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.