A new apparatus for measuring the vapour pressure of liquid mixtures excess Gibbs free energy of octamethylcyclotetrasiloxane + cyclohexane at 308.15 K

A new apparatus for measuring the vapour pressure of liquid mixtures is described. In conjunction with an automatic pressure controller, a capacitance manometer is used as a null device to isolate the liquid and vapour. The vapour pressure is measured with a precision mercury manometer. The continuous-dilution technique for sample introduction has been incorporated in the new apparatus, so that the composition range of a mixture can be covered in two runs. The accuracy of each measured quantity is: pressure, 3 Pa; temperature (IPTS-68), 0.002 K; volume, 0.002 cm³. G^E for cyclohexane + octamethylcyclotetrasiloxane (abbreviated throughout this paper as omcts) at 308.15 K has been determined: the minimum value of ?68 J mol^?1 occurs near x₂(omcts) = 0.5.