The influence of concentration, ageing and pH of the gel medium on the periodic precipitation of cobalt oxinate in agar gel is reported. The results are explained on the basis of Shinohara’s revised flocculation theory. The flocculation value (F) increases with increase in the gel concentration whereas it decreases with increase in ageing and pH of the gel. The raise in temperature of the gel increases the solubility of the sparingly soluble substance and hence theF value. The effect of additives on the periodic precipitation of cobalt (II) oxinate is reported.

The influence of temperature on periodic crystallisation of magnesium hydroxide in agar-agar gel has been studied. The increase in velocity constant with temperature is attributed to the increase in the diffusion constant with temperature. The activation energy for diffusion of aqueous ammonia is calculated from the temperature — velocity constant correlation. The solubility of Mg(OH)₂ decreases with temperature. The decrease in the spacing coefficient and fiocculation value of Mg(OH)₂ with temperature is also explained because of the increase in temperature. Matalon and Packter’s equation correlating the spacing coefficient and concentration of the inner electrolyte is suitably modified to satisfy the temperature dependence of the spacing coefficient.