Equivalent volumes of mixtures of molten alkali and alkaline earth nitrates

Abstract
The densities of a selection of binary mixtures of fused alkali nitrates with alkaline earth nitrates have been measured by means of a manometric densitometer. Within the range of liquid stability all results are expressible as a linear function of temperature. For any pair of salts the isotherms of equivalent volume as a function of equivalent composition have been found to be straight lines. Although decomposition did not permit observations over the whole temperature range, any excess volumes of mixing are sufficiently small to justify extrapolation to determine the theoretical equivalent volumes of the alkaline earth nitrates. The partial equivalent volumes V m (the volume of melt containing one gram-ion of nitrate ion) of the constituents are thus effectively independent of composition at a given temperature and are given by: NaNO 3 V m = 44.18 + 1.76 x 10 -2 ( t - 300) KNO 3 V m = 53.25 + 2.29 x 10 -2 ( t - 300) RbNO 3 V m = 58.37 + 2.62 x 10 -2 ( t - 300) CsNO 3 V m = 66.25 + 3.06 x 10 -2 ( t - 300) 1/2 Mg (NO 3 ) 2 V m = 38.80 + 1.12 x 10 -2 ( t - 300) 1/2 Ca(NO 3 ) 2 V m = 38.70 + 1.01 x 10 -2 ( t - 300) 1/2 Sr(NO 3 ) 2 V m = 39.55 + 1.02 x 10 -2 ( t - 300) 1/2 Ba(NO 3 ) 2 V m = 41.75 + 1.03 x 10 -2 ( t - 300) where t is the temperature in degrees Celsius. V m is correct to ±0.1 % and the expansion coefficient to 1.3%. An interpretation of the effectively ideal behaviour of these systems is discussed on the basis of simple structural models for the packing of nitrate ions.

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