We ought first to say a few words about modern explosives. Old-fashioned gunpowder, or black powder as it is now usually called, is composed, as everybody knows, of saltpetre, charcoal, and sulphur mixed together in the proportion usually of seventy-five, fifteen, and ten parts respectively.
Two chief varieties of the new brown powders are now made, and are known as 'slow-burning cocoa'—from the fact that cocoa-nut fibres were first employed in the experiments—and 'Prism brown I.' The former contains about four per cent. of sulphur, and burns rather more rapidly than the latter, which contains only two per cent. Baked straw is the material now used to supplant the charcoal, as it provides a form of cellulose which may be readily reduced to a fine state of division. The shape is still the perforated hexagonal prism introduced in America.
The burning of these powders is steady and the increase of pressure gradual, attaining a maximum when the bullet is about half-way down the barrel of the gun. The damage inflicted on the firing-chamber is very slight; perhaps as slight as ever will be obtained with such large charges of powder.
Uniformity of velocity is secured by ensuring that in the making the proportions employed shall be accurate and the mixing complete. The prisms of any given class of powder are made exactly the same in weight and composition, and in consequence, a charge composed of a given number of prisms will give in every case almost exactly the same propelling force. It is thus that fine aiming adjustments are made possible, as two consecutive bullets of the same weight may be propelled almost exactly the same distance—varying only a few yards in a range of several miles—by equal weights of powder of uniform composition.
But explosives of the present day are composed of other substances. Cordite, of which we now hear so much, is made of nitro-glycerine, gun-cotton, and mineral jelly in the proportion of fifty-seven, thirty-eight, and five parts. It is also steeped in a preparation of acetone. Gun-cotton itself is dipped in a mixture of three parts of sulphuric to one of nitric acid. The force of cordite over gunpowder may be judged from the following facts. A cartridge containing seventy grains of black powder fired in the ordinary rifle of the army will give what is called a muzzle velocity of one thousand three hundred and fifty feet a second, while thirty grains only of cordite will give a velocity of two thousand feet. In larger arms, a little less than a pound of cordite fired in a twelve-pounder gun will give more velocity than four pounds of black powder fired in the same weapon. It need hardly be said that in the experiments at Shoeburyness it is the new-fashioned explosive which is chiefly used.
Let us examine one of the guns, a breech-loader, and see what improvements have been made which may conduce to rapidity of fire. We see that in the older pattern three motions were necessary to open the breech. First the bar which is fixed across the base of the block had to be removed, then a half turn had to be given to the block to free it in its bed, and then it had to be pulled forward. Firstly, it had to be thrown back on its hinge so as to open the gun from end to end. We are shown that in later patterns the cavity or bed into which the block fits is made in the form of a cone, so that the breech-block itself can be turned back without any preliminary motion forward. In artillery work, time is everything, and any one motion of the gunner's hands and arms saved is a point gained. Now let us look at the mechanism by which the recoil or backward movement of the gun is checked at the moment of firing. The gun slides in its cradle, and its recoil is counteracted by buffers which work in oil, something in the fashion of the oil springs which we see on doors. Iron spiral springs push the gun back again into place. Another interesting piece of mechanism is the electric machinery by which the gun is fired. When the recoil has taken place, the wire, along which runs the electric current, is pushed out of place, so that it is impossible to fire the gun, even though it be loaded, until it has been again fixed in its proper position on the cradle. Truly a modern cannon is a wonderful machine, and yet it is only a development from the sort of iron gas-pipe which was used in the middle ages. Hard by is a gun which has come to grief. In experiments which are carried on at Shoeburyness, guns are charged to their full, or, as in this case, more than their full strength. There is an ugly gash running down the outer case or jacket, as it is called, of the gun, and the latter has broken, and nearly jumped out of its cradle. Nursery phraseology certainly comes in strongly in the technical slang of gunnery when we have to do with Woolwich Infants.
After looking at the guns we naturally go on to look at the targets at which they are fired. Targets at The New Range are not so much marks as specimens of armour-plates and other protections. Some of these are built up with a strength which to the uninitiated appears to be proof against any attack. Here, for instance, we find a steel plate of eighteen inches in thickness, and behind this six inches of iron, the whole backed up by huge balks of timber. But notwithstanding its depth, the enormous mass has been dented and cracked, and in places pierced. When we look at plates which are not quite so thick, we see that the shells have formed what are pretty and regular patterns, for small triangles of metal have been splintered off and turned back, so that the aperture is decorated with a circle of leaves, and resembles a rose with the centre cut out. Where the shell has entered the plate before it bursts, the pattern remains very perfect; but when it explodes as it touches the surface, some of the encircling leaves are entirely cut off.
One target is pointed out to us which represents the iron casing of the vulnerable portions of a torpedo boat, consisting of engine-room, boilers, and coal-bunkers. These compartments have been riddled again and again. Even a service-rifle bullet can penetrate one side, and a shell of the smallest size will go through both, for torpedo boats are not very heavily built.