第14章 THE CHEMISTRY OF A CANDLE (I) 蜡烛的化学知识（I）

“AND now, uncle,” asked Harry, who was a favourite with the old gentleman,“can you tell me what you do when you put a candle out?”

“Put an extinguisher on it, you young rogue, to be sure.”

“Oh, but I mean, you cut off its supply of oxygen,” said Master Harry.

“Cut off its what?”

“He means something he heard at the Royal Institution,” observed Mrs. Wilkinson. “He reads a great deal about chemistry, and he attended Professor Faraday's lectures there on the chemical history of a candle, and has been full of it ever since.”

“Now, you, sir,” said Uncle Bagges, “come you here to me, and tell me what you have to say about this chemical, eh? — or comical, which? — this — comical chemical history of a candle.”

“Harry, don't be troublesome to your uncle,” said Mrs Wilkinson.

“Troublesome? Oh, not at all. I like to hear him.”

“Let us get a wax candle then, uncle. There's one on the mantle-shelf. Let me light it.”

“Take care you don't bum your fingers, or set anything on fire,” said Mrs. Wilkinson.

“Now, uncle,” commenced Harry, having drawn his chair to the side of Mr. Bagges, “we have got our candle burning. Look down on the top of it, around the wick. See, it is a little cup full of melted wax. The heat of the flame has melted the wax just round the wick. The cold air keeps the outside of it hard, so as to make the rim of it. The melted wax in the little cup goes up through the wick to be burned, just as oil does in the wick of a lamp. What do you think makes it go up, uncle”

“Why — why, the flame draws it up, doesn't it?”

“Not exactly, uncle. It goes up through little tiny passages in the cotton wick, because very, very small channels, or pipes, or pores, have the power in themselves of sucking up liquids. What they do it by is called capillary attraction;— just as a sponge sucks up water, or a bit of lump-sugar the little drop of tea or coffee left in the bottom of a cup.

“Now, I'll blow the candle out; not to be in the dark, but to find out what it is.— Look at the smoke rising from the wick. I'll hold a bit of lighted paper in the smoke so as not to touch the wick. But see, for all that, the candle lights again! So this shows that the melted wax sucked up through the wick is turned into vapour, and the vapour burns. The heat of the burning vapour keeps on melting more wax, and that is sucked up too within the flame, and turned into vapour and burned;and so on the wax is all used up and the candle is gone. So the flame, uncle, you see, is the last of the candle; and the candle seems to go through the flame into nothing, although it doesn't, but goes into several things; — and isn't it curious, as Professor Faraday said, that the candle should look so splendid and glorious in going away?

“I dare say that the flam of the candle looks flat to you; but if we were to put a lamp-glass over it, so as to shelter it from the draught, you would see it is round— round sideways, and running up to a peak. It is drawn up by the hot air. You know that hot air always rises, and that is the way smoke is taken up the chimney. What do you think is in the middle of the flame.”

“I should say fire,” replied Uncle Bagges.

“Oh, no. The flame is hollow. The bright flame we see is something no thicker than a thin peel or skin, and it doesn't touch the wick. Inside of it is the vapour I told you of just now. If you put one end of a bent pipe into the middle of the flame, and let the other end of the pipe dip into a warm bottle, the vapour or gas from the candle will mix with the air there; and if you were to set fire to the mixture of gas from the candle and air in the bottle, it would go off with a bang.”

“I wish you'd do that, Harry,” said Master Tom, the younger brother of the juvenile lecturer.

“I want the proper things,” answered Harry. — “Well, uncle, the flame of the candle is a little shining case, with gas in the inside of it and air on the outside, so that the case of flame is between the air and the gas. The gas keeps going into the flame to burn; and when the candle bums properly, none of the gas ever passes out through the flame, and none of the air ever gets in through the flame to the gas. The greatest heat of the candle is in this skin, or peel, or case of flame.”

“Case of flame!” repeated Mr. Bagges. “Live and learn. I should have thought a candle-flame was as thick as my poor old noddle.”

“I can show you the contrary,” said Harry. “I take this piece of white paper, look, and hold it a second or two down on the candle-flame, keeping the flame very steady. Now, I'll rub off the black of the smoke, and — there — You find that the paper is scorched in the shape of a ring, but inside the ring it is only dirtied, and not singed at all.”

“Seeing is believing,” remarked the uncle.

“But,” proceeded Harry, “there is more in the candle-flame than the gas that comes out of the candle. You know a candle won't bum without air. There must be always air around the gas, and touching it, as it were, to make it burn. If a candle hasn't got enough of air it goes out, or burns badly, so that some of the vapour inside of the flame comes out through it in the form of smoke; and this is the reason of a candle smoking. So now you know why a great clumsy dip smokes more than a neat wax candle: it is because the thick wick of the dip makes too much fuel in proportion to the air that can get to it.

“What should you say now,” continued Harry, “if I were to tell you that the smoke that comes out of a candle is the very thing that makes a candle burn with a bright light? Yee; a candle shines by consuming its own smoke. The smoke of a candle is a cloud of small dust; and the little grains of dust are bits of charcoal, or carbon, as chemists call it. They are burned the moment they are made; and the place they are made in is the case of flame itself, where the strongest heat is. The great heat separates them from the gas which comes from the melted wax; and as soon as they touch the air on the outside of the thin case of flame they burn.”

“Can you tell me how it is that the little bits of carbon cause the brightness of the flame?” asked Mr. Wilkinson.

“Because they are pieces of solid matter,” answered Harry. “To make a flame shine, there must always be some solid, or at least dense, matter in it.”

“Very good,” said Mr. Bagges; “solid stuff necessary to brightness!”

“Some gases and other things,” resumed Harry, “that burn with a flame you can hardly see, burn splendidly when something solid is put into them. Hydrogen gas if blown through a pipe, bums with very little light; but if the flame is blown upon a piece of quick-lime, it gets so bright as to be quite dazzling. If you now send some oxygen on to the flame, the flame gets no brighter, but the lime shines like a little sun. Make the smoke of oil of turpentine pass through the same oxygen, and it gives the flame a beautiful brightness directly. Well, carbon, or charcoal, is what causes the brightness of all lamps, and candles, and other common lights; so, of course, there is carbon in what they are all made of.”

“So carbon is smoke, eh? and light is owing to your carbon. Giving light out of smoke, eh? as they say in the classics,” observed Mr. Bagges.

Words

answered,replied.

beautiful,lovely.

brightness,brilliancy.

chimney,smoke-vent.

clumsy,coarse.

comical,funny.

commenced,began.

consuming,absorbing.

contrary,opposite.

Curious,strange.

dazzling,blinding.

directly,immediately.

draught,air-current.

enough,plenty.

exactly,precisely.

extinguisher,cap.

juvenile,youthful.

melted,dissolved.

mixture,Union.

necessary,essential.

noddle,head.

observed,remarked.

pores,passages.

proceeded,continued.

properly,rightly.

rogue,rascal.

scorched,blackened.

separates,disjoins.

shelter,protect.

solid,substantial.

splendid,grand.

troublesome,tiresome.

vapour,gas.

Questions

When a candle burns, why does the melted wax go up through the wick? What happens when you hold a bit of lighted paper in the smoke of a candle after it has been extinguished? What does this show? Of what does the flame of a candle consist? What is inside? How can this be shown? Without what will a candle not born? Why does a “clumsy dip smoke more than a nest wax candle”? What in reality la the smoke of a candle? Why la it that the little bits of oar bon cause the brightness of the flame? Illustrate this by the example of the oxy-hydrogen lime-light.

“现在，叔叔，”哈利，这位老绅士最喜欢的一个侄子问道，“您能告诉我怎样熄灭一支蜡烛吗？”

“你这小家伙，在上面放上灭火的东西肯定就能把它熄灭。”

“哦，但我的意思是，你切断它氧气的来源，”哈利少爷说道。

“切断它的什么？”

“他说的是从皇家学院听到的，”威尔肯森夫人说道。“他读了大量的关于化学的书籍，还参加了法拉德教授在学院办的关于蜡烛化学史的讲座，从那儿以后，他脑子里一定净是这些东西。”

“现在，先生您，”巴格斯叔叔说道，“您来我这儿，告诉我关于这种化学物你有什么看法，嗯？——或者关于它的有趣的事情？——这个——蜡烛的趣味化学史。”

“哈利，别去烦你叔叔。”威尔肯森夫人说道。

“烦我？哦，一点儿也没有。我喜欢听他说话。”

“那叔叔，咱们先拿出一段蜡烛来。在柜架上就有一段，咱们把它点燃吧。”

“小心别烧到手，也别点着任何东西，”威尔肯森夫人说。

“现在，叔叔，”哈利开始把自己的椅子拖到巴格斯先生旁边，“我们得让蜡烛烧着。低头看看它的顶部，就在烛芯周围。看，那是一湾融化的蜡。火焰的热度融化了烛芯周围的蜡。冷的空气使它外围变得坚硬，从而形成了它的边缘。这一湾融化的蜡从烛芯向上走，被燃烧，和灯油在油灯灯芯中的工作原理是一样的。你觉得是什么让蜡往上走，叔叔？”

“是什么呢——什么呢，是火焰让它往上走的，是不是？”

“不完全正确，叔叔。蜡从棉质的芯子中间的微小的通道向上走，因为那非常非常微小的通道，或管道，或空隙自身有一种将液体吸附起来的力量。这种力量叫作毛细管引力；——就像海绵能吸水，或者糖能把杯子里剩余的一点茶或咖啡吸附掉一个道理。”

“现在，我把蜡烛吹灭；不是为了恢复黑暗，而是为了看看究竟是怎么回事。——看看从蜡芯那里升起来的烟。我会拿一小片纸放到那冒烟的地方，但不接触到蜡芯。看吧，那蜡烛居然又燃起来了！因此这就表明融化的蜡被从蜡芯中吸起来，变成蒸汽，而蒸汽被点燃了。燃烧的蒸汽的热度会融化更多的蜡，而这些蜡又被吸进了火焰，变成蒸汽燃烧；如此下去蜡就会被烧尽，而蜡烛也就用完了。因此这火焰，叔叔，您看，是蜡烛最后的部分；而通过火焰，蜡烛似乎变不成任何东西，但情况并非如此，蜡烛实际上变成了好几样东西；——这不是很奇妙吗，正如法拉德教授说的那样，蜡烛燃烧的时候应该看起来美丽而耀眼吗？”

“我敢说，蜡烛的火焰在您的眼中看来平淡无奇；但如果我们在上头罩上一个玻璃灯罩保护它免得干燥的话，你就会看到它是圆形的——边缘是圆形的，向上形成一个峰状。它是被热空气抽上去的。您知道，热空气上升，这就是烟为什么能从烟囱出去的原理。您认为火焰中间是什么东西。”

“我说是火。”巴格斯叔叔回答道。

“哦，不。火焰是空心的。我们看到的明亮的火焰并不比薄薄的果皮或皮肤厚多少，它也并不和蜡芯接触。它中间是我刚才给您讲的蒸汽。如果你把一段弯折的管子的末端放在火焰中间，让管子的另一端进入到一个温暖的瓶子里，那么从蜡烛中蒸发的蒸汽或气体就会和空气在那里混合；如果你将这种由蜡烛蒸汽和瓶子里的空气混合而成的气体点燃，它就马上会发出一声爆炸声。”

“我想让你试试，哈利，”汤姆少爷说，他是哈利的弟弟。

“我想把事情说清楚，”哈利回答道——“好的，叔叔，蜡烛的火焰是一个小小的闪亮的圈子，中间有气体蜡，外面有空气的包围，因此火焰圈是介于空气和气体蜡之间。不断有气体蜡进入到火焰中燃烧；当蜡烛燃烧顺利的时候，没有气体蜡从火焰中溢出，也没有空气能进入到火焰中的气体蜡中间。蜡烛温度最高的部分是在火焰的表面，或叫焰表，或是外焰。”

“外焰！”巴格斯先生重复道。“真是活到老学到老。我本来以为蜡烛的火焰就像我这个老笨蛋一样厚实。”

“我可以给您看看，事实恰恰相反，”哈利说道。“我拿出这张白纸，看，把它放在蜡烛的火焰上一两秒钟，让火焰稳定燃烧。现在，我把黑烟的部分弄掉了，然后，你会发现纸被灼烧后呈环状，而环状的内部只不过是发黑，其实并没有被烧透。”

“眼见为实啊。”他叔叔说道。

“但是，”哈利继续说，“蜡烛的火焰产生的不仅仅是气体蜡这一种东西。你知道蜡烛没有空气燃烧不了。气体蜡周围一定要有空气的存在，然后和空气接触才能燃烧。如果没有充足的空气，那么蜡烛就会熄灭，或者燃烧不佳，因此一些火焰内部的蒸汽蜡会从火焰中以烟的形式跑出来；这也就是蜡烛会冒烟的原因。所以现在您知道了为什么一支巨大的火炬冒的烟要比小小的蜡烛产生的烟要少的原因了：那是因为火炬厚实的芯子产生太多的燃料，却没有相当数量的空气可以与之接触。”

“现在您觉得怎么样，”哈利继续说，“是我要告诉您，正是从蜡烛里跑出来的烟让蜡烛燃烧时产生光亮；蜡烛通过消耗掉自身产生的烟而发光。蜡烛的烟是一团小小的灰尘团；而这些小的灰尘团，化学家把它叫作木炭或碳。它们一产生就被燃烧掉了；而它们正是在火焰外焰部，也就是最热的地方产生的。高温将它们和由融化的蜡转化而成的气体蜡分离开来；它们只要一接触到薄薄的外焰外面的空气，就马上燃烧起来。”

“你能告诉我，那些小的碳团是怎么产生火焰的光亮的吗？”威尔肯森夫人问道。

“因为它们是固态的，”哈利回答道。“使火焰发光，就必须包含有一些固态的，或至少形态紧密的物质。”

“非常好，”巴格斯先生说，“产生光亮，必须有固态的物质！”

“还有一些气体和别的东西，”哈利继续说道，“它们燃烧时的火焰肉眼几乎看不到，只有当一些固态的东西加进去的时候，它们才能绚丽地燃烧。氢气，如果通过一根管子吹进去的话，燃烧的时候会产生很微弱的光；如果火焰是在石灰石上燃烧的话，就会产生让人目眩的光亮。如果你现在输送一些氧气到火焰上的话，火焰并不会变得更明亮，但石灰石却会变得像小小的太阳一样闪耀。在同样的氧气中放上松脂油产生的烟，火焰就会立马变得绚丽耀眼。嗯，碳或者木炭，是让所有的灯，蜡烛，和其他常见的灯发光的原因。”

“所以，碳就是烟，而光是因为碳产生的。是从烟当中产生的，对吧？就像人们在经典著作中总结的那样。”巴格斯先生总结道。