92 



CHEMICAL CONSTITUTION OF VEGETABLES. 



From the experiments of Clement, it appears that the heating 

 power of charcoal is equal to 7050 units. Dry wood containing, aa 

 we have seen, 5*2 per cent, of charcoal, its healing power has been 

 deduced theoretically, as equal to 3066. Mr. Marcus Bull in Amer- 

 ica, made a series of experiments to determine the relative quantities 

 of heat given out by ditlerent kinds of wood, from which M. Peclel 

 has been led to conclude that the same weight of dry wood of every 

 kind has the same heating power, and that this for a kilogramme, 

 or 2.2 lbs. avoird. of wood dried by artificial means, is equal to 3500 

 units, while the same quantity of the same wood having been cut 

 and seasoned during from ten to twelve months, and containing froui 

 20 to 25 percent, of water, is no higher than about 260 units. 



By way of coniparison, 1 shall here add the healing power of the 

 several combustibles in general use, in contrast wiih that of wood : 



1 kilo^m. or 2.'2 lbs. avoird. of wood-chrircoal protlucps 7226 units of heat. 



colli r<o»)o 



" " JKMt 30(1.) 



" " peal chnrcoal WOO " 



Although the same quantities of wood, brought to the same d^groo 

 of dryness, appear to have the same absolute calorific power, all are 

 not alike adapted to the same purposes. Hard wimds burn slowly, 

 and give out less heat in a certain lime than the less compact kinds 

 of wood. This is the reason why fir is preferred to oak m furnaces 

 where the object is to obtain the most intense heats. It were for- 

 eign to our object \o enter upon any considerati«)n of the various 

 qualities, or of the adaptation to particular uses, of dilTerent species 

 of timber. I may, however, add a table of the ordinary dimensions 

 of well-grown trees of ditTerent kind i, such as are conuuonly found 

 in these countries . 



