Editing Avogadro constant (section)

=== Origin of the concept ===
[[File:Jean Perrin 1926.jpg|right|thumb|Jean Perrin in 1926]]
The Avogadro constant is named after the Italian scientist [[Amedeo Avogadro]] (1776–1856), who, in 1811, first proposed that the volume of a gas (at a given pressure and temperature) is proportional to the number of [[atom]]s or [[molecule]]s regardless of the nature of the gas.<ref name=avog1811/>

Avogadro's hypothesis was popularized four years after his death by [[Stanislao Cannizzaro]], who advocated Avogadro's work at the [[Karlsruhe Congress]] in 1860.<ref>{{Cite web |date=June 2016 |title=Stanislao Cannizzaro {{!}} Science History Institute |url=https://www.sciencehistory.org/historical-profile/stanislao-cannizzaro |access-date=June 2, 2022 |website=Science History Institute}}</ref>

The name ''Avogadro's number'' was coined in 1909 by the physicist [[Jean Baptiste Perrin|Jean Perrin]], who defined it as the number of molecules in exactly 32 grams of [[oxygen]] gas.<ref name="perrin1909" /> The goal of this definition was to make the mass of a mole of a substance, in grams, be numerically equal to the mass of one molecule relative to the mass of the hydrogen atom; which, because of the [[law of definite proportions]], was the natural unit of atomic mass, and was assumed to be {{sfrac|1|16}} of the atomic mass of oxygen.