70 AGRICULTURAL ANALYSIS 



2. Water-Soluble Phosphoric Acid. To 20 grams of the 

 substance in a liter flask, are added 800 cubic centimeters of water, 

 shaken every 15 minutes for two hours; the volume is made 

 up to the mark and the phosphoric acid in 50 cubic centimeters 

 of the filtrate, equalling one gram substance, is determined as un- 

 der total. 



3. Reverted Citrate-Soluble Phosphoric Acid. Two and five- 

 tenths grams substance are rubbed up with water, washed upon 

 the filter with about 100 cubic centimeters of water, the residue 

 on the filter washed into a flask with a part of the measured cit- 

 rate solution, and digested one hour at from 35 to 40 with 200 

 cubic centimeters of Petermann's citrate solution. The water and 

 citrate extracts are made up to a quarter of a liter each, and 

 the phosphoric acid determined in from 25 to 50 cubic centime- 

 ters, according to the quantity present. 



Solutions, i. Molybdate Solution. Three hundred and seven- 

 ty-five grams of ammonium molybdate are dissolved in two and 

 five-tenths liters of water, and the solution poured into two and 

 five-tenths liters of nitric acid of 1.20 specific gravity. 



2. Magnesia Mixture. Two hundred and seventy-five grams 

 of crystallized magnesium chlorid and 350 grams of ammonium 

 chlorid are dissolved in 3250 cubic centimeters of water and filled 

 up to five liters with ammonia of 0.96 specific gravity. 



3. Petermann's Solution. One kilogram of citric acid is dis- 

 solved in about two liters of water and 1350 cubic centimeters of 

 ammonia of 0.925 specific gravity and filled up with water to 

 5750 cubic centimeters. The solution then has a specific gravity 

 of 1.09; 300 cubic centimeters of ammonia of 0.925 specific grav- 

 ity are added. 



79. The Molybdic Acid Method as Practiced by Members 

 of the Union of the German Experiment Stations. The method 

 adopted by the German experiment stations is essentially that 

 used at Halle. 50 The samples are brought into solution in the 

 following way: For the estimation of phosphoric acid in bone- 

 meal, fish-guano, flesh preparations and raw phosphates, and the 

 total phosphoric acid in superphosphates, five grams of the sample 

 50 Die landwirtschaftlichen Versuchs-Stationen, 1891, 38 : 306. 



