234 AGRICULTURAL ANALYSIS 



lion has been carried on correctly, there occurs only a slight pre- 

 cipitate of Ca 3 P 2 O 8 amounting only to a few milligrams. In 

 some cases it may be necessary to dissolve the precipitate and 

 reprecipitate the iron and aluminum phosphates a fourth time. 



The whole time required for the triple precipitation, according 

 to Hess, if all the operations be properly conducted, is from 

 three to four hours. It is therefore possible by this variation of 

 the acetate method to secure a determination of the iron and 

 alumina as phosphates in the same time which is occupied by 

 the Glaser-Jones method, when the separation of lime is taken 

 into account. 



If the solution of the mineral phosphate employed contains any 

 notable quantity of organic material, it must be destroyed by 

 boiling with bromin or some other oxidizing agent, before the 

 precipitation by the acetate method is commenced. 



The presence of silicic acid need not be taken into special con- 

 sideration since this can be detected and determined in the phos- 

 phate precipitates after they have been ignited and weighed. 

 The determinations of the phosphoric acid were made by direct 

 precipitation with ammonium in the presence of citrate; they 

 agreed perfectly with the previous precipitations with molybdic 

 solution. 



206. Method of Eugen Glaser. The principle on which this 

 method rests, depends on the preliminary removal of the lime by 

 conversion into calcium sulfate and its precipitation in the presence 

 of strong alcohol. 91 This process does not require the use of 

 acetic acid which in the old method dissolved more or less of the 

 aluminum phosphate, thus introducing errors of considerable 

 magnitude in those cases where the mineral phosphates contained 

 notable quantities of alumina. It is conducted as follows : 



Five grams of the phosphate are dissolved in a mixture of 

 25 cubic centimeters of nitric acid of 1.2 specific gravity and 

 about 12.5 cubic centimeters of hydrochloric acid of 1.12 specific 

 gravity, made up to a volume of half a liter, and filtered. One 

 hundred cubic centimeters of the filtrate, equivalent to one gram 

 of the substance, are placed in a quarter-liter flask and 25 cubic 

 91 Zeitschrift fur angewandte Chemie, 1889, 2 : 636. 



