TREES OF Ar4 ERICA. 175 



but it is not compact enough for liquor-barrels : 

 it is a great deal used for fuel, but it makes 

 an unpleasant fire, on account of its snapping 

 so much : the charcoal made from it, however, 

 is excellent.'' 



" Uncle Philipj what is the reason of that 

 snapping, do you know, sir ?" 



" I know, but I am not sure that I can 

 make you understand it : chestnut-wood you 

 know, is very porous, that is, it has little 

 holes and cracks in every part of it, and is 

 not close and solid, like locust or cherry-wood : 

 well, these little holes are full of air, and it is 

 one of the properties of air to expand or swell 

 when it is exposed to heat : you can satisfy 

 yourselves about this if you like, by blowing 

 air into a bladder until it is almost full and 

 tight, then tie the neck of it and lay it before 

 a fire, and you will see it swell till it is 

 perfectly full and hard ; and then if you 

 sprinkle cold water on it, or take it away from 

 the fire and let it cool, it will shrink again to 

 the same size it was before. Just so it is with 

 the air in the chestnut, v/hen the wood is put 

 on the fire ; the air that is confined in the 

 pores begins to swell, and it swells and swells 

 till at last it bursts open the place in which 



