The complete scientist

EILHARD MITSCHERLICH was born on (January 17, 1794) at Neuende, Jever, Germany, the son of a minister. He attended the local school which was headed by a historian, who encouraged him in the study of liberal arts.

In 1911, Mitscherlich entered the University of Heidelberg where he studied Oriental languages.

He shifted to the University of Paris and learned with enthusiasm Persian, as he intended to enter the diplomatic corps.

With Napoleon's fall, that prospect ended; so he returned to Germany to read medicine and science and enrolled in the University of Goettingen (1817).

This choice was dictated by his determination to reach the Orient, as a ship's doctor, if not as a diplomat. Simultaneously with his medical studies, Mitscherlich pursued his research on ancient Persian texts, which earned him the doctorate degree.

His interests turned increasingly toward chemistry captivated by the lectures of his teacher at Goettingen, Strohmeyer.

In 1818 he went to the University of Berlin to work in the botanical laboratory of Henrich Link. After four years, he moved to the chemistry department at the university. He served as professor for 38 years from 1825 till the end of his life (February 28, 1863).

He was director of the laboratory attached to the observatory of the Berlin Academy of Sciences.

He made extensive use of this laboratory for teaching as well as for research, since the university had no facilities for practical instruction in chemistry.

Studies on crystallography

At the beginning of his career, Mitscherlich was struck by the similarity between potassium phosphate and potassium arsenate crystals.

With his curiosity spurred, he approached Gustav Rose (1798- 1873), a mineralogist, for learning the technique of precise measurements of crystal angles.

He then applied spherical trigonometry to the data he obtained and confirmed his first observation of identical crystal forms. He published this finding in a journal of the Prussian Academy, which was translated into French (1820) in the Annales de chimie.

The great chemist Berzeliius (1779-1848) came to know of the work and recognised its significance.

When the Prussian Ministry offered Berzelius the chair of chemistry, the latter recommended Mitscherlich, who was considered too young for the post.

The law of Isomorphism

Berzelius invited Mitscherlich to join his laboratory in Stockholm for two years. During this fruitful partnership, Mitscherlich extended his studies from arsenates and phosphates to carbonates, deducing that similar crystal form (which he named isomorphism) implies similar constitutions.

He established the isomorphism that exists between a number of specific compounds such as potassium chromates and potassium magnate potassium perchlorate and potassium permanganate``.

He thus stated the law: "an equal number of atoms, combined in the same way, produce the same crystal forms: the crystal form does not depend on the nature of the atoms, but only on their number and mode of combination".

Berzelius acclaimed Mitscherlich's law as a great discovery, as significant as the law of chemical proportions.

He was at this time working on the determination of the atomic weights of the elements and found the law of isomorphism a valuable tool correcting the atomic weights for 21 elements (1826).

When Mitscherlich saw the limitations of his law, he modified it to recognise the existence of two different crystalline forms of one substance (dimorphism).

Mitscherlich worked in a number of areas of both inorganic and organic chemistry.

He investigated (1830) the higher compounds of manganese, the mixture of magnate and permanganate that Glauber, in the 17th century, had called then "chameleon material".

He showed that its red and green salts were derivatives of two different acids. He also worked on a modification of Dumas's apparatus for determining vapour densities for many inorganic substances, by employing a metal bath for measuring higher temperatures. His results were highly accurate.

The name "benzene" is due to Mitscherlich. He obtained it from benzonic acid and lime.

He also obtained various benzene derivatives such as nitrobenzene from the reduction of benzene with fuming nitric acid, and a number of halogenated benzenes such as trichlrobenzene.

Mitscherlich showed (1834) that a mixture of ether and water distills out of a mixture of alcohol and dilute sulfuric acid, the latter acting as a dehydrating agent. He enunciated his "contact theory", whereby certain chemical reactions can take place only in the presence of certain other substances. He applied the theory to explain fermentation, the contact in this process being yeast which si necessary for the conversion of sugar into alcohol. He gave impetus to the sugar industry by inventing the first polarization apparatus.

His interest in geology and mineralogy, like his work on isomorphism, continued throughout his scientific career.

He worked with some success on the production of artificial minerals through the fusion of silica with various metallic oxides.

His work Textbook of Chemistry, containing, the lectures he delivered on all aspects of pure and applied chemistry including ingenious experiments, with judicious amount of material on physics, received praise from his contemporaries Berzelius and Liebig. By 1847 it ran into four editions in German, as well as two editions in French and one in English.

His son, Alexander, discovered the Mitscherlich process for extracting cellulose from wood through boiling with calcium bisulfite, which created the base for German cellulose industry (The Dictionary of Scientific Biography).

R. Parthasarathy

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