Equilibrium between van der Waals liquid of a constant density and gas in the supercritical region

The suggestion is made that the properties of an adsorbate in zeolite cavit ies are largely determined by the virtually constant volume of these caviti es in wide temperature and pressure ranges. The van der Waals model is used to qualitatively estimate equilibrium between a liquid of a constant densi ty (isochoric liquid) and vapor and gas in the subcritical and supercritica l regions. The isochoric conditions for the liquid and equilibrium gas are created by an imaginary system in which a gas insoluble in the liquid acts on it and, under piston pressure, maintains the isochoric conditions for th e liquid.