also necessitates a conservation of "mass" indicating, for a constant sample size, an isosbestic point in the data curves.3. If the points lie in a straight line, one can determine a reaction rate constant, k, for A = B from the spacing of the points.4. If the points fall on a line through the origin, the proportion of A and B is constant and the sample size is changing. The distance from the origin along this line is proportional to the sample size. 5. If one uses a constant sample size and runs an unknown mixture and successive dilutions of this mixture with one component, the composition of the unknown mixture can be determined from its distance from the boundaries along a line parallel to 9. Figure 10 is an example for a 50:50 "unknown" mixture of A and B. Three other samples are prepared by sequential dilutions (1:1) withIf the sample size is not constant, the points will not be in a line, but the analysis can still be obtained by passing line 9 through each original sample point and measuring as above.
ACKNOWLEDGMENTThe discussions with William Lawton and the help of Paul Taylor with some of the experimental work and with the final drawings are greatly appreciated.
The diffusion coefficients of seven octane isomers in helium were measured by the chromatographic broadening technique with excellent precision and a n estimated accuracy of 1%. This was accomplished by computer manipulation of the data. It is found that as branching increases, the diffusion coefficients also increase. This can be explained by Giddings' shielding treatment. A direct correlation is found between the diffusion coefficients of the isomers and their critical volumes and related parameters. Data analysis indicates that the critical volume of 2,2,4-trimethylpentane quoted in the literature might be too high. An attempt is made to modify the Fuller, Schettler, and Giddings estimating equation to take into account molecular branching.Mass transport phenomena play a major role in many and diverse fields of both basic and practical science. For example, diffusion is important in chemical reactions and in designing absorbers, distillation columns, etc. Two excellent reviews by Mason and Marrero1,2 recently appeared which contained both a theoretical treatment of diffusion and a discussion of experimental diffusion measurements. There are many equations which attempt to (15)
Coefficients by Gas ChromatographyGas chromatography, in addition to being a well-established separation tool, is increasingly being used to obtain thermodynamic (/), kinetic (2), and kinetic-molecular information (8). In this paper we would like to describe an instrumental analysis or physical chemistry experiment involving the measurement of the diffusion coefficient, D, of a binary gaseous mixture. This experiment is attractive since, in addition to the measurement of diffusion coefficients,
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