368 EXPERIMENT STATION RECORD. 



described above, care beiii<;' taken to prevent ])recipitation of gypsum 

 on tlie iilter wlien examining sn])eri)liospliates. Tlie residue on the 

 filter is washed until the filtrate amounts to at least HOO cc. The filter 

 with its contents is then brought into a 250 cc. flask containing 100 cc. 

 of Petermann's alkaline ammonium citrate, thoroughly shaken, allowed 

 to stand for 15 hours in the cold, and then digested for 1 hour in a 

 water bath at 40° 0. A few drops of hydrochloric acid are added to 

 the water solution and the flask filled to the mark (250 cc. ?). After 

 cooling, tlie flask containing the citrate solution is also filled to the 

 mark. The solution is ])assed through a, filter and 50 cc. mciasurcd out 

 into a beaker, with a pipette for the determination. An equal amount 

 of the water solution is measured out in the same way. Both beakers 

 are then iflaced in a mechanical stirrer aud 35 cc. of magnesia mixture, 

 drop by drop, and 10 cc. of ammonia are added. The stirring is con- 

 tinued for 25 minutes. When the ])re(-ipitates have settled the solu- 

 tions are filtered and the precipitate is washed with 2.5 per cent 

 ammonia until free from chlorids, ignited first over a simple burner, 

 then over a blast lamp, aud weighed. 



Dctcrmhuitlon of the relative assiniilahiliti/ of crude phosphates. — The 

 Congress requested the experiment stations to study this subject. 



Determination of iron and alumina in crude phosphates. — The Congress 

 urred the use of a uniform method and adopted that of Crispo, which 

 has given concordant results. This method is carried out as follows: 

 Five grams of phosphate is dissolved in aqua regia (40 cc. of HCl of 1.1 

 sp. gr. aud 10 cc. of UNO) of 1.2 sp. gr.) and the solution made up to 

 500 cc. To 50 cc. of this solution 2 cc. of ammonia (0.90 sj). gr.) is added 

 (leaving the solution still acid) and finally 50 cc. of half saturated 

 ammonium chlorid. The solution is then boiled aud if it becomes 

 cloudy it is cleared up with a few drops of nitric acid. Ten cubic cen- 

 timeters of ammonium acetate solution (1.106 sp. gr.) is now added, the 

 solution ])oiled 2 or 3 minutes, cooled, and filtered. The i)recipitate 

 thus obtained is washed twice with dilute ammonium chlorid solution 

 (j^q), dissolved in 2 cc. nitric acid, aud the filter washed out with hot 

 water. The ])hosphoric acid is i)recipitated with about 40 cc. of 

 molybdic solution, the solution filtered, and the precipitate washed 3 or 

 4 times with 1 per cent nitric acid. Fifty cubic centimeters of half 

 saturated ammonium chlorid solution and a slight excess of ammonia 

 are added to the filtrate, the solution is heated a few minutes aud 

 filtered, and the i)reci})itate washed 3 or 4 times Avith hot water. The 

 precipitate is again dissolved in 2 cc. of nitric acid and the filter washed 

 out with hot water. To tlie solution thus obtained 50 cc. of ammonium 

 chlorid solution and a slight excess of ammonia- are again added with 

 heating. The preci])itate is collected on a filter washed with hot water, 

 ignited, and weighed. 



The determination of nitrogen in nitrates and nitrogen deriva- 

 tives in the wet "way, M. KrijctER {Ber. deut. ehem. Ges., 27 {1894) 



