246 AGRICULTURAL ANALYSIS 



iron-aluminum precipitate with calcium phosphate may be en- 

 tirely avoided. The problem of separating the phosphoric acid 

 by the citrate method, followed by a destruction of the citric acid 

 in the filtrate by combustion with sulfuric acid according to the 

 kjeldahl process, and final separation of the iron and alumina in 

 the residues was already under way when our attention was called 

 to substantially the same process described by Jean. 5 The meth- 

 cd merits a further critical examination. 



217. Methods of the German Fertilizer Association. The meth- 

 ods of determining phosphoric acid and other constituents in min- 

 eral phosphates according to the directions prescribed by the 

 Union of German Fertilizer Manufacturers differ only in unim- 

 portant details from other German methods described. 6 



Water-Soluble Phosphoric Acid. This method is applied to 

 superphosphate, phosphate precipitates and raw phosphates, but 

 is not applicable to phosphatic slags. The extraction is performed 

 upon 20 grams of superphosphate in a liter flask. The sample is 

 covered with 800 cubic centimeters of water, shaken for 30 

 minutes and filled up to the mark. The ordinary shaking ma- 

 chine is used. In cases of double phosphates they should be pre- 

 viously boiled with nitric acid in order to convert any pyrophos- 

 phate into orthophosphate. It is recommended that the final 

 precipitation of the phosphoric acid be conducted according to the 

 usual molybdic acid method with only a few unimportant varia- 

 tions. 



The Citrate Method. In lieu of the molybdic acid method the 

 Union of German Fertilizer Manufacturers also recommends 

 the citrate method, which is carried out as has already been de- 

 scribed, with unimportant variations. 



Volumetric Method by Titration with Uranium Salts. This 

 method, although recognized as being a very old one, is recom- 

 mended in cases where there are no large quantities of iron and 

 alumina. The method as used does not differ in any marked re- 

 pect from- that already given. 



Citrate-Soluble Phosphoric Acid. The method of securing the 



5 Journal de Pharmacie et de Chirnie, 1895, [6], 1 : 99. 



Chemisches Central-Blatt, 1895, 1 : 562. 

 * Methoden zur Untersuchung der Kunstdiingemittel, 1903 : 2. 



