The objectives of the research were to measure the electrical potential across sodium bentonite membranes due to a thermal gradient using sodium chloride solutions of various concentrations and combine these data with equations derived from the thermodynamics of irreversible processes to predict the rate of electrolyte transport. This is of interest to the understanding of the source of brines in aquifers. The electrical potential measurements have shown that for a 1/4 inch Wyoming Bentonite membrane and sodium chloride solutions, the potential gradient, dE/dT, varies in a log-log fashion with concentration. Data are presented that can be used to estimate heats of transport for the sodium ion assuming negligible water and chloride ion transport. The data collected thus far are not sufficient to indicate much about the transport mechanism in the membrane.