On the cataphoresis of gliadin Part II—The effect of strong electrolytes upon the mobility

Abstract

Careful analyses of the cataphoretic velocity of a colloid particle suspended in an electrolyte solution have been made by Smoluchowski, by Debye and Hückel, and by Henry. No actual test of their theoretical conclusions over a sufficiently wide range of ionic strength appears yet to have been made, with the exception of some experimental work recorded by Audubert, whose results indicate good agreement for particles of radius 60 - 130 A, but not for particles of radius 2-8 μ. Unfortunately, no details are given of the measurement of the sizes of such small particles. In adopting the hypothesis of Pauli that a colloidal particle behaves like a large polyvalent ion, it is assumed that on altering the electrolyte concentration there is no change in valency of the ion when the theory of Debye-Hückel and of Henry is applied. In practice those colloids whose charge is derived mainly from adsorption of ions do not exhibit constant valency on variation of the ionic strength of the electrolyte. According to Abramson, quartz particles covered with protein behave as ions of constant valency in solutions of the same ionic strength and hydrion activity. This assumption can be valid only over a restricted range of concentrations. Thus, at high ionic strengths, the valency may be altered appreciably by the adsorption of electrolyte ions, whilst it may reasonably be anticipated that at small ionic strengths the effect of the restriction of ions inside the double layer will lead to an alteration in the effective valency of the particle. In general a Donnan equilibrium is set up wherever one ionic species is constrained in any manner from free diffusion; modification of the effective valency of the colloid ion may be expected in very dilute electrolyte solutions on this account.