COMBUSTION. 37 



fuel, which also unites with the oxygen of 

 the air, and produces carbonic acid gas. 



Q. What is carbonic acid gas ? 



A. Only carbon (or charcoal) com- 

 bined with oxygen gas. 



Q. Why does FIRE produce HEAT ? 



A. 1st By liberating latent heat 

 from the air and fuel : and 



2ndly By throwing into rapid motion 

 the atoms of matter. 



Q. How is latent HEAT liberated by COM- 

 BUSTION ? 



A. When the oxygen of the air com- 

 bines with the hydrogen of the fuel, the 

 two gases condense into water; and 

 latent heat is squeezed out, as water 

 from a sponge. 



Q. How are the ATOMS OF MATTER DISTUR- 

 BED by COMBUSTION? 



A. 1st When hydrogen of fuel and 

 oxygen of air condense into water, a 

 vacuum is made ; and the air is disturbed, 

 as a pond would be, if a pail of water 

 were taken out of it : and 



2ndly When the carbon of fuel and 

 oxygen of air expand into carbonic acid 



