Josef Loschmidt nsIn thermodynamics, Josef Loschmidt (1821-1895) was an Austrian physical chemist notable for being a mentor to Ludwig Boltzmann, at the Vienna school of thermodynamics, and for having pointed out, in 1876, the reversibility paradox, otherwise known as Loschmidt’s paradox, between reversible classical dynamics and irreversible thermodynamics; thus prompting Boltzmann to write his 1877 article “On the Relation of a General Mechanical Theorem to the Second Law of Thermodynamics” in efforts to reconcile the issue. [1] Loschmidt is also noted for being the first to draw double and triple bonds in molecules, as found in his 1861 book Chemische Studien (Chemical Studies). [2]

Loschmidt became professor of physical chemistry at the Vienna University in 1868.

Size of air molecules
Loschmidt was the first to calculate the size of air molecules as one millionth of a millimeter, as described in his 1865 article "On the Size of Air Molecules", using the kinetic theory of gases. [5]
Loschmidt's double bonds and triple bonds (1861)

Double and triple bonds
See main: History of chemical bonding theory
In 1861, during his studies of chemical structure, Loschmidt originated the use of double lines and triple lines to represent double bonds and triple bonds, respectively, in molecules. [4] The following are Loschmidt's 1861 molecular drawings of ethylene H2C=CH2 and acetylene HC≡CH, the first depictions of double bonds and triple bonds, a step away from the olden-days hooked atom theory of bonding.

1. Boltzmann, Ludwig. (1877). “On the Relation of a General Mechanical Theorem to the Second Law of Thermodynamics” (“Uber die Beziehung eines Allgemeine Mechanischen Satzes zum zweiten Hauptsatze der Warmetheorie”), Sitzungsberichte Akad. Wiss., Vienna, Part II, 75: 67-73.
2. Lindley, David. (2001). Boltzmann’s Atom: the Great Debate that Launched a Revolution in Physics (double and triple bonds, pg. 23). The Free Press.
4. Loschmidt, Joseph. (1861). Chemische Studien: Constitutions-Formeln der organischen Chemie in graphischer Darstellung : Das Mariott'sche Gesetz (Chemical studies: Constitutions formulas of organic chemistry in graphical representation: The Act Mariott'sche). Gerold.
5. Loschmidt, Josef. (1865). “Zur Grosse der Luftmolecule”, Academy of Vienna, Oct. 12.

Further reading
● Fleischhacker, Wilhelm an Schonfeld, Thomas. (1997). Pioneering Ideas for the Physical and Chemical Sciences: proceedings of the Joseph Loschmidt Symposium, held June 25-27, 1995, in Vienna, Austria (section: The Scientific Publications of Josef Loschmidt, pgs. 307-08). Springer.
● Bader, A. & Parker, L. (2001). "Joseph Loschmidt", Physics Today, Mar.
● Capri, Anton Z. (2007). Quips, Quotes, and Quanta (ch. 1: Thermodynamics: Founders and Flounderers, pgs. 1-10) [PDF]. World Scientific.

External links
Josef Loschmidt – Wikipedia.

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