144 CHEMISTRY. 



at the same time that doors and windows are opened below, 

 windows are opened or broken in above, as is often the case, 

 the air sweeps up and through with great force, feeding 

 rapidly the fire with oxygen. 



184. Blowing out a Candle. The fact that a puff of breath 

 or a gust of wind puts out a candle seems at first thought 

 inconsistent with what we have stated, for really more oxy- 

 gen is thus carried to the candle than it gets when the air 

 is still. It is easy to see, however, that there is no inconsist- 

 ency. There is a certain amount of heat required to keep 

 up the combustion, and the air, therefore, may be made to 

 come so rapidly to the light as to take away sufficient heat 

 to stop the combustion. The more rapidly the air comes 

 to the light, the more oxygen, it is true, is brought to it ; 

 but this is not adequate to compensate for the loss of heat. 

 You have undoubtedly noticed that it is easier to avoid 

 having a lamp or candle go out in carrying it up stairs 

 than in carrying it down. The reason is that the flame is 

 blown in the first case, if you hold the candle inclined a 

 little forward, directly down upon the wick, increasing 

 therefore the fire and the heat, while in the other case the 

 flame is blown away from the wick. For the same reason, 

 in carrying a lighted taper or stick, you point it forward. 

 You see now what is the chemistry of a lantern, as we may 

 express it. The air is admitted freely that the light may 

 have a good supply of oxygen, but the orifices are so small 

 that no gusts of wind can reach the light and reduce its 

 heat below the burning point. 



185. Putting out Fires. Water is the common means of 

 putting out fires, and this acts in two ways. First, it shuts 

 out the oxygen of the air from the combustible substance, 

 acting as a covering to it, thin indeed, but yet effectual ; 

 and, secondly, it takes away some of the heat, and therefore 

 lessens the combustion. Of course, the colder the water is, 



