788 



THE MECHANISM OF AGGLUTINATION 



STABILITY AND CHARGE 



Whatever the source of the potential on the particles, it follows that similarly 

 charged particles would tend to repel one another and thereby render the suspension 

 stable. If, however, the particle as a whole is electrically neutral, this repulsion would 

 not obey Coulomb's inverse square law, but would become effective only when the 

 particles approached one another so closely that the outside of the double layers over- 

 lapped. This conclusion is borne out by Perrin's observation' that the distribution 



TABLE I* 



* Powis, F.: Zlschr.f. phys. Cliemie, 89, 191. 1914-15. 



of charged particles is abnormal when the distance beween them is less than about 

 1.7 times the radius. When the charge is removed, this anomalous distribution dis- 

 appears. This experiment furnishes strong evidence that the particles are held apart 

 by their electric charge. 



It was first noted by Hardy' that suspensions of denatured proteins were most un- 

 stable at the isoelectric point, and he suggested that this was due to the fact that they 

 were electrically neutral at this point. This conclusion was verified qualitatively by a 

 large number of workers.-' A number of cases were found, however, in which there 

 seemed to be no direct connection between the stability and the potential. 



Ellis^ made a number of measurements on oil emulsions and found that the stabil- 



■ Perrin, J.: Compt. rend. Soc. de bioL, 158, 116S. 1914. 



2 Hardy, W. B.: Proc. Roy. Soc, 66, no. 1900. 



3 Burton, E. F.: op. c'U., p. 149. 1921. 



" Kllis, R.: Zlschr.f. phys. Chemic, 78, 321. 1911-12; 80, 597. 1912. 



