Thermodynamic studies of aqueous solutions of non-electrolytes.

The excess enthalpies and excess volumes of mixing of water with a number of cyclic ethers have been measured. The results are discussed in the light of present day understanding of the structure of aqueous solutions of non-electrolytes . By correlation with data obtained using other techniques it appears that inter component hydrogen bonding plays a large role in these systems over the major part of the composition range. In the highly aqueous regions, however, this is not the case and it is likely that hydro- phobic stabilisation of water structure is a dominant factor. The mutual solubility curve for water + propylene oxide has been determined, showing the occurrence of an upper critical solution temperature, A lower critical solution temperature has been shown to exist for water + tetrahydro- furan. 'Freezing point measurements on water + 1,3-dioxolane and water + 1,3-dioxan mixtures have confirmed the existence of a structure II hydrate of the former and discovered a previously unreported hydrate of" the latter (probably structure II). Highly accurate excess enthalpies of mixing for water + acetonitrile, measured in the present work, have been used by other workers, to successfully predict the ultrasonic absorption behaviour of these solutions. An outline of the treatment is given.