Background

Friedrich Kohlrausch was born on October 14, 1840, in Rinteln, Germany. He was the son of Rudolf Heinrich Arndt Kohlrausch, a physicist and university professor, and his wife Maria Carolina Friederika Elisabetha Dempwolff. He had a younger brother Wilhelm Friedrich Kohlrausch, who, like his father, also became a noted physicist and professor of physics. He was also the grandson of Friedrich Kohlrausch, and the nephew of Otto Kohlrausch.

Education

Kohlrausch was educated at the Polytechnikum at Kassel and at the universities of Marburg, Erlangen, and Gottingen, receiving his doctor’s degree at Gottingen in 1863 under Wilhelm Weber.

Career

In 1863 Kohlrausch acted as an assistant in the astronomical observatory at Gottingen and in the laboratory of the Physical Society at Frankfurt before being appointed extraordinary professor at the University of Gottingen (1866-1870).

Kohlrausch held the professorship of physics in the ETH Zurich (1870-1871), at Darmstadt (1871-1875), and at the University of Wurzburg (1875-1888), and then succeeded Kundt as director of the physical laboratory at Strasbourg. On the death of Helmholtz in 1894, he left Strasbourg to accept the appointment of director of the Physikalisch Technische Reichsanstalt at Charlottenburg.

Achievements

• Friedrich Kohlrausch went down in history as a distinguished physicist who laid the foundations for scientific knowledge which promoted and advanced industry and technology. His work on the conductivity of electrolytic solutions became important in leading to the eventual statement by Arrhenius postulating the electrolytic dissociation theory of solution structure. Kohlrausch was also one of the first teachers to prepare an instructive work on physical laboratory methods, Leitfaden der praktischen Physik, which was widely used and republished, being translated into four languages, including English.
  
  He was awarded the Pour le Mérite for Sciences and Arts in 1896, the Bavarian Maximilian Order for Science and Art in 1896, the Robert Wilhelm Bunsen Medal in 1908, and was nominated six times for the Nobel Prize in Physics.

Works

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• book

  • An Introduction to Physical Measurements 1873
  • Leitfaden Der Praktischen Physik, Mit Einem Anhange 1872
  • Das leitvermögen der elektrolyte, insbesondere der wässrigen lösungen 1916
  • Gesammelte Abhandlungen 1911
  • Methoden, Resultate Und Chemische Anwendungen 1898
  • Lehrbuch der praktischen Physik 1905
  • Die gegenwärtigen Anschauungen über die Elektrolyse von Lösungen 1887

Views

Kohlrausch’s contributions to physical science were characterized by a high degree of precision. They included research on the electrical conductivity of electrolytes, on elasticity (begun in 1866), on magnetic measurements (begun in 1869), and on the determination of the electrochemical equivalent of silver in 1886 with his brother Wilhelm.

When Kohlrausch began his research in conductivity of solutions, the structure of a solution was controversial. The determination of whether or not Ohm’s law applied to electrolytic solutions was confused by the question of polarization of the electrodes. When a direct current was forced through the electrolyte, ions gathered around the electrodes and partially neutralized the electric potential, decreasing the current; the effect produced inconsistent values for the conductivity of the solution being measured.

In 1868 Kohlrausch began to study the problem, developing the technique of using an alternating current rather than a direct current. In this way the decompositions which took place at the electrodes was reversed many times each second. The alteration of the solution was thus kept at a minimum while conductivity measurements were being made. At the same time, the products of decomposition were not allowed to collect at the electrodes, and polarization was thus also reduced to a minimum. In a paper published in 1870 with W. A. Nippoldt, Kohlrausch showed that there was a maximum in the conductivity curve of sulfuric acid diluted with increasing amounts of water. He concluded that there was something fundamentally associated with the act of mixing itself that imparted conductivity to solutions. In a later paper, written with Otto Grotrian (1874), Kohlrausch showed that the conductivity of solutions increased with increasing temperature.

In 1876 Kohlrausch pointed out that, following the work of Hittorf on the migration of ions, the ions in very dilute solutions did not encounter appreciable resistance to their movement from other similar ions, and that the water in which the ions were dissolved provided the only friction serving to retard their motion. He concluded that “in a dilute solution every electrochemical element has a perfectly definite resistance pertaining to it, independent of the compound from which it is electrolyzed.” Thus the conductivity of electrochemically equivalent solutions of two electrolytes which have a component in common would vary inversely with the transference numbers of the common component. Kohlrausch was able to substantiate his conclusion by a comparison of the transference numbers measured by Hittorf with his own values for the conductivity of the same solutions.

Membership

Kohlrausch was elected a member of the Academy of Sciences in Berlin in 1895 and was a member of scientific societies in many countries.

Connections

In 1867, Kohlrausch married Margaretha Eleonora Hermina Schilling, the daughter of Doctor David Eduard Schilling. The couple had one son and four daughters.

Father:

Rudolf Heinrich Arndt Kohlrausch

Mother:

Maria Carolina Friederika Elisabetha Dempwolff

Spouse:

Margaretha Eleonora Hermina Schilling

Brother:

Wilhelm Friedrich Kohlrausch

Grandfather:

Friedrich Kohlrausch

Uncle:

Otto Kohlrausch

father-in-law:

David Eduard Schilling

Son:

Otto Wilhelm Eduard Kohlrausch

Daughter:

Marie Kohlrausch

Doctoral advisor:

Wilhelm Eduard Weber

colleague:

W. A. Nippoldt

colleague:

Otto Grotrian

References

• Dictionary of Scientific Biography, Volume 7
  1973