THE great Russian chemist, Dmitri Ivanovitch Mendeleef, died in St. Petersburg, February 2, 1907, at the age of 73. Prof. Mendeleef may well be ranked among the foremost chemists and scientists of his time, and it is not too much to say that his name was esteemed and revered throughout the civilized world. He was well known in England, and as long ago as 1882 he was, together with Lothar Meyer, awarded the Davy Medal of the Royal Society, for researches on the periodic classification of elements. To this we shall refer later on. In 1892 he was made a foreign member of the Royal Society—a distinction to which none but the foremost among scientists attain. In 1889 he gave the Faraday Lecture before the Chemical Society of London, and in 1905 was honored by the Royal Society with the Copley Medal. Such is a brief record of the recognition of his abilities shown by that country, and brilliant though it is, it cannot be considered in any way to go beyond what he deserved. Mendeleef was the youngest of a large family, and was born in February, 1834, at Tobolsk. Here he obtained his primary education, afterward studying natural science at the University of St. Petersburg, taking his degree in 1856. After having taught for some time at Simferopol in the Crimea, and at Odessa, he went at the age of twenty-six to Heidelberg, where he set up in business as an analytical chemist. He was not long there, however, but returned to St. Petersburg in order to become Professor of Chemistry at the Technological Institute. Three years after accepting this post he was offered the Chair of Chemistry at the St. Petersburg University, he being then about thirty years of age. Perhaps Mendeleef's name will in future be best remembered by reason of his enunciation of what Is termed the periodic law of elements. As early as 1869 he made a communication to the Russian Chemical Society. In this he pointed out how that the chemical elements, if arranged in order of their atomic weights, show a periodicity of properties, and form a series of groups which possess more or less distinctive characteristics. This subject he followed up much more systematically and scientifically than had ever been done before. Others had previously noticed that there were a certain number of coincidences of the kind, but there were so many exceptions that it was by no means looked upon in the light of a law, and it remained for Mendeleef to have the courage to surmise that the atomic weights of those substances which did not conform to the “lew” had been wrongly ascertained. His surmises were subsequently proved to be correct, and his law established. An additional result to the correction of certain atomic weights was the prediction of undiscovered elements. The existence of three of these he definitely indicated. He found three blanks in his table which manifestly should be filled, and he foretold the existence of three undiscovered elements, to which he gave the provisional names of eka-boron, eka-aluml- nium, and eka-silicon. Not only this, but he set out in detail the attributes which should belong to these elements. His prophecy, which was made in 1871, was found to be wonderfully accurate. Four years later one of the missing elements was discovered by Lecocq de Bois Baudran, who called it gallium. Five years afterward Nilson found another in scandium, and in 1886 Clemens Winkler discovered the third, and called it germanium. These elements not only fitted correctly into the position assigned to them by Mendeleef, but approximated very closely in their properties to those which he had assigned to them. Still later in history the rare gas elements, argon, helium, neon, krypton, etc., have found correct places in the table. Taking his process of deduction still further, Mendeleef suggested that what is known as the ether might consist of an absolutely inert gas of an atomic weight very greatly less than that of hydrogen. He could not subscribe to the theory that the ether had no weight, and was imponderable, but he suggested that the majority, at all events, of observed phenomena were compatible with the existence of such a gas as he had indicated, which gas would possess such penetrative power that it could pass with ease through any other substance, and pervade it thoroughly. The study of the periodic law and the various investigations to which it naturally led, though, as we have said, the work by which he will always be best known, by no means constituted his only sphere of labor. Indeed, his field of investigation and research was particularly wide. He was greatly interested in the researches at low temperatures. He carried out many investigations regarding the behavior of gases under varying pressures and temperatures. He was the author of numerous works on chemical subjects, among these being “Principles of Chemistry,” 1870; “Naphtha Production in America and the Caucasus,” 1877; and “The Investigation of Solutions from their Specific Gravity,” 1887. His attention was by no means entirely confined to theoretical studies; indeed, he was constantly at work suggesting means of utilizing the products of his country and of improving her manufactures. He was also for some time engaged in experimenting with smokeless powders for the Russian government.—Engineer.