The Story-Book of the Fields 



black visible lumps, but it exists in the air as 

 an invisible substance. In order to make 

 this clearer let us consider sugar. This is 

 white, hard, and crackles when bitten. We 

 will put a little of it in water. The sugar 

 melts, is dispersed in the water, and at once is 

 neither white, hard, nor does it crackle when 

 bitten. It is even invisible to the keenest 

 sight. But this invisible sugar exists all the 

 same. One proof of this is that it has im- 

 parted the taste of sugar to the water. Besides, 

 when the water has gone, being evaporated 

 on a plate in the sun, the sugar remains and 

 reappears as it was at first. This instance 

 will prove that a substance without ceasing to 

 be the same, may change from colour to 

 colourless, from tangible to intangible, from 

 visible to invisible. 



Well, coal when burning acts in the same 

 way. It is dissolved in the air and becomes 

 invisible. That which is not really coal, being 

 indissoluble, remains on the hearth and forms 

 the ashes. All the coal disappears, dissolved 

 in the air and seems to be annihilated because 

 we can no longer see it. This dissolution is 

 accompanied by heat and is called combustion. 



What do we do if we want to encourage the 

 fire ? We turn the air on to the fuel with 



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