io8 



PHYSICAL CHEMISTRY 



ently zinc ions cannot reverse the charge of the porcelain. The 

 author observed that if a concentrated solution of zinc sulphate 

 were placed on each side of a porcelain membrane (kindly loaned 

 by Dr. Bartell) and an electric current passed, water was drawn 

 through the membrane to the cathode by electroendosmose. This 

 showed that the water was charged positively, and the water on 

 passing through capillary spaces always takes the opposite charge 

 to the charge of the walls. 



©-V+ 



+ + 





I 



•*■ , I 



+ J I 



+ ' '. 



Fig. 27. Scheme showing the mode of diffusion of anions through a 

 large pore in a negatively charged membrane, thus causing negative os- 

 mose by electroendosmose. 



Bartell and Hocker explain negative osmose as electroendos- 

 mose. Since the dilute side becomes charged negatively, it pulls 

 the positively charged water through the membrane, causing the 

 flow to be toward the dilute side. 



In Fig. 27 is represented a negatively charged membrane with 

 a large pore. If the pore were small a negative ion could not 

 enter it since it would be repelled by the negative charge of the 

 walls. If cations pass through small pores they tend to make 



