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      This period was a hard one for D. I. Mendeleyev also by another reason. It seemed to him that he didn’t have enough energy in order to realize his creative potential sufficiently. However, he kept working, and the periodical law, discovered by him, got more and more followers among the scientists of the world.

      From the very beginning appeared the question of the priority of the discovery, started by the number of English and German scientists: W. Odling, L. Meyer, etc., in connection with the fundamental importance of the law. Mendeleyev devoted his publication “To the question of the system of elements”, which appeared in the “Reports of German Chemical Society” in 1871, right to this problem. In his small article the scientist mentioned the most important stages of his discovery and suggested for the first time to call his system periodical, because of the periodical law being its basis: “The measurable chemical and physical characteristics of the elements and their connections depend periodically on the atomic weights of the elements.”

      The article “The periodical legality of the chemical elements”, which was the result of more than two years of work of the scientist, was published in 1871 in the “Annals of Pharmacy” (“Annalen der Pharmacie”), the oldest chemical magazine, founded in 1832 by the German chemist J. Libich. That is the evaluation of this article by Mendeleyev at the end of the 1890’s:

      “This is the best code of my opinions and considerations about the periodicity of elements and this is the original, according to which there was written so much about this system. This is the main reason of my scientific reputation…”

      In the same article the scientist gave the criterion of the solidity of the laws of nature in general: “Every law of nature gets the scientific meaning only in case that it, so to say, allows practical consequences, i. e. such logical conclusions, which explain unaccounted and point to the phenomena unknown before, and especially if the law leads to the predictions, which may be checked by experiment. In the last case the meaning of the law is evident and it is possible to check its equity, which at least impulses to the development of the new spheres of the science.”

      By applying this thesis to the periodical law, he mentioned the following opportunities of its application: 1) to the system of elements;

      2) to the definition of the characteristics of yet unknown elements;

      3) to the definition of the atomic weight of scantily explored elements;

      4) to the correction of the values of atomic weights; 5) to the renewal of the data concerning the forms of chemical compounds. Besides, Mendeleyev pointed to the possibility of “application of the periodical law: for the correct idea of the so-called associated compounds; for the comparative research of the physical characteristics of simple and compound bodies.” Mendeleyev thought when the physical sense of the periodical law would have been understood and the essence of the elements’ distinction would have been discovered on this basis, “then, certainly, chemistry would be able to leave the hypothetical field of static ideas, which are dominating there nowadays, and then there would be an opportunity to place it under the dynamic direction, which is already applied productively enough to the study of most of the physical phenomena.”

      It is possible to say that the scientist outlined by this article the broad programm of the research on the subject of inorganic chemistry, based on the law of periodicity. Indeed, many important directions of inorganic chemistry were developed actually at the end of the 19^th – beginning of the 20^th century according to the ways, designed by D. I. Mendeleyev.