THE METHOD OF PELLET 129 



molybdate, containing 1 10 grams of molybdic acid dissolved in 

 400 cubic centimeters of ammonium, 0.96 specific gravity, and 

 the solution poured slowly into 1500 cubic centimeters of nitric 

 acid of i. 20 specific gravity. The solution is cooled to about 

 70 and allowed to rest for 15 to 30 minutes. The precipitate 

 sinks very rapidly, leaving a perfectly limpid liquid. The greater 

 part of the liquid is siphoned off from the precipitate, which 

 is afterwards put on a filter and washed two or three times with 

 water containing one per cent, of nitric acid. The phospho- 

 molybdate of ammonium is then ready to be dried. 



All these operations require very little time because the pre- 

 cipitate is already freed from its mother liquors by the liquids 

 which have been used for washing out the flasks. 



The precipitate, after removing from the funnel, is first 

 placed on filter paper, with care so as not to break the paper, and 

 is afterwards transferred to the drying oven where it is dried 

 for two hours at a temperature of from 105 to 110, as above 

 described. 



The different factors which should be used for calculating the 

 amount of phosphoric acid from the weight of phosphomolyb- 

 date vary among different authors and the factor finally selected 

 is 0.0375, which is only slightly different from that proposed by 

 Boussingault, i. e., 0.0373." 



115. The Method of Pellet. In 1887 Pellet proposed to the 

 French chemists the method of determining phosphoric acid by 

 weighing ammonium phosphomolybdate, and this method has 

 been employed by a certain number of chemists in France since 

 that time. 1 Pellet is led to believe from the results of his in- 

 vestigations that, when precipitated in the presence of a citrate, 

 ammonium phosphomolybdate is of constant composition and 

 can be accurately dried and weighed on tared filter paper. The 

 factor used for calculating the phosphoric anhydrid is O.O374. 2 



Atti del VI Congresso inter uazionale di Chimica applicata, Roma, 

 1906, 1 : 64. 



1 Atti del VI Congresso internazionale di Chimica applicata, Roma, 

 1906, 1 : 321. 



2 Bulletin del' Association des Chimistes de Sucrerie et de Distillerie, 

 1906-07, 24 : 525. 



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