and in the Condensation of Vapours. 415 



This is, according to the results of this calculation, 

 the highest temperature which we ought to expect to 

 find amid the strongest charcoal fire fed by atmospheric 

 air. 



But we are very certain that the intensity pf the heat 

 of the strongest charcoal fire is far superior to the above 

 calculation ; consequently we are authorized to conclude 

 that the capacity for heat of the carbonic acid, and that 

 of nitrogen gas, are much diminished when these elastic 

 fluids are exposed to a very high temperature. 



If, in endeavouring to discover the limit of intensity 

 of a charcoal fire, I have supposed the fire to be very 

 large^ it is not because I suppose that the heat developed 

 in combustion is more intense at the primitive source in a 

 large than in a small fire ; but as a small fire is always 

 surrounded by bodies relatively very cold, such as the 

 bars of the grate, etc., the products of the combustion 

 (which are always at the instant of their formation at the 

 same temperature) are so rapidly cooled when the fire is 

 small, that the temperature which we may find in such a 

 fire is necessarily lower than that which we find in the 

 midst of a larger fire, where a greater quantity of the 

 same kind of combustible is employed. 



When a large charcoal fire is well lighted up in a close 

 stove, constructed with bricks or fire-stones, all the inte- 

 rior surfaces become excessively hot, and the heat accu- 

 mulates and becomes very intense throughout the whole 

 interior of the stove, so that iron and even stones are 

 melted in it, and flow like liquids ; but when the fire- 

 place is small, it is with difficulty that it can be heated 

 so much as to make the sides red-hot ; and if the fire- 

 place be very small, a charcoal fire cannot be kept up at 

 all, even with continual blowing. We may truly say 



