THE COMMON METHOD, 697 



All wood for carbonisation should be spread out in dry parts 

 of the felling-area or of landing depots until it is air-dry, in 

 order that there may be the least possible waste of heat in 

 driving oft" moisture from the wood. Only in very hot summers, 

 or when the wood is highly resinous, is it advisable to use some- 

 what green wood so that the process may not be too rapid, or 

 else the workmen may not be able to keep the combustion of 

 the wood well in hand. 



The shape and dimensions of the billets have considerable 

 influence on the process of carbonisation. Although all parts 

 of a kiln do not burn at the same rate, yet it is advisable to 

 have the billets as uniform in shape as possible. As a rule, 

 therefore, only one assortment of wood is used in a kiln ; only 

 in cases of necessity, in very large kilns or in carbonising stump- 

 wood, should deviations from this rule be allowed. 



One of the chief points of difterence between the common and 

 Alpine methods of carbonisation is that, in the former, the wood 

 is generally split and used in small pieces, large pieces of sound 

 wood being used in the latter. 



The length of the billets may be either that usual for fire- 

 wood, or a special length may be given to charcoal-billets (rarely 

 exceeding 6 feet). The shorter the pieces the easier it is to give 

 the kiln its requisite shape, and the less the cost of its construc- 

 tion. Excepting small round billets under 2| inches (7 cm.) thick, 

 the wood should all be split and stump-wood should, as far as 

 possible, be split into small pieces. This is especially necessary 

 for broad-leaved woods, which burn slowly. In order that the 

 wood may be packed closely, all snags and unevennesses should 

 be trimmed off" and fairly smooth, straight pieces set aside on 

 the felling-area for charcoal-making. Crooked and bent branch- 

 wood is only used in short pieces. In piling the kiln, besides 

 the round and split billets, short little pieces of wood are used to 

 fill interstices between the billets. 



ii. Shape and Size of Kilns. 

 The usual shape of a kiln is that of a paraboloid, the volume 

 of which is ,, X ,: , where {d) is the diameter and {h) the 



