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Italian chemist
Born August 9, 1776
Died July 9, 1856

Lorenzo Romano Amedeo Carlo Avogadro, Count of Quaregna and Cerrato, was born into a distinguished legal family in Turin, Italy. His father Count Filippo Avogadro was a lawyer and civil servant who held a number of public offices. Amedeo was expected to follow in the family tradition; he became a bachelor in jurisprudence aged 16 and graduated with a doctorate in ecclesiastical law aged 20, beginning a career as a lawyer.

However, his interest in science took over, and he started to study mathematics and physics in 1800. Impressed by the work of his countryman Alessandro Volta, he did work on electricity in 1803 with his brother Felice. This work led to an 1804 nomination to the Royal Academy of Sciences of Turin. Soon after, science became his career as well as his hobby. In 1806 he became a demonstrator at the Academy of Turin, and in 1809 he started teaching at the Royal College in Vericelli.

There, inspired by the work of John Dalton and Joseph-Louis Gay-Lussac, who were turning chemistry into an exact science, he formulated the law that now bears his name. Avogadro's law states that equal volumes of gases, at the same temperature and pressure, contain the same number of molecules. This was published in 1811 in Jean Claude de Lamétherie's Journal de Physique, de Chemie et d'Histoire naturelle (Journal of Physics, Chemistry and Natural History) under the title "Essai d'une manière de déterminer les masses relatives des molecules élémentaires des corps, et les proportions selon lesquelles elles entrent dans ces combinaisons" (Essay on a Manner of Determining the Relative Masses of the Elementary Molecules of Bodies, and the Proportions in Which They Enter into These Compounds).

Avogadro's paper began:

M. Gay-Lussac has shown in an interesting memoir (Mémoires de la Société d'Arcueil, Tome II.) that gases always unite in a very simple proportion by volume, and that when the result of the union is a gas, its volume is very simply related to those of its components. But the quantitative proportions of substances in compounds seem only to depend on the relative number of composite molecules which result. It must be then admitted that very simple relations also exist between the volumes of gaseous substances and the numbers of simple or compound molecules which form them. The first hypothesis to present itself in this connection, and apparently even the only admissible one, is the supposition that the number of integral molecules in any gas is always the same for equal volumes, or always proportional to the volumes. (Avogadro 1811, section 1.)

At the time the difference between atoms and molecules was not well-understood, and his idea was not immediately accepted. But based on his hypothesis, Avogadro deduced that molecules of some gases, such as nitrogen and oxygen, might be made up of 2 or more atoms of the same element; although we now know this to be correct, it was not widely accepted at the time, and without a convincing proof, his theory was weakened.

Following this publication, Avogadro continued in his scientific career. In 1819 he became a full member of the Academy of Sciences of Turin. The following year he was the first holder of the chair in mathematical physics at Turin University. However after two years, he was removed from this position for political reasons; he returned in 1834, and remained until he retired in 1850. His research interests included electrity, thermal expansion, and specific heat. His most notable publication came in 1841 when he finished his four-volume Fisica dei corpi ponderabili, ossia Trattato della costituzione materiale de' corpi (The physics of measurable bodies, being a treatise on the material composition of bodies).

His law became accepted soon after his death, and he is also remembered in the name of the constant called Avogadro's Number (sometimes called Avogadro's constant), the number of molecules per gram-mole which is constant for all gases and which has subsequently been determined to be approximately 6.0221367 x 1023. Avogadro is also remembered every year by chemistry teachers and students on National Mole Day.

Little is known about his private life. He succeeded to his father's title of Count in 1787. Avogadro had six children by his wife Felicita Mazzé. His son Luigi had a successful military career, and Felice was a prominent jurist. Most accounts say that Avogadro was a religious man. However, he has been accused of womanizing, and there are rumours he may have funded Sardinian revolutionaries in the 1820s in their fight against the King of Sardinia.


  • About.com. "Amedeo Avogadro". Chemistry History. http://chemistry.about.com/library/weekly/aa111602a.htm (July 25, 2003).
  • Amedeo Avogadro. "Essay on a Manner of Determining the Relative Masses of the Elementary Molecules of Bodies, and the Proportions in Which They Enter into These Compounds". Journal de Physique 73, 58-76 (1811). http://webserver.lemoyne.edu/faculty/giunta/avogadro.html (July 25, 2003).
  • Gayle Brickert-Albrecht and Dan Morton. "A Biographical Interview with Lorenzo Romano Amedeo Carlo Avogadro". Woodrow Wilson Leadership Program in Chemistry. http://www.woodrow.org/teachers/chemistry/institutes/1992/Avogadro.html (July 25, 2003).
  • Chris Johnson. "Amedeo Avogadro". http://www.bulldog.u-net.com/avogadro/avoga.html (July 25, 2003).
  • "Amedeo Avogadro". University of Eastern Piedmont. http://www.med.unipmn.it/avobio_uk.htm (July 25, 2003).

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