Liquid Helium, a centenary

This month has seen the centenary of the first liquefaction of helium:

On July 10, 1908, a complicated apparatus working in the laboratory of Heike Kamerlingh Onnes in Leiden, Holland, managed to produce 60 ml of liquid helium, at a temperature of 4.2 Kelvin, or −269°C.

Kamerlingh Onnes had been experimenting with cold gases since quite some time before, as he was trying to check the theories of his fellow countryman Johannes Diderik van der Waals on the equation of state of real gases. He had been scooped in the liquefaction of hydrogen (at 20.3 K) in 1898 by James Dewar (who, in the process, had invented the Dewar flask).

But as it turned out, the liquefaction of helium required a multi-step strategy and a big laboratory, and this was Kamerlingh Onnes' business: Using first with liquid air, then liquid hydrogen, helium could finally be cooled enough, via the Joule-Thomson effect, to condense into the liquid state. The physics laboratory in Leiden had become the "coldest place on Earth", and immediately turned to the international centre for low-temperature physics.

Three years later, in 1911, Onnes found that mercury lost its electrical resistivity when cooled to the temperature of liquid helium - this was the discovery of superconductivity.


Source: http://backreaction.blogspot.com/