Chapter I

. that nothing will burn without air. The air that presses toward a fire feeds it, as it is expressed. It does not all go up the chimney as heated air. Some of it is used in the burning of the wood and coal; and what goes up the chimney is, as I have told you in the first part of this chapter, partly heated air and partly gas.

[Sidenote: A free supply of air necessary to make a fire burn well.]

[Sidenote: Anecdote.]

Now a fire will not burn well unless it has a free supply of air. Fresh air must keep coming to it to feed it. But this can not be unless there is a good upward current from the fire. Firemen very well understand this in putting out fires. If the fire be inside of a building, the more shut up it can be kept the less rapidly will the fire spread, and the more easily can it be put out. If all the doors should be opened, and the windows broken out, the fire would rage, because the air would come in freely at the doors and lower windows, and go out freely at the upper windows. The fire would then have the same upward current that it has in a chimney. I will relate to you an anecdote, which will show how much can be saved by understanding such things. A fire was discovered early one morning by a flickering light shining through the windows in the upper room of a shop. An acquaintance of mine was among the first to get there, and he found a man about to beat the door in with an axe, so as to get at the fire. He kept him from doing this, and would not let him touch the door till they had got a good supply of water on hand. After he was satisfied that there was enough water to put out the fire, he then let the man use the axe, and they rushed up and easily put out the fire. If he had let him break open the door at first, it would have let in the air to feed the fire, and the fire would have got well agoing before the water was brought; and, as it was in a block of wooden buildings, we should have, had a great fire.

[Sidenote: Tall chimneys of factories.]

[Sidenote: Lamp chimneys.]

The brisker the upward current of a fire is, the more briskly does the fire burn. This is the reason that foundries and other factories, where they want a very hot fire, have such tall chimneys. The air and gas in such a chimney are kept hot for some time, instead of being cooled by spreading out in the open air. The current, therefore, up the chimney is very rapid, and so fresh air comes rapidly to the fire, and makes it burn very briskly. For the same reason, a very brilliant light is given by those lamps that have tall glass chimneys. The wick is thus made to burn briskly.

_Questions._--Why does smoke go up a chimney? What is smoke? What is there in smoke that you can see? What is soot? Tell how it is that the smoke is pushed up the chimney. What is said about the air in a room where there is a fire? What will happen to a light if you hold it near the fire-place? What if you hold it near a crack in the wall of the room? Tell about the rooms with folding-doors between them. Why do we open a door or a window to stop the smoking of a fire-place? Why is a fire-place not apt to smoke when the fire has been going for some time? Tell about holding a light at the lower part and at the upper part of a door that opens out into a cold entry. How is some of the air that presses toward a fire used? What is necessary to have a fire burn well? What is said about a building that is on fire inside? Tell the anecdote about the fire in a shop. Why do some factories have tall chimneys? What is said about the chimneys of some lamps?

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