This report summarizes information concerning the sorption isotherms of water on four lignite samples. The four lignite samples are all from North Dakota and have been described in detail in earlier quarterly reports of this project. The earlier measurements of sorption isotherms at 30/sup 0/C have now been supplemented by data obtained at 50 and 60/sup 0/C. From these data, isosteric heats of sorption may be calculated. In addition to the data on the sorption of water by the as-received lignites, the present report also examines data on the sorption of water by demineralized samples. This work was motivated by a need to know whether cations or mineral species might play a role in moisture retention on the lignites. Clearly, the design of a thermal dewatering process could be influenced by a large extent of moisture retention by mineral species which are unaffected by mild pyrolytic treatment. Data now in hand imply a significant amount of moisture is held by inorganic species. 3 refs., 2 figs.