“The water of the wet blankets would put it out,” said Rollo.
“No,” said his father; “it would be the same with any thing dry, if it would keep out the air. I presume, if a great quantity of dry sand was poured over it, it would put it out. But wet blankets or dry sand put over a barrel of gunpowder, even if we could have time to do it, would have no effect at all in stopping the burning; for the burning is not dependent upon the outward air at all; the combustion is entirely within itself; that is the essential peculiarity of gunpowder, on which all its powers depend.”
“I don’t see why it should burst open what it is confined in, after all,” said Rollo’s mother.
“Nor I,” said Rollo. “I should think it might burn up, without tearing things to pieces.”
“I don’t know myself,” replied Mr. Holiday, “exactly why it has such an expansive force. I’ll look in some book, when I get home, and see if I can find an explanation of it. But, at any rate, you see the difference in the manner of its burning. Now, there is wood, for example; it burns by degrees, as fast as the fresh air can come to it. When you put a stick of wood upon the fire, if it is dry and warm, and the fire is hot, first the outside takes fire. This burns because the air can get access to it. But the inside does not burn at all. If we were to take a stick off the fire, after it had been burning for half an hour, and saw it in two, we should find the middle as sound and solid as ever.”
“Should we sir?” said Rollo; “I should expect to find it all black coals.”
“No,” replied his father. “The blackness only extends in a very little distance; and the wood within is not burned any faster than the outside gets burned off out of the way, so as to let the air come to the inner layers, one after another.
“And there is a very curious contrivance in nature,” continued Mr. Holiday, “for supplying the fire all the time with fresh air.”
“What is it?” asked Rollo’s mother.
“Why, air is so constituted, that heat swells it, and makes it lighter; so that the air that is next to the outer layer of the wood, when the wood first begins to burn, becomes heated, and swells, and so, growing lighter, it immediately rises and goes out of the way, and a new supply of good, fresh air comes in to take its place. By the time that this is no longer good to promote the burning, it gets heated and rises; and so, there is a constant stream of hot air, that has passed through the fire, rising, and fresh air coming in to take its place. That is the reason, Rollo, why we have chimneys in a house. A chimney is nothing but an opening over a fire, so that the air can rise up through it as fast as it passes through the fire, and all the smoke and sparks pass up too.”