英国学生科学读本 第94期:一副风箱(2)

 　　for when you shut the bellows 1, the valve cannot close the air-hole because of your finger, 因为, 当你关闭风箱把手时, 你的手指使得阀门无法关闭空气进出的圆孔,

　　and most of the air then escapes through this hole instead of going out through the nozzle. 那么大部分空气也就通过这个孔逃了出去而不是通过喷嘴透出。
　　Every one knows that we use the bellows to make the fire burn more brightly. 大家都知道, 我们使用风箱来增强火焰的燃烧。
　　But how do they do this? 然而, 这其中的原理是什么呢?
　　It is by causing more air to pass among the hot coals. 因为我们促使更多的空气穿过了炙热的火炭。
　　Air is a mixture of several gases, and one of these gases—oxygen —is necessary for making the coals burn. 空气是一种混合气体, 而这其中的氧气则是煤炭燃烧的关键所在。
　　If your mother has no bellows, what does she do when she wants the fire to burn more brightly ? 如果你的母亲没有风箱, 那么当她希望让火焰更旺时会怎么做呢?
　　She opens either the door or the window, to let more air into the room, 她会打开门或者窗户, 使得房间中的空气更加充沛；
　　or she stirs the fire with the poker 2, to let the air pass freely among the coals. 或者, 她会使用拨火棍来搅动火堆, 促使空气能够大量穿过火炭。
　　Have you ever watched a blacksmith working at his forge? 你有没有看到过铁匠在锻造工厂的工作情景?
　　He needs a very hot fire to heat the iron bars which he makes into horse-shoes and many other things; and he could not have this without using bellows. 要制造马蹄铁或者其他诸多铁制产品, 需要极为炎热的火焰来加热铁条, 而风箱就必不可少。
　　If you look carefully, you will see that there is a difference between the bellows of the blacksmith's forge and those which you use for your kitchen fire. 如果你仔细观察的话, 就会发现, 锻造工厂所用的风箱与你家厨房里的有所不同。
　　The air comes out of your kitchen bellows in puffs 4, but it comes out of the blacksmith's bellows in a steady stream. 厨房风箱吹出的风一阵一阵, 而铁匠的风箱却能持续不断地吹出风来。
　　If we were to take a common pair of bellows, and hinge the lower board of another pair to their under side, 如果我们拿起一副日常家用的风箱, 将它上方的木片与另一幅风箱的下方木片固定在一起，
　　in the same way as the two boards are hinged together, we should then have bellows somewhat like those of the blacksmith. 就好似一副风箱中两块木片的固定方式一样——就可以得到一个类似于铁匠使用的风箱了。
　　The middle board is fixed 5; the under board is worked by a handle; and the top board is free to rise when air is forced in.  中间的木片固定不动；下方的木片通过把手进行移动, 而上方的木片则能够在空气流入时自由抬起。
　　When the blacksmith works his bellows, air is sent from the lower chamber 6 into the upper chamber in puffs, 当铁匠使用风箱时, 空气通过下气室一阵一阵地进入上气室；
　　and is then driven out through the nozzle by the weight of the uppermost board. 然后, 在最上层木片的重力作用下通过喷嘴透出。
　　But air can be sent in through the valve faster than it can escape through the nozzle, 然而, 通过阀门流入的空气比喷嘴流出的空气数量更多,
　　and before the first puff 3 is forced out, more air has been received from the chamber below.  当第一阵空气尚未透出时, 下气室又送来了更多空气。
　　Thus there is a steady stream of air sent through the fire, instead of a series of puffs. 结果, 燃烧的火焰就能不停地得到新鲜空气。