260 Charcoal [Book Vf. 



in fuch a manner as to reduce \t to charcoal, which, 

 when well made, contains carbon united with only a 

 very fmall proportion of fuch matter contained in 

 vegetable fubftances as cannot be driven off by heat, 

 fuch as earthy and faline matter, with a very minute 

 portion of iron. In order to convert wood into char- 

 coal, the only circumftances neceffary are the applica- 

 tion of heat while the air is nearly excluded. The only 

 elementary fubftances which feem-to be univerfal in 

 the vegetable kingdom are, carbon, hydrogen, and 

 oxygen. The former of thefe fubftances has very 

 little attraction for caloric, or the matter of heat, and 

 therefore cannot be driven off in vapour, at leaft by the 

 heat of ordinary fires; the two latter, however, have 

 a ftrong attraction for that principle, and therefore 

 eafily affume a gaffcous ftate. In the ordinary tem- 

 perature of the atmofphere the carbon, hydrogen, and 

 oxygen, which conftitute the woody fibre, feem to exift 

 in a ftate of triple combination j but this is not the 

 cafe when the temperature is altered. According to 

 M. Lavoifier, if a heat, not exceeding that of boiling 

 water, is applied, one part of the hydrogen combines 

 with oxygen, and forms water, the reft of the hydrogen 

 combines with a part of the carbon, and forms volatile 

 ' oil, while the remainder of the carbon remains fixed 

 at the bottom of the veffel. If a red heat, however, 

 is applied, no water comes over, carbon having a 

 ftronger attraction at that temperature for oxygen than 

 hydrogen has, and therefore carbonic acicl is produced ; 

 and the hydrogen being left free from other combina- 

 tions, unites with caloric, and comes over in the form 

 of hydrogen gas. In this high temperature no oil is 

 produced. 



The folidity of charcoal depends on that of the wood 

 from which it is procured, and the care with which 



the 



