Popular Science Monthly/Volume 40/December 1891/Sketch of Dimitri Ivanovich Mendeleef
|SKETCH OF DIMITRI IVANOVICH MENDELEEF.|
THE discovery of the periodic law in the atomic weights of the elements has furnished chemists with a new standard of accuracy and a new guide in research. While it must be regarded as Mendeleef's most conspicuous scientific achievement, the Russian chemist is the author of many other labors of hardly less real importance.
Dimitri Ivanovich Mendeleef was born at Tobolsk, Siberia, February 7, 1834, the seventeenth and youngest child of Ivan Paulovich Mendeleef, director of the gymnasium there. Soon after his birth the father became blind and had to resign his position, leaving the care of the family upon the mother, a competent and energetic woman. She established and managed a glass-works, and brought up and educated her family upon its profits. Dimitri was sent to the gymnasium at Tobolsk, and, at sixteen years of age, to St. Petersburg, where he was to study chemistry in the university, under Zinin; but was transferred to the Pedagogical Institute in the same building with the university, where he entered the physico-mathematical department, or that of the natural sciences. He studied chemistry, physics, mathematics, botany, zoölogy, mineralogy, and astronomy, under teachers who were most of them also professors in the university. Having concluded his course here, he was appointed to the gymnasium at Simferopol, in the Crimea; then, during the Crimean War, to a gymnasium in Odessa; and in 1856 he became a Privat Docent in the University of St. Petersburg, where he had already received the degree of Master of Chemistry. In 1859, having obtained permission from the Government to travel, he became engaged at Heidelberg in the determination of the physical constants of chemical compounds. In 1863 he was made Professor of Chemistry at the Technological Institute of St. Petersburg, and in 1836 at the university, where he received the degree of Doctor of Chemistry.
Mendeleef had already before his engagement as a Privat Docent entered upon the career of research and publication in which he has so brilliantly distinguished himself. His first paper, on Isomorphism, was prepared while he was still in the Pedagogical Institute. He entered into the discussion of the relations between the specific gravities of substances and their molecular weights, and presented to the physico-mathematical faculty of the university a number of theses or problems relating to specific volumes; and as early as 1856 he accepted Gerhardt's mode of determining the chemical molecule. His researches on specific volumes were continued till 1870, and in them, according to Prof. T. E. Thorpe, from whose memoir in Nature we derive most of the material of this sketch, he extends Kopp's generalizations, and traces the specific volumes of substances through various phases of chemical changes. In a paper on the thermal expansion of liquids above their boiling-points, he showed that the empirical expressions given by Kopp, Pierre, and others are equally applicable to much higher temperatures, and that the expansion-coefficient gradually increases with the diminution in molecular cohesion of the liquid, until, in the case of some liquids, it becomes even greater than that of the gas. In 1883 he contributed to the English Chemical Society a paper giving a simple general expression for the expansion of liquids under constant pressure between zero and their boiling-points—a formula analogous to that which expresses Gay-Lussac's law of the uniformity of expansion of gases; but which, like Gay-Lussac's law, however correct in theory, is subject to deviations in application. These deviations were shown to be related to the molecular weights of the gases.
Researches in thermal chemistry, made in 1882, showed him that the data obtained by Berthelot, Thomson, and others, regarding the "heats of formation" of hydrocarbons, stood in need of correction, because allowance had not been made for the physical changes involving absorption or evolution of heat which accompany the chemical changes considered; and he gave a table giving the heats of formation from marsh-gas, carbon monoxide, and carbon dioxide, of a series of hydrocarbons, for chemical reactions that actually occurred, while the reactions given by Berthelot and others were not realized in practice.
In the investigation of solutions, Mendeleef propounded in 1884 the law that in solutions of salts the densities increase with the molecular weights; but if we take, instead of the molecular weights, the weights of their equivalents or those of the equivalents of metals, the regularity of increase disappears; and, though his research was not yet finished, he submitted an equation as preliminary to ulterior results promising to give a more general formula. The results of the determination of the specific gravity of aqueous solutions of alcohol were applied, according to Prof. Thorpe's memoir, toward the elucidation of a theory of solution in which Dalton's doctrine of the atomic constitution of matter could be reconciled with modern views concerning dissociation and the dynamical equilibrium of molecules. "According to Mendeleef, solutions are to be regarded as strictly definite atomic chemical combinations at temperatures higher than their dissociation temperature; and, just as definite chemical substances may be either formed or decomposed at temperatures which are higher than those at which dissociation commences, so we may have the same phenomenon in solutions; at ordinary temperatures they can be either formed or decomposed. In addition, the equilibrium between the quantity of the definite compound and of its products of dissociation is defined by the laws of chemical equilibrium, which require a relation between equal volumes and their dependence on the mass of the active component parts."
In 1881 Mendeleef turned his attention to experiments on the elasticity of the gases, which he continued with the aid of several of his pupils. They led to many interesting results, among which was one showing that the deviations from Marriotte's law were in opposite directions at pressures above and below that of the atmosphere; indicating that air, for instance, as well as carbonic acid and sulphurous acid gases, experience a change of compressibility at certain pressures.
The results of these experiments were used in studies of the physical nature of the rarefied air of the upper atmosphere and the application of aeronautics, and he attempted to organize meteorological observations in the upper atmosphere by means of balloons.
The principles on which Mendeleef based the periodic law were first explained in a paper read before the Russian Chemical Society in 1869. As repeated by the author in his Faraday lecture to the English Chemical Society, they declare that the elements, if arranged according to their atomic weights, exhibit a periodicity of properties; that elements which are similar in chemical properties have atomic weights that are nearly of the same value or which increase regularly; that the arrangement of the elements or groups of elements in the order of their atomic weights corresponds to their so-called valencies, and, to some extent, to their distinctive chemical properties; that the elements which are the most widely diffused have small atomic weights; that the magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body; that the discovery of many yet unknown elements may be expected; that the calculation of the atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements; and that certain characteristic properties of elements can be foretold from their atomic weights. The theory was founded upon experiment, and assumed the adoption of the definite numerical values of the atomic weights, and the recognition that the relations between the atomic weights of analogous elements were governed by some general law, with a more accurate knowledge of the relations and analogies of the rarer elements as necessary for the completing and proving of it. In accordance with the theory as thus developed, a table was composed by Mendeleef and Victor Meyer, including nearly but not quite all of the elements —for there were a few of which, not enough was yet accurately known to determine their subjection to the rule—arranged in the order of their atomic weights and in groups or periods showing their relations and analogies. These periods might be said to be self-constituted; for, without departing from the orderly arrangement which Mendeleef had declared to exist, they so fell in line as to exhibit the very likenesses and differences which he had insisted upon as a part of his theory. Arranging them in parallel columns, it appeared that the several members of each period were substances that showed no similarity or community of chemical properties with one another; but that the members of the different periods showed an unmistakable parallelism with the corresponding members of the previous period. The columns also exhibited a regular gradation of electro-chemical properties, the most electro-positive elements occupying the places at their heads, and the extreme electro-negative elements the bottom places. The results of later discoveries and more accurate determinations have all been to confirm the correctness of the tabulation and the periodic theory. Thus scandium, gallium, and germanium, when discovered and examined, were found to fit into vacant places in the table, and to possess the atomic weights and the properties which the authors had predicted should belong to the elements falling in those places; and Mendeleef was able to say, in his Faraday lecture, delivered twenty years after the first suggestion of his theory, "When, in 1871, I described to the Russian Chemical Society the properties, clearly defined by the periodic law, which such elements ought to possess, I never hoped to live to mention their discovery to the Chemical Society of Great Britain as a confirmation of the exactitude and the generality of the periodic law." Up to the time of the formulation of this law. Prof. Thorpe says in his article: "The determination of the atomic value or valency of an element was a purely empirical matter, with no apparent necessary relation to the atomic value of other elements. But to-day this value is as much a matter of a priori knowledge as is the very existence of the element or any one of its properties. Striking examples of the aid which the law affords in determining the substituting value of an element are presented in the cases of indium, cerium, yttrium, beryllium, scandium, and thorium. In certain of these cases, the particular value demanded by the law, and the change in representation of the molecular composition of the compounds of these elements, have been confirmed by all those experimental criteria on which chemists are accustomed to depend. . . . The law has, moreover, enabled many of the physical properties of the elements to be referred to the principle of periodicity. At the Moscow Congress of Russian Physicists, in August, 1879, Mendeleef pointed out the relations which existed between the density and the atomic weights of the elements; these were subsequently more fully examined by Lothar Meyer, and are embodied in the well-known curve in his Modern Theories of Chemistry. Similar relations have been observed in certain other properties, such as ductility, fusibility, hardness, volatility, crystalline form, and thermal expansion; in the refraction equivalents of the elements, and in their conductivities for heat and electricity; in their magnetic properties and electro-chemical behavior; in the heats of formation of their haloid compounds; and even in such properties as their elasticity, breaking stress, etc." While one may be readily inclined and many have been led to look for a connection between the periodic law and theories of the unitary origin of matter, Mendeleef has not allowed his studies in the subject to be embarrassed by any such prepossession. He said in his Faraday lecture: "The periodic law, based as it is on the solid and wholesome ground of experimental research, has been evolved independently of any conception as to the nature of the elements; it does not in the least originate in the idea of a unique matter; and it has no historical connection with that relic of the torments of classical thought, and therefore it affords no more indication of the unity of matter, or of the compound nature of the elements, than do the laws of Avogadro or Gerhardt, or the law of specific heats, or even the conclusions of spectrum analysis." The periodic law is developed in the author's Principles of Chemistry, which was first published in 1869, and appeared in a fourth edition, after a thorough revision, with many important additions and modifications, in 1882.
In a lecture before the Royal Institution in 1889, Mendeleef sought to apply a broader generalization and to discover a harmonious law regulating both chemical and astronomical phenomena. The immediate object of the lecture was to show that, starting from Newton's third law of motion, it is possible to preserve to chemistry all the advantages arising from structural teaching, without being obliged to build up molecules in solid and motionless figures, or to attempt to ascribe to atoms definite limited valencies, directions of cohesion, or affinities. He supposed that harmonious order reigns in the invisible and apparently chaotic motions of the universe, reaching from the stars to the minutest atoms, which is commonly mistaken for complete rest, but which is really a consequence of the conservation of dynamic equilibrium that was discovered by Newton, and has been traced by his successors as relative immobility in the midst of universal and active movement. The unseen world of chemical changes was regarded as analogous to the invisible world of the heavenly bodies," since our atoms form distinct portions of an invisible world, as planets, satellites, and comets form distinct portions "of the astronomer's universe; our atoms may therefore be compared to the solar system, or to the systems of double or single stars. . . . Now that the indestructibility of the elements has been acknowledged, chemical changes can not be otherwise explained than as changes of motion, and the production by chemical reactions of galvanic currents, of light, of heat, or of steam-power, demonstrate visibly that the processes of chemical reaction are inevitably connected with enormous though unseen displacements, originating in the movements of atoms in molecules."
When, in 1880, the St. Petersburg Academy of Sciences refused, in the face of strongly signed recommendations, to elect Mendeleef a member in its Chemical Section, other scientific societies hastened to express their appreciation of him by making him an honorary member. Among these were the University of Moscow; the Russian Chemical and Physical Society, which presented him an address where it spoke of him as "a chemist who has no equal among Russian chemists"; the University of Kiev, the Society of Hygiene, etc. From England he received the Davy medal of the Royal Society in 1882, and the Faraday medal of the Chemical Society in 1889.
Prof. Mendeleef is the author of a treatise on Organic Chemistry which was a standard work in its time, and which, according to Prof. Thorpe, exercised a great influence in spreading abroad the conceptions which are associated with the development of modern chemistry. In 1863 he published a cyclopædia of chemical technology—the first really important work of the kind produced in Russia. He has frequently been commissioned to report on the progress of chemical industry as illustrated at the various international exhibitions. His investigations and reports on petroleum have been an important factor in the developing of the trade at Baku, and in removing the monopoly which formerly dominated the market there.
We quote again, in concluding, from Prof. Thorpe: "No man in Russia," he says, "has exercised a greater or more lasting influence on the development of physical science than Mendeleef. His mode of work and of thought is so absolutely his own, the manner of his teaching and lecturing is so entirely original, and the success of the great generalization with which his name and fame are bound up is so strikingly complete, that to the outer world of Europe and America he has become to Russia what Berzelius was to Sweden, or Liebig to Germany, or Dumas to France."