His 1924 monograph on the solubility of non-electrolytes,
Solubility, was the classic reference for almost half a century. In 1927, Hildebrand coined the term "
regular solution" (to be contrasted with "
ideal solution") and discussed their thermodynamic aspects in 1929. A regular solution is one involving no entropy change when a small amount of one of its components is transferred to it from an ideal solution of the same composition, the total volume remaining unchanged. Hildebrand's many scientific papers and chemistry texts include
An Introduction to Molecular Kinetic Theory (1963) and
Viscosity and Diffusivity (1977). He received the Distinguished Service Medal in 1918 and the King's Medal (British) in 1948. Hildebrand served on the council of the
National Academy of Sciences, of which he was a member, and was also a member of the Citizens Advisory Committee on Education to the California Legislature. He was elected to the
American Philosophical Society in 1951. Hildebrand made several discoveries of which the most notable was the introduction in the mid-1920s of
helium and
oxygen breathing mixtures to replace
air for divers to alleviate the condition known as
the bends. He realized that the problem was caused by
nitrogen gas dissolved in blood at high
pressure, which was expelled too rapidly on return to the surface. Helium does not cause the same problem due to its much lower solubility in aqueous solutions such as blood. This discovery was later used to save the lives of 33 members of the
submarine USS Squalus which went down in 1939. Hildebrand won virtually every major prize in the field of chemistry except the
Nobel Prize. The
American Chemical Society created the
Joel Henry Hildebrand Award in his honor for work pertaining to the field of theoretical and experimental chemistry of liquids. The first award was presented to Hildebrand himself in 1981 as part of the observances of his 100th birthday. He has been identified by Kantha in 2001, as one of the 35 centenarian scientists who belonged to an unusual cluster that was newly formed in the 20th century. Hildebrand often said he most cherished his role as a teacher. In an interview conducted shortly before his 100th birthday, he observed: "Good teaching is primarily an art, and can neither be defined or standardized ... Good teachers are born
and made; neither part of the process can be omitted." He remained committed to working with undergraduate students even at the age of 100. He came to his office on campus nearly every school day until declining health made it impossible. Hildebrand was also active in the
Sierra Club, and was its president from 1937 through 1940. As a member he contributed to many important land-use reports about State and
National Parks in California. He also managed the 1936 US Olympic Ski Team. ==Scientific contributions==