Nitro-Explosives: A Practical Treatise Part 14

With hydrogen it forms the acid fulminate of silver. It is used in crackers and bon-bons, and other toy fireworks, in minute quant.i.ties. Gay Lussac found it to be composed as follows:--Carbon, 7.92 per cent.; nitrogen, 9.24 per cent.; silver, 72.19 per cent.; oxygen, 10.65 per cent.; and he a.s.signed to it the formula, C_{2}N_{2}Ag_{2}O_{2}. Laurent and Gerhardt give it the formula, C_{2}N(NO_{2})Ag_{2}, and thus suppose it to contain nitryl, NO_{2}.

On adding pota.s.sium chloride to a boiling solution of argentic fulminate, as long as a precipitate of argentic chloride forms, there is obtained on evaporation brilliant white plates, of a very explosive nature, of pota.s.sic argentic fulminate, C(NO_{2})KAg.CN, from whose aqueous solution nitric acid precipitates a white powder of hydric argentic fulminate, C(NO_{2})HAg.CN. All attempts to prepare fulminic acid, or nitro-aceto- nitrile, C(NO_{2})H_{2}CN, from the fulminates have failed. There is a fulminate of gold, which is a violently explosive buff precipitate, formed when ammonia is added to ter-chloride of gold, and fulminate of platinum, a black precipitate formed by the addition of ammonia to a solution of oxide platinum, in dilute sulphuric acid.

Fulminating silver is a compound obtained by the action of ammonia on oxide of silver. It is a very violent explosive. Pure mercury fulminate may be kept an indefinite length of time. Water does not affect it. It explodes at 187 C., and on contact with an ignited body. It is very sensitive to shock and friction, even that of wood upon wood. It is used for discharging bullets in saloon rifles. Its inflammation is so sudden that it scatters black powder on which it is placed without igniting it, but it is sufficient to place it in an envelope, however weak, for ignition to take place, and the more resisting the envelope the more violent is the shock, a circ.u.mstance that plays an important part in caps and detonators. The presence of 30 per cent. of water prevents decomposition, 10 per cent. prevents explosion. This is, however, only true for small quant.i.ties, and does not apply to silver fulminate, which explodes under water by friction. Moist fulminates slowly decompose on contact with the oxidisable metals. The (reduced) volume of gases obtained from 1 kilo. is according to Berthelot, 235.6 litres. The equation of its decomposition is C_{2}HgN_{2}O_{2} = 2CO + N_{2} + Hg.

Fulminate of mercury is manufactured upon the large scale by two methods.

One of these, commonly known as the German method, is conducted as follows:--One part of mercury is dissolved in 12 parts of nitric acid of a specific gravity of 1.375, and to this solution 16.5 parts of absolute alcohol are added by degrees, and heat is then slowly applied to the mixture until the dense fumes first formed have disappeared, and when the action has become more violent some more alcohol is added, equal in volume to that which has already been added. This is added very gradually. The product obtained, which is mercury fulminate, is 112 per cent. of the mercury employed. Another method is to dissolve 10 parts of mercury in 100 parts of nitric acid of a gravity of 1.4, and when the solution has reached a temperature of 54 C, to pour it slowly through a gla.s.s funnel into 83 parts of alcohol. When the effervescence ceases, it is filtered through paper filters, washed, and dried over hot water, at a temperature not exceeding 100 C. The fulminate is then carefully packed in paper boxes, or in corked bottles. The product obtained by this process is 130 per cent. of the mercury taken. This process is the safest, and at the same time the cheapest. Fulminate should be kept, if possible, in a damp state. Commercial fulminate is often adulterated with chlorate of potash.

~Detonators~, or caps, are metallic capsules, usually of copper, and resemble very long percussion caps. The explosive is pure fulminate of mercury, or a mixture of that substance with nitrate or chlorate of potash, gun-powder, or sulphur. The following is a common cap mixture:-- 100 parts of fulminate of mercury and 50 parts of pota.s.sium nitrate, or 100 parts of fulminate and 60 parts of meal powder. Silver fulminate is also sometimes used in caps. There are eight sizes made, which vary in dimensions and in amount of explosive contained. They are further distinguished as singles, doubles, trebles, &c., according to their number. Colonel Cundill, R.A. ("Dict. of Explosives"), gives the following list:--

No. 1 contains 300 grms. of explosive per 1000.

" 2 " 400 " " " " "

" 3 " 540 " " " " "

" 4 " 650 " " " " "

" 5 " 800 " " " " "

" 6 " 1,000 " " " " "

" 7 " 1,500 " " " " "

" 8 " 2,000 " " " " "

Trebles are generally used for ordinary dynamite, 5, 6, or 7 for gun-cotton, blasting gelatine, roburite, &c.

In the British service percussion caps, fuses, &c., are formed of 6 parts by weight of fulminate of mercury, 6 of chlorate of potash, and 4 of sulphide of antimony; time fuses of 4 parts of fulminate, 6 of pota.s.sium chlorate, 4 of sulphide of antimony, the mixture being damped with a varnish consisting of 645 grains of sh.e.l.lac dissolved in a pint of methylated spirit. Abel's fuse (No. 1) consists of a mixture of sulphide of copper, phosphide of copper, chlorate of potash, and No. 2 of a mixture of gun-cotton and gun-powder. They are detonated by means of a platinum wire heated to redness by means of an electric current. Bain's fuse mixture is a mixture of subphosphide of copper, sulphide of antimony, and chlorate of potash.

In the manufacture of percussion caps and detonators the copper blanks are cut from copper strips and stamped to the required shape. The blanks are then placed in a gun-metal plate, with the concave side uppermost--a tool composed of a plate of gun-metal, in which are inserted a number of copper points, each of the same length, and so s.p.a.ced apart as to exactly fit each point into a cap when inverted over a plate containing the blanks.

The points are dipped into a vessel containing the cap composition, which has been previously moistened with methylated spirit. It is then removed and placed over the blanks, and a slight blow serves to deposit a small portion of the cap mixture into each cap. A similar tool is then dipped into sh.e.l.lac varnish, removed and placed over the caps, when a drop of varnish from each of the copper points falls into the caps, which are then allowed to dry. This is a very safe and efficacious method of working.

At the works of the Cotton-Powder Company Limited, at Faversham, the fulminate is mixed wet with a very finely ground mixture of gun-cotton and chlorate of potash, in about the proportions of 6 parts fulminate, 1 part gun-cotton, and 1 part chlorate. The water in which the fulminate is usually stored is first drained off, and replaced by displacement by methyl-alcohol. While the fulminate is moist with alcohol, the gun-cotton and chlorate mixture is added, and well mixed with it. This mixture is then distributed in the detonators standing in a frame, and each detonator is put separately into a machine for the purpose of pressing the paste into the detonator sh.e.l.l.

At the eleventh annual meeting of the representatives of the Bavarian chemical industries at Regensburg, attention was drawn to the unhealthy nature of the process of charging percussion caps. Numerous miniature explosions occur, and the air becomes laden with mercurial vapours, which exercise a deleterious influence upon the health of the operatives. There is equally just cause for apprehension in respect to the poisonous gases which are evolved during the solution of mercury in nitric acid, and especially during the subsequent treatment with alcohol. Many methods have been proposed for dealing with the waste products arising during the manufacture and manipulation of fulminate of mercury, but according to Kaemmerer, only one of comparatively recent introduction appears to be at all satisfactory. It is based upon the fact that mercuric fulminate, when heated with a large volume of water under high pressure, splits up into metallic mercury and non-explosive mercurial compounds of unknown composition.

In mixing the various ingredients with mercury fulminate to form cap mixtures, they should not be too dry; in fact, they are generally more or less wet, and mixed in small quant.i.ties at a time, in a special house, the floors of which are covered with carpet, and the tables with felt. Felt shoes are also worn by the workpeople employed. All the tools and apparatus used must be kept very clean; for granulating, hair sieves are used, and the granulated mixture is afterwards dried on light frames, with canvas trays the bottoms of which are covered with thin paper, and the frames fitted with indiarubber cushions, to reduce any jars they may receive. The windows of the building should be painted white to keep out the rays of the sun.

Mr H. Maxim, of New York, has lately patented a composition for detonators for use with high explosives, which can also be thrown from ordnance in considerable quant.i.ties with safety. The composition is prepared as follows:--Nitro-glycerine is thickened with pyroxyline to the consistency of raw rubber. This is done by employing about 75 to 85 per cent. of nitro-glycerine, and 15 to 25 per cent. of pyroxyline, according to the stiffness or elasticity of the compound desired. Some solvent that dissolves the nitro-cotton is also used. The product thus formed is a kind of blasting gelatine, and should be in a pasty condition, in order that it may be mixed with fulminate of mercury. The solvent used is acetone, and the quant.i.ty of fulminate is between 75 to 85 per cent. of the entire compound. If desired, the compound can be made less sensitive to shocks by giving it a spongy consistency by agitating it with air while it is still in a syrupy condition. The nitro-glycerine, especially in this latter case, may be omitted. In some cases, when it is desirable to add a deterring medium, nitro-benzene or some suitable gum is added.

[Ill.u.s.tration: FIG. 34. METHOD OF PREPARING THE CHARGE.]

The method of preparing a blasting charge is as follows:--A piece of Bickford fuse of the required length is cut clean and is inserted into a detonator until it reaches the fulminate. The upper portion of the detonator is then squeezed round the fuse with a pair of nippers. The object of this is not only to secure that the full power of the detonator may be developed, but also to fix the fuse in the cap (Fig. 34). When the detonator, &c., is to be used under water, or in a damp situation, grease or tallow should be placed round the junction of the cap with the fuse, in order to make a water-tight joint. A cartridge is then opened and a hole made in its upper end, and the detonator pushed in nearly up to the top.

Gun-cotton or tonite cartridges generally have a hole already made in the end of the charge. Small charges of dry gun-cotton, known as primers, are generally used to explode wet gun-cotton. The detonators (which are often fired by electrical means) are placed inside these primers (Fig. 35).

[Ill.u.s.tration: FIG. 35. PRIMER.]

One of the forms of electric exploders used is shown in Fig. 36. This apparatus is made by Messrs John Davis & Son, and is simply a small hand dynamo, capable of producing a current of electricity of high tension.

This firm are also makers of various forms of low tension exploders. A charge having been prepared, as in Fig. 34, insert into the bore-hole one or more cartridges as judged necessary, and squeeze each one down separately with a _wooden_ rammer, so as to leave no s.p.a.ce round the charge, and above this insert the cartridge containing the fuse and detonator. Now fill up the rest of the bore-hole with sand, gravel, water, or other tamping. With gelatine dynamites a firm tamping may be used, but with ordinary dynamite loose sand is better. The charge is now ready for firing.

[Ill.u.s.tration: FIG. 36.--ELECTRIC EXPLODER.]

CHAPTER VI.

_SMOKELESS POWDERS._

Smokeless Powder in General--Cordite--Axite--Ballist.i.te--U.S. Naval Powder--Schultze's E.G. Powder--Indurite--Vielle Poudre--Rifleite-- Cannonite--Walsrode--Cooppal Powders--Amberite--Troisdorf--Maximite-- Picric Acid Powders, &c., &c.

The progress made in recent years in the manufacture of smokeless powders has been very great. With a few exceptions, nearly all these powders are nitro compounds, and chiefly consist of some form of nitro-cellulose, either in the form of nitro-cotton or nitro-lignine; or else contain, in addition to the above, nitro-glycerine, with very often some such substance as camphor, which is used to reduce the sensitiveness of the explosive. Other nitro bodies that are used, or have been proposed, are nitro-starch, nitro-jute, nitrated paper, nitro-benzene, di-nitro-benzene, mixed with a large number of other chemical substances, such as nitrates, chlorates, &c. And lastly, there are the picrate powders, consisting of picric acid, either alone or mixed with other substances.

The various smokeless powders may be roughly divided into military and sporting powders. But this cla.s.sification is very rough; because although some of the better known purely military powders are not suited for use in sporting guns, nearly all the manufacturers of sporting powders also manufacture a special variety of their particular explosive, fitted for use in modern rifles or machine guns, and occasionally, it is claimed, for big guns also.

Of the purely military powders, the best known are cordite, ballist.i.te, and the French B.N. powder, the German smokeless (which contains nitro- glycerine and nitro-cotton); and among the general powders, two varieties of which are manufactured either for rifles or sporting guns, Schultze's, the E.C. Powders, Walsrode powder, cannonite, Cooppal powder, amberite, &c., &c.

~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 bra.s.s-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 a.s.sumes a buff colour. During kneading the ma.s.s becomes heated, and therefore cold water is pa.s.sed 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 gla.s.s door, in order to prevent as far as possible the evaporation of the solvent. When the various ingredients are formed into a h.o.m.ogeneous ma.s.s, the mixture is taken to the press house, where in the form of a plastic ma.s.s 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.]

[Ill.u.s.tration: Fig. 37 Scale, 1 inch = 1 foot. Single Strand Reel.]

[Ill.u.s.tration: FIG. 38.--"TEN-STRANDING."]

In some experiments made by Captain Sir A. n.o.ble,[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 quant.i.ty of heat developed was 1,260 gramme units. In the case of cordite, as also with ballist.i.te, a considerable quant.i.ty 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 quant.i.ties 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. n.o.ble 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. n.o.ble 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 antic.i.p.ated from the higher heat of ballist.i.te, 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."

TABLE GIVING SOME OF SIR. A. n.o.bLE'S EXPERIMENTS.

________________________________________________________________________ | | | VELOCITIES OBTAINED. | |________________________________________________________________________| | | | | | | | | In a 40 | In a 50 | In a 75 | In a 100 | | | Cal. Gun.| Cal. Gun.| Cal. Gun.| Cal. Gun.| |____________________________|__________|__________|__________|__________| | | | | | | | |Foot Secs.|Foot Secs.|Foot Sees.|Foot Secs.| | | | | | | |With cordite 0.4 in. diam. | 2,794 | 2,940 | 3,166 | 3,286 | | " " 0.3 " | 2,469 | 2,619 | 2,811 | 2,905 | | " ballist.i.te 0.3 in. cubes| 2,416 | 2,537 | 2,713 | 2,806 | | " French B.N. for | | | | | | 6-inch guns | 2,249 | 2,360 | 2,536 | 2,616 | | " prismatic amide | 2,218 | 2,342 | 2,511 | 2,574 | | | | | | | |____________________________|__________|__________|__________|__________| | | | ENERGIES REPRESENTED BY ABOVE VELOCITIES. | |________________________________________________________________________| | | | | | | | |Foot Tons.|Foot Tons.|Foot Tons.|Foot Tons.| | | | | | | | Cordite 0.4 inch | 5,413 | 5,994 | 6,950 | 7,478 | | Ballist.i.te 0.3 inch cubes | 4,227 | 4,754 | 5,479 | 5,852 | | French B.N. | 4,047 | 4,463 | 5,104 | 5,460 | | Prismatic amide | 3,507 | 3,862 | 4.460 | 4,745 | |____________________________|__________|__________|__________|__________|

And again, in speaking of his own experiments, he says: "One 4.7-inch gun has fired 1,219 rounds, and another 953, all with full charges of cordite, while a 6-inch gun has fired 588 rounds with full charges, of which 355 were cordite. In the whole of these guns, so far as I can judge, the erosion is certainly not greater than with ordinary powder, and differs from it remarkably in appearance. With ordinary powder a gun, when much eroded, is deeply furrowed (these furrows having a great tendency to develop into cracks), and presents much the appearance in miniature of a very roughly ploughed field. With cordite, on the contrary, the surface appears to be pretty smoothly swept away, while the length of the surface eroded is considerably less."

[Ill.u.s.tration: FIG. 39.--COMPARATIVE PRESSURE CURVES OF CORDITE AND BLACK POWDER. _a_, Charge, 48 lbs. powder; _b_, charge, 13 lbs. 4 oz. cordite; _c_, charge, 13 lbs. 4 oz. powder. Weight of projectile, 100 lbs. in 6-inch gun. M.V. Cordite = 1960 feet seconds.]

The pressures given by cordite compared with those given by black powder in the 6-inch gun will be seen upon reference to Fig. 39, which is taken from Professor V.B. Lewes's paper, read before the Society of Arts; and due to Dr W. Anderson, F.R.S., the Director-General of Ordnance Factories.