“You can see it goes into smoke, which makes soot, for one thing,” pursued Harry. “There are other things it goes into, not to be seen by only looking, but you can get to see them by taking the right means—just put your hand over the candle, uncle.”
“Thank you, young gentleman, I had 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 very long, slender gas-burner 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 come 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 sort of 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 in burning—water, coming out of fire. A jet of oil gives above a pint of water in burning. In some lighthouses they burn, Professor Faraday says, up to two gallons of oil in a night, and if the windows are cold, the steam from the oil clouds the inside of the windows, 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 either from 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. The part that comes from the wax isn’t water, and the part that comes from the air isn’t water, but when put together they become water. Water is a mixture of two things, then. This can be shown. Put some iron wire or turnings into a gun-barrel open at both ends. Heat the middle of the barrel red-hot in a little furnace. Keep the heat up, and send the steam of boiling water through the red-hot gun-barrel. What will come out at the other end of the barrel won’t be steam; it will be gas, which doesn’t turn to water again when it gets cold, and which burns if you put a light to it. Take the turnings out of the gun-barrel, and you will find them changed to rust, and heavier than when they were put in. Part of the water is the gas that comes out of the barrel, the other part is what mixes with the iron turnings, and changes them to rust, and makes them heavier. You can fill a bladder with the gas that comes out of the gun-barrel, or you can pass bubbles of it up into a jar of water turned upside down in a trough, and, as I said, you can make this part of the water burn.”
“Eh?” cried Mr. Bagges. “Upon my word. One of these days, we shall have you setting the Thames on fire.”
“Nothing more easy,” said Harry, “than to burn part of the Thames, or any other water; I mean the gas that I have just told you about, which is called hydrogen. In burning, hydrogen produces water again, like the flame of the candle. Indeed, hydrogen is that part of the water, formed by a candle burning, that comes from the wax. All things that have hydrogen in them produce water in burning, and the more there is in them, the more they produce. When pure hydrogen burns, nothing comes from it but water, no smoke or soot at all. If you were to burn one ounce of it, the water you would get would be just nine ounces. There are many ways of making hydrogen, besides out of steam by the hot gun-barrel. I could show it you in a moment by pouring a little sulphuric acid mixed with water into a bottle upon a few zinc or steel filings, and putting a cork in the bottle with a little pipe through it, and setting fire to the gas that would come from the mouth of the pipe. We should find the flame very hot, but having scarcely any brightness. I should like you to see the curious qualities of hydrogen, particularly how light it is, so as to carry things up in the air; and I wish I had a small balloon to fill with it and make go up to the ceiling, or a bag-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.