1st—Because the coat of water (which wraps the fuel round) prevents the oxygen of the air from getting to the fuel, to form into carbonic acid gas: and
2ndly—Heat is perpetually carried off, by the formation of the sap or water into steam.
(Carbonic acid gas is a compound of carbon and oxygen. The solid part of the fuel is carbon, and one of the gases of the air is oxygen.)
Q. What has carbonic acid gas to do with combustion?
A. Combustion is produced by the chemical action which takes place, while the carbon of fuel unites with the oxygen of air, and forms “carbonic acid gas.” (See p. [36].)
Q. Why do stones snap and fly about, when heated in the fire?
A. The air in the stones (expanded by the heat of the fire), meets with great resistance from the close texture of the stone; and, therefore, bursts forth with great violence, tearing the stone to atoms, and forcing the fragments into the room.
Q. Must not air be very strong, to shatter into atoms a hard stone?
A. Yes. All the dreadful effects of gunpowder are merely the results of the sudden expansion of air.