S. L. Jodidi and E. H. Kellogg 91 



washing, no bluish color (due to slight reduction) appears, so that 

 the endpoint of the titration of the ammoniiim phosphomolybdate 

 can be ascertained much more distinctly. 



ECONOMY OF THE PAPER PULP FILTER. Ten S. & S. filtcrs, 12. 5 



cm. in diameter, were shaken with about 1200 c.c. of distilled water^ 

 and the resultant pulp used for the filtration of yellow precipitates 

 obtained in a definite way.^^ It was found that the pulp was suffi- 

 cient for the filtration of 42 individual precipitates of ammonium 

 phosphomolybdate. Another lot of ten filters, reduced to pulp, gave 

 exactly the same result. In other words, ten filters which, when 

 used as such, would sufiice for ten analyses only, were, in the form 

 of pulp, sufiicient for 42 analyses — a reduction in the use of filter 

 paper to 2 1 .4 percent. The actual saving is greater, however, when we 

 consider that filters, in order to be fit for use in quantitative analysis, 

 must be faultless, which they sometimes are not. On the other 

 hand, paper pulp, when used for Volumetrie analysis, may be made 

 of any filter paper; for instance, of broken and faulty filters, of 

 sheet filter-paper, of filter-paper waste, etc. Only when the paper 

 pulp is to be employed for gravimetric analysis is it advantageous to 

 prepare the pulp from ashless filter-paper. 



When this paper was ready for publication we noticed an article 

 by Raper,^^ who mentioned, in but three sentences, the employment 

 of a pulp filter for the Separation of the ammonium-phosphomolyb- 

 date precipitate. 



Below are given the results of phosphoric-acid estimations show- 

 ing how completely the ammonium-phosphomolybdate precipitate is 

 retained by the pulp filter, despite the fact that the filtration of the 

 yellow precipitate and its repeated washing on the pulp takes only 

 about five minutes. 



Ten grams of crystallized disodium hydrogen phosphate were 

 dissolved in water and made up to 5 liters. Of this sol. four por- 

 tions (250 c.c. each) were analyzed gravimetrically. They were 

 found to yield 0.1756, 0.1754, 0.1757 and 0.1753, respectively, with 

 a mean of 0.1755, gm. of magnesium pyro-phosphate, which is 

 equivalent to 0.1955 mg. of phosphorus per c.c. of sol. 



i*' Jodidi: Jonr. Amer. Chem. Soc, 37, 1709 (1915). 

 iiRaper: Biochcm. Jour., 8, 652 (1914). 



