Harold Clayton Urey ForMemRS (/ˈjʊəri/ YOOR-ee; April 29, 1893 – January 5, 1981) was an American physical chemist whose pioneering work on isotopes earned him the Nobel Prize in Chemistry in 1934 for the discovery of deuterium.

[1] Born in Walkerton, Indiana, Urey studied thermodynamics under Gilbert N. Lewis at the University of California, Berkeley.

After he received his PhD in 1923, he was awarded a fellowship by the American-Scandinavian Foundation to study at the Niels Bohr Institute in Copenhagen.

During World War II, Urey turned his knowledge of isotope separation to the problem of uranium enrichment.

He headed the group located at Columbia University that developed isotope separation using gaseous diffusion.

One of his Chicago graduate students was Stanley L. Miller, who showed in the Miller–Urey experiment that, if such a mixture were exposed to electric sparks and water, it can interact to produce amino acids, commonly considered the building blocks of life.

In 1958, he accepted a post as a professor at large at the new University of California, San Diego (UCSD),[2][3] where he helped create the science faculty.

The family moved to Glendora, California, after Samuel became seriously ill with tuberculosis, in hopes that the climate would improve his health.

When it became clear that he would die, the family moved back to Indiana to live with Cora's widowed mother.

[8] After graduating in 1911, he obtained a teacher's certificate from Earlham College,[11] and taught in a small school house in Indiana.

Urey took a job with the Barrett Chemical Company in Philadelphia, making TNT, rather than joining the army as a soldier.

[14][11] An academic career required a doctorate, so in 1921 Urey enrolled in a PhD program at the University of California, Berkeley, where he studied thermodynamics under Gilbert N.

[16][17] Urey then wrote his thesis on the ionization states of an ideal gas, which was subsequently published in the Astrophysical Journal.

[18] After he received his PhD in 1923, Urey was awarded a fellowship by the American-Scandinavian Foundation to study at the Niels Bohr Institute in Copenhagen, where he met Werner Heisenberg, Hans Kramers, Wolfgang Pauli, Georg von Hevesy, and John Slater.

[19] In 1929, Urey became an associate professor of chemistry at Columbia University, where his colleagues included Rudolph Schoenheimer, David Rittenberg, and T. I.

Urey had access to a 21-foot (6.4 m) grating spectrograph, a sensitive device that had been recently installed at Columbia and was capable of resolving the Balmer series.

[23] Urey and Murphy calculated from the Debye model that the heavy isotope would have a slightly higher boiling point than the light one.

[23] The paper announcing the discovery of heavy hydrogen, later named deuterium, was jointly published by Urey, Murphy, and Brickwedde in 1932.

[30][31] Working with Edward W. Washburn from the Bureau of Standards, Urey subsequently discovered the cause of the anomalous sample.

Moreover, Francis William Aston had reported that his calculated value for the atomic weight of hydrogen was wrong, thereby invalidating Birge and Menzel's original reasoning.

He supported Atlanticist Clarence Streit's proposal for a federal union of the world's major democracies, and the republican cause during the Spanish Civil War.

He was an early opponent of German Nazism and assisted refugee scientists, including Enrico Fermi, by helping them find work in the United States, and to adjust to life in a new country.

[42] In 1941, Urey and George B. Pegram led a diplomatic mission to England to establish co-operation on development of the atomic bomb.

[49] The process involved hundreds of cascades, in which corrosive uranium hexafluoride diffused through gaseous barriers, becoming progressively more enriched at every stage.

[48] A major problem was finding proper seals for the pumps, but by far the greatest difficulty lay in constructing an appropriate diffusion barrier.

[53][51] For his work on the Manhattan Project, Urey was awarded the Medal for Merit by the Project director, Major General Leslie R. Groves, Jr.[52] After the war, Urey became professor of chemistry at the Institute for Nuclear Studies, and then became Ryerson professor of chemistry at the University of Chicago in 1952.

However, applying the knowledge gained with hydrogen to oxygen, he realized that the fractionation between carbonate and water for oxygen-18 and oxygen-16 would decrease by a factor of 1.04 between 0 and 25 °C (32 and 77 °F).

He argued publicly on behalf of Ethel and Julius Rosenberg, and was called before the House Un-American Activities Committee.

One of his Chicago graduate students, Stanley L. Miller, showed in the Miller–Urey experiment that, if such a mixture is exposed to electric sparks and to water, it can interact to produce amino acids, commonly considered the building blocks of life.

He was one of the founding members of UCSD's school of chemistry, which was created in 1960, along with Stanley Miller, Hans Suess, and Jim Arnold.