24O AGRICULTURAL ANALYSIS 



1. The precipitation of a small quantity of calcium phosphate 

 with the ferric and aluminum phosphates. 



2. The possible precipitation of basic phosphates if all the 

 iron and alumina are not combined with phosphoric acid in the 

 mineral. 



3. The partial solubility of ferric and aluminum phosphates 

 in dilute acetic acid. 



4. The decomposition of ferric orthophosphate into soluble 

 acid phosphate and insoluble basic salt by washing with boiling 

 water. 



To avoid these errors the following procedure is proposed : 

 From one to five grams of the sample according to its richness 

 in phosphoric acid is boiled in a flask for 10 minutes with 15 

 cubic centimeters of strong hydrochloric acid, and afterwards 

 diluted with a double volume of water. A few crystals of potas- 

 sium chlorate are added, or several drops of nitric acid, and the 

 liquid boiled to expel chlorin. The solution is filtered and the filter 

 washed until the volume of the filtered liquid amounts to 150 

 cubic centimeters. After cooling, a half-gram of neutral ammo- 

 nium phosphate in solution is added, and two cubic centimeters 

 of glacial acetic acid, followed by ammonia, drop by drop, until 

 a slight precipitate persists on stirring. The mixture is made 

 decidedly alkaline by adding ammonia gradually until the alkaline 

 reaction is established. Again the same quantity of acetic acid 

 is added as above, well shaken, and left for two hours. The pre- 

 cipitate is collected on a filter and washed with a 10 per cent, 

 ammonium phosphate solution. The precipitate is dissolved by a 

 minimum quantity of hydrochloric acid and the solution collected 

 in the same vessel in which the precipitation took place. A 

 second precipitation is conducted just as described above. The 

 precipitate is washed as above described and ignited at a dull red 

 heat. Half the weight obtained represents the ferric oxid and 

 alumina. 



Following these variations, in which the principal novelty is the 

 solvent action on the mixed precipitates produced by ammonia, 

 by which all are dissolved save the iron and aluminum phosphates, 

 the authors claim to get accurate results. 



