5". L. Jodidi and E. H. Kellogg 



93 



TABLE 2 



Data pertaining to the comparative cfficicncy of the ptilp filter and the folded 



filter. {See also Table i) 



the ammoniiim-phosphomolybdate precipitate, which is not abso- 

 lutely insoluble in water. Inasmuch as the employment of the pulp 

 filter enables one to accompHsh both the isolation of the yellow pre- 

 cipitate, and its purification by washing with a small cjuantity of 

 water, in but five minutes, it was reasonable to asstime that the 

 results would be the same whether the yellow precipitate is washed 

 with ice-cold water or with water at room-temperature. Flimmer 

 and Bayliss^^ expressed the opinion that, with rapid filtration of the 

 yellow precipitate by means of a special pattern of filtering tube, it is 

 imnecessary to wash the yellow precipitate with ice-cold water. They 

 did not give any data confirming their viewpoint, however. Below 

 are reported the results of a number of phosphoric-acid estimations in 

 which the yellow precipitates were washed either with ice-cold water 

 or with water at room-temperature. The phosphate sol. contained 

 15 gm. of disodium hydrogen phosphate in 5 liters of water. All 

 of the yellow precipitates, prepared in the manner mentioned above, 

 were, after filtration, washed with 25 c.c. of distilled water; the 

 washing was repeated twice. The results are summarized in 

 Table 3. 



A glance at Table 3 shows that the yellow precipitates washed 

 with ice-cold water required for their neutralization 5.03 c.c. of n/2 

 sodium hydroxid sol. (total average), while the yellow precipitates 



1* Plimmer and Bayliss : Loc. cit. 



