Kamerlingh Onnes Liquefies Helium (Great Events: 1900-2001)
Article abstract: Heike Kamerlingh Onnes transformed helium gas into liquid helium, initiating the study of matter at temperatures approaching the lowest achievable temperature, absolute zero.
The Search for Liquid Air
Perhaps the most familiar example of liquefaction is rain, which is caused by the condensation of water vapor in the air. In the late eighteenth century, Antoine-Laurent Lavoisier predicted that other constituents of air would also liquefy if they became cold enough. Lacking effective cooling techniques, scientists wondered whether all gases could be liquefied. Early researchers tried to liquefy gases by compression, forcing molecules closer together. The Dutch scientist Martinus van Marum liquefied ammonia by compression, but attempts by others to liquefy air at high pressures failed. Studies of gases in the nineteenth century suggested the reason for this failure: A gas will liquefy only if its temperature and pressure are below characteristic critical values. These conditions were not then obtainable for the pressurized air.
One way to cool a gas is to force it to expand quickly. Pursing one’s lips and blowing on one’s palm illustrates this effect, which is the basis of household refrigerators and air conditioners. In 1877, Louis-Paul Cailletet liquefied oxygen and nitrogen by using more extreme expansion. This produced temperatures below –120 degrees Celsius, at which point the...
(The entire section is 1005 words.)
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