32 



THE EEASON WHY. 



r Stand in awe and sin not : commune with your own heart upon your bed and 

 be still." PSALM iv. 



Because as they breathe more rapidly, the combustion of the 

 carbon in the blood is increased by the oxygen inhaled, and greater 

 heat is developed. 



27. Why does the fire burn more brightly when blown ly a 

 bellows ? 



Because it receives, with every current of air, a fresh supply of 

 oxygen, which unites with the carbon and hydrogen of the coals, 

 causing more rapid combustion and increased heat. 



28. Why does not the oxygen of the air sometimes take 

 fire? 



Because oxygen, by itself, is incombustible. The wick of a 

 candle, which retains the slightest spark, being immersed in oxygen, 

 will instantly burst into a brilliant flame ; and even a piece of iron 

 wire made red-hot, and dipped in oxygen, will burn rapidly and 

 brilliantly. Oxygen, though non-combustible of itself, is the most 

 powerful supporter of combustion. 



29. Why do we know that oxygen will not burn of itself ? 

 Because when we immerse a burning substance into a jar of 



oxygen, it immediately burns with intense brilliancy ; but directly 

 it is withdrawn from the oxygen, the intensity of the flame diminishes, 

 and the oxygen which remains is unaffected. 



30. Why do we Tcnow that oxygen is necessary to our 

 existence ? 



Because animals placed in any kind of gas, or in any combination 

 of gases, where oxygen does not exist, die in a very short time. 



31. Where is oxygen found ? 



It is found in the air, mixed with nitrogen ; in water combined 

 with hydrogen ; in the tissues of vegetables and animals ; in our 

 blood; and in various compounds called, from the presence of 

 oxygen, oxides. 



32. Why is the oxygen of the air mixed so largely with 

 nitrogen ? 



Because oxygen in any greater proportion than that in which it 

 is found in the atmosphere, would be too exciting to the animal 



