Hans Landolt (1831-1910) RALPH E. OESPER University of Cincinnati, Cincinnati, Ohio
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ANDOLT" signifies a variety of things. To some . ~tmeans the Landolt-Bornstein "Physikalischchemische Tabellen"; to some it recalls the classic text on the optical rotation of organic compounds; others think of his studies of molecular refraction; still others know him as the discoverer of the "clock reaction (HI03 4- HzSOa); many others consider his fastidious testing of the law of conservation of mass during chemical reactions as one of the finest quantitative studies in the whole history of chemistry. Hans Heinrich Landolt was horn at Ziirich on December 11, 1831. For many generations, the family had provided competent sons for the army and civil services. His parents died while he was quite young, and the boy was brought up by his grandparents. They encouraged his early interest in science and allowed him to set up a lahoratory in the cellar. At 13 he was making fireworks; the usual damage to his hands and clothes resulted. More serious effortsfollowed, particularly because one of his companions was the son of Karl Lowig (1803-1890) professor of chemistry a t the University of Ziirich.' The latter took a keen interest in Hans, and gave him private lessons in chemistry. Soon the youth was entertaining his friends with lectures accompanied by demonstrations. He entered the university and stfidied under Uwig for three years. His first paper appeared before he was 20. I t dealt with antimony methyl. In a second paper (1853) he published the important finding that the Sh(CH3)4group functions as a radical and combines with a number of negative materials to produce salts analogous to the corresponding ammonium and potassium compounds. Uwig succeeded Bunsen a t Breslau in 1853, and took Landolt along as his assistant. Bunsen welcomed them and was so favorably impressed by the young man that he invited him to he his companion on an inspection of the famous salt mines a t Wieliczka in Galicia. Landolt's doctoral thesis and the succeeding paper (1853) dealt with arsenic ethyls. These studies were clearly influenced by Bnnsen, whose masterful study of cacodyl compounds (1837 ff.) had made him an authority on the chemistry of the organic compounds of arsenic. At Breslau he found few opportunities to learn and . develop, and Landolt accordingly entered the University of Berlin. Mitscherlich and Rose were the chemical luminaries of .the Prussian capital, but Landolt was particularly fascinated by the lectures in physiology. He seriously considered going into hiochemistry and sought Bunsea's advice. "Why do you wish to work with these smeary things; they certainly I n d o l t paid tribute to his friend and mentor in the obituary published in Bcr., 23,905 (1890).
offer no prospects. You would do far better to comef o me at Heidelberg and work here in a clean, tidy fashion." Consequently, in 1855 Landolt joined Bunsen, who was then at the threshold of the most fruitful period of his remarkable career. Landolt soon learned Bunsen's methods of gas analysis and was entrusted with a study of the combustion products coming from the hurner, which Bunsen had recently invented. Landolt also studied the electrolytic preparation of lithium, calcium, and other metals, whose salts were fused over the Bunsen burner. Besides such instruction, his most valuable acquisition was the development of close friendship with the &ted young men then active in Heidelberg. Among these were Lothar Meyer, Roscoe, Kekul4, Beilstein, Carius, Liehen, Pehal, Volhard. In this atmosphere he had ample opportunity to ripen both his manual and mental abilities. At Lowig's invitation, Landolt returned to Breslau to begin his teaching career. He habilitated as Privatdozent in 1856 with an essay, "The chemical processes in the flame of illuminating gas." He had found it possible to analyze the flame by using a specially constructed hurner. The heavy hydrocarbons remain unchanged in the flame until they reach its upper portions, whereas hydrogen decreases rapidly and then increases, due to the action of free carbon on water vapor. Photometric measurements showed that the most luminous portion is just above the top of the dark cone. He gave successful, well-attended courses in physical chemistry and gas analysis. Due to the general adoption of Liehig's methods of chemical instruction2 there was a great demand for teachers to take charge of the new courses in which the lahoratory work was to play a major role. Bischoff, the ordinarius a t Bonn, was senescent, tired, and little inclined to adopt the changing order of things. A special post was created, and Landolt, on Lowig's suggestion, was appointed extraordinarius in organic chemistry. He began his new work in the fall of 1857. His lahoratory was a small room in the old palace. There were 2 windows and 12 working places, which, before long, were forced to accommodate 30 students. The budget totalled 400 talers (1200 marks). Of this, 120 talers went to the Diener (janitor-handyman), 90 to the assistants, and 90 for gas and coal. The remainder was supposed to cover the cost of chemicals and apparatus, obviously an impossibility. Every year, after long negotiations, the authorities appropriated an extra amount that covered about half the inevitable deficit; the rest was paid by Landolt out of his
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Most of Landolt's students were older than he. Bischoff's health failed and Landolt was then obliged to take over the inorganic lectures with about 100 registrants, mostly medical students. The auditorium, which belonged to the botany department, held only 50, and consequently Landolt had to give each lecture twice, once in the morning and again in the afternoon. These miserable accommodations persisted almost 10 years, but Landolt, young, adaptable, and not demanding, endured his lot without complaint, comforted by the thought that many of his chemical colleagues a t other schools were just as poorly housed. The picture suddenly changed when A. W. Hofmann was called to Bonn, from London where he had made a notable success. Funds were provided for a large new chemistry building. .Before i t was completed Hofmann accepted a call to Berlin, and, in his place, Kekul6 was called from Ghent.' Landolt, who by this time had reached the rank of ordinarius, was given co-direction of the new building. They worked together in complete harmony. A number of studies on organic, inorganic, and analytical topics record Landolt's indefatigable spirit for original investigation. His close friend, Beer, the well-known physicist whose specialty was optics, interested Landolt in the relation of chemical properties to refraction and dispersion of light. The studies on the refractive indices of liquid homologous compounds were the first of his long series of researches that gained for him a place of honor among those who laid the foundations of physical chemistry. He invented the terms "molecutar refraction" and "refraction equivalent," and, on the basis of a host of observations, worked out the relation of these constants for a number of isomers, metamers, polymers, and also determined the effect of substituents. He developed a simple but reliable method of analyzing mixtures of liquids that differ markedly in refractive powers. Another instance of his concern with the relations between physical properties and chemical composition was exhibited in his study of the vapor tension of homologous compounds. His ingenious apparatus permitted these measurements with quite small quantities of material. A valuable contribution of this period was the method of determining phenol as tribromphenol, a procedure still in use. In 1869, Landolt was called to the newly founded techr;ical university a t Aachen as professor of inorganic and organic chemistry. He was allowed to plan, build, and furnkh his laboratory. The 60 places were soon occupied, and when 4 years later, students had to be turned away, 1,000,000 marks were gladly authorized for an additional building. To a friend he wrote: "I try to embellish my lectures with as many experiments as possible and I have to devise many new ones and try them out; this consumes a lot of time. I have always been able to provide every lecture with interesting and useful demonstrations. If general chemistry is presented in purely theoretical lecDARMSTAEDTER, L..AND R. E. OBSPER. THISJOURNAL, 4.
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tures, there is.great danger of becoming boresome." This credo was followed faithfully and many of the standard lecture demonstrations of today are due to Landolt. His richly illustrated lectures a t Aachen were &dely attended and an affirmative response to, "Is Landolt doing demonstrations today?" was invariably a signal for even nonregistrants to flock to his auditorium. He was a skilled manipulator and seldom if ever failed. "If a demonstration goes wrong in my' hands, I do not worry, but if an assistant bungles one, it makes me angry." One thing he could not endurethe mirror-like surfaces of his mercury haths must not be smudged with the finger prints of over-curious students. On entering the auditorium, his first move was to survey the lecture table; one glance was enough to disclose the damage. Once he declared: "I see that the apparatus has been fingered and brought into disorder; I cannot carry out the experiments today." When this remonstrance had only a temporary effect, he placed a barrier before the table, but it was opened after the lecture because he welcomed the stream of those who wished to see the setups closer. Never was he too busy to supplement his formal remarks and answer the flood of questions that came from this after-audience. As a pupil of Bunsen's, he naturally was a skilled glass-worker; much of the lecture equipment was his own handiwork. By means of a projector he showed his audience such things as the evolution of colored gases, the absorption of hydrogen by palladium, the liquefaction of gases in Faraday tubes, crystallizations, sublimations, etc. The Drnmmond lime light of his projection apparatus was a constant nuisance. It had an almost insatiable appetite for oxygen which, in those days, had to be prepared by chemical methods. The advent of electric lighting offered the possibility of relief. Lqdolt bought a dynamo in 1873 and after expending much time and effort finally produced a workable electrically illuminated projector that was the forerunner of the modern equipment. He also fitted his auditorium and especially his lecture table with electric lighting fixtures. Only those who remember the inadequacy and inconvenience of gas lighting can really appreciate the importance of this advance. The preparation of liquid carbomdioxide was always a big day on the demonstration calendar. The Natterer compression pump was torn down a week before, cleaned, and tried out. Five collaborators were needed, including two laborers who spelled each other a t the wheel. The yield was 200 to 300 grains of liquid. Landolt was the first to make carbon dioxide snow, as a lecture demonstration, by the now familiar method of allowing the liquid to evaporate into a cloth bag. He developed a simple method of determining molecular weights from gas volumes. The volume of vapor obtained from a known weight of the sample was compared with that produced from a known weight of a standard, chloroform, for instance. A series of tubes containing different quantities of the standard were kept on hand, and the sample weight adjusted, accord-
ing to the suspected molecular weight, to give a volume of vapor equal to that of one of the standard tubes. Temperature and pressure corrections are not necessary in this method, which can he used effectively as a lecture experiment. He also devised the familiar demonstration in which equi-molar weights of liquids are introduced above the mercury in tubes of the same width standing in a mercury trough. When heated with steam, the mercury falls at differentrates according to the various vapor tensions, but soon the level becomes the same in all of the tubes. In 1873 Landolt began his important fundamental studies of the rotation of polarized light. This field occupied his chief attention for quite a number of years. He amassed a wealth of experimental data from which he deduced several excellent general conclusions. This work was of great value to van't Hoff and his successors in founding stereochemistry. The literature was scattered through many journals, and Landolt, acceding to the urgiugs of the readers of his excellent papers, consented to prepare a comprehensive treatment of the whole subject. The first edition of his classic book4was published in 1879 and brought him an international reputation in both scientific and technical circles. His preoccupation with physical-chemical problems was remarkable in that era, when the outlook of the chemical world was predominantly organic. When asked why he did not go with the current he replied: "I feel no need of increasing by one the number of organic chemists." In 1880, Landolt accepted a call to Berlin as head of the chemistry department of the newly founded school of agriculture. His work on the determination of sugars was primarily responsible for this appointment. The next year the institute was raised to the rank of technical university and Landolt was elected its first rector. He filled this office with his usual quiet efficiency, maintaining the best of feeling within the faculty, and with the authorities responsible for appropriations. The funds were generous, and Landolt could buy whatever apparatus he pleased. His special pride was his auditorium, whose blinds were operated hydraulically. In 1883, with the collaboration of his colleague Richard Bornstein (1852-1913), Landolt issued the first edition (560 pages) of the now famous "Physikalisch-chemische Tabellen." This was an outgrowth of a few conversion tables that Landolt had published for the convenience of his students in physical chemistry. These proved so valuable that i t seemed worth while to extend the scope by including a collection of physical constants. A distinctive feature was the inclusion of the literature reference for each set of data. The careful and conscientious labors of the authors were no small factor in the ultimate widespread success of this invaluable work. Landolt was one of the prime figures in the establish-
' The English translation by Robb and Veley
"Handbook of the Polariscope and Its Practical Applications" was published in London in 1882.
ment (1880) of the Zeitschrgt f f r Instrumentenkunde and he served as chairman of its executive board. It was generally acknowledged that he, in no small measure, was responsible for the remarkable advance in Germany of the production of scientific instruments. Naturally he was a prominent member of the committee that planned the founding of the Physikalischtechnische Reichsanstalt, a national institute for testing precision equipment and for carrying out comdrehensive physical studies. He was an active member of its governing board until his death. The experimental labors of his Berlin laboratory dealt with a continuation of his study of optical rotation. He also carried out extensive investigations of the molecular refraction of organic liquids. Four papers were devoted to the iodine clock reaction, that is, the time period of the reaction between iodic and sulfurous acids. This "Landolt reaction" was one of his favorite lecture experiments, and the sudden appearance of the deep blue a t exactly the predicted instant never failed to evoke applause. Such diverse topics as the life period of thiosulfuric acid in aqueous solution, and the effect of the electric current on sugar solutions show the range of his interests. Exact measurements with the polaristrobometer had long engaged his attention and he introduced many improvements, particularly in methods of illumination. He also developed formulas for calculating the specific rotation of a circularly polarizing material under a variety of conditions. Such achievements put himin the first rank of those who were primarily interested in physical-chemical phenomena. He was elected to the Prussian Academy in 1882 and his inaugural address dealt with the history of the studies concerning the relation of physical properties and chemical constitution. He closed with the prediction: "The time will come, and it cannot be far distant, when the light shed by modem physics will also begin to shine into chemistry. We may then hope that the latter will show achievements that will be the envy of later generations. At present we can do no more than bring up stones for the future building, and call to the attention of the rising generation of investigators the tools with whose aid they will some time he able to erect a lofty and substantial edifice." In May, 1887, a call came from Leipsic to succeed Wiedemann in the chair of physical chemistry. Landolt, who refused because the laboratory did not suit him, suggested several others. Negotiations vith these men came to nothing and Landolt was again approached. Every possible inducement was held out to him, including the finest polarization equipment and the best cigars. His negative reply was not easy. This .was the only professorship of its kind in Germany and he would have been free to devote almost his entire attention to his chosen field, instead of literally stealing time from his Sundays and holidays, since the rest of his week was taken up with inorganic lectures and conducting the analytical l a b o r a t ~ r y .His ~ decision to re-
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5 Ostwald accepted the Leipsic post. See O s s p ~ nR. , E., THIS JOURNAL, 21,470 (1944).
main in Berlin was greeted with joy. A great testimonial dinner was arranged and though he privately threatened to poison himself secretly on that day so that he need not appear, the occasion was a huge success. "I am certain that never again will I consent to a celehration in my honor, it gives me an indescribably unpleasant feeling. Those persons, who enjoy that sort of thing, must have a terrifically thick skin." He now embarked on a number of studies, such as the nitrification of ammonium salts in the soil, and the vapor tension of fatty acids. After a critical examination of the determination of melting points, he concluded that reliable results are only obtained by melting and then freezing considerable amounts (20 grams a t least) of the sample. In 1888, he accepted an invitation to participate in the revision of the old Graham-Otto "Lehrbuch." After studying the situation, he decided that this was an opportunity to cover, in critical fashion, the whole subject of the relation of physical properties and chemical constitution. He assembled a corps of expert collaborators. Ten years passed before this monumental volume appeared6 and by this time, so much that was fundamentally new and different had appeared, that much of the original manuscript had to be radically revised. Landolt's election to the Academy of Sciences carried with it the privilege of giving courses in the University of Berlin. He became a full-time member of this faculty in 1891 when he succeeded Rammelsberg as professor of inorganic chemistry. Chemical Laboratory I1 was put in his charge and a t once he remodeled it to serve the purposes of physical chemistry. A wide variety of research was begun, with particular emphasis, of course, on various aspects of polarization, refraction, etc. In all, Landolt in his entire teaching career, supervised 65 doctorate dissertations. His own papers numbered around 80. A ,second edition of the "Tabellen" was issued in 1894; its extended scope required the collaboration of 15 carefully selected men. The thud edition (1905) was still larger and the staff numbered 45. This was the last edition in which Landolt took an active part, but his interest in this monumental work never flagged. Bornstein wrote: "Our joint labors and many conferences on this matter have left me the very fond memory of an exceptionally fine and good gentleman of the highest reliability." An entirely revised edition of the text on optical activity was published in 1898. Here, too, Landolt drew on the services of a corps of competent coworkers.' In 1890 Landolt began a series of measurements that earned him a place in the chemical hall of fame. Intermittently he worked on this problem for the next 20 "Lehrbuch der Physikalischen und Theoretischen Chemie," AND A. WINKEL3rd edition, by A. HORSTMANN, H. LANDOLT, MANN. Part 3. Edited by H. LANDOLT. Brunswick, 1898. This was translated bv Lone and published at Easton in 1902 with the title: "The 06tica1 kotat& Power of Organic Substances and Its ~racticalApplications."
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years, and the final report was edited and issued after his death.= Prout's hypothesis leads to the conclusion that the atomic weights of all elements should be exact multiples of that of the prime substance, hydrogen. Its failure in many cases has now been adequately explained. However, in 1890, fractional atomic weights were thought by some to be due to luminiferous ether combined with or adsorbed on the atom. Others attributed this &$ct to adhesion of fragments of atoms. In any event, the quantity of these extraneous materials would probably not remain constant during chemical reactions, and hence, assuming that these materials could pass through the walls of sealed vessels, i t followed that the law of conservation of mass might not hold perfectly. Though this law had been taken as axiomatic since antiquity, and particularly since Lavoisier's formulation of it, authoritative experimental validation was lacking. Even though studies such as Stas' synthesis of silver halides could be taken as proof of the validity of the "Lavoisier" law, yet the inevitable deviations he obtained were ascribed to experimental error, impure reagents, etc. In other words, studies designed expressly to test the law of conservation of mass were needed, and Landolt was singularly fitted for this task. "He had everything that could ensure success: energy and pertinacity in pursuing an objective, extreme conscientiousness, extraordinary experimental skill, a gift for devising all sorts of aids, an unprejudiced sense for seeking only the truth, and, in addition, an equable temperament, which kept him on the proper path, despite the numerous diversions inherent in such delicate studies." From 1890 to 1892, Landolt carried out a number of reactions in sealed vessels. No decided changes in weight were detected. Others then carried out similar studies, and they, like Landolt, found that most of the minute deviations were in the direction of loss of weight. Were these fairly consistent results due to experimental errors or did they have a fundamental significance? Landolt in a second period of this study (1902 to 1905) introduced every conceivable improvement. The main point was to secure a balance of unquestioned reliability and sensitivity. This instrument was finally constructed by Rueprecht of Vienna, and embodied the suggestions which were the fruit of Landolt's years of experience with precision instruments. It was set up in Landolt's laboratory, where he soon found that the traffic vibrations compelled him, to use i t only in the quiet hours of the night.= It is reported that he made no fewer thati 27,700 telescope readings during his testing of this magnificent instrument, whose maximum error he found to be *0.03 mg. The changes in weight, though smaller than in the first period, were still predominantly The third period (1906 to 1907) . neeative. "Uber die Erhaltung der Massebei chemischen Umsetzungen." Nach dem Tode des Verfassers aus dessen Nachlass ver6ffentlicht von W. Marckwald. Abhdl. d. Akad. d. Wissenschaften, Berlin, 1910. 158pp. * OESPER.R. E.. THISJOURNAL. 17. 312 (1940) ~ i v e pictures s of this balance and the reaction vessel;.
Landolt relinquished his professorship in 1905; he was succeeded by Nernst. A great gold medal was struck and presented a t the ceremonial retirement dinner. Among his honors were numerous orders, and membership in the Royal Society and the Academy a t St. Petersburg. Like Bunsen, he practically never wore his ribbons and regalia. In the spring of 1906. Landolt moved his equipment, and as soon as possible continued his weighiigs. He wrote: "At times I regret that I have completely hung the schoolmaster on the' hook. I am now working in the Physikalische Reichsanstalt. I cannot use an assistant for the delicate weighings, and so things move forward but slowly." His health broke again, but nonetheless he persisted in composing the extensive manuscript of the first paper on the conservation of mass. "This cost me much trouble, because I had to write i t during an attack of influenza." His results were attacked by Zenghelis, of Athens, who thought he had proved that vapors escaped through the glass walls during exothermic kactions. Idandolt's last Dmer embodied his refutation of this claim. Landolt and his wife had always thought the years in Bonn were the best they had spent together. However, his plan to live out the rest of his life there was never realized. Recurrent illnesses were interspersed with periods when he could work. During his last days, despite terrific pains, he refused hypodermic injections of morphine because he wished his mind to remain clear. He dictated explicit directions about what was to be included or omitted from the final report on his great work, which he held most precious and which he wished to leave in the best possible form as his heritage to the scientific world. The end came on March 15, 1910. His remains, in accordance with his wish, were buried in the old cemetery a t Bonn. Among his neighbors in this lovely God's acre are Beethoven's parents, Clara and Robert Schumann, Plucker. the physicist, and Mohr the chemi~t.'~ Material for this paper has been taken from hiographies of Landolt by (1) W. MARCKWALD, Chem. Ztg., 34,297(1910); (2) H. C. JONES,Am. Chem. J., 43,425 For a critical review of the t e t i n g of the law of conserva- (1910); (3) H. T. C., J. Chem. Soc., 1911T,1653; and Ber., 44, 3337 (1911), which tion of mass see FREUND. S., "The Study of Chemical Composi- especially (4) R. PRIBRAM, tion," Cambridge, 19M, pp. 61-75;' 101-106. Actual data ob- contains a complete bibliography of Landolt's puhlicatained by Landdt are given there. His summary was: "None of the reactions employed show a certain change of weight. If such tions, including the doctorate theses prepared under his changes should after all occur, they must be so small as to he of supervision.
showed eventually that the heat of reaction removed part of the moisture adhering to the walls of the reaction vessel, which in addition expanded slightly. The moisture film was rebtablished in two or three days, the original volume was attained only after as many weeks. The net finding was that the change in weight, if any, was less than the maximum experimental error, or of the order of one part in ten millions.1° The strain of these arduous labors told on his health. He wished to retire, but hoped to complete his program with his beloved new balance. A strenuous medical treatment brought temporary relief from a complicated set of ailments. "Now I can again smoke my eight cigars every day, and have my pint of Pomeril, i. e., alcohol-free apple juice, every evening." A relapse came soon, and a major operation was declared imperative, a serious matter a t his age. "If that is the way things are, I want to smoke a particularly good cigar just beforehand" and he specified the brand that was to be brought to him. In May, 1901, his gall bladder was removed, together with three large stones. By September he was back in his laboratory. To Rueprecht he wrote: "I am now insured against gall stones for the rest of my life, and I look forward to a healthy evening of life. I again smoke eight or nine cigars a day, including three imported ones, and I notice not the slightest trace of harm." His inordinate love for cigars is apparent in many of his letters. Commenting on the suicide of an eminent colleague he wrote: "How can anyone be so unscientific as to hang or shoot himself? A chemist would certainly take prussic acid, best in the form of maraschino. For my part, for the past 60 years I have been trying to poison myself with nicotine, and I shall certainly succeed some day." From 1897 on, Landolt took a prominent part in the affairs of the German Chemical Society; in 1896 and 1899 he was its president. He was a member of the publication board of the Berichte for more than 25 years, an onerous post a t best. In 1897 he headed the Society's commission on atomic weights, and carried on the extensive correspondence that eventually led to the establishment of the International Committee on Atomic Weichts."
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no prictical importance to thechemist." OESPER. R. E., THISJOUXNAL. 17, 562 (1940). See also LANDOLT, H., Ber., 40,4627 (1908).
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"There hos been t o o , m w h disposition on thepart of businessmen to look on educators as impractical theorists who don't know the value of a dollar and on thepart of educators to regard businessmen as a bunch of penny-pinching skinflints."-Ralph Bradford, General Manager, U. S . Chamber of Commdrce, in the preface to "Education an Insestment in People"
