9 6 



AGRICULTURAL ANALYSIS 



possible after the addition of the citrate solution to avoid a sep- 

 aration of crystalline calcium phosphate. On the addition of the 

 citrate solution there is always a rise in temperature. Inasmuch 

 as the precipitation of the phosphoric acid with magnesia must 

 take place in the cold, the liquid must be cooled after the addi- 

 tion of the citrate, and the cooling should take place as quickly 

 as possible. 



The above method was adopted by the chemical section of the 

 International Agricultural Congress held at Vienna, September, 

 i890. 67 



In order to hasten the precipitation of the ammonium magne- 

 sium phosphate and to prevent the fixation of the precipitate on 

 the walls of the erlenmeyer, the flask should be shaken for half 

 an hour. For this purpose the flasks should be closed with smooth 

 well-fitting rubber stoppers and placed in a shaking machine. The 

 shaking machine of the form given in Fig. 4, recommended by 

 the Halle station, is very conveniently used for this purpose. 



Fig. 4. Shaking M*achine for Ammonium Magnesium Phosphate. 



On a vertical axis are carried two platforms for holding the 

 flasks. The flasks are prevented from striking each other by 

 means of the partitions shown. The apparatus is conveniently 

 driven by a small water-motor, as indicated, which imparts to the 

 platforms a partial back and forth revolution. 



After shaking for half an hour, any precipitate adhering to the 

 rubber stoppers is carefully washed off with ammonia water into 

 the flask. The filtration can be made immediately after the shak- 

 ing or after two or three days ; the results are the same. 

 T Chemiker-Zeitung, 1890, 14 : 1246. 



