226 METHODS IN TEACHING 



the flame, which is not hot enough to consume it all. Com- 

 pare the flame in this respect with the flame of a kerosene 

 lamp without the chimney. The effect of the chimney is to 

 cause this carbon smoke to be completely consumed, thus 

 making the flame larger and brighter. Is the flame of the 

 lamp hotter with or without the chimney? Call attention 

 to the dark area in the center of the candle flame. Thrust 

 a toothpick through the base of the flame and hold it there 

 until it begins to burn. Remove it quickly and blow out 

 the flame. Note that it began to burn at the two places 

 in contact with the outer surfaces of the flame, but that it 

 did not burn in the middle of the flame. The flame is hol- 

 low. Why? Because air does not get into the center and 

 nothing can burn without oxygen. What is in this central 

 portion that we have said was hollow? Take a piece of 

 glass tubing about ten inches long, and, holding it at an 

 angle of about 45, thrust its lower end into the dark cen- 

 ter of the flame. A gray gas, reminding us of the gas 

 from the paper lighter, rises through the tube. Have some 

 pupil light this at the upper end of the tube. Discuss its 

 origin, and, if necessary, heat a small piece of tallow in a 

 spoon until it vaporizes and takes fire? When pupils rec- 

 ognize this gas as vaporized tallow, ask again why it does 

 not burn in the center of the candle flame? To fix this 

 point still further, thrust the head of a sulphur match into 

 the dark center of the flame, and call attention to the fact 

 that it does not at once take fire and burn, although it may 

 blacken by heat. When removed, it immediately takes fire. 

 Try again, this time only touching the head of the match 

 to the outer surface of the flame, where the air reaches it. 

 What is the result? 



