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.