FROM CALORIMETRY TO EQUATIONS OF STATE

Volume thermal expansivities (alpha(p)) can be measured in a pressure-controlled scanning calorimeter (PCSC) over wide ranges of pressure and temperature. Studies on a series of liquids have revealed some characteristic features, such as the crossing of alpha(p) isotherms, minima in the C-p isotherms, a unique crossing point of alpha(p) isotherms for simple liquids, the shifting of the crossing point to higher pressures with addition of an associative component, etc. The reproduction of all these properties by an equation of state of the van der Waals type is made possible when the hard-sphere repulsive term is replaced by the soft-sphere repulsive contribution. The PCSC can also serve as a guide in searching further for better EOS for much more complicated condensed matter systems. Thus, the use of calorimetry can compensate the lack of a reference state at high pressure and can be used as a verification of EOS and their structure.