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COLLOIDS IN BIOLOGY AND MEDICINE 



side. This process is called electro-endosmosis. In principle the two 

 phenomena are the same. For the exact study of electrical migra- 

 tion, which was first investigated by G. WIEDEMANN and G. QUINCKE, 

 electro-endosmosis proved to be experimentally more easily avail- 

 able. A. COEHN * has shown that it is a general and quantitative law, 



FIG. 8. Apparatus for electro-endosmosis. (H. Freundlich.) 



that substances possessing higher dielectric constants are positively 

 charged when brought into contact with substances of lower dielectric 

 constants. 



We have already seen that numerous substances are negatively 

 charged in respect to water while others are positively charged and 

 that under the influence of the electric current there occurs a move- 

 ment of the suspended substance or of the water. This migration 

 may be influenced by the addition of electrolytes. J. PERRIN used 

 diaphragms of porous carborundum and of naphthalin and measured 

 the amount of water which passed through the porous wall by -en- 

 dosmosis, under the influence of an electric current. 



In the following table + indicates passage to the positive, to 

 the negative pole. 



1 I tried to cause naphthalin suspensions to migrate in strong currents (400 volts) but could not 

 observe any cataphoresis either in neutral, in acid or in alkaline solution. Nor could I obtain a 

 migration of suspensions of naphthol and naphthylamin in neutral, very faintly acid or very faintly 

 alkaline solution (hitherto unpublished). 



