REAGENTS l8l 



ted with water to one liter. In this solution the phosphoric acid 

 is determined gravimetrically by the molybdate or citrate method, 

 and the value of the solution marked on the flask containing it. 



Titrated Uranium Solution. Two hundred and fifty grams of 

 uranium nitrate are dissolved in water, 25 grams of sodium ace- 

 tate 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 pro- 

 ceed 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 por- 

 celain dish with ammonia, acidified with acetic, treated with 10 

 cubic centimeters of sodium acetate solution and warmed. Through 

 a burette as much uranium solution is allowed to flow as is neces- 

 sary 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 25 cubic centimeters of calcium 

 phosphate solution. Example : 



Twenty-five cubic centimeters of the calcium phosphate solu- 

 tion containing 0.10317 gram of phosphorus pentoxid, gave as a 

 mean of three determinations 23.2 cubic centimeters of the ura- 

 nium solution necessary to produce the brown color with potas- 



o 10^17 

 sium ferrocyanid. Consequently '- - = 0.00445 gram of 



phosphorus pentoxid equivalent to one cubic centimeter of ura- 

 nium solution. If, for instance, a quantity of fertilizer weighing 

 exactly five grams, requires 10 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 10X0.00445, equivalent to 0.0445 gram of 

 phosphorus pentoxid. The fertilizer, therefore, contains 0.89 per 

 cent, of phosphorus pentoxid. 



Conduct of the Molybdate 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. 



