Nitro-Explosives: A Practical Treatise Part 15

It has been found that the erosive effect is in direct proportion to the nitro-glycerine present. The cordite M.D., which contains only 30 per cent. nitro-glycerine, gives only about half the erosive effect of the old service cordite. With regard to the heating effect of cordite and cordite M.D. on a rifle, Mr T.W. Jones made some experiments. He fired fifty rounds of .303 cartridges in fifteen minutes in the service rifle. Cordite raised the temperature of the rifle 270 F., and cordite M.D. 160 F.

only.

With regard to the effect of heat upon cordite, there is some difference of opinion. Dr W. Anderson, F.R.S., says that there is no doubt that the effect of heat upon cordite is greater than upon black powder. At a temperature of 110 F. the cordite used in the 4.7-inch gun is considerably affected as regards pressure.

Colonel Barker, R.A., in reply to a question raised by Colonel Trench, R.A. (at the Royal Artillery Inst.i.tution), concerning the shooting qualities of cordite heated to a temperature of 110 F., said: "Heating cordite and firing it hot undoubtedly does disturb its shooting qualities, but as far as we can see, not much more than gunpowder. I fear that we must always expect abnormal results with heated propellants, either gunpowder or cordite; and when fired hot, the increase in pressure and velocities will depend upon the heat above the normal or average temperature at which firing takes place." Colonel Barker also, in referring to experiments that had been made in foreign climates, said: "Climatic trials have been carried out all over the world, and they have so far proved eminently satisfactory. The Arctic cold of the winter in Canada, with the temperature below zero, and the tropical sun of India, have as yet failed to shake the stability of the composition, or abnormally injure its shooting qualities." Dr Anderson is of opinion that cordite should not be stored in naval magazines near to the boilers.

Professor Vivian B. Lewes, in his recent Cantor Lectures before the Society of Arts, suggests that the magazines of wars.h.i.+ps should be water- jacketed, and maintained at a temperature that does not rise above 100 F.

~Axite.~--This powder is manufactured by Messrs Kynock Limited, at their works at Witton, Birmingham. The main const.i.tuents of cordite are retained although the proportions are altered; ingredients are added which impart properties not possessed by cordite, and the methods of its manufacture have been modified. The form has also been altered. Axite is made in the form of a ribbon, the cross section being similar in shape to a double- headed rail. It is claimed for this powder, that it does not corrode the barrel in the way cordite does, that with equal pressure it gives greatly increased velocity, and therefore flatter trajectory. That the effect of temperature on the pressure and velocity with axite is only half that with cordite. That the maximum flame temperature of axite is considerably less than that of cordite, and the erosive effect is therefore considerably less. That the deposit left in the barrel after firing axite cartridges reduces the friction between the bullet and the barrel. It is therefore practicable to use axite cartridges giving higher velocities than can be employed with cordite, as with such velocities the latter would nickel the barrel by excessive friction. It is also claimed that the accuracy is greatly increased. The following results have been obtained with this same time, and under the same conditions:--

~Axite~ Cartridges with 200-grain bullets.

Velocity 2,726 F.S.

Pressure 20.95 tons.

~Axite~ Cartridges with 215-grain bullets.

Velocity 2,498 F.S.

Pressure 19.24 tons.

~Axite~ Service Cartridges.

Velocity 2,179 F.S.

Pressure 15.76 tons.

~Cordite~ Service Cartridges.

Velocity 2,010 F.S.

Pressure 15.67 tons.

Five rounds from the Service axite and Service cordite were placed in an oven and heated to a temperature of 110 F. for one hour, and were then fired for pressure. The following results were obtained:--

~Axite.~ ~Cordite.~ Before heating 15.76 tons per sq. in. 15.67 tons per sq. in.

After " 16.73 " " 17.21 " "

_____ _____

Increase .97 = 6.1% 1.54 = 9.8%

Average Velocities-- Before heating 2,150 F.S. 2,030 F.S.

After " 2,180 " 2,090 "

_____ _____

Increase 30 F.S. = 1-1/2% 60.0 F.S. = 3%

In order to show the accuracy given by axite, seven rounds were fired from a machine rest at a target fixed at 100 yards from a rifle. Six of the seven shots could be covered by a penny piece, the other being just outside. In order to ascertain the relative heat imparted to a rifle by the explosion of axite and cordite, ten rounds each of axite and cordite cartridges were fired from a .303 rifle, at intervals of ten seconds, the temperature of the rifle barrel being taken before and after each series:--

THE RISE IN TEMPERATURE OF THE RIFLE BARREL

With axite was 71 F.

With cordite was 89 F.

Difference in favour of axite 18 F. = 20.2%

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.

~Ballist.i.te.~--n.o.bel's powder, known as ballist.i.te, 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 pa.s.sed 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 ballist.i.te 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 pa.s.sed between hot rollers, and rolled into sheets, which are afterwards put through a cutting machine and granulated. Sir A. n.o.bel'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 ballist.i.te generates 615 c.c. of permanent gases, and gives rise to 1,365 grm. units of heat. Ballist.i.te 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 ballist.i.te 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 pota.s.sium, 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, pota.s.sium nitrate 4 parts, and calcium carbonate 1 part. The percentage of nitrogen contained in the insoluble nitro-cellulose must be 13.300.15, and in the soluble 11.600.15, 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 ma.s.s becomes a h.o.m.ogeneous paste. This pasty ma.s.s 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 h.o.m.ogeneous 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 ma.s.s of uniform density and of such dimensions as to fit it for the final or powder press. The cylindrical ma.s.ses 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 pa.s.ses 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 pota.s.sium 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.

~The Schultze Powder.~--One of the earliest of the successful powders introduced into this country was Schultze's powder, the invention of Colonel Schultze, of the Prussian Artillery, and is now manufactured by the Schultze Gunpowder Company Limited, of London. The composition of this powder, as given in the "Dictionary of Explosives" by the late Colonel Cundall, is as follows:--

Soluble nitro-lignine 14.83 per cent.

Insoluble " 23.36 "

Lignine (unconverted) 13.14 "

Nitrates of K and Ba 32.35 "

Paraffin 3.65 "

Matters soluble in alcohol 0.11 "

Moisture 2.56 "

This powder was the first to solve the difficulty of making a smokeless, or nearly smokeless powder which could be used with safety and success in small arms. Previously, gun-cotton had been tried in various forms, and in nearly every instance disaster to the weapon had followed, owing to the difficulty of taming the combustion to a safe degree. But about 1866 Colonel Schultze produced, as the result of experiments, a nitrated wood fibre which gave great promise of being more pliable and more easily regulated in its burning than gun-cotton, and this was at once introduced into England, and the Schultze Gunpowder Company Limited was formed to commence its manufacture, which it did in the year 1868. During the years from its first appearance, Schultze gunpowder has pa.s.sed through various modifications. It was first made in a small cubical grain formed by cutting the actual fibre of timber transversely, and then breaking this veneer into cubes. Later on improvements were introduced, and the wood fibre so produced was crushed to a fine degree, and then reformed into small irregular grains. Again, an advance was made in the form of the wood fibre used, the fibre being broken down by the action of chemicals under high temperature, and so producing an extremely pure form of woody fibre.

The next improvement was to render the grains of the powder practically waterproof and less affected by the atmospheric influences of moisture and dryness, and the last improvement to the process was that of hardening the grains by means of a solvent of nitro-lignine, so as to do away with the dust that was often formed from the rubbing of the grains during transit.

Minor modifications have from time to time also been made, in order to meet the gradual alteration which has taken place during this long period in the manufacture of sporting guns and cartridge cases to be used with this powder, but through all its evolution this Company has adhered to the first idea of using woody fibre in preference to cotton as the basis of their smokeless powder, as experience has confirmed the original opinion that a powder can be thus made less sensitive to occasional differences in loading, and more satisfactory all round than when made from the cotton base. The powder has always been regulated so that bulk for bulk it occupies the same measure as the best black powder, and as regards its weight, just one half of that of black.

The process of manufacture of this powder is briefly as follows:--

Wood of clean growth is treated by the well-known sulphite process for producing pure woody fibre, which is very carefully purified, and this, after drying, is steeped in a mixture of nitric and sulphuric acids, to render it a nitro-compound and the explosive base of the powder. This nitro compound is carefully purified until it stands the very high purity requirements of the Home Office, and is then ground with oxygen-bearing salts, &c., and the whole is formed into little irregular-shaped grains of the desired size, which grains are dried and hardened by steeping in a suitable solvent for the nitro compound, and after finally drying, sifting, &c., the powder is stored in magazines for several months before it is issued. When issued, a very large blend is made of many tons weight, which ensures absolute uniformity in the material.

There is in England a standard load adopted by every one for testing a sporting powder; this charge is 42 grains of powder and 1-1/8 oz. No. 6 shot--this shot fired from a 12-bore gun, patterns being taken at 40 yards, the velocity at any required distance.

The standard muzzle velocity of Schultze gunpowder is 1,220 feet per second.

The mean 40 yards ditto is 875 feet per second.

The mean 20 yards ditto is 1,050 feet per second.