The self‐diffusion in benzene‐toluene and benzene‐cyclohexane solutions have been measured at different temperatures. The capillary‐cell method was employed. The activation parameters of self‐diffusion for the systems are presented. The data have been used to test the validity of various diffusion equations proposed in the literature. The hypothesis that the self‐diffusion was realized by movement of aggregates of molecules is suggested.

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The self‐diffusion coefficients of acetonitrile, water and iodide ion and the conductance of Et4NI have been measured at 25.0°C in acetonitrile water mixtures for the whole composition range of the binary solvent, for the salt molarity ranging from 3 · 10−5 to 1 · 10−2. The limiting self‐diffusion coefficient of iodide ions is in the range between 1.6 · 10−5 and 2.8 · 10−5 cm2 s−1 with a minimum at about 10 mole% CH3CN, whereas the limiting self‐diffusion coefficient of tetraethylammonium ions increases monotonously form 0.8 · 10−5 in aqueous solution up to 2.2 · 10−5 in acetonitrile solution. Basing on the composition dependences of ionic radii an influence of the mixed solvent composition on the solvation of ions is discussed. Tetraethylammonium ion has been found to be unsolvated and to lose its hydrophobic properties in the presence of acetonitrile. The association constant, calculated from the conductivity measurements, increases monotonously with decreasing static dielectric constant of the acetonitrile‐water mixtures. The decrease of the self‐diffusion coefficients of water and of acetonitrile in the presence of Et4NJ results from the increase of the solution viscosity. The lack of the effect of Et4NI on the microphase separation of the acetonitrile‐water mixtures has been observed.

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