413. We see our breath on cold days and not on warm days.

414. The electric arc is exceedingly hot.

415. Rock candy is made by hanging a string in a strong syrup left open to the air.

416. Dishes in which candy has been made should be put to soak.

417. Moisture gathers on eyegla.s.ses when the wearer comes from a cold room into a warm one.

418. Sprinkling the street on a hot day makes the air cool.

419. You cannot see things in a dark room.

420. Where air is rising there is likely to be rain.

SECTION 45. _Softening due to oil or water._

Why does fog deaden a tennis racket?

How does cold cream keep your face from becoming chapped?

Let us now imagine that animal and plant substances have suddenly lost their ability to be softened by oil or water.

All living things soon feel very uncomfortable. Your face and hands sting and crack; the skin all over your body becomes harsh and dry; your mouth feels parched. The shoes you are wearing feel as if they had been dried over a radiator after being very wet, only they are still harder and more uncomfortable.

A man driving a horse feels the lines stiffening in his hands; and the harness soon becomes so dry and brittle that it cracks and perhaps breaks if the horse stops suddenly.

The leaves on the trees begin to rattle and break into pieces as the wind blows against them. Although they keep their greenness, they act like the driest leaves of autumn.

I doubt whether you or any one can stay alive long enough to notice such effects. For the muscles of your body, including those that make you breathe and make your heart beat, probably become so harsh and stiff that they entirely fail to work, and you drop dead among thousands of other stiff, harsh-skinned animals and people.

So it is well that in the real world oil and water soften practically all plant and animal tissues. Of course, in living plants and animals the oil and water come largely from within themselves. Your skin is kept moist and slightly oily all the time by little glands within it, some of which, called _sweat glands_, secrete perspiration and others of which secrete oil. But sometimes the oil is washed off the surface of your hands, as when you wash an article in gasoline or strong soap.

Then you feel that your skin is dry and harsh.

And when you want to soften it again you rub into it oily substances, like cold cream or vaseline.

In the same way if harness or shoes get wet and then are dried out, they can be made properly flexible by oiling. You could wet them, of course, and this would soften them as long as they stayed wet. But water evaporates rather quickly; so when you want a thing to _stay_ soft, you usually apply some kind of oil or grease.

Just as diffusion and the forming of solutions are increased by heat, this softening by oil and water works better if the oil or water is warm. That is why you soak your hands in _warm_ water before manicuring your nails.

_APPLICATION 67._ Explain why women dampen clothes before ironing them; why crackers are put up in waterproof cartons; why an oil shoe polish is better than one containing water.

INFERENCE EXERCISE

Explain the following:

421. You can shorten your finger nails by filing them.

422. You can do it more quickly after washing them than before.

423. After a flashlight picture is taken, the smoke soon reaches all parts of the room.

424. A jeweler wears a convex lens on his eye when he works with small objects.

425. Shoemakers soak the leather before half-soling shoes.

426. Lightning often sets fire to houses or trees that it strikes.

427. The directions on many bottles of medicine and of preparations for household use say, "Shake well before using."

428. If you set a cold tumbler inside of one that has just been washed in hot water, the outer one will crack in a few minutes.

429. A dry cloth hung out at night becomes wet, while a wet cloth hung out on a clear day dries.

430. Putting cold cream or tallow around the roots of your finger nails will help to prevent hangnails.

CHAPTER TEN

CHEMICAL CHANGE AND ENERGY

SECTION 46. _What things are made of: Elements._

What is water made of?

What is iron made of?

Is everything made out of dust?

One of the most natural questions in the world is, "What is this made of?" If we are talking about a piece of bread, the answer is, of course, "flour, water, milk, shortening, sugar, salt, and yeast." But what is each of these made of? Flour is made of wheat, and the wheat is made of materials that the plant gets from the earth, water, and air. Then what are the earth, water, and air made of? A chemist is a person who can answer these questions and who can tell what almost everything is made of. And a strange thing that chemists have found out is this: Everything in the world is made out of one or more of about eighty-five simple substances called _elements_.

WHAT AN ELEMENT IS. An element is a substance that is not made of anything else but itself. Gold is one of the eighty-five elements; there are no other substances known to man that you can put together to make gold. It is made of gold and that is all. There is a theory that maybe all the elements are made of electrons in different arrangements, or of electrons and one other thing; but we do not know that, it is only a theory. Carbon is another element; pure charcoal is carbon. The part of the air that we use when we breathe or when we burn things is called _oxygen_. Oxygen is an element; it is not made of anything but itself. There is another gas which is often used to fill balloons that are to go very high; it is the lightest in the world and is called _hydrogen_. Hydrogen is an element.

For a long time people thought that water was an element. Water certainly looks and seems as if it were made only of itself. Yet during the thousands of years that people believed water was an element, they were daily putting two elements together and making water out of them. When you put a kettle, or anything cold, over a fire, tiny drops of water always form on it. These are not drops of water that were dissolved in the air, and that condense on the sides of the cold kettle; if they were, they would gather on the kettle better in the open air than over the hot fire. Really there is some of that very light gas, hydrogen, in the wood or coal or gas that you use, and this hydrogen joins the oxygen in the air to make water whenever we burn ordinary fuel.

But the best way to prove that water is made of two gases is to take the water apart and get the gases from it. Here are the directions for doing this:

EXPERIMENT 90. A regular bought electrolysis apparatus may be used, or you can make a simple one as follows:

Use a tumbler and two test tubes. If the test tubes are rather small (3/8"" X 3"") they will fill more quickly. Dissolve a little lye (about 1/8 teaspoonful) in half a pint of water to make the water conduct electricity easily, or you may use sulfuric acid in place of lye. Pour half of this solution into the tumbler. Pour as much more as possible into the test tubes, filling both tubes brim full. Cover the mouth of each test tube with a small square of dry paper or cardboard, and turn it upside down, lowering it into the tumbler.

The "electrodes" are two 3/4"" pieces of platinum wire (#30), which are soldered to two pieces of insulated copper wire, each about 2 feet long.[8] The other ends of the copper wire are bare. Fasten the bare end of one copper wire to one nail of the nail plug if you have direct current (d. c.) in the laboratory, and fasten the bare end of the other wire to the other nail; then turn on the electricity. If you do not have direct current in the laboratory, attach the copper wires to the two poles of a battery instead.

[Footnote 8: If the copper wire is drawn through a piece of 1/4-inch soft gla.s.s tubing so that only the platinum wire projects from the end of the tube, and the tube is then sealed around the platinum by holding it in a Bunsen burner a few minutes, your electrodes will be more permanent and more satisfactory. The pieces of gla.s.s tubing should be about 6 inches long (see Fig. 160).]