Flow-cell studies of thermal diffusion in liquids. Part 1.—Cell construction and calibration

Abstract

An improved apparatus for measuring thermal diffusion in laminar flow is described. The flow cell is calibrated with 0.05 m aqueous cadmium sulphate chosen for its known thermal diffusion properties and its suitability for conductimetric analysis. Agreement with theoretical predictions (the phenomenological equations are solved in part 2 of this paper) is found to be excellent over the entire approach to the diffusional steady state.

Convection effects, which are the main source of error in the conventional pure Soret effect cell, appear to be negligible. This fact makes it possible to operate the flow cell close to the steady state where the relation between the Soret coefficient and the measured separation is independent of the calibration. Versatility is a further inherent advantage in the flow cell. Large samples of liquid are collected which can be analyzed at leisure after termination of the experiment by any analytical technique appropriate to the system under investigation. It is therefore possible to examine systems of widely different physical properties without material alteration to the cell.