v HOW PLANTS OBTAIN FOOD FROM AIR 43 



notice some curious facts about the burning of 

 different substances. 



The Air is Altered by Burning Substances 



You must have often observed that when a fire is 

 burning, the air in the room is drawn into the fire 

 through the bars and then passes up the chimney, 

 and that, if deprived of a plentiful supply of air, the 

 fire would go out. 



Let us look into this matter more closely, and try 

 and determine what part the air plays when the 

 wood or coal. is burning. 



We do not yet know if this air is in any way 

 changed by passing through the flame, and so must 

 try by a simple experiment 

 to find out if any change 

 has taken place. 



Experiment 26 



Light a candle and then 

 cover it over with a bell-jar, 

 so as to shut in with the 

 flame a fixed amount of air. 

 At first the flame burns 



^/ [ | \ 



brightly, but soon begins Fio n 



to burn feebler and feebler, 



and then goes out. Now light a match and plunge 



it into the bell-jar. The match also goes out at once. 



