Cannizzaro, Stanislao

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Cannizzaro, Stanislao (1826-1910), Italian chemist, born in Palermo, Sicily. After participating in the 1848 Sicilian revolution, Cannizzaro worked (1849-51) in a laboratory in Paris. He was appointed professor of chemistry at the institute in Alessandria (1851) and at the universities of Genoa (1855), Pisa (1861), and Rome (1871). At Alessandria he discovered the reaction that bears his name, Cannizzaro's reaction, which proves that aldehydes in the presence of concentrated alkali are reduced to a mixture of their corresponding alcohol and acid; for example, benzaldehyde yields benzyl alcohol and benzoic acid.

Cannizzaro made a great contribution to atomic theory by clarifying (1858) the distinction between atomic weight and molecular weight. He showed how unknown atomic weights of elements in volatile compounds can be arrived at from known molecular weights of the compounds. Cannizzaro also determined that atomic weights of elements in compounds can be determined if specific heats are known even though vapor densities are unknown. His work on atomic theory was based on Avogadro's law, which states that equal volumes of any two gases contain an equal number of molecules when held under identical conditions of temperature and pressure.

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