Popular Science Monthly/Volume 54/January 1899/Sketch of August Kekule

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"THIS news," said Herr H. Landrelt, president, announcing Kekulé's death in the German Chemical Society at Berlin, "will be received with sorrow not only by our society but by the whole chemical world. Science has again lost one of its greatest representatives, one of those extremely rare spirits who were called upon to found a new epoch in it and push it mightily forward."

Friedeich August Kekulé was born at Darmstadt, September 7, 1829, and died, after a long illness, at Bonn, July 13, 1896. He was originally destined by his father for the profession of an architect; and some houses, he told his students in a festival address, still existed (in 1892) in Darmstadt of which he drew the plans when, a youth, he was attending the gymnasium. The leading events of his life were very tersely told by himself in an address responding to an ovation from the students of the University of Bonn on the twenty-fifth anniversary of his professorship there; a translation of which, from the Kölnische Zeitung, was published by Mr. J. E. Martin in Nature, June 30, 1892.

At Giessen, he said, where he went to study architecture, he attended Liebig's lectures, and was thereby attracted to chemistry. But his relatives would not at first hear of his changing his profession, and he was given a half-year's grace to think over it. He spent his time in the Polytechnicum at Darmstadt. His first teacher in chemistry at Darmstadt was Moldenhauer, the inventor of lucifer matches. His leisure time was spent in modeling in plaster and at the lathe. He was then permitted to return to Giessen. "I attended," he said, "the lectures, first of Will and then of Liebig. Liebig was at work on a new edition of his letters on Chemistry, for which many experiments had to be carried out. I had to make estimations of ash, of albumen, to investigate gluten in plants, etc. The names of the young chemists who helped Liebig were mentioned in the book, among them mine. The proposal was then made to me, just at the time Liebig intended to make me his assistant, that I should go for a year abroad, either to Berlin, which was at that time to Giessen a foreign land, or to Paris. 'Go,' said Liebig, 'to Paris; there your views will be widened; you will learn a new language; you will get acquainted with the life of a great city; but you will not learn chemistry there.' In that, however, Liebig was wrong. I attended lectures by Frémy, Wurtz, Pouillet, Regnault; by Marchandis on physiology, and by Payen on technology. One day, as I was sauntering along the streets, my eyes encountered a large poster with the words Leçons de philosophie chimique par Charles Gerhardt, exprofesseur de Montpellier. Gerhardt had resigned his professorship at Montpellier, and was teaching philosophy and chemistry as privat docent in Paris. That attracted me, and I entered my name on the list. Some days later I received a card from Gerhardt; he had seen my name in Liebig's Letters on Chemistry. On my calling upon him he received me with great kindness, and made me the offer, which I could not accept, that I should become his assistant. My visit took place at noon, and I did not leave his house till midnight, after a long talk on chemistry. These discussions continued between us at least twice a week for over a year. Then I received the offer of the post of assistant to von Plauter, at the Castle of Reichenau, near Chur, which I accepted, contrary to Liebig's wish, who recommended me as assistant to Fehling, at Stuttgart. So I went to Switzerland, where I had leisure to digest what I had learned in Paris during my intercourse with Gerhardt. Then I received an invitation from Stenhouse, in London, to become his assistant, an invitation I was loath to accept, since I regarded him, if I may be allowed the expression, as a Schmierchemiker. By chance, however, Bunsen came to Chur on a visit to his brother-in-law, at whose house I first met him. I consulted Bunsen as to Stenhouse's offer, and he advised me by all means to accept it. I should learn a new language, but I should not learn chemistry. So I came to London, where as Stenhouse's assistant I did not learn much. By means of a friend, however, I became acquainted with Williamson. The latter had just published his ether theory, and was at work on the polybasic acids (in particular on the action of PCl5 on H2SO4). Chemistry was at one of its turning points. The theory of polybasic radicals was being evolved. With Williamson was also associated Odling. Williamson insisted on plain, simple formulae, without commas, without the buckles of Kolbe or the brackets of Gerhardt. It was a capital school to encourage independent thought. The wish was expressed that I should stay in England and become a technologist, but I was too much attached to home. I wished to teach in a German university. But where? In order to get acquainted with the circumstances at several universities, I became a traveling student. In this capacity I came, among other universities, to Bonn. Here there was no chemist of eminence, and hence there were no prospects. Nowhere did there seem so much promise and so great a future as at Heidelberg. I could ask no help of Bunsen. 'I can do nothing for you,' he said, 'at least not openly. I will not stand in your way, but more I can not promise.' I fitted up a small private laboratory in the principal street of Heidelberg at the house of a corn merchant—Gross, by name—a single room with an adjoining kitchen. I took a few pupils, among whom was Baeyer. In our little kitchen I finished my work on fulminate of silver, while Baeyer carried out the researches, which subsequently became famous, on cacodyl. That the walls were coated thick with arsenious acid, and that silver fulminate is explosive, we took no thought about. After two years and a half I received a call to Ghent as ordinary professor. There I stayed nine years, and had to lecture in French. With me to Ghent came Baeyer. Through the kindness of the then Prime Minister of Belgium, Rogier, I obtained the means to establish a small laboratory. I had there with me a number of students, among whom I may name Baeyer, Hübner, Ladenburg, Wichelhaus, Linnemann, Radzizewski. There was not so much a systematic course of instruction as a free and pleasant academic intercourse. After nine years' work I received the call to Bonn. Professor Kekulée concluded his address with some account of his work at Bonn, and of the great attention he had always received from his pupils. For a full account of Kekulé's scientific career and achievements, we are indebted to the memorial address made by President Landelt to the German Chemical Society on the occasion of his death, of which we translate the more important passages from the Berichte:

"The works which Kekulé has left behind him belong, as we all know, to the bases of all chemistry. His teachings have so passed into our flesh and blood that it seems almost superfluous to remind a circle of professional chemists of them. I shall be able to present only in the most general outlines this evening the immense influence which the dead master has exercised upon science; a complete view of all his labors is a subject for a biography, which we must wait for.

"Kekulé's scientific work began in 1854, with the discovery of thiacetic acid, by which he at once separated from the old school of chemistry that was still prevailing, and, founding a new one, revealed himself as an adherent of the new doctrine of types. After his habilitation at Heidelberg, which followed in 1856, came the essay on fulminating mercury, in which the view so important for the future was expressed, that to the three typical combinations of chlorhydrogen, water, and ammonia, hitherto recognized, might be added a fourth, marsh gas. In the next essay, on binary combinations and the theory of polyatomic radicals, he put forward the conception of mixed types, and first reached the knowledge of various atomicity or valency of the radicals. These researches were continued, and there appeared shortly afterward, in the spring of 1858, the two great treatises which have since exercised so powerful an influence on chemistry—that on the constitution and metamorphoses of chemical combinations, and that on the chemical nature of carbon. In these theses Kekulé passed from the valency of the radicals to that of the elements themselves, and showed that the composition of all those compounds that contain one atom of carbon lead to the conclusion that that element is quadrivalent; and that, further, the relations of combination of a complex of carbon atoms are explainable if we suppose that the latter are mutually bound by a certain number of their four unities of attraction. This idea was suggested very carefully, and the words which the author added at the end of his essay read very curiously to-day: 'Finally, I think I ought still to insist that I attach only little value to speculations of this sort. Since one delving in chemistry must once in a while, in the lack of exact scientific principles, content himself with probabilities and temporary hypotheses, it seems proper to communicate these conceptions, because, as it appears to me, they furnish a simple and fairly general expression for the newest discoveries, and because, therefore, the use of them may assist in the discovery of new facts.' How diffident the words sound, and how far have the expectations been exceeded! We all know that the theory of valency is to-day the leading guide through all our science; and, although another investigator had a share in its origination, no one disputes that its main foundation and its eminent value in organic chemistry are primarily due to Kekule's idea of the quadrivalency of carbon.

"After he was called to the University of Ghent, in 1858, Kekulé exhibited an indefatigable activity. He began the great series of investigations of the organic acids which, beginning with succinic acid, malic acid, and tartaric acid, and extending afterward to many others, have given complete conclusions as to the nature of these bodies. Contemporaneously, in 1860, appeared the first number of the Lehrbuch der organischen Chemie, which was soon followed by other numbers, so that the whole first volume was completed in 1861. All his fellow-chemists who are acquainted with the events of that period will remember the enthusiasm with which the work was received. For the first time, in place of the former system of organic chemistry based on the old radicals of Berzelius, a system of treatment appeared which in the dress of the theory of types had the doctrine of valency as its foundation, and exposed the construction as well as the isomeric relations of the numerous carbon compounds with wonderful clearness. The work, the first two published volumes of which contained the substances designated by Kekulé as the fatty compounds, is still recognized as the prototype of many text-books that followed it.

"In 1855 Kekulé put forth the second of his great theories. First in the Bulletin of the Chemical Society of Paris, and afterward in fuller form in Liebig's Annalen, appeared the essay, Researches among the Aromatic Compounds, in which he showed that the substances so designated all contain six or more atoms of carbon, and that they could be described as derivatives of the simplest of them, benzene. He proposed two hypotheses to explain the constitution of this substance, one of which, the only one afterward pursued, supposed that the six carbon atoms are associated in a ring, and alternately linked by one and two valencies. By replacing the hydrogen atoms corresponding to each carbon atom by other elements or radicals one could arrive at the knowledge of the constitution of a large number of aromatic bodies which now figure as benzol derivatives. These considerations led, however, to another question—namely, whether or not the supplied places of the six hydrogen atoms are chemically equivalent. The question of space relations in chemistry first came up in connection with this investigation, and Kekulé at once endeavored to solve it. All these ideas were, however, expressed at first with reserve, and this essay closes with the words, 'I place no more value on these views than they are worth, and I believe that much labor must still be applied before such speculations can be regarded as anything else than more or less elegant hypotheses; but I believe, too, that at least experimental speculations of this kind must be used in chemistry.'

"In this case, again, Kekulé's modest expectations have been surpassed. The wonderful results that have accrued from the benzol theory are patent to all of us. We know that it was the instigation to the carrying out of an innumerable multitude of researches which are still pursued with undiminished industry. Rarely has a thought exercised so fructifying and forwarding an influence on chemistry, and so redounded to the advantage of both pure science and art. Thankfulness for this gift, as you know, prompted our society to honor the author of the benzol theory and the twenty-fifth year of the announcement of it by a public festival; and the Kekulé celebration, which took place in this house on the 11th of March, 1890, is memorable to all for the brilliant and witty speech with which the master responded to the many addresses made to him. It is preserved in our reports (Berichte 23, 1892), and the repeated reading of it always affords rich enjoyment."

Kekulé assumed his last position, as professor at the University of Bonn, in the fall of 1867. He there devoted his attention for a period to the erection of a new institute building, but it was not long before numerous works began again to appear—some of them by himself alone, like the important investigation of the condensation products of aldehyde; and others in co-operation with his many students. The continuation of his Lehrbuch was taken in hand at the same time. In 1867 he gratified his fellow-chemists by the publication of the first volume of his Chemistry of the Benzol Derivatives. This was followed from 1880 to 1887 by single numbers, prepared with the help of co-workers, of the second and third volumes.

Prof. F. R. Japp, in the Kekulé memorial lecture before the Chemical Society of London, speaking of Kekulê's residence in that city, September, 1897, said that he always acknowledged the influence which Liebig and Odling and Williamson, with whom he became acquainted in London, exercised on the formation of his opinions. Kekulé's theories, Professor Japp said, were based on Gerhardt's type theory; on Williamson's theory of polyvalent radicals, which by their power of linking together other radicals render possible the existence of multiple types; and Odling's theory of mixed types, which was a deduction from Williamson's theory. Less consciously, perhaps, his opinions were influenced by E. Frankland's theory of the valency of elementary atoms, and by Kolbe's speculation on the constitution of organic compounds. Kekulé gathered together the various ideas which he found scattered throughout the writings of his predecessors, added to them, and welded the whole into the consistent system which forms our present theory of chemical structure. In 1857, in the course of a memoir on the constitution of fulminic acid, he gave a tabular arrangement of compounds formulated on the type of marsh gas, this being the earliest statement, though put forward only in an imperfect form, of the tetravalency of carbon. In the same year he published an important theoretical paper On the So-called Conjugated Compounds and the Theory of Polyatomic Radicals, which contains a complete system of multiple types and mixed types. In 1858 the celebrated paper, On the Constitution and Metamorphoses of Chemical Compounds, and on the Chemical Nature of Carbon, appeared. It embodies the fully developed doctrine of the tetravalency of carbon, together with Kekulé's views on the linking of atoms and on the valency of such chains of atoms, the foundation on which our modern system of constitutional chemistry rests. In 1865 Kekulé put forward his well-known benzene theory—pronounced by Professor Japp the crowning achievement, in his hands, of the doctrine of the linking of atoms, and the most brilliant piece of scientific prediction to be found in the whole range of organic chemistry. The conception of closed chains, or cycloids, which he thus introduced, has shown itself to be capable of boundless expansion.

Kekulé's students all speak admiringly of his qualities as a teacher. The memorialist of the German Chemical Society said: "All of us who have attended his lectures or heard him in other places will ever remember what a teacher Kekulé was. With incomparable lucidity and sometimes with the happiest humor, he could go playfully through the theme he was considering, masterfully presenting it in new and often surprising aspects. The charm of his personality affected all who came in contact with him; it was the geniality which shone out of his whole being, and involuntarily commanded admiration. Numerous pupils flocked to him, and many of those who to-day fill chairs of chemistry in Germany and other countries have made his name highly honored."

Professor Thorpe, of London, who spent a little time in Kekulé's laboratory, describes him as having been one of the very best expositors, with the single possible exception of Kirchhoff, to whom it had been his lot to listen. As a laboratory teacher he was excellent. He was a most severe judge of work, striving to exact the same high manipulative finish, the same neatness and order, which he invariably bestowed on everything he did, and he was absolutely intolerant of anything slovenly or "sloppy." "But it was as a lecturer that he was seen at his best. He was singularly luminous as a thinker, a close and accurate reasoner, with a remarkable power of concentrated expression. . . . His language was apt and well chosen, and his delivery easy and natural"; and his whole address showed that every detail had been carefully considered.

At a distance of thirty years, Professor Dewar said, at the London memorial meeting, that to look back and call to mind the presence and personality of the great chemist as he knew him was indeed a pleasure. He was a man of noble mien, handsome, dignified, and yet of a homely and kindly disposition. He was a severe critic, having a haughty contempt for the accidental and bizarre in scientific work. His originality and suggestiveness seemed endless, so that he had no need to commit trespass or to follow just in the wake of other people's ideas. "Everything that passed through the Kekulé alembic was indeed transmuted into pure gold. His precision of thought and diction rendered his papers profoundly suggestive to other workers."

"The last years of the master's life," his German eulogist says, "were often troubled by illness, but there were not wanting bright days which the love of his students and colleagues prepared for him." Such a one was the celebration of the twenty-fifth anniversary of his professorship at Bonn, June 1, 1892, in which the students and officers participated with cordial unanimity. The ceremony began in the morning with an enthusiastic ovation by the students. The chemical theater was decorated with plants; the benzene hexagon was figured on the blackboard with garlands of flowers, in the midst of which the letters A. K. were wrought in a monogram of roses. Alfred Helle, one of the chemical students, delivered a felicitous address, in which he congratulated his fellow-students on being privileged to sit at the feet of the greatest of living chemists, after which three cheers were given to the professor. Kekulé responded to the offering in an address giving some of the details of his life, from which we have already quoted. Kekulé's personal staff and the officers of the university then presented their congratulations.

In the evening the students honored him with a torchlight procession, it being the third time he had received this, the most conspicuous honor which is bestowed by German students. The first occasion was in 1875, when he declined the professorship at Munich; the second was in 1878, when he was rector of the university, and was given in celebration of the restoration of unity among the students, after a long period of disunion. Among the torchbearers on that occasion was the present Emperor of Germany.

During the later period of his life Kekulé was comparatively sterile. Those who knew him, however, Professor Thorpe says, "would be the first to affirm that this seeming apathy sprang from no natural indifference. There is no doubt that he suffered, even in the early period of middle life, from the intense stress and strain of his mental labors prior to the Ghent period. He too surely exemplified the sad truth of Liebig's saying that he who would become a great chemist must pay for his pre-eminence by the sacrifice of his health. There is reason to know that it was the consciousness of failing power which prevented him from finishing much to which he had put his hand, and that his fastidiousness and his sense of 'finish,' amounting almost to hypercriticism, restrained him from publishing much which he realized fell short of his ideal."

The last time Kekulé's name was brought before the public was on the occasion of the renewal of the ancient title of nobility of his family, as August Kekulé von Stradowitz.