Reduction of metals. Ages later, man began to use fire to make metals and to form them into spears and hatchets for hunting and fighting. The alchemists, as we know, used fire in their attempts to change the base metals into gold, and today fires are burning in many furnaces producing, if not gold, metals of far greater value to the progress of civilization. Copper, bronze, iron, and steel, produced by fire, have been the stepping stones of man's progress through the ages. The chemistry involved in the extraction, purification, and alloying of metals is so interesting and of such great importance that volumes have been written on this subject.

　　Heating homes. We are so accustomed to living in heated homes that it is only when something goes wrong with the furnace that we give any thought to the blessed fire. To the savage shivering in his cave, however, a fire was a real blessing, even if it did fill his eyes with smoke. Keeping the home fires burning

　　was a difficult task for the American Indian, who delegated this to his wife. Woe be to the squaw(印第安女子或妻子) who let the fire go out. In the wintertime, the fire was built on the ground in the center of the tent, which had a small hole in the top to act as a smokestack. Even the palaces of the wealthy in the Middle Ages were cold and damp, the fireplaces being so inefficient that only a portion of one room could be heated at a time. Not until a comparatively recent date (1742) were stoves invented, and furnaces were unknown even when your grandfather was a boy.

　　How fires are started and stopped. You have learned that burning is rapid oxidation which gives off light and heat. In order to start a fire, three conditions are necessary: (1) something to burn; (2) something to support the combustion; and (3) a means of lighting the fuel (raising it to its kindling temperature). Having lived all his life in a home where the furnace is kept burning all winter, the average person seldom thinks of the difficulty of starting a fire.

　　To get some idea of the difficulty of starting fires, imagine yourself shipwrecked like Robinson Crusoe upon an uninhabited island. To build a fire, the first condition would be met by collecting some wood. The second condition would be no problem as air is always present to support combustion. The third condition, raising the fuel to its kindling temperature, would offer a real difficulty. Two methods have been used. The first is to employ the heat of friction caused by rubbing two dry sticks together. This sounds simple, but much skill and practice are essential to the success of this operation. The second method is to make sparks by striking two pieces of flint (極硬的東西, 燧石) together. This may work if the operator is persistent and if his fuel is sufficiently fine and dry. But before he succeeds in getting a fire started by either method, our Robinson Crusoe will do some thinking about the usefulness of the common match.

　　Poison matches. There are two kinds of phosphorus used in making matches, white and red. White phosphorus has an advantage and a disadvantage. White phosphorus is cheaper and, at one time, its use was quite common. White phosphorus is poisonous, however, and for this reason its use in making matches is prohibited by law in nearly all civilized countries. Men working in match factories which used white phosphorus were subject to a disease which caused the jaw bones to decay. The danger of small children being poisoned by these matches is also evident.

　　Fortunately, chemists have discovered a method of making a form of phosphorus which is not poisonous. When white phosphorus is gently heated for several hours in a closed vessel from which air is excluded, it slowly changes in color and the no-poisonous red phosphorus is formed. In addition to the fact that it is not poisonous, red phosphorus has other advantages. Its kindling temperature is much higher than that of the white variety, and this makes red phosphorus less dangerous to ship and to store. Another method of making phosphorus safe for use in matches is to combine it with sulphur. To do this, the two elements are mixed and heated in the absence of air. The phosphorus sulphide, which is formed, is not poisonous.

　　1. With the help of his brother, Prometheus succeeded in presenting fire to man.

　　2. Fire gave man an advantage over other animals.

　　3. Man learned to cook by accident.

　　4. In the Middle Ages even the palaces of the wealthy were cold because wood was much too expensive.

　　5. In striking a match, friction raises the phosphorus compound in the tip to the kindling temperature.

　　6. Red phosphorus is the only means of making phosphorus safe.

　　7. Fire has played an important role in the progress of civilization.

　　8. The small hole in the top of the American Indian tent was used as a______.

　　9. Employees in match factories used to suffer from a disease______the jaw bones.

　　10. Air is needed to start a fire because it______.

　　答案：1. N 2. Y 3. Y 4. N 5. NG 6. N 7. Y 8. smokestack 9. which decayed 10. supports combustion