142 PHILOSOPHICAL TRANSACTIONS. [ANNO 17 Q7. 



being obliged to issue out at so small an opening as the vent, which was no more 

 than -sV of an inch in diameter, instead of giving a smart report, would come ou 

 with something like a hissing noise; and I intended, in a future experiment, to 

 confine the generated elastic fluid entirely, by adding a valve to the vent, as in some 

 of the experiments in my paper published in the 71st volume of the Philos. Trans. 

 But on setting fire to the charge, instead of a hissing noise, I was surprized by a 

 very sharp and a very loud report; and, on examining the barrel, I found the 

 vent augmented to at least 4 times it former dimensions, and both the screws 

 loosened.* 



Finding, by the result of this experiment, that I had to do with an agent much 

 more troublesome to manage than I had imagined, I redoubled my precautions. As 

 the barrel was not essentially injured, its ends were now closed up by 2 new screws, 

 which were firmly fixed in their places by solder, and a new vent was opened in the 

 barrel itself. As both ends of 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 T v 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 introduce the powder into the cham- 

 ber, 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 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 in- 

 wards, so as to leave a small vacuity between its surface and the concave surface of 

 the bore of the vent. But though all possible care was taken in the construction 

 of this instrument, to render it perfect in all its parts, the experiment was as unsuc- 

 cessful as the former: on firing the powder 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 in- 

 stead of coming out with a hissing noise, it gave a report nearly as sharp and as 

 loud as a common musket. On 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 making the experiment. 



I afterwards repeated the experiment with a simple vent, made very narrow, and 

 lined with gold, to prevent its being corroded by the acid vapour generated in the 

 combustion of the gunpowder; but this vent was found to be as little able to with- 



• This effect is nothing more than almost similar to what was experienced by Mr. Robins, viz. when 

 the bullets were placed in the gun-barrel at some distance from the charge of powder : for then it wag 

 found that the barrel was greatly enlarged, like a blown bladder, just behind the bullet. An effect ob- 

 viously produced by the elastic fluid acting there as a momentum, or percussive force. 



