METHODS OF COLLOID RESEARCH 



91 



FIG. 10. A fish bladder 

 (condom) dialyzer. 



glass rods are laid over a tall narrow beaker, in which the water is 

 placed. Parchment tubes are suspended in a similar manner. To 

 avoid tying one end of the tube, it is hung up in U-fashion so that 

 both open ends are pressed together by the glass rods (see Fig. 10). 



Precautions: In filling and hanging the parchment tubes the air must be en- 

 tirely pressed out before fastening the ends, for should water dialyze in, consider- 

 able pressure will develop, which may burst the mem- 

 brane. All the precautions given on page 90 must be 

 observed (degreasing, absorption, etc.). 



Excellent dialysis membranes may be pre- 

 pared of collodion or glacial acetic acid-collo- 

 dion. Their great advantage is that they 

 may be prepared in any desired size, shape 

 and degree of permeability, and are easily 

 sterilized. 



As an example, we shall explain how to 

 make one such membrane. A test tube is 

 dipped into collodion and then allowed to drip, 

 being twirled meanwhile, and when it has skinned 

 over, the whole tube is quickly immersed in 

 water. In a short time, the tube is circumcised 

 at a height which will give a membrane of the 

 desired length; with a little practice, the membrane can be removed 

 from the tube with ease. The membrane may be formed inside the 

 tube also by rinsing the test tube with collodion or glacial acetic 

 collodion and then filling it with water. In a similar manner, spher- 

 ical or cylindrical membranes of 30 .to 40 cm. long and 10 cm. 

 diameter may be made (see Fig. 11). Such sacs may be fastened 

 to a glass tube with thread or collodion so as to form a water- 

 tight joint. The membranes are best preserved in water to 

 which a little chloroform has been added to prevent the growth of 

 moulds. 



In making his collodion sacs, G. MALFITANO 1 uses glass tubes of the 

 shape shown in the accompanying diagram, which are rotated by a 

 motor to secure uniform drying. The spherical swelling affords an 

 easier removal of the rim (see Fig. 12). After the cut is made 

 through the collodion skin at the equator of the sphere ( ), it is 

 carefully loosened from the glass and turned inside out or the rim is 

 fastened to a large glass tube which is exhausted, thus the skin is 

 loosened from the spherical portion. J. DUCLAUX uses very thin 

 tubes, about 1 cm. in diameter and 1 meter long, so as to get the 

 largest possible surface. 



1 According to a personal communication. 



