OF FOREST-TREES. 



259 



mouth of the tunnel, stopping it as close as may be with some of the CHAP. IV. 

 former dust and rubbish. Lasty, with the handles of your rakes, or the '^^'v"'*^ 

 like, you must make vent-holes, or registers, (as our chemists name them,) 

 through the stuff which covers your heap to the very wood, these in ran- 

 gers of two or three feet distance, quite round within a foot (or there- 

 about) of the top, though some begin them at the bottom : a day after, 

 begin another row of holes a foot and a half beneath the former, and so 

 more till they arrive to the ground, as occasion requires. Note. That as 

 the pit does coal and sink towards the centre, it is continually to be fed 

 with short and fitting wood, that no part remain unfired ; and if it chars 

 faster at one part than at the other, there close up the vent-holes, and 

 open them where need is. A pit will in this manner be burning off and 

 charring five or six days ; and as it coals, the smoke, from thick and gross 

 clouds, will grow more blue and livid, and the whole mass sink accord- 

 ingly, so as by these indications you may the better know how to stop 

 and govern your spiracles. Two or three days it wiU only require for 

 cooling, which the vents being stopped, they assist by taking now off the 

 outward covering with a rabil or rubber ; but this not far above the 

 space of one yard breadth at a time ; and first they remove the coarsest 

 and grossest of it, throwing the finer over the heap again, that so it may 

 neither cool too hastily, nor endanger the burning and reducing all to 

 ashes, should the whole pit be uncovered and exposed to the air at once ; 

 therefore, they open it thus round by degrees. 



When now, by all the former symptoms, you judge it fully charred, 

 you may begin to draw, that is, to take out the coals, first round the 

 bottom, by which means the coals, rubbish, and dust, sinking and falling 

 in together, may choke and extinguish the fire. 



Your coals sufficiently cooled, with a very long-toothed rake and a 

 vaiin, you may load them into the coal-wains, which are made close 

 with boards purposely to carry them to market. Of these coals the 

 grosser sort are commonly reserved for the forges and iron-works, the 

 middling and smoother put up in sacks, and carried by the colliers to 

 London and the adjacent towns : those which are charred of the roots, 

 if picked out, are accounted best for chemical fires, and where a lasting 

 and extraordinary blast is required. 



Coal for the powder-mills is made of Alder-wood, (but Lime-tree were 

 much better, had we it in that plenty which we easily might,) cut, 



