260 
Steel. 
opening. The pile is covered with earth all round, leav- 
ing just vent enough here and therefor the fire to spread 
and to dissipate all the acid of the wood, the water, the j 
oil, the air, &c, but without consuming the substance so 
as to destroy its bulk or shape : this requires the attention 
of 3 or 4 days to bum 150 or 200 bushels at a time of 
charcoal. The lightest w r oods (generally speaking) make i 
the best charcoal. The charcoal thus burnt, should pre- 
serve the shape, and texture, and fibre of the wood. It 
should be of a deep shining black colour, light, dry, brit- 
tle, porous, giving out a ringing sound when struck, and 
frequently hard enough to strike fire with steel. Hence 
its powder is used by mathematical instrument-makers, 
and engravers, to polish their brass and copper ; also to 
polish horn, See. 
This method of making it, is not sufficiently nice and 
accurate for the purposes of gunpowder. In that mamn < 
facture, the wood is distilled in large iron cylinders, to 
which a tube is adjusted, and the substances distilled 
over, are detained in close vessels, being chiefly, an acid 
liquor sold to the callico printers under the name of pyro- 
ligneous acid, water, and oily matter. The heat given is 
very strong ; and in this way, all access of common air 
is prevented. The charcoal is very light, very black, 
and comparatively very pure, containing nothing but car- 
bon, with a small quantity of ashes and earth. 
In the common method of making charcoal, much of it 
is very imperfectly burnt, still containing moisture, hydro- 
gen, atmospheric air, oily matter, and pyroligneous acid, 
that is, the acid liquor distilled, from green wood by means 
of heat. The carbon of the wood also becomes oxyge- 
nated by decomposing moisture during the process of 
making charcoal, as well as by imbibing atmospheric air ; 
which it requires a high degree of heat to drive off ; the 
