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Diffusion and refractive index data at 25°are reported for the binary systems glycine-H20, gIycylglycine-H20, -amino-n-butyric acid-H20, and d!Z-valine-H20. The diffusion data are combined with other available thermodynamic data to compute mutual frictional coefficients for these systems. These mutual frictional coefficients are compared with those for other binary systems which have been calculated from the data in the literature. A relationship between relative frictional coefficients and relative viscosity is tested.Many papers in recent years have reported diffusion coefficients for both binary and ternary isothermal diffusion.For binary diffusion these coefficients, which are defined by Tick's first law,1 11relate the flow of a given component to the corresponding concentration gradient when relative motion of the components is taking place. It has been emphasised that, when reporting diffusion coefficients, the frame of reference should be specified2-3 and coefficients for several frames of reference have been given in the literature, both for binary3 and ternary diffusion.4-13 However, as has been previously indicated, it is possible to define mutual frictional coefficients,14-20 independent of the frame of reference, which may be computed from the measured diffusion coefficients and certain corresponding thermodynamic data. It is the purpose of this paper to report frictional and diffusion coefficients for the systems glycine-H20, glycylglycine-H20, aamino-n-butyric acid-H20, and di-valine-H20 and to compare these frictional coefficients with others which may be computed from the diffusion and thermodynamic data in the literature. ExperimentalApparatus. Almost all the diffusion measurements were.made with a Gouy diffusiometer21 which was supported and aligned on a 9-m. lathe bed. This optical bench was mounted kinematically on three stainless steel ball bearings, 7.6 cm. in diameter, which rested in steel supports on top of three concrete pillars which were isolated from the floor of the room and set 1.8 m. into the earth.

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