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56 INTERNATIONAL EXHIBITION, 1876. solution of potassium silicate to retard combustion, and in regulating the density by weaving it into cloth, or twisting it into ropes, to secure uniformity of action. This Austrian success led the British War Office to renew experiments; and, beginning his investigations in 1863, Mr. Abel has succeeded in so greatly improving the manu facture that gun-cotton is now recognized as the safest known ex plosive. Although not suited for use in artillery, it has been adopted by many nations for the torpedo service, and is very largely used for blasting purposes. Abel’s principal improvements consist in thoroughly pulping the gun-cotton after its treatment with the mixed acids and moulding it into disks which are strongly compressed by applying pressure ranging from four to six tons per square inch. He employs ordinary cotton-waste, instead of the expensive long staple variety adopted by Lenk; and his pulping process effectually removes all free acid, which could not certainly be done in the Austrian method of manufacture. The recent discovery that even wet gun cotton can be detonated by exploding a dry disk in contact with it, while it is absolutely safe against ordinary accidents, has largely added to the value of this new explosive. If frozen, however, it recovers its liability to detonation. It is reported that works will soon be established in the United States, under the Abel patent, with a view to introducing gun-cotton into general use here. The chemical formula of gun-cotton is C 6 H,N 3 O n . Ignited (in the form of disks) in small quantities and unconfined it burns with a strong blaze. Fired by a detonating fuse, or raised to a temperature of about 350° Fah. in a stout case, it explodes with great violence. Very recently attempts hare been made to furnish the slightly de ficient supply of oxygen by soaking in a solution of potassium nitrate or chlorate, and experiments in this direction, as well as the manu facture in a granulated form, mark the latest stages of progress. ' In practice, the detonation of all modern explosives is usually effected by the use of small initial charges of fulminates, and some very surprising facts have recently been established which go far to induce a belief that synchronism in vibration is an important element. Thus, compressed .gun-cotton may be detonated by five grains of fulminating mercury, but requires fifty grains of chloride of nitrogen, and fails with one hundred grains of iodide of nitrogen, and even with one hundred and twenty-four grains of nitro-glycerine itself, which develops far more heat and mechanical force. On the other hand, a small initial charge of gun-cotton readily detonates nitro glycerine. Fulminating mercury is usually adopted in practice for this use, to which it appears to be especially suited.
