THE HISTOEY OF EXPLOSIVE AGENTS. 
503 
path of a solid mass which is set into very rapid motion. In other words, a detonation 
exerts a mechanical effect upon resisting bodies precisely similar to that of a blow, as 
from a falling hammer or a projectile propelled from a gun. Just as the force of a 
sufficiently sudden or powerful blow from a hammer is transformed into heat by the 
resistance to the motion of the hammer which the particles of an opposing body present, 
and by the consequent friction established between those particles, so the force or con- 
cussive action exerted by the matter set in motion when a solid or liquid is converted 
into gas or vapour, will also be transformed into heat, the development of which in an 
opposing body will he proportionate to the resistance to motion which its particles offer, 
and to the suddenness and violence of the concussion to which it is subjected. 
The power of accomplishing the explosion or detonation of gun-cotton or nitro- 
glycerine in open air through the agency of a detonation produced in its vicinity, would 
therefore appear to be correctly ascribable to the heat suddenly developed in some 
portion of the mass by the mechanical effect, or blow, exerted by that detonation, and 
would seem to be regulated by the violence and suddenness (either singly or combined) 
of the detonation, by the extent to which the explosive material is in a condition to 
oppose resistance to the force, and by the degree of sensitiveness of the substance to 
explosion by percussion. 
The following points appear to support this view : — 
1. Gun-cotton, freely exposed, cannot be detonated by any explosive agent less sudden 
and violent in its action than mercuric fulminate. Explosive mixtures (such as percus- 
sion-cap composition, see page 498, and mixtures of potassic chlorate with potassic 
pierate, &c.) which are apparently but little inferior to the fulminate in the rapidity of 
their explosive powers, will not detonate gun-cotton even though confined charges of 
them, amounting to about ten times the quantity of mercuric fulminate required to 
produce the effect with perfect certainty, are employed. 
2. On the other hand, nitroglycerine, which is much more readily exploded by a blow 
than gun-cotton, may be detonated through the agency of explosive mixtures less violent 
and sudden in their action than the fulminate. A quantity of percussion-cap composi- 
tion, about one-half that of the minimum of fulmiiiate required to detonate gun-cotton, 
will suffice to detonate nitroglycerine. 
3. If the suddenness of the detonation produced by means of mercuric fulminate be 
•increased, as described at page 490, by its confinement in a strong envelope, a very much 
smaller quantity suffices to develope the detonation of gun-cotton than if the fulminate 
be exploded in open air, or in an envelope which offers but slight initial resistance. 
4. The mechanical condition of the gun-cotton most materially influences the result 
obtained by its exposure to detonation. A considerable compactness or density, and a 
consequently great resistance to motion of the particles, is essential for the detonation 
of gun-cotton, as pointed out at page 497. 
There are, however, several well-known facts, and some results of experiments insti- 
tuted with special reference to this subject, which do not appear to be in harmony with 
the assumption that the detonation of nitroglycerine and gun-cotton in the manner 
