At the head of the list of deadly explosives must of course be placed
gunpowder, which is so well known that nothing needs to be said
regarding it. Interest attaches to recent inventions, still as it
were in their infancy. The most important of these new explosives is
gun-cotton, a substance of most peculiar nature and properties. It is
prepared by immersing cotton-waste (previously rendered chemically
clean) in a mixture of nitric and sulphuric acid—the latter acid
merely acting as a mechanical aid to the former. The cotton is
afterwards thoroughly washed, reduced to a pulp, and finally dried
and compressed into slabs or discs; the last operation being the only
process throughout its manufacture which is attended with danger.
Even where the greatest precautions are taken, the constant handling
of a dangerous substance with impunity will sooner or later lead to
carelessness, or at anyrate to forgetfulness of its terrible character.
The disastrous explosion some years ago at the large gun-cotton works
at Stowmarket, where the most stringent rules for the common safety
were in force, is an illustration of this. It is needless to dwell upon
the impossibility of tracing the immediate cause of such a fatality—the
guilty hand being of course one of the first to suffer the dread
penalty.
It is a curious peculiarity of gun-cotton that the intensity of its
action depends upon the manner in which it is ignited. A smouldering
spark will induce it to smoulder also; a flame will cause it to go
off in a feeble puff; but a detonating fuse will, as it were, enrage
it, causing it to explode with a force ten times that of gunpowder.
Gun-cotton is not adapted for the rifle, where extreme uniformity of
combustion is one of the conditions of accurate shooting; but it can
be used for sporting purposes, provided that the risk of frictional
ignition in ramming home be obviated by the use of a breech-loading
gun. Its force can, by dilution with pure cotton or other inert
substance, be brought more to the level of gunpowder, but only at the
sacrifice of those good qualities, such as freedom from smoke and
reduction of fouling, which really constitute the chief advantages of
its use. It is, we believe, used exclusively for charging torpedoes;
and a suggestion has been thrown out that it might also be used with
great advantage in savage warfare for the destruction of palisades and
defences of a similar kind, in dense jungle impenetrable by artillery.
The next explosive in order of usefulness is nitro-glycerine, to make
which, ordinary glycerine is acted upon (as in the case of gun-cotton)
with nitric and sulphuric acid. It has the appearance of a yellow
oil, insoluble in, and heavier than water. The many accidents which
have occurred from its use seem to be due to some decomposing quality
which it possesses, and which at present is little understood. Unlike
gunpowder, it burns harmlessly away when a flame is applied to it;
but when heated to the temperature of boiling water, its explosive
force is most violent. Many means have been suggested for rendering
it less liable to spontaneous explosion, for in its crude state it
cannot be stored away with any security for its good behaviour. The
most successful plan is to mix it with a particular kind of porous
earth, under which transformation it is known as ‘dynamite.’ On taking
this solid form, it will bear comparatively rough usage, while its
violent character is in no way diminished. Our readers will perhaps
remember that dynamite was the agent used in that terrible explosion
at Bremerhafen, which cost so many lives and such destruction of
property. With fiendish ingenuity it was placed in a case together with
a clockwork apparatus calculated to explode a fuse in a given time; the
object of the crime being to secure the money for which the steamer
that was to carry the terrible burden had been insured. By an error of
calculation the explosion happened, with the most awful consequences,
before the package had been removed from the quay. The practicability
of employing dynamite under water has lately been demonstrated in a
very shameful manner by a wholesale destruction of fish by its aid. The
righteous indignation of all true anglers will most probably find vent
in stopping without delay such a barbarous practice. Lithofracteur is
the name of another preparation of nitro-glycerine, so like dynamite in
its general properties that we need not further allude to it.
A totally different class of explosives from those which we have
previously considered, are the fulminates of the different metals.
They are chiefly used diluted with some other matter (such as ordinary
gunpowder) for the priming of percussion caps, and for the detonating
fuses which play so important a part in the firing of mines, &c. The
manner of accomplishing this by the ignition of an electric fuse is,
in its neatness and freedom from danger, a great contrast to the old
system, where the operator had to light a slow-match, and take to
his heels until distance had lent more enchantment to his position.
Undiluted, the fulminates are almost useless, for the touch of a hair
is sometimes sufficient to explode them; and when fired, their power is
of the most terrible character. There are many other compounds which,
on account of their uncontrollable nature, are of no practical value,
and are never prepared except for purposes of experiment.
It will perhaps now be understood that although there is a family
likeness between the various mixtures which we have mentioned, their
individual behaviour is most unlike. It therefore becomes necessary in
dealing with any one of them to consider first for what particular use
it is required. It is possible, for instance, to charge a shell with
an explosive which has the power of reducing it to tiny fragments; a
result which would of course almost nullify its effect. It is sometimes
perhaps necessary to throw dust in the eyes of an enemy, but certainly
not in a sense so literal as this. Again, many compounds would cause a
shell to burst with the concussion it receives when blown from the gun;
and thus prove more destructive to friends than foes. Such an accident
is next to impossible with either gunpowder or cotton. The latter is
employed with very startling results in combination with water in the
so-called water-shells. A very small charge of compressed gun-cotton
is placed in a shell, the remaining space being filled with water.
In practice it is found that a shell so charged explodes into eight
times as many fragments as it will when _filled_ with gunpowder in the
ordinary way. The effects of gun-cotton are different from those of
powder, in that it exerts a sudden splitting power. The blasting of
rocks, for instance, is often commenced with the former, which splits
the mineral into cracks and fissures. These cracks are afterwards
filled with powder, which detaches huge masses from their beds with a
lifting power of which gun-cotton alone, is incapable.
Many plans have at various times been proposed to render explosives
harmless during manufacture and transport. The suggestion of mixing
pulverised glass with gunpowder is effective in separating mechanically
the grains, and so preventing the initial flash from penetrating
beyond the particular ones submitted to inflammation. In consequence,
probably, of the exposure entailed in the mixing as well as during
the subsequent process of sifting out the glass before the powder
can be used, the process has not attained any practical importance.
Gun-cotton, on the other hand, by being saturated with water is
rendered quite inert; the subsequent process of removing the excess of
moisture being free from danger. Special conditions are necessary to
its explosion in a damp state, conditions not easily brought about by
mere accident. Dr Sprengle has suggested several powerful explosives
which claim the advantage of safety, for their constituents are
harmless in themselves, and need not be blended until they are actually
required for use. Concerning Schultz’s wood-powder we may perhaps have
a few words to say in a future paper.
Before quitting our subject it will be in some measure a relief
to reflect that the things of which we have spoken are not wholly
dedicated to bloodshed. Besides their use in our mines and quarries,
whereby an incalculable amount of manual labour is dispensed with,
many of them are in constant requisition for the demolition of old
structures, such as the piers of bridges, and for the removal of
submarine structures of all kinds. In the excavations for the Suez
Canal, gunpowder was largely used; and many other engineering schemes
owe their ready accomplishment to the employment of a like agent.
The greatest recorded undertaking of the kind is the destruction in
1876 of the Hellgate rocks, which formed such a dangerous obstruction
to navigation in East River, New York. No less than sixty thousand
pounds of dynamite were consumed on this occasion, the watery field of
operation covering about three acres. Some years had been previously
employed in making the necessary excavations for the reception of the
cartridges, which were eventually fired by an electric battery of one
thousand cells. The results gained quite surpassed the most sanguine
expectations of the engineers engaged, and other obstructions in
neighbouring rivers are shortly to receive similar treatment. Some
of the good people of New York were terribly agitated at the thought
even of the contemplated scheme, and left the city with the firm
conviction that they would return only to find it in ruins. But the
fair city still exists unharmed—with the advantage of a much-improved
tideway—and the good folk alluded to are forced to acknowledge that
their prognostications of evil have ended in smoke.