# The How and Why Library/Wonders/Section III
#### III. Air

Besides land and water on the earth, there is something that is all around it, and all through both land and water. You cannot see it, or feel it, or taste it, or smell it, or hear it. But you can prove that it is all around you in a great many ways. You can take it to pieces, too, and find out what it is made of.
Measure your chest with a tape line. Twenty-eight inches? Now breathe deep, deeper. Hold your breath and measure again. Thirty inches! You filled your lungs with air. They were just as full of air as this glass pitcher is of water. This drinking glass looks as if it was empty, but it is full of air. Turn it upside down, and press the open end on the top of the water in the pitcher. Push it straight down under the water—steady; don't let the glass tip up. The water rises outside the glass and overflows. Lift the glass carefully. It is dry inside, except for a narrow rim at the top. Some water did get inside, by squeezing the air in the glass into a little smaller space. See how much water was forced out of the pitcher. Nearly a glass full!
Big boys who dive and swim under water, fill their lungs with air first and hold their breath, so water cannot get into them. That is a very useful thing to learn to do. It saves people from drowning and makes them able to save other people.
Have you ever heard people say: "As light as air?" Perhaps you think air doesn't weigh anything. Did you ever pump water from a well by working a pump handle? You had to pump several times before the water came, didn't you?You had to lift the air out of the hollow pump before the water could come in. Pumping air is hard work. There are several simple ways of proving that air weighs something. Empty the teakettle of water and take the lid off. Now lay a sheet of rubber cloth over the top. Put a glass or rubber tube into the spout, and draw the air through the tube into your lungs. Breathe again. Suck all the air out of the kettle. See the rubber cloth sink. The air on top is pushing it into the kettle. There it goes, down inside. There is no air in the kettle to hold it up.
Now blow into a little rubber balloon. See it swell. Blow again, the rubber stretches. See how much air you can blow into it. Ah, it burst! There was more air inside the balloon than there was outside. Fill a glass with water until it overflows. Cover the top with a sheet of thick, smooth letter paper. Press it all around the edges so you are sure no air can get between the glass and the paper, to let the water out. Now take hold of the glass by the bottom and turn it upside down. The water will not spill, the air below holds it up. Turn back to Air in this book and find out what air weighs.
Just as fish and sea plants may live at the bottom of the ocean of water, so land animals and plants live at the bottom of the ocean of air. The top of this ocean of air is level, too. Do you think the air on a mountain peak would be as deep or as heavy as the air in a low valley? A glass full of water has no color. But an ocean full of water looks blue. We cannot see air itself, but we can see the color of it. When it is forty miles deep air looks blue, too.
Robert likes to climb trees, so he is just the boy to get up on a step ladder and take down those dusty curtains. Warm up there, Robert? Hot air goes up, so it is always warmer near the ceiling. You remember how warm air carries vapor up to make rain? It is the hot air that carries smoke up from chimneys. Did you ever send up a red paper balloon on the Fourth of July? You lit a tiny candle at the bottom. Soon the sides of the balloon swelled and stretched tight. Air expands when it is heated. That is, ittakes less hot air to fill anything than it does cold, so it grows lighter. The balloon floated around the sky until the candle burned out.
Warm air is always going up and cold coming down. Out of doors Mother Nature attends to this pushing, but in houses we have to help, by letting the warm air out at the top and cold air in at the bottom. Air is always in motion unless it is in prison, and prisoned air is very bad to breathe. Still air is dead; live air is always in motion.
Sometimes air rivers flow up and down so rapidly, pushing each other out of place that they make—what? See the leaves blowing on the trees. Wind! Wind is air that is in a hurry. You can feel it. Draw a quick breath. You felt a tiny wind in your nose, didn't you? You cannot feel air, but you can feel wind, or air in motion. You can feel the temperature of air, too. Your skin tells you if air is hot or cold. You can feel if it is damp or dry. You cannot smell air, but you can smell odors in it—the perfume of flowers, the freshness of rain, bad odors of decay, or smoke. You can train yourself to tell if the air in a room is fresh or stale. Doctors always come into a sick room with suspicious noses in the air. As we have to pay doctors for telling us when the air is bad, let us see if we can find out for ourselves.
When you were up on the step ladder, Robert, did you notice anything beside the heat? You felt smothered, then dizzy? You don't feel that way on the hottest summer day out of doors, do you? Let us see what was the matter with that air.
Put half an inch of water in a pie pan. Twist a bit of soft newspaper, light it with a match and drop it into a drinking glass. Let the glass fill with smoke, but while the paper is still burning turn the glass upside down in the pan of water. The flame goes out, leaving some paper unburned. The water rises in the glass, much higher than in the pan outside, and stays there. Something was burned out of the air, making room for the water to rise. The part that is gone is oxygen. If you had shut a live fly in the glass it would have died as quickly as the flame. Animals and fire cannot live without oxygen. By breathing air in you burn up oxygen. It would not take you very long to use up all the oxygen in a small room. Then, if you couldn't get any fresh air at all you would "go out" like the burning paper, and the fly in the glass.
Beside using up the oxygen in the air, when you breathe in, you make a poisonous gas when you breathe out. Fire does thesame thing. Here is a bottle of clear lime water. It cost two cents at the drug store. Divide this lime water between two small fruit jars. In one of the jars hang an inch of lighted candle above the lime water, by a wire twisted around the candle and hooked over the top. Cover the top of the jar with a folded napkin. The flame goes out as soon as the oxygen in the jar is used up, of course. But something else happens, too. The clear lime water turns milky. The flame gave out a gas called carbon dioxide, or carbonic acid gas.
Put a tube of rubber or glass, or a big lemonade straw, into the lime water in the other jar. Blow your breath through the tube, into the water. You can tell when you have forced your breath in, for you make bubbles. Do this several times. This water turns milky, too, from the carbonic acid gas in your breath. Your breath is warm so it goes up to the ceiling. The air made by a gas flame, a heat register or radiator goes up, too. All this warm air has been used by fire and by people. The oxygen has been burned out of it, and carbonic acid has been put into it. It would not feed a fire or a pair of lungs, and it becomes even poisonous. This is bad air. It will go out of doors if you help it, and be purified.
Beside helping to keep people well, to know about air may help them at any time to put out a fire. Fire cannot burn without oxygen, so it can be smothered. If your clothing catches fire roll up in a rug or heavy bed clothes. Keep the fire from getting air and it will go out.
Out of doors, nature is always purifying air. She does it by having plants and animals live together. Plants make oxygen and use up the carbonic acid gas that is poisonous to breathing animals. In the sea fishes and water plants help each other, in the same way. They get air out of the water. Seeds and worms and beetles get air out of the earth. If you plant seeds too deep, or pack the earth too hard above them, they will rot. So you must read the directions on your little paper of flower seeds and obey them, or you will have no flowers. You can kill little animals by stopping up their holes sometimes.
See how wonderfully this world is mixed up. Earth is solid, water is fluid, air a gas. But there is water and air in the earth, earth and air in the water, and earth dust and water vapor in the air. They all need each other, and plants and animals need all three. Air is the freest and sets everything else in motion.Wind, or air in motion, is a great worker and wonder-worker. It tosses the tree tops, whirls the dust, carries vapor clouds to make rain, scatters seeds. It turns the long arms of windmills and sends sailing vessels flying over the water. It waits for nobody. It says how-do-you-do and good-by, and is gone. There isn't a bit of use to get out of humor with it, if it blows our hats off and turns umbrellas wrong side out. The wind can't help blowing. It is being pushed and jostled about itself. Besides it has the most important work in the world to do—keeping air in motion and purifying it. So get off the track. Wind has the right of way. See Air, page 33; Respiration, 1602.