and in the Condensation of Vapours. 405 



they furnished more heat than I could find, I have not 

 hesitated to adopt their results instead of relying upon 

 my own. 



SECTION VIII. Quantities of Heat developed in the Com- 

 bustion of Wood. 



In a memoir which I had the honour to present to the 

 Class on the pth 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 dif- 

 ferent 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 dif- 

 ference 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 



