OF FOREST-TREES

259

mouth of the tunnel, stopping it as close as may be with some of the chapformer dust and rubbish. Lastly, with the handles of your rakes, or thelike, you must make vent-holes, or registers, (as our chymists 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 somore till they arrive to the ground, as occasion requires. Note, That, asthe pit does coal and sink towards the centre, it is continually to be fedwith short and fitting wood, that no part remain unfired; and if it charsfaster at one part than at the other, there close up the vent-holes, andopen them where need is. A pit will in this manner be burning off andcharring five or six days; and as it coals, the smoke, from thick and grofsclouds, will grow more blue and livid, and the whole mafs sink accord-ingly, so as by these indications you may the better know bow to stopand govern your spiracles. Two or three days it will only require forcooling, which, the vents being stopped, they afsist by taking now off theoutward covering wdth a rabil or rubber ; but this not far above thespace of one yard breadth at a time; and first they remove the coarsestand grofsest of it, throwing the finer over the heap again, that so it mayneither cool too hastily, nor endanger the burning and reducing all toashes, should the whole pit be uncovered and exposed to the air at once 3therefore they open it thus round by degrees.

When now, by all the former fymptoms, you judge it fully charred,you may begin to draw, that is, to take out the coals, first round thebottom, by which means the coals, rubbish, and dust, sinking and fallingin together, may choak and extinguish the fire.

Your coals sufficiently cooled, with a very long-toothed rake anda vann, you may load them into the coal-wains, which are made closewith boards purposely to carry them to market. Of these coals thegrofser sort are commonly reserved for the forges and iron-works, themiddling and smoother put up in sacks, and carried by the colliers toLondon and the adjacent towns: Those which are charred of the roots,if picked out, are accounted best for chymical fires, and where a lastingand extraordinary blast is required.

Coal for the powder-mills is made of Alder-wood (but Lime-tree weremuch better, had we it in that plenty which we easily might) cut,