STUDIES OF DIFFUSION THROUGH RUBBER 



MEMBRANES 



4. The comparative diffusibility of various pigments in 



different solvents 



GEORGE D. BEAL and GEORGE A. GEIGER 



{Biochemical Laboratory of Columbia University, at the College of 

 Physicians and Surgeons, New York) 



I. INTRODUCTION 



Dr. Gies and his associates have shown that many biological 

 substances diffuse through rubber under suitable conditions (page 

 55). Inorganic as well as organic substances exhibit this capacity 

 and various colloids share it with crystalloids. Lipochrome and 

 ferric sulfocyanate are among the colored substances which, in the 

 early experiments, were found to be diffusible from ether Solution 

 through rubber membranes into ether. 



At Dr. Gies' Suggestion we undertook a similar study of the 

 diffusibility of common pigments, especially " food colors." Fol- 

 lowing his advice we also sought data which might be of service in 

 devising methods for the purification of pigments, and for their 

 Separation and detection under various circumstances. 



Our diffusion tests were conducted by the following general 

 method: A moderate quantity of the pigment was mixed with 15- 

 25 c.c. of the solvent. The Solution, or Suspension, was carefully 

 poured into a rubber Condom in such a way as to preclude the pos- 

 sibility of overflow upon the external surface. The bag was then 

 immersed in about 50 c.c. of solvent in a narrow salt-mouth bottle 7 

 inches high. With the bag suspended at füll extension in this Posi- 

 tion, its mouth was about an inch above the opening in the bottle. 

 The protruding condom was supported in the neck of the bottle by 

 a tightly fitting cork stopper, which served to keep both the bag and 

 the bottle closed. The diffusion periods varied from a few minutes 

 \o a week or more, according to the obvious requirements in each 

 case for a definite conclusion regarding diffusibility. 



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