Why Does a Fire Go Out?
Fire will go out naturally when there is nothing left to burn, or it will go out if it cannot secure enough oxygen out of the air to keep it going. In the first case it dies what we might call a “natural death,” and in the latter case the fire practically suffocates. The fire in the open fireplace, if it has plenty of air, will burn up everything burnable that it can reach. The stones of the fireplace or other parts of a stove will not burn, because they have already been burned, and you cannot burn anything a second time, if all of the oxygen in it was burned out of it the first time.
Now, then, to burn up a thing, you must first start a fire under it, and then keep a constant draft of air playing on it from beneath, or the fire will die out. The more difficult a thing is to burn, the more important it is that you have plenty of draft. If the ashes accumulate under the fire the air cannot go through them in sufficient quantity and the fire will go out. Other things which prevent the current of air from going up through the fire will cause it to go out. That is why we close the lower door of the furnace, to keep the fire from burning out. When we shut off the draft of air from below, the fire in the furnace burns slowly, i. e., it just hangs on, so to speak.