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Loschmidt, Johann Joseph

value vienna theory size

[loh shmit] (1821–95) German physical chemist: early worker on valence theory and on molecular size.

Born into a peasant family in what is now the Czech Republic, Loschmidt studied in Prague and Vienna. In the 1840s he tried to establish himself in business but the times were difficult and in 1854 he became bankrupt. He taught science in Vienna, and became a friend of . His book Chemical Studies I (1861; there was never a Part II), included some novel and correct ideas: that sugar is an ether-like compound, that ozone is O3 , that benzene is cyclic and that double and triple bonds can usefully be shown as connecting lines. He assumed variable valences for some atoms (eg 2, 4 or 6 for sulphur) but fixed values for C (4), O (2) and H (1). His book had little influence, and Loschmidt moved to work on the kinetic theory of gases; he calculated the first accurate value for the size of air molecules. From this he calculated in 1867 the number of molecules of gas per cm 3 , but his value is about 30 times too small. However, for this pioneer attempt to obtain a value for the constant N A , the constant is sometimes named as the Loschmidt number ( L ); Avogadro never gave any pertinent numerical calculations on this.

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