Heat capacity anomaly near the critical point of aniline-cyclohexane

The heat capacity of the liquid-liquid mixture aniline-cyclohexane has been measured for the first time near its upper critical consolute point using an adiabatic calorimeter. Two data runs provide heat capacity data that are fitted by equations with background terms and a critical term. The critical exponent ct was determined to be 0.104 +/- 0.011, consistent with theoretical predictions. When a was fixed at its theoretical value of 0.11 to determine the critical amplitudes A(+) and A(-), our value for the amplitude ratio A(+)/A(-) = 0.59 +/- 0.03 was consistent with most experimental determinations in liquid-liquid mixtures, but was slightly larger than either theoretical predictions or recent experimental values in liquid-vapor systems. The two-scale-factor universality ratio X, now consistent among experiments and theories with a value between 0.019 and 0.020, is consistent in this system using one published value for the correlation length, but not with another. (C) 1998 American Institute of Physics. [S0021-9606(98)50534-X].