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.