THE ORIGIN OF THE ELECTRICAL CHARGES OF 



COLLOIDAL PARTICLES AND OF 



LIVING TISSUES. 



By JACQUES LOEB. 

 (From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, November 19, 1921.) 



I. Stability of Suspensions, Electrical Charges of Micelles, and Donnan 



Equilibrium, 



The stability of suspensions is, perhaps, the chief problem of a theory 

 of colloidal behavior. Hardy has shown that this problem is linked 

 with the problem of the origin of the electrical charges of the particles 

 in suspension (which we will term micellae, when they consist of 

 aggregates of ions or molecules) inasmuch as the micellae carrying a 

 sufficiently large electrical charge will be forced by mutual electro- 

 static repulsion to stay in suspension. By his experiments on the 

 migration of suspended particles of coagulated white of egg in an 

 electrical field he proved that they have a positive charge in the 

 presence of acid, a negative charge in the presence of alkali, and no 

 charge at an intermediate point which he termed the isoelectric 

 point of the particles. He was able to demonstrate that the 

 stability of colloidal suspensions is a minimum at the isoelectric 

 point. 1 



He and others found, moreover, that low concentrations of neutral 

 salts diminish the stability of colloidal suspensions in the presence of 

 acids or alkalies and that the efficient ion of the salt has the opposite 

 sign of charge from the colloidal particle; since the precipitating 

 efficiency of a salt increases rapidly with the valency of that ion of 

 the salt which has the opposite sign of charge from the colloidal 

 particle. It seemed natural to infer that the precipitation of colloidal 



' Hardy, W.B., Proc. Roy. Soc. London, Series B, 1899-1900, Ixvi, 110; J. 

 Physiol., 1903, xxix, p. xxvi. Wood, T. B., and Hardy, W. B., Proc. Roy. Soc. 

 London, 1909, Uxxi, 38. 



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