Coexistence curve of acetonitrile and cyclohexane liquid system

Abstract

The paper reports a detailed determination of the coexistence curve for the binary liquid system acetonitrile+cyclohexane, which have very closely matched densities and the data points get affected by gravity only for t=(T_c-T)/ T_c=10^-6. About 100 samples were measured over the range 10^-6<t<5×10^-1. The order parameter exponent is found to be 0.322 ± 0.004 and the value of Δ is nearly 0.50 ± 0.05 as expected theoretically. There is also a definite anomaly in the diameter which is carefully examined with reference to the predictions of the various theories. The data, when expressed in terms of the volume fraction as the composition variable and analyzed in the asymptotic region, give an exponent of 0.9 for the diameter in keeping with the (1-α ) exponent theoretically predicted, the value of a being 0.11 in binary liquids. The extrapolation properties of the Wegner expansion procedure is somewhat inferior to the extrapolation obtained using a renormalization group (RG) crossover expansion. The use of the new variables proposed by Johnston et al. and Vnuk in making the coexistence curve appear symmetric in the new variables is pointed out.