Periodic precipitation of silver chromate/dichromate in gelatin

The spatial and temporal evolution of silver chromate/dichromate Liesegang Rings (LR) in gelatin is studied microdensitometrically and microscopically. The analysis of the distribution of various ionic species in dichromate solutions leads to a notion of the possibility of both silver chromate and silver dichromate precipitation. A simple mathematical model of diffusion in thin layers has been developed. The results of the turbidity front progression measurements are consistent with this model and, together with the secondary structure observations, support the postnucleation hypothesis of primary LR formation.