660 



REVERSAL BY TRIVALENT CATIONS 



m/1,024 CeCls, so that in regard to CeCls or LaCls the liquid is 

 the same on both sides of the membrane. Any osmotic effect can 

 therefore only be due to the CaCl2. This allows us to investigate 

 the question of the reversal of the sign of charge of the membrane by 

 the Ce ions. Fig. 1 shows that the CeCls can only reverse the sign 

 of charge of the membrane if the latter has previously been treated 

 with gelatin. The lower curve gives the initial rate of diffusion of 

 water (after 20 minutes) into CaCl2 solutions (of different concentra- 



te 



C 

 .9 



09 



CO 



?-. 



4096 2D48 10Z4 512 256 126 64 32 16 8 4 2 



Concentration o[ CaCl^ 



Fig. 1 . Showing that CeCls renders a collodion membrane positive only when 

 it has been treated with a protein, since CaCl2 below m/16 attracts water only 

 when the membrane is positively and the water negatively charged. 



tion) through collodion membranes not treated with gelatin. The 

 membrane is negatively charged since no rise of the level of water 

 in the solution occurs as long as the concentration of CaClo is be- 

 low m/8. The rise of the curve at a higher concentration has a dif- 

 ferent cause which need not be considered in this connection. The 

 upper curve gives the influence of the same CaCl2 solutions on the 

 rate of diffusion of water from pure water into solution when the 

 membrane has previously received a gelatin treatment. In this case 

 the level of liquid rises in the solution and the more so the higher 



