Effect of Moisture on Liesegang Ring Formation in Ammonia–Hydrogen Chloride System

IF ammonium chloride is formed by counter-current diffusion of ammonia and hydrogen chloride gases in a long tube, periodic precipitation of the product in the form of rings is observed. This phenomenon has been explained by considering that nucleation and deposition of the product occur only when conditions of super-saturation exist, that is, when the concentration product of the reactants greatly exceeds the solubility product of ammonium chloride. By using this concept of super-saturation, Wagner1 has developed a mathematical model which accounts for the formation of the “Liesegang rings” and which predicts accurately the frequency and separation of the rings.