THE ELECTRICAL CHARGES OF MICELLA 151 



ions of the alkali were adsorbed by the colloidal particle in pref- 

 erence to the other ions on account of their greater rapidity of 

 migration; 1 and this idea was also accepted by Perrin 2 in his 

 experiments on electrical endosmose, where it was necessary 

 to account for the fact that certain membranes become posi- 

 tively charged in the presence of acid and negatively in the 

 presence of alkali. Those who accept the adsorption hypothesis 

 explain the fact that the electrical charges of the particles are 

 apparently diminished or destroyed by the addition of a salt on 

 the assumption of a preferential adsorption of one of the ions of 

 the salt by the micellae; yet such an assumption is incompatible 

 with the purely stoichiometrical behavior of proteins. It is 

 also difficult to account on the basis of the adsorption hypothesis 

 for the fact that the addition of little acid increases while the 

 addition of more acid depresses the electrical charge of micellae. 



A second possibility was pointed out by the writer in 1904, 3 

 namely, that Hardy's migration experiments might be explained 

 in the case of proteins by the fact that proteins are amphoteric 

 electrolytes which in the presence of alkali dissociate electro- 

 lytically by giving rise to a protein anion and in the presence of 

 acid giving rise to a protein cation; while at the isoelectric point 

 no protein ion would be formed. This idea could, however, not 

 explain why the addition of a salt in low concentration should 

 diminish the charge of aggregates of ions, i.e., the micellae, except 

 by assuming that in this case the electrolytic dissociation of the 

 protein salts should be repressed. The concentration of salts 

 required for the precipitation of colloidal suspensions is, however, 

 much too small to make such a suggestion acceptable. The 

 idea is, however, correct if applied to the migration of isolated 

 protein ions in the electrical field. 



In 1916 J. A. Wilson 4 suggested that these electrical charges of 

 micellae were caused by the establishment of a Donnan equilib- 

 rium between the colloidal particle and the surrounding solution. 

 There were, however, no measurements of membrane potentials 



1 HARDY, W. B., J. physiol, vol. 29, p. xxvi, 1903. 



2 PERRIN, J., 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. 



3 LOEB, J., Univ. Cat. Pub., Physiology, vol. 1, p. 149, 1904. 



4 WILSON, J. A., J. Am. Chem. Soc., vol. 38, p. 1982, 1916. 



