356 CARBON. 



compound blowpipe, evidently effected, the fusion of the entire plum- 

 bago, including the carbon, the earths and iron.* 



(d.) BITUMINOUS COAL. The basis of this is carbon, which, un- 

 der the name of coak, is obtained, after the bitumen, the inflammable 

 gas, and other volatile ingredients have been expelled by heat. It 

 contains some earthy and metallic impurities, but burns away almost 

 entirely in oxygen gas, producing carbonic acid. 



3. ARTIFICIAL CHARCOAL. 



(a.) CHARCOAL is, after the diamond, the purest form of carbon ; it 

 is prepared in the large way, by a smothered combustion of billets of 

 wood, properly arranged, so as to admit a very partial supply of air, 

 through holes at the bottom ; the pile is covered with turf, earth or 

 clay, except a few spiracles, or one hole at the top ; and these are 

 stopped, when the dark smoke is replaced by clear whitish clouds. 

 The emission of volatile matter, consisting of inflammable gases, va- 

 por of oils, and water, and pyroligneous acid, and other things, chem- 

 ically or mechanically raised, finally ceases; and the heap is suffered 

 gradually to cool, which takes several days or weeks, according to its 

 size. 



The principle of the process is, that the combustion of a por- 

 tion of the wood produces strong ignition in the remainder, and thus 

 expels every thing volatile. 



(b.) Its formation may be shewn, by plunging small pieces of wood 

 beneath melted lead or tin,-\ or beneath sand heated to redness in a 

 crucible, in a furnace ;J when cold, it should be immediately removed, 

 and corked up for use. 



(c.) Prepared also in cast iron cylinders, for the manufacture of 

 gun powder,^ and the charcoal is the same from whatever wood pre- 

 pared, although alder, dog-wood, and willow have been heretofore 

 preferred. The cylinders are placed across a furnace, and there is 

 vent only for the aerial matter, consisting of inflammable gas, pyro- 

 ligneous acid || and tar, all of which are useful products. 



4. PROPERTIES. 



(.) Slack, brittle, shining, inodorous, and easily pulverized ; it 

 is so porous that it is easy to blow through it. 



* See Am. Jour. Vol. VI, p. 352. 



t Arrangement for class exhibition. A small earthen furnace, filled with burn- 

 ing charcoal, is supported by bricks or a stone upon a table, and upon this rests a large 

 ladle nearly full of melted lead, which should be nearly red hot, and the wood held 

 by small tongs is plunged beneath it; the fluid metal will boil vehemently, and the 

 inflammable gas, may be fired as it rises ; when all is quiet, the charcoal is devel- 

 oped, and maybe cooled beneath mercury. t Aikin, Vol. If, 235. 



Or still more neatly, by wrapping a piece of wood in platiua foil, and holding in 

 the flame of alcoholic lamp. The liberated gases take fire and burn brilliantly, and 

 well formed charcoal remains within. J. G. 



|| 'The charcoal made in this manner, is kept from the air when it is to be used for 

 the manufacture of gun powder ; it has not more than half the specific gravity of 



