Cy sag.) Hustory of Detonating Agents. 187
—_y ie er eS ~
: | ‘nflamed by the heat developed where the fulminate is de-T
 H E C H E M I C A L N E Ww S ‘onated, a result which is obtained with greater certainty
: = he less violent the detonation produced by the fulminate
:harge, If, however, the gun-cotton be converted into a
:ompact form, either by ramming the wool or thread very
tightly into a case, or better still, by reducing the guncotton
 fibre to a very fine state of division, and compressing
it, when in that condition, into compa& masses, it becomes
susceptible of detonation by the initiative a&ion of mersuric
 fulminate, and the quantity of the latter required to
ring about detonation is small (down to the limit which
1as been named above) in proportion as the compa&ness
or density of the compressed material is increased.
Detonation, when established in compressed gun-cotton,
's transmitted with great velocity throughout the mass, as
already stated, or from one to another of contiguous
nasses, laid out in long rows, and even, though at a
‘educed rate, if small spaces exist between the individual
nasses. But, if a small mass of compressed gun-cotton
reely exposed to air be detonated when in immediate con-:a@
 with gun-cotton wool or loosely twisted yarn, the
letonation will not be transmitted to these, but they will
merely be scattered and perhaps inflamed.
The difference in the behaviour of nitro-glycerin and of
zun-cotton when presented to the ation of a so-called
nitiative detonation under the different conditions spoken
of above, admits of ready explanation.
[t was established, in the first instance, that the aéion
of an initiative detonation is not ascribable to the heat
leveloped within the detonating material itself in underjoing
 chemical metamorphosis. If it were so, the deto-1ating
 mixture known as percussion-cap composition and
sther explosive mixtures, the detonation of which is
ittended by much greater development of heat than is
sbtained by the action of pure mercuric fulminate, should
letonate gun-cotton more readily than the latter does,
whereas very much larger quantities of such materials are
required to attain that result. Moreover, the readiness
with which gun-cotton is detonated should be solely prosortionate
 to the amount of fulminate used, which has
seen shown not to be the case; and gun-cotton should be
nore readily detonated when in the loose and open conlition
 than in the highly compressed or compa& form,
secause the latter presents it in the condition least favour
ible, and the former in that most favourable, to ready and
rapid transformation by heat. Again, the actual temperaure
 required for the explosion of nitro-glycerin is very
considerably above the exploding temperature of gun-:otton,
 yet a very much smaller charge is required for the
letonation of nitro-glycerin than is needed for the detonadon
 of gun-cotton, On the other hand, a quantity of
confined percussion-cap composition which, if it were pure
mercuric fulminate, would be altogether inadequate for
the detonation of gun-cotton, suffices for the detonation
of nitro-glycerin.
The action of an initiative detonation has already been
zompared to that of a blow from a hammer or falling
weight. The readiness and certainty with which gun.
powder, gun-cotton, and other explosive agents are detoated
 by the latter agency are regulated by several circumstances;
 they are in dire& proportion to the weight of the
‘alling body, to the height of its fall, and to the force with
which it is impelled downwards; to the velocity of its
motion; tothe mass and rigidity or hardness of the support
upon which the substance to be detonated rests; lastly, to
the quantity and mechanical condition of the explosive
agent struck, and to its sensitiveness,
Gunpowder is much more readily detonated by a sharp
blow from a small hammer than by the simple fall of a
heavy hammer, or by a comparatively weak blow from the
latter. It is very difficult by repeated blows, applied at
very brief intervals, to detonate gun-cotton if placed upon
1 support of wood or lead, both of which materials yield
to a blow, the force applied by that blow being transferred
_hrough the explosive agent and absorbed in work done
pon the material composing the support. But if the latter

Vor. XXXIX, No, 1014.