The physical and thermodynamic properties of some associated solutions II. Heat capacities and compressibilities

The heat capacities of liquid piperidine, tetrahydropyran, and cyclohexane, and of binary mixtures formed therefrom, have been determined in the temperature range 20 to 60 $^\circ$C at atmospheric pressure. Measurements of ultrasonic velocity and density have enabled adiabatic and isothermal compressibilities to be evaluated. The heat capacities at constant volume have been resolved into four components in the cases of cyclohexane and tetrahydropyran, the structural contributions being approximately $\frac{1}{2}$R and R cal mole$^{-1}$ deg$^{-1}$ respectively. For cyclohexane, the volume dependence of the heat capacity has also been calculated. Differences between molecular association due to dipolar interaction and that due to hydrogen bonding, evidenced by the properties of pure tetrahydropyran and piperidine, are also apparent in the excess heat capacities, excess compressibilities, and excess volumes of the systems.