APPARENT MOLAL VOLUMES OF LITHIUM AND SODIUM HALIDES . CRITICAL-TYPE TRANSITIONS IN AQUEOUS SOLUTION

Measurements of the apparent molal volumes of LiCl, LiBr, LiI, NaCl, NaBr, and NaI have been made with primary emphasis on obtaining precise values of Δφv/Δ√c at small intervals. Most results were at 25°, a few at 5°, and one at 35°. For LiBr, LiI, NaBr, and NaI, the curves of Δφv/Δ√c vs. √c appear to be discontinuous in a form suggesting a λ-shaped region for the integral curve or inverted for NaBr. Different series of measurements with LiI gave the apparent discontinuity at different concentrations and one of the four LiI runs did not show the apparent discontinuity. For NaCl the existence of a singularity is not definite and LiCl showed no sign of a singularity. It is suggested that these singularities are due to a new kind of transition of the critical type in the solution. Two possible sources of the transition are either in a change of solution structure as previously suggested or in a change in form of the ion radial distribution function as found by Kirkwood.