But by 1908 all of them had been liquefied, including the inert gases argon, neon and, of course, helium, which was discovered in the atmosphere after the mid 1890s. 1 Until 1877 it was believed that the permanent gases-hydrogen, oxygen, nitrogen and carbon monoxide-were not capable of existing in liquid form.

The passage was quoted by Jean-Baptiste Dumas (1800–84), the permanent secretary of the Académie des Sciences in Paris, as an indication of his satisfaction that it was a Frenchman who pioneered the liquefaction of the so-called permanent gases and opened the way to the production of ‘new liquids’ in the laboratory. A transformation of this kind would thus produce new liquids of which we as yet have no idea.’ The liquefaction of oxygen in December 1877 by the French physicist Louis Paul Cailletet (1832–1913) and a few days later by the Swiss physicist Raoul Pictet (1846–1929) was received by the French scientific community with enthusiasm as an event that fulfilled Lavoisier's prediction that ‘he air, or at least some of its constituents, would cease to remain an invisible gas and would turn into the liquid stage.

Liquid oxygen temperature