Herrick Lee Johnston (29 March 1898 – 6 October 1965) was an American scientist specializing in cryogenics, born in Jacksonville, Ohio.
Johnston was a researcher at the University of California at Berkeley 1925-28 and an associate of cryogenics pioneer William Giauque when his experiments proved the existence of oxygen isotopes with atomic masses 17 and 18.
Previously it had been believed that oxygen only existed as 16O; as atomic masses of other elements were calculated on the basis of 16.0 not 16.0035, this was a significant discovery.
Johnston was appointed assistant professor at Ohio State University in 1929 with plans to create a cryogenics laboratory to rival that at Berkeley, but sufficient funds were not available until 1939, boosted by federal money earmarked for war-related research, notably the Manhattan Project, for which he was a director from 1942 to 1946.
One of his PhD students, Paul J Flory, who won the Nobel Prize for chemistry in 1974, cited Johnston's 'boundless zeal' as an inspiration.