Microbiology and Immunology

Urey, Harold WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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At the end of the war, Urey returned to Montana State

University where he began teaching chemistry. In 1921 he

decided to resume his college education and enrolled in the

doctoral program in physical chemistry at the University of

California at Berkeley. His faculty advisor at Berkeley was

the great physical chemist Gilbert Newton Lewis. Urey

received his doctorate in 1923 for research on the calculation

of heat capacities and entropies (the degree of randomness in

a system) of gases, based on information obtained through the

use of a spectroscope. He then left for a year of postdoctoral

study at the Institute for Theoretical Physics at the University

of Copenhagen where Niels Bohr, a Danish physicist, was

researching the structure of the atom. Urey’s interest in

Bohr’s research had been cultivated while studying with

Lewis, who had proposed many early theories on the nature

of chemical bonding.

Upon his return to the United States in 1925, Urey

accepted an appointment as an associate in chemistry at the

Johns Hopkins University in Baltimore, a post he held until

1929. He interrupted his work at Johns Hopkins briefly to
      marry Frieda Daum in Lawrence, Kansas, in 1926. Daum was
      a bacteriologist and daughter of a prominent Lawrence educa-
      tor. The Ureys later had four children.
      In 1929, Urey left Johns Hopkins to become associate
      professor of chemistry at Columbia University, and in 1930,
      he published his first book, Atoms, Molecules, and Quanta,
      written with A. E. Ruark. Writing in the Dictionary of
      Scientific Biography,Joseph N. Tatarewicz called this work
      “the first comprehensive English language textbook on atomic
      structure and a major bridge between the new quantum
      physics and the field of chemistry.” At this time he also began
      his search for an isotope of hydrogen. Since Frederick Soddy,
      an English chemist, discovered isotopes in 1913, scientists had
      been looking for isotopes of a number of elements. Urey
      believed that if an isotope of heavy hydrogen existed, one way
      to separate it from the ordinary hydrogen isotope would be
      through the vaporization of liquid hydrogen. Urey’s subse-
      quent isolation of deuterium made Urey famous in the scien-
      tific world, and only three years later he was awarded the
      Nobel Prize in chemistry for his discovery.
      During the latter part of the 1930s, Urey extended his
      work on isotopes to other elements besides hydrogen. Urey
      found that the mass differences in isotopes can result in mod-
      est differences in their reaction rates
      The practical consequences of this discovery became
      apparent during World War II. In 1939, word reached the
      United States about the discovery of nuclear fission by the
      German scientists Otto Hahn and Fritz Strassmann. The mili-
      tary consequences of the Hahn-Strassmann discovery were
      apparent to many scientists, including Urey. He was one of the
      first, therefore, to become involved in the U.S. effort to build
      a nuclear weapon, recognizing the threat posed by such a
      weapon in the hands of Nazi Germany. However, Urey was
      deeply concerned about the potential destructiveness of a fis-
      sion weapon. Actively involved in political topics during the
      1930s, Urey was a member of the Committee to Defend
      America by Aiding the Allies and worked vigorously against
      the fascist regimes in Germany, Italy, and Spain. He explained

the importance of his political activism by saying that “no dic-

tator knows enough to tell scientists what to do. Only in dem-

ocratic nations can science flourish.”

Urey worked on the Manhattan Project to build the

nation’s first atomic bomb. As a leading expert on the separa-

tion of isotopes, Urey made critical contributions to the solu-

tion of the Manhattan Project’s single most difficult problem,

the isolation of^235 uranium.

At the conclusion of World War II, Urey left Columbia

to join the Enrico Fermi Institute of Nuclear Studies at the

University of Chicago where Urey continued to work on new

applications of his isotope research. During the late 1940s and

early 1950s, he explored the relationship between the isotopes

of oxygen and past planetary climates. Since isotopes differ in

the rate of chemical reactions, Urey said that the amount of

each oxygen isotope in an organism is a result of atmospheric

temperatures. During periods when the earth was warmer than

normal, organisms would take in more of a lighter isotope of

oxygen and less of a heavier isotope. During cool periods, the

differences among isotopic concentrations would not be as

great. Over a period of time, Urey was able to develop a scale,

or an “oxygen thermometer,” that related the relative concen-

trations of oxygen isotopes in the shells of sea animals with

atmospheric temperatures. Some of those studies continue to

Harold Urey won the 1934 Nobel Prize in Chemistry for his discovery

of heavy hydrogen (deuterium).

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