Ultrasonic absorption studies are carried out in carboxylic acid-dioxan mixtures for various concentrations at 30±0.1°C. The measured absorption is much higher than the classical absorption. The excess absorption initially increases with increase of carboxylic acid concentration, attains a maximum and then decreases with further increase in concentration. The related parameters such as volume viscosity, relaxation time and free energy difference between the two states (ΔF) have also been calculated. The results can be explained satisfactorily using Hall’s two-state model.

Ultrasonic absorption was measured in ortho and para hydroxy benzoic acid (OHBA and PHBA) in dioxan at room temperature for various solute concentrations. The variation of ultrasonic absorption in both solutions with the solute concentration showed two maxima, one at lower solute concentration and the other at higher solute concentration. The first maximum is explained as due to formation of hydrogen bonds between the O-H groups of OHBA and PHBA molecules and the oxygen of dioxan molecules and the second maximum as due to the COOH group of the OHBA/PHBA molecules and oxygen of dioxan molecules. In both systems the measured absorption is explained on the basis of Hall’s two-state model.