YIELD OF CHARCOAL. 717 



(f) Different kinds of kilns. — The diflerent methods of carbon- 

 isation yield different -volumes of charcoal, but it is difficult, 

 considering the extremely variable conditions in any case, to 

 decide which method is most productive. 



The yield in the common method varies according as the 

 Idndling is applied from above or below. Although in both cases 

 the fire first develops at the top of the kiln, in kindling from 

 above the fire never consumes the chimney so thoroughly and 

 develops so well in the centre of the Idln as when it is kindled 

 from below. Filling is therefore more difficult to effect in the 

 former case ; hollows then develop which have to be repeatedly 

 filled, a circumstance which must have bad effects on the yield. 

 By kindling from below, the fire in the centre of the kiln, 

 persisting from the first, gradually heats all the wood in the 

 kiln : when, however, the kiln is kindled from above and the fire 

 gradually descends, it constantly meets with cold wood ; this 

 delays the process and reduces the yield. In many districts, 

 therefore, and especially for hardwoods, kindling from below is 

 preferred. 



The Alpine method is usually applied only to coniferous 

 wood ; the kilns are then exceptionally large, while they are 

 burned for years on the same site. These circumstances have 

 so much influence on the yield that it is difficult to say what 

 are the direct effects of the method. The charcoal from Alpine 

 kilns is not inferior in quality to that produced by the common 

 method ; it may be lighter, owing to the repeated fillings of the 

 chimney, but owing to the large size of the billets it yields 

 larger pieces of charcoal than the latter. There is, however, a 

 falling-o£f in quantity in proportion to the volume of wood 

 burned as compared with the common method, owing to the 

 fact that billets are green, and un split. A good deal of char- 

 coal is also expended in filling the chimney, and the large billets 

 remain exposed to the heat for a longer time than the smaller 

 split billets in a common kiln ; this necessarily reduces the 

 yield. 



Horizontal kilns are employed only when timber can be spared 

 for charcoal-making, they are therefore comparatively rare in 

 Europe. The construction of these kilns and the process of 

 burning are easier than in vertical kilns, there is no need for 



