96 



COLLOIDS IN BIOLOGY AND MEDICINE 



Since some may desire to make the filters, brief direction for doing 

 so are given. 1 



The most useful kinds of filter paper are No. 566 and No. 575 of 

 SCHLEICHER and SCHULL. These are cut into discs of 9 cm. in 

 diameter and impregnated with the jellies under atmospheric pres- 

 sure in a glass trough from which the air has previously been ex- 

 hausted, making a vacuum. 2 



The square trough T (see "Fig. 15) has its cover ground airtight. 

 On the cross bar B a number of filter papers are suspended. The 

 cover C has two openings; through No. 1 pass two tubes, one of 

 which leads to the air pump A and the other to the pressure gauge 



FIG. 15. Trough for the preparation of ultrafilters. (H. Bechhold.) 



m. When the air is exhausted from the trough, the fluid jelly is al- 

 lowed to enter through the funnel F, which has a cock and a tube 

 leading to the bottom, until sufficient is admitted to cover the filters. 

 Then the valve leading from the funnel is closed and the valve 

 through which the air was exhausted is opened so that the jelly is 

 forced into the filters under atmospheric pressure. After a time 

 (with diluted jellies 10 to 20 min. with concentrated jellies one or 

 two hours) the cover is taken off and the rod with the filters is re- 

 moved from the fluids. While the filters are draining, they are 

 constantly shaken. Finally the whole filter is rapidly gelatinized by 

 plunging it into a suitable fluid. In the case of glacial acetic acid 



1 Given in detail in the original paper of H. Bechhold.* 4 



2 May be obtained from the Vereinigten Fabriken fiir Laboratoriumsbedarf, 

 Berlin. 



