Johann Josef Loschmidt

Jan or Johann Josef Loschmidt (March 15 1821 - July 8 1895) who referred to himself mostly as 'Josef' (omitting his first name), was a notable Austrian scientist who performed groundbreaking work in chemistry, physics (thermodynamics, optics, electrodynamics) and crystal forms.

Born of poor Bohemian farming stock in Počerny (Putschirn), now part of 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 a 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 the philosophy professor Franz 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.

In 1856, while still a secondary school teacher, Loschmidt determined the size of the molecules in air.

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. Among these were aromatic molecules such as benzene (C6H6 (A.K.A. benzol)), 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, 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 determine the number of molecules of an ideal gas in 1 cm3. This is now known as the "Loschmidt number" L = 2.687 &times; 1019 cm-3.

Later, using Avogadro's result that any gas under the same conditions has the same number of molecules per Mole (unit), Loschmidt determined that number, now called Avogadro's number as being 6.023 &times; 1023 molecules. This is why on rare occasions this "Avogadro number" is called the "Loschmidt number" in English (in German, though, "Loschmidt'sche Zahl" is the commonly used name).

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 microscopic states corresponding to a given thermodynamic state.

Loschmidt retired from university in 1891 and died in 1895 in Vienna. His only child had died before him at the age of ten.