Before the adoption of smokeless powder, the cake powder invented by General Rodman had been highly developed and improved in the form of “cocoa powder.” This was made in hexagonal prisms, each perforated longitudinally, so as to have a hollow core. These grains were carefully arranged in the cartridges so as to have this core continuous from one grain to another, in order that upon ignition the combustion would begin in the interior and produce a constantly increasing volume of gas as the exterior surface of the grain was reached. Though the time of combustion was too rapid to be appreciated by the ordinary senses, it was, nevertheless, quite different from the practically instantaneous combustion of the old small-grain powder, and was susceptible of accurate measurement. Much difficulty was experienced in overcoming the detonating tendencies of the smokeless powders, but at last the requisite slow-burning properties were obtained. The smokeless powder for large guns is made in cartridges composed of bundles of strips or cords, or in the same prismatic form as the cocoa powder, and the process of combustion is the same.
MORTAR ON REVOLVING HOIST.
The form of the gun is dependent entirely upon the nature of the powder used. As the pressure of the gas constantly increases with the burning of the powder, the maximum force will be reached at the moment the combustion is complete. The length of the bore should, therefore, be just sufficient to enable the powder to be entirely consumed at the exact instant the projectile leaves the muzzle of the piece. A shorter bore would cause much of the powder to be thrown out unconsumed, while a much greater length would retard the projectile by subjecting it to the friction of the bore after the maximum force of the powder had been reached. This accounts for the greatly increased length of the modern cannon. A change in the method of gun construction has accordingly become necessary. Guns are no longer made of cast iron, but are “built up” of steel. The explosion of the powder is, of course, exerted in every direction, against the bore and sides of the piece as well as against the base of the projectile. This produces two strains; a longitudinal strain which is exerted in the direction of the axis of the piece, and a transverse strain which tends to burst the gun. It is necessary, therefore, to have the piece so strong, especially at the points of first explosion, as to counteract these strains, and thus cause the entire force to be exerted upon the projectile in the direction of the “least resistance.” This strength, or “initial tension,” is obtained by shrinking cylinders of steel over the original cylinder of the piece, each outer cylinder or jacket being a few thousandths of an inch smaller in its interior diameter than the outer diameter of the cylinder which it incloses, and being expanded by heating to a sufficient degree to enable it to be slipped over the latter. Upon cooling, the jacket exerts a constant and powerful force of compression, which counteracts the outward pressure of the force of explosion. The longitudinal strain is less dangerous than the other, and is usually counteracted by an interlocking of some of the cylinders or hoops, to which the strain is transmitted from the breech-plug. The art of building up guns has been of slow growth, the first efforts in this direction having been made by Sir W. G. Armstrong nearly half a century ago. The weight of the projectile of the present 16-inch gun in the United States service is 2370 pounds; the charge of powder weighs 1060 pounds, and the extreme range is more than 14 miles. The cost of each shot is $450, and when we consider that this does not include the wear and tear of the gun, it is evident that money has become more than ever before “the sinews of war.”
Not less remarkable than the improvement in cannon is the improvement in mortars. These mortars are very unlike the clumsy weapons of that name manipulated by hand-spikes, which were known in our great war. They are now mounted on a platform which turns on rollers. They are elevated or depressed by a mechanical appliance, are loaded at the breech, are accurately rifled, and can drop their projectiles on the decks of hostile vessels at a range of six miles. They are placed in groups of four, each in a separate pit, some batteries containing as many as four groups, or sixteen mortars. In all important sea-coast batteries both guns and mortars are so arranged as to be fired by electricity, either singly or in volleys.
A dynamite gun has been devised by Captain Zalinsky for the purpose, as the name implies, of throwing a projectile containing dynamite. Attempts to fire dynamite projectiles by means of powder have thus far failed. In the Zalinsky gun the propelling power is compressed air. The projectile contains from fifty to sixty pounds of gelatine dynamite, the explosion of which is terrific. Excellent results have been obtained with Zalinsky’s gun up to a range of 2000 yards, but as this is insignificant in comparison with the enormous range of high-power cannon using powder as a charge, the dynamite gun is still a weapon of limited usefulness. Although the dynamite gun has not as yet fulfilled the desired requirements as to range, promising experiments have been made in firing shells charged with high explosives from mortars using charges of powder, and it is probably a question of only a short time before means will be found for successfully firing dynamite in a similar manner.
The great improvements in field artillery make the cannon of the early battlefields of the century seem, in comparison, almost like harmless toys. The modern field gun is made of steel, is rifled, loads at the breech, and has great rapidity and accuracy of fire. The extreme range of the 3.2-inch field gun in the United States service is about four miles. This, in fact, is beyond the ordinary range of human vision, and it is but rarely that the ground for so great a distance is free from features that obstruct the view. For these reasons the fire of field guns can seldom be utilized beyond a range of two miles. The projectile of the 3.2-inch field gun weighs 13½ pounds, and the charge of powder 3½ pounds. The 3.6-inch gun is a still more powerful weapon, the weight of the projectile and charge being 20 and 4½ pounds respectively. Shells are used against inanimate objects, such as earthworks or buildings; but the great artillery projectile for the battlefield is shrapnel. It is now very different from the crude projectile known by the same name in the early years of the century. The bullets are assembled in circular layers and held in position by “separators,” which are short cast-iron cylinders with hemispherical cavities into which the bullets fit. The bottom separator fits by means of lugs into recesses at the base of the shrapnel, and prevents independent rotation of the charge of bullets. The top separator is smooth on its upper side, and is kept firmly in place by the head of the projectile, which screws against it. The separators prevent movement or deformation of the bullets under shock of discharge, and being weakened by radial cuts, increase the effect by furnishing additional fragments of effective weight. The shrapnel for the 3.2-inch gun contains 162 bullets one half inch in diameter and weighing 41 to the pound. The total number of bullets and individual pieces in the shrapnel is 201.
MODERN SHRAPNEL.
The heavy sea-coast guns are now mounted either in armored turrets, en barbette, or on disappearing gun-carriages. The first system is very costly and is not generally used in the United States. The second system, in which the guns are fired over a parapet and are constantly exposed, is used only in rare cases. The third has been perfected in the United States in the Buffington-Crozier and the Gordon disappearing gun-carriages. These carriages enable the gun to be loaded in safety under cover of the carriage pit, and then to be raised by means of counterweights or compressed air to a position from which it can fire over the parapet. With trained cannoneers, the gun can be raised and fired in twenty seconds, and this brief period of exposure, especially when smokeless powder is used, renders it almost impossible for the enemy to locate the gun with any degree of accuracy. The shock of the recoil, taken up by pneumatic or hydraulic cylinders, brings the piece back, quickly but gently, to the loading position, whence it is again raised for firing.