Distillation is the most common method used to separate and purify liquids. The process consists of heating a liquid to its boiling point, conducting the vapours to a cooling device where they are allowed to condense, and collecting the condensate.General PrinciplesIf a liquid is kept in a sealed container, some molecules escape from the liquid's surface into the space above it. When equilibrium is established, the number of molecules escaping the liquid equals the number of molecules in the vapour that strike the liquid surface and stick. The molecules in the vapour also strike the walls of the container and exert a pressure, defined as the vapour pressure of the liquid. If the temperature of the liquid is raised, a greater number of molecules escape to the vapour phase until equilibrium is once again established; the vapour pressure of the liquid increases with increasing temperature.