Concentration profiles of sodium in the surface layer of glasses dealkalized with ammonium sulphate were measured by the stepwise etching method and subsequent chemical analysis of the solutions obtained as well as by the ESCA method. The results allow conclude that the difference in hydrolytical resistance of glass surfaces dealkatized by different procedures can be explained by the parallel effects of the chemical dealkalizing reaction, and of the diffusion processes involved. At the lower temperatures (of approx. 400_C) the concentration profiles formed are stable in character, whereas at the higher temperature (800_C), following exhaustion of the reaction agent, the difference in the concentration of sodium will be gradually eliminated by diffusion within the concentration gradient zone formed.
