Jahn, Hans Max

(b. Küstrin, Germany [now Kostrzyn, on the Oder, Poland], 4 July 1853; d. Berlin, Germany, 7 August 1906)

Physical chemistry.

Jahn studied chemistry and mathematics at the universities of Berlin and Heidelberg. During his student years he was a private assistant to A. W. von Hofmann at Berlin, where in 1875 he earned his doctorate with a work on the derivatives of secondary octly alcohol. He then went to Athens, where he was an instructor and then a professor at the university. He moved to Vienna in 1877 and worked as Privatdozent in association with Ernst Ludwig. In 1883 he married Sophie von Sichrovsky.

In 1884 Jahn went to Graz University in Austria and, in 1889, to the Landwirtschaftliche Hochschule in Berlin to work with Hans Landolt. When the latter was appointed to the University of Berlin, Jahn went with him and taught at his institute, first as an instructor and later as an assistant professor, lecturing on electrochemistry. But his hearing steadily deteriorated, hindering his career. He died unexpectedly of complications stemming from an appendectomy.

Jahn’s earliest scientific works dealt with organic chemistry, as did most German writings of that period on chemistry. His most important publications concerned the decomposition of simple organic compounds by means of zinc dust. While at the university in Graz, he turned his attention to the field of electrochemistry. In numerous works he considered various thermodynamic problems raised by electrochemical phenomena. In his studies on the relationship of the chemical energy and electrical energy of galvanic cells and on the equivalence of these two kinds of energy, he presented experimental evidence (1886) suggesting that the total chemical energy is modified only when the electromotive force does not change with the temperature. He thereby provided the quantitative demonstration of the validity for electrochemical phenomena of the so-called Gibbs- Helmholtz equation (1878-1882).

Jahn also demonstrated the existence of reversible Peltier heat effects in voltaic cells and, with Otto Schönrock, investigated electrochemical polarization In his last years Jahn was concerned with electrolytic dissociation, attempting to calculate the relationship between degree of dissociation and electrical conductance in weak and strong electrolytes; he was unsuccessful in this endeavor. His last works are devoted to improvements in cryoscopic methods.

BIBLIOGRAPHY

Jahn’s major works are; Die Grundsätze der Thermochemie und ihre Bedeutung für die theoretische Chemie (Vienna, 1882); Die Elektrolyse und ihre Bedeutung für die theoretische und angewandte Chemie (Vienna, 1883); and Grundriss der Elektrochemie (Vienna, 1895). In addition to those Jahn produced about fifty other publications.

For a biographical treatment of Jahn, see H. Landolt, “Hans Jahn,” in Berichte der Deutschen chemischen Gesellschaft, 39 (1906), 4463, with portrait.

Fereng Szabadvary