SWELLING PRESSURE OF Na‐MONTMORILLONITE IN NaCl SOLUTIONS

Abstract

Summary Pressures exerted against a confining restraint by Na‐montmorillonite in equilibrium with NaCl solutions were measured. The swelling pressures decreased with increasing NaCl concentration as predicted theoretically, but the rate of decrease was lower than calculated so that the ratio of observed to calculated pressure increased with increasing salt concentration. These larger swelling pressures could result from a higher activity of the ions between interacting clay particles compared with the ions in the neutral salt of the dialysis solution. It is then not necessary to postulate a non‐osmotic force of repulsion.