176 THE NATURE STUDY COURSE* 



Combustion and Candle Flame. — The growing tree fed 



upon the carbon dioxide in the air and out of the elements of 

 that gas and water made its wood. The part that remains as 

 ash when the wood is burned came from the soil. When 

 you burn a match you set in operation a partial reversal of the 

 operations that produced the wood. This process restores the 

 carbon dioxide to the air and is called combustion. 



Light a candle and observe three zones, a dark central zone 

 where there is little or no combustion, a radiant zone where 

 there is partial combustion and a mantle where the combustion 

 is perfect. Place the tip of slow-lighting matches succes- 

 sively in these three zones and observe the differences in the 

 times of lighting. Place a match stick across the flame and 

 observe where it burns most. Place a piece of white card- 

 board over the flame almost touching the top of the wick ; 

 remove carefully and observe the differences in the soot 

 rings. 



Carbon Dioxide. — Burn a candle for a few minutes in a 

 gem jar. Remove the candle, put in an ounce of limewater 

 and shake the jar. Observe the milkiness in the limewater. 

 With a tube or straw breathe into a bottle containing an ounce 

 of limewater. Account for the similar effects upon the lime- 

 water in each case. The milkiness is due to the formation of 

 fine particles of limestone by the carbon dioxide and the lime 

 dissolved in water. 



Fire needs Air. — Light a short candle, set it on a smooth 

 surface and invert a tumbler over it. The flame soon goes 

 out. Infer what should be done when clothing catches fire. 

 Water puts out fire by cutting the air supply off from the 

 coal that it surrounds and by cooling the carbon. Carbon 

 does not burn when the temperature is reduced below a 

 certain degree. 



