Comments on the determination of tracer-diffusion coefficients using the capillary method

A method of computation which eliminates some of the experimental difficulties associated with the open-ended capillary method for determining tracer-diffusion coefficients is outlined. The calculations were based on a diffusion equation containing the corrected radioactivity (Asub(t)-Asub(i)) of the reservoir solution. Using reasonable guesses for Asub(infinity) and Asub(i), the individual diffusion coefficients Dsub(t) for all diffusion times investigated were computed. The calculations were repeated for other values of Asub(infinity) and Asub(i) to find that combination which minimizes Σ(Dsub(t)-anti D)2, anti D being the average of the set of Dsub(t). The application of this method of computation to several other sets of experimental data resulted, without exception, in error curves with well-defined minima. It may be concluded that the method described will ordinarily result in a unique value for the diffusion coefficient. (T.I.)