206 CARBONIZATION IN ORDINARY KILNS. 



size of the kiln. Fig. 66 A shows the disposition of the wood in 



Fig. 66, 



Paraboloidal over-ground kiln with upright stack inff. 

 A. — Before firing. B. — Carionixaiion comj/lete, 



a kiln composed of three tiers. The upright pieces should rest ou 

 their thick end, so that they may incline more and more towiirds 

 the chimney the further away they are set up from it ; there is no 

 other -way of giving to the sides of the kiln the slope necessary for 

 their stability, which slope should nowhere exceed 65°. It is evi- 

 dent that all the upright pieces in the lower tiers should be of equal 

 length in one and the same tier. Those in the topmost tier, being 

 laid horizontally, must, on the other hand, he necessarily of differ- 

 ent lengths to admit of being closely packed together and to enable 

 the apex of the kiln to be properly rounded off. It is not neces- 

 sary that the whole of a tier should he completed before the next 

 one is begun ; indeed, it is always more convenient to commence 

 building up this latter when the other has been about half com- 

 pleted. In the topmost tier, as in all the rest, the laying of the 

 pieces should progress from the chimney outwards, and great care 

 must be taken to secure an even paraboloidal outline without plac- 

 ing any piece on the outside in such a way that it must fall off when 

 the kiln begins to subside with the progress of the carbonization. 

 The packing should everywhere be as close as possible, for the 

 volume of every piece must diminish considerably as it becomes 

 carbonized, thus causing all originally empty spaces to grow larger 

 and thereby diminishing the stability of the kiln. As a further 

 precaution, the mimerous intervals that must remain even after the 

 most careful packing should be filled up tight with thin pieces and 

 chips, preferably of completely dry or, better still, if at hand, of half- 

 carbonized wood. 



If the kiln is to bo fired from below, a narrow passage, extend- 

 ing as far as the chimney, should be left open along the ground, 



