science · 15 May 1821 · 203 years ago
birth
Born 15 May 1821; died 8 Jul 1895 at age 74.
Johann Joseph Loschmidt was an Austrian chemist and physicist who was the first to propose (1861) some kind of cyclic structure for benzene and many aromatic hydrocarbons. (Four years later, Kekulé devised the correct ring structure, for which his name is remembered while Loschmidt's contribution is overlooked.) He deduced the size of air molecules to be around one nanometer, with two approaches: relating the size of gas molecules to the distance travelled between collisions, and considering the packed volume of molecules in a cold liquid. Completing Avogadro's insight that all gases have the same number of molecules in a given volume, Loschmidt measured Avogadro's constant to be 6.03 x 1023 molecules in one mole of a gas (1865).
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