Referred to unit of mass of the solid, the difference (at constant temperature) between the @E02141@ of a solid completely immersed in a @WT07250@ liquid, and that of the solid and the liquid taken separately. It must be specified whether the solid in the initial state is in contact with vacuum or with the vapour of the liquid at a given @P04420@. Measurements of the @E02141@ of @WT07250@ of a solid equilibrated with varying relative pressures of the vapour of a pure @WT07250@ liquid may be used to derive the differential @E02141@ of adsorption of the vapour.