82 AGRICULTURAL ANALYSIS 



Jorgensen calls especial attention to the tests which he has 

 made on the influence of impurities in the phosphatic materials 

 which are to be determined, and especially of the maximum quan- 

 tities of silica, iron, calcium, aluminum, or salts thereof, which 

 may be present without interfering with the accuracy of the pro- 

 cess. He also uses a concentrated molybdate solution of which 

 about 61 cubic centimeters are necessary for the precipitation of 

 0.2 gram (P 2 O 5 ) on the supposition that one part of phosphorus 

 is best precipitated in the presence of about 12 parts of molyb- 

 denum. 



In the application of the method for fertilizing materials Jor- 

 gensen prefers that they should be brought into solution either 

 with hydrochloric or sulfuric acids, hydrochloric preferred. For 

 the conversion of the pyrophosphates into phosphates, however, 

 nitric acid is necessary. If the solution contains about 0.2 of 

 pyrophosphoric acid in 50 cubic centimeters, it should be boiled 

 with 10 cubic centimeters of nitric acid of a specific gravity of 

 1.4 for a quarter of an hour, or 2.5 of nitric acid of the same 

 strength for half an hour, or 1.25 cubic centimeters for an hour. 

 In the precipitation of the phosphoric acid in the fertilizers, if 

 ferric oxid is present not exceeding in quantity 0.22 gram, 

 aluminic oxid in quantity not exceeding o.ii gram, calcium oxid in 

 quantity not exceeding 0.42 gram, and silica in quantities not ex- 

 ceeding 0.17 gram, these bodies do not exert any injurious effect. 

 The molybdate precipitate is washed about 10 times by decanta- 

 tion with from 20 to 25 cubic centimeters of a nitric acid solu- 

 tion of ammonium nitrate consisting of about one per cent, of 

 nitric acid to about five per cent, of ammonium nitrate in 100 parts 

 of the solution, and afterwards the precipitate is dissolved in a 

 measured quantity of 2.5 per cent, of ammonia in such a way 

 that about 100 cubic centimeters of the solution are used for 

 each 0.2 gram phosphoric anhydrid, with similar quantities of 

 phosphoric acid and correspondingly less quantities of the sul- 

 phate. If the filter is not considered well washed, a small quan- 

 tity of water may be used afterwards for this purpose. The solu- 

 tion is then heated in a covered beaker until bubbles of steam 

 begin to escape, and drop by drop treated with a neutral mag- 



