A gunpowder is smoky when its products of combustion are not all gaseous. Only about forty-four per cent. of the products of combustion of black gunpowder is gaseous. The rest is inert solid matter, which makes the smoke.
The products of combustion of smokeless powder, however, are practically all gaseous. Consequently, weight for weight, it is much more powerful than black powder.
Black gunpowder is a mechanical mixture of charcoal, sulphur and saltpeter, the charcoal and sulphur being the combustible elements, and the saltpeter the oxidizing element or the element that supplies the oxygen.
In smokeless powder the oxygen is held in chemical union with nitrogen and hydrogen, but the bond between the nitrogen and the other elements is weak, so that when ignited the other more active elements are enabled easily to unite at the expense of the nitrogen.
In the combustion of all explosive materials, great heat is generated, and the force of the explosion is dependent upon the volume of gases and the high temperature to which they are raised.
The smokeless powder used in the United States is made by dissolving a special kind of guncotton or nitrocellulose in ether and alcohol, just sufficient of the solvent being used to gelatinate the nitrocellulose, which is then stuffed through a forming die into rods. The rods are cut into sections of about three diameters long. The die, the invention of the writer, contains seven mandrels arranged in such wise that when the material is forced through the die the bar is multi-perforated with seven holes at equal distances apart. The grains or rods of smokeless powder are then dried for use.
When burned in a cannon, all of the surfaces of the material are practically instantly ignited by a small flash charge of black rifle powder used for the purpose of setting fire to the charge of smokeless powder. The combustion in the perforations causes them to become larger and larger until the grain is all consumed. This form of grain tends better to maintain the pressure behind the projectile in its flight through the gun, and enables the use of larger charges of powder with lower pressures than could otherwise be employed. In fact, it would be impossible to use a smokeless powder made of pure nitrocellulose in big guns without the multi-perforations.
In certain European countries where the multi-perforated powder has not been adopted, nitroglycerin is employed, combined with the nitrocellulose, which causes the material to burn through a greater thickness in a given time. Thus a smokeless powder may be made without the multi-perforations, but smokeless powders containing nitroglycerin erode the guns and destroy them very quickly, while guns employing pure nitrocellulose smokeless powders last much longer.
When one of our big army or navy cannon is fired, the time which elapses from the instant of complete ignition of the powder charge to the instant that the projectile leaves the muzzle of the gun is about the fiftieth or the sixtieth of a second, and in that time the hard and horn-like smokeless powder material is burned through only about a sixteenth of an inch; hence the rate of combustion or rate of explosion of smokeless powder in a cannon is about four inches per second, while it has been ascertained by actual experiments that the rate of combustion or rate of explosion of dynamite and other high explosives is about four miles per second, so that the rate of consumption of smokeless powder, as compared to that of a high explosive, is as are four inches to four miles.
As the time required for the projectile to be thrown from a twelve-inch cannon is only about the sixtieth of a second, sixty of these huge guns could be placed side by side and fired by electricity one after the other, while grandfather’s clock is making but one tick.