_DYNAMITE AND GELATINES._
Kieselguhr Dynamite--Classification of Dynamites--Properties and
Efficiency of Ordinary Dynamite--Other Forms of Dynamite--Gelatine and
Gelatine Dynamites, Suitable Gun-Cotton for, and Treatment of--Other
Materials used--Composition of Gelignite--Blasting Gelatine--Gelatine
Dynamite--Absorbing Materials--Wood Pulp--Potassium Nitrate, &c.--
Manufacture and Apparatus used, and Properties of Gelatine Dynamites--
Cordite--Composition and Manufacture.
~Dynamite.~--Dynamite consists of nitro-glycerine either absorbed by some
porous material, or mixed with some other substance or substances which
are either explosives or merely inert materials. Among the porous
substances used is kieselguhr, a silicious earth which consists chiefly of
the skeletons of various species of diatoms. This earth occurs in beds
chiefly in Hanover, Sweden, and Scotland. The best quality for the purpose
of manufacturing dynamite is that which contains the largest quantity of
the long tubular _bacillariæ_, and less of the round and lancet-shaped
forms, such as _pleurosigmata_ and _diclyochæ_, as the tube-shaped diatoms
absorb the nitro-glycerine better, and it becomes packed into the centre
of the silicious skeleton of the diatoms, the skeleton acting as a kind of
tamping, and increasing the intensity of the explosion.
Dynamites are classified by the late Colonel Cundill, R.A., in his
"Dictionary of Explosives" as follows:--
1. Dynamites with an inert base, acting merely as an absorbent.
2. Dynamites with an active base, i.e., an explosive base. No. 2 may be
again divided into three minor classes, which contain as base--
(_a._) Charcoal.
(_b._) Gunpowder or other nitrate, or chlorate mixture.
(_c._) Gun-cotton or other nitro compound (nitro-benzol, &c.).
The first of these, viz., charcoal, was one of the first absorbents for
nitro-glycerine ever used; the second is represented by the well-known
Atlas powder; and the last includes the well-known and largely used
gelatine compounds, viz., gelignite and gelatine dynamite, and also tonite
No. 3, &c.
In the year 1867 Nobel produced dynamite by absorbing the nitro-glycerine
in an inert substance, forming a plastic mass. In his patent he says:
"This invention relates to the use of nitro-glycerine in an altered
condition, which renders it far more practical and safe for use. The
altered condition of the nitro-glycerine is effected by causing it to be
absorbed in porous unexplosive substances, such as charcoal, silica,
paper, or similar materials, whereby it is converted into a powder, which
I call dynamite, or Nobel's safety powder. By the absorption of the nitro-
glycerine in some porous substance it acquires the property of being in a
high degree insensible to shocks, and it can also be burned over a fire
without exploding."
Ordinary dynamite consists of a mixture of 75 per cent. of nitro-glycerine
and 25 per cent. of kieselguhr. The guhr as imported (Messrs A. Haake &
Co. are the chief importers) contains from 20 to 30 per cent. of water and
organic matter. The water may be very easily estimated by drying a weighed
quantity in a platinum crucible at 100° C. for some time and re-weighing,
and the organic matter by igniting the residue strongly over a Bunsen
burner. Before the guhr can be used for making dynamite it must be
calcined, in order not only to get rid of moisture, but also the organic
matter.
A good guhr should absorb four times its weight of nitro-glycerine, and
should then form a comparatively dry mixture. It should be pale pink, red
brown, or white. The pink is generally preferred, and it should be as free
as possible from grit of all kinds, quartz particles, &c., and should have
a smooth feeling when rubbed between the finger and thumb, and should show
a large quantity of diatoms when viewed under the microscope. The
following was the analysis of a dried sample of kieselguhr:--Silica,
94.30; magnesia, 2.10; oxide of iron and alumina, 1.3; organic matter,
0.40; moisture, 1.90 per cent.
The guhr is generally dried in a reverberatory muffle furnace. It is
spread out on the bottom to the thickness of 3 or 4 inches, and should
every now and then be turned over and raked about with an iron rabble or
hoe. The temperature should be sufficiently high to make the guhr red hot,
or the organic matter will not be burnt off. The time occupied in
calcining will depend of course upon the quality of the guhr being
operated upon. Those containing a high percentage of water and organic
matter will of course take longer than those that do not. A sample of the
calcined guhr should not contain more than 0.5 per cent. of moisture and
organic matter together.
After the guhr is dry it requires to be sifted and crushed. The crushing
is done by passing it between iron rollers fixed at the bottom of a cone
or hopper, and revolving at a moderate speed. Beneath the rollers a fine
sieve should be placed, through which the guhr must be made to pass.
The kieselguhr having been dried, crushed, and sifted, should be packed
away in bags, and care should be taken that it does not again absorb
moisture, as if it contains anything above about five-tenths per cent. of
water it will cause the dynamite made with it to exude. The guhr thus
prepared is taken up to the danger area, and mixed with nitro-glycerine.
The nitro-glycerine used should be quite free from water, and clear, and
should have been standing for a day or two in the precipitating house. The
guhr and nitro-glycerine are mixed in lead tanks (about 1-1/2 foot deep,
and 2 to 3 feet long), in the proportions of 75 of the nitro-glycerine to
25 of the guhr, unless the guhr is found to be too absorbent, which will
cause the dynamite to be too dry and to crumble. In this case a small
quantity of barium sulphate, say about 1 per cent., should be added to the
guhr. This will lessen its absorbing powers, or a highly absorptive sample
of guhr may be mixed with one of less absorptive power, in the proportions
found by experiment to be the best suited to make a fairly moist dynamite,
but one that will not exude.
The mixing itself is generally performed in a separate house. In a series
of lead-lined tanks the guhr is weighed, placed in a tank, and the nitro-
glycerine poured on to it. The nitro-glycerine may be weighed out in
indiarubber buckets. The whole is then mixed by hand, and well rubbed
between the hands, and afterwards passed through a sieve. At this stage
the dynamite should be dry and powdery, and of a uniform colour.
It is now ready to be made up into cartridges, and should be taken over to
the cartridge huts. These are small buildings surrounded with mounds, and
contain a single cartridge machine. Each hut requires three girls--one to
work the press, and two to wrap up the cartridges. The cartridge press
consists of a short cylinder of the diameter of the cartridge that it is
intended to make. Into this cylinder a piston, pointed with ivory or
lignum vitæ wood, works up and down from a spring worked by a lever. Round
the upper edge of the cylinder is fastened a canvas bag, into which the
powdery dynamite is placed by means of a wooden scoop, and the descending
piston forces the dynamite down the cylinder and out of the open end,
where the compressed dynamite can be broken off at convenient lengths. The
whole machine should be made of gun-metal, and should be upright against
the wall of the building. The two girls, who sit at tables placed on each
side of the press, wrap the cartridges in parchment paper. From these huts
the cartridges are collected by boys every ten minutes or a quarter of an
hour, and taken to the packing room, where they are packed in 5-lb.
cardboard boxes, which are then further packed in deal boxes lined with
indiarubber, and fastened down air tight. The wooden lids are then nailed
down with brass or zinc nails, and a label pasted on the outside giving
the weight and description of the contents. The boxes should then be
removed to the magazines. It is well to take a certain number of
cartridges from the packing house at different times during the day, say
three or four samples, and to test them by the heat test. A sample cut
from a cartridge, about 1 inch long, should be placed under a glass shade,
together with water (a large desiccator, in fact), and left for some days.
A good dynamite should not, under these conditions, show any signs of
exudation, even after weeks.[A]
[Footnote A: For analysis of dynamite, see chapter on "Analysis," and
author's article in _Chem. News_, 23rd September 1892.]
~Properties of Kieselguhr Dynamite.~--One cubic foot of dynamite weighs 76
lbs. 4 oz. The specific gravity of 75 per cent. dynamite is, however,
1.50. It is a red or grey colour, and rather greasy to the touch. It is
much less sensitive to shock than nitro-glycerine, but explodes
occasionally with the shock of a rifle bullet, or when struck. The
addition of a few per cent. of camphor will considerably diminish its
explosive qualities to such an extent that it can be made non-explosive
except to a very strong fulminate detonator. The direct contact of water
disintegrates dynamite, separating the nitro-glycerine, hence great
caution is necessary in using it in wet places. It freezes at about 40°
Fahr. (4° C.), and remains frozen at temperatures considerably exceeding
that point. When frozen, it is comparatively useless as an explosive
agent, and must be thawed with care. This is best done by placing the
cartridges in a warming pan, which consists of a tin can, with double
sides and bottom, into which hot water (130° Fahr.) can be poured. The
dynamite will require to be left in for some considerable time before it
becomes soft. On no account must it be placed on a hot stove or near a
fire, as many serious accidents have occurred in this way.
Frozen dynamite is a hard mass, with altered properties, and requires 1.5
grm. of fulminate instead of 0.5 grm. to explode it. Thawing may also
cause exudation of the nitro-glycerine, which is much more sensitive to
shock, and if accidentally struck with an iron tool, may explode. It is a
dangerous thing to cut a frozen cartridge with a knife. Ramming is even
more dangerous; in fact it is not only dangerous, but wasteful, to use
dynamite when in a frozen state.
Dynamite explodes at a temperature of 360° Fahr., and is very sensitive to
friction when hot. In hot countries it should never be exposed to the rays
of the sun. It should, however, not be kept in a damp or moist place, as
this is liable to cause exudation. Sunlight, if direct, can cause a slow
decomposition, as with all nitro and nitric compounds. Electric sparks
ignite, without exploding it, at least when operating in the open air.
Dynamite, when made with neutral nitro-glycerine, appears to keep
indefinitely. Sodium or calcium carbonate to the extent of 1 per cent. is
often added to dynamite to ensure its being neutral. If it has commenced
to undergo change, however, it rapidly becomes acid, and sometimes
explodes spontaneously, especially if contained in resisting envelopes.
Nevertheless, neutral and well-made dynamite has been kept for years in a
magazine without loss of its explosive force. If water is brought into
contact with it, the nitro-glycerine is gradually displaced from the
silica (guhr). This action tends to render all wet dynamite dangerous.
It has been observed that a dynamite made with wood sawdust can be
moistened and then dried without marked alteration, and from 15 to 20 per
cent. of water may be added to cellulose dynamite without depriving it of
the power of exploding by strong detonator (this is similar to wet
gun-cotton). It is, however, rendered much less sensitive to shock. With
regard to the power of No. 1 dynamite, experiments made in lead cylinders
give the relative value of No. 1 dynamite, 1.0; blasting gelatine, 1.4;
and nitro-glycerine, 1.4. The heat liberated by the sudden explosion of
dynamite is the same as its heat of combustion,[A] and proportionate to
the weight of nitro-glycerine contained in the mixture. The gases formed
are carbonic acid, water, nitrogen, and oxygen.
[Footnote A: Berthelot, "Explosives and their Power."]
The "explosive wave" (of Berthelot) for dynamite is about 5,000 metres per
second. At this rate the explosion of a cartridge a foot long would only
occupy 1/24000 part of a second, while a ton of dynamite cartridges about
7/8 diameter, laid end to end, and measuring one mile in length, would be
exploded in one-quarter of a second by detonating a cartridge at either
end.[A] Mr C. Napier Hake, F.I.C., the Inspector of Explosives for the
Victorian Government, in his paper, "Notes on Explosives," says: "The
theoretical efficiency of an explosive cannot in practice be realised in
useful work for several reasons, as for instance in blasting rock--
"1. Incomplete combustion.
"2. Compression and chemical changes induced in surrounding material.
"3. Energy expended in cracking and heating of the material which is not
displaced.
"4. The escape of gas through the blast-hole and the fissures caused by
the explosion.
"The useful work consists partly in displacing the shattered masses. The
proportion of useful work obtainable has been variously estimated at from
14 to 33 per cent. of the theoretical maximum potential."
[Footnote A: C.N. Hake, "Notes on Explosives," _Jour. Soc. Chem. Ind._,
1889.]
Among the various forms of dynamite that are manufactured is carbo-
dynamite, the invention of Messrs Walter F. Reid and W.D. Borland. The
base is nitro-glycerine, and the absorbent is carbon in the form of burnt
cork. It is as cheap as ordinary dynamite, and has greater explosive
force, seeing that 90 per cent. of the mixture is pure nitro-glycerine,
and the absorbent itself is highly combustible. It is also claimed that if
this dynamite becomes wet, no exudation takes place.
Atlas powder is a dynamite, chiefly manufactured in America at the Repanno
Chemical Works, Philadelphia. It is a composition of nitro-glycerine,
wood-pulp, nitrate of soda, and carbonate of magnesia. This was the
explosive used in the outrages committed in London, by the so-called
"dynamiters." Different varieties contain from 20 to 75 per cent. of
nitro-glycerine.
The Rhenish dynamite, considerably used in the mines of Cornwall, is
composed of 70 parts of a solution of 2 to 3 per cent. of naphthalene in
nitro-glycerine, 3 parts of chalk, 7 parts of sulphate of barium, and 20
of kieselguhr.
Kieselguhr dynamites are being largely given up in favour of gelatine
explosives. The late Colonel Cundill, in his "Dictionary of Explosives,"
gives a list of about 125 kinds of dynamites. Many of these, however, are
not manufactured. Among the best known after the ordinary No. 1 dynamite
are forcite, ammonia dynamite, litho-fracteur, rendock, Atlas powder,
giant powder, and the various explosive gelatines. They all contain nitro-
glycerine, mixed with a variety of other substances, such as absorbent
earths, wood-pulp, nitro-cotton, carbon in some form or other, nitro-
benzol, paraffin, sulphur, nitrates, or chlorates, &c. &c.
~Blasting Gelatine and Gelatine Dynamite.~--The gelatine explosives
chiefly in use are known under the names of blasting gelatine, gelatine
dynamite, and gelignite. They all consist of the variety of nitro-
cellulose known as collodion-cotton, i.e., a mixture of the penta- and
tetra-nitrates dissolved in nitro-glycerine, and made up with various
proportions of wood-pulp, and some nitrate, or other material of a similar
nature. As the gun-cotton contains too little oxygen for complete
combustion, and the nitro-glycerine an excess, a mixture of the two
substances is very beneficial.
Blasting gelatine consists of collodion-cotton and nitro-glycerine without
any other substance, and was patented by Mr Alfred Nobel in 1875. It is a
clear, semi-transparent, jelly-like substance, of a specific gravity of
1.5 to 1.55, slightly elastic, resembling indiarubber, and generally
consists of 92 per cent. to 93 per cent. of nitro-glycerine, and 7 to 8
per cent. of nitro-cotton. The cotton from which it is made should be of
good quality. The following is the analysis of a sample of nitro-cellulose
which made very good gelatine:-
Soluble cotton 99.118 per cent.
Gun-cotton 0.642 "
Non-nitrated cotton 0.240 "
Nitrogen 11.64 "
Total ash 0.25 "
The soluble cotton, which is a mixture of the tetra- and penta-nitrates,
is soluble in ether-alcohol, and also in nitro-glycerine, and many other
solvents, whereas the hexa-nitrate (gun-cotton),
C_{12}H_{14}O_{4}(ONO_{2})_{6}, is not soluble in the above liquids,
although it is soluble in acetone or acetic ether. It is very essential,
therefore, that the nitro-cotton used in the manufacture of the gelatine
explosives should be as free as possible from gun-cotton, otherwise little
lumps of undissolved nitro-cotton will be left in the finished gelatine.
The non-nitrated or unconverted cotton should also be very low, in fact
considerably under 1/2 per cent.
The nitro-cotton and the nitro-glycerine used should always be tested
before use by the heat test, because if they do not separately stand this
test, it cannot be expected that the gelatine made from them will do so.
It often occurs, however, that although both the ingredients stand this
test separately before being mixed, that after the process of manufacture
one or other or both fail to do so.
The nitro-cotton most suitable for gelatine making is that which has been
finely pulped. If it is not already fine enough, it must be passed through
a fine brass wire sieve. It will be found that it requires to be rubbed
through by hand, and will not go through at all if in the least degree
damp. It is better, therefore, to dry it first. The percentage of nitrogen
in the nitrated cotton should be over 11 per cent. It should be as free as
possible from sand or grit, and should give but little ash upon ignition,
not more than 0.25 per cent. The cotton, which is generally packed wet in
zinc-lined wooden boxes, will require to be dried, as it is very essential
indeed that none of the materials used in the manufacture of gelatine
should contain more than the slightest trace of water. If they do, the
gelatine subsequently made from them will most certainly exude, and become
dangerous and comparatively valueless. It will also be much more difficult
to make the nitro-cotton dissolve in the nitro-glycerine if either
contains water.
In order to find out how long any sample of cotton requires to be dried, a
sample should be taken from the centre of several boxes, well mixed, and
about 1,000 grms. spread out on a paper tray, weighed, and the whole then
placed in the water oven at 100° C., and dried for an hour or so, and
again weighed, and the percentage of moisture calculated from the loss in
weight. This will be a guide to the time that the cotton will probably
require to be in the drying house. Samples generally contain from 20 to 30
per cent. of water. After drying for a period of forty-eight hours, a
sample should be again dried in the oven at 100° C., and the moisture
determined, and so on at intervals until the bulk of the cotton is found
to be dry, i.e., to contain from 0.25 to 0.5 per cent. of moisture. It is
then ready to be sifted. During the process of removing to the sifting
house and the sifting itself, the cotton should be exposed to the air as
little as possible, as dry nitro-cotton absorbs as much as 2 per cent. of
moisture from the air at ordinary temperatures and average dryness.
The drying house usually consists of a wooden building, the inside of
which is fitted with shelves, or rather framework to contain drawers, made
of wood, with brass or copper wire netting bottoms. A current of hot air
is made to pass through the shelves and over the surface of the cotton,
which is spread out upon them to the depth of about 2 inches. This current
of air can be obtained in any way that may be found convenient, such as by
means of a fan or Root's blower, the air being passed over hot bricks, or
hot-water pipes before entering the building. The cotton should also be
occasionally turned over by hand in order that a fresh surface may be
continually exposed to the action of the hot air. The building itself may
be heated by means of hot-water pipes, but on no account should any of the
pipes be exposed. They should all be most carefully covered over with
wood-work, because when the dry nitro-cotton is moved, as in turning it
over, very fine particles get into the air, and gradually settling on the
pipes, window ledges, &c., may become very hot, when the slightest
friction might cause explosion. It is on this account that this house
should be very carefully swept out every day. It is also very desirable
that the floor of this house should be covered with oilcloth or linoleum,
as being soft, it lessens the friction.
List shoes should always be worn in this building, and a thermometer hung
up somewhere about the centre of the house, and one should also be kept in
one of the trays to give the temperature of the cotton, especially the
bottom of the trays. The one nearest to the hot air inlet should be
selected. If the temperature of the house is kept at about 40° C. it will
be quite high enough. The building must of course be properly ventilated,
and it will be found very useful to have the walls made double, and the
intervening space filled with cinders, and the roof covered with felt, as
this helps to prevent the loss of heat through radiation, and to preserve
a uniform temperature, which is very desirable.
The dry cotton thus obtained, if not already fine enough, should be sifted
through a brass sieve, and packed away ready for use in zinc air-tight
cases, or in indiarubber bags. The various gelatine compounds, gelignite,
gelatine dynamite, and blasting gelatine, are manufactured in exactly the
same way. The forms known as gelatine dynamite differ from blasting
gelatine in containing certain proportions of wood-pulp and potassium
nitrate, &c. The following are analyses of some typical samples of the
three compounds:--
Gelatine Blasting
Gelignite. Dynamite. Gelatine.
Nitro-glycerine 60.514 71.128 92.94 per cent.
Nitro-cellulose 4.888 7.632 7.06 "
Wood-pulp 7.178 4.259 ... "
Potassium nitrate 27.420 16.720 ... "
Water ... 0.261 ... "
The gelignite and gelatine dynamites consist, therefore, of blasting
gelatine, thickened up with a mixture of absorbing materials. Although the
blasting gelatine is weight for weight more powerful, it is more difficult
to make than either of the other two compounds, it being somewhat
difficult to make it stand the exudation and melting tests. The higher
percentage of nitro-cotton, too, makes it expensive.
When the dry nitro-cotton, which has been carefully weighed out in the
proportions necessary either for blasting gelatine or any of the other
gelatine explosives, is brought to the gelatine making house, it is placed
in a lead-lined trough, and the necessary quantity of pure dry nitro-
glycerine poured upon it. The whole is then well stirred up, and kept at a
temperature of from 40° to 45° C. It should not be allowed to go much
above 40° C.; but higher temperatures may be used if the nitro-cotton is
very obstinate,[A] and will not dissolve. Great caution must, however, be
observed in this case. The mixture should be constantly worked about by
the workman with a wooden paddle for at least half an hour. At a
temperature of 40° to 45° the nitro-glycerine acts upon the nitro-cotton
and forms a jelly. Without heat the gelatinisation is very imperfect
indeed, and at temperatures under 40° C. takes place very slowly.
[Footnote A: Generally due to the nitro-cotton being damp.]
[Illustration: FIG. 30.--WERNER, PFLEIDERER, & PERKINS' MIXING MACHINE.]
The limit of temperature is 50° C. or thereabouts. Beyond this the jelly
should never be allowed to go, and to 50° only under exceptional
circumstances.
The tank in which the jelly is made is double-lined, in order to allow of
the passage of hot water between its inner and outer linings. A series of
such tanks are generally built in a wooden framework, and the double
linings are made to communicate, so that the hot water can flow from one
to the other consecutively. The temperature of the water should be about
60° C. if it is intended to gelatinise at 45° C., and about 80° if at
50° C.; but this point must, of course, be found by experiment for the
particular plant used. An arrangement should be made to enable the workman
to at once cut off the supply of hot water and pass cold water through the
tanks in case the explosive becomes too hot.
[Illustration: FIG. 31.--MR M'ROBERTS' MIXER FOR GELATINE EXPLOSIVES.]
The best way to keep the temperature of the water constant is to have a
large tank of water raised upon a platform, some 5 or 6 feet high, outside
the building, which is automatically supplied with water, and into which
steam is turned. A thermometer stuck through a piece of cork and floated
upon the surface of the tank will give the means of regulating the
temperature.
When the jelly in the tanks has become semi-transparent and the cotton has
entirely dissolved, the mixture should be transferred to the mixing
machine. The mixing machines are specially designed for this work, and are
built in iron, with steel or bronze kneading- and mixing-blades, according
to requirements.
A suitable machine for the purpose is that known as the Nito-Universal
Incorporator, shown in Fig. 30, which has been specially constructed by
Messrs Werner, Pfleiderer, & Perkins, Ltd., after many years' experience
in the mixing of explosive materials, and is now almost exclusively
adopted in both Government and private factories. Mr George M'Roberts'[A]
mixing machine, however, which is shown in Fig. 31, is still used in some
factories for dynamite jelly.
[Footnote A: See _Jour. Soc. Chem. Ind._, 1890, 267.]
If it is intended to make gelignite, or gelatine dynamite, it is at this
point that the proper proportions of wood-pulp[A] and potassium nitrate
should be added, and the whole well mixed for at least half an hour, until
the various ingredients are thoroughly incorporated.
[Footnote A: Most of the wood-pulp used in England is obtained from
pine-trees, but poplar, lime, birch, and beech wood are also used. It is
chiefly imported as wood-pulp. The pulp is prepared as follows:--The bark
and roots are first removed, and the logs then sawn into boards, from
which the knots are removed. The pieces of wood are afterwards put through
a machine which breaks them up into small pieces about an inch long, which
are then crushed between rollers. These fragments are finally boiled with
a solution of sodium bisulphite, under a pressure of about 90 lbs. per
square inch, the duration of the boiling being from ten to twelve hours.
Sulphurous acid has also been used. Pine-wood yields about 45 per cent.
and birch about 40 per cent. of pulp when treated by this process. The
pulp is afterwards bleached and washed, &c.
Birch. Beech. Lime. Pine. Poplar.
Cellulose 55.52 45.47 53.09 56.99 62.77 per cent.
Resin 1.14 0.41 3.93 0.97 1.37 "
Aqueous extract 2.65 2.47 3.56 1.26 2.88 "
Water 12.48 12.57 10.10 13.87 12.10 "
Lignine 28.21 39.14 29.32 26.91 20.88 "]
The following analysis of woods is by Dr H. Müller:--These mixing machines
can either be turned by hand, or a shaft can be brought into the house and
the machine worked by means of a belt at twenty to thirty revolutions per
minute. The bearings should be kept constantly greased and examined, and
the explosive mixture carefully excluded. When the gelatine mixture has
been thoroughly incorporated, and neither particles of nitrate or wood
meal can be detected in the mass, it should be transferred to wooden boxes
and carried away to the cartridge-making machines to be worked up into
cartridges.
[Illustration: FIG. 32.--PLAN OF THE BOX CONTAINING THE EXPLOSIVE, IN
M'ROBERTS' MACHINE.]
The application of heat in the manufacture of the jelly from collodion-
cotton and nitro-glycerine is absolutely necessary, unless some other
solvent is used besides the nitro-glycerine, such as acetone, acetic
ether, methyl, or ethyl-alcohol. (They are all too expensive, with the
exception of acetone and methyl-alcohol, for use upon the large scale.)
These liquids not only dissolve the nitro-cellulose in the cold, but
render the resulting gelatine compound less sensitive to concussion, and
reduce its quickness of explosion (as in cordite). They also lower the
temperature at which the nitro-glycerine becomes congealed, i.e., they
lower the freezing point[A] of the resulting gelatine.
[Footnote A: It has been proposed to mix dynamite with amyl alcohol for
this purpose. Di-nitro-mono-chlorhydrine has also been proposed.]
The finished gelatine paste, upon entering the cartridge huts, is at once
transferred to the cartridge-making machine, which is very like an
ordinary sausage-making machine[A] (Fig. 33). The whole thing must be made
of gun-metal or brass, and it consists of a conical case containing a
shaft and screw. The revolutions of the shaft cause the thread of the
screw to push forward the gelatine introduced by the hopper on the top to
the nozzle, the apex of the cone-shaped case, from whence the gelatine
issues as a continuous rope. The nozzle is of course of a diameter
according to the size of cartridge required.
[Footnote A: G. M'Roberts, _Jour. Soc. Chem. Ind._, 31st March 1890, p.
266.]
[Illustration: FIG. 33.--CARTRIDGE-MAKING MACHINE FOR GELATINE
EXPLOSIVES.]
The issuing gelatine can of course be cut off at any length. This is best
done with a piece of hard wood planed down to a cutting edge, i.e.,
wedge-shaped. Mr Trench has devised a kind of brass frame, into which the
gelatine issuing from the nozzle of the cartridge machine is forced,
finding its way along a series of grooves. When the frame is full, a
wooden frame, which is hinged to one end of the bottom frame, and fitted
with a series of brass knives, is shut down, thereby cutting the gelatine
up into lengths of about 4 inches.
It is essential that the cartridge machines should have no metallic
contacts inside. The bearing for the screw shaft must be fixed outside the
cone containing the gelatine. One of these machines can convert from 5 to
10 cwt. of gelatine into cartridges per diem, depending upon the diameter
of the cartridges made.
After being cut up into lengths of about 3 inches, the gelatine is rolled
up in cartridge paper. Waterproof paper is generally used. The cartridges
are then packed away in cardboard boxes, which are again packed in deal
boxes lined with indiarubber, and screwed down air tight, brass screws or
zinc or brass nails being used for the purpose. These boxes are sent to
the magazines. Before the boxes are fastened down a cartridge or so should
be removed and tested by the heat test, the liquefaction test, and the
test for liability to exudation. (Appendix, p. 6, Explosives Act, 1875.) A
cartridge also should be stored in the magazine in case of any subsequent
dispute after the bulk of the material has left the factory.
The object of the liquefaction test is to ensure that the gelatine shall
be able to withstand a fairly high temperature (such as it might encounter
in a ship's hold) without melting or running together. The test is carried
out as follows:--A cylinder of the gelatine dynamite is cut from the
cartridge of a length equal to its diameter. The edges must be sharp. This
cylinder is to be placed on end on a flat surface (such as paper), and
secured by a pin through the centre, and exposed for 144 consecutive hours
to a temperature of 85° to 90° F., and during such time the cylinder
should not diminish in height by more than one-fourth of an inch, and the
cut edges should remain sharp. There should also be no stain of
nitroglycerine upon the paper.
The exudation test consists in freezing and thawing the gelatine three
times in succession. Under these conditions there should be no exudation
of nitro-glycerine. All the materials used in the manufacture of gelatine
explosives should be subjected to analytical examination before use, as
success largely depends upon the purity of the raw materials. The
wood-pulp, for instance, must be examined for acidity.
~Properties of the Gelatine Compounds.~--Blasting gelatine is generally
composed of 93 to 95 parts nitro-glycerine, and 5 to 7 parts of nitro-
cellulose, but the relative proportions of explosive base and nitro-
glycerine, &c., in the various forms of the gelatine explosives do not
always correspond to those necessary for total combustion, either because
an incomplete combustion gives rise to a greater volume of gas, or because
the rapidity of decomposition and the law of expansion varies according to
the relative proportions and the conditions of application. The various
additions to blasting gelatine generally have the effect of lowering the
strength by reducing the amount of nitro-glycerine, but this is sometimes
done in order to change a shattering agent into a propulsive force. If
this process be carried too far, we of course lose the advantages due to
the presence of nitro-glycerine. There is therefore a limit to these
additions.[A]
[Footnote A: Mica is said to increase the rapidity of explosion when mixed
with gelatine.]
The homogeneousness and stability of the mixture are of the highest
importance. It is highly essential that the nitro-glycerine should be
completely absorbed by the substances with which it is mixed, and that it
should not subsequently exude when subjected to heat or damp. It is also
important that there should be no excess of nitro-glycerine, as this may
diminish instead of augment the strength, owing to a difference in the
mode of the propagation of the explosive wave in the liquid, and in the
mixture. Nitro-glycerine at its freezing point has a tendency to separate
from its absorbing material, in fact to exude. When frozen, too, it
requires a more powerful detonation to explode it, but it is less
sensitive to shock. The specific gravity of blasting gelatine is 1.5
(i.e., nearly equal to that of nitro-glycerol); that of gun-cotton (dry)
is 1.0.
Blasting gelatine burns in the air when unconfined without explosion, at
least in small quantities and when not previously heated, but it is rather
uncertain in this respect. It can be kept at a moderately high temperature
(70° C.) without decomposition. At higher temperatures the nitro-glycerine
will partially evaporate. When slowly heated, it explodes at 204° C. If,
however, it contains as much as 10 per cent. of camphor, it burns without
exploding. According to Berthelot,[A] gelatine composed of 91.6 per cent.
nitro-glycerine and 8.4 per cent. of nitro-cellulose, which are the
proportions corresponding to total combustion, produces by explosion
177CO_{2}+ 143H_{2}O + 8N_{2}.
[Footnote A: Berthelot, "Explosives and their Powers."]
He takes C_{24}H_{22}(NO_{3}H)_{9}O_{11} as the formula of the nitro-
cellulose, and 51C_{3}H_{2}(NO_{3}H)_{3} + C_{24}H_{22}(NO_{3}H)_{9}O_{11}
as the formula of the gelatine itself, its equivalent weight being 12,360
grms. The heat liberated by its explosion is equal to 19,381 calories, or
for 1 kilo. 1,535 calories. Volume of gases reduced temperature equals
8,950 litres. The relative value[A] of blasting gelatine to nitro-
glycerine is as 1.4 to 1.45, kieselguhr dynamite being taken as 1.0.
[Footnote A: Roux and Sarran.]