D. I. Mendeleev's concept of chemical elements and the principles of chemistry

The text of the first and later editions of The Principles of Chem. with its background is analyzed, and the role played by Dmitrii Ivanovich Mendeleev's concept of the chem. elements in the discovery of the periodic law and its later development are shown. Mendeleev's concept of the chem. elements as a stable, intermediate level of matter, not necessarily based on the speculative concept of the atom, corresponded to the state of chem. in the mid-19th century. Ironically, this helped Mendeleev in his discovery of the periodic law. This deep insight, which assured him of the validity of his discovery, allowed Mendeleev to fully apply the concept to the chem. of his time, without being bothered by a seeming regularity in nos. in the one hand, or being misled by a speculative primordial matter on the other.