Avogadro's law states that equal volumes of any two different gases if they are at the same temperature and pressure contain equal number of molecules. The law holds except at high pressures, when gases tend to liquefy. Avogadro's law is useful to chemists working with gases because they can simply measure the volumes of reacting gases to determine the equivalent amounts of materials; the difficulties of weighing gases are eliminated.
The hypothesis was virtually ignored by chemists because when it was tested in 1811, appropriate temperatures were not used by other scientists. It was reintroduced in 1858 by Avogadro's countryman Stanislao Cannizzaro.
Gerald C. Roper
Last modified on: Monday, October 20, 1997.