6l2 AGRICULTURAL ANALYSIS 



may contain basic ferric phosphate. In this latter case it should 

 be ignited and weighed, then dissolved in hydrochloric acid and 

 the ferric oxid estimated in the solution and from the difference 

 the quantity of combined phosphoric acid calculated. 



The separation of the iron from the phosphoric acid may be 

 accomplished by adding tartaric acid to the hydrochloric acid 

 solution of the iron phosphate above obtained and then ammo- 

 nium chlorid and ammonia. The mixture is placed in a flask 

 and ammonium sulfid added. The flask is closed, placed in a 

 warm place and allowed to stand until the supernatant liquid is 

 clear and of a pure yellow color without a trace of green. The 

 iron is separated by filtration, washed, dissolved, and estimated 

 in the usual way. 



If manganese and alumina be present the iron and manganese 

 are separated from the phosphoric acid and alumina by the pro- 

 cesses just given for the separation of iron from phosphoric acid. 

 In the filtrate the alumina and phosphoric acid are separated as 

 follows: The filtrate is evaporated in a platinum dish after the 

 addition of an excess of pure sodium carbonate until no ammo- 

 nia is set free by a further addition of the carbonate. Some 

 nitric acid is then added and the evaporation continued to dry- 

 ness. The residue is fused and after cooling softened with water, 

 washed into a small beaker, some hydrochloric acid added, 

 warmed, and filtered. Ammonia is added until the reaction is 

 alkaline. If no precipitate be produced no alumina is present. In 

 this case more nitric acid is added, the solution again evaporated 

 and the phosphoric acid determined by the usual methods. 



In case a precipitate is formed, showing the presence of alu- 

 mina, nitric acid is added until the precipitate is dissolved, and 

 then in slight excess and after evaporation the phosphoric acid 

 separated by molybdic solution and determined as usual. From 

 the filtrate the excess of molybdic acid is removed by hydrogen 

 sulfid and the alumina determined in the filtrate : Or the alumina 

 may be determined directly in the hydrochloric acid solution of 

 the melt above obtained as aluminum phosphate by adding so- 

 dium phosphate, ammonia and acetic acid. The aluminum phos- 

 phate is separated by filtration and determined in the usual man- 



