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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.

An instrument is described which was designed for precision studies of isothermal diffusion in liquids by optical methods using interference fringes. This optical diffusiometer is described in some detail because it has been found to function exceptionally well for such studies and also because its main components and general design allow it to be adapted to a wide variety of optical measurements and other studies. It is basically a large precision optical bench. An 884 cm long steel beam serves as the rigid base on which are bolted stainless steel dovetail ways which extend along the full length of the beam; the contact surfaces of these ways are straight and flat to about 0.005 cm over their entire length. Riders which support the optical components may be clamped at any position along the 884 cm length of the ways. The riders are designed so that components mounted on them may be centered on and made perpendicular to the optic axis of the instrument. A special measuring rider is used in conjunction with measuring notches cut every 30.48 cm (12 in.) in one edge of the ways in order to determine the position along the ways of any other rider with an accuracy of about 0.002 cm. The entire instrument was designed with special emphasis on versatility, rigidity, precision, ease of adjustment, and freedom from vibration. This instrument permits diffusion coefficients to be measured with a greater precision than has been possible with previous models.

Time-of-flight measurements have been made on the flux of molecules from the surface of ammonium salts vaporizing under vacuum. As expected with ammonium halides and ammonium bisulfate the TOF distributions correspond to equimolar fluxes of ammonia and the corresponding acid. In the case of ammonium perchlorate the vapor subliming from a single crystal surface comprised ammonia and perchloric acid. When the source was compressed powder the vapor was a mixture of lower molecular weight species. This result seems best explained in terms of decomposition of the vapor after dissociative sublimation in the subsurface interstices of the pressed material.

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