The apparent molal volumes of ZnSO ₄ and CuSO ₄ have been determined from density data over the temperature range 15–55°C and concentration range 0–15 molal. The volume data have been fitted to the Pitzer formalism over the entire temperature and concentration range. The volume changes for the formation of ZnSO ₄ and CuSO ₄ ion pairs have been estimated over the temperature range covered and the partial molal volumes of ZnSO ₄ and CuSO ₄ ion pairs have been derived. The results were used to explain the hydration structure of the ion pair. UV spectral effects accompanying a change of temperature in the 15–65°C range in CuSO ₄ solution indicate direct coordination of sulfate anion to the cupric cation. The process is favored by an increase in temperature.