A thermistor type adiabatic calorimeter has been designed with the capability of measuring the heat of wetting of high surface area solids in organic liquids. Since the primary source of error in this type of experiment is trace water in the organic liquid, a method has been devised for introducing freshly distilled liquids directly into the calorimeter vessel and for maintaining dry conditions while introducing additional sample bulbs for measurements. The main feature in the design of the calorimeter vessel is the arrangement for removing the sample and readmitting a new sample under a positive pressure of dry nitrogen. This design allows this single‐bulb calorimeter to achieve the advantages of a multibulb calorimeter for detecting the presence and effects of trace water in the organic wetting liquid. The sensitivity of the calorimeter, which contains a volume of 50–100 ml, was found to have an experimental uncertainty of ±0.03 cal. A series of heat of immersion experiments of NiO in organic liquids, where consecutive immersions were determined in the same liquid, yielded reproducibility results which were within experimental error and indicated that water was not present in measurable amounts in the wetting liquid.