88 A Simple, Efficient, and Economic Filter 



duction of which meant marked progress in analytical chemistry. 

 The use of the Gooch crucible in connection with the asbestos filter 

 enables one to save time and labor, and also to obtain very accurate 

 results. A disadvantage, however, lies in the fact that the prepara- 

 tion of a good asbestos filter requires some skill and presumes the 

 use of asbestos that is soft, long-fibred and cut into uniform, small 

 pieces, etc. The paper-pulp filter, on the other band, is exceedingly 

 easy to prepare, being so efficient and economic that it seems worth 

 while to describe it in some detail. 



Preparation of filter-paper pulp. When good filter paper 

 is at band, such as ashless filter paper washed with hydrochloric and 

 hydrofluoric acids, Swedish or S. & S. filter paper, all that is neces- 

 sary is to transfer some of it to a flask, to add a sufficient quantity 

 of distilled water, and to shake the stoppered flask vigorously for a 

 minute or two. The paper is now reduced to pulp (it appears to the 

 naked eye to consist chiefly of separate or coherent fibers and of 

 flake-like fragments), which is ready for immediate use. In case 

 the pulp is too thin or too thick, it can easily be corrected by pouring 

 off some of the supernatant liquid, on standing, or by adding more 

 distilled water and shaking until a Suspension of the desired con- 

 sistency is obtained. We have found that by using a S. & S. filter, 

 12.5 cm. in diameter, 100-150 c.c. of distilled water is the proper 

 amount to apply for the reduction of the paper to a Suspension with 

 which it is easy to make a good pulp-filter. In other words, one 

 I sq. c. of filter paper of ordinary thickness requires about i c.c. of 

 water for its reduction to a well filtering pulp. 



If only common filter paper is at band, and it is desirable to free 

 it from some of its mineral constituents, it is first reduced to pulp 

 with distilled water, whereupon mineral acid, usually hydrochloric 

 or nitric, is added, to a conc. of from 2 to 10 percent. The acid- 

 containing pulp is allowed to stand at room-temperature for an hour 

 or more, depending on the conc. of the acid and the object sought. 

 The pulp is now thrown on a large porcelain filter-plate, or, most 

 conveniently, on a Buchner funnel, and washed free from acid with 

 distilled water. The washed pulp is transferred to a flask where, on 

 mixing with the necessary amount of distilled water, it is kept ready 



