502 
ME. E. A. ABEL’S CONTEIBUTIONS TO 
the support. If, however, the latter be of iron, which does not yield permanently to the 
blow of the hammer, the detonation of these substances is readily accomplished. If the 
quantity of explosive agent employed be so considerable as to form a thick layer between 
the hammer and support, the force applied appears to be to so great an extent absorbed 
in the motion imparted to the particles of the compressible mass, that its explosion is 
not readily accomplished ; and if the material be in a loose or porous condition (as, for 
example, in a state of powder or of loose wool), much work has to be accomplished in 
moving particles of the mass through a comparatively considerable space, and a second 
or even third blow is therefore required to determine its explosion. 
These circumstances would appear to afford support for the belief that the detonation 
of an explosive material through the agency of a blow is the result of the development 
of heat, sufficient to establish energetic chemical change, by the expenditure of force in 
the compression of the material, or by the friction of the particles against each other, 
consequent upon a motion being momentarily imparted to them. It is conceivable 
that, from either of these causes, sufficient heat may be accumulated with almost 
instantaneous rapidity, in some portion of the mass struck, to develope sudden chemical 
change*. The circumstance, that the detonation of those portions of an explosive 
compound (such as gun-cotton or nitroglycerine) which are immediately between the 
surfaces of the hammer and the support is not communicated to the surrounding por- 
tions, may be ascribed to a combination of two causes, the instantaneous nature of the 
explosion, and the close confinement of the portions struck at the instant of their 
explosion. The mechanical effect of the detonation is absorbed by the masses of metal 
between which it occurred, and the gases developed disperse the surrounding portions 
of the explosive agent, as they rush away from between the two surfaces. It is possible 
also to detonate gunpowder and other explosive mixtures by a blow in such a manner 
that only the portions immediately struck are ignited ; but those substances may also 
be exploded, though much less violently, by a less sudden or powerful application of 
force, in which case they detonate much more feebly ; their explosion is accompanied 
by a larger volume of flame, and by the ignition of those portions which surround the 
part struck by the hammer. 
The exceedingly violent motion of particles resulting from the sudden or extremely 
rapid transformation of a solid or liquid explosive body into highly expanded gas or 
vapour, must obviously exert a force which operates upon a resisting body, in the 
vicinity, in a manner precisely similar to the force applied by opposing a body in the 
* In illustration of the effect of friction of particles of a mass against each other in determining the develop- 
ment of an explosion, the following experiment may be quoted. A very porous pellet of a mixture of potassic 
chlorate and amorphous phosphorus (carefully purified from ordinary phosphorus) was placed between two 
polished metal plates, and a somewhat rapidly accumulating pressure was then applied ; the mass exploded 
almost directly, before, in fact, sufficient force had been expended to convert the loose aggregate of particles 
into a compact mass. A second similar pellet, also placed between two polished surfaces, was submitted to 
pressure very gradually and carefully applied, and was thus converted into a compact mass without being 
exploded ; on afterwards submitting this to rapidly increasing pressure precisely as in the first experiment, a 
much more considerable accumulation of force was required to accomplish the explosion of the mass. 
