THK PARABOLOIDAL OVKU-GKOUND KILN. 209 



5. — Firing of the kiln. 



If the kiln is to be fired from below, a torch is formed at the 

 end of a long pole with grass and some highly inflammable chips 

 of wood. The lighted torch is inserted into the open passage left 

 along the ground and pttshed home against the bottom of the chim- 

 ney, the pole being at once withdrawn. The draught along the 

 ground and up the chimney carries the fire into the latter, from 

 which then as centre it is able to spread outwards amongst the 

 wood to be carbonized. The chips and other small fragments of 

 wood placed in the chimney are quickly consumed ; as they sub- 

 side, fresh pieces must hence be gradually stoked in from the top. 

 Ultimately, when the fire has become established and has begun to 

 spread outside the chimney, this latter is filled up tight to the top 

 with short billets of wood. If this last operation is not properly 

 done, the chimney will soon become empty and cause the wood 

 from the sides to fall in, thus leading to unequal subsidence and 

 to the breaking up of the kiln. After the chimney is full, and even 

 earlier if the wood is very dry or a strong wind is blowing, the 

 tunnel along the ground is filled up with short straight billets well 

 packed together. When the combustion inside the kiln is in full 

 progress, the covering is completed over the open extremities of 

 the chimney and tunnel. It requires some experience and judg- 

 ment to close these openings at the proper time. 



If the firing is to take place from above, a dishful of live coal is 

 dropped into the chimney and the fire worked into the chips below 

 with a thin bar of iron or even a green sapling. The fire is stoked 

 from time to time with small piecep of dry wood, and, finally, when 

 the wood in the chimney is in full combustion and the fire has 

 reached the bottom, the chimney is filled up and closed in the 

 same manner as in the method of firing from below, already 

 described. 



Firing from below is always troublesome, and the necessity of 

 leaving a passage open along the ground breaks up the regularity 

 of the stacking and renders the kiln liable to excessive subsidence 

 on one side during the process of carbonization. Tq compensate 

 for these drawbacks, it is more certain in its results, as unless the 

 chimney is properly constructed and the fire skilfully stoked, fire 

 lighted from above may fail to reach the bottom of the chimney, 

 thereby rendering the carbonization of the lowest tier of wood a 

 difficult matter, or at any rate entailing the everburning of the wood 

 in the upper tiers after it has already become carbonized. 



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