An adiabatic calorimeter for the simultaneous measurement of enthalpies of vaporization and vapor pressures of certain coal chemicals is described. The calorimeter was tested using benzene for which accurate experimental data exists in the literature. Benzene is one of the substances recommended by IUPAC as a reference substance for calorimetric studies. The uncertainty in the benzene data is ±5 J/mole in the temperature range of 350 K (very close to the boiling point) to 480 K (around 0.85 times the critical temperature). Both vapor pressure and enthalpies of vaporization of benzene showed excellent agreement with the available literature data.