Many solid porous compounds, especially zeolites, are well known for their adsorbing properties. In order to measure their adsorption capacity, a special experimental set-up has been designed for the C80 calorimeter. This device allows characterizing the adsorption of vapor on a solid under reduced pressures. The liquid to be adsorbed is initially frozen, then kept at a well-defined temperature, determining a well-known vapor pressure. This vapor is adsorbed on the solid, previously regenerated under vacuum.