108 EFFECTS OF HEAT. 



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. Wliy 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 Jbrfh 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. 



