68 AGRICULTURAL ANALYSIS 



75. Methods of the German Experiment Stations. The pro- 

 cesses adopted by the union of the German agricultural experi- 

 ment stations are based on the general methods of procedure 

 already outlined as is seen from the following resume. 48 The 

 sample containing the phosphoric acid is dissolved in aqua regia 

 in the proportion of five grams of the sample to 50 cubic centi- 

 meters of the acid, made by mixing three parts of hydrochloric 

 acid of 1. 1 2 specific gravity with one part of nitric acid of 

 1.25 specific gravity or 20 cubic centimeters of nitric acid of 1.42 

 specific gravity with 50 cubic centimeters of sulfuric acid 

 of 1.8 specific gravity. With the latter reagent the boiling is con- 

 tinued for 30 minutes. The phosphoric acid is then determined 

 by the direct (Bottcher) method. 47 



76. Water-Soluble Phosphoric Acid. The soluble acid in acid 

 phosphates is extracted by treating 20 grams of the sample in a 

 liter flask with 800 cubic centimeters of water for 30 minutes with 

 vigorous shaking, filling the flask to the mark, shaking and filling. 

 A mechanical shaker is recommended with a vibration or rotation 

 of 150 turns a minute. The acid is determined in an aliquot part 

 of the filtrate by the magnesia citrate method. Solutions of double 

 acid phosphates are boiled with nitric acid before treatment in 

 order to bring all the phosphoric acid in the ortho form. When 

 required the content in water-soluble and citrate-soluble acid 

 must be returned separately and not in one figure as citrate-solu- 

 ble acid. It was decided that the new Wagner method for de- 

 termining citrate-soluble acid in basic slag should be adopted. 

 This method is given in another paragraph, and it is not to be 

 applied to other phosphatic materials such as bone-meal. 



77. Official Norwegian Methods. The Director of the Chemical 

 Control Station of Norway, expresses the opinion, that for Nor- 

 wegian, Swedish, Danish and German conditions, the quantities 

 of material required by the American methods for the determina- 

 tion of phosphoric acid, notwithstanding their analytical exact- 



46 Die landwirtschaftlichen Versuchs-Stationen, 1904, 60 : 371. 



47 Die landwirtschaftlichen Versuchs-Stationen, 1903-4, 59:313; 1904, 

 60 : 221. 



