced, the liquid is free from iron and alumina. In this case from ten to fifty cubic centimeters of the solution containing about one-tenth gram of phosphorus pentoxid are treated with ten cubic centimeters of sodium acetate, and afterwards with a quantity of uranium solution corresponding, as nearly as possible, to its supposed content of phosphorus pentoxid, and heated to boiling. From the heated liquid by means of a glass rod, one or two drops are taken and placed upon a porcelain plate and one drop of a freshly prepared solution of potassium ferrocyanid allowed to flow on it. If no brown color be seen at the point of contact of the two drops, additional quantities of the uranium solution are added and, after boiling, again tested with potassium ferrocyanid until a brown color is distinctly visible. The quantity of the uranium solution thus having been determined, duplicate analyses can be made and the whole quantity of the uranium solution added at once with the exception of the last drops, which are added as before. (2) _Solutions containing iron and alumina._ The solution is treated with the ammonium citrate solution of Joulie, the magnesia mixture added slowly, and the precipitate collected on a filter and washed with two and one-half per cent ammonia. The precipitate is then dissolved in nitric acid, made alkaline with ammonia, and then acid with acetic. This solution is then treated with ten cubic centimeters of sodium acetate and titrated with uranium, as described in (1). As an alternative method, 200 cubic centimeters of the superphosphate solution may be treated with fifty cubic centimeters of sodium acetate, allowed to stand for some time, and filtered through a filter of known ash content. In fifty cubic centimeters of the filtrate, which correspond to forty cubic centimeters of the original solution, phosphoric acid may be determined as described above. The precipitate, consisting of iron and aluminum phosphates, is washed three times on the filter with boiling water, dried, and ignited in a platinum dish. The weight of ignited precipitate, diminished by the weight of the ash contained in the filter and divided by two, gives the quantity of phosphorus pentoxid which it is necessary to add to that obtained by titration. =117. Determination of the Phosphoric Acid in all Phosphates and Basic Slags.=— (1) _Total phosphoric Acid_: