The coexistence curves for {x(CHCOOC2H5)(2) + (1 - x)CH3(CH2)(5)CH3} have been determined within about 10 K from the critical temperature by measurements of the refractive index. The critical amplitude B, and the critical exponent beta have been deduced from (T,n), (T,x) and (T,phi) curves where n, x, and phi are the refractive index, the mole fraction and the volume fraction, respectively. The values of beta are consistent with theoretical predictions. The experimental results have also been analysed in order to determine the Wegner correction terms, and the behaviour of the diameters of the coexistence curves in various units over the 10K temperature range from the critical temperature. The coexistence curves have been successfully described by a combination of the Wegner equation and the expression for diameter.