Abstract: Particle size distributions in samples of Belle Fourche, Wyoming, Aberdeen, Utah, and Cheto bentonite were obtained by a centrifugation technique. From these distributions and the clay density the number of particles per gram was calculated for the different samples. Then the clays were mixed in different proportions with water and the clay concentrations required for thixotropy were determined. It was found that a smooth curve was obtained when the clay concentration required for thixotropy was plotted against the number of particles per gram of clay. A smooth curve was also obtained when the clay concentration at the upper plastic limit was plotted against the number of particles per gram of clay.
In each suspension the water tension at the upper plastic limit was measured at several temperatures. From the resulting data, the relative partial molar free energy, entropy and heat content of the water were calculated. In all cases the values were negative, suggesting that the water in the suspension had more order than pure bulk water.
When the water tension was measured in different suspensions of Aberdeen and Cheto bentonite it was found that the tension remained zero until the clay concentration was sufficient to allow gelation of the suspension. Thereafter, the tension increased rapidly with clay concentration. Consequently, it was concluded that the sol-gel transformation was accompanied by a change in the energy status of the included water. This conclusion was supported by reference to other investigations in which changes in water properties were noted on gelation.