Josef Loschmidt (1821-1895) MORITZ KOHN New Y o r k C i t y (Translated by Ralph E. Oesper, University of Cincinnuti, Cincinnati, Ohio)
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HYSICISTS and chemists designate the number of Loschmidt, despite these failures, had real ability molecules contained in one milliliter of an ideal gas, as a technical chemist. He knew how to work out under standard conditions, as "Loschmidt's Number." chemical processes. He possessed a good knowledge The first calculation of this important constant was of chemistry, which was supplemented by a thorough made by the Viennese physicist, Josef Loschmidt. grasp of physics. Nevertheless, he found in industry He was active as a chemist also, and his relations to no rewards or satisfaction commensurate with his chemistry form the chief basis of this paper. abilities. The rather monotonous work of a factory He was horn on March 15, 1821, a t Putschim, near chemist was not congenial to his active mind; fnrtherCarlshad, Bohemia, then a part of the Austrian em- more, his poor health was a decided handicap in such a pire. The young boy had to labor in the fields to con- demanding industry. Consequently, he resolved to tribute to the support of the poor peasant family. retum to Vienna. However, the local pastor-teacher recognized his exHe amved almost penniless and was sick besides. ceptional mental abilities and gave what help he could. At first he made a scanty living by giving private lesAfter passing through the lower schools, Loschmidt sons. His love of teaching led him to qualify by exentered the University of Prague and took up phi- amination for a position that corresponded approxilosphy and natural science. Franz Exner, the professor mately to the lower grades of an American high school. of philosophy, was attracted to the intelligent youth Almost a t once, in 1856, he was fortunate enough to sewho was attending his lectures. Exner's eyes were cure an appointment. He was thus relieved of his most weak, and he had to have a reader who could take his pressing cares, and his material needs were satisfied, a t place when necessary. He gave this post to Loschmidt. least in a modest way. The writer knew an old gentleLater Exner moved to Vienna, where, by commission man who had been Loschmidt's pupil in this secondary of the educational authorities, he contributed much to school. He was fond of acknowledging the debt he the reorganization of the Austrian universities. owed to this remarkable teacher, who had made a lastPhilosophy had no lasting attraction for Loschmidt. ing impression on his classes, both through his personHe became interested in chemistry, and in 1842 he ality and his interesting, effective pedagogic methods. transferred to Vienna, where he worked in Anton von Loschmidt devoted whatever free time he could Schrotter's' laboratory a t the Polytechnikum. Here snatch from his heavy teaching duties to scientific Loschmidt became well acquainted with his fellow stu- work, especially the theoretical basis of chemistry. dent BenediM Margnlies. Together they worked out In 1861 he published his "Chemische Studien I." a method of making potassium nitrate from the sodium (This will he discussed later.) The physics department salt. This procedure was the basis of a chemical work a t the University of Vienna had been founded by that they started a t Atzgersdorf in the outskirts of Christian Doppler (1803-1853), whose name is comVienna. They secured a contract from the govern- memorated in the well-known "Doppler Principle." ment for 6000 centners per year, a t a price which Josef Stefan (18351893)became head of this laboratory allowed them a fair profit. However,,in 1849, Austria in 1866. Though he was 14 years younger than Lowent to war with Hungary. The pnce of potash, an Schmidt, the two became close friends. They admired -essential ingredient in their process, rose sharply and each other's scientific abilities, and the older man was they could no longer deliver their product a t the a welcome guest in the laboratory. The calibre of agreed price, except a t a considerableloss. The factory Loschmidt's extracumcular scientific activities was was closed in 1850. Loschmidt then became director of soon recognized by the highest authorities. He was a paper mill a t Peggau in Styria. Here he invented a elected correspondent of the Academy of Sciences in method of making oxalic acid from rag wastes. He 1867, and full member in 1870. He habilitated as also added the manufacture of saltpeter and aluminum Privatdozent a t the University in 1866, was appointed .sulfate to the output of this factory, but the enterprise, associate professor in 1868, and full professor in 1872. none the less, made no profits. He was then engaged He never had the means or time to finish the preby a corporation to set up a factory for making saltpeter scribed courses, and it was a tribute to the acumen of and prussiate of potash near Briinn, but again the busi- the university authorities when they conferred an honorary doctorate of philosophy on him in 1868. ness made no money. Having reached the age limit, he retired in 1891. His 1 For an account of Schriitter's accomplishments see KOHN, successor was Franz Exner, the son of the philosopher M . . THISTOURNAL. 21. 522 (1944).
who had befriended him in Prague. After a long, painful illness, Loschmidt died in Vienna on July 8, 1895. The Vienna Society for Chemistry and Physics was founded by the gifted chemist, Heinrich Hlasiwetz (1825-1875).2 This organization became a valued ad-
book printed privately. This was a real sacrifice because his funds must have been very limited. Sales, if any, were vanishingly small, and, in all likelihood, he presented copies to anyone who showed any interest in the contents. It would have been far better if he had
JosEa (1821-1895) JosEa LOSCHMIDT
junct to both sciences. Stefan also was an active participant in its meetings. When he died in 1893, his pupil Ludwig Boltzmann (1844-1906) was called from Munich to succeed him in the chair of theoretical physics.3 At the request of the members of this ChemischPhysikalische Gesellschaft, Boltzmann delivered a memorial address in honor of Loschmidt on October 29, 1895.' He was also the principal speaker (November 25, 1896) a t the unveiling of the Loschmidt monument a t the University of Vienna. On March 15, 1921, the Society observed the centenary of Loschmidt's birth with appropriate ceremonies. In 1861 Loschmidt published his "Chemische Stndien I."' The author was still a nonentity, and accordingly could hardly hope to find a publisher. However, he loved science so much that be had the little ' KOHN,M., THISJOURNAL, 22, 55 (1945). 8
law.
'
Their names are linked in the Stefan-Boltzmann radiation
BOLTZMANN. L., "Populire Schriften." Leipsic. 1905, pp. 228-40. 6 No further volumes appeared
STEFAN
(1%35-1893)
published his ideas in a periodical; they then would have received some attention. The first part of this book is entitled "Constitutional Formulas of Organic Chemistry in Graphic Representation." Loschmidt differentiated elements with one, two, three, etc. "positions," which correspond, of course, to the present day uni-, di-, tri-valent elements. The C-atoms were represented by larger circles, Hatoms by smaller ones. 0-atoms and N-atoms were pictured as double and triple circles, respectively. Thus (I) is Loschmidt's representation of methyl alcohol. It should be noted that even then he used the term "Kern" (= radical). According to him the compounds of the ethyl series contain the "ethyl" radical. Particularly important is the fact that he postulated the benzene radical or nucleus which played the role of a sexivalent element. In this he preceded KekulC by four years. His schematic representation of benzene. phenol, and aniline were (II), (III), and (IV), respectively. He further saw the possibility of the existence of the hydrocarbon C3Hs with three adjoining methylene groups (V). His prediction was confirmed 20 years later when A. Freund prepared trimethylene
(cyclopropane) by the action of metallic sodium on trimethylene bromide. Loschmidt's brochure is also of great significance with regard to the history of the development of inorganic chemistry. He was the first to represent ozone by On, a view substantiated in 1866 and 1867 by Soret's masterly studies proving that the density of ozone is one and one-half times that of oxygen. Likewise, Loschmidt was correct in his predictions concerning sulfur, to which he assigned a valency of six in sulfuric acid. In 1863, Butlerov stated that the difference between sulfurous and sulfuric acids would reside in the fact that sulfur exhibits four units of d n i t y in the former and six in the latter. The existence of SO* and SO8 made this assumption not unlikely. In 1864, Erlenmeyer declared that i t had become the general opinion that sexi-valence of sulfur was quite possible. The foregoing examples were selected from the wealth of original ideas contained in the "Chemische Studien I." Not once in later years did Loschmidt urge his claims to priority. As a member of the Vienna Academy, which met about 25 times each year, he had ample opportunity to rise and state the contents of his book, or he could have inserted pertinent remarks in the Proceedings. His silence was a reflection of his painfully modest nature. The furore aroused by Kekule's formulation of the aromatic compounds, which was announced four years after Loschmidt's proposals, would have provided an exceptionally favorable'opportunity for Loschmidt to raise his voice in defense of his own brainchild. He maintained strict silence. Not until 1912 was the matter brought to the attention of the chemical world. Richard Anschiitz (1852-1937), pupil, coworker, friend, and s'uccessor of Kekule, a t Bonn, and author of the great two-volume biography of Kekul6, was responsible for the disinterment of Loschmidt's forgotten book. He secured a copy of this rare item and reported on its contents to the German Chemical Society.# Anschiitz said: "It is no exaggeration to designate J. Loschmidt's text as a classic attempt to represent the formulas of organic compounds, including even the most complicated, in a uniform and quite original fashion, and a t a period when the valence theory was just beginning to gain acceptance." He regarded the Loschmidt booklet so highly that he had the pertinent part reprinted.' Early in the 19th century (1803 and ff) another schoolmaster, John Dalton (176G1844) of Manchester, revived the ancient atomic theory but with the addition of quantitative postulates. These enabled him to interpret and coordinate the laws of combination by weight, naniely, the laws of fixed and multiple proportions. However, atoms and molecules were first differentiated - by the Italian physicist, Amadeo Avogadro ANSCHUTZ, R., B c I . , ~539 ~ , (1912); idem, ''Aug~lstKekuE," vol. 1, p. 302, Berlin, 1929. See also EXNER, F., NatuwissenR., Chem. Ztg., 45, 321 schaften, 9, 177 (1921); WEOSCHEIDER, 119211 \----,I
Loswmr, J., "Konstitutions-FameIn der organischen
Chernie in graphischer Darstellung." No. 190 of Ostwald's "Klassiker der exakteu Wissenschaften." Edited by R. ANscadrz. Leipsic, 1913.
(177&1856), when in 1811 he postulated that "the number of integral molecules in any gases is always the same for equal volumes, or always proportional to the volnmes."8 This was a mighty achievement. Avogadro's hypothesis and the laws of thermodynamics have become comer stones of modem theoretical chemistry. However, the significance of Avogadro's idea was not appreciated until the dust of almost a half-century had settled on his work. In 1858, his fellow countryman, Stanislao Cannizzaro (1826-1910), brought it into the light of day and demonstrated, by word and pen, the meaning and importance of. Avogadro's hypothesis. Particularly helpful was Cannizzaro's participation in the great chemical conference a t Karlsmhe (1860), which met a t the invitation of Wnrtz and Kekule to attempt to introduce order into the confusion that was prevailing regarding equivalents, atoms, and molecules. Cannizzaro distributed copies of his "Sketch of a Course of Chemical Philosophy held in the Royal University of Genoa." This pamphlet brought conviction to most of those who a$tended the conference.= The distinction between atoms and molecules was clearly recognized, but there were no real notions as to the numbers and size of molecules. Only speculations and phantasies as to these figures and magnitudes existed. However, the aim of science is to reduce its problems to mathematical terms. The molar weight (M) of an ideal gas is expressed by the equation: M = N.,. According to Avogadro's rule, NO,which represents the number of molecules per mol, is a constant for all ideal gases. Since M is known, it follows that if No can be determined, then m, the weight of the individual molecule, can be calculated. Nemstlo suggested that No be called the "Loschmidt - -
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See MELDRUM$ A. N., "Avogadro and Dalton," Edinburgh, 1904. Alembic Club Reprints, No. 4, p. 29, Edinburgh, 1906; Ostwdd's "Klassiker." No. 8. Leiosic. 1889. % I thas been iss&d in tianslatioh as No. 30 of Ostwald's "Klassiker" and No. 18 of the Alembic Club Reprints. Minutes of the Karlsruhe Conference are given in Anschiitz's biography of KekulC, vol. 1, p. 6718. lo NERNST, W., "Theoretical Chemistry, from the Standpoint of Avogrdro's Rule and Thermodynamics" translated by L. W. CODD,8-10 Edition. London. 1923, p. 507.
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Number" because the Viennese physicist made the first calculation of this constant. This suggestion has not been generally accepted. The term "Avogadro Number" is more often employed, although i t should be emphasized that Avogadro never made any calculation of this number. The Loschmidt number, on the other hand, is now commonly taken to be the number of molecules in one milliliter of an ideal gas. Since, under standard conditions, one mol of an ideal gas occupies 22,415 ml., the Loschmidt Number = Avogadro Number/22,415. Loschrnidt announced his results a t a meeting of the Vienna Academy on October 12, 1865. This paper, the most important of all his contributions, carried the title: "The size of the air molecules." His derivation and the calculation of this important and fundamental constant cover only a few pages. His method was based on the kinetic theory of gases. He acknowledged that his results could be only an approximation, but stated the true value was probably no more than onetenth larger or smaller." He calculated the diameter of the air molecule to be 1 X 10-6 millimeter, and concluded that the material contents of one cubic centimeter of a gas would cover one square meter with continuous film. His value for the number of molecules per milliliter was 1 X 10'8. (The modern value is 2.69 X 10'9.) However, his estimate of this constant was of great value in k i n g the order of the quantities involved. The results obtained for the Avogadro Number by various investigators using entirely independent methods agree within close limits. This concordance (6.02 X lo2%) is a weighty argument for the validity of Avogadro's hypothesis, and hence, by implication, of the actual existence of molecules. Loschmidt's interests also included thermodynamics. He was the first to recognize the significance of the second law in the solution of chemical problems. He read his work on this subject before the Vienna Academy on February 25, 1869. Horstmann's very important study on the calculation of the heat of vaporization of ammonium chloride appeared several months late^.'^ The monumental studies of J. Willard Gibbs appeared from 1874 to 1878. Neither Gibbs nor Horstmann knew of Loschmidt's paper. Boltzmann tells that Loschmidt, in connection with his thermodynamic
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la HORSTMANN, A,,
Ber., 2, 137 (1869)
studies, .set up three very long tubes filled with salt solution in the cellar of the physics building. He hoped to establish the concentration changes that should ensue in the course of time. This was a labor of love, however, because when he had almost completed the installation, he finished his calculations, which showed that 3000 years would elapse before he could hope to find a detectable difference in the concentration of the upper and lower levels. The Stefan memorial a t the University of Vienna was unveiled on December 8, 1895. Boltzmann gave the main address. In part, he said: "Stefan was practical minded; he gladly and expertly applied his scientific knowledge to technical and industrial ends. Loschmidt, even though he had had industrial experience, was the typical impractical scholar. Stefan made for himself a much wider reputation; he was elected Dean and also Rector of the University of Vienna; he was Secretary. and later Vice-president of the Academy of Sciences. Loschmidt, in contrast, remained almost completely unknown. The two had only one characteristic in common: their utter undemanding, simple, and unpretentious natures. They never paraded their mental superiorities . . . . So far as I know, neither of them ever journied beyond the borders of their Austrian fatherland. Certainly, they never attended a scientific convention, and never developed intimate, personal relations with outside scholars. I cannot approve of this. I am sure that they would have achieved still more had they practiced less seclusion; in any event. their accomplishments would have become known sooner, and thus been more fruitful." Loschmidt's publications numbered only 20, but this small total in no way detracts from his fame. Doubtless he could have produced much more. There are various reasons why he did not. In the first place, he was interested only in problems of first rate importance, and it did not seem, to him, to be worth while to expend time and energy on minor topics. Furthermore, he did not have the necessary financial resources. Boltzmann gives instances of discoveries made by others that had to be passed up by Loschmidt for lack of adequate apparatus. According to Boltzmann there is hardly a comparable case of a scientist to whom so much had been denied. Though, unfortunately, this is true, the importance of the contents of Loschmidt's few papers is so great that Boltzmann was quite justified in saying that these studies "constitute a cornerpillar that will be plainly visible even a t a distance so long as natural science endures."
The great scientific discoseries of the post hundred years haw been child's play compared to the titanic forces that will be released when man applies himself to the understanding and mastery of his oron nature.
