146 AGRICULTURAL ANALYSIS 



Mineral phosphate, five grams of the material dissolved in 

 20 cubic centimeters of hydrochloric acid. 



Water, sufficient quantity to make 100 cubic centimeters. 



Quantity used, 10 cubic centimeters=o.5o gram of the sample 

 under examination. 



Solution of uranium required 15.3 cubic centimeters. 



Correction 0.2 cubic centimeters. 



Actual quantity of uranium solution 15.1 cubic centimeters. 



Strength of the solution of uranium, one cubic centimeter=five 

 milligrams P 2 O 5 . 



Then P 2 O 5 in 0.50 gram of the material = 5 X 15.1 = 75-5 

 milligrams. 



Then the per cent, of P,O 5 = 75 ' 5 * I( * =15.10. 



The sample under examination ought always to be prepared in 

 duplicate, either by making a single precipitation and re-solution 

 of the ammonium magnesium phosphate which is made up to a 

 certain volume and an aliquot portion of which is taken for the 

 analysis, or by making two precipitations under the conditions 

 previously described. When the content of phosphoric acid in 

 the material under examination is very nearly known, the double 

 operation may be avoided, especially if it be required to have 

 rapid and only approximate analyses, such as those which are 

 made for general control and for the conduct of manufacturing 

 operations. But when analyses are to be used to serve as the 

 basis of a law action or for the control of a market, they should 

 always be made in duplicate, and the results ought not to be ac- 

 cepted when the numbers obtained are widely different, since the 

 agreement of the two numbers will tend to show that the work 

 has been well executed. 



This method of analysis, much longer to describe than to exe- 

 cute, gives results perfectly exact and always concordant when 

 it is well carried out, provided that the standard solutions upon 

 which it rests for its accuracy are correctly prepared and fre- 

 quently verified in the manner indicated. 



The strength of the solution of uranium ought to be verified 



