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Johann Josef Loschmidt

Johann Josef Loschmidt
Johann Josef Loschmidt
Born(1821-03-15)15 March 1821
Putschirn, Austrian Empire (now Počerny, Karlovy Vary, Czech Republic)
Died8 July 1895(1895-07-08) (aged 74)
Known for
Scientific career
Fieldschemistry, physics
Doctoral advisorJoseph Stefan

Johann Josef Loschmidt (15 March 1821 – 8 July 1895), who mostly called himself Josef Loschmidt (omitting his first name), was an Austrian scientist who performed ground-breaking work in chemistry, physics (thermodynamics, optics, electrodynamics), and crystal forms.

Born in Karlsbad, a town in the Austrian Empire (now Karlovy Vary, Czech Republic), Loschmidt became professor of physical chemistry at the University of Vienna in 1868.

He had two early mentors. The first was Bohemian priest Adalbert Czech, who persuaded Loschmidt's parents to send young Josef to high school in the Piarist monastery in Schlackenwerth and, in 1837, to advanced high-school classes in Prague.

This was followed by two years of philosophy and mathematics at Prague's Charles University, where Loschmidt met his second important mentor. This was philosophy professor Franz Serafin Exner, whose eyesight was failing, and who asked Loschmidt to be his personal reader. Exner was known for his innovative school reforms, which included promoting mathematics and science as important subjects. He suggested to Loschmidt, who became a close personal friend, that he apply mathematics to psychological phenomena. In the process of doing this, he became a very able mathematician.

The era, when Loschmidt gradually developed his ideas on molecular structures, was to be a notable epoch in science. It was the time when the Kinetic Theory of Gases was being developed.[1]

His 1861 booklet, Chemische Studien ("chemical studies"), proposed two-dimensional representations for over 300 molecules in a style remarkably similar to that used by modern chemists.[2][3] Among these were aromatic molecules such as benzene (C6H6), and related triazines. Loschmidt symbolized the benzene nucleus by a large circle, which he said was to indicate the yet-undetermined structure of the compound. Some have argued,[4][5] however, that he intended this as the suggestion of a cyclical structure, four years before that of Kekulé, who is better known and is generally credited with the discovery of benzene's cyclic structure.

In 1865, Loschmidt was the first to estimate the size of air molecules:[6] his result was only twice the true size, a remarkable feat given the approximations he had to make. His method allowed the size of any gas molecules to be related to measurable phenomena, and hence to determine how many molecules are in a given volume of gas. This latter quantity is now known as the Loschmidt constant in his honour, and its modern value is 2.65×1019 molecules per cubic centimetre at standard temperature and pressure (STP).[7]

Loschmidt and his younger university colleague Ludwig Boltzmann became good friends. His critique of Boltzmann's attempt to derive the second law of thermodynamics from kinetic theory became famous as the "reversibility paradox". It led Boltzmann to his statistical concept of entropy as a logarithmic tally of the number of microstates corresponding to a given thermodynamic state.

Loschmidt retired from university in 1891 and died in 1895 in Vienna.


  1. ^ (from the Kinetic Theory of Gases, Wikipedia) ... In 1856 August Krönig (probably after reading a paper of Waterston) created a simple gas-kinetic model, which only considered the translational motion of the particles.
    In 1857 Rudolf Clausius, according to his own words independently of Krönig, developed a similar, but much more sophisticated version of the theory which included translational and contrary to Krönig also rotational and vibrational molecular motions. In this same work he introduced the concept of mean free path of a particle.
    In 1859, after reading a paper by Clausius, James Clerk Maxwell formulated the Maxwell distribution of molecular velocities, which gave the proportion of molecules having a certain velocity in a specific range. This was the first-ever statistical law in physics.
    In his 1873 thirteen page article 'Molecules', Maxwell states: "we are told that an 'atom' is a material point, invested and surrounded by 'potential forces' and that when 'flying molecules' strike against a solid body in constant succession it causes what is called pressure of air and other gases."
    In 1871, Ludwig Boltzmann generalized Maxwell's achievement and formulated the Maxwell–Boltzmann distribution. Also the logarithmic connection between entropy and probability was first stated by him...
  2. ^ See:
  3. ^ Rzepa, Henry S. (2005). "Joseph Loschmidt: Structural formulae, 1861". Retrieved 28 September 2008.
  4. ^ See the book:
    • Pioneering Ideas for the Physical and Chemical Sciences : Josef Loschmidt's Contributions and Modern Developments in Structural Organic Chemistry, Atomistics, and Statistical Mechanics; Editors: Fleischhacker, W., Schönfeld, T. (Eds.),
      • particularly, pages 67–79 of Pioneering Ideas ... , having an article with the title, Loschmidt's Graphic Formulae of 1861, about the book, Chemische Studien of Loschmidt, by A. Bader.
  5. ^ A website dedicated to Loschmidt, containing Famous chemistry firsts arrived at by Locschmidt
  6. ^ See:
    • Loschmidt, J. (1865). "Zur Grösse der Luftmoleküle" [On the size of molecules of air]. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe. Wien. 52 (2): 395–413.
    • English translation: J. Loschmidt with William Porterfield and Walter Kruse, trans. (October 1995) "On the size of the air molecules", Journal of Chemical Education, 72 (10) : 870–875.
  7. ^ "2022 CODATA Value: Loschmidt constant (273.15 K, 100 kPa)". The NIST Reference on Constants, Units, and Uncertainty. NIST. May 2024. Retrieved 18 May 2024.

Further reading

  • Peter M. Schuster: From Curiosity to Passion: Loschmidt's Route from Philosophy to Natural Science, in: W. Fleischhacker and T. Schönfeld (Editors): Pioneering Ideas for the Physical and Chemical Sciences, Proceedings of the Josef Loschmidt Symposium, held in Vienna, Austria, June 25–27, 1995; Plenum Press, 1997, New York. – ISBN 0-306-45684-2
  • John Buckingham: Chasing the Molecule; Sutton Publishing, 2004, Gloucestershire. – ISBN 0-7509-3345-3

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Johann Josef Loschmidt
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