126 ' AGRICULTURAL ANALYSIS 



opinion, none of the methods which have heretofore been pro- 

 posed for this process has been introduced into the experiment 

 stations for the purpose of applying it to the estimation of 

 phosphoric acid in fertilizers, these stations having continued to 

 follow the time-consuming method of the direct precipitation of 

 the phosphoric acid in the citrate solutions, although this method 

 has led to no certain results. 



The method of P. Neumann is preferred as the process for 

 securing the phosphoric acid, because it requires less time than 

 the other methods proposed and is equally exact. 97 Berju, there- 

 fore, has applied the principles of this method for general use in 

 the investigation of fertilizers containing phosphoric acid. The 

 accuracy of the method was first ascertained by its application to 

 pure sodium phosphate (Na 2 HPO 4 -)-i2H 2 O). For the formula 

 of the precipitate he adopts that proposed by Hundeshagen, name- 

 ly, i2MoO 3 PO 4 (NH 4 ) 3 , which contains 3.78 per cent. P 2 O 5 . 98 

 The method of procedure is the following: 



Fifty cubic centimeters of the phosphate solution, correspond- 

 ing to 0.5 gram of sodium phosphate, are treated with five cubic 

 centimeters of nitric acid of 1.2 specific gravity, and with 75 

 cubic centimeters of ammonium nitrate-molybdate solution pre- 

 pared according to the directions of Wagner-Stutzer, for the pur- 

 pose of precipitating the phosphoric acid. The mixture is stirred 

 for a quarter of an hour, and after three-quarters of an hour, the 

 precipitate is collected upon a gooch after decanting three times 

 with about 30 cubic centimeters of the aqueous solution of a five 

 per cent, ammonium nitrate solution and one per cent, nitric acid. 

 The filtrate is washed six times and the precipitate collected as 

 nearly as possible upon the asbestos felt. 



The gooch is placed in a somewhat higher porcelain crucible 

 and the precipitate carefully dried over a free flame, the tempera- 

 ture being gradually raised to about 150 to 180 until the 

 ammonium nitrate is completely removed. This is determined 

 by placing a watch glass upon the top of the crucible for at least 

 half a minute and noticing whether any deposit is found thereon. 

 " Zeitschrift fiir analytische Chemie, 1898, 37 : 303. 

 96 Zeitschrift fiir analytische Chemie, 1889, 28 : 141. 



