THE (LIQUID PLUS LIQUID) CRITICAL PHENOMENA OF (A POLAR LIQUID PLUS AN N-ALKANE) .5. COEXISTENCE CURVES OF (N,N-DIMETHYLACETAMIDE PLUS HEPTANE)

The coexistence curves of liquid (N,N-dimethylacetamide + heptane) hav e been determined within 15 K of the critical temperature by measureme nts of the refractive index n. The critical amplitudes B and the criti cal exponents beta have been deduced from (T, n), (T, x), and (T, phi) curves. Experimental values of beta are consistent with the theoretic al prediction. The results have also been analysed to determine Wegner correction terms when beta and Delta are fixed at the theoretical val ues, and to examine the behaviour of the diameters of the coexistence curves. Molar mass-dependences of B and the critical volume fraction p hi(c) have been derived from the classical theory without the limitati on of phi(c) much less than 1, and tested against the experimental res ults. (C) 1996 Academic Press Limited