An apparatus to perform volumetric measurements of fluid-phase pure compounds and binary mixtures has been tested by the measurements of 11 vapor pressures and 18 saturated densities of acetonitrile, at intervals of 10 K, over the temperature range 363.15-463.15 K. For the gas phase, density and virial coefficients corrected for adsorption were determined, without knowing the compound’s volume or mass, over the temperature range from 403.15 to 463.15 K.