2015-04-01
337
Compressed and Liquefied Gases
Nearly all the machines or inventions that employ air use it for its compressibility. Pneumatic tyres, air-guns, pneumatic drills, chisels and riveters all make use of the fact that pressure makes air contract and that when the pressure is released, it expands once more. Air behaves like a perfect spring.
Air and all other gases are very compressible and if the pressures are not too enormous they are all equally compressible. It may seem odd that gases as different as oxygen, hydrogen, chlorine, and steam are all equally compressible, but the reason is not difficult to understand.
It follows first from the fact that all molecules have the same average energy at any given temperature; in other words, any molecule, at, say, 10 °C, whether of oxygen or hydrogen or chlorine, on the average hits just as hard as any other. The light swift molecules of hydrogen on an average hit just as hard as the slow heavy ones of chlorine. Secondly, it follows from the interesting fact that the same volume of any gas contains the same number of molecules. In actual fact, a gallon of oxygen, hydrogen or any other gas at 0 °C contains 1.23x10 (123,000,000,000,000,000,000,000) molecules.
Very well, then, every gas contains (under the same conditions) just as many molecules as any other and every kind of molecule on the average hits just as hard as every other kind, and it is the blow of these molecules that are the pressure of a gas [2, С. 70 - 71].
2.9.4 Look through texts 2.9.1 - 2.9.3 and find the English equivalents for the following Russian phrases and word-combinations:
Совокупность очень рассеянных молекул; в тысячу раз больше простора, чем молекула жидкости; это следует из того, что; по последней причине; люди пришли к пониманию того, что; для различных химических целей; изобретения, которые работают (используют) на воздухе; заставляют воздух сжиматься; расширяется снова; другими словами.
Read the text, translate it and answer the questions: For what purposes are gases liquefied? How can we make gases liquefy? What is the regenerative cooling?
