Excess volumes P of mixing for eight binary mixtures as a function of temperature and composition have been determined and the results have been used in examining the theory of Hory for binary mixtures differing in shape and size. Prigogine's refined version of the cell theory using average potential model has also been examined.
Phase-diagrams of carbon tetrachloride + cyclohexane, benzene + cyclohexane and carbon tetrachloride + benzene have been obtained by the method of thermal analysis.Mixtures of carbon tetrachloride and cyclohexane show complete miscibility in the liquid phase with some evidence of partial miscibility in the solid phase. The phase-diagram for benzene + cyclohexane shows a eutectic. The equilibrium diagram of carbon tetrachloride 4-benzene indicates the formation of two compounds having the formulae C6H6. Cc14 and C6H6. 2cc14.The thermodynamic analysis of the equilibrium data for mixtures of carbon tetrachloride and cyclohexane indicates the system to be a regular one. v. and p which are related to interchange energies in the liquid and solid phase respectively, are found to depend on temperature in the following manner, loglo cc = 5.67 -0.01 114T;loglo j3 = 5.73 -0.01115T. It appears from the analysis that CI and j3 increase enormously as the freezing point is approached. Guggenheim's analysis of the vapour pressure data for the system yields a value of v. at 30°C of 65.5 cal/mole whereas according to present investigation this reaches 930 cal/mole at -30°C.The system benzene + cyclohexane is found to be far from regular, in agreement with Scatchard's finding based on the examination of the vapour-liquid equilibrium data. This is due to the wide difference in the size and the shape of the two molecules.Binary mixtures of carbon tetrachloride, benzene and cyclohexane are thermodynamically interesting. Scatchard 1 and co-workers have measured the vapour pressure of mixtures of carbon tetrachloride + benzene, carbon tetrachloride + cyclohexane and benzene + cyclohexane. Data referring to the first two mixtures have been used by Guggenheim 2 for testing the regular solution theory. In order to study the magnitude of interchange energies in the solid and liquid phases near the freezing point, it was thought desirable to make a detailed experimental study of the solid-liquid equilibria of these systems.
EXPERIMENTALMATERIALS AND THEIR PURIFICATION CARBON TETRAcHLoRIDE.-Carbon tetrachloride (A.R.) was purified by fractional distillation using a Precise Fractionation Assembly, model A, Todd Scientific Company, Springfield, P.A. The ratio of the still head was adjusted to 25 : 1. The purity of carbon tetrachloride was tested by a freezing-point 3 determination.BENzENE.-Benzene (B.D.H.) was purified by shaking with about 15 % of its volume of conc. HzSO4 in a stoppered funnel until the acid layer was colourless and thiophene was absent. After each shaking lasting for a few minutes, the mixture was allowed to settle and the lower layer of the acid was drawn off. It was shaken twice with water to remove most of the acid and then twice with a 10 % solution of NazC03. Finally it
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