490 
ME. E. A. ABEL’S CONTEIBITTIONS TO 
by enclosing it in an envelope or bag of paper, or in a vessel of which the opening is 
loosely closed, the escape of heat is impeded until the gases developed can exert suffi- 
cient pressure to pass away freely by bursting open the envelope or aperture, and the 
result of the more or less brief confinement of the gases is a more rapid or violent ex- 
plosion, and consequently more perfect metamorphosis of the gun-cotton. So, within 
obvious limits, the explosion of gun-cotton by the application of flame or any highly 
heated body is more perfect in proportion to the amount of resistance offered in the 
first instance to the escape of the gases; in other words, in proportion as the strength of 
the receptacle enclosing the gun-cotton, and the consequent initial pressure developed by 
the explosion, is increased. Hence, while gun-cotton has been found too rapid or 
violent in its explosive action when confined in guns, and has proved a most formidable 
agent of destruction if enclosed in metal shells or other strong receptacles, it has hitherto 
been found comparatively harmless as an explosive agent if inflamed in open air or 
only confined in weak receptacles. 
Other explosive compounds, and also explosive mixtures, are similarly influenced, 
though generally not in such various ways, by the circumstances attending their meta- 
morphosis. Thus the rapidity of the explosion of gunpowder is modified by variations 
in its density and state of division, and in the ^degree of facility afforded for the escape 
of the generated gases, and consequently of the heat which is disengaged during the 
explosion. Mercuric fulminate may be inflamed in open air upon a piece of very thin 
sheet metal without indenting it, and furnishes under these circumstances a compara- 
tively feeble explosion ; but if even a very much smaller quantity be enclosed in a case 
or receptacle made of the same description of sheet metal, the latter will be shattered 
into many pieces when the fulminate is inflamed, and the explosion will be attended 
by a violent report. 
Modifications, apparently slight, of the manner in which the source of heat is applied to 
these explosive agents, when exposed to air under circumstances in other respects uniform, 
suffice to modify the character of their explosions in a remarkable manner. Thus a modi- 
fication of the position in which the source of heat is placed with reference to the body of 
a charge of gunpowder, which is only partially confined, suffice to alter altogether the 
character of the explosion produced. This is illustrated by the following experiment. 
A cylindrical case of sheet tin, 2 5 inches diameter, 6 inches long, and open at one 
end to its full diameter, was inserted up to its opening in stiff clay soil, which was 
tightly rammed round it. The cylinder was filled with fine-grain gunpowder (about 1 lb.), 
and the charge was inflamed by means of a small electric fuse inserted just beneath the 
exposed surface of powder. The latter burned with a violent rushing sound, similar to, 
only of much less duration than that produced by the first ignition of a rocket, and indi- 
cating a rapidly successive ignition of layers of the powder. The canister was split open 
in. the soldered seam, but was not thrown out of the hole. A small quantity of earth 
was thrown up, but fell back into the hole. A second corresponding charge of gun- 
powder was arranged in precisely the same manner as in the preceding experiment, 
