623 



Chemistry. — ''Electric charge and limit value of Colloids". By 

 Dr. H. R. Kruyt. (Communicated by Prof. Ernst Cohen). 



(Communicated in the meeting of June 27, 1914). 



1. The present conception as to tlie relative stability of the sns- 

 pensoid system and the way in which it may be suspended has been 

 developed according to the following train of thoughts. 



Hardy ^) and afterwards Burton ') have undoubtedly established 

 the fact that this relative stability falls and stands with the electric 

 charge of the suspended particle. Indeed, the permanently suspended 

 particle that exhibits a vivid Brown's motion, has a cataphoretic 



mobility of the order 2 — 4 jt per second and per — ^ ;if byaddition 



of an electrolyte one diminishes the relative stability, this velocity 

 also deci-eases and therefore, the electric charge of the particle has 

 evidently decreased also. The "iso-electric" point, where that charge 

 seems to have become zero, coincides with (he moment of the small- 

 est stability. Since the research of Whitney and Ober ^) we know 

 moreover, that with the repeal of the stability (the coagulation) is 

 coupled a combination of the coagulating ion with the particles, and 

 by Freundlich's ^) researches we arrived at the knowledge that these 

 phenomena are described quantitatively by the equation of the 

 adsorption-isotherm. 



Fi'om these elements is built up the theorj^ that the particle owes 

 its charge to the selective ion-absorption in its boujidary layer and 

 loses it by t^e selective adsorption of the oppositely charged ion of 

 the coagulating electrolyte. As specific properties of the adsorbent are 

 usually of but very subordinate influence on the order of the charac- 

 terizing quantities in the adsorption, the action of diverse electro- 

 lytes on all capillaiT-electric phenomena ought to exhibit the same 

 order, which the researches as to the electro-endosmotic phenomena 

 compared with those of the coagulation of colloids have indeed 

 confirmed. 



It now occurs to me that the researches on the current potentials, 

 particularly those which have been communicated in the preceding 

 paper, are capable of furnishing us not only with a new proof of 

 that equality of order, but also demonstrate that the influence which 



1) Z. f. physik. Gliem. 33, 385 (1900). 



2) Phil. Mag. [6] 11, 425; 12, 472 (190G) and 17, 583 (1909). 

 8) Z. f. physik. Chem. 39, 630 (1902). 



+) Zeitsciir. f. physik. Chem. 73, 885 ^1910) and 85, 641 (1913). 



