Importance of dialysis in the study of colloids

Summary

The changes in the cataphoretic speed, stability and conductivity of colloidal zinc ferrocyanide dialysed, diluted, allowed to age and exposed to sunlight for different periods have been studied.

With the progress of dialysis the cataphoretic speed first increases and then decreases, while the stability and conductivity continuously decrease.

In the case of sols dialysed for periods shorter than the maximum in the cataphoretic speed-dialysis curve, the cataphoretic speed first increases and then decreases on dilution, while for sols dialysed for longer periods the cataphoretic speed continuously decreases. The stability and conductivity, however, continuously decrease on dilution in all the cases.

It is found that for short period dialysed sols, the cataphoretic speed first increases and then decreases on adding small increasing amounts of KCl, K₂SO₄, K₄Fe (CN)₆, MgCl₂ and MgSO₄; for long period dialysed sols the cataphoretic speed continuously decreases with all the electrolytes except K₄Fe (CN)₆ where it first increases and then decreases. The idea of critical potential is not supported.

On allowing both the short period and long period dialysed sols to age or exposing them to sunlight, the cataphoretic speed, stability and conductivity continuously decrease.

The results are interpreted by means of assumptions similar to those employed in the case of the other colloidal solutions investigated in this laboratory.