GRAPHITE. 91 



remains for 12 hours. The volatile matter is thus expelled, 

 and the cokes produced are ponderous, extremely hard, of a 

 light gray color, and having a metallic luster. To make 

 another kind of coke, like charcoal, the pit coal is placed in 

 a receptacle more like a baker's oven, and the air has 

 more free access. Both of these kinds of coke are used in 

 smelting. 



2-V. graphite. — Plumbago. M£> • C 



Occasionally in six-sided prisms, with a transversely fohV"S<JW**~< 

 ated structure. Usually foliated, and massive ; also granu- 

 lar and compact. 



Luster metallic, and color iron black to dark steel gray. 

 Thin lamina flexible. H = l— 2. Gr = 2*09. Soils paper, 

 and feels greasy. 



Composition. 90 to 96 per cent, of carbon, with the rest 

 iron. Some specimens from Brazil contain scarcely a trace 

 of iron. It is often called carburet of iron, but is not a 

 chemical compound. It is infusible before the blowpipe, 

 Doth alone and with reagents ; it is not acted upon by acids. 



Dif. Resembles molybdenite, but differs in being unaf- 

 fected by the blowpipe and acids. The same characters 

 distinguish the granular varieties from any metallic ores 

 they resemble. 



Obs. Graphite (called also black lead) is found in crys- 

 talline rocks, especially in gneiss, mica slate and granular 

 limestone ; also in granite and argillite, and rarely in green- 

 stone. Its principal English locality is at Borrowdale, in 

 Cumberland. Ure observes that this mineral became so 

 common a subject of robbery, a century ago, as to have En- 

 riched many living in the neighborhood ; a body of miners 

 would break into the mine and hold possession of it for a 

 considerable time. The place is now protected by a strong 

 building, and the workmen are required to put on a working 

 dress in an apartment on going in and take it off on coming 

 out. In an inner room two men are seated at a large table 

 assorting and dressing the graphite, who are locked in while 

 at work and watched by the steward from an adjoining room, 

 who is armed with two loaded blunderbusses. This is 

 leemed necessary to check the pilfering spirit of the Cum- 



What is the appearance of graphite ] What is its prominent char- 

 acteristic 1 its composition 1 Where does it occur 1 Where is it worked 

 in England ? 



