When the molecules of a diffusing substance react with the medium into which they diffuse in such a manner that they no longer take part in the diffusion process, a sharp boundary line results which is displaced at a rate determined by the conditions of the particular experiment. A theory of this phenomenon was presented by J. J. Hermans and was applied to determine the diffusion constants in some ionhyphen;gel systems. In the present paper the method of moments which was recently worked out by Yamada to deal with the boundaryhyphen;layer equations is applied to obtain approximate solutions of the basic equations of the J. J. Hermans theory for both linear and cylindrical diffusions. The particular concern of the present paper is to analyze the experimental data obtained by J. J. Hermans for cylindrical diffusion in a copper ionhyphen;cellulose xanthate system on a more reliable basis than in J. J. Hermans' paper referred to. It is found that the present analysis provides the diffusion constants which are considerably higher (about 2.6 times) than those evaluated by J. J. Hermans. Nevertheless, the values found are still too low as compared with the experimental value determined by the steadyhyphen;state method, and a further research of the problem needs to be made.
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