A solution of the diffusion equation

A nonstationary solution is obtained for the diffusion equation in the case of two gas containers of arbitrary volume, connected by a capillary. If the volume of the capillary is regarded as negligibly small in comparison with the flask volumes, the solution turns into the formula derived by Ney and Armsteady, and as the volume of one of the flasks approaches infinity, the solution turns into the one derived by Frank-Kamenetskii.