PRELIMINARY EXPERIMENTS xxi 



boys and girls feel like dancing about when they go out 

 from a warm schoolroom ? What makes the flame dance 

 or flicker when the chimney is raised by the pencils ? 

 Because it gets fresh air under the chimney. 



Repeat the first experiment, in which the flame grows 

 gradually smaller till it is extinguished. Why does the 

 flame die out now ? Is it really necessary to have fresh 

 air in order to keep a flame burning? 



To prove this further, let the candle be relighted. Place 

 the chimney over it, now having the top completely closed 

 by a piece of paper. Have ready a lighted splinter or 

 match, and just as soon as the candle is extinguished 

 remove the paper from the chimney top and thrust in the 

 lighted splinter. Why does the light on the splinter go 

 out? What became of the freshness that was in the air ? 

 It was destroyed by the burning candle. 



Evidently there is some decided difference between un- 

 burned air and burned air, since a flame can continue to 

 burn only in air that has the quality known as freshness. 

 This quality of fresh air is due to oxygen, represented by O. 

 Why was the splinter put out instantly, while the candle 

 flame died out gradually ? When the splinter was thrust 

 in, the air had no freshness or oxygen at all, while when 

 the candle was placed under the chimney, it had whatever 

 oxygen was originally in the air within the chimney. 



Endeavor to have this point clearly understood : that the 

 candle did not go out as long as the air had any oxygen 

 and that the splinter was extinguished immediately because 

 there was no oxygen left. 



Relight the candle. A former question may now be 

 repeated : Is anything else burning besides the candle? 



When the subject of the necessity of fresh air and con- 

 sequently of oxygen for the burning of the candle seems 



