214 AGRICULTURAL ANALYSIS 



main essentially more favorable, since not all, but always an equal- 

 ly proportionate part, of the bases go into solution. 



In order to prove whether these objections against the solution 

 with aqua regia were correct, Bottcher in different bone meals 

 carried out the estimation of the total phosphoric acid, both by 

 solution with aqua regia and with sulfuric acid. In samples of 

 50 cubic centimeters of the acid phosphate solution the phosphoric 

 acid was precipitated, according to the methods of the German 

 association, by direct precipitation with citrate solution and 

 magnesia mixture, and in other samples of 50 cubic centimeters 

 according to the modification of Schenke, that is, the approximate 

 neutralization of the solutions with ammonia before the addition 

 of the citrate solution and magnesia mixture. 



The data which were obtained show that the objections urged 

 by Schenke are not well founded and that in the case of bone 

 meals, etc., as good results were obtained by solution with aqua 

 regia as with sulfuric acid. If sometimes lower results are ob- 

 tained after solution in sulfuric acid, the reason lies perhaps in 

 the fact that after the treatment of strong sulfuric acid phosphate 

 solutions with ammoniacal citrate solution a marked heating of the 

 mixture takes place and it is not sufficiently cooled before the 

 addition of the magnesia mixture. This subsequent cooling be- 

 fore precipitation is necessary since otherwise the results fall 

 too low. 



187. Estimation of Phosphoric Acid in Slags. The further 

 discussion of determining the phosphoric acid in slags by the cit- 

 rate method by Schenke and Mach has introduced certain modi- 

 fications of an unimportant character, in the process. 88 



In the estimation of the citrate-soluble phosphoric acid in slags 

 by the molybdate method, Schenke follows in general the Wagner 

 method, heating the precipitate only 15 to 30 minutes in a water 

 bath at 80 or 90 and allowing to cool for two or three hours. 

 By this method the precipitation of molybdic acid is most cer- 

 tainly avoided and a bright and clear solution of the precipitate 

 is easily secured in cold dilute ammonia. Impurities due to 

 silicic acid are also avoided. 



88 Die landwirtschaftlichen Versuchs-Stationen, 1905, 62 : 3 ; 1906, 

 64 : 87. 



