36 CHEMICAL ACTION. 



an animal cannot live in it : it abounds 

 in animal and vegetable substances, and 

 is the chief ingredient of the common 

 air.* 



Q. Why is there so much nitrogen in the air ? 



A. In order to dilute the oxygen. 

 If the oxygen were not thus diluted, 

 fires would burn out, and life would be 

 exhausted too quickly. 



Q. What three elements are necessary to pro- 

 duce COMBUSTION ? 



A. Hydrogen gas, carbon, and oxygen 

 gas ; the two former in the fuel, and the 

 last in the air which surrounds the fuel. 



Q. What causes the combustion of the fuel ? 



A. The hydrogen gas of the fuel 

 being set free, and excited by a piece of 

 lighted paper, instantly unites with the 

 oxygen of the air, and makes a yellow 

 flame : this flame heats the carbon of the 



* Nitrogen gas may easily be obtained thus: Put a 

 piece of burning phosphorus on a little stand, in a plate of 

 water ; and cover a bell glass over. (Be sure the edge of the 

 glass stands in the water.} In a few minutes the air will be 

 decomposed, and nitrogen alone remain in the bell glass. 



(N. B. The white fume which will arise and be absorbed 

 by the water in this experiment, is phosphoric acid; i.e. 

 phosphorus combined with oxygen of the air.) 



