EILHARD MITSCHERLICH (1794-1863) His Life and Achievements RUDOLF WINDERLICH Oldenburg i. Oldenburg, Germany (Translofed by Rolph E. Oesper, University of Cincinnatz)
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DECEMBER 1, 1894, a t the unveiling of the statue medicine. This led him to chemistry. In 1818 he went of Eilhard Mitscherlich before the University of Berlin, to Berlin and worked in the laboratory of the botanist Wilhelm Ostwald, the speaker of the day, stated: H. F. Link. He chose to study phosphates and arsen"Mitscherlich m-as a prince in the realm of the mind, and ates and was soon forcefully impressed by the similarity a hero in the battle for the light." Nonetheless, few, in the crystal forms of the corresponding salts. He except specialists, have a knowledge of the work of this therefore took lessons in crystallography from his scientist and its permanent value; even chemists friend Gustav Rose, the mineralogist at the University, vaguely remember little except his name. He himself and with the newly acquired hovledge discovered the was largely responsible for this semioblivion, because he law concerning "the relation which exists between rryshad a pronounced shyness about publicizing his dis- talline form and chemical composition." In his words, coveries. When his "Collected Works" were published "the same number of atoms combined in the same manby his son1 it was necessary to preface the first, and ner produce the same crystalline form; the crystalline probably the greatest of his works, with the remark: "This paper has never before appeared in German." For 75 years, only excerpts of it were h o w n in Germany, and only then, for the first time, was there available a complete translation in his native language of the original (1821) Swedish text.2 This tendency against publishing became more pronounced from year to year so that Ostwald could truthfully declare: "Toward the last, the titles of the papers delivered by him before the ~ c ~ d became e m ~ the only trace which he allowed the outside world to obtain of his indefatigable a ~ t i v i t y . " ~ Eilhard Mitscherlich was born on Januarv 7. 1794. at Neuende near Jever in Oldenburg. His father, the killage pastor, wished to provide the best possible education for his bright son so he sent him to bever to live in the home of the historian, Friedrich Christoph Schlosser. At the latter's advice. Mitscherlich s~ecializedin oriental languages and history. &ter securing his doctorate at Gottingen, with a dissertation on a Persian historical work, he abandoned this field and turned to
ow ever,
"Gesammelte Schriften von Eilhard Mitscherlich. Lebcnsbild, Briefweschsel und Abhandlungen." Published by Alexander Mit,soherlirh. Berlin. 1896. fi7X nares. This translation, &ted by P. v. Groth, is available as No. 04 of "Ostwsld's Klassiker," Leipsic, 1894. Mitscherlieh promised to write a Supplement on crystsllagraphy for the Bersclius "Lehrbuch dcr Chemie," and the latter designated this promised contribution as something extraordinary. But he waited for it in vain, even though a, few of his many letters were snsuwed with a solemn promise to fulfill the obligation a t once. Finally, the "Lehrbuch" was published without the Mitscherlich supplement. The farce was repeated with the next edition. I n 1840, when Mitscherlich visited Berzelius, and again offered to make his promise good, he received the reply: "We are no longer negotiating on this point. At present, I am limiting my demands that a t least before you die, you yourself publish your crystallographic studies!' ~
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form does not depend on the nature of the atoms, hut solely on their number and mode of combination." The announcement of this law of isomorphism (isos = like and morphe = form) aroused considerable attention, and it made a particular impression on Berzelius during his 1819 stay in B e r h 4 Berzelius necessarily saw that this law was an iuvaluable acquisition to chemistry, because it could be a decisive factor in determining the choice between two hotly contested possibilities. R. J. Haiiy, the founder of geometrical crystallography, had championed the view that crystal form determines the chemical structure of a mineral, whereas Berzelius had taken as the basis for his mineral svstem the assumution that the crystal form is dependent on the chemical nature of the mineral. No one then could possibly have foreseed the full value of the law of isomorphism, because its real import was not revealed until the close of the 19th centurv. Since 1870 P. v. Groth had been enlralred in an attempt to elucidate the relation between crisial stmctnre and chemical stmcture. He started with Mitscherlich's thought that crystallographically equal directions a+e also physically equal, and accordmgly, from 1895 on, regarded the chemical atoms of a crystalline material as points of space lattices whose constants are determined by thekind, number, and position of the atoms. The space lattice of a crystal remains (almost) unchanged when an element of like valence is incorporated in place of one of the original elements. These bold postulates were brilliantly verified in 1912by Max von Laue. By means of the interference patterns produced by the diffraction of X-rays on crystal lattices, he proved the manner in which the structural units are arranged. At the same time, he established the wave nature of X-rays, and provided scientists with a new tool for penetrating into the structure of materials. Of course, Berzelius could not anticipate any such radical effect of the law of isomorphism on present-day views of the fine structure of matter; for him the new law was valuable enough when it fvas applied in deciding the choice between atomic weights#and in demonstrating the correctness of his mineral system. Consequently he proposed to v. Altenstein, the Pmssian Minister of Education, that the promising young scientist be entrusted with the chemistry professorship at the University of Berlin. The chair had been vacant since the death (January 1, 1817) of Martin Heinrich Klaproth, the distinguished analyst and discoverer of uranium, zirconium, titanium, and cerium. I t was offered to Berzelius who declined for patriotic reasons. After due deliberation v. Altenstein decided that Mitscherlich would need to he thoroughly trained for the post by Berzelius through a stay in the great chemist's private laboratory. Mitscherlich was in Stockholm, at the government's expense, for two years (December, 1819 to November, 1821). He worked so independently and For a n excellent review of Mitscherlich's work on isomorphism and dimorphism see Ida Freund, "A Study of Chemical Composition," Cambridge, 1904, Chapter XV.
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diligently that Berzelius was able to report to the Minister: "He has been more my student collaborator than my pupil." Such laudatory statements by Berzelius brought Mitscherlich not only election to the Pmssian Academy of Sciences, despite the opposition of Weiss (mineralogist) and Seebeck (physicist), but also this same year (1822) an appointment as extraordinary professor at the university. Three years later he was promoted to the,full professorship. His letter of thanks to Berzelius reveals not only his joy for the 800 talers, the annual salary, but still more the anticipation of having a good laboratory with adequate funds for its operation. Freedom from financial worries was highly important to him. He made this quite clear to Berzelius (letter of July 18, 1826) when he told his fatherly friend that he had taken a highly cultured wife of considerable means and "would never be forced to make a milch cow of science." The marriage turned out exceedingly
5Mit.9eherlich's handwriting was outstandingly poor. Bereeiius m o t e to him (February 2, 1828): "Your latest letter, provided with your variety of logiblo script, seemingly was sent to the Royal Office of Foreign Mail, from which I receive many of my letters from abroad. The clerk read the address a8 "Mademoiselle Hochschild," who frequently gets letters from her brother, who is Minister in Copenhagen, and accordingly t,he letter was sent to her. Fortunately, she is the sister-in-law of my good friend Poppius. One evening a t his home, they were talking about the stray letter, whose address could not be read by even President Poppius. They asked me to try. I recognized your writing s t once, and to the horror of everybody broke the letter open. They thought I had done this through a misunderstanding. How they laughed when I deciphered for them my name in the address. Consequently, from now on, have your wife write the addresses."
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Closely related to his law of isomorphism, was his relation to these also, namely, that the shorter exes exsecond (1821) great discovery, dimorphism. He found pand relatively more than the longer." His inquiries that "one and the same proportions, can assume two into the regularity, magnitude, and cause of optical different forms." Aragonite, which he had found to be effects,especially double refraction, under the influence isomorphous with the naturally occurring lead carbo- of heat, were eventually extended also to noncrystalline nate (cerussite), is a variety of calcium carbonate, dif- materials. fering in crystal form from the ordinary calcite, with In 1827 he constructed a new type of goniometer but which it is dimorphous. After Mitscherlich had recog- did not publish anything about it until 16 years later. nized that the crystals of sulfur obtained from its solu- With its aid he increased the accuracy of reading the retions differ from those separating from its melts, he flected angle to several seconds, as contrasted with the (1823) modified his statement to read: "that one and five minutes possible with the Wollaston instrument. Extensive studies of the constituents of the slags in the same material, be it simple or compound, can assume two different crystalline forms." The fact did not the dumps of Swedish copper smelters gave rise to sucescape his notice that heat is liberated when monoclinic cessful attempts to produce minerals artificially. He sulfur changes into the rhombic form. was.thus able to refute the general belief "that chemisSubsequently, Mitscherlich expended much labor and try could indeed decompose minerals into their constitucare on the mental and experimental solution of various ents, but since forces of Nature were active at the forproblems connected with crystal systems. He wrote to mation of the natural compounds, they could never be Berselius (June 14, 1823) that his objective was: "to reproduced artificially." In connection mith these studarrive a t definite conclusions concerning the distribu- ies he developed a "theory of the smelting ont of coption of matter itself in crystalline bodies, and also con- per," in which his chief objective was "to demonstrate cerning the relation of heat and matter." He showed clearly that in this process silica behaves entirely . - as an "that the expansion of crystals is exactly in the direction acid." of the crystallographic axes, and, since the latter are Mitscherlich's intense interest in minerals and crysconnected with the optical axes, they stand in a certain tals persisted throughout his life. He frequently devoted himself to eeoloxical ~roblems,to whose solution he made notable contributions: the formation of ore veins; the source of mineral springs; volcanic processes; the metamorphosis of rocks by heat; etc. Other areas of inorganic chemistry were enriched by him. He discovered selenic acid, developed a simple method of detecting free phosphorus, and cleared up the nature of permanganic acid. I n his "Jahrbuch," for 1834 Berselius commented admiringly th.?t the last of these studies had yielded "the unexpected result that this metal has two acids, of which one, manganic acid, consists of 1 atom of manganese and 3 atoms of oxygen, while the other, which Mitscherlich calls permanganic acid, consists of 2 atoms of manganese and 7 atoms of ~ x y g e n . " ~ The basic importance of the isomorphism of the perchlorates and permanganates was stressed by Mitscherlich. He recognized the prime importance of the vapor densities of gasified substances. By numerous accurate analyses he extended the conclusion reached by Dumas "that sulfur gas (vapor) contains three times as many atoms as an equal volume of oxygen." This presented the physicists and chemists mith a troublesome situation, because at that stage they were not able to distinguish clearly between atoms and molecules and yet they did not wish to abandon Avogadro's hypothesis that under like conditions of temperature and pressure equal volumes of gases contain equal numbers of "atoms." This difficulty finally compelled the scientists to make a sharp differentiation between atom and molecule. Mitscherlich's contributions to organic chemistry were no less important than his achievements in the inorganic field. His investigations (1834) on benzene and 6 According to the then prevailing oxygen theory of acids, MnOI and MnrO,, i. e., anhydrides of H2Mn0, snd HMnO,.
JULY, 1949 its compounds revealed the relation between "bicarburet of hydrogen" (discovered in 1825by Faraday and studied by him with astounding exactness) and the acid obtained from benzoin resin. Dry distillation of calcium benzoate yielded an easily volatile liquid, which Mitscherlich recognized as identical with Faraday's hydrocarbon. Because of its origin, Mitscherlich proposed the name "benzin." Liebig objected and changed it to "benzol," the form that is still used in German. Mitscherlich was the first to prepare nitrobenzene, azobenzene, benzenesulfonic acid, etc., and so, in a sense, laid the foundations of the dyestuff industry. His theoretical conclusions concerning the benzene derivative wrr~'nor approved by Jk.rrt.liu;, nnd i l l .Junr, 1835. 3 I i t 4 f d i v l 1wrote: "Tl~i.;work on lrenzin rml it. publication have lost all pleasure for me, and I wish I had never started it, since it is the first time that you do
decomposition~and~ombination through contact to a no longer disappearing, indispensable concept, which sheds lieht over manv thines" (letter of October 31. 18311. ~ i t a l y t i cconsic?eratio& la'tkr guided Mitscherlich in hk studies of yeast fermentation and microorganisms. Eilhard Mitscherlich must he classed among the leading investigators. Beyond this, he possessed and freely utl I I t l i t i k i n I n t y r n nnmcly 111t. itllility to trnrh wll, Lotlt by mouth and by ~ n w I 1rt1rl11111 1 h n iI l e er :I critical Berzelius that he wished to have it translated into Swedish. "You have a great talent, dear Mitscherlich, of being interesting, terse, and instructive" (letter of August 27, 1832). Mitscherlich repeatedly stressed his love for teaching. He enlivened and reinforced his lectures with appropriate demonstrations, even though scarcity of the necessary equipment caused him cousiderable difficulty. He complain,ed to Berzelius (July 14, 1826): "Of all that I anticipated here and had a right to expect from the Ministry, Phave obtained nothing." The promised funds for the purchase of instruments were not granted, with the consequence that he had to dip into his own pocket. At that time the men in authority in Germany, especially in Berlin, were indifferent or even inimical to the natural sciences. When Ostwald stated that "Mitscherlich was a hero in the battle for the light," he was referring to the struggle against the natural philosophers, concerning whom
' Mitseherlich's papers on "Benein" are reproduced as No. 98 (editcd hy J. Wislicenus) of "Ostwald's Xlassiker," Leipsic, 1898.
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A Hitherto Unpublished Likeness of Mitscherlich
Mitscherlich stated to Berzelius (May 30, 1827): "they declare war on the healthy human intelligence." The battle against these obscurantists was difficult, because the authorities "had set aside an annual sum of 4000 talers to support their activities." On the other hand, the construction of a teaching labdratory vas not authorized. In an illuminating letter (May 20, 1837) he told Berzelius: "The installation of my collections and apparatus consumes practically all of the time which I can devote to scientific activities. In order to maintain the building, and to spare myself other annoyances, I have taken upon myself a part of the expense of fitting up the laboratory and all the cost of the scientific furnishings." A man who thought thus, acted thus, and who made such wide-reaching discoveries, deserves not to he forgotten. He died on August 28, 1863.
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