THE HISTOET OE EXPLOSIVE AGENTS. 
491 
and was inflamed by means of an electric fuse placed at the bottom of the charge. A 
loud explosion was produced ; much earth was thrown up and scattered, the bottom of 
the tin case was found in the crater produced, but the body of the case was not reco- 
vered; it had evidently been projected to a considerable distance. In this experiment 
the main body of the charge obviously acts, at the moment of ignition, as tamping does 
in a blast-hole, by presenting a resistance to the escape of the gases generated, and thus 
for a moment establishing the pressure essential to the violent or perfect explosion of 
the portion of gunpowder first inflamed, whereupon the same character of explosion ex- 
tends throughout the charge. 
Mercuric fulminate furnishes still more striking illustrations of the manner in which 
the position of the source of heat, with reference to the main body of the explosive ma- 
terial to be inflamed, influences the character of the explosion. In pursuing some ex- 
periments, to be presently discussed, on the explosion of gun-cotton, I was led to com- 
pare the effects obtained by the explosion of small charges of mercuric fulminate, closely 
confined, with those produced by comparatively large quantities of that substance freely 
exposed to air. In firing the latter by means of small electric fuses, I was surprised to 
find, on the one hand, that a small quantity (0-65 grm, = 10 grains) of the fulminate 
produced occasionally a very much more violent explosion than was obtained with double 
the quantity of the same fulminate inflamed apparently in the same way, and, on the 
other hand, that equal quantities of the fulminate, successively inflamed, produced, in 
one instance, a dull report such as is well known to be furnished when flame is applied 
to a small quantity of freely exposed fulminate, while in the other instance a very sharp 
detonation was obtained, like that observed when a small quantity of closely confined 
fulminate is exploded. Believing that this remarkable difference of result might per- 
haps be caused by a variation in the force of explosion of the small electric fuse, I sub- 
stituted a platinum-wire for the latter as the inflaming agent, and still the same variable 
results were obtained. These were at first thought to be due to a variation in the sur- 
face of the fulminate heated at one time, but they were soon traced to variations in 
the position of the source of heat. T32 grm. (25 grains) and 2 - 64grms. (50 grains) of 
the fulminate, inflamed by allowing the incandescent wire just to touch the top or 
edge of the heap, exploded with a dull report, and produced no effect upon the thin 
flat plate of copper sheet upon which they rested; but about 1 grm. (15-5 grains) of the 
same fulminate, heaped up over the platinum-wire, produced a sharp and violent explo- 
sion, the force of which deeply indented and bent up the support of sheet copper. 
Equal quantities of the fulminate were made to explode feebly or detonate violently at 
pleasure, simply by varying their arrangement with reference to the position of the 
source of heat. 
A few substances, of which the metamorphosis into gaseous products and vapours, is 
developed by much less powerful impulses from without than those just instanced, the 
explosion of which is therefore determined by but little elevation of temperature or by 
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