in Combustion, and in the Condensation of Vapours. 299 
§ X. Quantities of Heat developed in the Combustion of 
Wood. 
In a memoir which I had the honour to present to the 
Class on the 9th of September 1812, I gave an account of 
a considerable number of experiments (upwards of fifty) 
which I made, in order to determine the quantities of heat 
which are developed in the combustion of different kinds of 
wood. 
From the results of these experiments, it appears that, at 
equal weights, the light and soft woods give out a little 
more heat than the compact and heavy woods: but as the 
difference is very small, we may rather ascribe it to a greater 
degree of humidity in the latter. 
It is certain that the compact retain humidity with more 
tenacity than the light woods, and a small difference in the 
dryness of a wood ought to produce a sensible effect on its 
apparent weight, and consequently upon the result of the 
calculations which we employ in order to determine the 
heat which it furnishes. ; 
In physical and chemical researches, it is always satis- 
factory to be able to compare the results of new experi= 
ments with those of more ancient date, particularly when 
the latter have been made by persons remarkable for their 
accuracy. 
¢ M. Lavoisier has shown that equal quantities of heat are 
produced in the combustion of 1089 parts in weight of oak, 
and 600 parts of charcoal: consequently equal quantities 
of heat ought to be furnished in the combustion of one 
pound of oak and 0°55 of a pound of charcoal. 
According to the experiments of Mr. Crawford, one 
pound of charcoal furnishes in its combustion enough of 
heat to raise the temperature of 57°608 pounds of water to 
180° of Fahrenheit. 
Consequently the temperature of 31°684 pounds of water 
would he raised the same number of degrees by the heat fur- 
nished in the combustion of 0°55 pound of charcoal. 
According to the result of the experiments of M. Lavoi- 
sier, this same quantity of heat ought to be furnished in the 
combustion of one pound of oak. 
Having made four consecutive experiments with very 
good dry oak wood, aud in very thin slips, burnt so as to 
give out neither smoke nor smell, and which Jeft but an in- 
appreciable quantity of ashes and no charcoaj, | obtained 
the following results ; 
‘Number 
