2.9.2 Have you ever bought gases? Are you sure? Read the text, translate it and, however, say what gases you happened to buy and for what porposes. The Ways of Storing Gases

On the industrial scale, there are three favourite ways of storing gases. First, they are stored in gasometers over water, or under a sliding piston or diaphragm.

Secondly, gases are stored in cylinders under pressures as high as 1,800 lbs. per square inch. This squeezes a lot of gas into a little space.

Thirdly, some gases can be made into liquids by compressing them, and these are sold in strong glass syphons or iron cylinders. When the valve at the top of the syphon is opened, the liquid evaporates and the gas rushes out. One gas, acetylene, explodes when it is strongly compressed, so it is dissolved under moderate pressure in a liquid called acetone, just as carbon dioxide is dissolved under pressure in water to make soda-water. When the cylinder of acetylene dissolved in acetone is opened, the acetylene comes bubbling out like the carbon dioxide from soda-water. To prevent the acetone from being spilt, it is soaked up in porous material.

The selling of gas is now a big industry, and at least eighteen different kinds can be bought.

The great chemical works usually make their gases and use them on the spot. Oxygen is sold to engineers for welding with the oxyacet-ylene blowpipe, and to doctors for sustaining pneumonia patients. Nitrogen, which does not burn, is sold for filling electric lamps and some other purposes. Hydrogen is sold for filling balloons and for various chemical purposes. Chlorine — the green poison-gas — is sold for bleaching and for making various chemicals. Carbon dioxide is sold in cylinders for making fizzy drinks and soda-water, which are simply still drinks or water into which this gas has been forced under pres­sure. Ethylene and ethyl chloride are used as anaesthetics. Acetylene is used for lighting. Liquefied ammonia (not the solution in water you buy at the chemist’s) is used for refrigerators, and so is liquefied sulphur dioxide. Argon — obtained from air — is sold for filling elec­tric light bulbs, and neon, a gas of which the air contains only one part in 55,000, is extracted from it and is used to fill those brilliant neon tubes which make the modern street so gay at night. So there are at least thirteen familiar gases you can buy, packed in cylinders or “siphons”.

One more gas is familiar to us all, the coal-gas, which is supplied to houses. This is a mixture of half-a-dozen gases. It is mostly hydro­gen and methane — the gas which causes explosions in coal mines — but it also contains the poisonous carbon monoxide and small amounts of several other gases.

2.9.3 Read the text, translate it and answer: What unique features distinguish gases? 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.