On the wave-like character of periodic precipitates

Summary

It is pointed out that the suggestion of an analogy between periodic waves and rhythmic precipitation would be without physical significance unless it can be shown that the characteristic superposition effects observable with waves are also demonstrable with Liesegang patterns. Fourteen photomicrographs and enlargements of Liesegang precipitates of silver chloride and of silver chromate are reproduced with the paper which show that such superposition effects are actually to be observed, both in regard to the intensity of the deposits and in respect of their geometrical configuration. These examples illustrate the varying effects of the superposition of two wave-trains when their wave-length, direction and amplitude are individually or collectively different. It is shown theoretically that when groups of waves interfere, we have a group-interference pattern on a large scale in addition to a wave-interference pattern on a fine scale, the two being separate and distinguishable effects. It is observed that the so-called primary and secondary rings obtained with silver chromate precipitates in gelatin are related to each other as a group is to the individual waves of which it is composed. Independent wave-interferences and group-interferences are exhibited by such precipitates.