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Abstract

The coexistence curve and diffusion coefficient for the binary liquid system heptane-nitrobenzene have been obtained using an optical technique in which laser light is refracted through a quartz sample cell. Analysis of the resulting fringe patterns shows that the molar concentration difference ΔΧ between the coexisting liquid phases is equal to (.24±.01)x (Tc-T)•³³³±•⁰⁰⁵ over the temperature range .0001° ≤ (Tc -T) ≤ 11° C, and that the diffusion coefficient D at critical concentration is equal to (3.7±1.5)xl0⁻⁷(T-Tc ) •⁷⁰±•⁰⁵ cm²/sec over the range .005° ≤ (T-Tc ) ≤ 2.7° C. It was found that the coexistence curve is symmetric about Xc, and that the diffusion coefficient as a function of concentration at a given temperature is also symmetric about Xc, near Xc. The critical temperature Tc = 19.07±.05°C. Temperature differences near Tc were known to within .0001°C. The critical molar concentration of nitrobenzene Xc = .470±.003. In terms of dimensionless variables, where [formula omitted] over the range [formula omitted].