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Discoverer of heavy hydrogen

SCIENCE DEVELOPS by a series of revolutions. Each revolution gives rise to a new way of working which is followed by a period - what Thomas Kuhn, the historian of science, calls ``normal science'', when scientists work to fit their world picture into the new framework.

Few American scientists realised this better than G. N. Lewis (TheHindu, Dec. 28, 2000) who taught Harold Urey at Berkley and encouraged his interest in pursuing the relation between physics and chemistry.Harold Urey was born on April 29, 1893 in Walkerton, Indiana (U.S.). His father, a school teacher, died when the boy was six years old. His progress in school was marked with difficulty. After receiving the high school diploma in 1911 and some three months' teacher training, he taught in country schools in Indiana and later in Montana. He entered the University of Montana in 1914 and graduated with a degree in Zoology (1917).

Urey took a job as research chemist with the Barreet Chemical Company near Philadelphia. In 1919 he returned to the University of Montana to teach biology for two years. He then entered the University of California, Berkley. His teacher G. N. Levis (1875- 1946) encouraged his interest in atomic and molecular structure. In a short time, he earned his Ph.D. in Chemistry (1923). He proceeded to Copenhagen for further studies at Niel's Bohr Institute for Theoretical Physics, where he augmented his knowledge of physics.

Urey's career in academic positions was spread amongst three institutions: John Hopkins (1924-29), Columbia University (1929- 45) and University of Chicago (1945-58). The last phase from 1958 of his long and active academic life were spent in the University of California, La Jolla, as professor emeritus till the age of 88 (January 5, 1981).

Between 1923 and 1929, Urey published 20 scientific papers on some aspects of atomic structure and molecular band spectroscopy. His book in collaboration with Arthur Ruark ``Atoms, Molecules, and Quanta'' appeared in 1930 and remained for a long time one of the standard textbooks.

Discovery of heavy hydrogen

As early as 1919 Otto Stern (Nobel Laureate, 1943) had sought unsuccessfully for a heavy isotope of hydrogen to account for the discrepancy in the atomic weight of hydrogen. At Columbia University, Urey made a determined search for this isotope, in collaboration with his colleagues F. Brickwedde and G. Murphy, by the controlled evaporation of liquid hydrogen from 4 litres to 1 milli litre. Spectrospic examination of the residue showed a clear line corresponding to the isotope with twice the mass of hydrogen, which he named deuterium.

Urey received the 1934 Nobel Prize for Chemistry, for his discovery of heavy hydrogen. In his Nobel lecture, he said ``it is my expectation that the next few years will witness the separation of the isotopes of the lighter elements in sufficient quantities for effective research in chemistry, physics and biology. If this can be effected, the work on deuterium is only the beginning of a very interesting scientific development.''

Urey's discovery accelerated isotope research and found practical applications. For example, deutrium can replace hydrogen in water molecules to produce ``heavy water'' used as a moderator in nuclear reactions; it can also be used to trace biochemical reactions in living tissue.

In 1942 the U.S. Government organized the Manhattan Project for developing the atomic bomb. At Columbia full-scale work was begun on the separation of the fissionable lighter isotope of uranium 235 from the much more abundant Uranium 238. Urey was asked to head the project. The experience was unhappy, though the project was successful.

After the war, Urey left Columbia for Chicago to build the Institute for Nuclear Studies (which became later the Enrico Fermit Institute). For a while, Urey, still suffering from the trauma of the war period, tended to drift seeking new fields to conquer. He took up problems concerning the past history of the earth and the planetary systems. Urey became interested in the moon, many of his later papers concerned the possible character of its formation and past history.

Work on planetary science

From 1958, Urey moved to the Scripps Institution of Oceanography at la Jolla, where he continued to teach and do active research in the field of geochemistry and planetary science. He explored the possibility of producing organic chemicals by passing electric sparks through a mixture of hot gases. These experiments simulated the early composition of the earth's atmosphere.

Urey was a warm, helpful guide to his students: his house was known for its hospitality. His other interests were - Greek and Hindu sculpture, raising orchards. He coined the name `chemical physics' by founding in 1933 the ``Journal of Chemical Physics'', published by the American Institute of Physics.

Besides the Nobel Prize, Urey received numerous awards: 25 honorary doctorates; Gibbs Medal (1934), Dary Medal (1940), Franklin Medal (1945), Kepler Medal (1971), Priestly Medal (1973), member or fellow of some 25 prestigious academies.

(H. W. Wilson Biographical Dictionary, New York 1987)

R. Parthasarathy

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