BKRJU'S MODIFICATION OF P. NEUMANN'S METHOD 125 



the addition 'of 10 cubic centimeters of nitric acid. The precipi- 

 tate is collected in the gooch crucible, washed first with the acid 

 ammonium nitrate above described, then with alcohol and finally 

 with ether. The precipitate is ignited at first gently and then with 

 a medium flame until the surface assumes a brilliant crystalline 

 deep blue-black appearance. The precipitate is represented by 

 the formula 24Mo 3 P 2 O 5 , and contains 3.946 per cent, of P 2 O 5 . 



Lorenz regrets that the German experiment stations have per- 

 sisted in retaining the direct citrate method which is not a strict- 

 ly scientific proceeding, but asserts that his own method of 

 drying the yellow precipitate with ether without ignition con- 

 sumes less time and is more accurate than Woy's modification as 

 given above. 92 



Sherman and Hyde slightly modify the processes of Woy 

 and have been able to obtain results with this method on some 20 

 samples of fertilizers, embracing all the common sources of phos- 

 phoric acid, which agree within two-tenths of one per cent, with 

 results obtained by the molybdate-magnesia method, except in the 

 case of a phosphatic slag, in which the variation was three-tenths 

 per cent. 9 *' 95 As the precipitate of magnesium pyrophosphate con- 

 tained iron, the results by the gravimetric method were probably 

 high. The authors use a three per cent, solution of neutral am- 

 monium molybdate and add from five to eight cubic centimeters 

 of nitric acid to the neutral phosphate solution. The ammonium 

 phosphomolybdate is washed with one per cent, nitric acid until 

 the washings amount to from 250 to 300 cubic centimeters, and 

 ignited at a low heat in the usual way without dissolving and re- 

 precipitating. The weight of the phosphomolybdate multiplied by 

 0.3949 gives the phosphoric acid. 



113. Berju's Modification of P. Neumann's Method. Berju calls 

 attention to the fact that for at least 10 years it has been well 

 known that phosphoric acid could be determined with great exact- 

 ness by the direct weighing of the phosphomolybdate precipitate. 90 

 During this period the fact has been repeatedly verified. In his 



93 Chemiker-Zeitung, 1903, 27 : 495. 



94 Journal of the American Chemical Society, 1900, 22 : 652. 



95 Chemiker-Zeitung, 1897, 21 : 441, 469. 



96 Journal fiir Laudwirtschaft, 1906, 54 : 31. 



