Avogadro, Amedeo, conte di Quaregna (ämādāˈō kônˈtā dē kwärāˈnyä ävōgäˈdrō) [key], 1776–1856, Italian physicist, b. Turin. He became professor of physics at the Univ. of Turin in 1820. In 1811 he advanced the hypothesis, since known as Avogadro's law, that equal volumes of gases under identical conditions of pressure and temperature contain the same number of molecules. Since then, through the work of other physicists, the number of molecules in the gram molecular volume has been determined and found to be the same for all gases. This number (6.02×1023) has been called Avogadro's number. Avogadro's hypothesis, though not accepted for some fifty years after its introduction, is now one of the fundamental concepts of the atomic theory of matter.
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