EXAMINATION OF COMMERCIAL FERTILIZERS 137 



as recommended for the determination of total 

 phosphoric acid. 



With phosphatic slags the first hydrochloric 

 acid solution should be evaporated to dryness 

 in order to remove the silica (which would other- 

 wise appear in gelatinous form). Before pro- 

 ceeding with phosphate rock, the proportion of 

 iron and alumina oxides is of much importance 

 on account of their tendency to afford the so- 

 called "reduced phosphate" in the finished prod- 

 uct. A good method consists in dissolving the 

 sample in aqua regia, adding sulphuric acid, 

 and then a large excess of alcohol, which pre- 

 cipitates the calcium sulphate. In the clear 

 alcoholic solution the iron and alumina, as 

 phosphates, may be determined. 



Another plan affording good results when 

 carefully conducted would be to dissolve 2.5 

 gms. of the material in 10 cc. of hydrochloric 

 acid and 1 or 2 cc. of nitric acid. Then add 10 

 cc. of concentrated sulphuric acid, mix in well, 

 and add strong alcohol, 90 per cent or over, 

 in sufficient quantity to bring the bulk of the 

 solution, when well mixed and cold, up to 250 

 cc. Shake well, and allow to settle for 30 to 60 

 minutes. Then filter off rapidly 200 cc. (represent- 

 ing 2 gms.), neutralize very exactly with am- 

 monia, boil out the alcohol, avoiding evapora- 

 tion to dryness, and then render alkaline with 

 a little ammonia, boil and filter. The precipitate, 

 consisting of iron and alumina phosphate, is 



