COMBUSTION. 



137 



you will find that the middle is not burned at all, while 

 it is charred where the outer portions of the flame 

 touched it. So, also, it is possible to thrust a match so 

 quickly into the dark part of the flame that the phos- 

 phorus on its end will not take fire, while the wood that 

 is in the outer part of the flame burns readily. For the 

 same reason a piece of white paper 

 pressed down on the flame, nearly to 

 the wick, for an instant, Fig. 55, will 

 have a black ring marked on it. These 

 experiments prove that flame is really 

 hollow. If you blow out a candle, and 

 present a lighted taper to the smoke 

 at the distance of two or three inches, Fig. 56, you can see 

 a train of fire go along the smoke 

 till it reaches the candle and 

 lights it. This train of fire is 

 the burning of the gas that you 

 blow from the inside of the shell 

 of flame as you put out the can- 

 dle. To succeed in this experi- 

 ment you must do it very quiet- 

 ly, and at the same time quickly. 

 174. Experiment with Metals. 

 If you take a slip of some 

 metal, as copper, which is tar- 

 nished that is, oxidized on its K& 8ft> 

 surface and hold it across the flame, the tarnish will be 

 removed from its middle portion, while it will be increased 

 each side of this where the metal is in contact with the very 

 outer part of the flame. The explanation is this : In this 

 outer faint blue part of the flame there is plenty of oxy- 

 gen from the surrounding air, and some of this unites with 

 the metal, increasing the oxide or tarnish. But in the inner 



