By using various mixtures, properties of molten nitrates can be studied at temperatures well below the freezing points of any pure nitrates of alkalis or alkaline earths. Molar volumes, viscosities, electrical conductivities and ultra-violet absorption spectra have been investigated in this way for mixed nitrate melts down to 140°C. For a typical pair of uni-univalent cations, such as potassium and sodium, each of these properties shows practically linear variation for all mixtures down to the lowest temperatures studied. On the other hand, cations such as calcium with a higher polarizing power cause marked deviations from linearity in transport properties and absorption spectra in certain mixtures. However, even in such mixtures no excess volume is found, and temperature variation of the molar volume remains linear. Effects observed are discussed in terms of the closest approach between cations and the nitrate anions in these melts. As the temperature falls, there appears to be progressive formation of regions of increased packing density in the melt and corresponding irregular voids. These more densely packed regions may be termed ‘clusters’ or ‘associated’ groups of ions. Although probably smaller, such transient clusters have analogies with ‘flickering clusters’ proposed in some models for water near its freezing point.
CXXXII.—The ultra-violet absorption spectra of aromatic compounds. Part I. Benzene and certain mono-substituted derivatives
