Editing Oxygen (section)

===Later history===
[[File:Goddard and Rocket.jpg|thumb|upright|[[Robert H. Goddard]] and a liquid oxygen-gasoline [[rocket]]|alt=A metal frame structure stands on the snow near a tree. A middle-aged man wearing a coat, boots, leather gloves and a cap stands by the structure and holds it with his right hand.]]

[[John Dalton]]'s original [[History of atomic theory#Dalton|atomic hypothesis]] presumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula was HO, leading to the conclusion that the [[atomic mass]] of oxygen was 8 times that of hydrogen, instead of the modern value of about 16.<ref>{{cite book| title = The Interactive Textbook of PFP96 |chapter= Do We Take Atoms for Granted?|chapter-url=http://www.physics.upenn.edu/courses/gladney/mathphys/subsubsection1_1_3_2.html |url=http://www.physics.upenn.edu/courses/gladney/mathphys/Contents.html |first1=Dennis |last1=DeTurck |last2=Gladney|first2=Larry|last3=Pietrovito|first3=Anthony| publisher=University of Pennsylvania|date=1997|access-date=January 28, 2008|archive-url = https://web.archive.org/web/20080117230939/http://www.physics.upenn.edu/courses/gladney/mathphys/subsubsection1_1_3_2.html |archive-date = January 17, 2008|url-status=dead}}</ref> In 1805, [[Joseph Louis Gay-Lussac]] and [[Alexander von Humboldt]] showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811 [[Amedeo Avogadro]] had arrived at the correct interpretation of water's composition, based on what is now called [[Avogadro's law]] and the diatomic elemental molecules in those gases.<ref>{{cite book|title=A Treatise on Chemistry|first1=Henry Enfield |last1=Roscoe |last2=Schorlemmer|first2=Carl|page=38|date=1883|publisher=D. Appleton and Co.}}</ref><ref group=lower-alpha>These results were mostly ignored until 1860. Part of this rejection was due to the belief that atoms of one element would have no [[chemical affinity]] towards atoms of the same element, and part was due to apparent exceptions to Avogadro's law that were not explained until later in terms of dissociating molecules.</ref>

The first commercial method of producing oxygen was chemical, the so-called [[Brin process]] involving a reversible reaction of [[barium oxide]]. It was invented in 1852 and commercialized in 1884, but was displaced by newer methods in early 20th century.

By the late 19th century scientists realized that air could be liquefied and its components isolated by compressing and cooling it. Using a [[Cascade (chemical engineering)|cascade]] method, Swiss chemist and physicist [[Raoul Pictet|Raoul Pierre Pictet]] [[evaporation|evaporated]] liquid [[sulfur dioxide]] in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877, to the [[French Academy of Sciences]] in Paris announcing his discovery of [[liquid oxygen]].<ref name="BES707">{{cite book|title=Biographical Encyclopedia of Scientists|last=Daintith|first=John|date=1994|publisher=CRC Press|isbn=978-0-7503-0287-6|page=707}}</ref> Just two days later, French physicist [[Louis Paul Cailletet]] announced his own method of liquefying molecular oxygen.<ref name="BES707" /> Only a few drops of the liquid were produced in each case and no meaningful analysis could be conducted. Oxygen was liquefied in a stable state for the first time on March 29, 1883, by Polish scientists from [[Jagiellonian University]], [[Zygmunt Wróblewski]] and [[Karol Olszewski]].<ref>{{cite journal|title = Louis Paul Cailletet: The liquefaction of oxygen and the emergence of low-temperature research |first =Faidra |last = Papanelopoulou |journal =Notes and Records of the Royal Society of London |date = 2013|volume = 67 |issue=4|pages = 355–73|doi = 10.1098/rsnr.2013.0047 |pmc=3826198}}</ref>
[[File:A setup for preparation of Oxygen.jpg|alt=An experiment setup with test tubes to prepare oxygen|left|thumb|280x280px|An experiment setup for preparation of oxygen in academic laboratories]]
In 1891 Scottish chemist [[James Dewar]] was able to produce enough liquid oxygen for study.<ref name="NBB303">[[#Reference-idEmsley2001|Emsley 2001]], p. 303</ref> The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer [[Carl von Linde]] and British engineer [[William Hampson]]. Both men lowered the temperature of air until it liquefied and then [[distillation|distilled]] the component gases by boiling them off one at a time and capturing them separately.<ref name="HPAM">{{cite book|title=How Products are Made|chapter=Oxygen|publisher=The Gale Group, Inc.|date=2002|chapter-url=http://www.answers.com/topic/oxygen|access-date=December 16, 2007|archive-date=April 3, 2019|archive-url=https://web.archive.org/web/20190403220006/http://www.answers.com/topic/oxygen|url-status=live}}</ref> Later, in 1901, oxyacetylene [[welding]] was demonstrated for the first time by burning a mixture of [[acetylene]] and compressed {{chem|O|2}}. This method of welding and cutting metal later became common.<ref name="HPAM" />

In 1923, the American scientist [[Robert H. Goddard]] became the first person to develop a [[rocket engine]] that burned liquid fuel; the engine used [[gasoline]] for fuel and liquid oxygen as the [[oxidizer]]. Goddard successfully flew a small liquid-fueled rocket 56&nbsp;m at 97&nbsp;km/h on March 16, 1926, in [[Auburn, Massachusetts]], US.<ref name="HPAM" /><ref>{{cite web|title=Goddard-1926 |url=http://grin.hq.nasa.gov/ABSTRACTS/GPN-2002-000132.html |publisher=NASA |access-date=November 18, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20071108225824/http://grin.hq.nasa.gov/ABSTRACTS/GPN-2002-000132.html |archive-date=November 8, 2007 }}</ref>

In academic laboratories, oxygen can be prepared by heating together potassium chlorate mixed with a small proportion of manganese dioxide.<ref>{{Cite book|url=https://archive.org/details/flescscho_1114918|title=A school chemistry|last=Flecker|first=Oriel Joyce|publisher=Oxford, Clarendon press|others=MIT Libraries|year=1924|page=[https://archive.org/details/flescscho_1114918/page/n41 30]}}</ref>

Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil-fuel burning.<ref>{{cite web|url=http://scrippso2.ucsd.edu/|title=Atmospheric Oxygen Research|author=Scripps Institute|access-date=October 8, 2011|archive-date=July 25, 2017|archive-url=https://web.archive.org/web/20170725074925/http://scrippso2.ucsd.edu/|url-status=live}}</ref>

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