The ammonite is filled into the metallic cartridges by means of an archimedian screw working through a bra.s.s tube, pushing off the cartridges as the explosive is fed into them against a slight back pressure; a cover is screwed on, and they then go to the dipping room, where they are dipped in hot wax to seal the ends; they are then packed in boxes of 5 lbs. each and are ready for delivery. The di-nitro-naphthalene is made at the factory. Mono-nitro-naphthalene is first made as follows:--12 parts of commercial nitrate of soda are ground to a fine powder, and further ground with the addition of 15 parts of refined naphthalene until thoroughly incorporated; it is then placed in an earthenware pan, and 30 parts of sulphuric acid of 66 B. added, 2 parts at a time, during forty-eight hours (the rate of adding H_{2}SO_{4} depends on the condition of the charge, and keeping it in a fluid state), with frequent agitation, day and night, during the first three or four days, afterwards three or four times a day. In all fourteen days are occupied in the nitration process. It is then strained through an earthenware strainer, washed with warm water, drained, and dried. For the purpose of producing this material in a granulated condition, which is found more convenient for drying, and further nitrification, it is placed in a tub, and live steam pa.s.sed through, until brought up to the boiling point (the tub should be about half full), cold water is then run in whilst violently agitating the contents until the naphthalene solidifies; it can then be easily drained and dried. For the further treatment to make di-nitro-naphthalene, 18 parts of nitro-naphthalene are placed in an earthenware pan, together with 39 parts of sulphuric acid of 66 B., then 15 parts of nitric acid of 40 B. are added, in small quant.i.ties at a time, stirring the mixture continually. This adding of nitric acid is controlled by the fuming, which should be kept down as much as possible. The operation takes ten to twelve days, when 100 times the above quant.i.ties, taken in kilogrammes, are taken. At the end of the nitration the di-nitro-naphthalene is removed to earthenware strainers, allowed to drain, washed with hot water and soda until all acid is removed, washed with water and dried. The di-nitro- naphthalene gives some trouble in washing, as some acid is held in the crystals which is liable to make its appearance when crushed. To avoid this it should be ground and washed with carbonate of soda before drying; an excess of carbonate of soda should not, however, be used.

~Electronite.~--This is a high explosive designed to afford safety in coal getting. This important end has been attained by using such ingredients, and so proportioning them, as will ensure on detonation a degree of heat insufficient under the conditions of a "blown-out" shot, to ignite fire damp or coal dust. It is of the nitrate of ammonium cla.s.s of permitted explosives. It contains about 75 per cent. of nitrate of ammonium, with the addition of nitrate of barium, wood meal, and starch. The gases resulting from detonation are chiefly water in the gaseous form, nitrogen, and a little carbon dioxide. It is granulated with the object of preventing missfires from ramming, to which nitrate of ammonium explosives are somewhat susceptible. This explosive underwent some exhaustive experiments at the experimental station near Wigan in 1895, when 8 oz. or 12 oz. charges were fired unstemmed into an admixture of coal dust and 10 per cent. of gas, without any ignition taking place. It is manufactured by Messrs Curtis's & Harvey Ltd. at their factory, Tonbridge, Kent.

~Sprengel's Explosives.~--This is a large cla.s.s of explosives. The essential principle of them all is the admixture of an oxidising with a combustible agent at the time of, or just before, being required for use, the const.i.tuents of the mixture being very often non-explosive bodies.

This type of explosive is due to the late Dr Herman Sprengel, F.R.S.

Following up the idea that an explosion is a sudden combustion, he submitted a variety of mixtures of oxidising and combustible agents to the violent shock of a detonator of fulminate. These mixtures were made in such proportions that the mutual oxidation or de-oxidation should be theoretically complete. Among them are the following:--

1. One chemical equivalent of nitro-benzene to equivalents of nitric acid.

2. Five equivalents of picric acid to 13 equivalents of nitric acid.

3. Eighty-seven equivalents of nitro-naphthalene to 413 equivalents of nitric acid.

4. Porous cakes, or lumps of chlorate of potash, exploded violently with bisulphide of carbon, nitro-benzol, carbonic acid, sulphur, benzene, and mixtures of these substances.

No. 1 covers the explosive known as _h.e.l.lhoffite_, and No. 2 is really oxonite, and No. 4 resembles rack-a-rock, an explosive invented by Mr S.R.

Divine, and consisting of a mixture of chlorate of potash and nitro- benzol. Roburite, bellite, and securite should perhaps be regarded as belonging to the Sprengel cla.s.s of explosives, otherwise this cla.s.s is not manufactured or used in England. The princ.i.p.al members are known as _h.e.l.lhoffite_, consisting of a mixture of nitro-petroleum or nitro-tar oils and nitric acid, or of meta-di-nitro-benzol and nitric acid; _Oxonite_, consisting of picric and nitric acids; and _Panclast.i.te_, a name given to various mixtures, proposed by M. Turpin, such as liquid nitric peroxide, with bisulphide of carbon, benzol, petroleum, ether, or mineral oils.

~Picric Acid, Tri-nitro-Phenol, or Carbazotic Acid.~--Picric acid, or a tri-nitro-phenol (C_{6}H_{2}(NO_{2})_{3}OH)[2:4:6], is produced by the action of nitric acid on many organic substances, such as phenol, indigo, wool, aniline, resins, &c. At one time a yellow gum from Botany Bay (_Xanthorrhoea hastilis_) was chiefly used. One part of phenol (carbolic acid), C_{6}H_{5}OH, is added to 3 parts of strong fuming nitric acid, slightly warmed, and when the violence of the reaction has subsided, boiled till nitrous fumes are no longer evolved. The resinous ma.s.s thus produced is boiled with water, the resulting picric acid is converted into a sodium salt by a solution of sodium carbonate, which throws down sodium picrate in crystals.

Phenol-sulphuric acid is now, however, more generally used, and the apparatus employed for producing it closely resembles that used in making nitro-benzol. It is also made commercially by melting carbolic acid, and mixing it with strong sulphuric acid, then diluting the "sulpho- carbolic"[A] acid with water, and afterwards running it slowly into a stone tank containing nitric acid. This is allowed to cool, where the crude picric acid crystallises out, and the acid liquid (which contains practically no picric acid, but only sulphuric acid, with some nitric acid) being poured down the drains. The crude picric acid is then dissolved in water by the aid of steam, and allowed to cool when most of the picric acid recrystallises. The mother liquor is transferred to a tank and treated with sulphuric acid, when a further crop of picric acid crystals is obtained. The crystals of picric acid are further purified by recrystallisation, drained, and dried at 100 F. on glazed earthenware trays by the aid of steam. It can also be obtained by the action of nitric acid on ortho-nitro-phenol, para-nitro-phenol, and di-nitro-phenol (2:4 and 2:6), but not from meta-nitro-phenol, a fact which indicates its const.i.tution.[B]

[Footnote A: O. and p. phenolsulphonic acids.

C_{3}H_{4}(OH).SO_{3}H + 3HNO_{3} = C_{6}H_{2}(NO_{2})_{3}OH + H_{2}SO_{4} + 2H_{2}O. (Picric acid).]

[Footnote B: Carey Lea, _Amer. Jour. Sci._, (ii.), x.x.xii. 180.]

Picric acid crystallises in yellow shining prisms or laminae having an intensely bitter taste, and is poisonous. It melts at 122.5 C., sublimes when cautiously heated, dissolves sparingly in cold water, more easily in hot water, still more in alcohol. It stains the skin an intense yellow colour, and is used as a dye for wool and silk. It is a strong acid, forming well crystallised yellow salts, which detonate violently when heated, some of them also by percussion. The pota.s.sium salt, C_{6}H_{2}(NO_{2})_{3}OK, crystallises in long needles very slightly soluble in water. The sodium, ammonium, and barium salts are, however, easily soluble in water. Picric acid, when heated, burns with a luminous and smoky flame, and may be burnt away in large quant.i.ty without explosion; but the mere contact of certain metallic oxides, with picric acid, in the presence of heat, develops powerful explosives, which are capable of acting as detonators to an indefinite amount of the acid, wet or dry, which is within reach of their detonative influence. The formula of picric acid is

C_{6}H_{2}|(NO_{2})_{3} |OH.

which shows its formation from phenol (C_{6}H_{5}OH.), three hydrogen atoms being displaced by the NO_{2} group. The equation of its formation from phenol is as follows:--

C_{6}H_{5}.OH + 3HNO_{3} = C_{6}H_{2}(NO_{2})_{3}OH + 3H_{2}O.

According to Berthelot, its heat of formation from its elements equals 49.1 calories, and its heat of total combustion by free oxygen is equal to +618.4 cals. It hardly contains more than half the oxygen necessary for its complete combustion.

2C_{6}H_{2}(NO_{2})_{3}OH + O_{10} = 12CO_{2} + 3H_{2} + 3N_{2}.

The percentage composition of picric acid is--Nitrogen, 18.34; oxygen, 49.22; hydrogen, 1.00; and carbon, 31.44, equal to 60.26 per cent. of NO_{2}. The products of decomposition are carbonic acid, carbonic oxide, carbon, hydrogen, and nitrogen, and the heat liberated, according to Berthelot, would be 130.6 cals., or 570 cals. per kilogramme. The reduced volume of the gases would be 190 litres per equivalent, or 829 litres per kilogramme. To obtain a total combustion of picric acid it is necessary to mix with it an oxidising agent, such as a nitrate, chlorate, &c. It has been proposed to mix picric acid (10 parts) with sodium nitrate (10 parts) and pota.s.sium bichromate (8.3 parts). These proportions would furnish a third of oxygen in excess of the necessary proportion.

Picric acid was not considered to be an explosive, properly so called, for a long time after its discovery, but the disastrous accident which occurred at Manchester (_vide_ Gov. Rep. No. Lx.x.xI., by Colonel (now Sir V.D.) Majendie, C.B.), and some experiments made by Dr Dupre and Colonel Majendie to ascertain the cause of the accident, conclusively proved that this view was wrong. The experiments of Berthelot (_Bull. de la Soc. Chim.

de Paris_, xlix., p. 456) on the explosive decomposition of picric acid are also deserving of attention in this connection. If a small quant.i.ty of picric acid be heated in a moderate fire, in a crucible, or even in an open test tube, it will melt (at 120 C. commercial acid), then give off vapours which catch fire upon contact with air, and burn with a sooty flame, without exploding. If the burning liquid be poured out upon a cold slab, it will soon go out. A small quant.i.ty carefully heated in a tube, closed at one end, can even be completely volatilised without apparent decomposition. It is thus obvious that picric acid is much less explosive than the nitric ethers, such as nitro-glycerol and nitro-cellulose, and very considerably less explosive than the nitrogen compounds and fulminates.

It would, however, be quite erroneous to a.s.sume that picric acid cannot explode when simply heated. On the contrary, Berthelot has proved that this is not the case. If a gla.s.s tube be heated to redness, and a minute quant.i.ty of picric acid crystals be then thrown in, it will explode with a curious characteristic noise. If the quant.i.ty be increased so that the temperature of the tube is materially reduced, no explosion will take place at once, but the substance will volatilise and then explode, though with much less violence than before, in the upper part of the tube.

Finally, if the amount of picric acid be still further increased under these conditions, it will undergo partial decomposition and volatilise, but will not even deflagrate. Nitro-benzene, di-nitrobenzene, and mono-, di-, and tri-nitro-naphthalenes behave similarly.

The manner in which picric acid will decompose is thus dependent upon the initial temperature of the decomposition, and if the surrounding material absorb heat as fast as it is produced by the decomposition, there will be no explosion and no deflagration. If, however, the absorption is not sufficient to prevent deflagration, this may so increase the temperature of the surrounding materials that the deflagration will then end in explosion. Thus, if an explosion were started in an isolated spot, it would extend throughout the ma.s.s, and give rise to a general explosion.

In the manufacture of picric acid the first obvious and most necessary precaution is to isolate the substance from other chemicals with which it might accidentally come into contact. If pure materials only are used, the manufacture presents no danger. The finished material, however, must be carefully kept from contact with nitrates, chlorates, or oxides. If only a little bit of lime or plaster become accidentally mixed with it, it may become highly dangerous. A local explosion may occur which might have the effect of causing the explosion of the whole ma.s.s. Picric acid can be fired by a detonator, 5-grain fulminate, and M. Turpin patented the use of picric acid, unmixed with any other substance, in 1885. The detonation of a small quant.i.ty of dry picric acid is sufficient to detonate a much larger quant.i.ty containing as much as 17 per cent. of water.

It is chiefly due to French chemists (and to Dr Sprengel) that picric acid has come to the front as an explosive. Melinite,[A] a substance used by the French Government for filling sh.e.l.ls, was due to M. Turpin, and is supposed to be little else than fused picric acid mixed with gun-cotton dissolved in some solvent (acetone or ether-alcohol). Sir F.A. Abel has also proposed to use picric acid, mixed with nitrate of potash (3 parts) and picrate of ammonia (2 parts) as a filling for sh.e.l.ls. This substance requires a violent blow and strong confinement to explode it. I am not aware, however, that it has ever been officially adopted in this country.

Messrs Designolles and Brugere have introduced military powders, consisting of mixtures of pota.s.sium and ammonium picrates with nitrate of pota.s.sium. M. Designolles introduced three kinds of picrate powders, composed as follows:--

___________________________________________________________________ | | | | | | | For Torpedoes | For Guns. | For Small | | | and Sh.e.l.ls. | Ordinary. Heavy. | Arms. | |___________________|_______________|___________________|___________| | | | | | | | Picrate of Potash | 55-50 | 16.4- 9.6 | 9 | 28.6-22.9 | | Saltpetre | 45-50 | 74.4-79.7 | 80 | 65.0-69.4 | | Charcoal | ... | 9.2-10.7 | 11 | 6.4- 7.7 | |___________________|_______________|___________|_______|___________|

They were made much like ordinary gunpowder, 6 to 14 per cent. of moisture being added when being milled. The advantages claimed over gunpowder are greater strength, and consequently greater ballistic or disruptive effect, comparative absence of smoke, and freedom from injurious action on the bores of guns, owing to the absence of sulphur. Brugere's powder is composed of ammonium picrate and nitre, the proportions being 54 per cent.

picrate of ammonia and 46 per cent. pota.s.sic nitrate. It is stable, safe to manufacture and handle, but expensive. It gives good results in the Cha.s.sepot rifle, very little smoke, and its residue is small, and consists of carbonate of potash. It is stated that 2.6 grms. used in a rifle gave an effect equal to 5.5 grms. of ordinary gunpowder.

[Footnote A: The British Lydite and the j.a.panese Shimose are said to be identical with Melinite.]

Turpin has patented various mixtures of picric acid, with gum-arabic, oils, fats, collodion jelly, &c. When the last-named substance is diluted in the proportion of from 3 to 5 per cent. in a mixture of ether and alcohol, he states that the blocks of picric acid moulded with it will explode in a closed chamber with a priming of from 1 to 3 grammes of fulminate. He also casts picric acid into projectiles, the cast acid having a density of about 1.6. In this state it resists the shock produced by the firing of a cannon, when contained in a projectile, having an initial velocity of 600 metres. It is made in the following way:--The acid is fused in a vessel provided with a false bottom, heated to 130 to 145 C. by a current of steam under pressure, or simply by the circulation under the false bottom of a liquid, such as oil, chloride of zinc, glycerine, &c., heated to the same temperature. The melted picric acid is run into moulds of a form corresponding to that of the blocks required, or it may be run into projectiles, which should be heated to a temperature of about 100 C., in order to prevent too rapid solidification.

When cresylic acid (or cresol, C_{6}H_{4}(CH_{3})OH.) is acted upon by nitric acid it produces a series of nitro compounds very similar to those formed by nitric acids on phenol, such as sodium di-nitro-cresylate, known in the arts as victoria yellow. Naphthol, a phenol-like body obtained from naphthalene, under the same conditions, produces sodium di-nitro- naphthalic acid, C_{10}H_{6}(NO_{2})_{2}O. The explosive known as "roburite" contains chloro-nitro-naphthalene, and romit, a Swedish explosive, nitro-naphthalene.

~Tri-nitro-cresol~, C_{7}H_{4}(NO_{2})_{3}OH.--A body very similar to tri- nitro-phenol, crystallises in yellow needles, slightly soluble in cold water, rather more so in boiling water, alcohol, and ether. It melts at about 100 C. In France it is known as "Cresilite," and mixed with melinite, is used for charging sh.e.l.ls. By neutralising a boiling saturated solution of tri-nitro-cresol with ammonia, a double salt of ammonium and nitro-cresol crystallises out upon cooling, which is similar to ammonium picrate. This salt is known as "Ecrasite," and has been used in Austria for charging sh.e.l.ls. It is a bright yellow solid, greasy to the touch, melts at 100 C., is unaffected by moisture, heat, or cold, ignites when brought into contact with an incandescent body or open flame, burning harmlessly away unless strongly confined, and is insensitive to friction or concussion. It is claimed to possess double the strength of dynamite, and requires a special detonator (not less than 2 grms. of fulminate) to provoke its full force. Notwithstanding the excellent properties attributed to this explosive, Lieut. W. Walke ("Lectures on Explosives,"

p. 181) says, "Several imperfectly explained and unexpected explosions have occurred in loading sh.e.l.ls with this substance, and have prevented its general adoption up to the present time."

~The Fulminates.~--The fulminates are salts of fulminic acid, C_{2}N_{2}O_{2}H_{2}. Their const.i.tution is not very well understood. Dr E. Divers, F.R.S., and Mr Kawakita (_Chem. Soc. Jour._, 1884, pp. 13-19), give the formulae of mercury and silver fulminates as

OC = N AgOC = N / | | Hg | O and | O | / | / -C = N AgC = N

whereas Dr H.E. Armstrong, F.R.S., would prefer to write the formula of fulminic acid

ON.C.OH.

| C(N.OH),

and A.F. Holleman (_Berichte_, v. xxvi., p. 1403), a.s.signs to mercury fulminate the formula

C:N.O Hg | | C:N.O,

and R. Schol (_Ber._, v. xxiii., p. 3505),

C:NO || Hg.

C:NO

They are very generally regarded as iso-nitroso compounds.

The princ.i.p.al compound of fulminic acid is the mercury salt commonly known as fulminating mercury. It is prepared by dissolving mercury in nitric acid, and then adding alcohol to the solution, 1 part of mercury and 12 parts of nitric acid of specific gravity 1.36, and 5-1/2 parts of 90 per cent. alcohol being used. As soon as the mixture is in violent reaction, 6 parts more of alcohol are added slowly to moderate the action. At first the mixture blackens from the separation of mercury, but this soon vanishes, and is succeeded by crystalline flocks of mercury fulminate which fall to the bottom of the vessel. During the reaction, large quant.i.ties of volatile oxidation products of alcohol, such as aldehyde, ethylic nitrate, &c., are evolved from the boiling liquid, whilst others, such as glycollic acid, remain in solution. The mercury fulminate is then crystallised from hot water. It forms white silky, delicate needles, which are with difficulty soluble in cold water. In the dry state it is extremely explosive, detonating on heating, or by friction or percussion, as also on contact with concentrated sulphuric acid. The reaction that takes place upon its decomposition is as follows:--

C_{2}N_{2}O_{2}Hg = Hg + 2CO + N_{2} (284)

According to this equation 1 grm. of the fulminate should yield 235.8 c.c.

(= 66.96 litres for 284 grms.). Berthelot and Vicille have obtained a yield of 234.2 c.c., equal to 66.7 litres for one equivalent 284 grms.

Dry fulminate explodes violently when struck, compressed, or touched with sulphuric acid, or as an incandescent body. If heated slowly, it explodes at 152 C., or if heated rapidly, at 187 C. It is often used mixed with pota.s.sium chlorate in detonators. The reaction which takes place in this case is 3C_{2}N_{2}O_{2}Hg + 2KClO_{3} = 3Hg + 6CO_{2} + 3N_{2} + 2KCl.

On adding copper or zinc to a hot saturated solution of the salt, fulminate of copper or zinc is formed. The copper salt forms highly explosive green crystals. There is also a double fulminate of copper of ammonia, and of copper and pota.s.sium. Silver fulminite, C_{2}N_{2}O_{2}Ag_{2}, is prepared in a similar manner to the mercury salt. It separates in fine white needles, which dissolve in 36 parts of boiling water, and are with difficulty soluble in cold water. At above 100 C., or on the weakest blow, it explodes with fearful violence. Even when covered with water it is more sensitive than the mercury salt. It forms a very sensitive double salt with ammonia and several other metals.