Nitro Explosives: A Practical Treatise by P. Gerald Sanford

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~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 deg. to 85 deg. 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 deg. C.; specific
gravity at 0 deg. 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 deg. C.,
and is still liquid at 28 deg. 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 deg. C. |
| |
| C_{6}H_{4}(NO_{2})_{2} Ortho-, meta-, and para- di-nitro-benzenes. |
| Solid. M.P. 118 deg., 90 deg., and 172 deg. C. |
| |
| C_{6}H_{3}(NO_{3})_{3} S.-Tri-nitro-benzene. Solid. M.P. 121 deg. C. |
|____________________________________________________________________|
| |
| C_{6}H_{4}(CH_{3})NO_{2} Ortho-, meta-, and para- nitro-toluenes. |
| B.P. 218 deg., 230 deg., and 234 deg. 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 deg. 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 deg. 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 deg. 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 deg. 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 deg., and
para-di-nitro, melting point 172 deg., are also produced. The melting point of
the commercial product is between 85 deg. to 87 deg. 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 deg. 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 deg. C., and of ammonium nitrate as 1,130 deg. C., whereas that of
blasting gelatine is as much as 3,220 deg. 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 | ... | ... |
|__________________________|_____________|_____________|_____________|

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