Relative densities and heat capacity ratios have been measured for selected aqueous systems. These measurements have been used to calculate apparent molar volumes and heat capacities. Densities of aqueous sodium bromide have been measured from 374 to 522 K and 10.00 to 30.00 MPa using a recently developed high temperature and pressure vibrating tube densimeter. These data have been used to test the utility of an automated high temperature and pressure densimetric data analysis program. Apparent molar volumes and heat capacities of several aqueous rare earth sulphate systems at 298.15 K and 0.10 MPa have been reported, and discussed in terms of ionic contributions. Single ion partial molar volumes and heat capacities for aqueous trivalent rare earth species have been estimated in a review of apparent molar data from the literature and through the use of semi-empirical Debye-Huckel equation. These singles ion properties have subsequently been used to estimate the single ion properties of the monosulphate and disulphate rare earth complex species. Rigorous relaxation calculations are presented in a discussion of apparent molar heat capacities, where relaxation contributions are shown to be negative. Apparent molar volumes and densities for aqueous L-histidine, L-phenylalanine, L-tyrosine, L-tryptophan, and L-dopa have been used to estimate reported partial molar properties have been added to several reported properites for other amino acids and peptides to construct an additivity scheme that utilises the revised Helgeson, Kirkham, and Flowers (HKF) equations of state for neutral organic species. A volumetric study of aqueous glycine, L-serine, and glyclylglycine has been conducted at temperatures from 298 K to 423 K and pressures from 0.10 to 30.00 MPa. These data have been used to evaluate HKF coefficients in a discussion of peptide stability at elevated temperatures and pressures. / xvii, 220 leaves : ill. ; 28 cm.