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Dmitri Ivanovich Mendeleyev

chemistry, nature, elements, st and law

MENDELEYEV, DMITRI IVANOVICH Russian chemist, the youngest of a family of seventeen, was born at Tobolsk, Siberia, on Feb. 7, 1834. After attending the gym nasium of his native place, he went to study science at St. Peters burg, where he graduated in chemistry in 1856, subsequently be coming privatdozent. He became professor of chemistry in the technological institute at St. Petersburg in 1863, and three years later succeeded to the chair in the university. In 1890 he re signed the professorship and in 1893 became director of the Bureau of Weights and Measures, a post which he occupied till his death at St. Petersburg on Feb. 2, 1907.

Mendeleyev's name is best known for his work on the Periodic Law (q.v.). Various chemists had traced numerical sequences among the atomic weights of some of the elements and noted connections between them and the properties of the different substances ; but it was left to him to give a full expression to the generalization, and to treat it not merely as a system of classify ing the elements according to certain observed facts, but as a "law of nature" which could be relied upon to predict new facts. Thus in 1871 he was led by certain gaps in his tables to assert the existence of three new elements so far unknown to the chemist, and to assign them definite properties. These three he called eka-boron, eka-aluminium, and eka-silicon ; and his prophecy was completely vindicated within fifteen years by the discovery of gallium in 1871, scandium in 1879, and germanium in 1886. Again, in several cases he ventured to question the correctness of the "accepted atomic weights," on the ground that they did not correspond with the Periodic Law, and here also he was justi fied by subsequent investigation. Mendeleyev also devoted much

study to the nature of solutions, which he looked upon as homo geneous liquid systems of unstable dissociating compounds of the solvent with the substance dissolved. In another department of physical chemistry he investigated the expansion of liquids with heat, and devised a formula for its expression, while so far back as 1861 he anticipated T. Andrews's conception of the critical temperature of gases (see LIQUEFACTION 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 vapour, irrespective of the pressure and volume. He also gave much time to the study of the nature and origin of petroleum.

Mendeleyev's best known book is The Principles of Chemistry, which was written in 1868-1870, and has gone through many sub sequent editions in various languages (Eng. ed. 2 vols., 1905). He was awarded the Davy medal of the Royal Society in 1882, and in 1905 he received its Copley medal. He was one of the greatest teachers of his time. His lecture room was always thronged with students. "Many of them," writes one of these, "I am afraid, could not follow Mendeleev, but for the few of us who could it was a stimulant to the intellect and a lesson in scientific thinking which must have left deep traces in their development." See W . A. Tilden, "Mendeleeff Memorial Lecture," Jour. Chem. Soc., 95 ; P. Walden, "D. I. Mendelejeff" in Berichte d. deutsch. Chem. Ges. (1908) ; T. E. Thorpe, Essays in Historical Chemistry (1911) ; W. A. Tilden, Famous Chemists (1921).