Non-ideality in liquid mixtures: the prediction and measurement of thermodynamic excess functions

This thesis may be separated readily into three sectors: firstly, the mathematical prediction.of the excess functions of some well-known systems, and also of some new systems, the experimental data for which were gathered in the course of this work; secondly, the measurement of the excess enthalpies and volumes of mixing of three systems, for comparison with the predicted values; thirdly, the development of a method for obtaining excess free energies of mixing by measurement of the bubble- and dew-points of mixtures of approximately known composition. The thesis is presented more or less in the order in which the work was carried out, which was not that of the sectors just described. The Appendix to the thesis contains details of the numerous computer programmes required and written in the course of this work, including the major programme, for analysis of the data from bubble- and dew- point measurements, which yields an equation for the excess free energy in terms of composition. The predictive work was based on the use of two equations of state, that of van der Waals, produced in 1900, and that of Guggenheim, produced in 1965. Van der Waals’s own approach to obtaining the adjustable parameters a and b for the mixture was employed, and two different methods fur obtaining the mixed critical values were tested. The measurements of both the excess enthalpies and volumes were carried out using small, mercury- filled, batch- type devices, the dilatometer being particularly simple, but quite accurate. The apparatus eventually produced for the measurement of bubble- and dew- points was large and complex, and the third chapter suggests means by which the method might be adapted for a small, semi- automatic system