Amedeo Avogadro

# Biography
Amedeo Avogadro was born in Turin to a noble family of Piedmont, Italy.
He graduated in ecclesiastical law at the early age of 20 and began to practice. Soon after, he dedicated himself to physics and mathematics (then called positive philosophy), and in 1809 started teaching them at a liceo (high school) in Vercelli, where his family had property.
In 1811, he published an article with the title Essai d'une maniere de determiner les masses relatives des molecules elementaires des corps, et les proportions selon lesquelles elles entrent dans ces combinaisons ("Essay on Determining the Relative Masses of the Elementary Molecules of Bodies and the Proportions by Which They Enter These Combinations"), which contains Avogadro's hypothesis. Avogadro submitted this essay to a French journal, De Lametherie's Journal de Physique, de Chimie et d'Histoire naturelle (Journal of Physics, Chemistry and Natural History) so it was written in French, not Italian. (Note: In 1811, northern Italy was under the rule of the French Emperor Napoleon Bonaparte.)
In 1820, he became professor of physics at the University of Turin. After the downfall of Napoleon in 1815, northern Italy came under control of this kingdom.
He was active in the revolutionary movements of 1821 against the king of Sardinia (who became ruler of Piedmont with Turin as his capital).  As a result, he lost his chair in 1823 (or the university officially declared, it was "very glad to allow this interesting scientist to take a rest from heavy teaching duties, in order to be able to give better attention to his researches").
Eventually, Charles Albert granted a Constitution (Statuto Albertino) in 1848. Well before this, Avogadro had been recalled to the university in Turin in 1833, where he taught for another twenty years.
Little is known about Avogadro's private life, which appears to have been sober and religious. He married Felicita Mazze and had six children.
Some historians suggest that he sponsored some Sardinian revolutionaries, who were stopped by the announcement of Charles Albert's constitution.
Avogadro held posts dealing with statistics, meteorology, and weights and measures (he introduced the metric system into Piedmont) and was a member of the Royal Superior Council on Public Instruction.
In honour of Avogadro's contributions to the theory of molarity and molecular weights, the number of molecules in one mole was named Avogadro's number, NA or "Avogadro's constant". It is approximately 6.0221415  1023.  Avogadro's number is used to compute the results of chemical reactions. It allows chemists to determine the exact amounts of substances produced in a given reaction.
Johann Josef Loschmidt first calculated the value of Avogadro's number, often referred to as the Loschmidt number in German-speaking countries (Loschmidt constant now has another meaning).

# Accomplishments
Avogadro's Law states that the relationship between the masses of the same volume of different gases (at the same temperature and pressure) corresponds to the relationship between their respective molecular weights. Hence, the relative molecular mass of a gas can be calculated from the mass of sample of known volume.
Avogadro developed this hypothesis after Joseph Louis Gay-Lussac had published in 1808 his law on volumes (and combining gases). The greatest problem Avogadro had to resolve was the confusion at that time regarding atoms and molecules. One of his most important contributions was clearly distinguishing one from the other, stating that gases are composed of molecules, and these molecules are composed of atoms. For instance, John Dalton did not consider this possibility. Avogadro did not actually use the word "atom" as the words "atom" and "molecule" were used almost without difference. He believed that there were three kinds of "molecules," including an "elementary molecule" (our "atom"). Also, more attention was given to the definition of mass, as distinguished from weight.
In 1814, he published Memoire sur les masses relatives des molecules des corps simples, ou densites presumees de leur gaz, et sur la constitution de quelques-uns de leur composes, pour servir de suite a l'Essai sur le meme sujet, publie dans le Journal de Physique, juillet 1811 ("Note on the Relative Masses of Elementary Molecules, or Suggested Densities of Their Gases, and on the Constituents of Some of Their Compounds, As a Follow-up to the Essay on the Same Subject, Published in the Journal of Physics, July 1811") (), about gas densities.
In 1821 he published another paper, Nouvelles considerations sur la theorie des proportions determinees dans les combinaisons, et sur la determination des masses des molecules des corps (New Considerations on the Theory of Proportions Determined in Combinations, and on Determination of the Masses of Atoms) and shortly afterwards, Memoire sur la maniere de ramener les composes organiques aux lois ordinaires des proportions determinees (Note on the Manner of Finding the Organic Composition by the Ordinary Laws of Determined Proportions).
In 1841, he published his work in Fisica dei corpi ponderabili, ossia Trattato della costituzione materiale de' corpi, 4 volumes.

# Response to the theory
The scientific community did not give great attention to his theory, so Avogadro's hypothesis was not immediately accepted. Andre-Marie Ampere achieved the same results three years later by another method (in his Sur la determination des proportions dans lesquelles les corps se combinent d'apres le nombre et la disposition respective des molecules dont leurs particules integrantes sont composees -- On the Determination of Proportions in which Bodies Combine According to the Number and the Respective Disposition of the Molecules by Which Their Integral Particles Are Made), but the same indifference was shown to his theory as well.
Only through studies by Charles Frederic Gerhardt and Auguste Laurent on organic chemistry was it possible to demonstrate that Avogadro's law explained why the same quantities of molecules in a gas have the same volume.
Unfortunately, related experiments with some inorganic substances showed seeming exceptions to the law. This was finally resolved by Stanislao Cannizzaro, as announced at Karlsruhe Congress in 1860, four years after Avogadro's death. He explained that these exceptions were due to  molecular dissociations at certain temperatures, and that Avogadro's law determined not only molecular masses, but atomic masses as well.
In 1911, a meeting in Turin commemorated the hundredth anniversary of the publication of Avogadro's classic 1811 paper. King Victor Emmanuel III attended. Thus, Avogadro's great contribution to chemistry was recognised.
Rudolf Clausius, with his kinetic theory on gases, gave another confirmation of Avogadro's Law. Jacobus Henricus van 't Hoff showed that Avogadro's theory also held in dilute solutions.
Avogadro is hailed as a founder of the atomic-molecular theory.

# Further reading
- Pierson (1984), "Avogadro and His Work: Amedeo Avogadro.", Science (published 1984 Oct 26), 226 (4673), pp. 432433, doi:10.1126/science.226.4673.432, PMID:17799933 Check date values in: |year=, |publication-date= (help).mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
- Hinshelwood; Pauling (1956), "Amedeo Avogadro.", Science (published 1956 Oct 19), 124 (3225), pp. 708713, doi:10.1126/science.124.3225.708, PMID:17757602 Check date values in: |year=, |publication-date= (help)
- CAVANNA, D (1956), "", Minerva farmaceutica (published 1956 Jun), 5 (6), pp. 1347, PMID:13369233 Check date values in: |year=, |publication-date= (help)
- Crosland, M.P. (1970). "Avogadro, Amedeo". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. pp. 343350. ISBN 0684101149.
- Morselli, Mario. (1984). Amedeo Avogadro, a scientific biography. Kluwer. ISBN 9027716242.