152 PHILOSOPHICAL TRANSACTIONS. [[ANNO \7Qfl. 



considerably heated in these experiments. Was this occasioned by the caloric, dis- 

 engaged from the powder in its combustion, making its escape through the iron ? 

 And is this a proof of the existence of caloric, considered as a fluid sui generis ; and 

 that it actually enters into the composition of inflammable bodies, or of pure air, 

 and is necessary to their combustion ? I dare not take upon me to decide on such 

 important questions. I once thought that the heat acquired by a piece of ordnance 

 in being fired, arose from the vibration or friction of its parts, occasioned by the 

 violent blow it received in the explosion of the powder ; but I acknowledge fairly, 

 that it does not seem to be possible to account in a satisfactory manner for the very 

 considerable degree of heat which the barrel acquired in these experiments, merely 

 on that supposition.* 



That this hard substance, found in the barrel after an experiment in which the 

 generated elastic vapour had been completely confined, was actually in a fluid or 

 elastic state in the moment of the explosion, is evident from hence, that in all those 

 cases in which the weight was raised, and the stopper blown out of the bore, no- 

 thing was found remaining in the barrel. It was very remarkable that this hard 

 substance was not found distributed about in all parts of the barrel indifferently, but 

 more of it was always found near the middle of the length of the bore, than at 

 either of its extremities ; and the upper part of the vent tube in particular was 

 always found quite filled with it. It should seem from hence, that it attached it- 

 self to those parts of the barrel which were soonest cooled ; and hence the reason, 

 most probably, why none of it was ever found in the lower part of the vent-tube, 

 where it was kept hot by the red-hot ball by which the powder was set on fire. 



I found by a particular experiment, that the gunpowder employed, when it was 

 well shaken together, occupied rather less space in any given measure, than the 

 same weight of water ; consequently, when gunpowder of this kind is fired in a 

 confined space which it fills, the density of the generated elastic fluid must be at 

 least equal to the density of water.-f~ The real specific gravity of the solid grains of 

 gunpowder, determined by weighing them in air and water, is to the specific gravity 

 of water, as 1.868 to l.OOO. But if a measure, whose capacity is 1 cubic foot, 

 hold 1000 ounces of water, the same measure will hold just 1077 ounces of fine 

 grained gunpowder, such as was employed in these experiments ; that is to say, 

 when it is well shaken together. When it was moderately shaken together, its 

 weight was exactly equal to that of an equal volume, or rather measure, of water. 

 But it is evident that the weight of any given measure of gunpowder, must depend 

 much on the forms and sizes of its grains. I shall add only one observation more, 

 relative to the particular appearances which attended the experiments in which the 



* It seems probable however, that the heat may be accounted for on this principle, as, from the con- 

 fined state of the barrel, the shock from the explosion must be sudden and extremely great.— + Not so : 

 because only a part of the composition of powder, (about -J), is changed into an elastic fluid. So that 

 the density of the fluid is but about \ of the density of water. 



