being an expansion of one volume into 787·3. But as the temperature of the gases, at the instant of their combustive formation, must be incandescent, this volume may be safely estimated at three times the above amount, or considerably upwards of 2,000 times the bulk of the explosive solid.
“It is obvious that the more sulphur, the more sulphurous acid will be generated, and the less forcibly explosive will be the gunpowder. This was confirmed by the experiments at Essonne, where the gunpowder that contained twelve of sulphur, twelve of charcoal, in 100 parts, did not throw the proof shell so far as that which contained only nine of sulphur and fifteen of charcoal. The conservative property is, however, of so much importance for humid climates and our remote colonies, that it justifies a slight sacrifice of strength.
“When in a state of explosion, the volume,” Dr. Hutton calculates, “is at least increased eight times, and hence its immense power. The pressure exerted, if in a state of confinement, will depend on the dimensions of the vessel containing it; so that it would be no difficult undertaking to obtain any pressure above that of the atmosphere, up, we may fearlessly say, to the enormous amount of 4,000 lbs. per square inch.”
The same quantity of gunpowder subjected to a variety of experimental tests, differs materially in its results; at the same time it is only by such a method that we can arrive at the relative strength or power which it possesses. Dr. Hutton, whose authority in all mathematical calculations is very high, and whose opinions and judgment in matters of this nature ought not to be unthinkingly controverted, states 2,000 feet per second (with cannon) as the highest velocity which any projectile had attained, at the time of his writing, which had gunpowder for its propellant power. A much greater velocity is now given in all guns fired at high elevations. “Monks’” gun attained a velocity of 2,400 feet in the first second of its flight, and this is now exceeded by rifled cannon.
This advantage does not arise, in our opinion, so much from the superior quality of the gunpowder, as from the improvements which have taken place in the manner of applying it. For instance, where experiments are conducted, as was the case with Dr. Hutton, with moving eprouvettes, a certain loss is sustained, in the same degree as the instrument is made to recoil from its original position; therefore, by restraining the recoil, an increase of momentum is given to the projectile, to the same extent as had been exerted upon the eprouvette, or cannon, in driving it several feet backward; and instead of dividing the force thus acquired between the shot and the gun, by having the latter firmly fixed and the recoil destroyed, the whole power is exerted upon the former, and its velocity accelerated in the same proportion.
Gunpowder, though astonishing in its effect, and tremendous in power, may nevertheless be controlled within a limited sphere, and bounds put upon its destructive energy. The following curious experiment, first tried at Woolwich on a small scale, has since been carried out to a great extent. Screw into each end of the breech part of a gun-barrel a well-fitted plug; drill a communication, and put in a nipple; having filled the barrel with powder, screw in the breech, and fire a cap on it, and the explosive fluid will escape by the small orifice like steam from a pipe. If the barrel be good, it may safely be held in the hand, merely using a towel to protect the hand from the heat the barrel absorbs. We have done it repeatedly with no inconvenience, and even carried this experiment much further; firing two ounces of the best powder in a barrel of good quality (though not in the hand) yet the barrel did not receive any violent motion by which it could be inferred that it might not be done with safety.
We have before observed, that, with very short guns, fine gunpowder produces the greatest result, inasmuch as there is no greater column of air in the barrel than the explosive fluid is equal to displace; or, in other words, the charge leaving the muzzle of the gun at the very moment when the explosive force is strongest, all the power is thus obtained of which it is capable; but if used in a longer barrel, and the fluid has obtained its greatest power when the charge has twelve inches of the barrel still to travel, the column of compressed air yet remaining in the muzzle of the barrel, exerts a resisting influence, in proportion to its density, upon the charge, and creates a dangerous and unpleasant recoil.
If a cartridge be placed in the centre of an open barrel eight feet in length, having a bullet abutting at each end large enough to fill the barrel, and a touch-hole is drilled as near the centre of the cartridge as possible, when it is fired, the balls will certainly be discharged from the barrel, but with a very small degree of force: in fact, merely driven out. With the same instrument, vary the experiment: place in it a cartridge charged with one ball, three feet from the muzzle, leaving a column of air five feet in length to act against the explosive force of the gunpowder, and the ball will be driven one hundred yards with considerable force. Again, let a third cartridge be introduced similar to the last, two feet from the muzzle, increasing the column of air to six feet; and the result, in distance and velocity, will nearly double what has been obtained by the last experiment; tending to prove that air thus forced back upon itself obtains a density, and consequent resisting influence, nearly equal to a well-screwed breech. In order to test this principle further, I put into the same tube a double charge of gunpowder, merely backed by a wadding, two feet from the muzzle, and then rammed down four balls as tight as possible into the short portion; in discharging it, the tube was burst immediately in rear of the charge.
In another experiment, I took a common musket barrel, having a plug of iron firmly fixed into the muzzle; the breech being unscrewed, and a ball introduced one-tenth of an inch less in diameter than the bore of the barrel, together with one drachm of gunpowder, I then fired the gunpowder, and the explosive matter escaped by the touch-hole. On examination, it was found that the ball was flattened to the extent of one-third of its sphere. The charge for the next experiment was increased to two drachms; when the ball in the discharge struck the muzzle very slightly, altering its shape in the least conceivable degree. The charge was next increased to three drachms, and the ball was extracted without any perceptible defect. In the fourth trial, another drachm was added, with which the effect was greater than the tube was able to resist; it was in consequence burst, about three inches from the muzzle.
From this I infer that, in the first trial, the velocity of the ball was not so great, but that the air escaped past it, by what is technically called the windage, allowing it to strike the plug at the end of the barrel with sufficient force to alter the shape of the lead in the manner described. The second trial gave an increased velocity; the opposing forces being so nearly balanced that the ball scarcely reached the end of the barrel, and was very little injured. In the third trial the velocity became so great, and the air was condensed to such an extent, that the ball struck upon a cushion-like surface so highly elastic that it was extracted without the least injury to its shape. The last charge was too powerful, inasmuch as the lateral pressure of compressed air rent the tube asunder.