354 



NA TURE 



\Avgtist 8, 1889 



AN ATTEMPT TO APPLY TO CHEMISTRY 

 ONE OF THE PRINCIPLES OF NEWTON S 

 NATURAL PHILOSOPHY} 



IVTATURE, inert to the eyes of the ancients, has been revealed 

 to us as full of life and activity. The conviction that motion 

 pervaded all things, which was first realized with respect to the 

 stellar universe, has now extended to ihe unseen world of atoms. 

 No sooner had the human understanding denied to the eirth a 

 fixed position and launched it along its path in space, than it 

 was sought to fix immovably the sun and the stars. But astronomy 

 has demonstrated that the sun moves with unswerving regularity 

 through the star-set universe at the rate of about 50 kilometres 

 per second. Among the fo called fixed stars are now discerned 

 manifold changes and various orders of movement. Ligh*-, heat, 

 €lectricity — like sound — have been proved to be modes of mo- 

 tion ; to the realization of this fact modern science is indebted 

 for powers which have been used with such brilliant success, and 

 which have been expounded so clearly at this lecture-table by 

 Faraday and by his successors. As in the imagination of Dante 

 the invisible air became peopled with spiritual beings, so before 

 the eyes of earnest inve-tigators, and especially before those of 

 Clerk Maxwell, the invisible mass of gases became peopled with 

 particles : their rapid movements, their collisions, and impacts 

 became so manifest that it seemed almost possible to count the 

 impacts and determine many of the peculiarities or laws of their 

 ■collisions. The fact of the existence of these invisible motions 

 may at once be made apparent by demonstrating the difference 

 in the rate of diffusion through porous bodies of the light and 

 rapidly moving atoms of hydrogen and the heavier and -more 

 sluggish particles of air. Within the masses of liquid and of 

 solid bodies we have been forced to acknowledge the existence 

 •of persistent though limited motion of their ultimate particles, 

 for othcrv\ise it wculd be impossible to explain, for example, the 

 celebrated experiments of Graham on' diffusion through liquid and 

 •colloidal substances. If there were, in our times, no belief in 

 the molecular motion in solid bodies, could the famous Spring 

 have hoped to attain any result by mixing carefully dried powders 

 •of potash saltpetre, and acetate of soda, in order to produce, by 

 pressure, a chemical reaction between these substances through 

 the interchange of their metals, and have derived, for the con- 

 ■viction of the incredulous, a mixture of two hygroscopic though 

 5olid salts — nitrate of soda and acetate of potash ? 



In these invisible and apparently chaotic movements, reaching 

 from the stars to the minutest atoms, there reigns, however, an 

 harmonious order which is commonly mistaken foi' complete 

 rest, but which is really a consequence of the conservation of 

 that dynamic equilibrium which was first discerned by the genius 

 of Newton, and which has been traced by his successors in the 

 -detailed analysis of the particular consequences of the great 

 generalization, — namely, relative immovability in the midst of 

 universal and active movement. 



But the unseen world of chemical changes is closely analogous 

 to the visible 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 c >mpared to the solar systein, or to 

 the systems of double or of single stars, for example, ammonia 

 (NHj) may be represented in the simplest manner by supposing 

 the sun nitrogen surrounded by its planets of hydrogen ; and 

 •common salt (NaCl) maybe looked upon as a double star formed 

 ■of nitrogen and chlorine. Besides, now that the indestructibility 

 •of the elements has been acknowledged, chemical changes 

 cannot otherwise be explained than as changes of motion, and 

 the production by chemical reactions of galvanic currents, of 

 light, of heat, of pressure, or of steam power, demonstrate 

 visibly that the processes of chemical reaction are inevitably 

 •connected with enormous though unseen displacements, originat- 

 ing in the movements of atoms in molecules. Astronomers and 

 natural philosophers, in studying the visible motions of the 

 heavenly bodies and of matter on the earth, have understood and 

 have estimated the value of this store of energy. But the chemist 

 has had to pursue a contrary course. Observing in the physical 

 and mechanical phenomena which accompany chemical reactions 

 the quantity of energy manifested by the atoms and molecules, 

 he is constrained to acknowledge that within the molecules there 

 -exist atoms in m.otion, endowed with an energy which, like 

 matter itself, is neither being created nor is capable of being 



' The Frid.-iy eveninst lecture delivered at the Roval Institution of Great 

 Britain, on May 31, 1889, by Prof. D Mendeleeff, Prore>so.- of Chemistry in 

 ihe University of St. Petersburg. 



destroyed. Therefore, in chemistry, we must seek dynamic 

 equilibrium not only between the molecules but also in their 

 midst among their component atoms. Many conditions of such 

 equilibrium have been determined, but much remains to be done, 

 and it is not uncommon, even in these days, to find that some 

 chemists forget that there is the possibility of motion in the 

 interior of molecules, and therefore represent them as being in a 

 condition of death-like inactivity. 



Chemical combinations take place with so much ease and 

 rapidity, possess so many special characteristics, and are so 

 numerous, that their simplicity and order was for a long time hid 

 from investigators. Sympathy, relationship, all the caprices or 

 all the fancifulness of human intercourse, seemed to have found 

 complete analogies, in chemical combinations, but with this 

 difference, that the characteristics of the material substances — 

 such as silver, for example, or of any other body — remain un- 

 changed in every subdivision from the largest masses to the 

 smallest particles, and consequently their characteristics must be 

 a property of its particles. But the world of heavenly lumin- 

 aries appeared equally fanciful at man's first acquaintance with 

 it, so much so that the astrologers imagined a connection be- 

 tween the individualities of men and the conjunctions of planets. 

 Thanks to the genius of Lavoisier and of Dalton, man has been 

 able, in the unseen world of chemical combinations, to recog- 

 nize laws of the same simple order as those which Copernicus 

 and Kepler proved to exist in the planetary universe. Man dis- 

 covered, and continues every hour to discover, what remains 

 unchanged in chemical evolution, and Iioiv changes take place 

 in combinations of the unchangeable. He has learned to pre- 

 dict, not only what possible combinations may take place, but 

 also the very existence of atoms of unknown elementary bodic^, 

 and has besides succeeded in making innumerable practical ap- 

 plications of his knowledge, to the great advantage of his race, 

 and has rccomplished this notwithstanding that notions of sym- 

 pathy and affinity still preserve a strong vitality in science. At 

 present we cannot apply Newton's principles to chemistry, be- 

 cause the soil is only being now prepared. The invisible world 

 of chemical atoms is still waiting for the creator of chemical 

 mechanics. For him our age is collecting a mass of materials, 

 the inductions of well-digested facts, and many-sided inferences 

 similar to those which existed for astronomy and mechanics in 

 the days of Newton. It is well also to remember that Newton 

 devottd much time to chemical experiments, and while consider- 

 ing questions of celestial mechanics, per.-istently kept in view 

 the mutual action of those infinitely small worlds which are 

 concerned in chemical evolutions. For this reason, and also to 

 maintain the unity of laws, it seems to me that we must, in the 

 first instance, seek to harmonize the various phases of con- 

 temporary chemical theories with the immortal principles of the 

 Newtonian natural philosophy, and so hasten the advent of true 

 chemical mechanics. L^t the above considerations serve as my 

 justification for the attempt which I propose to make to act as 

 a champion of the universality of the Newtonian principles, 

 which I believe are competent to embrace every phenomenon 

 in the universe, from the rotation of the fixed stars, to the 

 interchanges of chemical atoms. 



In the first place, I consider it indispensable to bear in mind 

 that, up to quite recent times, only a one-sided affinity has been 

 recognized in chemical reactions. Thus, for example, from the 

 circumstance that red-hot iron decomposes water with the 

 evolution of hydrogen, it was concluded that oxygen had a 

 greater affinity for iron than for hydrogen. But hydrogen, in 

 presence of red-hot iron scale, appropriates its oxygen, and forms 

 water, whence an exactly opposite conclusion may be formed. 



During the last ten years a gradual, scarcely perceptible, but 

 most important change has taken place in the views, and con- 

 sequently in the researches, of chemists. They have sought 

 everywhere, and have always found systems of conservation or 

 dynamic equilibrium substantially similar to those which natural 

 ])hilosophers have long since discovered in the visible world, and 

 in virtue of which the position of the heavenly bodies in the 

 universe is determined. There, where one-sided affinities only 

 were at first detected, not only secondary or lateral ones have 

 been found, but even those which are diametrically opposite, yet 

 among these, dynamical equilibrium establishes itself, not by 

 excluding one or other of the forces, but regulating them all. 

 So the chemist finds in the flame of the blast-furnace, in the 

 formation of every salt, and, with especial clearness, in double 

 salts, and in the crystallization of solutions, not a fight ending 

 in the victoiy of one side, as used to be supposed, but the con- 

 junction of forces ; the peace of dynamic equilibrium resulting 



