This article is the third in the author’s investigations, devoted to the search for errors and discrepancies that were accumulated in the mathematical description of mass transport in solids, especially when trying to explain the Kirkendall’s effect. Darken theory contains a huge number of absurdities. Darken theory, unfortunately, was accepted by faith without any critical analysis of the arguments of its creator. The explanation of Kirkendall’s effect by Darken was briefly discussed in a previous article. It has been shown that the experiments conducted by Kirkendall are naturally explained on the basis of some approximation of Fick's second law. Bluff of Darken’s theory will be discussed in a next article.