This thesis is concerned with ultrasonic absorption in aqueous solutions and ultraviolet absorption spectra of the iodide ion in various solvents. The ultrasonic absorption properties of urea + water are discussed in terms of molecular equilibria. One theoretical treatment of sound absorption is applied to urea + water and accounts for the acoustic behaviour from a thermodynamic standpoint. A link is established between thermodynamic mixing functions and ultrasonic absorption in binary liquid mixtures. This link sheds some light on the factors responsible for the varied sound absorption properties- of amide + water mixtures. Ultrasonic absorption measurements are reported for sodium caprylate + water. The trends in ultrasonic absorption are discussed with reference to molecular models for micelle formation. Ultraviolet absorption spectra of iodide in aqueous agar solutions are reported and conclusions are drawn about the water structure in the gel state. The pressure dependences of the absorption spectra of iodide in three solvents are reported. Possible interpretations of the effect of pressure on the band parameters are reviewed.