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Liquid helium.

It had been ten years since Dewar liquefied hydrogen (see 1898) and left helium as the only unliquefied gas.

In 1908 the Dutch physicist Heike Kamerlingh Onnes (1853-1926) set about the task of liquefying helium. He built an elaborate device that would cool helium intensively by means of evaporating liquid hydrogen. When the helium had reached a very low temperature under compressed conditions, it would be allowed to expand so that it would cool still further.

In this way, liquid helium was finally collected in a flask set within a larger flask of liquid hydrogen, which was in turn contained in a still larger flask of liquid air-so that the liquid helium would gain heat and vaporize only very slowly.

It turned out that helium liquefied at a temperature of only 4 degrees above absolute zero. By allowing some of it to evaporate, Kamerlingh Onnes reached a temperature of only 0.8 degrees above absolute zero, but even then he could not solidify it.

For his liquefaction of helium, Kamerlingh Onnes was awarded the Nobel Prize in physics in 1913.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
Words:180
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