Nitro Explosives: A Practical Treatise by P. Gerald Sanford

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Gun-cotton is also dissolved in acetone or acetic ether until it has taken
the form of a jelly. It is then rolled into thin sheets, and when dry cut
up into little squares. In the manufacture of smokeless powders from
nitro-cellulose, nitro-lignine, &c., the various substances are mixed with
the gun-cotton or collodion-cotton before granulating.

~Collodion-Cotton.~--In the manufacture of collodion or soluble cotton the
finer qualities of cotton-waste are used and the acids used in the dipping
tanks are much weaker. The manufacture of collodion-cotton has become of
more importance than gun-cotton, by reason of its use for the manufacture
of the various forms of gelatine, such as gelatine dynamite, gelignite,
forcite, &c., and also on account of its extensive use in the manufacture
of many of the smokeless powders. It is also used for the manufacture of
"collodion," which is a solution of collodion-cotton in ether-alcohol; for
the preparation of celluloid, and many other purposes. It is less
explosive than gun-cotton, and consists of the lower nitrates of
cellulose. It is soluble in nitro-glycerine, and in a mixture of 2 parts
of ether and 1 of alcohol; also in acetone, acetic ether, and other
solvents. MM. Menard and Domonte were the first to prepare a soluble gun-
cotton, and its investigation was carried on by Bechamp, who showed that
its properties and composition were different to those of gun-cotton.

~Manufacture.~--The cotton used is cotton-waste.[A] It is thought by some
that Egyptian cotton is preferable, and especially long fibre varieties.
The strength of the acids used is, however, of more importance than the
quality of the cotton. The percentage composition of the acid mixture
which gives the best results is as follows:--Nitric acid, 23 per cent.;
sulphuric acid, 66 per cent.; and water, 11 per cent; and has a specific
gravity of 1.712 (about). It can be made by mixing sulphuric acid of
specific gravity 1.84 with nitric acid of specific gravity 1.368 in the
proportions of 66 per cent. and 34 per cent. respectively. (The production
of the penta-nitro-cellulose is aimed at if the collodion-cotton is for
use as an explosive.) If the acids are much weaker than this, or potassium
nitrate and sulphuric acid is used, the lower nitrates will be formed. The
product, while being entirely soluble in ether-alcohol or nitro-glycerine,
will have a low nitrogen content, whereas a material with as high a
nitrogen as 12 or 12.6 is to be aimed at.

[Footnote A: Raw cotton is often used.]

The cotton should not be allowed to remain in the dipping tanks for more
than five minutes, and the acid mixture should be kept at a temperature of
28 deg. C. or thereabouts; and the cotton should be removed after a few
minutes, and should not be pressed out, as in the case of gun-cotton, but
at once transferred to the pots and allowed to steep for forty-eight
hours. (Some prefer twenty-four hours, but there is more chance in this
case of the product containing non-nitrated cellulose.) When the nitration
is complete, the collodion-cotton is removed from the pots, and treated in
exactly the same manner as described under gun-cotton. The produce should
be entirely soluble in ether-alcohol and nitro-glycerine, and contain as
near 12.7 per cent. of nitrogen as possible. The theoretical nitrogen is
for the penta-nitro-cellulose 12.75 per cent. This will, however, seldom
if ever be obtained. The following are some of the results I have obtained
from different samples:--

Nitrogen.
(1.) (2.) (3.)
German make 11.64 11.48 11.49 per cent.
Stowmarket 12.57 12.60 11.22 "
Walsrode 11.61 12.07 11.99 "
Faversham 12.14 11.70 11.60 "

and the following was the analysis of a sample (No. 1) of German-made
collodion-cotton, which made very good blasting gelatine:--

_
Soluble cotton (collodion) 99.118 per cent.| Nitrogen = 11.64 per cent.
Gun-cotton 0.642 " _|
Non-nitrated cotton 0.240 "
Total ash 0.25 "

It should contain as little non-nitrated or unconverted cotton and as
little gun-cotton as possible, as they are both insoluble in nitro-
glycerol. The quality and composition of any sample of collodion-cotton
can be quickly inferred by determining the percentage of nitrogen by means
of the nitrometer and the use of the solubility test.[A] A high nitrogen
content coupled with a high solubility is the end to be aimed at; a high
nitrogen with a low solubility shows the presence of gun-cotton, and a low
nitrogen, together with a low solubility, the presence of unnitrated
cotton. Where complete solubility is essential and the percentage of
nitrogen less important, Dr Lunge recommends nitration with a mixture of
equal parts of sulphuric and nitric acids containing from 19 to 20 per
cent. of water.

[Footnote A: See Analysis of Explosives.]

Mr T.R. France claims to have invented some improvements in the
manufacture of soluble nitro-cellulose. His object has been to produce an
article as uniform as possible. His explanation of the imperfect action of
the acids is that, however uniform the mixed acids may be in strength and
proportions, and however carefully the operations of nitrating, &c., may
be conducted, there are variable elements found in different samples of
cotton. The cotton fibre has for its protection a glazed surface. It is
tubular and cellular in structure, and contains a natural semi-fluid
substance composed of oil or gum, which varies in nature according to the
nature of the soil upon which the cotton is grown. The tubes of the fibre
seem to be open at one end only when the fibre is of normal length. When,
therefore, the cotton is subjected to the action of the mixed acids, the
line of least resistance seems to be taken by them, viz., the insides of
the tubes constituting the fibre of the cotton, into which they are taken
by capillary attraction, and are subject to change as they progress, and
to the increased resistance from the oil or gum, &c., in their progress,
and therefore to modified action, the result of which is slower and slower
action, or chemical change. He also thinks it is possible that the power
of capillary attraction is balanced in the tubes by air contained therein,
after a little, sufficiently so to prevent the acids from taking full
effect. To get over this, Mr France uses his cotton in a fine state,
almost dust, in fact, and then nitrates in the usual mixture of acids at
40 deg. to 90 deg. F., the excess of acids being removed by pressure. He says he
does not find it necessary to wash this fine cotton dust in an alkaline
solution previous to nitration. His mixed acids consist of 8 parts HNO_{3}
= 42 deg. B., and 12 parts H_{2}SO_{4} = 66 deg. B., and he stirs in the dipping
tank for fifteen minutes, the temperature being 50 deg. F. to 100 deg. F., the
temperature preferred being 75 deg. F.

~"Nitrated" Gun-Cotton.~--The nitrates that are or have been mixed with
gun-cotton in order to supply oxygen are potassium nitrate, ammonium
nitrate, and barium nitrate (tonite). The total combustion of gun-cotton
by potassium nitrate corresponds to the equation:--

10[C_{24}H_{18}(NO_{3}H)_{11}O_{9}] + 82KNO_{3} = 199CO_{2} +
41K_{2}CO_{3} + 145H_{2}O + 96N_{2},

or 828 grms. of nitrate for 1,143 grms. of gun-cotton, or 42 per cent.
nitrate and 58 per cent. gun-cotton. The explosive made at Faversham by
the Cotton Powder Company, and known as tonite No. 1, consists of very
nearly half gun-cotton and half barium nitrate. The relations by weight of
total combustion would be 51.6 of gun-cotton to 48.4 of barium nitrate.
The average composition of tonite I have found by analysis to be 51 per
cent. gun-cotton to 49 per cent. barium nitrate. The heat liberated is
practically the same as for an equivalent weight of KNO_{3}; but the
barium nitrate mixture weighs 2,223 grms. instead of 1,971 grms., or
one-eighth more. The advantage in mixing a nitrate with gun-cotton is that
it supplies oxygen, and by converting all the carbon into carbonic acid,
prevents the formation of the poisonous gas carbonic oxide (CO). The
nitrates of potassium and barium are also used admixed with nitro-
cellulose in several of the sporting smokeless powders.

~The Manufacture of Tonite.~--The explosive tonite was patented by Messrs
Trench, Faure, and Mackie, and is manufactured at Faversham and Melling at
the works of the Cotton Powder Company, and at San Francisco by the Tonite
Powder Company. It consists of finely divided and macerated gun-cotton
incorporated with finely ground nitrate of barium which has been carefully
recrystallised. It is made by acting upon carbonate of barium[A] with
nitric acid. The wet and perfectly purified, finely pulped gun-cotton is
intimately mixed up between edge runners with about the same weight of
nitrate, and the mixing and grinding continued until the whole has become
an intimately mixed paste. This paste is then compressed into cartridges,
formed with a recess at one end for the purpose of inserting the
detonator. The whole is then covered with paraffined paper.

[Footnote A: Witherite, BaCO_{3} + 2HNO_{3} = Ba(NO_{3})_{2} + CO_{2} +
H_{2}O.]

The tonite No. 2 consisted of gun-cotton, nitrates of potash and soda,
charcoal and sulphur. Tonite No. 3[A] is composed as follows:--Gun-cotton,
19 per cent.; di-nitro-benzol, 13 per cent.; and barium nitrate, 68 per
cent. or similar proportions. It is a yellowish colour, and being slower
in its explosive action, is better adapted for blasting soft rock.

[Footnote A: Tonite No. 1 was patented by Messrs Trench, Faure, and
Mackie, and tonite Nos. 2 and 3 by Trench alone.]

Tonite is extensively used in torpedoes and for submarine blasting, also
for quarries, &c. Large quantities were used in the construction of the
Manchester Ship Canal. Among its advantages are, that the English railways
will take tonite on the same footing as gunpowder; it is a very dense
material; if wetted it can easily be dried in the sun; it very readily
explodes by the use of a proper detonator; while it burns very slowly and
without the least danger; the cartridges being waterproofed, it can be
employed in wet bore holes, and it can be tamped with water; and finally,
as it contains sufficient oxygen to oxidise the carbon, no carbonic oxide
(CO) gas is formed, i.e., its detonation is perfect. It is a very safe
explosive to use, being little susceptible to either blows or friction.

Not long ago, a committee, composed of Prof. P. Bedson, Drs Drummond and
Hume, Mr T. Bell, one of H.M. Inspectors of Coal Mines, and others, in
considering the problem whether the fumes produced by the combustion of
tonite were injurious to health, carried out a series of experiments in
coal mines for this purpose. The air at the "intake" was analysed, also
the air of the "return," and the smoky air in the vicinity of the shot
holes. The cartridge was surrounded by the flame-extinguishing mixture,
and packed in a brown paper bag. During the first experiment nineteen
shots were fired (= 6.29 lbs. tonite). The "return" air showed only a
trace of carbonic oxide gas (CO). At the second experiment thirteen shots
were fired (= 4.40 lbs. tonite), and analysis of the air of the "return"
showed that CO was present in traces only, whilst the fumes contained only
1.9 to 4.8 parts per 10,000.

~Dangers in connection with the Manufacture of Guncotton, &c.~--Of all the
nitro compounds, the least dangerous to manufacture are gun-cotton and
collodion-cotton. The fact that the Stowmarket Factory is within five
minutes' walk of the town shows how safe the manufacture of this explosive
is regarded. With the exception of the nitration and the compression into
blocks or discs, the whole process is worked with a large excess of water,
and the probability of an explosion is thus reduced to a minimum. Among
the precautions that should, however, be taken, are--first, the careful
extraction of the resinous and soluble substances from the cotton before
nitration, as it was shown many years ago by Sir F.A. Abel that the
instability of the gun-cotton first manufactured in England and Austria
was chiefly due to these compounds. They are generally removed by boiling
the cotton in a soda solution.

The actual nitration of cotton is not a dangerous operation, but the
operations of wringing in the hydro-extractors, and washing the nitro-
cotton after it leaves the first centrifugal machine, are somewhat so.
Great care should be taken that the wrung-out nitro-cotton at once comes
in contact with a large excess of water, i.e., is at once immersed
entirely in the water, since at this stage it is especially liable to
decomposition, which, once started, is very difficult to stop. The warmer
the mixture and the less water it contains, the more liable it is to
decomposition; hence it is that on warm and damp days the centrifugal
machines are most likely to fire. The commencement of decomposition may be
at once detected by the evolution of red fumes. Directly the gun-cotton is
immersed in the large quantity of water in the beater and poacher it is
safe.

In order that the final product may be stable and have good keeping
qualities, it is necessary that it should be washed completely free from
acid. The treatment in the beater and poacher, by causing the material to
assume the state of a fine pulp, in contact with a large quantity of
water, does a good deal to get rid of the free acid, but the boiling
process is absolutely necessary. It has been proposed to neutralise the
free acid with a dilute solution of ammonia; and Dr C.O. Weber has
published some experiments bearing upon this treatment. He found that
after treatment with ammonia, pyroxyline assumed a slightly yellowish
tinge, which was a sure sign of alkalinity. It was then removed from the
water, and roughly dried between folds of filter paper, and afterwards
dried in an oven at 70 deg. C. After three hours, however, an explosion took
place, which entirely destroyed the strong copper oven in which the nitro-
cotton (about one oz.) had been drying. The explosion was in some respects
remarkable. The pyroxyline was the di-nitro-cellulose (or possibly the
penta-nitro?), and the temperature was below the igniting point of this
material (40 deg. C. would have been a better temperature). Dr Weber
determined the ignition point of his di-nitro-cellulose, and found it to
be 194 deg. to 198 deg. C., and he is therefore of opinion that the explosion was
due to the treatment of the partially washed material with ammonia. A
certain quantity of ammonium nitrate was probably formed, and subsequently
dried upon the nitro-cellulose, in a state of very fine subdivision. The
faintest trace of acid would then be sufficient to bring about the
explosive ignition of the ammonium nitrate.

The drying of gun-cotton or collodion-cotton is also a somewhat dangerous
operation. A temperature of 40 deg. C. (104 deg. F.) should not be exceeded, and
thermometers should be placed in the nitro-cotton, and the temperature
frequently observed. An electric alarm thermometer is also a useful
adjunct to the cotton drying house. Great care must also be taken that
there are no exposed hot-water pipes or stoves in the drying house, as the
fine gun-cotton dust produced by the turning or moving of the material
upon the shelves would settle upon such pipes or stoves, and becoming hot,
would be very sensitive to the least friction. The floor also should be
covered with linoleum or indiarubber. When hot currents of air are made to
pass over the surface of gun-cotton, the gun-cotton becomes electrified.
It is important, therefore, to provide some means to carry it away. Mr
W.F. Reid, F.I.C., was the first to use metal frames, carriers, and
sieves, upon which is secured the cloth holding the gun-cotton, and to
earth them.

The compression of gun-cotton into blocks, discs, &c., is also attended
with considerable risk. Mr O. Guttmann, in an interesting paper upon "The
Dangers in the Manufacture of Explosives" (_Jour. Soc. Chem. Ind._, No. 3,
vol. xi., 1892), says: "The compression of gun-cotton into cartridges
requires far more care than that of gunpowder, as this is done in a warm
state, and gun-cotton even when cold, is more sensitive than gunpowder.
When coming out of the centrifugal machines, the gun-cotton should always
pass first through a sieve, in order to detect nails or matches which may
by chance have got into it. What has been said as to gunpowder presses
applies still more to those for gun-cotton, although the latter are always
hydraulic presses. Generally the pistons fit the mould perfectly, that is
to say, they make aspiration like the piston of a pump. But there is no
metal as yet known which for any length of time will stand the constant
friction of compression, and after some time the mould will be wider in
that part where the greatest compression takes place. The best metal for
this purpose has proved to be a special steel made by Krupp, but this also
is only relatively better; for pistons I prefer hard cast iron. If the
position of the moulds and pistons is not exactly the same in all cases,
what the Germans call 'Ecken' (English 'binding') will take place, viz.,
the mould will stand obliquely to the piston, and a dangerous friction
will result." "Of course, it is necessary to protect the man working the
hydraulic valves during compression. At Waltham Abbey they have a curtain
made of ship's hawsers, which is at the same time elastic and resistant."
Mr Guttmann has found that a partition wall 12 inches thick, made of
2-inch planks, and filled with ground cinders, gives very effective
protection. A door in this partition enables the workman to get to the
press, and a conical tube penetrates the wall, enabling the man to see the
whole work from a safe standpoint. The roof, or one side of the building,
should be of glass, so as to give the explosion a direction.

~Trench's Fire-extinguishing Compound~ is manufactured by the Cotton
Powder Company at Faversham, and is the invention of Mr George Trench,
F.C.S., the manager of the Company. The object of the invention is to
surround the cartridges of tonite, when used in coal mines, with a fire-
extinguishing compound. If a charge of tonite, dynamite, or gelatine
dynamite is put inside a few ounces of this mixture, and then fired, not
the least trace of flame can be observed, and experiments appear to show
that there is no flame at all. The compound consists of sawdust
impregnated with a mixture of alum and chlorides of sodium and ammonia.
Fig. 22 shows the manner of placing the tonite cartridge in the paper bag,
and surrounding it with the fire-extinguishing compound, _aa_. The
attachment of the fuse and detonator is also shown.

[Illustration: FIG. 22.--TRENCH'S FIRE-EXTINGUISHING CARTRIDGE.]

The following report (taken from the _Faversham News_, 22nd Oct. 1887) of
experiments conducted in the presence of several scientific and mining men
will show its value:--"A large wrought-iron tank, of 45 cubic feet
capacity, had been sunk level with the ground in the middle of the yard;
to this tank the gas had been laid on, for a purpose that will be
explained later on. The charges were fired by means of electricity, a
small dynamo firing machine being placed from 30 to 40 yards away from the
'mine.'" Operations were commenced by the top of the tank being covered
over and plastered down in order to make it air-tight; then a sufficient
quantity of coal gas was placed in it to make it highly inflammable and
explosive, the quantity being ascertained by a meter which had been fixed
specially for the purpose. Whilst the gas was being injected the cartridge
was prepared.

The first experiment was to try whether a small charge of tonite--fired
without the patent extinguisher--would ignite the gas. The gas having been
turned on, a miner's lamp was placed in the "tank," but this was
extinguished before the full quantity of gas had gone through the meter.
However, the gas being in, the charge of 1-1/4 oz. tonite was placed in
the "mine," the detonator was connected by means of long wires to the
dynamo machine, and the word was given to "fire." With a tremendous
report, and a flash of fire, the covering of the mine flew in all
directions, clearly showing that the gas had exploded. The next cartridge
(a similar charge) was prepared with the patent compound. First of all a
brown paper case of about 2 inches diameter was taken, and one of the
tonite cartridges was placed in the centre of it, the intervening space
between the charge and-the case being packed with the "fire-extinguishing
compound." The mine having had another supply of gas injected, the
protected cartridge was placed inside and fired. The result was
astonishing, the explosion not being nearly so loud, whilst there was not
the least flash of fire. "Protected" and "unprotected" charges were fired
at intervals, gas being turned into the tank on each occasion. Charges of
tonite varying from 1 to 6 oz. were also used with the compound. The
report was trifling, whilst no flash could be seen.

~Uses of Collodion-Cotton.~--The collodion or soluble gun-cotton is used
for a variety of purposes. The chief use is, however, for the manufacture
of the various explosive gelatine compounds, of which blasting gelatine is
the type. It is also very extensively used in the manufacture of smokeless
powders, both military and sporting--in fact, very few of them do not
contain it. In some, however, nitro-lignose or nitrated wood is used
instead. This, however, is chemically the same thing, viz., nitro-
cellulose, the cellulose being derived from the wood fibre. It is more
used in this connection than the higher nitrate gun-cotton. Another use to
which it has been applied very extensively, of recent years, is in the
manufacture of "celluloid." It is used in photography for the preparation
of the films on the sensitised plates, and many other purposes. Dissolved
in a solution of two parts ether and one of alcohol, it forms the solution
known as collodion, used for a variety of purposes, such as a varnish, as
a paint for signals; in surgery, for uniting the edges of wounds.

Quite lately, Mr Alfred Nobel, the well-known inventor of dynamite, has
patented the use of nitro-cellulose, hydro- or oxy-cellulose, as an
artificial substitute for indiarubber. For this purpose it is dissolved in
a suitable non-volatile or slightly volatile "solvent," such as nitro-
naphthalene, di-nitro-benzene, nitro-toluene, or its homologues; products
are obtained varying from a gelatinous consistency to the hardness of
ebonite. The proportions will vary from about 20 per cent. of nitro-
cellulose in the finished product, forming a soft rubber, to 50 per cent.
nitrating celluloid, and the "solvent" chosen will depend on the use to
which the rubber substitute is to be put, the liquids giving a more
elastic substance, whilst mixtures of solids and liquids may be employed
when the product is to be used at high temperatures. By means of rollers
steam heated, the incorporation may be accomplished without the aid of a
volatile liquid, or the nitro-cellulose may be employed wet, the water
being removed after "solution."

It is advisable to use the cellulose nitrated only just enough to render
it suitable, in order to reduce the inflammability of the finished
product. Mr W. Allen, M.P., of Gateshead, proposed to use celluloid for
cartridge cases, and thus to lighten ammunition, and prevent jambing, for
the case will be resolved into gases along with the powder. Extractors
will also be done away with.

~Celluloid~ is an intimate mechanical mixture of pyroxyline (gun-cotton or
collodion-cotton) with camphor, first made by Hyatt, of Newark, U.S.A.,
and obtained by adding the pyroxyline to melted camphor, or by strongly
compressing the two substances together, or by dissolving the constituents
in an appropriate solvent, e.g., alcohol or ether, and evaporating to
dryness. A combination of the two latter methods, i.e., partial solution,
with pressure, is now usually adapted. The pyroxyline employed is
generally the tetra- and penta-nitrated cellulose, the hexa-nitrate
(gun-cotton) being but seldom used on account of its explosive properties.

Care is taken to prevent the formation of the hexa-nitrate by immersing
the cellulose in only moderately strong nitric acid, or in a warm mixture
of nitric and sulphuric acids. The paper, either in small pieces or in
sheets, is immersed for about twenty-five minutes in a mixture of 2 parts
of nitric acid and 5 parts of sulphuric acid, at a temperature of about
30 deg. C., after which the nitrated cellulose is thoroughly washed with water
to remove the last traces of free acid, pressed, and whilst still moist,
mixed with the camphor.

In the process of Trebouillet and De Besancele, the cellulose, which may
be in the form of paper, cotton, or linen, is twice nitrated--first in the
acid mixture employed in a previous operation; and secondly, in a fresh
mixture of 3 parts sulphuric acid of 1.83 specific gravity, and 2 parts
concentrated nitric acid containing nitrous acid. After each nitration the
mass is subjected to pressure, and is then carefully washed with water, to
which, at the last, a small quantity of ammonia or caustic soda is added
to remove the final traces of acid. The impregnation of the pyroxyline
with the camphor is effected in a variety of ways.

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