Nitro-Explosives: A Practical Treatise

by P. Gerald Sanford

CHAPTER V.

NITRO-BENZOL, ROBURITE, BELLITE, PICRIC ACID, &c.

Explosives derived from Benzene—Toluene and Nitro-Benzene—Di- and
Tri-nitro-Benzene—Roburite: Properties and Manufacture—Bellite:
Properties, &c.—Securite—Tonite No. 3.—Nitro-Toluene—
Nitro-Naphthalene—Ammonite—Sprengel's Explosives—Picric Acid—
Picrates—Picric Powders—Melinite—Abel's Mixture—Brugère's Powders—
The Fulminates—Composition, Formula, Preparation, Danger of, &c.—
Detonators: Sizes, Composition, Manufacture—Fuses, &c.

~The Explosives derived from Benzene.~—There is a large class of explosives made from the nitrated hydro-carbons—benzene, C_{6}H_{6}; toluene, C_{7}H_{8}; naphthalene, C_{10}H_{8}; and also from phenol (or carbolic acid), C_{6}H_{5}OH. The benzene hydro-carbons are generally colourless liquids, insoluble in water, but soluble in alcohol and ether. They generally distil without decomposition. They burn with a smoky flame, and have an ethereal odour. They are easily nitrated and sulphurated; mono, di, and tri derivatives are readily prepared, according to the strength of the acids used. It is only the H-atoms of the benzene nucleus which enter into reaction.

Benzene was discovered by Faraday in 1825, and detected in coal-tar by Hofmann in 1845. It can be obtained from that portion of coal-tar which boils at 80° to 85° by fractionating or freezing.[A] The ordinary benzene of commerce contains thiophene (C_{4}H_{4}S), from which it may be freed by shaking with sulphuric acid. Its boiling point is 79° C.; specific gravity at 0° equals 0.9. It burns with a luminous smoky flame, and is a good solvent for fats, resins, sulphur, phosphorus, &c. Toluene was discovered in 1837, and is prepared from coal-tar. It boils at 110° C., and is still liquid at 28° C.

[Footnote A: It may be prepared chemically pure by distilling a mixture of benzoic acid and lime.]

The mono-, chloro-, bromo-, and iodo-benzenes are colourless liquids of peculiar odour. Di-chloro-, di-bromo-benzenes, tri- and hexa-chloro- and bromo-benzenes, are also known; and mono-chloro-, C_{6}H_{4}Cl(CH_{3}), and bromo-toluenes, together with di derivatives in the ortho, meta, and para modifications. The nitro-benzenes and toluenes are used as explosives. The following summary is taken from Dr A. Bernthsen's "Organic Chemistry":—

SUMMARY. ____________________________________________________________________ | | | C_{6}H_{5}(N0_{2}) Nitro-benzene. Liq. B.Pt. 206° C. | | | | C_{6}H_{4}(NO_{2}){2} Ortho-, meta-, and para- di-nitro-benzenes. | | Solid. M.P. 118°, 90°, and 172° C. | | | | C{6}H_{3}(NO_{3})_{3} S.-Tri-nitro-benzene. Solid. M.P. 121° C. | |____________________________________________________________________| | | | C_{6}H_{4}(CH_{3})NO_{2} Ortho-, meta-, and para- nitro-toluenes. | | B.P. 218°, 230°, and 234° C, Para compound solid. | |____________________________________________________________________| | | | C_{6}H_{3}(CH_{3}){2}NO{2} Nitro-xylene. Liquid. | |____________________________________________________________________| | | | C_{6}H_{2}(CH_{3}){3}NO{2} Nitro-mesitylene. Solid. | |____________________________________________________________________| | | | C_{6}H_{3}(CH_{3})(NO_{2})_{2} Di-nitro-toluenes. | |____________________________________________________________________| | | | C_{6}H_{4}Cl(NO_{2}) Nitro-chloro-benzenes. | | | | C_{6}Br_{4}(NO_{2})_{2} Tetra-bromo-di-nitrobenzene. | |____________________________________________________________________|

The nitro compounds are mostly pale yellow liquids, which distil unchanged, and volatilise with water vapour, or colourless or pale yellow needles or prisms. Some of them, however, are of an intense yellow colour. Many of them explode upon being heated. They are heavier than water, and insoluble in it, but mostly soluble in alcohol, ether, and glacial acetic acid.

Nitro-benzene, C_{6}H_{5}(NO_{2}), was discovered in 1834 by Mitscherlich. It is a yellow liquid, with a melting point of +3° C. It has an intense odour of bitter almonds. It solidifies in the cold. In di-nitro-benzene, the two nitro groups may be in the meta, ortho, or para position, the meta position being the most general (see fig., page 4). By recrystallising from alcohol, pure meta-di-nitro-benzene may be obtained in long colourless needles. The ortho compound crystallises in tables, and the para in needles. They are both colourless. When toluene is nitrated, the para and ortho are chiefly formed, and a very little of the meta compound.

~Nitro Compounds of Benzene and Toluene.~—The preparation of the nitro derivatives of the hydrocarbons of the benzene series is very simple. It is only necessary to bring the hydrocarbon into contact with strong nitric acid, when the reaction takes place, and one or more of the hydrogen atoms of the hydrocarbon are replaced by the nitryl group (NO_{2}). Thus by the action of nitric acid on benzene (or benzol), mono-nitro-benzene is formed:—

C_{6}H_{6} + HNO_{3} = C_{6}H_{5}.NO_{2} +H_{2}O.
Mono-nitro-benzene.

By the action of another molecule of nitric acid, the di-nitro-benzene is formed:—

C_{6}H_{5}.NO_{2} + HNO_{3} = C_{6}H_{4}(NO_{2}){2} + H{2}O.
Di-nitro-benzene.

These nitro bodies are not acids, nor are they ethereal salts of nitrous acid, as nitro-glycerine is of glycerine. They are regarded as formed from nitric acid by the replacement of hydroxyl by benzene radicals.

~Mono-nitro Benzene~ is made by treating benzene with concentrated nitric acid, or a mixture of nitric and sulphuric acids. The latter, as in the case of the nitration of glycerine, takes no part in the reaction, but only prevents the dilution of the nitric acid by the water formed in the reaction. Small quantities may be made thus:—Take 150 c.c. of H_{2}SO_{4} and 75 c.c. HNO_{3}, or 1 part nitric to 2 parts sulphuric acid, and put in a beaker standing in cold water; then add 15 to 20 c.c. of benzene, drop by drop, waiting between each addition for the completion of the reaction, and shake well during the operation. When finished, pour contents of beaker into about a litre of cold water; the nitro-benzol will sink to the bottom. Decant the water, and wash the nitro-benzol two or three times in a separating funnel with water. Finally, dry the product by adding a little granulated calcium chloride, and allowing to stand for some little time, it may then be distilled. Nitro-benzene is a heavy oily liquid which boils at 205° C., has a specific gravity of 1.2, and an odour like that of oil of bitter almonds. In the arts it is chiefly used in the preparation of aniline.

~Di-nitro Benzene~ is a product of the further action of nitric acid on benzene or nitro-benzene. It crystallises in long fine needles or thin rhombic plates, and melts at 89.9° C. It can be made thus:—The acid mixture used consists of equal parts of nitric and sulphuric acids, say 50 c.c. of each, and without cooling add very slowly 10 c.c. of benzene from a pipette. After the action is over, boil the mixture for a short time, then pour into about half a litre of water, filter off the crystals thus produced, press between layers of filter paper, and crystallise from alcohol. Di-nitro-benzene, or meta-di-nitro-benzene, as it is sometimes called, enters into the composition of several explosives, such as tonite No. 3, roburite, securite, bellite.

Nitro-benzene is manufactured upon the large scale as follows:—Along a bench a row of glass flasks, containing 1 gallon each (1 to 2 lbs. benzene), are placed, and the acids added in small portions at a time, the workmen commencing with the first, and adding a small quantity to each in turn, until the nitration was complete. This process was a dangerous one, and is now obsolete. The first nitro-benzene made commercially in England, by Messrs Simpson, Maule, and Nicholson, of Kennington, in 1856, was by this process. Now, however, vertical iron cylinders, made of cast-iron, are used for the nitrating operation. They are about 4 feet in diameter and 4 feet deep, and a series are generally arranged in a row, at a convenient height from the ground, beneath a line of shafting. Each cylinder is covered with a cast-iron lid having a raised rim all round. A central orifice gives passage to a vertical shaft, and two or more other conveniently arranged openings allow the benzene and the mixed acids to flow in. Each of these openings is surrounded with a deep rim, so that the whole top of the cylinder can be flooded with water some inches in depth, without any of it running into the interior of the nitrator. The lid overhangs the cylinder somewhat, and in the outer rim a number of shot- holes or tubes allow the water to flow down all over the outside of the cylinder into a shallow cast-iron dish, in which it stands. By means of a good supply of cold water, the top, sides, and bottom of the whole apparatus is thus cooled and continually flooded. The agitator consists of cast-iron arms keyed to a vertical shaft, with fixed arms or dash-plates secured to the sides of the cylinder. The shaft has a mitre wheel keyed on the top, which works into a corresponding wheel on the horizontal shafting running along the top of the converters. This latter is secured to a clutch; and there is a feather on the shaft, so that any one of the converters can if necessary be put either in or out of gear. This arrangement is necessary, as riggers or belts of leather, cotton, or indiarubber will not stand the atmosphere of the nitro-benzole house. Above and close to each nitrator stands its acid store tank, of iron or stoneware.

The building in which the nitration is carried out should consist of one story, have a light roof, walls of hard brick, and a concrete floor of 9 to 12 inches thick, and covered with pitch, to protect its surface from the action of the acids. The floor should be inclined to a drain, to save any nitro-benzol spilt. Fire hydrants should be placed at convenient places, and it should be possible to at once fill the building with steam. A 2-inch pipe, with a cock outside the building, is advisable. The building should also be as far as possible isolated.

The acids are mixed beforehand, and allowed to cool before use. The nitric acid used has a specific gravity of 1.388, and should be as free as possible from the lower oxides of nitrogen. The sulphuric acid has a specific gravity of 1.845, and contains from 95 to 96 per cent. of mono- hydrate. A good mixture is 100 parts of nitric to 140 parts of sulphuric acid, and 78 parts of benzene; or 128 parts HNO_{3}, 179 of H_{2}SO_{4}, and 100 of benzene (C_{6}H_{6}). The benzene having been introduced into the cylinder, the water is turned on and the apparatus cooled, the agitators are set running, and the acid cock turned on so as to allow it to flow in a very thin stream into the nitrator.

Should it be necessary to check the machinery even for a moment, the stream of acid must be stopped and the agitation continued for some time, as the action proceeds with such vigour that if the benzene being nitrated comes to rest and acid continues to flow, local heating occurs, and the mixture may inflame. Accidents from this cause have been not infrequent. The operation requires between eight to ten hours, agitation and cooling being kept up all the time. When all the acid is added the water is shut off, and the temperature allowed to rise a little, to about 100° C. When it ceases to rise the agitators are thrown out of gear, and the mixture allowed some hours to cool and settle. The acid is then drawn off, and the nitro-benzene is well washed with water, and sometimes distilled with wet steam, to recover a little unconverted benzene and a trace of paraffin (about .5 per cent. together). At many English works, 100 to 200 gallons, or 800 to 1,760 lbs., are nitrated at a time, and toluene is often used instead of benzene, especially if the nitro-benzene is for use as essence of myrbane. The waste acids, specific gravity 1.6 to 1.7, contain a little nitro-benzene in solution and some oxalic acid. They are concentrated in cast-iron pots and used over again.

~Di-nitro Benzene~ is obtained by treating a charge of the hydrocarbon benzene with double the quantity of mixed acids in two operations, or rather in two stages, the second lot of acid being run in directly after the first. The cooling water is then shut off, and the temperature allowed to rise rapidly, or nitro-benzene already manufactured is taken and again nitrated with acids. A large quantity of acid fumes come off, and some of the nitro- and di-nitro-benzol produced comes off at the high temperature which is attained, and a good condensing apparatus of stoneware must be used to prevent loss. The product is separated from the acids, washed with cold water and then with hot. It is slightly soluble in water, so that the washing waters must be kept and used over again. Finally it is allowed to settle, and run while still warm into iron trays, in which it solidifies in masses 2 or 4 inches thick. It should not contain any nitro-benzol, nor soil a piece of paper when laid on it, should be well crystallised, fairly hard, and almost odourless. The chief product is meta-di-nitro-benzene, melting point 89.8, but ortho-di-nitro-benzene, melting point 118°, and para-di-nitro, melting point 172°, are also produced. The melting point of the commercial product is between 85° to 87° C.

Di-nitro-toluene is made in a similar manner. The tri-nitro-benzene can only be made by using a very large excess of the mixed acids. Nitro- benzene, when reduced with iron, zinc, or tin, and hydrochloric acids, forms aniline.

~Roburite.~—This explosive is the invention of a German chemist, Dr Carl Roth (English patent 267A, 1887), and is now manufactured in England, at Gathurst, near Wigan. It consists of two component parts, non-explosive in themselves (Sprengel's principle), but which, when mixed, form a powerful explosive. The two substances are ammonium nitrate and chlorinated di-nitro-benzol. Nitro-naphthalene is also used. Nitrate of soda and sulphate of ammonium are allowed to be mixed with it. The advantages claimed for the introduction of chlorine into the nitro compound are that chlorine exerts a loosening effect upon the NO_{2} groups, and enables the compound to burn more rapidly than when the nitro groups alone are present.

The formula of chloro-di-nitro-benzol is C_{6}H_{3}Cl(NO_{2})_{2}. The theoretical percentage of nitrogen, therefore, is 13.82, and of chlorine 17.53. Dr Roth states that, from experiments he has made, the dynamic effect is considerably increased by the introduction of chlorine into the nitro compound. Roburite burns quickly, and is not sensitive to shock; it must be used dry; it cannot be made to explode by concussion, pressure, friction, fire, or lightning; it does not freeze; it does not give off deleterious fumes, and it is to all intents and purposes flameless; and when properly tamped and fired by electricity, can be safely used in fiery mines, neither fine dust nor gases being ignited by it. The action is rending and not pulverising. Compared to gunpowder, it is more powerful in a ratio ranging from 2-1/2 to 4 to 1, according to the substance acted upon. It is largely used in blasting, pit sinking, quarrying, &c., but especially in coal mining. According to Dr Roth, the following is the equation of its decomposition:—

C_{6}H_{3}Cl(NO_{2}){2} + 9HN{4}NO_{3} = 6CO_{2} + 20N + HCl.

In appearance roburite is a brownish yellow powder, with the characteristic smell of nitro-benzol. Its specific gravity is 1.40. The Company's statement that the fumes of roburite were harmless having been questioned by the miners of the Garswood Coal and Iron Works Colliery, a scientific committee was appointed by the management and the men jointly for the purpose of settling the question. The members of this committee were Dr N. Hannah, Dr D.J. Mouncey, and Professor H.B. Dixon, F.R.S., of Owens College. After a protracted investigation, a long and technical report was issued, completely vindicating the innocuousness of roburite when properly used. In the words of The Iron and Coal Trades' Review (May 24, 1889), "The verdict, though not on every point in favour of the use in all circumstances of roburite in coal mines, is yet of so pronounced a character in its favour as an explosive that it is impossible to resist the conclusion that the claims put forward on its behalf rest on solid grounds."

Roburite was also one of the explosives investigated by the committee appointed in September 1889 by the Durham Coalowners' and Miners' Associations, for the purpose of determining whether the fumes produced by certain explosives are injurious to health. Both owners and workmen were represented on the committee, which elected Mr T. Bell, H.M. Inspector of Mines, as its chairman, with Professor P.P. Bedson and Drs Drummond and Hume as professional advisers. The problem considered was whether the fumes produced by the combustion of certain explosives, one of which was roburite, were injurious to health. The trial comprised the chemical analysis of the air at the "intake," and of the vitiated air during the firing of the shots at the "return," and also of the smoky air in the vicinity of the shot-holes. Five pounds and a half of roburite were used in twenty-three shots. It had been asserted that the fumes from this explosive contained carbon-monoxide, CO, but no trace of this gas could be discovered after the explosion. On another occasion, however, when 4.7 lbs. of roburite were exploded in twenty-three shots, the air at the "return" showed traces of CO gas to the extent of .042 to .019 per cent. The medical report which Drs Hume and Drummond presented to the committee shows that they investigated every case of suspected illness produced by exposure to fumes, and they could find no evidence of acute illness being caused. They say, "No case of acute illness has, throughout the inquiry, been brought to our knowledge, and we are led to the conclusion that such cases have not occurred."

~Manufacture.~—As now made, roburite is a mixture of ammonium nitrate and chlorinated di-nitro-benzol. The nitrate of ammonia is first dried and ground, and then heated in a closed steam-jacketed vessel to a temperature of 80° C., and the melted organic compound is added, and the whole stirred until an intimate mixture is obtained. On cooling, the yellow powder is ready for use, and is stored in straight canisters or made up into cartridges. Owing to the deliquescent nature of the nitrate of ammonia, the finished explosive must be kept out of contact with the air, and for this reason the cartridges are waterproofed by dipping them in melted wax. Roburite is made in Germany, at Witten, Westphalia; and also at the English Company's extensive works at Gathurst, near Wigan, which have been at work now for some eighteen years, having started in 1888. These works are of considerable extent, covering 30 acres of ground, and are equal to an output of 10 tons a day. A canal runs through the centre, separating the chemical from the explosive portions of the works, and the Lancashire and Yorkshire Railway runs up to the doors. Besides sending large quantities of roburite itself abroad, the Company also export to the various colonies the two components, as manufactured in the chemical works, and which separately are quite non-explosive, and which, having arrived at their destination, can be easily mixed in the proper proportions.

Among the special advantages claimed for roburite are:—First, that it is impossible to explode a cartridge by percussion, fire, or electric sparks. If a cartridge or layer be struck with a heavy hammer, the portion struck is decomposed, owing to the large amount of heat developed by the blow. The remaining explosive is not in the least affected, and no detonation whatever takes place. If roburite be mixed with gunpowder, and the gunpowder fired, the explosion simply scatters the roburite without affecting it in the least. In fact, the only way to explode roburite is to detonate it by means of a cap of fulminate, containing at least 1 gramme of fulminate of mercury. Secondly, its great safety for use in coal mines. Roburite has the great advantage of exploding by detonation at a very low temperature, indeed so low that a very slight amount of tamping is required when fired in the most explosive mixture of air and coal gas possible, and not at all in a mixture of air and coal dust—a condition in which the use of gunpowder is highly dangerous.

Mr W.J. Orsman, F.I.C., in a paper read at the University College, Nottingham, in 1893, gives the temperature of detonation of roburite as below 2,100° C., and of ammonium nitrate as 1,130° C., whereas that of blasting gelatine is as much as 3,220° C. With regard to the composition of the fumes formed by the explosion of roburite, Mr Orsman says: "With certain safety explosives—roburite, for instance—an excess of the oxidising material is added, namely, nitrate of ammonia; but in this case the excess of oxygen here causes a diminution of temperature, as the nitrate of ammonia on being decomposed absorbs heat. This excess of oxygen effectually prevents the formation of carbon monoxide (CO) and the oxides of nitrogen."

The following table (A), also from Mr Orsman's paper, gives the composition of five prominent explosives, and shows the composition of the gases formed on explosion. The gases were collected after detonating 10 grms. of each in a closed strong steel cylinder, having an internal diameter of 5 inches.

With respect to the influence of ammonium nitrate in lowering the temperature of explosion of the various substances to which it is added, it was found by a French Commission that, when dry and finely powdered, ammonium nitrate succeeds in depreciating the heat of decomposition without reducing the power of the explosive below a useful limit. The following table (B) shows the composition of the explosives examined, and the temperatures which accompanied their explosion.

A
______________________________________________________________________
| | | |
| | | Composition of Gases. |
| |Volume |__________________________|
| Explosive. |of Gas | | | | |
| |formed.|CO_{2}.| CO. |CH_{4}| N. |
| | | | | &H. | |
|___________________________________|_______|_______|_____|______|_____|
| | | | | | |
| | | Per | Per | Per | Per |
| | c.c. | cent. |cent.|cent. |cent.|
|Gunpowder— | | | | | |
| Nitre 75 parts | | | | | |
| Sulphur 10 '' | 2,214 | 51.3 | 3.5| 3.5 | 41.7|
| Charcoal 15 '' | | | | | |
|Gelignite— | | | | | |
| Nitro-glycerine 56.5 parts | | | | | |
| Nitro-cotton 3.5 '' | 4,980 | 25 | 7 | … | 67 |
| Wood-meal 8.0 '' | | | | | |
| KNO_{3} 32.0 '' | | | | | |
|Tonite— | | | | | |
| Nitro-Cotton | 3,750 | 30 | 8 | … | 62 |
| Barium nitrate | | | | | |
|Roburite— | | | | | |
| Ammonium nitrate, 86 parts | | | | | |
| Di-nitro-chloro-benzol 14 '' | 4,780 | 32 | … | … | 68 |
|Carbonite | | | | | |
| Nitro-glycerine 25 parts | | | | | |
| Wood-meal 40 '' | 2,100 | 19 | 15 | 26 | … |
| Potas. nitrate 34 '' | | | | | |
|___________________________________|_______|_______|_____|______|_____|

B ____________________________________________________________________ | | | | | | | Original | Percentage | Final | | Explosive. | Temperature |NH_{4}.NO_{3}| Temperature | | |Co-efficient.| added. |Co-efficient.| |__________________________|_____________|_____________|_____________| | | | | | |Nitro-glycerine | 3,200 | … | … | |Blasting gelatine | | | | | (8 per cent. gun-cotton)| 3,090 | 88 | 1,493 | |Dynamite | | | | | (25 per cent. silica)| 2,940 | 80 | 1,468 | | | | | | |Gun-cotton, 1 | 2,650 | … | … | | | 2,060 | 90.5 | 1,450 | | | | | | |Ammonium nitrate | 1,130 | … | … | |__________________________|_____________|_____________|_____________|

~Bellite~ is the patent of Mr Carl Lamm, Managing Director of the Rötebro Explosive Company, of Stockholm, and is licensed for manufacture in England. It consists of a mixture of nitrate of ammonia with di- or tri-nitro-benzol, it has a specific gravity of 1.2 to 1.4 in its granulated state, and 1 litre weighs 800 to 875 grms. Heated in an open vessel, bellite loses its consistency at 90° C., but does not commence to separate before a temperature of 200° C. is reached, when it evaporates without exploding. If heated suddenly, it burns with a sooty flame, somewhat like tar, but if the source of heat is removed, it will cease burning, and assume a caramel-like structure. It absorbs very little moisture from the air after it has been pressed, and if the operation has been performed while the explosive is hot, the subsequent increase of weight is only 2 per cent. When subjected to the most powerful blow with a steel hammer upon an iron plate, it neither explodes nor ignites. A rifle bullet fired into it at 50 yards' distance will not explode it. Granulated bellite explodes fully by the aid of fulminating mercury. Fifteen grms. of bellite fired by means of fulminate, projected a shot from an ordinary mortar, weighing 90 lbs., a distance of 75 yards, 15 grms. of gunpowder, under the same conditions, throwing it only 12 yards. A weight of 7-1/2 lbs. falling 145 centimetres failed to explode 1 grm. of bellite.

Various experiments and trials have been made with this explosive by Professor P.T. Cleve, M.P.F. Chalon, C.N. Hake, and by a committee of officers of the Swedish Royal Artillery. It is claimed that it is a very powerful and extremely safe explosive; that it cannot be made to explode by friction, shock, or pressure, nor by electricity, fire, lightning, &c., and that it is specially adapted for use in coal mines, &c.; that it can only be exploded by means of a fulminate detonator, and is perfectly safe to handle and manufacture; that it does not freeze, can be used as a filling for shells, and lastly, can be cheaply manufactured.

~Securite~ consists of 26 parts of meta-di-nitro-benzol and 74 parts of ammonium nitrate. It is a yellow powder, with an odour of nitro-benzol. It was licensed in 1886. It sometimes contains tri-nitro-benzol, and tri-nitro-naphthalene. The equation of its combustion is given as

C_{6}H_{4}(NO_{2}){2} + 10(NH{4}NO_{3}) = 6CO_{2} + 22H_{2}O + 11N_{2}

and, like bellite and roburite, it is claimed to be perfectly safe to use in the presence of fire damp and coal dust.[A] The variety known as Flameless Securite consists of a mixture of nitrate and oxalate of ammonia and di-nitro-benzol.

[Footnote A: See paper by S.B. Coxon, North of Eng. Inst. Mining and
Mech. Eng., 11, 2, 87.]

~Kinetite.~—A few years ago an explosive called "Kinetite"[A] was introduced, but is not manufactured in England. It was the patent of Messrs Petry and Fallenstein, and consisted of nitro-benzol, thickened or gelatinised by the addition of some collodion-cotton, incorporated with finely ground chlorate of potash and precipitated sulphide of antimony. An analysis gave the following percentages:—

Nitro-benzol, 19.4 per cent.
Chlorate of potash, 76.9 per cent.
Sulphide of antimony nitro-cotton, 3.7 per cent.

[Footnote A: V. Watson Smith, Jour. Soc. Chem. Ind., January 1887.]

It requires a very high temperature to ignite it, and cannot, under ordinary circumstances, when unconfined, be exploded by the application of heat. It is little affected by immersion in water, unless prolonged, when the chlorate dissolves out, leaving a practical inexplosive residue.[A] It was found to be very sensitive to combined friction and percussion, and to be readily ignited by a glancing blow of wood upon wood. It was also deficient in chemical stability, and has been known to ignite spontaneously both in the laboratory and in a magazine. It is an orange- coloured plastic mass, and smells of nitro-benzol.

[Footnote A: Col. Cundill, R.A., "Dict. of Explosives," says: "If, however, it be exposed to moist and dry air alternately, the chlorate crystallises out on the surfaces, and renders the explosive very sensitive.">[

~Tonite No. 3~ contains 10 to 14 per cent. of nitro-benzol (see Tonite). Trench's Flameless Explosive contains 10 per cent. of di-nitro-benzol, together with 85 per cent. of nitrate of ammonia, and 5 per cent. of a mixture of alum, and the chlorides of sodium and ammonia.

~Tri-nitro-Toluene.~—Toluene, C_{7}H_{8}, now chiefly obtained from coal- tar, was formerly obtained by the dry distillation of tolu-balsam. It may be regarded as methyl-benzene, or benzene in which one hydrogen is replaced by methyl (CH_{3}), thus (C_{6}H_{5}CH_{3}), or as phenyl- methane, or methane in which one hydrogen atom is replaced by the radical phenyl (C_{6}H_{5}), thus (CH_{3}C_{6}H_{5}). Toluene is a colourless liquid, boiling at 110° C., has a specific gravity of .8824 at 0° C., and an aromatic odour. Tri-nitro-toluene is formed by the action of nitric acid on toluene. According to Häussermann, it is more advantageous to start with the ortho-para-di-nitro-toluene, which is prepared by allowing a mixture of 75 parts of 91 to 92 per cent. nitric acid and 150 parts of 95 to 96 per cent. sulphuric acid to run in a thin stream into 100 parts of para-nitro-toluene, while the latter is kept at a temperature between 60° to 65° C., and continually stirred. When the acid has all been run in, this mixture is heated for half an hour to 80° C., and allowed to stand till cold. The excess of nitric acid is then removed. The residue after this treatment is a homogeneous crystalline mass of ortho-para-di-nitro- toluene, of which the solidifying point is 69.5° C. To convert this mass into tri-nitro derivative, it is dissolved by gently heating it with four times its weight of sulphuric acid (95 to 96 per cent.), and it is then mixed with 1-1/2 times its weight of nitric acid (90 to 92 per cent.), the mixture being kept cool. Afterwards it is digested at 90° to 95° C., with occasional stirring, until the evolution of gas ceases. This takes place in about four or five hours.

The operation is now stopped, the product allowed to cool, and the excess of nitric acid separated from it. The residue is then washed with hot water and very dilute soda solution, and allowed to solidify without purification. The solidifying point is 70° C., and the mass is then white, with a radiating crystalline structure. Bright sparkling crystals, melting at 81.5° C. may, however, be obtained by recrystallisation from hot alcohol. The yield is from 100 parts di-nitro-toluene, 150 parts of the tri-nitro derivative. Häussermann states also that 1:2:4:6 tri-nitro- toluene can be obtained from ordinary commercial di-nitro-toluene melting at 60° to 64° C.; but when this is used, greater precautions must be exercised, for the reactions are more violent. Moreover, 10 per cent. more nitric acid is required, and the yield is 10 per cent. less. He also draws attention to the slight solubility of tri-nitro-toluene in hot water, and to the fact that it is decomposed by dilute alkalies and alkaline carbonates—facts which must be borne in mind in washing the substance. This material is neither difficult nor dangerous to make. It behaves as a very stable substance when exposed to the air under varying conditions of temperature (-10° to +50° C.) for several months. It cannot be exploded by flame, nor by heating it in an open vessel. It is only slightly decomposed by strong percussion on an anvil. A fulminate detonator produces the best explosive effect with tri-nitro-toluene. It can be used in conjunction with ammonium nitrate, but such admixture weakens the explosive power; but even then it is stated to be stronger than an equivalent mixture of di-nitro-benzene and ammonium nitrate. Mowbray patented a mixture of 3 parts nitro-toluol to 7 of nitro-glycerine, also in the proportions of 1 to 3, which he states to be a very safe explosive.

~Faversham Powder.~—One of the explosives on the permitted list (coal mines) is extensively used, and is manufactured by the Cotton Powder Co. Ltd. at Faversham. It is composed of tri-nitro-toluol 11 parts, ammonium nitrate 93 parts, and moisture 1 part. This explosive must be used only when contained in a case of an alloy of lead, tin, zinc, and antimony thoroughly waterproof; it must be used only with a detonator or electric detonator of not less strength than that known as No. 6.

~Nitro-Naphthalene.~—Nitro-naphthalene is formed by the action of nitric acid on naphthalene (C_{10}H_{8}). Its formula is C_{10}H_{7}NO_{2}, and it forms yellow needles, melting at 61° C.; and of di-nitro-naphthalene (C_{10}H_{6}(NO_{2})_{2}), melting point 216° C. There are also tri-nitro and tetra-nitro and [alpha] and [beta] derivatives of nitro-naphthalene. It is the di-nitro-naphthalene that is chiefly used in explosives. It is contained in roburite, securite, romit, Volney's powder, &c. Fehven has patented an explosive consisting of 10 parts of nitro-naphthalene mixed with the crude ingredients of gunpowder as follows:—Nitro-naphthalene, 10 parts; saltpetre, 75 parts; charcoal, 12.5 parts; and sulphur, 12.5 parts. He states that he obtains a mono-nitro-naphthalene, containing a small proportion of di-nitro-naphthalene, by digesting 1 part of naphthalene, with or without heat, in 4 parts of nitric acid (specific gravity 1.40) for five days.

Quite lately a patent has been taken out for a mixture of nitro- naphthalene or di-nitro-benzene with ammonium nitrate, and consists in using a solvent for one or other or both of the ingredients, effected in a wet state, and then evaporating off the solvent, care being taken not to melt the hydrocarbon. In this way a more intimate mixture is ensured between the particles of the components, and the explosive thus prepared can be fired by a small detonator, viz., by 0.54 grms. of fulminate. Favier's explosive also contains mono-nitro-naphthalene (8.5 parts), together with 91.5 parts of nitrate of ammonia. This explosive is made in England by the Miners' Safety Explosive Co. A variety of roburite contains chloro-nitro-naphthalene. Romit consists of 100 parts ammonium nitrate and 7 parts potassium chlorate mixed with a solution of 1 part nitro- naphthalene and 2 parts rectified paraffin oil.

~Ammonite.~—This explosive was originally made at Vilvorde in Belgium, under the title of the Favier Explosive, consisting of a compressed hollow cylinder composed of 91.5 per cent. of nitrate of ammonia, and 8.5 per cent. of mono-nitro-naphthalene filled inside with loose powder of the same composition. The cartridges were wrapped in paper saturated with paraffin-wax, and afterwards dipped in hot paraffin to secure their being water-tight. The Miners' Safety Explosives Co., when making this explosive at their factory at Stanford-le-Hope, Essex, abandoned after a short trial the above composition, and substituted di-nitro-naphthalene 11.5 per cent. for the mono-nitro-naphthalene, and used thin lead envelopes filled with loose powder slightly pressed in, in place of the compressed cylinders containing loose powder. The process of manufacture is shortly as follows:—132-3/4 lbs. of thoroughly dried nitrate of ammonium is placed in a mill pan, heated at the bottom with live steam, and ground for about twenty minutes until it becomes so dry that a slight dust follows the rollers; then 17-1/2 lbs. of thoroughly dry di-nitro-naphthalene is added, and the grinding continued for about ten minutes. Cold water is then circulated through the bottom of the pan until the material appears of a lightish colour and falls to powder. (While the pan is hot the whole mass looks slightly plastic and of a darker colour than when cold.) A slide in the bottom of the pan is then withdrawn, the whole mass working out until the pan is empty; it is now removed to the sifting machine, brushed through a wire sieve of about 12 holes to the inch, and is then ready for filling into cartridges. The hard core is returned from the sifting machine and turned into one of the pans a few minutes before the charge is withdrawn.

The ammonite is filled into the metallic cartridges by means of an archimedian screw working through a brass 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 passed 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 quantities 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 quantities, 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 class 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 class 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 constituents 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 Hellhoffite, 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 class of explosives, otherwise this class is not manufactured or used in England. The principal members are known as Hellhoffite, 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 Panclastite, 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 mass 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 constitution.[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.), xxxii. 180.]

Picric acid crystallises in yellow shining prisms or laminæ 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 potassium 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 quantity 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 potassium 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. LXXXI., by Colonel (now Sir V.D.) Majendie, C.B.), and some experiments made by Dr Duprè 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 quantity 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 quantity 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 assume that picric acid cannot explode when simply heated. On the contrary, Berthelot has proved that this is not the case. If a glass tube be heated to redness, and a minute quantity of picric acid crystals be then thrown in, it will explode with a curious characteristic noise. If the quantity 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 mass, 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 mass. 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 quantity of dry picric acid is sufficient to detonate a much larger quantity 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 shells, 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 shells. 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 Désignolles and Brugère have introduced military powders, consisting of mixtures of potassium and ammonium picrates with nitrate of potassium. M. Désignolles introduced three kinds of picrate powders, composed as follows:—

___________________________________________________________________ | | | | | | | For Torpedoes | For Guns. | For Small | | | and Shells. | 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. Brugère's powder is composed of ammonium picrate and nitre, the proportions being 54 per cent. picrate of ammonia and 46 per cent. potassic nitrate. It is stable, safe to manufacture and handle, but expensive. It gives good results in the Chassepôt 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 Japanese 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 shells. 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 shells. 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 shells 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 constitution is not very well understood. Dr
E. Divers, F.R.S., and Mr Kawakita (Chem. Soc. Jour., 1884, pp. 13-19),
give the formulæ 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), assigns 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 principal 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 quantities 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 potassium 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 potassium. 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. With hydrogen it forms the acid fulminate of silver. It is used in crackers and bon-bons, and other toy fireworks, in minute quantities. 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 assigned 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 potassium 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 potassic 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 circumstance 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 quantities, 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 glass 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 potassium 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 potassium chlorate, 4 of sulphide of antimony, the mixture being damped with a varnish consisting of 645 grains of shellac 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 spaced 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 shellac 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 shell.

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 Kæmmerer, 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 quantities 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 quantities 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 quantity 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.

[Illustration: 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).

[Illustration: 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 space 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.

[Illustration: FIG. 36.—ELECTRIC EXPLODER.]