Fluctuation of Refractive Index of Aqueous Sodium Chloride Solution and Oxygen Effect

Abstract

Fluctuation of the refractive index in aqueous electrolyte solutions has been measured for the purpose to see its concern with the internal structure of the solution. It is found that the fluctuation is anomalously enhanced at specific concentration with the copresence of oxygen. When oxygen is removed, enhancement does not occur. The results observed suggest the presence of a critical concentration which divides the structure of the solution into two phases: in one, the bulk solvent molecules are dominant, and in the other, the solvated ones are dominant. It is assumed that oxygen plays a catalytic function for the enhancement of the thermal flow in and out of the solution. The critical concentration for the sodium chloride solution was determined to be ca. 0.4-0.5mol/l, which almost coincides with the concentration of salt in sea water. Significance of the present finding in nature will be discussed as well as the usefulness of the measurements of fluctuation in analytical chemistry.