Studies on the Electrophoretic Velocity of Colloidal Particles by the Moving Boundary Method. Part IV. Critical Study of the Influence of Dialysis on the Electrophoretic Velocity of Fe(OH)3 Sol and the Peak Point of the ζ-C Curve in the Aspect of Charge Density and Ionic Strength

During the determination of electrophoretic velocity of FeO14)₃ sal at different stages of dialysib, a gradual increase is at first observed up to a certain stage of dialysis, followed by a decrease after attainment of the peak point. The specific conductance of the sol, proportional to the concentration of the residual elec­trolyte at different stages of dialysis, when plotted against the olectrophoretie velocity, which is proportional to the zeta-potential, provides a characteristic peak point. This observation has been explained by deriving a relation connecting the electruphoretic velocity, U, the ionic strength,\(^\frac{1}{2} \displaystyle \sum\)cz², and the charge on the colloidal particles. The concentration of the electrolyte in the colloidal system at the peak point has been suggested as corresponding to the critical stability concentration 'a' of the, KM, reported earlier in Bhattacharya's equations.