The vapour pressure (in Pascal) of a substance is defined as the saturation pressure above a solid or liquid substance and is determined at various temperatures (in Kelvin).
The methods used are: the dynamic method (Cottrell’s method), the static method, the isoteniscope Method, the effusion method: vapour pressure balance, the effusion method: Knudsen cell, the effusion method: isothermal thermogravimetry, the gas saturation method and the spinning rotor method. The vapour pressure from any of the preceding methods should be determined for at least two temperatures. Three or more are preferred in the range 0 to 50°C, in order to check the linearity of the vapour pressure curve. In case of Effusion methods and Gas saturation method, 120 to 150 °C is recommended for the measuring temperature range instead of 0 to 50°C.