From time to time in science, someone comes along whose original contributions are less significant than his or her ability to explain another's ideas. Such a person was Stanislao Cannizzaro. Cannizzaro was born in Palermo, Italy, on July 13, 1826, and died in Rome on May 10, 1910. He entered the University of Palermo as a medical student in 1841, but soon realized that the university could not provide the instruction in chemistry that he wanted and needed to learn. As a result, he moved to the University of Pisa, where he studied under the foremost Italian chemist of the day, Raffaele Piria.
In 1848, Cannizzaro's academic career was interrupted by political events. Revolutionaries in Sicily rose up against their master, the King of Naples and Cannizzaro joined the rebellion as an artillery officer and a member of the revolutionary government. When the rebellion failed in April 1849, he fled to France. Eventually, he took a position in the laboratory of Michel-Eugène Chevreul in Paris, France.
In 1851, Cannizzaro returned to Italy where he held successive posts at the Collegio Nazionale in Alessandria, the University of Genoa (1855), the University of Palermo (1861), and the University of Rome (1871). Throughout his academic career, Cannizzaro remained politically active. He took part in Garibaldi's successful rebellion to liberate Sicily in 1860 and, in Rome, became a senator of the new nation of Italy.
Cannizzaro devoted his research efforts entirely to the study of organic compounds, especially natural products. The discovery for which he is probably best known is a method for converting benzaldehyde into benzyl alcohol and benzoic acid. Students of organic chemistry today still know this reaction as Cannizzaro's reaction.
By far his greatest contribution to chemistry did not involve his own original research. Chemistry in the mid-1800s was in a terrible state of disarray. John Dalton's atomic theory had seemed to provide a promising theoretical basis for the science and had been widely and quickly adopted by most chemists. But problems of interpreting and applying Dalton's ideas began to appear almost immediately.
Chemists found it difficult to agree on exactly what the term atom really meant, how an atom was different from what Dalton called a compound atom and what we now know as a molecule, what were the true atomic and molecular weights for known elements and compounds, how to accurately represent the formulas of compounds, and so on. As a symptom of this confusion, Friedrich Kekulé was, at one point, able to list 19 different formulas for acetic acid.
The key concept needed to resolve much of this confusion had actually been proposed as early as 1811. In that year, Amedeo Avogadro had proposed and explained the concept of a molecule and had outlined his hypothesis that equal volumes of gases contained equal numbers of molecules. The problem was that Avogadro's ideas were not well known or well understood among chemists throughout Europe. As a result, his ideas disappeared into oblivion for over four decades.
Then, in 1858, Cannizzaro rediscovered his countryman's hypothesis and immediately saw the key it offered to resolving some current controversies in chemistry. He wrote a letter to a friend at the University of Pisa, Sebastiano de Luca, outlining Avogadro's ideas and showing their relevance to current debates in chemistry. The letter was later published in the Italian journal, Nuovo cimento (New Test) and reprinted as a pamphlet.
The main impact of Cannizzaro's ideas occurred at the First International Chemical Congress, held at Karlsruhe, Germany, in 1860. The Congress was organized at the request of a number of young chemists who were eager to bring some logic and organization to their profession. Cannizzaro read his pamphlet at the Congress and handed out copies to the delegates. He reiterated Avogadro's hypothesis, explained how atoms and molecules were different from each other, described a new method for determining atomic and molecular weights, and showed that the same chemical principles apply to both inorganic and organic chemistry.
Not all chemists understood or adopted Cannizzaro's presentation immediately. But, gradually they were convinced by the logic of his arguments. Julius Lothar Meyer (1830-1895), for example, claimed that "the scales fell from his eyes" when he read Cannizzaro's pamphlet. In the end, the pamphlet was probably the single most important factor in forging a new consensus in chemistry during the second half of the nineteenth century.
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