Direct experimental verification of the isomorphism hypothesis for critical phenomena

The heat capacity at constant volume of a mixture of methane and 0.0345 mol e fractions of heptane is experimentally studied over a wide range of densi ties and temperatures. In the case when the transition from a three-phase s tate takes place in the presence of a noncritical liquid phase, it is found that the behavior of the heat capacity in the vicinity of the upper end cr itical point is fully isomorphic with the behavior of the heat capacity in the vicinity of the liquid-vapor critical point of one-component fluid. It is shown that the measured quantity in this experiment is the heat capacity at constant volume and constant chemical potential mu of the heavy impurit y component C-v,C- mu. Thus, it has been confirmed by direct measurements t hat the anomaly of this heat capacity completely coincides in character wit h the anomaly of the heat capacity at constant volume in the vicinity of th e liquid-vapor critical point of one-component fluids. (C) 2000 MAIK "Nauka /Interperiodica".