The Wonders of Air

I F you will go out into the open on a clear night and find the North Star  and then look around a little you will see the constellation of the Big Dipper  on one side of it and the constellation of Cassiopeia,  which is formed like the letter W,  on the other side of it. Now draw an imaginary line through the middle of the Big Dipper, the North Star and Cassiopeia and let it project beyond the latter when it will pass through a hazy patch of light, and this is the Great Nebula of Andromeda. 

Where Our Atmosphere Came From.—On looking at this nebula through a powerful telescope you would instantly see that it is not made up of myriads of stars but of something that seems very much like fog, or vapor, or smoke, with a bright spot in its center and other and smaller bright spots scattered through it here and there, and these have quite a solid appearance. It was from just such a nebula as this that our solar system  was made, our sun  being formed of the bright central part, and our earth  and the other planets growing from the smaller bright parts. This nebula contained all of the gases and other elements which go to make up the earth, together with its envelope of air.

How the Atmosphere Behaves.—The atmosphere, as the air surrounding the earth is called, is often likened to a great ocean, the lower part resting on the surface of it just as water does, and it stays there for the same reason, and that is because it has weight. While a little air has no appreciable weight, the atmosphere reaches upward to a height of from fifty to two hundred miles and the amount of it is enough to make it press on the surface of the earth, at sea level, with a weight of nearly fifteen pounds to the square inch. This pressure is always changing a little, as some parts of it become heated more than others, and in equalizing the temperature the air is put into motion, and in this way the winds  are set up.

What the Atmosphere is Made Of.—While you cannot sense the air when it is perfectly still, you can feel  it when it is moving, that is when a breeze, or the wind, is blowing, and you can then also hear  the effects of it. Air is formed chiefly of two gases, oxygen  and nitrogen,  in the proportion of one part of the former to four parts of the latter.

These very unlike gases, however, are merely mixed together and not combined chemically; indeed if they were combined they would not form air but one of the oxides  of nitrogen.  The Chinese knew that air contained an active element, which is the oxygen in it, away back in the eighth century. They also knew that it would combine with sulphur, charcoal and some metals, and how to obtain it from saltpetre. The first person, however, to show that the air was formed of two gases was Leonardo da Vinci, who lived during the last half of the fifteenth century. But it was away along in the eighteenth century before the first pure sample of oxygen was made by Joseph Priestley, and this he did by heating mercuric oxide.  He called the gas so obtained dephlogisticated air,  and a few years later the name oxygen  was given to it by Lavoisier, the greatest chemist of his time.

Nitrogen,  the other chief gas of the air, was discovered by Rutherford, of Edinburgh, a couple of years before Priestley found a way to obtain oxygen. His experiment consisted of shutting up an animal in an air-tight compartment; he then removed the carbon dioxide,  which was given off when the animal breathed, by absorbing it with charcoal, when he found that a gas still remained which would not support life.

But the fact that nitrogen existed in the air as a separate gas was first shown by Lavoisier. He called it azote,  which means without life,  and the French still use this name for it. We get the word nitrogen  from the Latin nitrum,  which means saltpetre.  The oxygen of the air, then, is the gas that supports and sustains life, and the nitrogen simply serves to dilute and spread it about.

Other Substances in the Air.—Carbon Dioxide.—Here are two easy experiments which you should make. First,  take a glass of lime water  which is a clear and colorless solution, and blow through a straw into it when it will become milky white. Second,  light a piece of candle and let it down into a bottle which has a little lime water in it; you will not have long to wait until a white crust will begin to form on it. These experiments show very clearly that not only your breath and the candle give off some kind of a gas but that the gas in each case is the same. This gas is often called carbonic acid gas,  but its right name is carbon dioxide.

There is not very much carbon dioxide in the air compared with the oxygen and nitrogen, and it varies in different localities. In cities where fuels are burned the amount of it is in the neighborhood of six parts to 10,000 parts of air, while in the country there are only about three parts in 10,000 parts of air. The amount is kept pretty constant, for while growing vegetation absorbs large quantities of it, this is replaced all the time by animals which exhale it, burning fuels, decaying meats and vegetable matter and fermentation in wines, and in various other substances which keep giving it off.

The choke-damp  of the miners is really carbon dioxide, and while it is not poisonous it will not support life; this is the reason why deaths often result when men in mines have to breathe too much of it. The human body, though, can stand a considerable amount of carbon dioxide above the usual three or six per cent. without causing death or even producing any untoward result, as is shown in works where it is made for charging mineral and soda waters.

Water Vapor.—Another substance that is always found in the air, however dry it may seem to be, is water vapor.  When you step out of doors on a cold day you can see the water vapor that is in your warm breath every time you exhale it into the colder air. The amount of water vapor that the air can hold depends on the temperature of the latter. When the air contains as much water vapor as it can hold it is then said to be saturated,  and hot air can be saturated with more water vapor than cold air.

The reason you can see your breath when you exhale it into cold air is because the warm air which you exhale is not saturated with water vapor, but as your breath strikes the cold air the latter is saturated with it, which makes it visible. This also explains why moisture collects on a tumbler of cold water when it is placed in a warm room and frost forms on a window pane when it is warm inside and cold outside. Since cold air has less power to hold water vapor than warm air, as the warm moisture-laden air begins to cool off in the night, the water vapor condenses into water and clings to the grass and other objects, and this is what we call dew.

When there is a thick fog or it begins to rain, it is because the atmosphere is saturated with water vapor. The amount of water vapor in the atmosphere determines its humidity,  and when the saturation point is nearly reached, that is when the humidity is high, the pores of our bodies cannot throw off the excess water by evaporation and so we feel oppressed. And the reverse is also true, for when there is very little water vapor in the air, that is when the humidity is low, we perspire too freely and this, too, is unpleasant. Where hot air or steam is used to heat a room it tends to dry out the moisture in the air; this can be compensated for by placing a pan of water on the radiator or near the register so that the evaporation will make up for that which is lost.

Dust and Germs.—The air at all times contains dust of many varieties and germs of many kinds. When you are in a theatre and a spotlight  is thrown from the gallery onto the stage you will see the course of the beam of light, but this is only because the light is reflected by the dust particles in its path,—for a beam of light itself cannot be seen.

What we call dust is not made up of particles of dry matter alone, but frequently it contains millions of germs; that is, minute animals that are alive and kicking and which have the power, many of them, to produce disease unless our bodies are in such an excellent state of health as to be able to ward off their attacks. These germs for the most part are formed of single cells, and when we take them into our bodies where it is nice and warm and they have plenty of water and lots of good food, they start in to multiply at a great rate. Then there are yeasts that make wines ferment, and those of still another kind that cause meats and vegetables to decay. So you see there are good little germs as well as bad little germs.

Nitric Acid, Ammonia and Ozone.—Besides the chief gases which make up the atmosphere other substances are found in it which are very useful to us. The first of these is nitric acid,  and this is the way it is formed in the upper layers of air: Whenever a flash of lightning takes place, the heat of it causes the oxygen and nitrogen to combine, and this produces the oxides of nitrogen; in turn these combine with the water vapor that is in the air, and the result is nitric acid.  How nitric acid is extracted by electricity from the air and the many uses of it will be explained in a chapter further on.

There is also a very small amount of ammonia  in the atmosphere and its presence there is due to decaying vegetable and animal matter which gives it off; it is then distributed through the air by diffusion. When there is enough of it in the air it is dissolved by the water vapor and later when it rains it is carried to the soil. There it is converted into compounds of ammonium and these are finally changed into nitric acid, which is a good food for the soil.

Ozone  is a condensed form of oxygen, having three atoms of oxygen to a molecule instead of one, and this makes them act quite differently from one another. When an electric spark passes through the air it changes the oxygen into ozone, and so when there is an electric storm ozone is produced and some think that they can detect its presence by the peculiar refreshing odor, which is rather due to the cleanness of the air.

Recently Discovered Gases of the Air.—In 1894, Lord Rayleigh and Sir William Ramsay, British scientists of renown, discovered that the atmosphere contained traces of a new gas which they called argon.  The way they came to make the discovery was like this: They had obtained some nitrogen from the air by removing the oxygen, when they found that it was heavier than the nitrogen they had made by decomposing an ammonia compound called ammonium nitrite.

After many experiments they came to the conclusion that there must be some other substance in the air which made the nitrogen heavier than that which they obtained from other substances, and this they discovered to be a gas. They called this gas argon  from two Greek words which mean inactive,  as all attempts thus far to make it combine with other elements have proved unsuccessful.

Sir William Ramsay discovered three new gases in the atmosphere in 1898, when it became possible to make liquid air on a large scale, and these are neon,  xenon,  and krypton.  Neon, named from the Greek word which means new,  was separated from the air by letting a quart or so of liquid air evaporate. As the lighter gases passed off first, the heavier gases, of which neon  is one, remained at the bottom of the container. It was shown by Ramsay that there is one part of neon in 100,000 parts of air.

The gas xenon, which means stranger,  is another inactive chemical element that is left after the other gases have evaporated from liquid air. It is the heaviest of all the gases found in the air. Krypton, which means hidden,  is another of the rare gases which Ramsay discovered in the air, and it has a density of about twice that of argon. It exists in the proportion of about one part to a million parts of air.

How Air Supports Life.—If the air supply is cut off from an animal it will quickly die of suffocation. As you know, man and all the more highly developed animals breathe by means of lungs and in doing so they take the oxygen from the air. It is the oxygen that supports life and after it is received into the lungs it is absorbed by the blood and carried to every part of the body.

Now the cells of animals are made up very largely of carbon and hydrogen, and when the oxygen in the blood comes in contact with them they combine and produce two different compounds; that is, the oxygen which combines with the carbon of the cells produces carbon dioxide,  and the oxygen which combines with the hydrogen produces water.  The carbon dioxide is carried back by the blood to the lungs of the animal, where it is exhaled into the air, while the water is carried off by the kidneys, the lungs and the skin.

Plants breathe as well as animals, but they do this through little openings, called stomata,  on the under side of their leaves. But, different from animals, plants inhale the carbon dioxide that is in the air, and this is where the carbon comes from, of which they are so largely formed. The carbon dioxide also combines with some of the water that the roots have absorbed and this forms sugar,  starch  and cellulose,  which latter is the woody fibers of the plant. On combining with the water some oxygen is set free and this goes back into the air. From this cycle of operations you will see that there is a constant balance maintained between the oxygen that animals take out of the air and the plants take in, and the carbon dioxide that the plants take out of it and the animals exhale.

Experiments With Liquid Air.—How Liquid Air is Made.—In 1895, Linde, a Swedish chemist, discovered a process by which very low temperatures could be obtained—temperatures as low, nearly, as minus 200 degrees—and this method has since been used for the production of liquid air.  This process consists of compressing ordinary air and taking the heat out of it by making it flow through pipes immersed in cold water. When the compressed air is cool it is allowed to escape through a nozzle when the air expands, and this again very greatly lowers its temperature.

The chilled stream of air is next made to flow around the pipe which carries the air after it is cooled with water and before it escapes through the nozzle, and this process is repeated so that each time a lower temperature is had until finally a point is reached at which the air becomes a liquid. This is the process that is now in general use for liquefying air and other gases.

The Apparatus Used.—The apparatus of a liquid air plant is generally made up of a two-stage air compressor, that is a compressor having two cylinders, a low pressure and a high pressure one, and this is driven by steam or electric power. The air which is to be liquefied has the water vapor and carbon dioxide extracted from it when it is admitted into the first cylinder of the compressor, where it is compressed to about 200 pounds to the square inch.

The air under this pressure then flows through a coil of pipe immersed in cold water, and when it is thoroughly cooled it is allowed to flow through a small nozzle into the second cylinder of the compressor, where it is compressed to 2,000 pounds to the square inch. It is again made to flow through a coil of pipe and is cooled to a still lower temperature by the air which has previously been compressed and cooled, and this changes it into a liquid.

About Liquid Air.—The liquid air thus produced has a pale, sky-blue color, and if allowed to flow out on a plate or into a common bottle it will instantly commence to boil, as ordinary air is so much hotter than it is, and it will continue to boil until all of it has evaporated into the air again. How to keep liquid air after having obtained it was a great problem to the scientists for a while, but Sir James Dewar solved it by inventing a bottle with a double wall—a bottle within a bottle—and then pumping the air out of the space between them. This construction insulates the inside bottle from the outside one so that it takes a long time for the heat of the air outside to penetrate through the vacuum and reach it. This is the origin of the thermos bottle  which is now so popular for keeping hot liquids hot and cold liquids cold.

Experiments With Liquid Air.—If you have a quart or so of liquid air you can perform magical marvels the like of which the old and honored tribe of Hindu fakirs  never dreamed. Among these is freezing some mercury into the shape of a hammer; when it sets to a solid it looks very much like silver, and you can use it to drive nails. Drop a hollow rubber ball into a glass of liquid air and when it is frozen it becomes as brittle as though it were made of glass; now throw it on the floor and it will break into a hundred pieces. A beefsteak when frozen in liquid air will ring out like a gong if you strike it with a hammer, but you must not strike it too hard or it will fly to pieces. These are just a few of the many startling experiments that you can make with liquid air, and what it may lead to in the future no one knows.