A mixture of two miscible volatile ideal liquids P and Q (obeying Raoult's law) is kept in a vessel (molar ratio of P and Q in the mixture is m ). At a suitable temperature T , the vapour above the liquid is condensed in another vessel. The liquid obtained on condensation is allowed to evaporate and establish equilibrium with its vapour. The vapour is then condensed in another vessel. The process of such evaporation