Iron . 
95 
layer is commonly composed of small brush-wood. The 
whole is then covered with turf, the grassy side towards 
the wood ; a coating of earth is then applied all round 
the bottom of the pile, and firmly beat to prevent the un- 
necessary admission of air, A small funnel, or opening 
on the top, is preserved by the transverse position of the 
first layer of wood ; this is generally about 18 inches deep, 
into which the burning fuel is introduced. Combustion 
is in this manner first conveyed to the top of the pile, 
and is continued by feeding the small craters with pieces 
of wood for 4 or 5 days. When the interior part of the 
fire next the top is deemed sufficiently kindled and spread 
over the whole diameter, a row of holes is opened a few 
inches below, each about two inches diameter. The 
hole at the top is then entirely shut up, and the fire, now 
completely spread, slowly descends to where the air is ad- 
mitted by means of the small apertures. When this is 
observed by the burner, which is known by the disappear- 
ance of smoke and vapour, they are immediately shut up, 
and a second row opened 6 or 8 inches under the first. 
In this manner the fire is conducted to the foundation of 
the pile, and the whole mass exposed to proper combus- 
tion. The intention of the operation is to bring the 
whole pile to a state of complete ignition, but in such a 
manner that no greater a portion of it may undergo com- 
bustion than is necessary to produce that effect. Hence 
the necessity for guarding against too free an access of 
air during the process. As soon as the operation is end- 
ed, which may last for 10 or 14 days, the whole is more 
closely covered up, and kept so till such time as the char 
is deemed sufficiently cool to be fit for drawing : it is 
then separated from the earth, and carrried away in bags 
or in waggons. Those pieces of wood not sufficiently 
charred are by the workmen called brands , and are com- 
monly used for fuel to the next fire. 
