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As a first stage in a study of the low-temperature-region behavior of aqueous solutions, the composition regions of a large number of binary salt-water systems in which macroscopic samples can be obtained in the vitreous state have been determined. The glass transition temperatures Tg within these regions have also been measured. Correlations of the magnitude of Tg at a given composition with the formal charge on the cation (for salts with a common anion) and with the viscosity “B” coefficient of the anion (for salts with a common cation) are presented. In addition, an important correlation is found with the basicity of the anion which is interpreted in terms of the bonding of anions to the protons of the water molecules in the cationic hydration sheath. Thermodynamic relations for the composition dependence of Tg are presented. From the breaks in the otherwise monotonic composition dependence of Tg in the chloride systems, the existence of low temperature liquid–liquid immiscibility regions is proposed and is utilized in discussion of “total” hydration numbers. The Tg for pure water, obtained by extrapolation of the data, is found to be in agreement with the value obtained for vapor-deposited vitreous ice but to be incompatible with the value predicted from thermodynamic data; an interpretation in terms of different short-range order possibilities for water molecules is offered.

ConclusionStudies of the perchlorate anion Raman profiles have proved to be useful in the study of ion-solvent interactions. The use of the perchlorate anion in a ternary system of water and a second electrolyte has often been used to promote ion pairing of the second electrolyte.33,34 However, the assumption that the perchlorate anion is not also involved in ion pairing is not strictly true. The perchlorate anion has also been used as a "noninteracting" anion in (33) T. G.

Publication costs assisted by the National Science FoundationThe limit of supercooling determined by homogeneous nucleation has been investigated as a function of pressure for aqueous solutions of the common alkali halides LiC1, NaC1, KC1, CsC1, and KI for dilute solutions. The pressure dependence of the homogeneous nucleation temperature follows the pattern established earlier for HzO, TH decreasing curvilinearly until crystallization of ice I11 becomes favored at -2 kbar pressure and T C -90 "C. For 1 m solutions the TH vs. pressure plots are indistinguishable for these salts, implying that the TH depression, like the freezing point depression, is a colligative property. More concentrated solutions, containing 1 or more mol of salt per 20 mol of water (30 in the case of LiCl), fail to crystallize above -1.5 kbar and glassy phases may be obtained below -120 "C. The glass transition temperature shows a small positive pressure dependence. At constant alkali chloride concentration and pressure the glass transition temperature is a maximum for NaC1.