536 AUXILIARY FOREST INDUSTRIES. 



passage to the kindling material at the hottom of the flue, 

 that is thus fired. When kindled from above a little fire is 

 lighted at the top of the flue. The kiln is fired always on a 

 still morning before daybreak, whilst its base is open under 

 the lower supports. If the fire has caught properly, first 

 the flue and its contents are burned thoroughly, 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 off and the 



Fig. 313. Showing progress of carbonisation. 



arrangement of the wood disturbed. Too loose a soil under 

 the kiln or too rapid burning may thus imperil 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 carbonisa- 

 tion is in progress. Charcoal is formed first in the dome of 

 the kiln, proceeding downwards in a wedge (Fig. 313), and 

 the latter sinks down, carrying with it the covering, which 

 should adhere more or less firmly to it. If the carbonisation 

 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. 



