484 



ELECTRICAL CHARGES AND ANOMALOUS OSMOSIS 



protein in the way suggested, thereby giving rise to a double layer in 

 the pores in which the gelatin is positively and the liquid negatively 

 charged. Table VIII shows that at pH 4.7 there is a high p.d. across 

 the membrane in which the Ce(N03)3 solution assumes a positive 

 charge. If now the liquid inside the pores is negatively charged an 

 electrical transport of water from the water side into the solution must 

 occur. 



A comparison of the transport curve for Ce(N03)3 of pH 4.7 in 

 Fig. 6 with that in Fig. 4 shows that the latter is higher. This finds 

 its explanation in the fact (evident by a comparison of Tables VIII 

 and VII) that the p.d. across the membrane, i.e. the value E, is less 

 in the experiment with buffer salt in Fig. 6 than without it in Fig. 4. 



TABLE VIII. 

 P.D. in millivolts across the collodion-gelatin membrane between solutions of 

 Ce(N03)3 made up in buffer solution, and buffer solution free from Ce(N03)3. 

 The Ce(N03)3 solution is always positively charged. 



The transport curve at pH 3.4 is higher than at pH 4.7 and the 

 transport curve at pH 5.6 is lower than at pH 4.7 (Fig. 6) . Table VIII 

 shows that this finds its explanation in the fact that the p.d. across the 

 membrane varies correspondingly with the pH. 



As a consequence it seems possible that the Ce(N03)3 causes the 

 positive charge of gelatin by forming a dissociable salt with gelatin in 

 which the positive ion is a complex gelatin-Ce ion. In other words, 

 the salt reacts with isoelectric gelatin in a similar way as acid does. 

 If this assumption is correct the p.d. between gelatin and bounding 

 Ce(N03)3 solution must be ascribed to a Donnan equihbrium, in which 

 the Ce(N03)3 plays a similar role as the HCl. 



The difference between gelatin chloride and the hypothetical gela- 

 tin-Ce (NO3) 3 salt is this that it is much easier to remove by washing 

 the Ce(N03)3 from powdered gelatin than it is to rem.ove the HCl. 



