1824.] On the Heat produced by firing Gunpowder, fyc. 245 



but what the ingredients may be that have escaped detection, I 

 must leave to future experiments, if hereafter I may obtain a 

 larger supply of the crystals, to determine. J. G. C. 



P. S. From some very indecisive appearances that occurred 

 in the examination of the globule with salt of phosphorus, I am 

 inclined to think that alumina or silica, or both, may be consti- 

 tuent parts of the crystals ; but I have no means of confirming 

 or disproving the conjecture. 



Article II. 



On the Heat produced by "firing Gunpowder, and on the intense 

 Heat of Blast-furnaces. By W. T. Haycraft, Esq.* 



The following explanations on these subjects are suggested 

 by Mr. Haycraft, towards the conclusion of his paper on the 

 " Specific Heat of Gases." 



The increased capacity of air, when under lesser degrees of 

 atmospheric pressure, has been properly made use of to explain 

 the extreme cold which exists in high regions ; and its decreased 

 capacity under mechanical pressure also satisfactorily accounts 

 for the "heat evolved under that condition. This principle, so 

 far as I know, has not been used to explain one cause of the 

 intense heat produced during the combustion of gunpowder and 

 other explosive mixtures. If we reflect a moment, however, we 

 shall perceive that the resistance of the pressure of the atmo- 

 sphere to the expansion of the nascent gases produced by the 

 combustion, will cause them to exist in a state of greater den- 

 sity than when the resistance of the atmosphere has been finally 

 overcome. It is during this state of potential compression, if I 

 may use the term, that the intense heat is produced. After the 

 first explosion, however, the gaseous products will expand, and 

 then there will necessarily be absorption of caloric, and conse- 

 quently comparative coldness produced. In order to ascertain 

 whether there is a permanent evolution of caloric, occasioned by 

 the combustion of gunpowder, I made the following experiment. 



Having a receiver containing 528 cubic inches, filled with 

 water of a temperature of 52°, placed in a pneumatic trough, 

 the surrounding atmosphere being also 52°, I introduced 240 

 inches of the aeriform fluids, produced during the combustion of 

 that composition of gunpowder which is used for pyrotechnical 

 purposes. After the explosion, the gas in the upper part of the 

 receiver had acquired a temperature of nearly 54°, and the water 

 not so much. This experiment shows that though heat is 



• From the Transactions of tlic Royal Society of Edinburgh, 



