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Avogadro, Amedeo, Conte de Quaregna (1776-1856) was an Italian scientist who shares with his contemporary Claud Berthollet (1748-1822) the honour of being one of the founders of physical chemistry. Although he was a professor of physics, he acknowledged no boundary between physics and chemistry and based most of his findings on a mathematical approach. Principally remembered for the hypothesis subsequently known as Avogadro's Law (which states that, at a given temperature, equal volumes of all gases contain the same number of molecules), he gained no recognition for his achievement during his lifetime. He lived in what was a scientific backwater, with the result that his writings received scant examination or regard from the leading authorities of his day. Avogadro was born in Turin on 9 June 1776. He began his career in 1796 by obtaining a doctorate in law and for the next three years practised as a lawyer. In 1800 he began to take private lessons in mathematics and physics, made impressive progress and decided to make the natural sciences his vocation. He was appointed as a demonstrator at the Academy of Turin in 1806 and Professor of Natural Philosophy at the College of Vercelli in 1809, and when in 1820 the first professorship in mathematical physics in Italy was established at Turin, Avogadro was chosen for the post. Because of the political turmoil at that time the position was subsequently abolished, but calmer times permitted its re-establishment in 1832 and two years later Avogadro again held the appointment. He remained at Turin until his retirement in 1850. When he died there on 9 July 1856 his European contemporaries still regarded him as an incorrigibly self-deluding provincial professor of physics. In 1809 Joseph Gay-Lussac had discovered that all gases, when subjected to an equal rise in temperature, expand by the same amount. Avogadro therefore deduced (and announced in 1811) that at a given temperature all gases must contain the same number of particles per unit volume. He also made it clear that the gas particles need not be individual atoms but might consist of molecules, the term he introduced to describe combinations of atoms. No previous scientists had made this fundamental distinction between the atoms of a substance and its molecules. Using his hypothesis Avogadro provided the theoretical explanation of Gay-Lussac's law of combining volumes. It had already been observed that the electrolysis of water (to form hydrogen and oxygen) produces twice as much hydrogen (by volume) as oxygen. He reasoned that each molecule of water must contain hydrogen and oxygen atoms in the proportion of 2 to 1. Also, because the oxygen gas collected weighs eight times as much as the hydrogen, oxygen atoms must be 16 times as heavy as hydrogen atoms. It also follows from Avogadro's hypothesis that a molar volume of any substance (i.e., the volume whose mass is one gram molecular weight) contains the same number of molecules. This quantity, now known as Avogadro's number or constant, is equal to 6.02252 x 10(to the power of 23). Leading chemists of the day paid little attention to Avogadro's hypothesis, with the result that the confusion between atoms and molecules and between atomic weights and molecular weights continued for nearly 50 years. In 1858, only two years after Avogadro's death, his fellow Italian Stanislao Cannizzaro showed how the application of Avogadro' s hypothesis could solve many of the major problems in chemistry. At the Karlsruhe Chemical Congress of 1860 Avogadro's 1811 paper was read again to a much wider and more receptive audience of distinguished scientists. One of the most impressed was the young German chemist Julius Lothar Meyer. He found this final establishment of order in place of conflicting theories one of the great stimuli that eventually led him in 1870 to produce his most detailed exposition of the periodic law. A year later his namesake Viktor Meyer used Avogadro's law as his principal yardstick in theoretically explaining the nature of vapour density. It is interesting to analyse why such a fundamental and potentially useful work as Avogadro's lay fallow for nearly half a century. Various factors contributed to the delay. To begin with, Avogadro did not support his hypothesis with an impressive display of experimental results. He never acquired, nor did he deserve, a reputation for accurate experimental work; his contemporaries did not therefore regard him as a brilliant theoretician, merely as a careless experimenter. Also Avogadro extended his hypothesis to solid elements - and lacking experimental evidence he relied on analogy. So that whereas he was correct in considering molecules of oxygen and hydrogen to be diatomic, he had little justification for making a similar assumption about carbon and sulphur. His speculative treatment of metals in the vapour state (in his second paper of 1814) did little to advance his cause, revealing an excess of theorizing at the cost of attention to detail. Furthermore, Avogadro's idea of a diatomic molecule was at odds with the dominant dualistic outlook of Jöns Berzelius. According to the principles of electrochemistry, two atoms of the same element would have similar electric charges and therefore repel rather than attract each other (to form a molecule). During the 50 years after Avogadro' s original hypothesis most activity was being devoted to organic chemistry, whose analysis and classification was based chiefly on weights, not volumes. And even when Avogadro's work was translated and published, it tended to appear in obscure journals, perhaps as a result of his modesty and his geographical isolation from the mainstream of the chemistry of his time. Author not available, Avogadro, Amedeo, Conte de Quaregna (1776-1856). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |