Mechanism of Periodic Presepitation in a Lead Chromate System Containing Agar-agar Gel

The Pb(NO3)(3) and K2CrO4 were chosen as the interdiffusing electrolytes for periodic precipitation of PbCrO4 in an agar-agar gel. Six series of experiments in which the concentration of Pb(NO3)(3) solution was different from another were performed under illumination and dark respectively. On the basis of phenomena of the experiments a possible mechanism of formation of periodic precipitation was reported. It was considered that the PbCrO4 was dissociated partly under the light radiation, the growth velocity of the colioid nuclei was increased, and therefore presence of light was favorable for pattern formation.