the Force of fired. Gunpowder. 247 
away, the length of the barrel was of course diminished as 
much as the thickness of this plate amounted to, which was 
about part of an inch ; but in order that even this small 
diminution of the length of the barrel might have no effect on 
the results of the experiments, its bore was deepened of an 
inch when this plate was removed, so that the capacity of the 
bore remained the same as before. 
After making use of a great variety of expedients, the best 
and most convenient method of closing the end of the bore, 
and defending the flat surface of the steel hemisphere from the 
corroding vapours, was found to be this ; first, to cover the end 
of the bore with a circular plate of thin oiled leather, then to 
lay upon this a very thin circular plate of hammered brass, and 
upon this brass plate the flat surface of the hemisphere. When 
the elastic fluid made its escape, a part of the leather was con- 
stantly found to have been torn away, but never in more places 
than one ; that is to say, always on one side only. 
What was very remarkable in all those experiments in which 
the generated elastic vapour was completely confined, was the 
small degree of expansive force which this vapour appeared to 
possess after it had been suffered to remain a few minutes, or 
even only a few seconds, confined in the barrel; for, upon rais- 
ing the weight by means of its lever, and suffering this vapour 
to escape, instead of escaping with a loud report, it rushed out 
with a hissing noise hardly so loud or so sharp as the report 
of a common air-gun ; and its efforts against the leathern 
stopper, by which it assisted in raising the weight, were so 
very feeble as not to be sensible. Upon examining the barrel, 
however, this diminution of the force of the generated elastic 
fluid was easily explained ; for what was undoubtedly in the 
