VARIATION OF MARIONI AND TASSEXU 239 



washed into a platinum dish and evaporated to a small bulk on 

 the water bath. The dark brown color produced is due to the 

 presence of organic matter and this must be destroyed, as it pre- 

 vents the complete precipitation of the phosphate in the subse- 

 quent operation. 



The organic matter is best destroyed by removing the dish 

 from the bath, adding a small quantity of pure sodium nitrate, 

 and heating very carefully over the naked flame, keeping the 

 dish well covered with a watch-glass to avoid spattering. The 

 mass fuses to a colorless, viscous liquid, becoming glassy when 

 cooled and is readily soluble in a hot, very dilute solution of 

 nitric acid. The solution transferred to a beaker is made dis- 

 tinctly alkaline with ammonia and carefully neutralized with 

 acetic acid, diluted with hot water, boiled, and the precipitate of 

 iron and alumina phosphates allowed to settle, after which it is 

 separated by filtration. 



After the precipitate has been completely transferred to the 

 filter, the washing is completed with a dilute solution of ammo- 

 nium nitrate. The precipitate is dried, ignited, cooled, and 

 weighed. 



The determinations should be made in pairs, and one of the pre- 

 cipitates used for the estimation of phosphoric acid, by fusing with 

 a little sodium carbonate, and the other, after fusion with sodium 

 carbonate, is dissolved with sulfuric acid and the iron reduced 

 and titrated with potassium permanganate solution. The fil- 

 trate from the iron and alumina determination is evaporated 

 to a small bulk, made strongly ammoniacal and allowed to stand 

 for some time, when the magnesia present separates as ammonium 

 magnesium phosphate, which is determined in the usual way. 



If, during the evaporation of the filtrate, any flocculent matter 

 separates, it should be removed by filtration and examined before 

 precipitating the magnesia. 



211. Variation of Marioni and Tasselli. The old and classic 

 method of separating iron and alumina in the presence of ammo- 

 nium acetate has been shown to be subject to errors by Marioni 

 and Tasselli in the following respects : 97 



97 Le Stazioni sperimentali agrarie italiane, 1892, 23 : 31. 



