226 Count Rumford’s Experiments to determine 
the barrel were now closed up, it was necessary, in order to 
introduce the powder into the chamber, to make it pass through 
the vent, or to convey it through some other aperture made 
for that purpose. The method I employed was as follows : a 
hole being made in the barrel, about of an inch in diameter, 
a plug of steel was screwed into this hole ; and it was in the 
centre or axis of the plug that the vent was made. To intro- 
duce the powder into the chamber the plug was taken away. 
The vent was made conical, its largest diameter being inwards, 
or opening into the chamber ; and a conical pin, of hardened 
steel, was fitted into it ; which pin was intended to serve as a 
valve for closing up the vent, as soon as the powder in the 
chamber should be inflamed. To give a passage to the fire 
through the vent in entering the chamber, this pin was pushed 
a little inwards, so as to leave a small vacuity between its sur- 
face and the concave surface of the bore of the vent. But not- 
withstanding all possible care was taken in the construction of 
this instrument, to render it perfect in all its parts, the expe- 
riment was as unsuccessful as the former : upon firing the pow- 
der in the chamber, (though it did not fill more than half its 
cavity), the generated elastic fluid not only forced its way 
through the vent, notwithstanding the valve (which appeared 
not to have had time to close), but it issued with such an 
astonishing velocity from this small aperture, that instead of 
coming out with a hissing noise, it gave a report nearly as 
sharp and as loud as a common musket. Upon examining 
the vent-plug and the pin, they were both found to be much 
corroded and damaged ; though I had taken the precaution to 
harden them both before I made the experiment. 
I afterwards repeated the experiment with a simple vent, 
