150 AGRICULTURAL ANALYSIS 



100 cubic centimeters of ammonia of 22 strength, and distilled 

 water enough to make one liter. 



The solutions are thoroughly mixed in a precipitating glass, an 

 excess of ammonia added, and allowed to stand for 12 hours 

 under a bell jar. The phosphoric acid contained in the liquor is 

 separated as ammonium magnesium phosphate. It is collected 

 upon a small filter, washed with a little ammoniacal water, redis- 

 solved, and titrated with the uranium solution in the manner al- 

 ready indicated. 



Example. The following is an example of this kind of a de- 

 termination : 



(1) One and one-half grams of the superphosphate and dis- 

 tilled water enough to make 150 cubic centimeters. 



(2) Filter paper with reverted phosphates, 60 cubic centi- 

 meters of ammonium citrate, and a sufficient quantity of distilled 

 water to make 150 cubic centimeters. 



Aqueous solution (i) 25 cc. j = f the le< 



Citrate solution (2) 25 cc. ) 



Add magnesium solution 20 cubic centimeters and ammonia 

 in excess, and allow from 12 to 24 hours of digestion, then filter 

 and wash, dissolve and titrate. 



Required of solution of uranium 8.55 cubic centimeters (i cubic 

 centimeter = 5 milligrams P 2 O 5 ). 



Correction, 0.20 to be deducted=8-35 cubic centimeters. 



8.35X0.005=0.04175 gram P 2 O r , for 0.25 gram of the sample. 

 Then 0.04 175 -=-0.25 =16.7 per cent. 



From the above data there would be 16.7 per cent, of phos- 

 phoric acid soluble in water and in ammonium citrate. 



If it be desirable to have separately the phosphoric acid soluble 

 in water, a separate precipitation is made of the aqueous solution 

 alone by means of the magnesium citrate solution. The precipi- 

 tate washed with ammoniacal water is redissolved and titrated in 

 the manner indicated. 



In subtracting from the figures obtained with the two solutions 

 together the number obtained for the phosphoric acid soluble in 

 water, the number representing the phosphoric acid soluble in 

 ammonium citrate alone, is obtained. 



