256 AGRICULTURAL ANALYSIS 



Method of Study. Various quantities of the pure aluminum 

 sulfate are placed in a 12-ounce beaker with a solution of two 

 grams of ammonium phosphate, the resulting precipitate dis- 

 solved in hydrochloric acid, and 25 cubic centimeters of a 50 

 per cent, solution of ammonium chlorid added. The solution is 

 made alkaline with ammonia and the precipitate just dissolved 

 with hydrochloric acid, noting approximately the number of cubic 

 centimeters required after the solution has become acid ; the solu- 

 tion is diluted to about 250 cubic centimeters, and for each cubic 

 centimeter of hydrochloric acid added to the acid solution five 

 cubic centimeters of a 50 per cent, solution of ammonium thiosul- 

 fate were added dropwise, the beaker covered with a watch- 

 glass, the solution boiled half an hour, filtered, washed, dried 

 and ignited to constant weight. 



Washing 20 times with five per cent, ammonium nitrate gives 

 practically theoretical results. As many as 50 washings with 

 this solution give results slightly low, but still good. The other 

 solutions were rejected, as they showed a decided solvent effect, 

 except the ammonium nitrates plus ammonium phosphate, upon 

 prolonged washing. Twenty washings were required to free the 

 precipitate from chlorids, sulfates, and ammonium phosphate. 

 In all succeeding work five per cent, ammonium nitrate was used, 

 washing 20 times. Long heating with the blast from 10 to 20 

 minutes was required to reduce to constant weight. 



Composition of the Ignited Aluminum Phosphate. The phos- 

 phoric acid in the aluminum phosphate, washed 20 times with 

 five per cent, ammonium nitrate, was carefully determined by 

 precipitation with molybdate solution, washing the precipitate of 

 ammonium phosphomolybdate with dilute nitric acid, and wash- 

 ing the final precipitate free of chlorids. 



The salt obtained under the above mentioned conditions seems 

 to be the normal phosphate, A1PO 4 . 



Effect of Iron Salts. Five grams of ammonium ferric alum 

 dissolved in water, two grams of ammonium phosphate added, 

 and treated as for aluminum phosphate, precipitating while slight- 

 ly warm, washing 20 times with ammonium nitrate, gave an- 



