204 CAUBONISATION IN onDINARY KILNS. 



straighter sides, it is usual to dimimsh the contents given by the 

 formula by 4 — 6 per cent. 



1. — Size of the kiln. 



The larger the kiln is, the less will be the relative quantity of 

 covering material used, the more limited the space occupied, the 

 fewer the men required, and the smaller the proportion of wood 

 consumed in producing the heat necessary for carbonizing the 

 remainder, and hence the lower will be the cost of carbonization. 

 On the other hand, the larger kiln requires greater skill both to 

 build up and to manage during the burning, and produces a harder 

 charcoal. The largest kiln of the kind made in India seldom con- 

 tains more than 1,500 stacked cubic feet of wood. A very conve- 

 nient size for persons possessing little skill is one containing about 

 600 cubic feet. 



2. — Emplacement of the kiln. 



The site selected should be sheltered, even, and level, and it should 

 be close to abundant water and to the wood to be carbonized. If 

 the quantity of wood is large, there ought to be room enough for 

 several kilns, as the same party of burners can just as easily man- 

 age several kilns as a single one. The nature of the soil is also of 

 considerable importance. A soil that is too free and porous would 

 allow too strong an upward draught of air to pass through it into 

 the burning wood above, while a too stiff soil would, on the con- 

 trary, cause the kiln to burn too slowly. A loamy sand is the best, 

 as, besides possessing average stiffness, it absorbs at once the con- 

 densed vapours given off by the wood, which in a stiff soil would 

 clog the surface and interfere with the carbonization. It is abso- 

 lutely necessary that the soil of the entire site should be uniform, 

 otherwise the kiln would burn more rapidly at some points than at 

 others, the result being unequal subsidence and consequent exten- 

 sive and frequent breakages, and hence unequal carbonization and 

 unprofitable waste of wood. 



If a new site is used, it must be very carefully prepared. Such 

 preparation will consist in (1) clearing away all vegetation by the 

 roots ; (2) removing all stones, for parbonization will be unnecessa- 

 rily slow over boulders and injuriously quick over smaller elements ; 

 (3) raising the site about 8 to 12 inches in the middle and slopino- 

 it down outwards in every direction, so as to allow the liquid pro- 

 ducts of the kiln, which cannot be absorbed into the soil, to run out 



