_Titrated Uranium Solution._—Two hundred and fifty grams of uranium nitrate are dissolved in water, twenty-five grams of sodium acetate added, and the whole diluted to seven liters. One cubic centimeter of this solution corresponds to about 0.005 gram of phosphorus pentoxid. In order to determine its exact value proceed as follows: Twenty-five cubic centimeters of the calcium phosphate solution which, for example, has been found to contain 0.10317 gram of phosphorus pentoxid, are neutralized in a porcelain dish with ammonia, acidified with acetic, treated with ten cubic centimeters of sodium acetate solution, and warmed. Through a burette as much uranium solution is allowed to flow as is necessary to show in a drop of the solution taken out of the dish, when treated with a drop of pure potassium ferrocyanid, a slight brown color. In order to be certain, this operation is repeated two or three times with new quantities of twenty-five cubic centimeters of calcium phosphate solution. Example: Twenty-five cubic centimeters of the calcium phosphate solution containing 0.10317 gram of phosphorus pentoxid, gave as a mean of three determinations 23.2 cubic centimeters of the uranium solution necessary to produce the brown color with potassium ferrocyanid. Consequently 0.10317 ÷ 23.2 = 0.00445 gram of phosphorus pentoxid equivalent to one cubic centimeter of uranium solution. If, for instance, a quantity of fertilizer weighing exactly five grams, require ten cubic centimeters of the uranium solution for the complete precipitation of its phosphoric acid, then the quantity of phosphoric acid contained in the fertilizer would be equivalent to 10 × 0.0045, equivalent to 0.0445 gram of phosphorus pentoxid. The fertilizer, therefore, contains eight and nine-tenths per cent of phosphorus pentoxid. _Conduct of the Molybdenum Method._—This method rests upon the precipitation of the phosphorus pentoxid by a solution of ammonium molybdate in nitric acid, solution of the precipitate in ammonia, and subsequent precipitation with magnesia.