Self-diffusion coefficients of 15 liquids have been measured as a function of temperature between their melting and boiling points. The systems investigated were the benzenes, CBH5X where X = H, F, C1, Br, and I, n-paraffins, CnHnfe where n = 7, 9, 10, 12, 14, 16, and 18, acetone, acetic acid and water. The pulsed nmr technique was employed for the diffusion measurements. In addition, the viscosities of the halogenated benzenes have been measured between 2OoC and their melting points.The diffusion results obtained in this study have been found in excellent agreement with the best values available for benzene (Collings and Mills, 1970) and water (Longworth, 1960). The relation between the apparent H. ERTL and F. A. L. DULLIEN molecular diameter d (d = 2.24(7VD/RT)S) and the critical volume as suggested by Dullien (1972) has been extended to include the temperature dependence of d. It is also shown that the temperature dependence of d is similar for all liquids studied here with respect to the reduced temperature. The increase of d for T, < 0.46 shows the invalidity of the Stokes-Einstein relation for this temperature range (T, = T/Tc).A normalized plot of d has been found very useful in checking the consistency of viscosity and self-diffusion data. The relations proposed in this work can be used to predict self-diffusion coefficients and viscosities over the normal liquid range.

tion coefficient theories. The predictions are compared with the experimental results throughout the review. Part I will be followed by Part I1 in November reviewing self-diffusion, empirical predictive equations, and experimental techniques. A supplement of critical tabulations of all experimental diffusion data since 1956 has been prepared.

Part I1 of the review paper covers the self-diffusion theories and their comparison with experimental results. This is followed by a review of empirical and semi-empirical predictive equations of mutual and self-diffusion coefficients. Recent developments in experimental techniques for measuring liquid diffusivities are discussed in the last section. A supplement of experimental diffusion data since 1956 is available.

The liquid viscosities and self-diffusion coefficients of benzene, the monohalogenated benzene derivatives, and some normal paraffins have been determined as a function of temperature down to the proximity of the melting points. Based on these data it appears that Hildebrand's equation for viscosity is valid only down to T/Tc ~0.46, whereas in its original form the equation suggested by him for self-diffusion coefficient is not valid anywhere in the temperature range studied. A small modification of this equation, however, has been found to describe the experimental diffusivities well in every case.

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