Thermal Diffusion in Ternary Liquid Mixtures, Particularly Aqueous Solutions Containing Ferrous Chloride

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Abstract
The accumulative arrangement of Clusius and Dickel for thermal diffusion was used to study the concentration changes at the extreme ends of the apparatus that occur in various mixtures, particularly solutions of two solutes in water. The apparatus gave reasonably reproducible results. To avoid uncertainties due to creeping along the upper part of the hot wall, any apparatus intended for the study of slightly soluble substances should be designed, as was the apparatus used, so that it can be filled without leaving an air space between hot and cold wall. The enrichment of acetic acid in water solution at the cold (and lower) end is rather small, compared with that of glycerine, or many salts or strong acids. Addition of sodium acetate does not greatly affect the enrichment of acetic acid. The enrichment of ferrous chloride in water at the cold end is considerable, but in the presence of 1M HCl the enrichment occurs at the hot end. In the presence of 1N H2SO4 the enrichment was zero. The case is opposite with zinc chloride. Here the small cold‐end enrichment that occurs in the presence of a trace of acid to prevent hydrolysis is considerably increased in the presence of 1M HCl. In a solution of ferric chloride and 1M HCl the enrichment of iron was also at the hot end. Hydrolysis takes place, but this probably works against such a result. It appears that a heavy constituent of a ternary liquid solution can migrate from cold to hot end, against the direction normally expected. A simple function of the composition is given whose sign is the same as the sign of the enrichment at the cold end in all binary mixtures (liquid or gaseous) so far studied, but not always the same in ternary mixtures.

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