208 



CAEBONIZATION IN ORDINARY KILNS. 



material is loam containing a large proportion of vegetable remains, 

 and the best material of all is the earth obtained from an old kiln 

 with its large admixture of ashes and fine cinders. 



The first covering should be laid on beginning from the top, so 

 that every portion of it may be supported and prevented from slip- 

 ping downwards by the overlapping portion immediately below. 

 It should be thick enough to prevent the earth of the outer covering 

 from falling through amongst the wood and thus retarding and 

 even preventing carbonization. In order to obtain a good in- 

 draught of air while the kiln is taking fire, the covering should 

 not at first be put on too thick near the ground, and may even be 

 left open at a few points there, such openings being stopped only 

 when the carbonization is in full progress. Similarly, the vent of 

 the chimney should also be left open until then. 



The earth for the second covering should be freed of stones and 

 other large fragments, which would destroy its even texture and 

 let in unequal draughts of air. All clods should be broken up fine 

 and the whole mass of material thoroughly well worked up until 

 it is of uniform texture throughout. For the top of the kiln and 

 those portions which have a gentle slope, the earth need only be 

 moistened just sufficiently to keep the particles together, and then 

 it is best thrown on with a shovel, so that it may get evenly dis- 

 tributed and ultimately rest safely at the proper angle of repose. 

 For the steep portions, especially when grass is used inside, the 

 earth should be made into a sort of thick mud and plastered 

 over the grass. To prevent the earth from slipping off the steeper 

 portions, it has to be propped up, especially near the ground. Two 

 simple and effective modes of propping are shown in Fig. 67. 



Fig. 67. 



Mode of propping up oownng of Uln, Different styles slmvn at A and S. 



