Ever since Boyle (see 1662), it had been known that gases obeyed certain rules, which interrelated volume, pressure, and temperature.
In 1873, however, the Dutch physicist Johannes Diderik van der Waals (1837-1923) showed that gases would obey those simple laws exactly only if the volume of the molecules themselves were zero and if there were no attraction between them. Actually, molecules do have a small volume and there is a small attraction between them. If the pressure on the gas is low and the temperature is high, these facts scarcely matter, but as pressure goes up and temperature goes down, the facts grow increasingly important.
In 1873 van der Waals introduced a modified equation that gases followed much more closely than they do the simpler, unmodified one. Only perfect gases (which have zero-volume molecules and no intermolecular attraction--and which don't exist in reality) follow the unmodified equations.
As a result of van der Waals' work, it could be seen that the Joule-Thomson effect--that gases cool as they expand (see 1852)--only holds below a certain temperature. For most gases, that doesn't matter, because the temperature below which the effect holds is quite high. In the case of hydrogen, however, that temperature is quite low, so that attempts to liquefy hydrogen by means of the Joule-Thomson effect would fail if the gas was not sufficiently cooled to begin with.
In 1910 van der Waals received a Nobel Prize in physics for this work.
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|Publication:||Asimov's Chronology of Science & Discovery, Updated ed.|
|Article Type:||Reference Source|
|Date:||Jan 1, 1994|
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