304. Why, if a piece of paper be laid with its flat surface upon the fire, will it "char," but not ignite?
Because, as in the case of the proper candle-extinguisher, the carbonic acid gas accumulating beneath it prevents its igniting.
305. Why, if you direct a current of air towards the paper, will it burst into a blaze?
Because the carbonic acid gas is displaced by a current of air containing oxygen.
306. Why does water extinguish fire?
Because it saturates the fuel, and prevents the gases thereof from combining with the oxygen of the air.
307. As water contains oxygen, why does not the oxygen of the water support the fire?
Because the affinity between the hydrogen and oxygen of the water is so strong that fire cannot separate them.
Water may be decomposed by heat, as will be hereafter explained. But the heat of an ordinary fire is insufficient. There is, however, some reason for believing that, in cases of very large fires, such as the accidental burning of houses, &c., when the supply of water thrown upon the fire is very deficient, the water does become decomposed, and add to the fury of the flames.
308. Why does the blacksmith sprinkle water upon the coals of his forge?