Air 



209 



is burning, and this helps to keep the air of the room fit 

 for respiration. (Cf. Experiment 70.) 



141. We cannot well show directly that fresh air is 

 necessary to the continuance of animal life. We must 

 rest content with the statement of the fact that .some 

 of the operations which go on inside our bodies are 

 somewhat similar in character to those involved in the 

 burning of a candle, and require just as urgently for 

 their due performance a good supply of fresh air. 

 Lessening this supply lowers the vitality of the body 

 just as under similar circumstances the candle flame 

 flickers and weakens. 



142. Having discovered that air appears to be 

 necessary for burning to occur, let us next try to find 

 out whether all the air takes an active part in the burn- 

 ing. 



EXPERIMENT 77. Fix a short piece of candle, (7, to 

 a length of stout copper wire, W, as 

 in Fig. 63. Push the end of the wire 

 through a sheet of stiff cardboard, M , 

 and light the candle. Lower the card 

 and wire into a deep glass jar, G, so 

 that the card rests on and closes the 

 mouth of the jar. In a short time the 

 candle flame will be extinguished. 



Remove the candle, relight it, 

 and quickly replace it in the jar. 

 This time it goes out at once, or, if 

 the removal and replacement have 

 not been done deftly enough, burns 

 for a very short time, much shorter 

 than when previously plunged into the 

 jar. 



M 



\ 



W 



Fig. 63. 



It is evident from this experiment that the air in 

 H. D. s. 14 



