THE ELECTRICAL CHARGES OF MICELLAE 165 



apparently not due to a change in the pH since it occurred also 

 when the salt solution was buffered by the addition of a mixture 

 of Na acetate and acetic acid. 1 Perrin had noticed in his experi- 

 ments on electrical endosmose 2 that salts with trivalent cations 

 reversed the sign of charge of negatively charged membranes and 

 that tetravalent anions reversed the sign of charge of positively 

 charged membranes. 



As a possible explanation the writer suggested a loose combina- 

 tion between isoelectric gelatin and the salts with trivalent cations 

 or tetravalent anions, resulting in the formation of complex and 

 positively charged gelatin-Ce or gelatin-La ions or negatively 

 charged gelatin-Fe(CN) 6 ions. In other words, salts with 

 trivalent (and tetravalent?) cations would react with isoelectric 

 gelatin somewhat like acids, and salts with tetravalent anions 

 would react somewhat like alkalies, the former causing the forma- 

 tion of positively charged complex protein ions, the latter 

 causing the formation of negatively charged complex protein 

 ions, with this difference, that the protein-acid salts and metal 

 proteinates are much more stable than the complex salts formed 

 with trivalent cations and tetravalent anions. The result would 

 in both cases be the ionization of the protein salt, resulting in a 

 Donnan equilibrium and P.D. between solid protein and water. 



It should be added that the experiments in Chap. II show 

 that the Ce or Fe(CN) 6 ions can be washed away very easily, so 

 that their compounds with gelatin differ in this respect from the 

 compounds of gelatin with acid or alkali. 



The tendency of proteins to form durable films when in contact 

 with solid bodies probably explains the phenomenon that the 

 addition of a little gelatin keeps coarser particles in suspension 

 which without the gelatin would rapidly settle. If in this case 

 the gelatin forms a solid film on the surface of the particle the 

 latter will assume an electrical charge as long as the liquid has a 

 pH different from 4.7; since as long as the pH is either less or more 

 than 4.7 the P.D. between water and the gelatin-coated particles 

 will keep the latter from settling. When, however, the pH is 

 4.7, this protective influence of the gelatin must disappear. 



iLoEB, J., J. Gen. Physiol, vol. 4, p. 463, 1921-22. 

 2 PERRIN, J., /. chim. physique, vol. 2, p. 601, 1904; vol. 3, p. 50, 1905. 

 Notice sur les titres et travaux scientifiques de M. Jean Perrin, Paris, 1918. 



