The equipment used and the experimental set up are shown in Fig. 3.1. The equipment consisted of a syringe pump, a transfer cylinder, a core, a heater, a temperature sensor and a back pressure regulator. The core is kept in an air bath in which the temperature was kept constant at 298.15 K (25 °C) by the temperature sensor and heater. The pressure within the core was maintained at the desired pressure by the back pressure regulator at all times.