1811 (paper published) / Europe
Avogadro proposes equal molecular counts in equal gas volumes
At equal temperature and pressure, equal volumes of gases contain equal numbers of molecules: a hypothesis for understanding combining gas volumes.
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The story
Avogadro’s 1811 paper sought to reconcile combining gas volumes with atomism, allowing the particles of elemental gases to contain multiple atoms. Modern atom–molecule terminology is not identical to his historical vocabulary. The proposal did not immediately win general acceptance; later chemists clarified its implications. Its modern ideal-gas formulation also has limits for real gases. Avogadro did not measure the numerical constant that now bears his name.
Connections and context
Distinguishing atoms from molecules helped chemists establish formulas and relative atomic weights. A useful proposal can precede widespread agreement by decades.
Dates and precision
1811 (paper published) Documented date
Positioned by the documented year, month or day. Missing precision is not inferred.
Representative map location
Vercelli
The marker represents Avogadro’s teaching and research setting around 1811, not the printing location of the French journal.
Representative coordinates · 45.3233°, 8.4231°
A marker identifies one representative place, such as a manuscript collection, laboratory or observing site. It does not mean the work happened only there, or assign a shared discovery to one country.
Bibliography
- Le Moyne College, Carmen Giunta: Avogadro’s hypotheses — teaching notes
- American Physical Society: 1811 — Avogadro and the molecular world
- Università del Piemonte Orientale: Avogadro taught in Vercelli, 1809–1819
References are listed as plain bibliography titles. They support particular facts or context; a reference does not certify every interpretation in a story.