Heat capacity behavior in the critical region of the ionic binary mixture ethylammonium nitrate-n-octanol

At temperatures between 30 degreesC and 58 degreesC we have recorded the he at capacity of the ionic ethylammonium nitrate-n-octanol mixture of critica l composition and also of the constituents. Different samples of the binary mixture have been measured with its upper critical demixing temperature T- c varying between 41.04 degreesC and 46.87 degreesC, depending on small tra ces of water within the liquid under test. Almost identical heat capacity p rofiles result if the data are displayed as a function of the temperature d istance to the actual T-c value. In the homogeneous phase the critical cont ribution exhibits power law behavior with the critical exponent alpha =0.11 as theoretically predicted for nonionic liquids and in conformity with our understanding of the ionic criticality as being asymptotically Ising like. The noncritical background part of the heat capacity can be related to the heat capacities of the constituents using a simple mixture relation. In th e two-phase regime a series of almost perfectly reproducible events is foun d which may be taken to indicate the existence of nonequilibrium intermedia te states in the ethylammonium nitrate-n-octanol system.