same 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.
