FULMINATING ME11CURT. HJl 



needle, is to be drawn through (he hole. The screw being nor 

 fixed in its place, and the wire drawn tight, is to be secured by 

 pushing the irregular wooden plug into the aperture of the screw, 

 taking care to leave a passage for the air. The stop. cock is now to 

 be screwed on. The glass tube is bent, that it may more conve- 

 niently be introduced under the receiver of a pneumatic apparatus. 

 "Fromsomeoftheexperirnents (continues Mr. Howard) in which 

 the gunpowder proof and the gun were burst, it might be inferred, 

 that the astonishing force of the mercurial powder is to be attributed 

 to the rapidity of its combustion ; and a train of several inches in 

 length being consumed in a single flash, it is evident that its combus- 

 tion must be rapid. But from other experiments it is plain that this 

 force is restrained to a narrow limit, both because the block of wood 

 charged with the mercurial powder was more shattered than that 

 charged with the gunpowder, whilst the sand surrounding it was least 

 disturbed, and likewise because the glass globe withstood the explo- 

 sion often grains of the powder fixed in its centre; a charge I had 

 twice found sufficient to destroy old pistol barrels, which were not 

 injured by being fired when full of the best gunpowder. It also 

 appears from the last experiment, that ten grains of the powder 

 produced by ignition four cubical inches only of air; and it is not 

 to be supposed that the generation, however rapid, of four cubical 

 inches of air, will alone account for the described force ; neither 

 can it be accounted for by the formation of a little water, which, 

 as will hereafter be shewn, happens at the same moment; the 

 quantity formed from ten grains must be so trifling, that I cannot 

 ascribe much force to the expansion of its vapour. The sudden 

 vaporation of a part of the mercury seems to me a principal cause 

 of this immense yet limited force; because its limitation may then 

 be explained, as it is well known that mercury easily parts with ca- 

 loric, and requires a temperature of 600 of Fahrenheit, to be 

 maintained in the vaporous state. That the mercury. is really con. 

 terted into vapour, by ignition of the powder, may be inferred 

 from the thin coat of divided quicksilver, which, after the explo- 

 sion in the glass globe, covered its interior surface; and likewise 

 from the quicksilver with which a tallow candle, or a piece of gold, 

 may be evenly coated, by being held at a small distance from the 

 inflamed powder. These facts certainly render it more than pro- 

 bable, although they do not demonstrate that the mercury is Tola, 

 tilued; because it is not unlikely that many mercurial particles 



