Loschmidt’s number

Scientific article. — Science Progress, 1933, Vol. 27, pp. 634–649.Loschmidt’s number, N, is a basic atomic constant and defined as the number of atoms in a gram-atom or the number of molecules in a gram-molecule. This number is frequently referred to as "Avogadro’s Number," the term "Loschmidt’s Number" being then reserved for the number of molecules in a cubic centimetre of a gas under standard conditions. Unfortunately, these designations are often interchanged. Avogadro’s important hypothesis on the identity of the numbers of molecules in equal volumes of different gases at the same pressure and temperature was formulated in 1811, and is appropriately associated with his name; but Avogadro made no quantitative estimate of either of the above-mentioned constants. The first actual estimate of the number of molecules in one cubic centimetre of a gas under standard conditions was made in 1865 by Loschmidt, and from this the number of molecules (atoms) in a gram molecule (atom) was later evaluated. From the quantitative view-point it thus seems preferable to speak of "Loschmidt’s number per gram-molecule (atom)," and of "Loschmidt’s number per cubic centimetre," as is almost invariably done in the German scientific literature. This terminology avoids ambiguity, and has been adopted here.Author has made a survey of the more than eighty different experimental determinations of this number by 21 different methods. He concludes that the most probable value is (1933) N = (60.62 ± 0.03)10²² [2011: N = 60.2214078(18)·10²²].