and in the Condensation of Vapours. 385 



On the other hand, M. Lavoisier estimates the quan- 

 tity of heat developed in the combustion of charcoal 

 much higher than Dr. Crawford. I have many reasons 

 to believe that they both estimate it too high ; and, if 

 this opinion be confirmed, we must estimate the heat de- 

 veloped in the combustion of hydrogen a little higher 

 even than Crawford has done, to be able to account for 

 that manifested in my experiments. 



From several experiments, which I made five years ago, 

 it appeared to me that one pound of charcoal, dried as 

 much as possible before it was weighed by heating it red- 

 hot in a crucible, was not capable of raising more than 

 from 52 to 54 pounds of water from the temperature 

 of melting ice to a boiling heat. 



According to Crawford, this heat should suffice to boil 

 57. 606 pounds, and according to Lavoisier,72.375 pounds. 



We shall see how these estimates agree with the results 

 of my experiments. 



As the experiments made with wax yielded very uni- 

 form results, and as the analysis of this substance has 

 been made with great care, I shall examine how the 

 quantities of hydrogen and carbon in this substance 

 agree with the quantity of heat that it afforded me in 

 combustion. 



According to the analysis of Messrs. Gay-Lussacand 

 Thenard, a pound of this substance contains 



Carbon 0.8179 Ib. 



Free hydrogen . 0.1191 



If we adopt the calculations of Dr. Crawford, both for 

 the heat furnished by the hydrogen and that furnished by 

 the carbon, we shall have for the heat that should be 

 furnished by the combustion 



VOL. II. 25 



