and in the Condensation of Vapours. 407 



in agreeing in their results, whatever be the difference 

 of the methods employed : it is, nevertheless, necessary 

 to remark, that the coincidence in question could not 

 be so perfect as it appears, for everything depends upon 

 the equality of the humidity which may exist in the 

 wood and charcoal employed, a circumstance which it 

 is impossible to establish. 



SECTION IX. On the greatest Intensity of Heat which 

 it is -possible to produce by the Combustion of inflammable 

 Substances. 



It is well known that the heat of a small fire seems to 

 be less intense than that of a large fire, even when the 

 same species of combustible is employed ; but I do not 

 know that it has been attempted to determine, the limits 

 of the intensity of a fire, or the greatest degree of 

 heat which it is possible to produce by means of com- 

 bustion. 



In order to elucidate this subject, it is necessary to 

 consider attentively what passes in the chemical opera- 

 tion which we call combustion. 



In all known cases where two elementary substances 

 unite together so as to form a new substance, there is a 

 change of temperature, so that the new substance at 

 the moment of its formation has a temperature differing 

 strongly from that of the surrounding bodies. Conse- 

 quently, the surrounding bodies are always either heated 

 or cooled more or less by the new body which has been 

 formed. 



But in order that this effect may be sensible to our 

 organs, or capable of acting in a sensible manner upon 

 our apparatus, it is necessary that the quantity of the 



