Friedrich Wilhelm Georg Kohlrausch (14 October 1840 – 17 January 1910) was a German
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe.
Physicists generally are interested in the root or ultimate caus ...
who investigated the
conductive
In physics and electrical engineering, a conductor is an object or type of material that allows the flow of charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric current is gener ...
properties of
electrolytes
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon di ...
and contributed to knowledge of their behaviour. He also investigated
elasticity
Elasticity often refers to:
*Elasticity (physics), continuum mechanics of bodies that deform reversibly under stress
Elasticity may also refer to:
Information technology
* Elasticity (data store), the flexibility of the data model and the cl ...
,
thermoelasticity, and
thermal conduction
Conduction is the process by which heat is transferred from the hotter end to the colder end of an object. The ability of the object to conduct heat is known as its ''thermal conductivity'', and is denoted .
Heat spontaneously flows along a tem ...
as well as
magnetic
Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...
and electrical precision measurements.
Nowadays, Friedrich Kohlrausch is classed as one of the most important experimental physicists. His early work helped to extend the absolute system of
Carl Friedrich Gauss
Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
and
Wilhelm Weber to include electrical and magnetic measuring units.
Biography
Education
Son of
Rudolf Kohlrausch
Rudolf Hermann Arndt Kohlrausch (November 6, 1809 in Göttingen – March 8, 1858 in Erlangen) was a German physicist.
Biography
He was a native of Göttingen, the son of the Hanover#19th century, Royal Hanovarian director general of schools Frie ...
, Friedrich Wilhelm Georg Kohlrausch was born on October 14, 1840, in
Rinteln
Rinteln () is a small town in Lower Saxony, Germany. It is located on the banks of the Weser river above the Porta Westfalica. The town of Rinteln is in the broad valley between the hills of the Weserbergland and the North Lippe Bergland. In rela ...
,
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. After studying physics at
Erlangen
Erlangen (; East Franconian German, East Franconian: ''Erlang'', Bavarian language, Bavarian: ''Erlanga'') is a Middle Franconian city in Bavaria, Germany. It is the seat of the administrative district Erlangen-Höchstadt (former administrative d ...
and
Göttingen
Göttingen (, , ; nds, Chöttingen) is a college town, university city in Lower Saxony, central Germany, the Capital (political), capital of Göttingen (district), the eponymous district. The River Leine runs through it. At the end of 2019, t ...
, Friedrich Kohlrausch completed his doctorate in
Göttingen
Göttingen (, , ; nds, Chöttingen) is a college town, university city in Lower Saxony, central Germany, the Capital (political), capital of Göttingen (district), the eponymous district. The River Leine runs through it. At the end of 2019, t ...
.
Teaching
After a two-year work as a lecturer in
Frankfurt
Frankfurt, officially Frankfurt am Main (; Hessian: , "Frank ford on the Main"), is the most populous city in the German state of Hesse. Its 791,000 inhabitants as of 2022 make it the fifth-most populous city in Germany. Located on its na ...
, Kohlrausch was appointed a professor of physics at the
University of Göttingen
The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded ...
(1866–70).
During 1870 Kohlrausch became a professor at
ETH Zurich
(colloquially)
, former_name = eidgenössische polytechnische Schule
, image = ETHZ.JPG
, image_size =
, established =
, type = Public
, budget = CHF 1.896 billion (2021)
, rector = Günther Dissertori
, president = Joël Mesot
, ac ...
in
Switzerland
). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
. One year later, he moved to the
Darmstadt University of Technology
Darmstadt () is a city in the state of Hesse in Germany, located in the southern part of the Rhine-Main-Area (Frankfurt Metropolitan Region). Darmstadt has around 160,000 inhabitants, making it the fourth largest city in the state of Hesse a ...
in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
.
In 1875, he responded to an offer from the
University of Würzburg
The Julius Maximilian University of Würzburg (also referred to as the University of Würzburg, in German ''Julius-Maximilians-Universität Würzburg'') is a public research university in Würzburg, Germany. The University of Würzburg is one of ...
in southern
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, where he subsequently conducted his experiments in quantity determination and the conductivity of electrolytes. From 1888 he researched and taught at
Strasbourg University
The University of Strasbourg (french: Université de Strasbourg, Unistra) is a public research university located in Strasbourg, Alsace, France, with over 52,000 students and 3,300 researchers.
The French university traces its history to the ea ...
.
He refused a professorship at the
Humboldt University
Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative of ...
in
Berlin
Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...
in 1894, but from 1900 he was also a professor there. He was elected a member of the
Royal Swedish Academy of Sciences
The Royal Swedish Academy of Sciences ( sv, Kungliga Vetenskapsakademien) is one of the Swedish Royal Academies, royal academies of Sweden. Founded on 2 June 1739, it is an independent, non-governmental scientific organization that takes special ...
during 1902.
Research work
Kohlrausch was an important researcher of electrochemistry for many reasons. First, the experiments from which he deduced his law of independent migration of ions became canonical and disseminated from Kohlrausch's laboratories in
Göttingen
Göttingen (, , ; nds, Chöttingen) is a college town, university city in Lower Saxony, central Germany, the Capital (political), capital of Göttingen (district), the eponymous district. The River Leine runs through it. At the end of 2019, t ...
,
Zurich, and
Darmstadt
Darmstadt () is a city in the States of Germany, state of Hesse in Germany, located in the southern part of the Frankfurt Rhine Main Area, Rhine-Main-Area (Frankfurt Metropolitan Region). Darmstadt has around 160,000 inhabitants, making it th ...
;
Svante Arrhenius
Svante August Arrhenius ( , ; 19 February 1859 – 2 October 1927) was a Swedes, Swedish scientist. Originally a physicist, but often referred to as a chemist, Arrhenius was one of the founders of the science of physical chemistry. He received ...
,
Wilhelm Ostwald
Friedrich Wilhelm Ostwald (; 4 April 1932) was a Baltic German chemist and German philosophy, philosopher. Ostwald is credited with being one of the founders of the field of physical chemistry, with Jacobus Henricus van 't Hoff, Walther Nernst, ...
and
Jacobus Henricus van 't Hoff, the original
Ionists, all trained with methods and equipment of Kohlrauschian lineage. Moreover, because Kohlrausch also continued to test and confirm the Ionist theory after it had been first proposed, his work tied "measuring physics" and its consequent capability of producing plenty of empirical data to the results and methods of the Ionists and their devotees.
Electrolyte conductivity in solution
In 1874 he demonstrated that an
electrolyte
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
has a definite and constant amount of electrical resistance. By observing the dependence of conductivity upon
dilution
Dilution may refer to:
* Reducing the concentration of a chemical
* Serial dilution, a common way of going about this reduction of concentration
* Homeopathic dilution
* Dilution (equation), an equation to calculate the rate a gas dilutes
*Tradema ...
, he could determine the transfer velocities of the
ions
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
(charged atoms or molecules) in solution. He used
alternating current
Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
to prevent the formation of electrolysis products (
and gas evolution, or metal deposition); this enabled him to obtain very precise results.
From 1875 to 1879, he examined numerous
salt
Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
solutions,
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
s and solutions of other materials. His efforts resulted in the
law of the independent migration of ions, that is, each type of migrating ion has a specific limiting
molar conductivity
The molar conductivity of an electrolyte solution is defined as its conductivity divided by its molar concentration.
: \Lambda_\text = \frac,
where:
: ''κ'' is the measured conductivity (formerly known as specific conductance),
: ''c'' is the mol ...
no matter what combination of ions are in solution, and therefore that a solution's electrical resistance is due only to the migrating ions of a given substances. Kohlrausch showed for weak (incompletely dissociated)
electrolytes
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon di ...
that the more dilute a solution, the greater its
molar conductivity
The molar conductivity of an electrolyte solution is defined as its conductivity divided by its molar concentration.
: \Lambda_\text = \frac,
where:
: ''κ'' is the measured conductivity (formerly known as specific conductance),
: ''c'' is the mol ...
due to increased ionic
dissociation
Dissociation, in the wide sense of the word, is an act of disuniting or separating a complex object into parts. Dissociation may also refer to:
* Dissociation (chemistry), general process in which molecules or ionic compounds (complexes, or salts) ...
.
Measuring techniques and instruments
During 1895 he succeeded
Hermann von Helmholtz
Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, ...
as President of the Physikalisch-Technische Reichsanstalt (PTR – Imperial Physical Technical Institute), an office which he held until 1905.
Here, as in the past, his activities were focused on experimental and instrumental physics: he constructed
instruments
Instrument may refer to:
Science and technology
* Flight instruments, the devices used to measure the speed, altitude, and pertinent flight angles of various kinds of aircraft
* Laboratory equipment, the measuring tools used in a scientific lab ...
and devised new measuring techniques to examine electrolytic conduction in solutions. He concluded the setup of the PTR, a task which had not yet been completed on the death of its first president. He introduced fixed regulations, work schedules and working hours for the Institute.
Under direction of Kohlrausch, the PTR created numerous standards and calibration standards which were also used internationally outside
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
.
Kohlrausch was intent on creating optimum working conditions in the laboratories and to shield the labs from unwanted external influences. For six years, for instance, he fought against a streetcar line which was due to be laid near the PTR. However, before the streetcar was to make its first journey, the institute succeeded in developing an astatic
torsion
Torsion may refer to:
Science
* Torsion (mechanics), the twisting of an object due to an applied torque
* Torsion of spacetime, the field used in Einstein–Cartan theory and
** Alternatives to general relativity
* Torsion angle, in chemistry
Bio ...
magnetometer
A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...
which was uninfluenced by disturbing
electromagnetic field
An electromagnetic field (also EM field or EMF) is a classical (i.e. non-quantum) field produced by (stationary or moving) electric charges. It is the field described by classical electrodynamics (a classical field theory) and is the classical c ...
s. The use of this instrument and the shielded wire
galvanometer
A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely.
A galvanom ...
developed by
du Bois and Rubens meant that precision electrical and magnetic work continued to be possible.
Over the years, Kohlrausch added experiments which met the needs of physical chemistry and electrical technology in particular. He improved precision measuring instruments and developed numerous measuring methods in almost all of the fields of physics known during his lifetime, including a reflectivity meter, a
tangent galvanometer
In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. More ...
, and various types of magnetometers and dynamometers. The Kohlrausch bridge, which he invented at that time for the purpose of measuring conductivity, is still well known today.
Like
Helmholtz
Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, ...
and Siemens, Kohlrausch also saw the possibilities inherent in applied and basic research in the natural sciences and technology. He lay the foundations for scientific knowledge which promoted and advanced industry and technology. The PTR developed standardized precision instruments for university research institutes and industrial laboratories. It introduced uniform electrical units for Germany and also played a significant role in their international usage. In the period to 1905, there were many examples of the importance of the PTR for German industry, in particular for the high technologies of the time – the electrical, optical and mechanical industries.
Overall, Kohlrausch was involved in the measurement of electrical, magnetic and electrochemical phenomena for almost 50 years. In 1905 Kohlrausch retired from his post as President of the PTR.
Friedrich Kohlrausch died in
Marburg
Marburg ( or ) is a university town in the German federal state (''Bundesland'') of Hesse, capital of the Marburg-Biedenkopf district (''Landkreis''). The town area spreads along the valley of the river Lahn and has a population of approximate ...
on 17 January 1910 at the age of 69.
Writings
In the
University of Göttingen
The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded ...
, Kohlrausch documented his practical experiments resulting in the book ''Leitfaden der praktischen Physik'' (Guidelines to Practical Physics), which was published in 1870 as the first book of its type in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. It contained not only descriptions of experiments, experimental setups and measuring techniques, but also tables of physical quantities. It was issued in many editions (the 9th enlarged and revised edition of 1901 being entitled ''Lehrbuch der praktischen Physik''; a more elementary work based on it being entitled ''Kleiner Leitfaden der praktischen Physik'') and translated into English. It was considered the standard work on physical laboratory methods and measurements.
To this day, the textbook ''Praktische Physik'' (Practical Physics), which originated in Kohlrausch's ''Leitfaden der praktischen Physik'', is standard reading for physicists and engineers in
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. This is attributable, above all, to the detailed descriptions provided of the measuring methods that form the basis of technical and experimental applications in many fields in physics.
Kohlrausch was also the author of ''Ueber den absoluten Leitungswiderstand des Quecksilbers'' (On the electrical resistance of mercury, 1888), and of many papers contributed to the ''
Annalen der Physik und Chemie
''Annalen der Physik'' (English: ''Annals of Physics'') is one of the oldest scientific journals on physics; it has been published since 1799. The journal publishes original, peer-reviewed papers on experimental, theoretical, applied, and mathema ...
'', and other scientific journals.
List of works
*
*
Further reading
*
Biographical sketch and reprint of paper on conductivity*
*
*
External links
*
*
{{DEFAULTSORT:Kohlrausch, Friedrich
1840 births
1910 deaths
People from Rinteln
19th-century German physicists
Electrochemists
Foreign Members of the Royal Society
Foreign associates of the National Academy of Sciences
Members of the Prussian Academy of Sciences
People from the Electorate of Hesse
German scientific instrument makers
University of Marburg alumni
University of Erlangen-Nuremberg alumni
University of Göttingen alumni
University of Göttingen faculty
ETH Zurich faculty
Technische Universität Darmstadt faculty
University of Würzburg faculty
University of Strasbourg faculty
Members of the Royal Swedish Academy of Sciences
Recipients of the Pour le Mérite (civil class)