Fire and Heat 123 



another source, since it does not exist free in the air in quan- 

 tities sufficient to account for the amount of water produced. 

 We seem to be forced to conclude that hydrogen is a constit- 

 uent of the substance of the candle. This does not seem im- 

 probable. The substance of the candle is melted and passing 

 upward through the wick is changed by the heat into gases 

 which burn. Hydrogen must be one of the gases thus pro- 

 duced, because water is one of the products of the burning 

 candle. 



Exercise : Testing for hydrogen. Burn a lump of pure carbon, 

 such as charcoal, in oxygen. Cool the test tube or bottle to condense 

 any water vapor produced. Is moisture formed? If not, what does 

 its absence indicate as to the substances formed? Was hydrogen 

 present ? 



Test other familiar substances for hydrogen. Rendered beef 

 suet, lard, tallow, or butter, may be made into small candles with 

 wicks of cotton twine. If you test gas, alcohol, or kerosene as sug- 

 gested on page 114, and find water as the product of their burning, 

 you may conclude that they contain hydrogen. 



46. Another product of combustion. The flame of the can- 

 dle gives considerable light. The flame of hydrogen is hot, 

 but does not produce much light. It is in fact non-luminous. 

 This leads us to inquire what in the substance of the candle is 

 the cause of its light. We may find this by capturing and 

 questioning the products of its burning. We must provide, 

 however, a different condition from that which made the water 

 vapor visible as moisture. We know of course that, whatever 

 else any product of combustion may contain, it will always 

 contain oxygen, or be an oxid compound. We may imagine 

 also that, like water, it will not support combustion. These 

 characteristics we may expect in any product of burning sub- 

 stances. 



Limewater an indicator of one product of combustion. 

 The products of the burning candle are easily captured by hold- 

 ing a wide-mouth bottle directly over the flame. By cooling 

 the bottle the water vapor is made visible. But it may be that 



