92 



A Simple, Efficient, and Economic Filter 



In eight portions of the same sol. (25 c.c. each) the phosphorus 

 was precipitated as ammonium phosphomolybdate, which was fil- 

 tered (and washed) on a 12.5 cm. folded filter in accordance with 

 the directions given by Neumann. The resuhs are recorded in the 

 accompanying table (i). 



TABLE I 



Data pertaining to the comparative efficiency of the pulp filter and the folded 



filter. (See also Table 2) 



In nineteen other portions of the same sol. (25 c.c. each) the 

 yellow precipitate was filtered through a pulp filter prepared in the 

 manner already described. (During filtration and the washing of 

 the ammonium-phosphomolybdate precipitate, gentle suction must 

 be maintained, otherwise the pulp filter would be packed down 

 too tightly and filtration retarded.) Unlike filtration through a 

 folded filter, where decantation takes place, practically all of the 

 yellow precipitate was thrown on the pulp filter, whereupon the 

 precipitation flask was washed with about 25 c.c. of distilled water, 

 which was filtered through the pulp. This was repeated twice. 

 The last washings were always found to be neutral. The further 

 treatment of the washed yellow precipitate was exactly as outlined 

 elsewhere,^^ with the only difiference that no blanks were subtracted 

 from the n/2 sodium hydroxid sol. used for the neutralization of 

 the yellow precipitates referred to in the accompanying three tables. 

 Table 2 presents our data in this connection. 



A glance at Tables i and 2 shows that the work with the pulp 

 filter gave results as accurate as those with the paper filter, and 

 required considerably less labor and time. 



Neumann^^ laid stress on the use of ice-cold water for washing 



i2Jodidi and Kellogg: Jour. Frankl. Institute, 180, 349 (1915). 

 13 Neumann : Z. physiol. Chem., 37, 132 (1902-03). 



