~Cordite~, the smokeless powder adopted by the British Government, is the patent of the late Sir F.A. Abel and Sir James Dewar, and is somewhat similar to blasting gelatine. It is chiefly manufactured at the Royal Gunpowder Factory at Waltham Abbey, but also at two or three private factories, including those of the National Explosives Company Limited, the New Explosives Company Limited, the Cotton-Powder Company Limited, Messrs Kynock's, &c. As first manufactured it consisted of gun-cotton 37 per cent., nitro-glycerine 58 per cent., and vaseline 5 per cent., but the modified cordite now made consists of 65 per cent. gun-cotton, 30 per cent. of nitro-glycerine, and 5 per cent. of vaseline. The gun-cotton used is composed chiefly of the hexa-nitrate,[A] which is not soluble in nitro- glycerine. It is therefore necessary to use some solvent such as acetone, in order to form the jelly with nitro-glycerine. The process of manufacture of cordite is very similar, as far as the chemical part of the process is concerned, to that of blasting gelatine, with the exception that some solvent for the gun-cotton, other than nitro-glycerine has to be used. Both the nitro-glycerine and the gun-cotton employed must be as dry as possible, and the latter should not contain more than .6 per cent. of mineral matter and not more than 10 per cent. of soluble nitro-cellulose, and a nitrogen content of not less than 12.5 per cent. The dry gun-cotton (about 1 per cent. of moisture) is placed in an incorporating tank, which consists of a brass-lined box, some of the acetone is added, and the machine (Fig. 29), is started; after some time the rest of the acetone is added (20 per cent. in all) and the paste kneaded for three and a half hours. At the end of this time the Vaseline is added, and the kneading continued for a further three and a half hours. The kneading machine (Fig. 29) consists of a trough, composed of two halves of a cylinder, in each of which is a shaft which carries a revolving blade. These blades revolve in opposite directions, and one makes about half the number of revolutions of the other. As the blades very nearly touch the bottom of the trough, any material brought into the machine is divided into two parts, kneaded against the bottom, then pushed along the blade, turned over, and completely mixed. During kneading the acetone gradually penetrates the mixture, and dissolves both the nitro-cellulose and nitro-glycerine, and a uniform dough is obtained which gradually assumes a buff colour. During kneading the mass becomes heated, and therefore cold water is passed through the jacket of the machine to prevent heating the mixture above the normal temperature, and consequent evaporation of the acetone. The top of the machine is closed in with a glass door, in order to prevent as far as possible the evaporation of the solvent. When the various ingredients are formed into a homogeneous mass, the mixture is taken to the press house, where in the form of a plastic mass it is placed in cylindrical moulds. The mould is inserted in a specially designed press, and the cordite paste forced through a die with one or more holes. The paste is pressed out by hydraulic pressure, and the long cord is wound on a metal drum (Fig. 38), or cut into lengths; in either case the cordite is now sent to the drying houses, and dried at a temperature of about 100° F. from three to fourteen days, the time varying with the size. This operation drives off the acetone, and any moisture the cordite may still contain, and its diameter decreases somewhat. In case of the finer cordite, such as the rifle cordite, the next operation is blending. This process consists in mounting ten of the metal drums on a reeling machine similar to those used for yarns, and winding the ten cords on to one drum. This operation is known as "ten-stranding." Furthermore, six "ten-stranded" reels are afterwards wound upon one, and the "sixty-stranded" reel is then ready to be sent away, This is done in order to obtain a uniform blending of the material. With cordite of a larger diameter, the cord is cut into lengths of 12 inches. Every lot of cordite from each manufacturer has a consecutive number, numbers representing the size and one or more initial letters to identify the manufacturer. These regulations do not apply to the Royal Gunpowder Factory, Waltham Abbey. The finished cordite resembles a cord of gutta-percha, and its colour varies from light to dark brown. It should not look black or shrivelled, and should always possess sufficient elasticity to return to its original form after slight bending. Cordite is practically smokeless. On explosion a very thin vapour is produced, which is dissipated rapidly. This smokelessness can be understood from the fact that the products of combustion are nearly all non-condensible gases, and contain no solid products of combustion which would cause smoke. For the same muzzle velocity a smaller charge of cordite than gunpowder is required owing to the greater amount of gas produced. Cordite is very slow in burning compared to gunpowder. For firing blank cartridges cordite chips containing no vaseline is used. The rate at which cordite explodes depends in a measure upon the diameter of the cords, and the pressure developed upon its mechanical state. The sizes of cordite used are given by Colonel Barker, R.A., as follows:—
For the .303 rifle .0375 inch diameter. " 12 Pr. B.L. gun .05 " " " .075 " " 4.7-inch Q.F. gun .100 " " 6-inch Q.F. gun .300 " " heavy guns .40 to .50 "
For rifles the cordite is used in bundles of sixty strands, in field-guns in lengths of 11 to 12 inches, and the thicker cordite is cut up into 14-inch lengths. Colonel Barker says that the effect of heat upon cordite is not greater as regards its shooting qualities than upon black powder, and in speaking of the effect that cordite has upon the guns in which it is used (R.A. Inst.) said that they had at Waltham Abbey a 4.7-inch Q.F. gun that had fired 40 rounds of black powder, and 249 rounds of cordite (58 per cent. nitro-glycerine) and was still in excellent condition, and showed very little sign of action, and also a 12-lb. B.L. gun that had been much used and was in no wise injured.
[Footnote A: The gun-cotton used contains 12 per cent. of soluble gun-cotton, and a nitrogen content of not less than 12.8 to 13.1 per cent.]
[Illustration: Fig. 37 Scale, 1 inch = 1 foot. Single Strand Reel.]
[Illustration: FIG. 38.—"TEN-STRANDING.">[
In some experiments made by Captain Sir A. Noble,[A] with the old cordite containing 58 per cent. nitro-glycerine, a charge of 5 lbs. 10 oz. of cordite of 0.2 inch diameter was fired. The mean chamber crusher gauge pressure was 13.3 tons per square inch (maximum 13.6, minimum 12.9), or a mean of 2,027 atmospheres (max. 2,070, min. 1,970). The muzzle velocity was 2,146 foot seconds, and the muzzle energy 1,437 foot tons. A gramme of cordite generated 700 c.c. of permanent gases at 0° C. and 760 mm. pressure. The quantity of heat developed was 1,260 gramme units. In the case of cordite, as also with ballistite, a considerable quantity of aqueous vapour has to be added to the permanent gases formed. A similar trial, in which 12 lbs. of ordinary pebble powder was used, gave a pressure of 15.9 tons per square inch, or a mean of 2,424 atmospheres. It gave a 45-lb. projectile a mean muzzle velocity of 1,839 foot seconds, thus developing a muzzle energy of 1,055 foot tons. A gramme of this powder at 0° C. and 760 mm. generates 280 c.c. of permanent gases, and develops 720 grm. units of heat.
[Footnote A: Proc. Roy. Soc., vol. lii., No. 315.]
In a series of experiments conducted by the War Office Chemical Committee on Explosives in 1891, it was conclusively shown that considerable quantities of cordite may be burnt away without explosion. A number of wooden cases, containing 500 to 600 lbs. each of cordite, were placed upon a large bonfire of wood, and burned for over a quarter of an hour without explosion. At Woolwich in 1892 a brown paper packet containing ten cordite cartridges was fired into with a rifle (.303) loaded with cordite, without the explosion of a single one of them, which shows its insensibility to shock.
With respect to the action of cordite upon guns, Sir A. Noble points out that the erosion caused is of a totally different kind to that of black powder. The surface of the barrel in the case of cordite appears to be washed away smoothly by the gases, and not pitted and eaten into as with black powder. The erosion also extends over a shorter length of surface, and in small arms it is said to be no greater than in the case of black powder. Sir A. Noble says in this connection: "It is almost unnecessary to explain that freedom from rapid erosion is of very high importance in view of the rapid deterioration of the bores of large guns when fired with charges developing very high energies. As might perhaps be anticipated from the higher heat of ballistite, its erosive power is slightly greater than that of cordite, while the erosive power of cordite is again slightly greater than that of brown prismatic. Amide powder, on the other hand, possesses the peculiarity of eroding very much less than any other powder with which I have experimented, its erosive power being only one-fourth of that of the other powders enumerated."