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Richards, Theodore William

atomic mass chemistry relative

(1868–1928) US analytical chemist: famed for his accurate determination of relative atomic mass by quantitative chemical analysis.

From age 14 Richards was keenly interested in astronomy, but poor eyesight caused him to change his college studies to chemistry. After doing well at Harvard he visited Europe to learn the latest chemical methods; despite an offer at Göttingen he returned to a professorship at Harvard and stayed there. His particular interest became the exact determination of ‘atomic weights’ (ie relative atomic masses) and he carried classical gravimetric analysis to a level of high refinement in this work. He obtained accurate values for 25 elements, and his co-workers secured atomic weights for another 40, so giving a firm basis for quantitative analytical chemistry. He showed in 1913 that the atomic weight of ordinary lead differs from that of lead derived from uranium by radioactive decay; this work confirmed ideas on radioactive decay series and prediction of the existence of isotopes. Richards’s values for relative atomic mass were the best available until the widespread use of physical methods based on mass spectrometry gave even greater accuracy and precision, after the Second World War. He won the Nobel Prize for chemistry in 1914.

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