ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 253 



solute units of the potential into volts it is necessary to multiply 

 by the factor (1/200)2). 



It follows from the above that the velocity of the migration is 

 independent of the size of the particles, which agrees with the findings 

 of Burton"^*^ in colloidal silver solution containing particles of various 

 dimensions. 



We must be warned of an erroneous interpretation of the phenom- 

 enon of electrophoresis. Since it is observed that on the application 

 of an external potential the particles suspended in a hquid move 

 towards one of the poles, it might appear as if every particle behaved 

 as a body carrying a free electric charge and was attracted to the 

 oppositely charged pole, just as a charged hair is attracted towards a 

 charged piece of sealing wax. Such an interpretation would be quite 

 incorrect. The suspended particles, considered as a whole, are 



; + +'{ (X )i +i( CL )i + 



B 



Fig. 28 



electrically neutral, for the charges on the positive and negative 

 double layer are equal to each other. In a certain respect this attrac- 

 tion might be compared rather to that existing between an elec- 

 trically charged piece of sealing wax and an uncharged small metal 

 ball. In the latter case it is said that the metal ball becomes charged 

 or polarized under the influence of the electrical field of the seahng 

 wax. But this comparison is still unsuitable, for our metal ball 

 would be attracted equally well by a positive or a negative pole, 

 while the electrophoretically moving particle always migrates in a 

 definite direction away from one pole and towards the other pole. 

 It has no "free" charge which could be detected by bringing the liquid 

 containing the particles near an electroscope. The external field of 

 force of such a suspension or colloidal solution is naturalh^ equal to 



" E. F. Burton, Phil. Mag. 11, 439 (1906). 



