APPARENT MOLAR HEAT-CAPACITIES OF AQUEOUS ARGON, ETHYLENE, AND XENON AT TEMPERATURES UP TO 720-K AND PRESSURES TO 33-MPA

The apparent molar heat capacities, C//p//,// phi , of aqueous solutions of argon, ethylene, and xenon were measured at temperatures from 300 to 720 K with a flow, heat capacity calorimeter developed in our laboratory. For all three gases C//p//,// phi decreases as temperature is increased, goes through a shallow minimum at about 420 K, then rises to a maximum approximately 5000 J mol** minus **1 K** minus **1 at about 665 K, and decreases to a minimum approximately minus 5000 J mol** minus **1 K** minus **1 at 685 K for pressures near 33 MPa. This remarkable behavior at high temperatures is due to the proximity of the critical point of water. The behavior is qualitatively similar to ( PARTIAL **2 rho / PARTIAL T**2)//p where rho is the density of water.