[Illustration: GUN-COTTON FACTORY. Dipping cotton in nitrating troughs.]
There is something about fire which fascinates every one, yet the
action of explosives arouses even a livelier interest, since the
accompanying fiery phenomena are more intense and are attended with a
shocking report and a violent destruction of the surrounding material,
while this train of events, with all its marked effects, is set in
operation by what appears to be a very slight initial cause. It is
evident on brief consideration that these bodies, like a coiled spring,
a bent bow, or a head of water, are enormous reservoirs of energy which
can be released at a touch, and which, if the explosive be properly
placed in well-proportioned amounts and discharged at the right
time, can be made to do useful and important work that can not be as
conveniently and quickly accomplished in most cases, and in some cases
can not be accomplished at all by any other means.
[Illustration: GUN-COTTON FACTORY. Digestion troughs.]
The marked characteristic of all explosive substances, and especially
of the so-called high explosives, is that the energy, as developed, is
at high potential, and the uses to which energy in this condition can
be economically put are so manifold that the production of explosives
has become one of the most important of our chemical industries, this
country alone producing, in 1890, 108,735,980 pounds, having a value of
nearly $11,000,000.
The number of possible substances possessing explosive properties
is exceedingly large; the number actually known is so great that it
has taxed the ingenuity of inventors to provide them with suitable
names; but these various explosive substances vary to so great an
extent in the energy they will develop in practice and in their safety
in storage, transportation, and use that but a comparatively small
number have met with wide acceptance. All may be classified under the
heads of physical mixtures like gunpowder, or chemical compounds like
nitroglycerin, and they owe their development of energy to the fact
that, like gunpowder, they are mixtures in which combustible substances
such as charcoal are mixed with supporters of combustion such as niter;
or that, like chloride of nitrogen, they are chemical compounds, the
formation of whose molecules is attended with the absorption of heat;
or that, like gun cotton, they are chemical compounds whose molecules
contain both the combustible and the supporter of combustion, and
whose formation from their elements is attended with the absorption
of heat; while occupying a middle place between the gunpowder and the
gun cotton class, and possessing also to some degree the properties of
the nitrogen-chloride class, are the nitro-substitution explosives, of
which melinite, emmensite, lyddite, and joveite furnish conspicuous
examples.
[Illustration: GUN-COTTON FACTORY. Final press.]
It may lead to a clearer understanding of what is said regarding
the applications of explosives to dwell briefly on the methods by
which some of them are produced, since, although the raw material in
each case is different and the details of the operations vary, the
underlying principles of the methods are the same, and a good example
is found in the military gun cotton as made by the Abel process at the
United States Naval Torpedo Station.
[Illustration: GUNPOWDER GRAINS. The large ones are over five pounds
weight, each.]
The material employed is cotton, but whether fresh from the field or in
the form of waste, it must first be freed from dirt by hand picking and
sorting, and from grease and incrusting substances by boiling in a weak
soda solution. The cotton is now dried by wringing in a centrifugal
wringer and exposing to a current of hot air in a metal closet; but as
the compacted mass of cotton holds moisture with great persistency,
after partial drying the cotton is passed through a cotton picker to
open the fiber, so that it not only yields its contained water more
readily and completely, but it also absorbs the acids more speedily in
the dipping process to which it is subsequently exposed.
[Illustration: BURNING DISK OF GUN COTTON.]
[Illustration: EXTINGUISHING BURNING GUN COTTON.]
When the moisture, by the final drying, is reduced to one half of
one per cent the cotton is, while hot, placed in copper tanks which
close hermetically, where it cools to the atmospheric temperature
and in which it is transported to the dipping room, where a battery
of large iron troughs, filled with a mixture of one part of the most
concentrated nitric acid and three parts of the most concentrated
sulphuric acid, set in a large iron water bath to keep the mixture at
a uniform temperature, is placed under a hood against the wall. The
fluffy cotton, in one-pound lots, is dipped handful by handful under
the acid, by means of an iron fork, where it is allowed to remain
for ten minutes, when it is raised to the grating at the rear of the
trough and squeezed with the lever press to remove the excess of
acid. It still retains about ten pounds of the acid mixture, and in
this condition is placed in an acid-proof stoneware crock, where it
is squeezed by another iron press to cause the contained acid to rise
above the surface of the partly converted cotton. The covered crock
is now placed with others in wooden troughs containing running water
so as to keep the temperature uniform, where the cotton is allowed to
digest for about twenty-four hours. The acid is then wrung out in a
steel centrifugal, and the wrung gun cotton is thrown in small lots
into an immersion tank containing a large volume of flowing water, in
which a paddle wheel is revolving so as to rapidly dilute and wash away
the residual acid in the gun cotton without permitting any considerable
rise of temperature from the reaction of the water with the acid.
[Illustration: MAKING MERCURY FULMINATE.]
Even these severe means are not enough, for, as the cotton fiber is
in the form of hairlike tubes, traces of the acid sufficient to bring
about the subsequent decomposition of the gun cotton are retained
by capillarity. Therefore, after boiling with a dilute solution of
sodium carbonate, the gun cotton is pulped and washed in a beater or
rag engine until the fiber is reduced to the fineness of corn meal,
and a sample of it will pass the “heat test.” This is a test of the
resistance of gun cotton to decomposition, and requires that when the
air-dried sample of gun cotton is heated to 65.5° C. in a closed tube
in which a moistened strip of potassium iodide and starch paper is
suspended, the paper should not become discolored in less than fifteen
minutes’ exposure.
[Illustration: DETONATOR USED IN THE UNITED STATES NAVY. Contains
thirty-five grains of fulminate of mercury.]
This pulping of the gun cotton not only enables one to more completely
purify it, but it also renders it possible to mold it into convenient
forms and to compress it so as to greatly increase its efficiency in
use. For this purpose the pulp is suspended in water and pumped to a
molding press, where, under a hydraulic pressure of one hundred pounds
to the square inch, it is molded into cylinders or prisms about three
inches in diameter and five inches and a half high, and these are
compressed to two inches in height by a final press exerting a pressure
of about sixty-eight hundred pounds to the square inch. As this is
regarded as a somewhat hazardous operation, the press is surrounded
by a mantlet woven from stout rope to protect the workmen from flying
pieces of metal in case of an accident. The operation is analogous to
that employed in powder-making, where the gunpowder has been pressed in
a great variety of forms and into single grains weighing several pounds
apiece.
[Illustration: TORPEDO CASES AND BLOCKS OF WOOD DESTROYED BY A NAVAL
DETONATOR.]
[Illustration: TESTING DETONATORS ON IRON PLATES.]
[Illustration: IRON CYLINDER FILLED WITH WATER AND CONTAINING A NAVAL
DETONATOR. Before and after firing, shows the work accomplished by
thirty-five grains of mercury fulminate.]
Even under the enormous pressure of the final press the compressed gun
cotton still retains from twelve to sixteen per cent of water, and in
this form it is quite safe to store and handle. When dry it is very
combustible and burns readily when ignited, but it can be quenched by
pouring water upon it. When confined in the chamber of a gun or the
bore-hole of a rock, gun cotton will burn like gunpowder when ignited,
if dry, and produce an explosion, but, in common with nitroglycerin and
other high explosives, gun cotton is best exploded and develops its
maximum effect when detonated, a result which is secured by exploding a
small quantity of mercury fulminate in contact with the dry material.
[Illustration: SMOKELESS POWDERS. In the bottle is indurite in flake
grains. The larger grains are cylindrical and hexagonal multiperforated
United States army grains. The bent grain in the foreground, looking
like a piece of rubber tubing, is a grain of Maxim powder with a single
canal. The flat strips in the foreground on the left are grains of the
French B. N. powder. The flat strips in the foreground on the right are
grains of the United States navy “pyrocellulose” powder.]
Mercury fulminate is made by dissolving mercury in nitric acid and
pouring the solution thus produced into alcohol, when a violent
reaction takes place and the fulminate is deposited as a crystalline
gray powder. This powder is loaded in copper cases and, after drying,
it is primed with dry-mealed gun cotton, the mouth of the case being
closed with a sulphur-glass plug, through which pass two copper leading
wires joined by a bridge of platinum-iridium wire, two one-thousandths
of an inch in diameter, which becomes heated to incandescence when an
electric current is sent through it. This device is what is known as
the naval detonator. Mercury fulminate is so employed because it is the
most violent of all explosives in common use, and exerts a pressure of
forty-eight thousand atmospheres when fired in contact. Although the
naval detonator contains but thirty-five grains of mercury fulminate,
yet it will rupture stout iron and heavy tin torpedo cases when fired
suspended in them, it will rend thick blocks of wood when placed in
a hole and fired within them, and it will even pierce holes through
plates of the finest wrought iron one-sixteenth inch in thickness if
only the base of the detonator is in contact with the plate, and this
has been used as a test of their efficiency. Its force is markedly
shown by firing one in a stout iron cylinder filled with water and
closed tightly, when the cylinder is blown into a shredded sphere. When
used to detonate gun cotton, either when confined or in the open, the
detonator is placed in the hole which has been molded in the center of
the gun cotton disk or block, so that it shall be in close contact with
the gun cotton. I have found that perfectly dry compressed gun cotton
is detonated by 2.83 grains of mercury fulminate; but as a torpedo
attack is necessarily in the nature of a forlorn hope and should be
provided with every possible provision against failure, and since if
the detonator fails the attack fails, the naval detonator is supplied
with thirty-five grains, so as to give a large coefficient of assurance.
[Illustration: BLENDING MACHINE FOR CORDITE.]
[Illustration: CARTRIDGE OF CORDITE SMOKELESS POWDER. Charge for 6-inch
2 F gun, 13 pounds, 4 ounces. Cords, 22¾ inches long, 3 inches in
diameter.]
A characteristic feature of gun cotton is that it may be detonated even
when completely saturated with and immersed in water, if only some dry
gun cotton be detonated in contact with it. Thus in one experiment a
disk of dry gun cotton was covered with a water-proof coating and the
detonator inserted in the detonator hole of this disk. This dry disk
was laid upon four uncoated disks, the five lashed tightly together,
and sunk in Newport Harbor, where the column remained until the
uncoated disks were saturated with salt water, when the mine was fired
and the saturated disks were found by measurement of the work done to
have been completely exploded. I have found that three ounces of dry
compressed gun cotton will cause the detonation of wet compressed gun
cotton in contact with it, but forty ounces of dry gun cotton are used
as the primer in our naval mines and torpedoes, so as to give a large
coefficient of assurance.
[Illustration: GUN-COTTON SPAR TORPEDO.]
[Illustration: BLOWING UP THE SCHOONER JOSEPH HENRY.]
In the mining and other industries the fulminate is used in smaller
quantities and it is generally mixed with potassium chlorate, the
mixture being compressed in small copper cases and sold as blasting
caps. They are fired by means of a piece of Bickford or running
fuse, consisting of a woven cotton or hemp tube containing a core
of gunpowder, which is inserted in the mouth of the copper cap and
made fast within it by crimping. The capped fuse is then inserted in
a dynamite cartridge so that the cap is firmly in contact with the
dynamite, the mouth of the cartridge is fastened securely, and the
charge inserted in the bore-hole in the rock and tamped. The protruding
end of the fuse is lighted, and the fire travels at the rate of three
feet per minute down the train of gunpowder to the fulminate, which
then detonates and causes the detonation of the dynamite.
Although gun cotton, nitroglycerin, and their congeners can be and
usually are fired by detonation, there has within recent years been
a great number of compositions invented which, while formed from gun
cotton alone or mixtures of it with nitroglycerin, burn progressively
when ignited and are therefore available for use as propellants; and
since the products of their burning are almost wholly gaseous, they
produce but little or no smoke and are therefore called smokeless
powders. As upward of fifty-seven per cent of the products of the
burning of ordinary gunpowder are solids or easily compressed vapors,
this comparative smokelessness of the modern powders is a very
important characteristic, and when used in battle they seriously modify
our former accepted methods of handling troops. While this is the
feature of these powders which has attracted popular attention, a far
more important quality which they possess is the power to impart to
a projectile a much higher velocity than black powder does, without
exerting an undue pressure on the gun. A velocity of over twenty-four
hundred feet per second has been imparted to a one-hundred-pound
projectile with the powder that I have invented for our navy, while the
pressure on the gun was less than fifteen tons to the square inch.
[Illustration: TORPEDO PRACTICE. Bow discharge.]
Prior to my work in this field all the so-called smokeless powders were
mixtures of several ingredients, resembling gunpowder in this respect.
But, considering the precise and difficult work that was expected of
these high-powered powders and the difficulty which had always been
found in securing uniformity in mixtures, and that this difficulty had
become the more apparent as the gun became more highly developed, I
sought to produce a powder which should consist of a single chemical
substance in a state of chemical purity, and which could be formed into
grains of such form and size as were most suitable for the piece in
which the powder was to be used.
I succeeded in so treating cellulose nitrate of the highest degree of
nitration as to convert it into a mass like ivory and yet leave it
pure. In this indurated condition the gun cotton will burn freely, but
it has not been possible to detonate it even when closely confined and
exposed to the initial detonation of large masses of mercury fulminate.
[Illustration: TORPEDO PRACTICE ON THE CUSHING. Broadside discharge.]
I am happy to say that this principle has now been adopted by the
Russian Government, and by our navy in its specifications for smokeless
powder; but they have, I think unwisely, selected a cellulose nitrate
containing 12.5 per cent or less of nitrogen instead of that of the
highest nitration.
This work was completed, a factory established, and the processes well
marked out when I left the torpedo station in 1892. Besides this,
there were then already commercial works established elsewhere in this
country for the manufacture of the nitroglycerin-nitrocellulose powders
of the ballistite class, while large quantities of many varieties
could be easily procured abroad. Considering these facts, and that
France and Germany had already adopted smokeless powders in 1887, that
Italy adopted one in 1888, and England about the same time, it is
unpardonable that our services should not yet have adopted any of the
smokeless powders available when we were drawn into the conflict with
Spain.
Besides their use as ballistic agents, gun cotton, dynamite, and
explosive gelatin in their ordinary condition have found employment
and been adopted as service explosives in military and naval mining,
as their great energy and the violence with which they explode, even
when unconfined, especially adapt them for use in the various kinds of
torpedoes and mines which are in vogue in the service.
[Illustration: LAUNCHING PATRICK TORPEDO FROM THE WAYS.]
One form of these torpedoes was attached to the end of a spar or pole
which was rigged out from the bow of a launch or vessel so that it
could be thrust under the enemy’s vessel, and the detonators of such
spar torpedoes were not only connected with electric generators, so
that they could be fired at will, but they, in common with mines,
were frequently provided with a system of levers so arranged that the
enemy’s vessel fired the torpedoes and mines automatically as it came
in contact with the levers. It was with such a contact-spar torpedo,
containing thirty-three pounds of gun cotton, that the schooner Joseph
Henry was blown up in Newport Harbor in 1884.
[Illustration: PATRICK TORPEDO UNDER WAY. Moving at the rate of
twenty-three knots per hour.]
There are many types of the automobile torpedo. Among them the Hall,
Patrick, Whitehead, and Howell may be cited. The first three are
propelled by the energy resident in compressed gases; the Howell by
the energy stored in a heavy fly wheel, which also, by acting on the
gyroscopic principle, serves to maintain the direction imparted to
the torpedo as it is launched. The Hall, Whitehead, and Howell are
launched from tubes or guns by means of light powder charges, and
are independent of exterior control after launching. The Patrick is
launched from ways, and is controlled from the shore or boat by a
wire through which an electric current may be sent to its steering
mechanism. The charges are quite variable, but the war heads of the
larger torpedoes contain as much as five hundred pounds of gun cotton.
[_To be concluded._]