"Do you mean that the iron really burned as wood does?" said Belle.
"Why, certainly," replied Johnny: "iron will burn up more completely than wood; for when wood is burned, the earthy part remains in the form of ashes: but pure iron, which has no earthy matter in it, will burn up completely; it will all combine with the oxygen in the air to form gas. When iron is in a mass, it takes a very intense heat to produce this chemical union with oxygen; but when it is separated into very small particles, it will burn in an ordinary fire."
"If iron will burn up, I wonder we never see it burning so," said Alec. "I've been in blacksmiths' shops and foundries, and I never saw any iron burning up, although I've seen it at a white-heat."
"The fires in blacksmiths' shops and foundries are not hot enough to burn iron in the mass," replied Johnny; "or, if they are, they can't get enough oxygen near enough to combine with it. At the great Chicago fire, the intense heat caused such a high wind,—that is, such a flow of oxygen toward the fire,—that the fire became so intensely hot there was no difficulty in the iron blazing and burning more completely than the wood."
Here Johnny looked rather disconcerted at Alec's apparent incredulity.
"But, Alec," said he, "if little particles of iron, such as you would file off of a bar of iron, will burn up, of course the whole bar could be burned if it was all filed up; and if the filings could be burned in an ordinary lamp like this, why couldn't the whole bar be burned in a fire that was hot enough?"
"Yes," said Belle, who was troubled at Alec's being so impolite as to seem to doubt Johnny's word: "it's just like the difference between a log of wood and the sawdust produced by sawing the log in two; you couldn't burn the log without building a hot fire under it, while you could set the sawdust on fire with a match."
"That is a very good illustration," said Johnny. "Now, I lit this lamp to show you how nicely iron will burn."
Johnny took a large-mouthed bottle from the shelf, which was about half full of rather bright particles.
"These are steel-filings I got at a machine-shop; but, if you prefer, I will get a nail and file, and let you make some iron-filings yourself, which will answer just as well. I keep the steel-filings because they are so handy. I just ask the men for them, and they give me a whole lot that last ever so long."