OPTICAL AND ELECTRICAL PROPERTIES OF COLLOIDS 79 



It follows from this that the negative charge of negative diaphragms 

 (as is evident from the table) increased in alkaline solution. With 

 a decrease in the OH ion concentration (with naphthalin) or the in- 

 crease in the H ion concentration (with carborundum) a point was 

 reached in which there was no difference in potential between water 

 and diaphragm. With further increase in the H ion concentration 

 the diaphragm took on a stronger positive charge. 



If a positive diaphragm is chosen, as for instance chromium chlorid, 

 the conditions are reversed. 



J. PERRIN studied the influence of salts in the presence of acids 

 and bases. It was shown that they cause a loss of charge with moder- 

 ate concentrations and, in fact, that the strength of their action de- 

 pended, in the case of positively charged diaphragms, upon the 

 valence of the anions, while in the case of negatively charged dia- 

 phragms it depended upon the valence of the cations. With higher 

 concentration of polyvalent anions or cations a loss of charge may 

 occur. 



Upon calculating the concentration of salt which just halves the 

 amount of fluid (v in mm. /minutes) transferred, the following figures 

 were obtained: 



The last column - shows us that the discharging effect increases 



with the valence of the anions as 1 : 25 : 500 and in the case of 

 cations as 1 : 60 : 600. In the section on " flocculation, " we shall 

 see a very remarkable application of this phenomenon. 



Of the many theories proposed to explain these circumstances, 

 that of H. FREUNDLICH and L. MICHAELIS, according to which the 

 various ions are adsorbed to different degrees, seems to us most prob- 

 ably correct; in point of fact, the H and OH ion have especially 

 high adsorption coefficients. Since a separation of anion and cation 

 usually cannot occur, there arises a difference in potential at the 

 surface between the dispersed phase and the water. An indifferent 

 substance in a weakly acid solution will adsorb H ions and become 



