LESSON 15 The chemistry of a candle (II)
"But what becomes of the candle," pursued Harry, "as it burns away? where does it go?"
"Nowhere, I should think. It burns to nothing."
"Oh, dear, no!" said Harry; "everything goes somewhere. You can see it goes into smoke, which makes soot, for one thing. There are other things it goes into, not to be seen by merely looking, but you can get to see them by taking the right means. Just put your hand over the candle, uncle."
"Thank you, my young gentleman, I would rather be excused."
"Not close enough down to burn you, uncle;—higher up. There;—you feel a stream of hot air, so something seems to rise from the candle. Suppose you were to put a long glass lamp-chimney over the flame, and let the flame burn just within the end of it, as if it were a chimney, some of the hot steam would go up and pass out at the top, but a sort of dew would be left behind in the glass chimney, if the chimney was cold enough when you put it on. There are ways of collecting this dew; and when it is collected it turns out to be really water. I am not joking, uncle. Water is one of the things which the candle turns into while burning—water coming out of fire. In some light-houses, Professor Faraday says, two gallons of oil are burned in a single night; and if the windows are cold, the steam from the oil clouds them, and, in frosty weather, freezes into ice."
"Water out of a candle, eh?" exclaimed Mr. Bagges, "As hard to get, I should have thought, as blood out of a post. Where does it come from?"
"Part from the wax, and part from the air; and yet not a drop of it comes from either the air or the wax. What do you make of that, uncle?"
"Eh? Oh, I'm no hand at riddles! Give it up."
"No riddle at all, uncle. That which comes from the wax is a gas called hydrogen. We can obtain it from water by passing the steam of boiling water through a red-hot gun-barrel which contains a quantity of iron wire or turnings. Part of the steam will mix with the iron turnings, and change them into rust; and the other part, which comes out of the end of the barrel, will be hydrogen gas, and this part of the water we can set on fire."
"Eh?" cried Mr. Bagges. "Upon my word! One of these days we shall have you setting the river on fire!"
"Nothing more easy," said Harry. "When pure hydrogen burns, we get nothing but water. I should like to show you how light this hydrogen is; and I wish I had a small balloon to fill with it and send up to the ceiling; or a pipe full of it to blow soap-bubbles with, and show how much faster they rise than common ones blown with the breath."
"So do I," interposed Master Tom.
"And so," resumed Harry, "hydrogen, you know, uncle is part of water, and just one-ninth part. The other eight parts are a gas also, called oxygen. This is a very curious gas. It won't burn in air at all itself, like gas from a lamp; but it has a wonderful power of making things burn that are lighted and put into it. A lighted candle put into a jar of oxygen blazes up directly, and is consumed before you can say Jack Robinson. Charcoal burns away in it as fast, with beautiful bright sparks; phosphorus burns with a light that would dazzle you to look at; and a piece of iron or steel, just made red-hot at the end first, may be burned in oxygen more quickly than a stick could be in common air. The experiment of burning things in oxygen beats any fire-works."
"How funny that must be!" exclaimed Tom.
"Now we see, uncle," Harry continued, "that water is hydrogen and oxygen united together; that water is got whenever hydrogen is burned in common air; that a candle won't burn without air; and that when a candle burns, there is hydrogen in it burning and forming water. Now, then, where does the hydrogen of the candle get the oxygen, to turn into water with it?"
"From the air, eh?"
"Just so. It is the oxygen in the air that makes things burn; but if the air were noting but oxygen, a candle would not last above a minute.
"If a house were on fire in oxygen,' as Professor Faraday said, 'every iron bar, or, rather, every pillar, every nail and iron tool, and the grate itself; all the zinc and copper roofs, and leaden coverings, and gutters, and pipes, would consume and burn, increasing the combustion."
"That would be, indeed, 'burning like a house on fire,'" observed Mr. Bagges.
"But there is another gas, called nitrogen(1)," said Harry "which is mixed with the air; and it is this which prevents a candle from burning out too fast."
"Eh?" said Mr. Bagges. "Well, I do think we are under considerable obligations to nitrogen."
"I have explained to you, uncle," continued Harry "how a candle, in burning, turns into water. But it turns into something else besides that. The little bits of carbon that I told you about, which are burned in the flame of a candle, and which make the flame bright, mingle with the oxygen in burning, and form still another gas, called carbonic acid(2) gas, which is very destructive to life when we breathe it. So you see that a candle-flame is vapour burning; and that the vapour, in burning, turns into water and carbonic acid gas."
"Haven't you pretty nearly come to your candle's end?" said Mr. Wilkinson.
"Nearly. I only want to tell uncle that the burning of a candle is almost exactly like our breathing. Breathing is consuming oxygen, only not so fast as burning. In breathing, we throw out from our lungs water in the form of vapour, and carbonic acid gas, and take oxygen in. Oxygen is as necessary to support the life of the body as it is to keep up the flame of a candle."
"Well," said Mr. Bagges, "any more to tell us about the candle?"
"If I had time, I could tell you a great deal more that Professor Faraday said about oxygen, and hydrogen,and carbon, and water, and breathing; but you should go and hear him yourself, uncle."
"Eh? well I think I shall. Some of us seniors may learn something from a juvenile lecture, at any rate if given by a Faraday. And now, my boy, I tell you what," added Mr. Bagges; "I am very glad to find you so fond of study and science; and you deserve to be encouraged; and so I'll give you a—what-d'ye-call-it?—a galvanic battery(3) on your next birth-day; and so much for your teaching your old uncle the Chemistry of a Candle."
seniors, old folks.
What are the different things into which the candle goes when it burns? How is the water produced? What is it that prevents the candle from burning too fast? How is the carbonic acid gas produced? show how the burning of a candle resembles the process of breathing.