Avogadro and his Constant/John Murrell

Abstract

An account is given of the historical development of Avogadro’s hypothesis, and of

the principal methods of determining Avogadro’s constant which have been used over

the past 200 years. These include the kinetic theory of gases, Brownian motion,

measurement of the electron charge, black-body radiation, alpha particle emission, and

X-ray measurements.

The Mole, Amedeo Avogadro and Others/ L.Cerruti

Abstract

The nineteenth-century history of the mole concept, of the determination of the Loschmidt number and of the Avogadro constant, is interesting in several respects. While Avogadro’s hypothesis (1811) played a key role in the development of the mole concept, it was only one of the epistemic tools that chemists used in their long search for a consistent system of molecular and atomic weights. This line

of research and thought was fully mature in the 1880s.In this respect Loschmidt’s papers (1865) represented the transition between the two types of interest in the molecular reality. However, it was only in the first decade of the twentieth century that the theoretical and experimental determination of physical quantities directly related to the Avogadro constant received full attention by scientists such as Planck, Einstein, Rutherford and Perrin.

LOSCHMIDT'S NUMBER/By S. E. VIRGO, M.Sc.

Abstract

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.