The coexistence curves of liquid (N,N-dimethylacetamide + nonane) have been determined within 20 K of the critical temperature by measurements of refractive index n. The critical amplitudes B and the critical exponents beta have been deduced from (T, n), (T, x), and (T, phi) curves. The experimental value of beta is consistent with theoretical prediction. The results have also been analysed to determine Wegner correction terms when beta and Delta are fixed at the theoretical values and to examine the behaviour of the diameters of the coexistence curves.