"Fire is one of the most beautiful chemical unions known; and the burning of a match is an excellent illustration of the different temperatures which different substances require, in order that they may unite with the oxygen in the air, or be on fire as we call it."
As the match was pretty well burned by this time, Johnny applied the flame to a spirit-lamp upon the table, which was the principal purpose for which he had lighted the match.
"A very moderate amount of heat will cause phosphorus, which is the substance on the end of the match, to form a chemical union with the oxygen in the air: brimstone requires a little higher temperature than phosphorus, but not so high as wood requires. The heat produced by a little friction is enough to light the phosphorus, the heat produced by the burning phosphorus is enough to cause the brimstone to take fire, and that produced by the burning brimstone is enough to cause the wood to burn; that is, to form a chemical union with oxygen. And, although the burning phosphorus or brimstone would not have produced sufficient heat for lighting the lamp, the burning wood furnished the necessary temperature; so that the alcohol in the wick began the union at once, when the blaze of the wood came in contact with it."
"I see now how it is that we kindle a coal-fire," replied Alec. "First we put some paper in the grate, and then some pine-kindlings, and then some charcoal, and then the hard coal: then we set the paper on fire with a match, and presently the coal is burning."
"And we separate the kindlings so that the oxygen can get to them more easily," said Johnny.
"How queer we never understood exactly why a fire was kindled in that way, until now," said Belle. "And I should never have thought of fire being a chemical union."
"You can carry on the same principle a good deal farther," said Johnny. "From having a fire of coals, you might have a house on fire, and this would produce heat sufficient to set the neighboring houses on fire; and the uniting of such a quantity of carbon and hydrogen with oxygen, to make carbonic-acid gas, would create such a vacuum by the rising of the heated air and gas, that so much oxygen would rush in about the fire, in the form of a high wind, as to make the fire hotter and hotter, until, if it surrounded an iron building, it would burn it up just as easily as wood houses are burned in an ordinary fire; as was the case at the great Chicago fire, where so many fire-proof blocks were totally destroyed."
"But the iron buildings did not actually burn: they only melted down in the great heat," said Alec.
"Oh, no! they burned," said Johnny: "there is no trouble about burning iron up, if you get the right degree of heat."
"I should think there was a good deal of trouble about it, if great buildings they didn't mean to have burned, if there was a fire, did go and burn up right before their eyes," said Sue.