VEGETABLE FIBRE. 



153 



the south burns at least twice as long as that of the white 

 oak of the north, and the effects produced by the heat it 

 affords are great in the same proportion. 



The light, porous white woods afford a brittle, spongy 

 coal of less weight, and which may be easily reduced to 

 powder : this coal consumes quickly in our fire-places, but 

 is useful for some purposes, particularly in the manufac- 

 ture of gun-powder, for which use it is prepared by the 

 following process : a ditch of five or six feet square, and 

 of about four in depth, is dug in a dry soil ; the ditch is 

 heated by means of a fire made of split wood, the shoots 

 and leaves are stripped from the young branches of elders, 

 poplars, hazles, and willows, of which the coal is to be 

 made, and as soon as the ditch is sufficiently heated the 

 branches are thrown gradually in ; when carbonization is 

 at its height, the pit is covered over with wet woollen 

 cloths. This charcoal is more light and inflammable than 

 that of the denser woods, and is susceptible of being more 

 easily and completely pulverized. M. Proust, who has 

 made numerous experiments to ascertain the kind of plants 

 which furnish the best coal for powder, found that pro- 

 cured from the stalks of hemp to be preferable to any 

 other. 



The most perfect process of carbonization is performed 

 by means of a close apparatus : for this purpose a stone or 

 brick building is constructed, of from eighteen to twenty- 

 five feet square ; this is vaulted over, and the inside of it 

 lined with a brick wall ; through the extent of it cast-iron 

 cylinders are laid in such a manner, that one of the two 

 ends shall have an external communication, whilst the 

 other carries the smoke into one of the chimneys. As soon 

 as the building is filled with the wood for carbonization, the 

 cylinders may be heated. The vapor which is distilled 

 from the wood is received into sheet-iron pipes, placed in 

 the top, which convey it into tubs where it is condensed. 



The form and dimensions of these buildings for making 

 charcoal by means of a close apparatus, are greatly va- 

 ried, but of all which I happened to see, the one I have 

 here described appears to me the most perfect. There are 

 many advantages arising from the use of this method, 

 which more than repay the necessary expense of the appa- 

 ratus. In the first place, a much greater quantity of char- 

 coal is obtained, than by the ordinary process ; in the 

 second place, well made and clean charcoal is always pro- 



