powders, in which are contained chlorate of potash or fulminating
mercury. The action of that peculiar substance the chlorite of nitrogen
is still more remarkable. There is also another compound, containing
three parts of saltpetre, one part of carbonate of potash and one part
of sulphur, which when brought to a certain heat will explode with great
violence, its destructive force being very considerable; and this is
principally due to the rapidity of the evolution of the gas, for its
amount is less than that produced from gunpowder, but the complete
decomposition occurs in a much shorter time.
~In a damp state less quickly fired, and why.~
If gunpowder be in a damp state, the velocity of combustion will be less
than when dry, and also a longer time will be necessary to ignite it,
since the moisture upon its conversion into vapour, absorbs a certain
amount of heat which remains latent, and of which the useful effects so
far as igniting the powder is concerned, is entirely lost.
~Ignition by percussion.~
Gunpowder may be ignited by the percussion of copper against copper,
copper against iron, lead against lead, and even with lead against wood,
when the shock is very great. It is more difficult to ignite gunpowder
between copper and bronze,[1] or bronze and wood than between the other
substances. Again, out of ten samples which were wrapt in paper and
struck upon an anvil with a heavy hammer, seven of grained powder
exploded and nine of mealed.
[1] Bronze consists of 78 parts copper to 20 of tin. Bell metal--78
copper and 22 tin. Gun metal--100 copper to 8 to 10 tin. Brass--2
copper, 1 zinc and calamine stone, to harden and colour.
~Influence of shape of grain on ignition.~
If the part to which the heat is applied be of an angular shape, the
inflammation will take place quicker than if it be of a round or flat
form, on account of the greater surface that is exposed to the increased
temperature.
~The form of the grain influences the velocity of the transmission of
flame.~
If the grains are of a rounded form, there would be larger interstices,
and a greater facility will be afforded to the passage of the heated
gas, and therefore this shape is most favourable to the rapid and
complete inflammation of each grain in the whole charge. On the other
hand, particles of an angular or flat form, fitting into each other as
it were, offer greater obstruction to this motion, and the velocity of
the transmission of inflammation is thereby diminished.
~Effect of size on the velocity of transmission of inflammation.~
If the grains be small, the interstices will be small also, and the
facility to the expansion of the gas thereby diminished. In the
experiments with trains of powder, the increased surface exposed to the
heated gas was found to more than compensate for the diminished facility
to its expansion, and generally a train of small-grained powder laid
upon a surface without being enclosed, will be consumed more quickly
than a train of large-grained powder.
~Large grain best suited for heavy ordnance.~
But this is not the case in a piece of ordnance, a circumstance which
amongst others will account for the diminished initial velocity given to
the shot by a charge of small-grained musket powder, below that produced
by the large-grained usually adopted for this service.
~Velocity of the transmission of inflammation of the charge.~
~Estimate of Mr. Piobert.~
When a number of grains of powder are placed together as in the charge
of a gun, and a few of them are ignited at one end of the cartridge, a
certain quantity of gas is developed of a temperature sufficiently high
to ignite those in their immediate vicinity. This has also such
elasticity as to enable it to expand itself with considerable velocity.
Again, the grains which are so ignited continue the inflammation to
others in the same manner. The absolute velocity of expansion of this
gas is very considerable; but the grains of gunpowder in the charge
offer an obstruction to this motion, the gas having to wind its way
through the interstices, and consequently the velocity is considerably
diminished, but it is quite clear that it must be very much greater than
the velocity of combustion. Mr. Piobert estimates the velocity of
transmission of inflammation of a charge in a gun at about 38 feet per
second, and in all probability even this is much under the mark.
~Experiments made on this subject.~
Many experiments have been made by observing the velocity of
transmission of inflammation of trains of powder under various
circumstances, but they do not show us what would be the velocity in a
confined charge. The velocity increased with the section of the train,
and further when at the end first lighted, there was an obstruction to
the escape of gas, as in the case of a gun, a much shorter time was
required for complete inflammation.
~Time of decomposition depends upon form of grain.~
When the charge of powder in a gun is ignited the grains being enveloped
by the heated gas, we may consider that each grain is ignited over its
whole surface at once. If the grains of powder were of equal or regular
form, the time each would be consuming, might be easily calculated, but
since in ordinary cases they are irregular in form, although the grains
may be of the same weight, the time necessary for their complete
decomposition will be very different.
~Circumstances affecting combustion.~
The quickness of combustion will depend upon the dryness of the powder,
the density of the composition, the proportion of the ingredients, the
mode of manufacture, and the quality of the ingredients.
~Combustion of cubical grains considered.~
Were a cubical grain to be ignited upon its whole surface, the
decomposition may be supposed to take place gradually from the surface
to the centre, and the original cubical form to remain until the whole
is consumed, the cube becoming smaller and smaller. If, then, the rate
of burning be the same throughout, the quantity of gas generated in the
first half portion of the time will evidently be considerably more than
in the latter half, as in the latter case there will be a much lesser
surface under the influence of flame.
~Elongated and cylindrical grains.~
If the form of the grain be elongated, then will the quantity of gas
generated in a given time from a grain of similar weight to that of the
cube or sphere, be increased, on account of the greater ignited surface,
and consequently the time necessary for its combustion will be
diminished. If it be of a cylindrical form for example, this time must
be reckoned from the diameter of the cylinder, its length not
influencing it in the least, although as we have seen, it enters into
the consideration of the quantity of the gas generated in a given time.
~Large grain.~
In the ordinary large-grain powder, the majority of the grains are of
the elongated or flat form, from whence considerable advantage is
derived, particularly in short guns, since it causes the greatest
portion of the charge to be decomposed before the projectile is moved
sensibly from its original position.
~Mealed powder.~
If the charge be composed of mealed powder a longer time is found to be
necessary for the complete combustion of the whole than in the case
where the substance is granulated, and the initial velocity of a shot is
reduced about one third by employing the substance in that state.
~The effect of granulating gunpowder.~
A piece of pressed cake weighing 1·06oz., was put into a mortar, and a
globe of some light substance, placed upon it, and the powder being
consumed after ignition without ejecting the ball from the bore of the
piece. When an equal quantity was divided into seven or eight pieces,
the globe was thrown out of the mortar; breaking the cake into twelve
pieces; the ball ranged 3·3 yards; being further increased to fifty
grains, it ranged 10·77 yards; and when the ordinary powder was used,
the ball was projected 56·86 yards.
~Action depends upon size and form of grain.~
It will appear from the above remarks, that the force generated from the
charge of powder in a gun, will be greatly influenced by the size and
form of the grains composing it.
~Density of gunpowder.~
In order to obtain a gunpowder which shall possess a proper amount of
force, it is necessary that the ingredients should be thoroughly
incorporated, and the process of incorporation will in great measure
affect the density of the grains. After going through the process, it is
subjected to a certain pressure, in order that the substance in
travelling may not be reduced to a fine powder, which would cause the
velocity of transmission of inflammation to be diminished. But there is
a certain point beyond which it would not be advantageous to increase
the density, and this seems to vary with the size of the grain. With
large-grain powder the action in a musket, or in guns with small
charges, is greatest with a low density; while with very small grain,
the highest velocities are obtained generally with the gunpowder of
great density; but in heavy guns with ordinary charges, the
large-grained powder should be of considerable density in order to
obtain the greatest effect, though still it must not be too great.
~Advantages of glazing.~
The principal advantages of glazing are; first, that the powder so
prepared, will in travelling, owing to the smaller amount of destructive
force consequent on friction, produce less mealed powder; and secondly,
that in a damp country like England, the glazing imparts a preserving
power to the powder, as the polished surface is less likely to imbibe
moisture than the rough.
~Disadvantages of glazing.~
~Experiments as to glazing.~
~Glazing less hurtful to fine grains.~
The disadvantages of glazing consists in its polishing the surface, and
thus depriving it of those angular projections which cause the ignition
and combustion to be carried on with greater rapidity, by rendering the
interstices smaller, the consequence of which is, that there is not so
much gas produced previously to the projectile leaving the gun, and in
large charges a portion will be blown out unfired. There must be a limit
then to glazing, which it would not be proper to exceed. At an
experiment with glazed and unglazed powder, the ranges on the eprouvette
were 75 for glazed, and 98 for unglazed. This loss of power, consequent
on glazing, has caused it to be done away with in France and Russia.
With fine grain powder it is not of so much consequence, as it is, to a
certain degree, corrected by the size of the grain.
~Size of grain determined by size of charge.~
~Tight ramming bad.~
The rapidity with which a charge of gunpowder is consumed will depend
not only in a certain degree upon the size of the grain, but on the
manner in which the charge is put together, for if a charge is closely
pressed, the gases meeting resistance in their endeavours to escape
between the interstices, will not propagate the ignition so rapidly.
With large charges, there exists a positive advantage for the grains to
be rather large, so that the most distant parts of the charge should be
reached by the gases as quickly as possible; whilst with that of a
rifle, the charge being small, the fineness of the grain does not
interfere with the quantity of the gas developed. Whence it may
rationally be concluded that the dimensions of the grains should
increase in proportion to the quantity of the charges into which they
are to enter, that is to say, in proportion to the interstices. Ramming
down a charge tightly must therefore interfere with the velocity of
combustion.
NOTE--The foregoing on the explosive force of gunpowder was taken from
Lieut-Colonel E. M. Boxer’s Treatise on Artillery.
FOULING.
~Produce of decomposed gunpowder.~
The produce obtained by the decomposition of gunpowder are the gaseous
and the solid. The gaseous is chiefly nitrogen and carbonic acid. The
solid is sulphur and potassium, mixed with a little charcoal, but the
solid produce is nearly entirely volatilized at the moment of explosion
through the high temperature.
~Fouling.~
Fouling is occasioned by the deposition inside the barrel of the solid
residue proceeding from the combustion of the powder.
~Conditions of fouling depend on state of atmosphere~
One of the principal of these, namely, the sulphide of Potassa, is
deliquescent, or attracts water from the atmosphere. Hence, on a clear
day, when the air holds little moisture, the fouling does not attain
that semi-fluid state it so speedily attains in a damp day, and it is
not so easily removed, and tends to accumulate inside the barrel.
Fouling may also be increased or diminished, according to the quality of
the powder.
~Effects of Fouling.~
Fouling occasions loss of power from the increased friction, and causes
inaccuracy in direction and elevation, by filling the grooves, and thus
preventing the proper spiral motion being imparted to the projectile.
EFFECTS OF GUNPOWDER ON METALS.
~Difference of effect on brass and iron guns.~
The effect produced by Gunpowder on metals, in long continued and rapid
firing, is very extraordinary. Several of the guns employed at the siege
of San Sebastian were cut open, and the interior of some of the vent
holes, which were originally cylindrical, and only two-tenths of an inch
in diameter, were enlarged in a curious and irregular manner, from three
to five inches in one direction, and from two to three inches in
another, but the brass guns were much more affected than the iron. In
December, 1855, there were lying in the arsenal at Woolwich several of
the heaviest sea mortars, which had recently been used at the
bombardment of Sweaborg, and the continuous firing on that occasion had
split them into two nearly equal portions from muzzle to breech, a
trunnion being with each half.
Heavy guns for garrisons, sieges, &c., are made of cast iron; guns for
field purposes, where lightness is required, are made of gun metal.
~Difference of effect of brass and iron guns~
These guns are generally denominated brass guns. They can be loaded,
properly pointed at an object, and fired about four times in three
minutes, but they will not stand long continued rapid firing, or more
than 120 rounds a day, as the metal, when heated, softens, and the shot
then injures the bore. Heavy iron guns may be loaded, fired, &c., once
in two minutes. They suffer more from the total number of rounds that
have been fired from them, without reference to the intervals between
each round, than from the rapidity of the firing. Four hundred and five
hundred rounds per day have not rendered an iron gun unserviceable.
MISCELLANEOUS EXPERIMENTS.
The following experiments, extracted from Mr. Wilkinson’s “Engines of
War,” serve to illustrate the capability of metals to resist the force
of gunpowder, and may be of some practical utility, as well as prove
interesting merely as matter of curiosity.
Experiment 1.--A piece about 5 inches long was cut off the breech-end of
a common musket barrel. It was screwed at the part cut, and another plug
fitted, so as to have two plugs, one at each end, leaving an internal
space of about 3 inches. A percussion nipple was screwed into the end of
one of these plugs. This being arranged, one of the plugs was turned
out, and one drachm of gunpowder introduced. The plug was replaced, and
the powder fired by putting a copper cap on the nipple, and striking it
with a hammer. The whole force of the powder escaped at the hole in the
nipple. Two, three, four, five, and six drachms were successively
introduced, and fired in the same manner, without bursting or injuring
the piece of barrel. At last, seven drachms forced out one end, in
consequence of the screw having been carelessly fitted. This defect
being repaired, Mr. Marsh, of Woolwich, repeatedly fired it with five
drachms, merely holding it with a towel in his left hand, and firing it
with a blow of a hammer. Six drachms of powder is the full service
charge for a flint musket, and four drachms of a percussion musket; yet
this immense pressure can be resisted by a cylinder of iron not more
than one quarter of an inch thick, and not iron of the best quality.
Experiment 2.--A good musket barrel had a cylinder of brass, three
inches long, turned to fit the muzzle, and soldered in, so as to close
it air-tight. The plug, or breech-screw, was removed, and a felt wad was
pushed in with a short piece of wood, marked to the exact depth the
charge would occupy, to prevent the ball rolling forward. A musket ball
was then dropped in, and a cartridge, containing three drachms of
powder, was introduced. The breech being screwed in, left the barrel
loaded. It was fired by a percussion tube, but there was no report. On
removing the breech-screw, the ball was found to be flattened. A
repetition of this experiment, with four drachms, produced a similar
result, but the ball was rather more flattened. With five drachms, the
ball was perfectly round and uninjured. Six drachms burst the barrel
close under the bayonet stud; the ball escaped through the opening,
disfigured, but fell close to the barrel. In these experiments the
barrel always advanced, instead of recoiling, as usual.
Experiment 3.--Made at Woolwich Arsenal, with a Gomer mortar, the
chamber being bored conically, so that the shell, when dropped in, fits
closely all round, instead of being bored cylindrically, with a chamber
in the centre. The mortar being laid at an angle of 45°, one drachm of
powder was put into the bottom, and a 68-pounder iron shot over it. When
fired, the ball was projected two feet clear of the mortar. A wooden
ball, precisely the same diameter, but weighing only 5lbs., was scarcely
moved by the same charge, and with two drachms of powder it was just
lifted in the mortar, and fell into its place again. Here we find a
weight of 68lbs. thrown to the distance of two feet by the same power
which would not lift 5lbs., and the wooden ball scarcely moved by double
the powder.
This proves that the firing of gunpowder under such circumstances is not
instantaneous. In the first instance, the small quantity of powder had a
large space to fill below the ball, and a heavy weight to move;
therefore, could not stir it at all until the whole was ignited, when
the force was sufficient to throw it forward two feet. In the second
case, the first portion of gas that was generated by ignition of the
powder, was sufficient to lift the lighter weight, just enough to allow
all the force to escape round it before it had time to accumulate.
Experiment 4.--A cannon ball, weighing 24lbs., was placed exactly over
the vent-hole of a loaded 32-pounder cannon, which was fired by a train
of gunpowder, when the rush from the vent projected the 24-pounder ball
to a very considerable height in the air, although the diameter of the
hole was only two-tenths of an inch.
Experiment 5.--A most ingenious method of ascertaining the relative
quickness of ignition of different qualities of gunpowder.
A gun-barrel mounted on a carriage with wheels, and moving on a
perfectly horizontal railway, is placed at right angles to another short
railway, at any convenient distance (suppose fifty feet, or yards); on
the second railway a light carriage moves freely with any desired
velocity, being drawn forward by means of a weight and pulleys: a cord
is attached to the front of this carriage, which passes over a pulley at
the end of the railroad, and is continued up a high pole or staff over
another pulley at the top, at which end the weight is attached. A long
rectangular frame covered with paper is fixed perpendicularly on the
carriage, so that when it moves forward it passes across the direct line
of the barrel, and forms a long target. A percussion lock is attached to
the barrel, which is fired by a detent, or hair-trigger, and the wire
which pulls it is disengaged at the same instant to admit of recoil.
This wire is carried straight on to the target railroad, and fixed to a
small lever, against which the front part of the target-carriage strikes
as it is carried onwards by the weight. This constitutes the whole
apparatus. When required to be used, the barrel is loaded with gunpowder
accurately weighed, and a brass ball that fits the bore correctly: the
weight is then disengaged, and the target moves quickly along,
discharging the barrel as it passes, and the ball goes through it. With
the same powder tried at the same time, the ball constantly goes through
the same hole, or breaks into it. If the next powder tried be slower of
ignition than the preceding, the ball will pass through another part of
the target more in the rear; if quicker, more in advance; thus affording
a means of ascertaining this important quality of gunpowder with
considerable accuracy: the velocity of the target-carriage can be easily
regulated by increasing or diminishing the weight which draws it
forward. The differences in the distances between which the balls strike
the target with different kinds of powder was frequently as much as ten
or twelve inches; but it is not an apparatus commonly used, having been
merely constructed for experimental purposes.
ON THE TIME REQUIRED FOR IGNITION OF GUNPOWDER.
Gunpowder like all other inflammable substances requires to be raised to
a certain temperature, before it will ignite, viz., to a dull red heat,
or about 600° Fahrenheit. If the heat passes with such rapidity through
the powder, so as not to raise the temperature to the necessary degree,
then the powder will not ignite, from the velocity of transit, so that
it might be possible to calculate theoretically, the velocity that must
be given to a red hot ball to enable it to pass through a barrel of
gunpowder without causing explosion. The passage of electric fluid
through gunpowder may be adduced in evidence of the ignition being
dependent on the degree of velocity. The flame of all fulminating
powders will pass through the centre of a box filled with gunpowder
without igniting one grain of it. If a train of gunpowder be crossed at
right angles by a train of fulminating mercury, laid on a sheet of paper
or a table, and the powder be lighted with a red hot iron wire, the
flame will run on until it meets the cross train of fulminating mercury,
when the inflammation of the latter will be so instantaneous as to cut
off all connection with the continuous train of powder, leaving the
remaining portion of the gunpowder unignited. If on the contrary the
fulminating powder be lighted first, it will go straight on and pass
through the train of gunpowder so rapidly, as not to inflame it at all.
Were a gun to be charged with gun-cotton and gunpowder, the latter would
be fired out unignited.
EFFECTS OF ACCIDENTAL EXPLOSIONS OF GUNPOWDER.
Considering the combustible nature of the materials, accidents very
seldom occur; when they do, it is more frequently in the process at the
Mill while under the runners.
On one occasion at Waltham Abbey Mills, when the powder exploded, after
having been two hours under the runners, the doors and windows of the
Mills on the opposite side of the stream, were forced open outwards, and
the nails drawn. A similar effect took place when the Dartford Mills
blew up, January 1833, in consequence of an accident in the packing
house. A window which had been recently fitted up in Dartford Town,
about a mile and a half distant from the works, was blown outwards into
the street, and a considerable quantity of paper was carried as far as
Eltham and Lewisham, distances of eight and ten miles. The sudden
rarification of the air may account for this circumstance, the
atmospheric pressure being removed in the vicinity of the doors and
windows, they were forced open outwards by the expansive force of the
air contained within the buildings.
ON ANCIENT ENGINES OF WAR.
~War a painful topic.~
~Advantages of war being destructive.~