Effect of dispersion medium on the stability of silver iodide sol

Abstract

The effect of non-aqueous liquid as dispersion medium has been studied with a view to observe the variations in the stability of silver iodide sol. It has been noted that the stability increases with the decrease in the dielectric constant of the dispersion medium. The pH of the sol increases continously up to the coagulation point by addition of mono- and divalent coagulating electrolyte. After this point a sudden drop in pH is observed and when the dispersed phase completely settles down a slight rise in pH is again observed. These changes have been accounted for, due to the changes in the dielectric constant of the medium, effect in release of silver ions and due to the adsorption on the active centres of fine coagula. As the value of the dielectric constant of the sol is cut down, so the increase in pH is also reduced. More concentrated bivalent coagulating ions produce greater increase in pH than the dilute one, but N/4 potassium nitrate produces greater change in pH than N/3 potassium nitrate. During the course of coagulation the electrical conductance of the sol increases in each case and this increase is more rapid after coagulation, which accounts for the release of ions from the double layer.