第四课 黑铅

　　What is the black-lead in your pencil made of? If you take a bit of the metal which we call lead, you will find that it is grey in colour, very heavy, and not at all like the black-lead in your pencil. But the lead will make a mark on paper just as your pencil does.

　　小朋友，你铅笔里的铅芯是什么做的？拿一块儿叫"铅"的金属看看，铅是黑色的，特别重，跟铅芯一点儿也不一样。但 是铅也会在纸上留下印子，跟铅笔一样。

　　We call the stuff black-lead, because it makes marks like lead; but there is really no lead in it at all. Black-lead is not a metal. It is made of carbon, which is also found in coal and in many other things. It is the carbon in coal which makes it burn so well.

　　我们把铅芯里的东西叫石墨，就是"黑铅"的意思。这是因为，它在纸上也能像铅一样留下印子；但其实，铅芯里一点儿铅都没有。石墨是碳做的，煤里，就有碳，好多别的东西里也有碳。煤里正是有了碳，才会这么容易燃烧的。

　　If we make black-lead very hot, it will burn. But it will burn very slowly-so slowly that it would be of no use for making a fire.

　　如果把石墨弄得特别热，石墨就会燃烧起来，但是燃烧得特别慢，不能用它生火。

　　Black-lead is found in some kinds of rocks in big lumps. These lumps are ground into very fine powder, and then the powder is pressed into hard blocks.

　　有一些石头里面会有大块的石墨。人们把这些大块石墨，先磨成细粉，又压成硬块儿。

　　These blocks are next cut up into thin strips. Each strip of black-lead is made of just the right size to fit into the hollow that has been cut for it in the wood of the pencil.

　　这些硬块儿，最后又切成了细条。同时，在铅笔的木头上，也切出来了凹槽。每一根石墨的细条，大小都正好放进凹槽里面。

　　Your mother will tell you that black-lead is very useful to her in the house. She rubs it on stoves and grates, and many other things that are made of iron, to cover the iron and keep it from rusting.

　　小朋友，你的妈妈会告诉你，石墨在你家里也非常有用！妈妈把石墨涂在炉子、炉栅上面，涂在很多铁器上面，把铁盖起来，这样它们就不会生锈了。

　　The damp air makes the iron rust; but when we cover it with black-lead, the air cannot reach it, and it keeps bright.

　　潮湿的空气会让铁生锈，但是只要用石墨盖住，铁就接触不到空气，会一直亮闪闪的。

　　Have you ever seen a diamond? It is a very bright, hard kind of stone, and very dear. Diamonds are sometimes set in gold rings, and they are very pretty. Yet the diamond is made of pure carbon, just as black-lead is.

　　小朋友，你见过钻石吗？钻石，也叫金刚石，是一种非常光亮，非常坚硬的石头，价钱还特别贵。有些钻石嵌在金戒指上，漂亮极了。可是，钻石却是纯碳做的，就跟石墨一样！

　　Is it not strange that the dull black-lead, which costs so little, and the sparkling diamond, which costs so much, are both made of the same stuff that burns in the grate to keep us warm?

　　黑黑的石墨那么便宜，亮晶晶的钻石那么贵，这两种东西，却跟那烧在炉子里让我们取暖的煤，都是一样的东西做的，好奇怪呀！