Statement that, under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules (see Avogadro's number). First proposed by the Italian scientist Amedeo Avogadro (1776–1856) in 1811, it became accepted c. 1860. From the law, it follows that the volume occupied by one mole of gas (at standard conditions of 32 °F [0 °C] and 1 atmosphere of pressure) is the same for all gases (0.791 cubic feet [22.4 litres]).
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