Stability of lyophobic colloids, XI : investigations on the stability of the hydrous ferric oxide sols as related to the coagulating powers of the poly-valent precipitating ions

Abstract

It has been shown that simple Whetham's rule is only a first approximation for the ratios of the precipitating values of ions of varying valencies. Modifications of Whetham's rule have been deduced by S. Ghosh and also by Verwey and Overbeek on the electrostatic properties and also on the effect of electrolyte on the surface potential or the electric charge on the colloidal particles. These modifications have been critically examined here for the sols of hydrous ferric oxide at the varying dielectric constants of the dispersing medium at the different lengths of the time allowed for the contact of sol with the electrolyte. Our results show that in actual practice the relation of S. Ghosh or Verwey and Overbeek cannot be realised in a true sense because the sol is likely to coagulate, when the charge and hence, the surface potential becomes zero. But we have observed that the ratio of the precipitating ions of different valencies should decrease, as the charge on the colloidal particles decreases and it is well known that the stability of a sol decreases with increasing purity.