Average cross-sectional areas of molecules by gaseous diffusion methods

Abstract

1. A new and simple method for the determination of the diffusion coefficients of volatile substances is described. 2. From the diffusion coefficients the average cross-sectional areas of the molecules of iodine, benzene, naphthalene, anthracene, toluene diphenyl, aniline, and benzidine are calculated by the Stefan-Maxwell- Jeans equation. 3. The cross sections of molecules so determined are compared with the average cross sections of the molecules of benzene, naphthalene and anthracene proposed by Bragg from X-ray analysis. Models of Bragg's molecules have been constructed of wax, to scale, and the average cross sections determined by a shadow-projection method. The agreement is very good. Values determined from Huggins' models do not agree with the diffusion values quite so well. 4. It is shown that the carbon atoms in the chain of the «-octane molecule are probably arranged in the same zigzag manner as found by X-ray examination by Muller and Shearer for the alcohol part of ester molecules. The diffusion method confirms the conclusion, based on chemical evidence, that diphenyl and benzidine have a collapsed structure. © 1925, American Chemical Society. All rights reserved.