128 AGRICULTURAL ANALYSIS 



acid by weighing the ammonium phosphomolybdate. His pro- 

 cedure is based upon a solution containing a proper content 

 of nitric acid, of ammonium nitrate, and ammonium citrate. In 

 such a solution in the presence of an excess of nitromolybdate 

 ammonium, the phosphoric acid is precipitated rapidly at a tem- 

 perature of about 70. The precipitate which is formed is pure 

 and it is dried upon filter paper without decomposition at from 

 105 to 110. 



The method is used particularly in Belgium, where by an 

 agreement between Belgium, Holland, and the Grand-Duchy of 

 Luxembourg, only two methods of international examination of 

 phosphates are permitted, i. e. } the direct phosphomolybdate 

 method or the citro-magnesium method. The method by the 

 direct weighing of phosphomolybdate ammonium is therefore 

 employed only as a means of control in these countries. 



The solutions of phosphates are prepared according to the 

 methods prescribed by Kuss for the analysis of fertilizing ma- 

 terials, cattle feeds, and agricultural products for the Grand- 

 Duchy of Luxembourg. 



The acid solutions of the phosphates and basic slags are 

 neutralized by ammonium until precipitation commences. The 

 precipitate is redissolved by a few drops of nitric acid and 10 

 cubic centimeters of Petermann's citrate of ammonium solution 

 added. The rest of the process is the same as that employed 

 where citric acid or ammonium citrate is originally used for 

 securing a solution of phosphates soluble therein. 



The phosphoric acid having been thus obtained in the pres- 

 ence of a solution of citrate of ammonium, the samples are treated 

 as follows: 



There is added to each sample containing from o.i to 0.4 

 gram of the original material, according to its richness in phos- 

 phoric acid, from two to three cubic centimeters of concentrated 

 citric acid from 10 to 15 cubic centimeters of a saturated solu- 

 tion of ammonium nitrate, and from 50 to 70 cubic centimeters 

 cf water. The mixture is brought to the boiling point, the lamp 

 removed, and there is added from 60 to 100 cubic centimeters 

 (according to the richness of the sample) of ammonium nitro- 



