The lubricating action of axite is shown by the fact that a series of cordite cartridges fired from a .303 rifle in the ordinary way, followed by a second series, the barrel being lubricated between each shot by firing an axite cartridge alternately with the cordite cartridge. The mean velocity of the first series of cordite cartridges was 1,974 ft. per second; the mean velocity of the second series was 2,071 ft. per second; the increased velocity due to the lubricating effect of axite therefore was 97 ft. per second. This powder, it is evident, has very many very excellent qualities, and considerable advantages over cordite. It is understood that axite is at present under the consideration of the British Government for use as the Service powder.
~Ballistite.~—Nobel's powder, known as ballistite, originally consisted of a camphorated blasting gelatine, and was made of 10 parts of camphor in 100 parts of nitro-glycerine, to which 200 parts of benzol were then added, and 50 parts of nitro-cotton (soluble) were then steeped in this mixture, which was then heated to evaporate off the benzol, and the resulting compound afterwards passed between steam-heated rollers, and formed into sheets, which were then finally cut up into small squares or other shapes as convenient. The camphor contained in this substance was, however, found to be a disadvantage, and its use discontinued. The composition is now 50 per cent. of soluble nitro-cotton and 50 per cent. of nitro-glycerine. As nitro-glycerine will not dissolve its own weight of nitro-cotton (even the soluble variety), benzol is used as a solvent, but is afterwards removed from the finished product, just as the acetone is removed from cordite. About 1 per cent. of diphenylamine is added for the purpose of increasing its stability.
The colour of ballistite is a darkish brown. It burns in layers when ignited, and emits sparks. The size of the cubes into which it is cut is a 0.2-inch cube. Its density is 1.6. It is also, by means of a special machine, prepared in the form of sheets, after being mixed in a wooden trough fitted with double zinc plates, and subjected to the heating process by means of hot-water pipes. It is passed between hot rollers, and rolled into sheets, which are afterwards put through a cutting machine and granulated. Sir A. Nobel's experiments[A] with this powder gave the following results:—The charge used was 5 lbs. 8 oz., the size of the cubes being 0.2 inch. The mean crusher-gauge pressure was 14.3 tons per square inch (maximum, 2,210; minimum, 2,142), and average pressure 2,180 atmospheres. The muzzle velocity was 2,140 foot seconds, and the muzzle energy 1,429 foot tons. A gramme of ballistite generates 615 c.c. of permanent gases, and gives rise to 1,365 grm. units of heat. Ballistite is manufactured at Ardeer in Scotland, at Chilworth in Surrey, and also in Italy, under the name of Filite, which is in the form of cords instead of cubes. The ballistite made in Germany contained more nitro-cellulose, and the finished powder was coated with graphite. Its use has been discontinued as the Service powder in Germany, but it is still the Service powder in Italy.
[Footnote A: Proc. Roy. Soc., vol. lii., p. 315.]
~U.S. Naval Smokeless Powder.~—This powder is manufactured at the U.S. Naval Torpedo Station for use in guns of all calibres in the U.S. Navy. It is a nitro-cellulose powder, a mixture of insoluble and soluble nitro- cellulose together with the nitrates of barium and potassium, and a small percentage of calcium carbonate. The proportions in the case of the powder for the 6-inch rapid-fire gun are as follows:—Mixed nitro-cellulose (soluble and insoluble) 80 parts, barium nitrate 15 parts, potassium nitrate 4 parts, and calcium carbonate 1 part. The percentage of nitrogen contained in the insoluble nitro-cellulose must be 13.30±0.15, and in the soluble 11.60±0.15, and the mean nitration strength of the mixture must be 12.75 per cent. of nitrogen. The solvent used in making the powder is a mixture of ether (sp. gr. 0.720) 2 parts, and alcohol (95 per cent. by volume) 1 part. The process of manufacture is briefly as follows:[A]—The soluble and insoluble nitro-cellulose are dried separately at a temperature from 38° to 41° C., until they do not contain more than 0.1 per cent. of moisture. The calcium carbonate is also finely pulverised and dried, and is added to the mixed nitro-celluloses after they have been sifted through a 16-mesh sieve. The nitrates are next weighed out and dissolved in hot water, and to this solution is added the mixture of nitro-celluloses and calcium carbonate with constant stirring until the entire mass becomes a homogeneous paste. This pasty mass is next spread upon trays and re-dried at a temperature between 38° and 48° C., and when thoroughly dry it is transferred to the kneading machine. The ether- alcohol mixture is now added, and the process of kneading begun. It has been found by experiment that the amount of solvent required to secure thorough incorporation is about 500 c.c. to each 500 grms. of dried paste. To prevent loss of solvent due to evaporation, the kneading machine is made vapour light. The mixing or kneading is continued until the resulting greyish-yellow paste is absolutely homogeneous so far as can be detected by the eye, which requires from three to four hours. The paste is next treated in a preliminary press (known as the block press and is actuated by hydraulic power), where it is pressed into a cylindrical mass of uniform density and of such dimensions as to fit it for the final or powder press. The cylindrical masses from the block press are transferred to the final press, whence they are forced out of a die under a pressure of about 500 lbs. per square inch. As it emerges from the final press the powder is in the form of a ribbon or sheet, the width and thickness of which is determined by the dimensions of the powder chamber of the gun in which the powder is to be used. On the inner surface of the die are ribs extending in the direction of the powder as it emerges from the press, the object of these ribs being to score the sheets or ribbons in the direction of their length, so that the powder will yield uniformly to the pressure of the gases generated in the gun during the combustion of the charge. The ribbon or sheet is next cut into pieces of a width and length corresponding to the chamber of the gun for which it is intended, the general rule being that the thickness of the grain (when perfectly dry) shall be fifteen one-thousandths (.015) of the calibre of the gun, and the length equal to the length to fit the powder chamber. Thus, in case of the 6-inch rapid-fire gun the thickness of the grain (or sheet) is 0.09 of an inch and the length 32 inches. The sheets are next thoroughly dried, first between sheets of porous blotting-paper under moderate pressure and at a temperature between 15° C. and 21.5° C. for three days, and then exposed to free circulation of the air at about 21.5° C. for seven days, and finally subjected for a week or longer to a temperature not exceeding 38° C. until they cease to lose weight.
[Footnote A: Lieut. W. Walke, "Lectures on Explosives," p. 330.]
The sheets, when thoroughly dried, are of a uniform yellowish-grey colour, and of the characteristic colloidal consistency; they possess a perfectly smooth surface, and are free from internal blisters or cracks. The temperature of ignition of the finished powder should not be below 172° C., and when subjected to the heat or stability test, it is required to resist exposure to a temperature of 71° C. for thirty minutes without causing discoloration of the test paper.
~W.A. Powder.~—This powder is made by the American Smokeless Powder Company, and it was proposed for use in the United States Army and Navy. It is made in several grades according to the ballistic conditions required. It consists of insoluble gun-cotton and nitro-glycerine, together with metallic nitrates and an organic substance used as a deterrent or regulator. The details of its manufacture are very similar to those of cordite, with the exception that the nitro-glycerine is dissolved in a portion of the acetone, before it is added to the gun-cotton. The powder is pressed into solid threads, or tubular cords or cylinders, according to the calibre of the gun in which the powder is to be used. As the threads emerge from the press they are received upon a canvas belt, which passes over steam-heated pipes, and deposited in wire baskets. The larger cords or cylinders are cut into the proper lengths and exposed upon trays in the drying-house. The powder for small arms is granulated by cutting the threads into short cylinders, which are subsequently tumbled, dusted, and, if not perfectly dry, again placed upon trays in the drying- house. Before being sent away from the factory, from five to ten lots of 500 lbs. each are mixed in a blending machine, in order to obtain greater uniformity. The colour of the W.A. powder is very light grey, the grains are very uniform in size, dry and hard. The powder for larger guns is of a yellowish colour, almost translucent, and almost as hard as vulcanite. The powder is said to be unaffected by atmospheric or climatic conditions, to be stable, and to have given excellent ballistic results; it is not sensitive to the impact of bullets, and when ignited burns quietly, unless strongly confined.
Turning now to the smokeless powders, in which the chief ingredient is nitro-cellulose in some form (either gun-cotton or nitro-lignine, &c.), one of the first of these was Prentice's gun-cotton, which consisted of nitrated paper 15 parts, mixed with 85 parts of unconverted cellulose. It was rolled into a cylinder. Another was Punshon's gun-cotton powder, which consisted of gun-cotton soaked in a solution of sugar, and then mixed with a nitrate, such as sodium or potassium nitrate. Barium nitrate was afterwards used, and the material was granulated, and consisted of nitrated gun-cotton.
The explosive known as tonite, made at Faversham, was at first intended for use as a gunpowder, but is now only used for blasting.