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Biography of Stanislao Cannizzaro (1826-1910)

Italian chemist, born in Palermo (Sicily) on 13 July 1826 and died in Rome on May 10, 1910. He was son of a magistrate and Sicilian Police Chief, he studied natural sciences and medicine in his hometown, but during his student days he became interested in chemistry and attended various courses, coming to the conclusion that this science was the basis of Physiology, which attracted even more interest and perfected their knowledge of chemical in Pisa where he was as a teacher Professor Piria. In 1848 he was elected member of the Italian Parliament and in 1850 after the failure of a revolt in which he took part joining the artillery of the Sicilian rebels, Cannizzaro had to continue his studies of chemistry in Paris to escape the persecutions that awaited him in his homeland, in the French capital had as master Chevreul. It took two years until he returned to Italy, where he married and was a professor at several universities: in 1852 obtained a professorship in Alexandria (Piedmont), in 1855 it is transferred to Genoa in 1861 is Professor in Palermo, and finally in 1870 he moved to Rome. In 1871 he was named him Senator and this date he devoted himself primarily to public health.

As for his scientific achievements, it is worth mentioning that in 1853 Cannizzaro discovered the reaction that bears his name in which an aldehyde which has no hydrogens in a and is therefore unable to suffer an aldol condensation, experiences an autooxidacion-reduccion when heated in the presence of an alkali or strong base resulting from the same a salt and an alcohol. In the case of formaldehyde and acetaldehyde this reaction is of biological importance. The following examples of benzaldehyde and formaldehyde are typical:

2CH2 = or + NaOH - > HCOONa + CH3OH methanol Formate sodium

2PhCH = or + NaOH - > PhCOONa + PhCH2OH benzoate sodium Alcohol benzyl

Cannizaro discovered benzyl alcohol, employed the cyanamide in the synthesis and did work on the santonina.

But without a doubt, Cannizzaro became famous for his contribution during the 1860 Karlsruhe Congress to which they invited 140 eminent chemists. The purpose of it was to find answers to questions about atoms, molecules, radical and equivalent. This Conference was organized as a result of the controversy that for almost 50 years (from 1811 to 1858) remained unresolved and which referred to the problem of the determination of the scale of atomic weights. Various solutions had been proposed, to be abandoned when they fail when trying to explain a whole group of experimental facts. Finally there were those who believed that it was impossible to ever get to determine atomic weights and molecular formulas. The ultimate solution required only a slight extension of the reasoning of Avogadro and this is what suggested Stanislao Cannizzaro.

Cannizzaro based his method of determination of atomic weight on the idea that a molecule must contain a whole number of atoms of each of its constituent elements. According to this, it is clear that the molecular weight of a compound must have at least the weight of an atom of a certain element, or, if not an integer multiple of this weight. Therefore if a series of compounds of this element are discussed and compared the weights of it contained in a molecular weight of the different analyzed compounds, should finally become obvious that all these weights are integer multiples of some number that probably will be the weight of the atom. To use this method must first find the molecular weights of compounds. To this end, Cannizzaro resorted to the principle of Avogadro: since in the same conditions equal volumes of gas contain equal numbers of molecules, the weights of these same volumes must be in same reason that their molecules weights. With such system relating to available molecular weights, Cannizaro defined that the molecular weight of hydrogen was 2 and thus set the absolute values of all the others. A chemical analysis of the compared gases will give the weight fraction of the existing element in each of them, obtaining their weight in a molecular weight of each of the gases. The last step is to examine these data to correlate them fully. The lower weight of the element found in the molecular weight of a compound will be sought atomic weight and all other weights of that element that appear must be multiples of the same.

We can illustrate the experiment of Cannizzaro, reviewing the determination of the atomic weight of oxygen, analyzing to do so a number of gases, which this element is a component, the results will be:

Composite molecular weight oxygen regards H2 = 2 a molecular___Agua 18 nitric 16oxido 30 nitrous 16oxido 44 16bioxido of nitrogen 46 32bioxido of sulphur 64 carbon 32bioxido 44 32oxigeno 32 32Ozono 48 48

The lower weight found oxygen is 16 and all the rest are multiples of this.

When he presented his theory at the Karlsruhe Conference, Cannizzaro failed when trying to convince his listeners and bring them to their position, but the cold logic and usefulness of its proposal, became evident once members of Congress returned to their laboratories.

It is as well as by a skilful combination of the law of proportions with the principle of "equal iguales-numeros volumes" multiple, Cannizzaro eliminated the dilemma associated with the molecular formula-atomic weight and provided a lasting chemical base to the atomic theory.

Its scientific merits were recognized when the he lived and they earned him appointments of academic or member of almost all the scientific societies of the world. He chaired the International Congress of chemistry which was held in 1906 in Rome and by his discoveries deserved universal consideration. Together with other scientific as the Hoffman, Kekulé, Lieberman etc, can be held founder of modern organic chemistry. His death, in 1910, was a cause of national mourning in Italy.

His works include: course of agriculture (1845), lessons on the atomic theory (1850), the chemical and natural sciences (1850), product of the decomposition of the acid santonoso, about the life and work of Rafael Piria (1883), as well as journals in Italian and foreign magazines. He also published works of political content such as: the Sicilian revolution of 1848.

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