BRIEFER ARTICLES 
THE USE OF CELLOIDIN MEMBRANES FOR THE DEMON- 
STRATION OF OSMOSIS 
(WITH THREE FIGURES) 
Although the value of a celloidin film as an osmotic membrane is 
well known to botanists, little use of it has been made on account of 
the difficulties experienced in manipulation. A description of the 
method heretofore employed can be found in most textbooks on bacteri- 
ology. In this method, a celloidin solution is poured into a test tube 
or an Erlenmeyer flask and carefully rotated until a film which can be 
lifted out is formed on the inside of the tube, the sac thus formed being 
used as the membrane. Another method of preparing celloidin mem- 
branes, first described by BicELow and GEMBERLING,' is generally 
unknown to botanists, although considerable use has been made of it 
by chemists. This method consists in pouring a celloidin solution on a 
clean mercury surface from which the membrane thus formed is removed 
after the celloidin has sufficiently hardened. I have found that a three- 
inch Petri dish forms a very convenient container for the mercury. 
After carefully cleaning the surface of the mercury, enough ro per cent 
celloidin solution is poured on it to cover an area 3-4 cm. in diameter. 
In 2-5 min. the ether and alcohol have evaporated sufficiently to allow 
the membrane to be lifted. It is important that the celloidin film be 
“ripe” before attempting to lift it; otherwise a stringy mass will be 
formed instead of a sheet. As soon as its edge appears scalloped and the 
surface shows small polygonal patches, the film can be raised. Its 
general appearance at the time it is “ripe” enough to be taken off is 
shown in fig. 1. 
The best support for the osmotic membrane prepared as described 
above is the bulb of a thistle tube having a stem a half-inch in length, a 
thistle tube with a shortened stem being much more easily filled. It can 
be held in a test tube rack or in a small-necked bottle with the opening of 
the bulb uppermost and the celloidin membrane placed over its open 
end (fig. 2,4). The overlapping portion of the membrane should then 
be pressed to the sides of the flange of the bulb and tied securely with 
* BIGELow, S. L., and GEMBERLING , A., Collodion membranes. Jour. Am. Chem. 
Soc. 2921576-1599. 1907. 
225) [Botanical Gazette, vol. 56 

