666 



REVERSAL BY TRIVALENT CATIONS 



To understand this result we must discriminate between the effects 

 of the trivalent cations on the reversal of the sign of charge and on 

 the increase of the rate of diffusion of water into the solution, 

 which seems to be due to an increase in the density of charge of a 

 membrane already positive. On the alkaline side of the isoelectric 



treated with ^ela^tin i 



I 



a 

 o 



3 



CO 



Isoelectric 

 point 



Fig. 5. Although m /256 solutions of La and Ce charge the membrane posi- 

 tively on the alkaline side of the isoelectric point of gelatin, their attraction for 

 water rises very steeply on the acid side of the isoelectric point of gelatin. 



