2O6 AGRICULTURAL ANALYSIS 



179. Treatment of the Citric Acid Extract. The filtrate ob- 

 tained as above is as soon as possible subjected to the following 

 treatment : Fifty cubic centimeters of the filtrate in a beaker are 

 placed in a stutzer shaking apparatus, which is set in rapid mo- 

 tion from about 250 to 300 vibrations per minute ; 50 cubic centi- 

 meters of the iron-citrate-magnesia mixture, above noted, are 

 then added, and with the temperature at from 14 to 18 

 the shaking is continued for half an hour. The precipitate is put 

 in a gooch crucible or upon an ash-free filter, washed with two 

 per cent, ammonia, ignited and weighed in the usual way. If 

 the citric acid solution obtained above is exceptionally light col- 

 ored or entirely colorless the duplicate estimation is not made 

 according to the described method, but by the molybdate method 

 or by the Naumann method. 64 



The molybdate method is carried out as follows : Fifty cubic cen- 

 timeters in a beaker or flask are treated with from 50 to 80 cubic 

 centimeters of the molybdic solution, above mentioned, and 

 warmed in a water bath to about 65. The beaker is then 

 withdrawn from the water bath, cooled and its contents filtered, 

 and the molybdic precipitate carefully washed with a one per 

 cent, nitric acid solution and dissolved in about 100 cubic centi- 

 meters of two per cent, ammonia. The ammoniacal solution, with 

 constant stirring, is treated with 15 cubic centimeters of the mag- 

 nesia mixture, the beaker covered with a glass plate and set aside 

 for two hours. The precipitated ammonium magnesia phosphate 

 is collected upon an ash-free filter or gooch, ashed with two 

 per cent, ammonia, dried, the filter paper, if used, ashed over a 

 bunsen burner and finally ignited in a blast for two minutes, 

 cooled and weighed. 



180. Preparation of the Citric Acid Extract of Basic Slag. 

 The details of the preparation and treatment of the extract are 



important. It is self-evident that the citric acid solution with 

 which the slag is treated must be prepared exactly as described, 

 and thus must contain 20 grams of chemically pure crystallized 

 uneffloresced citric acid to the liter. For the purpose of diminish- 

 ing the amount of work it is advisable to keep on hand a quantity 

 54 Chemiker-Zeitung, 1903, 27 : 12, 27, 120, 155. 



