The analysis of thermomolecular pressure difference experiments to obtain information on thermal transport properties is critically examined. It is concluded that the finite difference form of the dustyhyphen;gas equation, which has been used to analyze the thermal transpiration phenomenon, is internally inconsistent. A form of the integrated dustyhyphen;gas equation developed in this paper, while more difficult to use than the finite difference equation, yields results for the Eucken factor which are in better agreement with direct measurements of this quantity than are obtained with the approximate equations. It is observed, however, that when using the integrated dustyhyphen;gas equation there is a temperature variation of the apparent capillary diameter which cannot be explained.
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