Diffusion thermoeffect measurements of heats of transport in ternary liquid toluene–chlorobenzene–bromobenzene mixtures at 25 and 35 °C

Abstract

Heats of transport in ternary nonelectrolyte liquid mixtures have been directly measured for the first time. Diffusion thermoeffect measurements have been made for ternary mixtures of toluene–chlorobenzene– bromobenzene at 25 ° and 35 °C. A new boundary sharpening technique was used in addition to a liquid gate withdrawal method. Both techniques yield consistent, accurate values of the heat of transport, but the new cell provides versatility in allowable densities and compositions of the initial phases. Heats of transport were obtained by nonlinear least-squares fitting of calculated to experimental temperature differences measured at positions symmetric about the initial diffusional interface. The two independent heats of transport, obtained by performing two runs with different starting composition gradients for each mean composition, were each fit to a polynomial in temperature and composition. The resultant analytical expression is valid only in the region bounded by 0.1⩽wi⩽0.6(i=1,2) and w3⩾0.1, where the composition is far enough from the binary limits that both of the two heats of transport remain defined and independently determinable. The results obtained for the heats of transport show a direct dependence on temperature and a strong dependence on the relative amount of the heavy component, bromobenzene. These facts are consistent with a proposed interpretive model of the diffusion thermoeffect.