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| {{Infobox scientist
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| | name = Joel Henry Hildebrand
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| | image =
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| | image_size =
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| | caption =
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| | birth_date = November 16, 1881
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| | birth_place = [[Camden, New Jersey|Camden]], [[New Jersey]]
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| | death_date = {{death date and age|1983|4|30|1881|11|16}}
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| | death_place = [[Kensington, California]]
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| | residence =
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| | citizenship =
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| | nationality = [[United States|American]]
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| | ethnicity =
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| | field = [[Chemistry]]
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| | work_institution = [[University of California, Berkeley]]
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| | alma_mater = [[University of Pennsylvania]]
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| | doctoral_advisor =
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| | doctoral_students =
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| | known_for = [[electrolyte|nonelectrolyte]] solutions.
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| | author_abbreviation_bot =
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| | author_abbreviation_zoo =
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| | prizes = [[Priestley Medal]]
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| | religion =
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| | footnotes = }}
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| '''Joel Henry Hildebrand''' (November 16, 1881 – April 30, 1983)<ref>{{cite web|title = 1985, University of California: In Memoriam|publisher = [[University of California]] (System) Academic Senate|year = 1985|url = http://content.cdlib.org/xtf/view?docId=hb4d5nb20m&chunk.id=div00068&brand=calisphere&doc.view=entire_text|accessdate = 2008-05-09}}</ref> was an [[USA|American]] educator and a pioneer [[chemistry|chemist]]. He was a major figure in chemistry research specializing in [[liquid]]s and [[electrolyte|nonelectrolyte]] solutions.<ref>{{cite journal|author=Seaborg, Glenn T.|authorlink=Glenn T. Seaborg|title=Obituary: Joel Henry Hildebrand|journal=Physics Today|date=October 1983|volume=36|issue=10|pages=100–101|url=http://www.physicstoday.org/resource/1/phtoad/v36/i10/p100_s1?bypassSSO=1|doi=10.1063/1.2915287}}</ref>
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| ==Education and professorship==
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| Hildebrand graduated from the [[University of Pennsylvania]] in 1903. He served briefly in the faculty before going to the [[University of California, Berkeley]] as a chemistry instructor in 1913. Within five years he became an Assistant Professor. In 1918 he was elevated to Associate Professor before finally being granted Full Professorship a year later in 1919. He served as the Dean of the College of Chemistry from 1949 through 1951. He retired from full-time teaching in 1952<ref>{{cite journal |journal= Annual Review of Physical Chemistry |volume= 14 |pages= 1–5 |year= 1963 |title= Fifty Years of Physical Chemistry in Berkeley |author= Hildebrand, JH |url= http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.pc.14.100163.000245 |doi=10.1146/annurev.pc.14.100163.000245|bibcode = 1963ARPC...14....1H }}</ref> but remained a University Professor at Berkeley until his death. Hildebrand Hall on the Berkeley campus is named for him.
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| ==Accomplishments, discoveries, honors==
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| 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.
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| Hildebrand served on the Council of the [[United States National Academy of Sciences|National Academy of Sciences]] and was also a member of the Citizens Advisory Committee on Education to the California Legislature. 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 [[Decompression sickness|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 Sailfish (SS-192)|USS Squalus]]'' which went down in 1939.
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| 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. The award is currently sponsored by [[Exxon Mobil]]. 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.
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| Professor 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." <ref>''California Monthly'' magazine, January 1983</ref> He remained committed to working with undergraduate students even [[centenarian|at the age of 100]]. He came to his office on campus nearly every school day until declining health made it impossible.
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| Hildebrand was also active in the [[Sierra Club]], serving as 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.
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| ==Legacy==
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| His study of the solubility of non electrolytes led to his formation of the "[[Hildebrand solubility parameter]]"
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| :<math>\delta = \sqrt{(\Delta H_v - RT) / V_m}</math>.
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| The general idea is that a potential solute will be soluble in a solvent which has a comparable value for <math>\delta</math>.
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| This work was then used in the formation of the more comprehensive "[[Hansen solubility parameter]]", which accounts not just for dispersion interactions between solvent and solute (as the Hildebrand parameter does) but also for hydrogen bonding and polar interactions – thus lifting the restriction of application to just non-polar species. Hansen shows great respect for Hildebrand and his work and indeed acknowledges that his work of the Hansen solubility parameter would not have been possible without the great contribution that Hildebrand made to this field.
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| Hildebrand was also outspoken on the manner in which small non-polar species exist in water. The dissolution of species such as methane in water is accompanied by both a negative enthalpy and a negative entropy. A common model for this behavior is the iceberg or clathrate type model, in which a network or cage of hydrogen bonded water develops around the methane molecule. This explains the drop in enthalpy since hydrogen bonding is increased compared to pure water and the drop in entropy since a solvent excluded volume has come into existence along with an ordered network of water molecules.
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| Hildebrand challenged this popular view in a series of papers in the late 1960s and 1970s and concluded that methane has a just a 40% lower diffusivity in water than in carbon tetrachloride. If water was enclatherated or in an iceberg type structure then he predicted that this diffusivity difference between water and carbon tetrachloride ought to be significantly larger.
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| This conflict of ideas still exists in the literature with publications between 2000–2010 for the clathrate type hydrophobic hydration still being submitted in computer simulations of various types. There are papers however which cite Hildebrand's earlier criticisms of this model and suggest that hydrophobicity arises from the small size of water increasing the free energy required to develop a suitable cavity for certain solutes to occupy.
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| Given the conflict in this field and the high level of interest involved it seems that Hildebrand may continue contributing to the scientific community for quite some time yet.
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| ==External links==
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| * [http://www.aip.org/history/ohilist/4672.html Oral History interview transcript with Joel Hildebrand 6 August 1962, American Institute of Physics, Niels Bohr Library and Archives]
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| * [http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/hildebrand-joel.pdf National Academy of Sciences Biographical Memoir]
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| ==References==
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| {{Refbegin}}
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| *Hildebrand J.H., To tell or to hear some new thing, American Scientist, Vol 51, p2-11, p194, 1963
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| *Hildebrand J.H., Is there a "hydrophobic effect"?, Proc. Natl. acad. Sci. USA, Vol 76, No. 1, p194, 1979
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| *Sri Kantha S, Centenarian scientists: an unusual cluster newly formed in the 20th century, Medical Hypotheses, 57, p 750-753, 2001
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| *Hofinger S. and Zerbetto F., Simple models for hydrophobic hydration, Chem. Soc. Rev., 34, p1012, 2005
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| *Silverstein T.P., Hydrophobic solvation NOT via clathrate water cages, J. Chem. Ed. Vol 85, No. 7, p917, 2008
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| {{reflist}}
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| {{Refend}}
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| {{Presidents of the American Chemical Society}}
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| {{Authority control|VIAF=97903920}}
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| {{Persondata <!-- Metadata: see [[Wikipedia:Persondata]]. -->
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| | NAME = Hildebrand, Joel Henry
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| | ALTERNATIVE NAMES =
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| | SHORT DESCRIPTION = American chemist
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| | DATE OF BIRTH = November 16, 1881
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| | PLACE OF BIRTH = [[Camden, New Jersey|Camden]], [[New Jersey]]
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| | DATE OF DEATH = 1983-04-30
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| | PLACE OF DEATH = Kensington, [[California]]
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| }}
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| {{DEFAULTSORT:Hildebrand, Joel Henry}}
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| [[Category:1881 births]]
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| [[Category:1983 deaths]]
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| [[Category:American centenarians]]
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| [[Category:American chemists]]
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| [[Category:University of Pennsylvania alumni]]
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| [[Category:University of California, Berkeley faculty]]
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