The expansion of porous glass on the adsorption of non-polar gases

The design and construction of an absolute dilatometer of high sensitivity to measure the small expansions resulting from the adsorption of non-polar gases on to porous glass at liquid-air temperatures are described. The expansions measured with this instrument are the first recorded with a rigid adsorbent for the case in which the adsorption is, with certainty, physical in nature. Experiments in which the gases argon, nitrogen, oxygen, hydrogen and krypton were used as adsorbates are reported. The effect of organic matter adsorbed on to the glass from the atmosphere, of unknown composition, on the expansion characteristics is indicated. A technique for the removal of this organic matter in situ without affecting the area of the glass is described. The results have confirmed the correctness of an equation which has been derived by the author (Yates 1952) $\left(\frac{\partial F}{\partial V}\right)_{T}=-\frac{3}{2}K$, where $\partial $V is the volumetric expansion at constant temperature resulting from $\partial $F, the surface free energy lowering, and where K is the bulk modulus of the adsorbent.