Abstract: By modifying Mathews' apparatus, an isolhermal-adiabatic vaporization calorimeter was constructed.Latent heats of vaporization of pure methanol, ethanol, benzene, toluene and water were determined with an accuracy of 0.1-0.2%, agreeing with literature in less than 0.3%.Binary systems of water-ethanol and benzene-methanol and domestic crude cuts were also studied.