,J62 CARBON. 



in Venice had undergone the same process. Dr. Robinson, in his in- 

 troduction to Dr. Black's lectures, says, "About forty years ago, a 

 number of pointed stakes were discovered in the bed of the Thames, 

 in the very spot where Tacitus says that the Britons fixed a vast 

 number of such stakes, to prevent Julius Ca3sar from passing his 

 army over by that ford. They were all charred to a considerable 

 depth, and retained their form completely ; and were so firm at the 

 heart, that a vast number of knife handles were manufactured from 

 them, and sold as antiques, at a high price."* 



5. POLARITY. Electro-positive; it is attracted to the negative pole. 



6. COMBINING WEIGHT 6, hydrogen being 1. 



7. MEDICAL AND OTHER USES. A preference is entertained by 

 some for charcoal made from particular substances, as from cedar or 

 cork ; it should be newly prepared or recently heated, j- It is thought 

 to correct a vitiated state of the stomach and bowels, and has been 

 celebrated in some stages of dyspepsia, and in dysentery and other 

 diseases of the alimentary canal. The dose cannot be critical ; from 

 10 grains to a table spoonful may be given, two or three times a day.J 

 It is applied with much advantage to foul ulcers, whose fetor it cor- 

 rects, and in the form of poultice to sores that are tending to gan- 

 grene. 



8. MISCELLANEOUS. 



(a.) Charcoal is said to be better if the bark is left on the wood, 

 which should not be split ; pieces of six or seven inches in diameter 

 are easily charred. Coak is the carbon of mineral coal ; it is pre- 

 pared by a process resembling in principle that for charcoal ; it pro- 

 duces an intense fire, and is much used in England in the manufac- 

 tures, especially of iron. || A charcoal is also extracted from peat. 

 The following table shows the proportion of volatile matter, charcoal 

 and ashes, in 100 parts of different woods. Ure. 



* I saw one of these stakes in the British Museum ; the charcoal on the outside 

 and the wood within, were apparently as perfect as the day it was driven. 



t If it is to be applied on a foul ulcer or sore, it should be taken red hot from the 

 fire, pulverized immediately in a metallic mortar, and used as soon as cold, and any 

 ,that remains should be bottled, tight from the air. + Coxe. 



It is conjectured that in the charring of wood, portions of it are sometimes con- 

 verted into pyrophorus, and that explosions in powder mills may occasionally be 

 owing to this cause. 



|| One ton of bituminous coal yields from 700 to 1100 Ibs. of coak. Much bitumen 

 and other volatile products are lost in the usual way of charring, but Lord Dundo- 

 nald, by heating the coal in a range of eighteen or twenty stoves, with as little ac- 

 cess of air as possible, and conducting the smoke through horizontal tunnels, and 

 finally into a brick tunnel 100 yards long, and covered at top by water, succeeded 

 in obtaining nearly 3 per cent, of bitumen in the form of tar ; 28 barrels of it yielded 

 21 of tar, and the volatile parts gave materials for varnish, besides ammonia. Ure. 



