text: Mendeleev made other important contributions to chemistry. The Russian chemist and science historian Lev Chugaev characterized him as "a chemist of genius, first-class physicist, a fruitful researcher in the fields of hydrodynamics, meteorology, geology, certain branches of chemical technology (explosives, petroleum, and fuels, for example) and other disciplines adjacent to chemistry and physics, a thorough expert of chemical industry and industry in general, and an original thinker in the field of economy." Mendeleev was one of the founders, in 1869, of the Russian Chemical Society. He worked on the theory and practice of protectionist trade and on agriculture.
  In an attempt at a chemical conception of the aether, he put forward a hypothesis that there existed two inert chemical elements of lesser atomic weight than hydrogen. Of these two proposed elements, he thought the lighter to be an all-penetrating, all-pervasive gas, and the slightly heavier one to be a proposed element, coronium.
  Mendeleev devoted much study and made important contributions to the determination of the nature of such indefinite compounds as solutions.
  In another department of physical chemistry, he investigated the expansion of liquids with heat, and devised a formula similar to Gay-Lussacs law of the uniformity of the expansion of gases, while in 1861 he anticipated Thomas Andrews conception of the critical temperature of gases by defining the absolute boiling-point of a substance as the temperature at which cohesion and heat of vaporization become equal to zero and the liquid changes to vapor, irrespective of the pressure and volume.
  Mendeleev is given credit for the introduction of the metric system to the Russian Empire.
  He invented pyrocollodion, a kind of smokeless powder based on nitrocellulose. This work had been commissioned by the Russian Navy, which however did not adopt its use. In 1892 Mendeleev organized its manufacture.
  Mendeleev studied petroleum origin and concluded hydrocarbons are abiogenic and form deep within the earth – see Abiogenic petroleum origin.
  He wrote: "The capital fact to note is that petroleum was born in the depths of the earth, and it is only there that we must seek its origin." (Dmitri Mendeleev, 1877)