148 C. J. MARTIN. 
This is accomplished by using the candle of a Pasteur-Chamberland 
filter as the scaffolding to hold the gelatin. 
The apparatus consists of — 
(1) A steel cylinder containing compressed air. 
(2) A pressure gauge, T junction, and connections of copper 
piping. 
(3) A gun-metal case to hold the filter, tinned inside. 
(4) A Pasteur-Chamberland filter, the pores of which have 
been filled with gelatin or gelatinous silica. 
The filters are securely fixed into the case by pressing the flange 
on them tightly against a rubber washer resting upon a small 
platform in the end of the filter case. On the outer surface of 
the flange is another rubber washer and then 
a disk of metal with a central aperture to 
allow the spout of the filter to project. This 
disk has five holes near its circumference 
through which screws pass to be inserted 
into a projecting rim on the end of the filter 
case.. When these are screwed home the 
flange is compressed between the washers and 
forms a tight joint. (Vide figure in text). 
A membrane of gelatin in the pores of 
the filter is produced, by first filtering 4 
hot 10% solution of gelatin through them, 
allowing the gelatin to set and subsequently 
washing the excess from the outside and 
inside of the filter with hot water. <A 
membrane of silicic acid is made by first 
sucking a solution of sodium silicate through 
the filter and afterwards converting this 
into gelatinous silica by immersing the filter 
in 2% hydrochloric acid for a couple of days. 
Either film entirely prevents the following substances from 
passing through : 
