The one great cause of this and other barrels bursting, arises from the velocity becoming too great, and thus driving back the air upon itself, until the mutual repulsion of the particles forms an almost impenetrable barrier, exerting a lateral pressure on the barrel, and resisting the passage of the elastic fluid. To make the explanation plain; supposing that the charge had condensed the air for the distance of three or four inches immediately preceding it, and then come to rest, the waves of vibration, travelling at the rate of 1,300 feet per second, would communicate to the remainder of the column the same pressure, and an equilibrium would take place. But this not being the case, and the air becoming still more highly compressed by the velocity not decreasing but increasing, the lateral pressure becomes greater than the fibres of the iron are able to withstand, and consequently the barrel is burst. Many accidents arise from this cause solely, and without any blame being attached to either the maker or user of the gun. While on this subject, we may remark that this is the more likely, inasmuch as the powder with which barrels are proved is not the strongest, and is also of a large grain; so that it is quite within the range of probability that a barrel may, and it does often, stand proof, and yet burst when it comes to be used with extremely fine-grained strong powder; as it is quite clear that a high velocity must create danger.
To pursue the subject still further: in order to procure conclusive evidence in support of this argument, I had a tube of iron manufactured, sufficiently good in quality to bear an enormous pressure; it was three feet in length, with a bore large enough to admit an ounce ball, and the sides of the arch were full a quarter of an inch in thickness. A piece of steel, one inch in length, was then turned of a size to fit the bore well, but not so tight as to prevent its free action: this I called a piston. From the centre of the tube to the muzzle, were drilled, on all sides, a number of small holes, a quarter of an inch distant from each other, in all amounting to sixty-eight; these were fitted with small pieces of steel needles, hardened, projecting into the interior of the tube a quarter of an inch, so that the piston, in its upward movement, should strike these pins, and thus enable me to judge how far it was driven by each experiment. Each end of the tube was then fitted with a breech, firmly screwed in; the upper one having a flat internal surface, the lower one, where ignition was to be communicated, being a conical or patent breech. This machine I termed an explosion metre; and it answered its purpose. With two drachms of the best canister gunpowder, the piston was propelled nineteen inches along the tube; breaking eight pins. The same quantity of the fine diamond grain reached only eighteen inches, or four pins. No. 3 grain, of both Laurence’s and Pigou and Wilks’ manufacture, reached twenty-four inches, or twenty-eight pins. A very superior powder, containing in one grain five of diamond, four of canister, and two of the above makers’ No. 2, reached twenty-seven inches, and broke forty pins. In each of these experiments the greatest accuracy was observed, in preparing the metre as well as in weighing the charge.
These facts go far to prove that, in all uses of gunpowder, the grain should be of a size proportioned to the length and bore of the gun; for if we have not an accelerating force to overcome the increasing resistance of the compressed column of air in the barrel, there is great danger that the gun may be burst, and probably be productive of great mischief; whilst a judicious application of the extraordinary power thus placed at our disposal, may be alike conducive to our safety and our pleasure. A musket ball can be driven through an half-inch boiler plate; but this can only be accomplished by using as much powder as will generate a gradually, though rapidly, increasing power, until the ball has passed the limits of the tube.
Nitre is not the only salt which has been employed in the manufacture of gunpowder. Its quantity or proportion in the mixture has been lessened, and the deficiency supplied by another elementary combination; namely, by the chlorate of potassa.
The French succeeded in making powder of which potassa forms one of the component parts, and they say it ranges the projectile double the distance; but this is doubtful. The proportions of the mixture are nitrate of potash twenty-five parts, chlorate of potassa forty-five, sulphur fifteen, charcoal seven and a half, and lycopodium seven and a half parts. In the year 1809, a similar kind of powder was proposed to the English Government, by a person of the name of Parr; but its introduction was very properly opposed by Sir William Congreve, on account of the danger attending its use, and also from the fact that there was no piece of ordnance in the service able to withstand its effects. The proportions were, chlorate of potassa six parts, fine charcoal one part, sulphur one part. These ingredients to be carefully mixed together and granulated. The above mixture was laid aside, not only from the want of power to restrain its effects, but because it was useless, from the very extreme rapidity of its explosion: it forms the atmospheric air into a wall of adamant, by the condensation confining it to a comparatively small space; it becomes lightning—an electric fluid, which, from its very intensity, cannot displace any great mass of air.
Neither can any advantage arise from any greater velocity in projectile force, except we can obtain that by a graduated scale; for masses cannot, from a state of rest, be put in extreme motion instantaneously: philosophy teaches us, and experience makes it evident, that a portion of time must be occupied, however short that may be. All motion is gradual, and cannot be obtained otherwise; and hence the fact, that lightning conveyed into a tube filled with projectiles would not drive them out: it would not project them, but the blow would break them in pieces. So is it with this mixture; it is useless from its very rapidity of ignition. We have shown that even fine grain gunpowder is too quick, and that its quickness destroys its power; how much more so is the other: and what would it avail us, with these disadvantages.
A writer mentions what he conceives to be a curious fact: he says, “If a train of gunpowder be crossed at right angles by a train of fulminating mercury, laid on a sheet of paper on a table, and the gunpowder lighted by a red hot wire, the flame will run on until it meets the cross train of fulminating mercury, when the inflammation of the latter will be so instantaneous as to cut off the connection with the continuous train of gunpowder, leaving one half of the train unignited:” and again, “If the fulminating powder be lighted first, it will go straight on, and pass through the train of gunpowder so rapidly as not to inflame it at all.” True; and the cause is quite apparent: the rapidity of combustion condenses the air so quickly, as to remove the grains of gunpowder liable to come in contact with the flame, and to form the condensed air into a line of demarcation: for heat cannot be taken up by the air quicker than the atmosphere will convey sound; and before the heat can evaporate the explosion is over, and is consequently noiseless.
In all mining operations: in the quarrying of stone, the destruction of sunken rocks, or in any other operations where it is desirable to detach large masses, the use of gunpowder is indispensable; not only because it decreases manual exertion but also because it can be used under circumstances and in situations unapproachable by other means. It becomes, therefore, a consideration for the miner what kind is best suited for the purpose; the finest grained powder is useless as is well known: it is also more expensive; but its principal defect arises from its quickness of combustion. Masses cannot be detached without first putting the whole in motion; and as this cannot be done in a very short time, it is necessary to prolong the explosion, so that the wave of vibration may have time to travel throughout the whole of the mass acted upon; and a repetition of these waves is necessary before any mass can move. Now, to obtain this, it is necessary that matter be so incorporated with the powder as to prolong that explosion; bituminous substances might be applied with effect, for their slow burning would keep the heat necessary to hold the permanent gases at their utmost stretch of expansion.
It is obvious, from the extremely high character English sporting gunpowder has obtained all over the world, that considerable improvement must have been effected by the private manufacturers, either in the purification or manipulation of ingredients; indeed the unwearied care bestowed on this point by several of our best makers is beyond all praise. To explain the various methods, or otherwise enlarge upon this point, would be injurious to individual skill and enterprise, and be the means of imparting knowledge to those who have not ability to invent, but who gather from the brains of others. The French set great value on the “Poudre de Chasse” of England. It is rather singular that we should excel those who pride themselves so much on their chemical knowledge; but, as before remarked, it is certain that the intimate incorporation of the ingredients is of more importance than the chemical proportions.
All military and naval gunpowder is not manufactured of the greatest strength that can be acquired “at the Government mills;” a sample is furnished to each contractor with each contract, and to this strength he is limited.