“I hope with your candle you you’ll throw some light upon the subject,” said Uncle Bagges. “I hope so,” answered Harry. “Recollect it is the burning of the smoke, or soot, or carbon of the candle that makes the candle-flame bright. Also that the candle won’t burn without air. Likewise that it will not burn in nitrogen, or air that has been deprived of oxygen. So the carbon of the candle mingles with oxygen, in burning, to make carbonic acid gas, just as the hydrogen does to form water. Carbonic acid gas, then, is carbon or charcoal dissolved in oxygen. Here is black soot getting invisible and changing into air; and this seems strange, uncle, doesn’t it?” “Ahem! Strange, if true,” answered Mr. Bagges. “Eh?—well! I suppose it’s all right.” “Quite so, uncle. Burn carbon or charcoal either in the air or in oxygen, and it is sure always to make carbonic acid, and nothing else, if it is dry. No dew or mist gathers in a cold glass jar if you burn dry charcoal in it. The charcoal goes entirely into carbonic acid gas, and leaves nothing behind but ashes, which are only earthy stuff that was in the charcoal, but not part of the charcoal itself. And now, shall I tell you something about carbon?” “With all my heart,” assented Mr. Bagges. “I said that there was carbon or charcoal in all common lights,—so there is in every common kind of fuel. If you heat coal or wood away from the air, some gas comes away, and leaves behind coke from coal, and charcoal from wood; both carbon, though not pure. Heat carbon as much as you will in a close vessel, and it does not change in the least; but let the air get to it, and then it burns and flies off in carbonic acid gas. This makes carbon so convenient for fuel. But it is ornamental as well as useful, uncle. The diamond is nothing else than carbon.” “The diamond, eh? You mean the black diamond.” “No; the diamond, really and truly. The diamond is only carbon in the shape of a crystal.” “Eh? and can’t some of your clever chemists crystallise a little bit of carbon, and make a Koh-i-noor?” “Ah, uncle, perhaps we shall, some day. In the meantime I suppose we must be content with making carbon so brilliant as it is in the flame of a candle. Well; now you see that a candle-flame is vapour burning, and the vapour, in burning, turns into water and carbonic acid gas. The oxygen of both the carbonic acid gas and the water comes from the air, and the hydrogen and carbon together are the vapour. They are distilled out of the melted wax by the heat. But, you know, carbon alone can’t be distilled by any heat. It can be distilled, though, when it is joined with hydrogen, as it is in the wax, and then the mixed hydrogen and carbon rise in gas of the same kind as the gas in the streets, and that also is distilled by heat from coal. So a candle is a little gas manufactory in itself, that burns the gas as fast as it makes it.” “Haven’t you pretty nearly come to your candle’s end?” said Mr. Wilkinson.