Coexistence curve of the ionic binary mixture ethylammomium nitrate-n-octanol: Critical properties

We present measurements of the coexistence curve of the ionic mixture ethylammonium nitrate - n-octanol within the reduced temperature range 2.6 x 10(-5) < t < 4.2 x 10(-2). The salt volume fraction is chosen as the order parameter as this gives the most symmetric phase diagram. The determination of the asymptotic critical exponent beta gives a value close to the 3-D Ising value although correction-to-scaling terms are necessary to fit the data. The effective exponent beta(eff) as a function of the reduced temperature does not show any crossover from the classical to the Ising value and suggests rather an approach, from below, to the asymptotic 3-D Ising value. The (1 - alpha) anomaly of the mean diameter could not be precisely determined although a deviation near T-c from the rectilinear law could be noticed.