Basically the apparatus consists of a sorption cell containing the adsorbent and the fluid at the density of the experimental isochore, and a reference cell without adsorbent.
Measurements start at a temperature ca.
15 K above the critical temperature Tc by adjusting the fluid density in the sorption and reference cell. Changes in the surface excess amount are therefore given in terms of volume changes of the sorption cell using a piston cylinder device operated by a step motor drive. Complementary tests, in which the influence of systematic changes of the experimental conditions on the result could be assessed, were also performed by sequences of telecommands. At temperatures well above Tc the surface excess amount gamma increases weakly with decreasing temperature as expected. It was suggested that this effect may be due to confinement effects of the fluid in the colloidal graphite substrate.