Replace the question mark with a numberMATH PUZZLE: Can you replace the question mark with a number?
Correct answers: 222
The first user who solved this task is Djordje Timotijevic.
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Louis-Paul CailletetBorn 21 Sep 1832; died 5 Jan 1913 at age 80.French physicist and iron master noted for his work on liquefaction of gases. Working at his father's metallurgy business, he investigated the permeability of iron to hydrogen and other gases, accounting for the unpredictable behaviour of some irons in terms of an excess of dissolved gases. In 1870, he began carefully measuring whether real gases deviate from "ideal" gas law behaviour. From this grew an interest in the liquefaction of gases. He used the Joule-Thomson effect - compressing a gas whilst cooling it, then allowing its rapid expansion to cool it still further - and in 1877-78, was first to produce droplets of liquid oxygen, hydrogen, nitrogen, carbon monoxide, nitrogen dioxide and acetylene. He also invented the altimeter and the high-pressure manometer.Image: Cailletet's liquefier.