THE BURNING OF WOOD AND COAL 91 



with the gases which escaped from the tube are all consumed 

 in the flames, while the charcoal remains on the grate to be 

 slowly oxidized to carbon dioxide, producing much heat but 

 little or no flame. 



102. A Study of Flame. It has been seen that it is the 

 vapor of the candle, of the gasoline, and of the kerosene that 

 burns. The hydrogen has been seen to burn with a flame. 

 The illuminating gas burns with a flame. The volatile matter 

 from the wood burns with a flame. In every case a flame is 

 produced by a burning vapor, or gas. Those fuels that are 

 gases or that maybe changed in to vapors, or gases, by means of 

 heat burn with a flame. Four conditions are necessary in 

 order that a flame be produced: (1) The material must be 

 in the form of a vapor or gas; (2) this vapor or gas must be 

 mixed with oxygen; (3) the mixture of oxygen and vapor or 

 gas must have concentration within certain limits; (4) the 

 mixture must be heated to the kindling temperature. If one 

 or more of these conditions are wanting there can be no flame. 



103. Blowing Out a Flame. A common expression is that 

 of "blowing out" a flame. Candle flames, lamp flames, 

 and even the flame of a fire just started may be blown out. 

 However, if the fire is well started, it may be impossible to 

 blow it out, but rather the blowing only serves to make the 

 fire burn faster. From what has been given in Art. 102, on 

 flames, it is evident that the effect of blowing into a candle 

 flame or a lamp flame is to scatter the particles of vapor or 

 gas and thus reduce their concentration (Art. 94) to such a 

 point that there can be no flame. Moreover, the cold blast 

 of air entering the flame serves to cool the burning materials 

 below their kindling temperature (Art. 95) . With a solid 

 fuel such as charcoal, however, the case is different. 



Exercise 30. Effect of Blowing upon Glowing Charcoal 



Place a piece of charcoal upon the gauze and heat it with a flame 

 until it glows. Now blow gently upon the glowing portion. Does 

 the blowing cause it to burn more or less rapidly? Can you blow it 

 out? Caution. Quench the charcoal in water. 



