Andrews's first memoir, attempts had been made to liquefy (and even to solidify) a certain number of gases by simul- taneous compression and cooling. Faraday's (1828-1845) and Thilorier's (1885) work on the condensation of quite a number of substances, such as C0 2 , H 2 S, HC1, S0 2 , NH 3 , Cl 2 , &c, is noticed in almost all books on chemistry. After the study of the critical state had demonstrated the preponderating influence of cooling, it was seen that to attain success in the liquefaction of gases particular atten- tion must be paid to the temperature. In 1877, Pictet succeeded in condensing oxygen by a process which differed from that of Faraday only in the use of a better cooling agent — liquid carbon dioxide boiling in a vacuum (— 180°). In the same year Gailletet made use of the cooling effect which accompanies the sudden expansion of a strongly compressed gas. 1 Operating in a glass tube he was able to show that this cooling was sufficient to par- tially condense, with formation of a more or less dense cloud, oxygen, nitrogen, methane, and carbonic oxide. In the case of hydrogen he saw only a very slight mist.
In 1888 Wroblewsky and Olczewsky liquefied oxygen by compressing it in a glass vessel cooled externally by liquid ethylene boiling in a vacuum (— 186 to — 152°). Nitrogen and carbonic oxide can be liquefied in the same way.
Thanks to the recent work of Bamsay, Dewar, and Linde, the liquefaction of air and of its constituents has almost become an industrial process. We can now succeed in making the mist, which Gailletet observed, in a continuous manner, and by the condensation of this we obtain a mass of liquid. To accomplish this process the gas is compressed and at the same time subjected to severe cooling; it is then allowed to escape through a narrow opening into a specially constructed receiver made of badly
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��- in expanding, the gas must perform a very considerable amount of work. If the phenomenon takes place adiabatically, it can be calculated that a fall of pressure from 300 atmospheres to 1 atmo- sphere produces a decrease in temperature of more than 200 degrees
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