410 On the Heat developed in Combustion 



instant when it is formed, is sufficient to raise the tem- 

 perature of i pound of water 10,063 degrees. 



If the capacity of the steam for heat was equal to that 

 of liquid water, it is very certain that the temperature 

 of the vapour at the instant of its formation would be 

 that of 10,063 F. 



In order to form an idea of this degree of intensity, 

 we may compare it to an intensity of heat which is 

 known. 



A piece of iron heated until it becomes red even in 

 daylight has then the temperature of 1000 F. ; con- 

 sequently the temperature of the steam at the instant 

 of its formation would be ten times higher than that of 

 red-hot iron : but as, according to Crawford, the capa- 

 city of the steam for heat is greater than that of water 

 in the proportion of 1.55 to i, the temperature in ques- 

 tion will be less than that of 10,063 in the same pro- 

 portion. It will therefore be equal to 8750 F. 



Here, therefore, is the limit of the intensity of the 

 heat in the midst of the greatest fire, in which pure 

 hydrogen would be employed as a combustible, and in 

 which the fire would be fed by pure oxygen. This is an 

 intensity which we may approach more or less, but which 

 we can never attain. 



As Wedgwood's pyrometer indicates much higher 

 temperatures, it seems demonstrated by the result of 

 this calculation that the scale of this pyrometer is faulty. 

 These doubts have been stated by other chemists. 



But in order to decide definitively upon this inter- 

 esting question, it would be indispensably necessary to 

 know accurately the capacity of steam for heat at different 

 temperatures ; a thing unknown, and which is difficult to 

 determine. 



