704 WOOD-CAKBONISATION. 



iiiuler the lower supports. If the fii-e has caught properly, the 

 tlue and its contents are first thoroughly hurned and then the 

 immediately adjoining wood, the fire rising to the top of the 

 kiln. As soon as the dome becomes very hot, steam mingled 

 with thick flocky smoke issues from it. At this period there is 

 always more or less danger of bursting owing to the formation 

 inside the kiln of an explosive mixture of air and combustible 

 gases, or a sudden development of steam. "Were such a mis- 

 fortune to happen, the covering would be blown oft' and the 

 arrangement of the wood disturbed. Too loose a soil under the 

 kihi or too rapid burning may thus impeiil matters, the risk of 

 bursting being greater with dry than with slightly green wood. 



After a few hours, the smoke acquires a pungent odour, a 

 sign that the wood is being decomposed and that carbonisation 

 is in progress. Charcoal is already formed in the dome of the 

 kiln and the latter sinks down, carrying with it the covering 

 which should adhere more or less firmly to it. If the carbon- 

 isation proceeds properly, a flame should issue from the top of 

 the chimney in the form of a symmetrical cone, widening out 

 more and more till flames protrude from the base of the kiln. 



vii. Mode of Condnctintj the J)i(rni)i;i. 



The normal process of carbonisation just described cannot 

 always be secured uninterruptedly. The draught is sometimes 

 greater in one particular direction and the kiln itself is 

 seldom uniformly built or covered, it may therefore settle down 

 unsymmetrically or burn too quickly or too slowly. Charcoal- 

 burners should know how to secure the kiln against these 

 mishaps, and keep it burning in as normal a manner as possible. 



This is elfected by the following procedure : — the fire should 

 be gradually led from the top of the kiln to its base, so that the 

 kiln may settle down symmetrically and without burning the 

 charcoal. The space left open at the base of the kiln, which is 

 subsequently closed, may be re-opened if more draught is re- 

 quired and holes made in the upper part of the covering through 

 which flames protrude in order to regulate the burning. On 

 the second or third day after kindling, the first holes are made 

 through both coverings down to the wood on the leeward side of 



