Periodic precipitation of cobalt hydroxide in agar gel: Effect of ionic strength

The present paper highlights the effect of ionic strength due to addition of potassium chloride (KCl) in a diffusing medium on the periodic precipitation (Liesegang patterns) of CoCl2 + NH4OH system. The patterns are obtained by addition of known amount of KCl in an agar gel medium in a glass tube. In the absence of KCl, the precipitating system exhibits a common trend of increase in spacing between consecutive bands with the movement of outer electrolyte towards the lower boundary of the tube thus maintaining constant value of spacing coefficient. However it was observed that the addition of KCl causes decrease in the value of spacing coefficient. The presence of KCl also results in a marked deviation in the width and the time of formation of the precipitating rings. Periodicity of the precipitation pattern is lost and continuous precipitation is obtained in the presence of excess KCl.