Apparent molar heat capacities and volumes for HClO4(aq) to 373 K

Heat capacities of aqueous HClO4 solutions from 298.15 to 373.15K, and densities from 296.02 to 371.82K, have been measured at 0.5 MPa using a how, differential heat capacity calorimeter and, in series, a vibrating-tube densimeter. Equations for the apparent molar heat capacities and volumes are reported as a function of temperature, and values for the ionic partial molar heat capacities and volumes of HClO4 (aq) are estimated. The experimental apparent molar heat capacities are compared with disparate values reported in the literature.