![]() ![]() In a publication of the Smithsonian Institution, he introduced a new value for the atomic weight ratio of oxygen to hydrogen, providing the most precise determination of the atomic weight of oxygen ever. In 1895 Edward Williams Morley provided scientists with a priceless tool that made all subsequent atomic weight calculations accurate. Moreover, a small error in the value of oxygen - a relatively light element - would be magnified proportionally for the heavier elements. Atomic weights for most other elements were determined by synthesis or analysis of oxides, and the accuracy of these weights depended directly on fixing oxygen’s weight. The most important atomic weight determination was oxygen’s. These methods were more laborious and far less precise than physical methods. Before the invention of such physical methods, 19 th century scientists used “wet chemistry” - procedures such as filtrations, solutions, and recrystallizations. Since the early 20 th century, atomic weights have been determined easily and precisely, using sophisticated instruments such as the mass spectrometer. Such knowledge was also fundamental to theories of the ultimate nature of matter. Interest was intense, and not only because atomic weight values were embedded within virtually all chemical calculations. Dalton, Humphry Davy, Jacob Berzelius, Joseph Gay-Lussac, Jean-Baptiste Dumas, Justus von Liebig, and many others contributed their ideas and research findings. Almost every important 19 th century chemist became involved with atomic weight determinations. Today it is hard to comprehend the degree to which the determination of elemental atomic weights drove the work of generations of scientists spanning the century. That is, all atomic weights were given as a multiple of that of the lightest element, hydrogen.Ītomic weight values were vital for determining chemical composition, understanding novel reactions, calculating reacting quantities in industrial processes - in short, for virtually all operations in pure and applied chemistry. Since atoms were far too small to be measurable in absolute terms during the 19 th century, chemists determined elemental atomic weights in relative terms. Each known element was presumed to consist of identical atoms, with the atoms of different elements distinguished by their differing weights. Determining Molecular Weights Using ‘Wet Chemistry’Įver since its introduction by the English natural philosopher John Dalton at the beginning of the 19 th century, the atomic theory has been central to chemistry. ![]()
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