Chemistry

Abstract

ALTHOUGH the Liesegang phenomenon, having engaged the attention of mineralogists, histologists and colloid chemists, has given rise to an extensive and scattered literature, the present work is the first monograph devoted exclusively to the subject. The author gives a full account of the experimental material, beginning with Liesegang's original silver chromate rings and enumerating the numerous other combinations of reactants which have since been found to produce periodic precipitates in certain gels andwithin certain limits of concentration. He then devotes a chapter to the various theories so far proposed, which have in turn postulated metastable super saturation, adsorption at the precipitate, membrane formation, variations in the rate of diffusion, periodic coagulation of a colloidal reaction product and periodic inhibition of precipitation by the second (soluble) reaction product as the principal agency. Most of these theories are based on a few, or even on isolated, examples and are incapable of explaining others. This is not really surprising, as there is no a priori reason for assuming that the mechanism of periodic precipitation is necessarily the same whatever the reaction producing it.