VOL. XC.] PHILOSOPHICAL TRANSACTIONS. 65] 



not moved from its position, though it was in no ways confined. The report was 

 feeble : the bullet, Mr. Keir conceived, from the impression made on the wood, 

 had been projected with about half the force it would have been by an ordinary 

 charge, or 68 gr., of the best gunpowder. We therefore re-charged the gun with 

 34 gr. of the mercurial powder ; and, as the great strength of the piece removed 

 any apprehension of danger, Mr. Keir fired it from his shoulder, aiming at the 

 same block of wood. The report was like the first in § 4, sharp, but not louder 

 than might have been expected from a charge of gunpowder. Fortunately, Mr. 

 Keir was not hurt, but the gun was burst in an extraordinary manner. The 

 breech was what is called a patent one, of the best forged iron, consisting of a 

 chamber 0.4 of an inch thick all round, and 0.4 of an inch in caliber ; it was torn 

 open and flawed in many directions, and the gold touch-hole driven out. The 

 barrel, into which the breech was screwed, was 0.5 of an inch thick ; it was split 

 by a single crack 3 inches long ; but this did not appear to me to be the imme- 

 diate effect of the explosion, I think the screw of the breech, being suddenly en- 

 larged, acted as a wedge on the barrel. The ball missed the block of wood, and 

 struck against a wall, which had already been the receptacle of so many bullets, 

 that we could not satisfy ourselves about the impression made by this last. 



§ 6. As it was pretty plain that no gun could confine a quantity of the mercu- 

 rial powder sufficient to project a bullet, with a greater force than an ordinary 

 charge of gunpowder, I determined to try its comparative strength in another way. 

 I procured 1 blocks of wood, very nearly of the same size and strength, and 

 bored them with the same instrument to the same depth. The one was charged 

 with 4/ oz. of the best Dartford gunpowder, and the other with 4. oz. of the mer- 

 curial powder ; both were alike buried in sand, and fired by a train communicating 

 with the powders by a small touch-hole. The block containing the gunpowder 

 was simply split into 3 pieces : that charged with the mercurial powder was burst 

 in every direction, and the parts immediately contiguous to the powder were abso- 

 lutely pounded, yet the whole hung together, whereas the block split by the gun- 

 powder had its parts fairly separated. The sand surrounding the gunpowder was 

 undoubtedly most disturbed: in short, the mercurial powder appeared to have 

 acted with the greatest energy, but only within certain limits. 



§ 7. The effects of the mercurial powder, in the last experiments, made me 

 believe that it might be confined, during its explosion, in the centre of a hollow 

 glass globe. Having therefore provided such a vessel, 7 inches in diameter, and 

 nearly half an inch thick, mounted with brass caps, and a stop cock, (see pi. 11, 

 fig. l), I placed 10 gr. of the mercurial powder on very thin paper, laid an iron 

 wire 149th of an inch thick across the paper, through the midst of the powder, 

 and, closing the paper, tied it fast at both extremities, with silk, to the wire. As 

 the inclosed powder was now attached to the middle of the wire, each end of 

 which was connected with the brass caps, the packet of powder became, by this 

 disposition, fixed in the centre of the globe. Such a charge of an electrical bat- 



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