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_.