Eilhard Mitscherlich

Eilhard Mitscherlich (7 January 1794 – 28 August 1863) was a German chemist, who is perhaps best remembered today for his law of isomorphism (1819), which states that compounds crystallizing together probably have similar structures and compositions. This relationship was used by Berzelius in early attempts to assign relative masses to the elements.

Early life and work

Mitscherlich was born at Neuende (now a part of Wilhelmshaven) in the Lordship of Jever, where his father was pastor. His uncle, Christoph Wilhelm Mitscherlich (1760–1854), professor at Göttingen, was in his day a celebrated scholar. He was educated at Jever under the historian Friedrich Christoph Schlosser, when he went to Heidelberg in 1811, and devoted himself to philology, giving special attention to the Persian language. In 1813 he went to Paris to obtain permission to join the embassy which Napoleon I of France was sending to Persia.

The events of 1814 put an end to this, and Mitscherlich resolved to study medicine in order that he might enjoy that freedom of travel usually allowed in the East to physicians. He began at Göttingen with the study of chemistry, and this so arrested his attention that he gave up the journey to Persia. From his Göttingen days dates the treatise on certain parts of Eurasian history, compiled from manuscripts in the university library and published in Persian and Latin in 1814, under the title Mirchondi historia Thaheridarum historicis nostris hucusque incognitorum Persiae principum.

In 1818 Mitscherlich went to Berlin and worked in the laboratory of Heinrich Friedrich Link (1767–1851). There he made analyses of phosphates and phosphites, arsenates and arsenites, confirming the conclusions of Jöns Jakob Berzelius as to their composition; and his observation that corresponding phosphates and arsenates crystallize in the same form was the germ from which grew the theory of isomorphism, which he communicated to the Berlin Academy in December 1819. In that year Berzelius suggested Mitscherlich to the Prussian education minister Karl vom Stein zum Altenstein as successor to Martin Heinrich Klaproth at Berlin. Altenstein did not immediately carry out this proposal, but he obtained for Mitscherlich a government grant to enable him to continue his studies in Berzelius' laboratory at the Karolinska Institutet in Stockholm. Mitscherlich returned to Berlin in 1821, and in the summer of 1822 he delivered his first lecture as extraordinary professor of chemistry in the university, where in 1825 he was appointed ordinary professor. In 1823, he was elected a foreign member of the Royal Swedish Academy of Sciences.

Isomorphism

Eilhard Mitscherlich

In the course of investigating slight differences discovered by William Hyde Wollaston in the angles of the rhombohedra of the carbonates isomorphous with calc-spar, Mitscherlich observed that the angle in the case of calc-spar varied with the temperature. On extending this inquiry to other allotropic crystals, he observed a similar variation, and was thus led, in 1825, to the discovery that allotropic crystals, when heated, expand unequally in the direction of dissimilar axes. In the following year he discovered the change, produced by change of temperature, in the direction of the optic axes of selenite. His investigation, also in 1826, of the two crystalline modifications of sulfur threw much light on the fact that the two minerals calc-spar and aragonite have the same composition but different crystalline forms, a property which Mitscherlich called isomorphism.^[1][2]

Later work and last years

In 1833 Mitscherlich made a series of careful determinations of the vapor densities of a large number of volatile substances, confirming the law of Gay-Lussac. In 1833-34, Mitscherlich investigated the synthesis of diethyl ether from ethanol and sulfuric acid.^[3] Through his careful studies, he realized that the acid was not being consumed during the production of the ether, although the reaction would not proceed unless the acid was present. After reviewing Mitscherlich's findings, Swedish chemist Jöns Jacob Berzelius was led to coin the term "catalysis" for the acceleration or enablement of a chemical reaction by a substance that itself was not consumed in the reaction.^[4] He obtained selenic acid in 1827 and showed that its salts are isomorphous with the sulphates, while a few years later he proved that the same thing is true of the manganates and the sulfates, and of the permanganates and the perchlorates. He investigated the relation of benzene to benzoic acid and to other derivatives. In 1829-1830 he published his Lehrbuch der Chemie, which embodied many original observations. His interest in mineralogy led him to study the geology of volcanic regions, and he made frequent visits to the Eifel with a view to the discovery of a theory of volcanic action. He did not, however, publish any papers on the subject, though after his death his notes were arranged and published by Dr. J. L. A. Roth in the Memoirs of the Berlin Academy (Ueber die vulkanischen Erscheinungen in der Eifel und über die Metamorphie der Gesteine durch erhöhte Temperatur, Berlin, 1865).^[5]

Mitscherlich was an honorary member of almost all the great scientific societies, and received the gold medal from the Royal Society of London for his discovery of the law of isomorphism.^[6] He was one of the few foreign associates of the French Institute.^[5]

In December 1861, symptoms of heart disease made their appearance, but Mitscherlich was able to carry on his academic work until December 1862. He died at Schöneberg near Berlin in 1863 and was buried in the St Matthäus Kirchhof Cemetery in Schöneberg close to the (eventual) gravesites of Gustav Kirchhoff and Leopold Kronecker.

Papers

Mitscherlich's grave in Berlin

Mitscherlich's published papers are chiefly to be found in the Abhandlungen of the Berlin Academy, in Poggendorff's Annalen, and in the Annales de chimie et de physique.

The fourth edition of Mitscherlich's Lehrbuch der Chemie was published in 1844-1847; a fifth was begun in 1855, but was never completed. A complete edition of his works was published at Berlin in 1896.^[6]

Notes

Further reading

• Eilhard Mitscherlich: Prince of Prussian Chemistry by Hans-Werner Scuhtt, 1997, ISBN 0-8412-3345-4
• Obituary of Eilhard Mitscherlich in Proceedings of the Royal Society of London, volume XIII, 1864 (pages ix - xvi, near the end of the volume)

References

•  This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Mitscherlich, Eilhardt". Encyclopædia Britannica (11th ed.). Cambridge University Press. 
• Eilhard Mitscherlich at the Mathematics Genealogy Project