62 HEAT 



24. Flames. 



In our experiments with combustibles we found 

 that, while some of them burned with a flame, others only 

 glowed. The difference is caused by a gas, as only gases 

 burn with a flame. But, you will say, you saw wood 

 burn with a flame, and wood is not a gas. That is true, 

 but when the wood is heated so that it ignites, part of it 

 is changed into a gas and it is the burning of this gas 

 which causes the flame. It is just the same with a candle. 

 The wax, when it is heated, changes into a gas and the 

 burning gas causes the flame. Whenever you see a 

 flame you may be sure that a gas is burning. 



There are two kinds of flames, those which give a 

 laro-e amount of light and those which give only a very 

 little light. Those flames which give light are called 

 luminous. Can you name some luminous flames? Name 

 one flame which is not luminous. How can you obtain 

 light from a flame which is not luminous? Luminous 

 flames show that the combustion is not complete, the 

 light being due to little particles which are not hot 

 enough to burn. A flame which can hardly be seen is 

 the result of very nearly complete combustion, and these 

 flames are much hotter than the luminous flames. 



Experiment 32. The Cause of Flames. 



Apparatus: Test tube, test-tube holder, alcohol 

 lamp, piece of glass tubing }/\" thick, 4" long. 



Materials: Bits of wood, candle. 



a. Put some bits of wood in a test tube and heat 

 them in the flame of an alcohol lamp. What do you see 



