alternating layers of a gel (containing a precipitate or free from a precipitate) arising as a result of the counterdiffusion of two solutes, which upon interaction form an insoluble compound. The residue precipitates in zones of fairly high supersaturation, where the reaction product separates out in the form of minute particles in the disperse phase. Liesegang bands arranged as concentric rings are known as Liesegang rings. These are formed during the radial diffusion (diffusion from the center outward into various directions) of one soluble substance through a gel containing a second substance. The Liesegang bands were named after the German chemist R. Liesegang, who first described this particular phenomenon in detail (1896).
The occurrence of Liesegang bands can be observed, for example, upon diffusion of silver nitrate (AgNO3) in gelatin containing potassium dichromate (K2Cr2O7). A similar phenomenon also takes place in compacted inert powders (for example, quartz, kieselguhr) impregnated with an appropriate reagent solution. The following phenomena are connected with the formation of Liesegang bands: the banded coloration of minerals (agate, jasper), the lamellar structure of mineral deposits in human and animal organs, and the striation of certain biological tissues, for example, striated muscles.
REFERENCESPeskov, N. P. Fiziko-khimicheskie osnovy kolloidnoi nauki, 2nd ed. Moscow-Leningrad, 1934. Page 412.
Pisarenko, A. P., K. A. Pospelova, and A. G. Iakovlev. Kurs kolloidnoi khimii, 3rd ed. Moscow, 1969. Page 239.
L. A. SHITS