Editing Heike Kamerlingh Onnes (section)

== Liquefaction of helium ==
[[File:Leiden - Kamerlingh Onnes Building - Commemorative plaque.jpg|thumb|Commemorative plaque in Leiden]]

On 10 July 1908, he was the first to liquefy [[helium]], using several precooling stages and the [[Hampson–Linde cycle]] based on the [[Joule–Thomson effect]]. This way he lowered the temperature to the boiling point of helium (−269&nbsp;°C, 4.2 K). By reducing the pressure of the liquid helium he achieved a temperature near 1.5 K. These were the [[Lowest temperature recorded on Earth|coldest temperatures achieved on earth]] at the time. The equipment employed is at the [[Museum Boerhaave]] in [[Leiden]].<ref name="nobel"/>

For further research on low-temperature, he needed large amounts of helium. This he obtained in 1911 from [[Carl Auer von Welsbach|Welsbach]]'s company, which processed [[thorianite]] to produce [[thorium]] for [[gas mantle]]s. Helium is produced as a side product. Previously, Onnes obtained helium from processing [[monazite]], and Onnes used the processed monazite (which still contained thorium) to trade for the helium. On earth, helium is usually found in coexistence with radioactive material, since it is a product of radioactive decay.<ref>{{Cite journal |last=van Delft |first=Dirk |date=2008-03-01 |title=Little cup of helium, big science |url=https://pubs.aip.org/physicstoday/article/61/3/36/413299/Little-cup-of-helium-big-scienceOne-hundred-years |journal=Physics Today |language=en |volume=61 |issue=3 |pages=36–42 |doi=10.1063/1.2897948 |issn=0031-9228|doi-access=free |bibcode=2008PhT....61c..36V }}</ref>