GUNPOWDER AND ITS MODERN EQUIVALENTS
The origin of gunpowder appears to be lost in antiquity. At all events
it has been in use for many centuries and is still made in many
countries.
Most boys have tried to make it at some time or other and with varying
degrees of success. Such experiments generally lead to a glorious blaze,
a delightfully horrid smell and no harm to anyone, the experimenter
owing his safety to his invariable lack of complete success, for
although other and better explosives have superseded it for many
purposes it is capable of doing a lot of harm when it is well made.
It consists of a mixture of charcoal, sulphur and saltpetre ground up
very fine and mixed very intimately together. The mixture is wetted and
pressed into cakes and dried, after which it is broken up into small
pieces. The precise proportions of the various materials seem to vary a
great deal in different countries, but generally speaking there is about
75 per cent of saltpetre (or to give it its scientific name, nitrate of
potash), 15 per cent of charcoal and 10 per cent of sulphur.
Now gunpowder, like all explosives, is simply some thing or mixture of
things which is capable of burning very quickly. When we light the fire
we set going the process which we call combustion, or burning, and, as
we know from our own experience, that process causes heat to be
generated.
What takes place in the fire-grate is that the carbon of the coal enters
into combination with oxygen from the air, the two together forming a
new compound called "carbonic acid gas." There is nothing lost or
destroyed in this process, the carbon and oxygen simply changing into
the new substance, and could we weigh the gas produced we should find
that it agreed precisely with the weight of the carbon and oxygen
consumed. For the purpose for which we require the fire, namely, to heat
the room, the chief feature about this process is not what is formed in
the shape of gas, for that simply goes off up the chimney, but the heat
which is liberated. We believe that in some mysterious way the heat is
locked up in the coal. Latent is the term we use, which means hidden: in
other words we believe that the heat is hidden in the coal: we cannot
feel it or perceive it in any way, but it comes out when we let the
carbon combine with the oxygen.
Why these two things combine at all is one of those mysteries which may
never be solved. We have theories on the subject, but all we really know
is that under certain conditions if they be in contact with one another
they will combine, apparently for the simple reason that it is their
nature so to do.
When we apply the match to the fire all we do is to set up the
conditions under which the carbon and oxygen are able to follow their
natural instincts, so to speak.
A coal fire, as we all know, burns slowly, for the simple reason that it
is only at the surface of the lumps that carbon and oxygen are in
contact. If we grind up the coal into a fine powder and then blow it
into a cloud, so that every tiny particle is surrounded with air, a
spark will cause an explosion. That is how these terrible explosions in
coal-pits are caused.
This is sometimes seen on a small scale when one shakes the empty
fire-shovel after putting coal on the fire to get rid of the fine dust
adhering to it and to save making a mess in the fender. That little
cloud of fine dust will often burst into flame like a mild explosion.
We see from this that to make an explosion we require fuel, just as we
do to make a fire: but we need that it shall be very intimately mixed
with oxygen, so that all of it can burn up in practically a single
instant. Now in gunpowder we get these conditions fulfilled. We have the
carbon in the shape of charcoal, we also have some sulphur which
likewise burns readily, and we have saltpetre which contains oxygen.
Thus, you see, we do not need to go to the air for the oxygen, for the
gunpowder possesses it already, locked up in the saltpetre. Moreover, we
can see now why it is so important for all the materials to be ground up
very fine, for it is only by so doing that we can ensure that every
particle of charcoal or sulphur shall have particles of saltpetre close
by ready to furnish oxygen at a moment's notice.
Another thing to be observed, for it lets us into the great key to the
manufacture of nearly all explosives, is the scientific name of
saltpetre. It is "nitrate of potassium," and all substances whose names
begin with "nitr-" contain nitrogen: while the termination "ate"
signifies the presence of oxygen. We need the oxygen to make the
explosion but we do not need the nitrogen, yet the latter has to be
present for without it the oxygen would be too slow in getting to work.
Nitrogen is one of the strangest substances on earth. Extremely lazy
itself, it has the knack of hustling its companions, particularly
oxygen, and making them work with tremendous fury. Whenever we get the
lazy gas nitrogen to enter into a combination with other things we may
confidently look for extraordinary activity of some sort.
So when we put a light to a quantity of gunpowder we set up those
conditions under which the carbon and oxygen can combine, and at the
same moment our lazy friend the nitrogen turns out his partner oxygen
from the nitrate in which they were till then combined and a sudden
burning is the result. The solid gunpowder is suddenly changed into a
volume of hot gas 2500 times as great. That is to say, one cubic inch of
gunpowder changes suddenly into 2500 cubic inches of gas. That sudden
expansion to 2500 times its volume is what we term an explosion. If it
takes place in an enclosed space so that the gas formed wants to expand
but cannot, the result is a pressure of about forty tons per square
inch.
If that enclosed space were the interior of a gun, that force of forty
tons per square inch would be available for driving out the projectile.
Now, gunpowder is still used for sporting purposes and also for some
special purposes in warfare, but it has the great disadvantage that it
makes a lot of smoke, so that the enemy would be easily able to locate
the guns were it to be used in them. As we know so well, by the messages
from France, guns and rifles drop their shells and bullets apparently
from nowhere and are extremely difficult to locate. That is owing to the
use of improved powders one of the great features of which is their
smokelessness.
The reason why gunpowder makes a dense smoke, is because the burning
which takes place is very incomplete. Therefore, by some such means as a
more intimate mixture of the materials a better and more complete
burning must be brought about.
One of the best known of the new powders (they are all spoken of as
powders, whatever their form, since they have taken the place of the old
gunpowder) is nitro-glycerine, the basis of which is glycerine.
The way in which we obtain this useful material has already been
explained. It consists of carbon, a lot of hydrogen and some oxygen.
These are not merely mixed together but are in combination, just as
oxygen and hydrogen are combined in water. Carbon and hydrogen will both
combine with oxygen and will give off heat in the process, but in
glycerine they are already happily united together and so glycerine
itself is no use as an explosive. If, however, we bring nitric acid and
sulphuric acid into contact with it a pair of new partnerships is set
up, one being water and the other a compound containing carbon and
hydrogen, a lot of oxygen and, most important of all, some of that
disturbing, restless though lazy nitrogen.
This is nitro-glycerine, a particularly furious explosive, for that
curious nitrogen seems to be so uncomfortable in his new surroundings
that at the smallest provocation he will break up the whole combination
and then there will be a mass of free atoms of carbon, hydrogen and
oxygen, all seeking new partners, just right for a glorious explosion.
So furious and untamed is this stuff that it was almost useless until
the famous Nobel hit upon the idea of taming it down by mixing it with
an earth called Kieselguhr, which reduces its sensitiveness sufficiently
to make it a very safe explosive to use. To this mixture Nobel gave the
name of dynamite.
It is interesting at this point to compare the action of this typical
modern explosive with that of the older gunpowder. The latter is only a
mixture: the former is a chemical compound. The smallest particle of
material in the gunpowder is a little lump containing millions of
molecules and still more of atoms: when the nitrogen has broken up the
original nitro-glycerine, just before the explosion actually takes
place, we have a mixture of _single atoms_. Thus the mixture is far more
intimate in the latter case and the burning is therefore quicker and
more thorough.
[Illustration: MACHINE-GUN _versus_ RIFLE.
This illustrates the rapidity and accuracy with which the modern rifle
can be used. Sergeant O'Leary, V.C., tackled a gun crew of five and
killed them all before they had time to slew their gun round--a striking
contrast to the "Brown Bess" of a hundred years ago.]
Another well-known explosive is gun-cotton. Surely this must be a fancy
name, for what can harmless, simple cotton have to do in connection with
guns. It is a perfectly genuine descriptive name, however. It seems very
strange at first, but it is perfectly true that nitrogen, as it turned
glycerine into dynamite, can also turn cotton into gun-cotton. Cotton
consists mainly of cellulose, a compound of carbon, hydrogen and oxygen,
happily combined together and therefore showing, as we well know from
experience, no tendency whatever to change into anything else, least of
all to "go off bang." But that state of things is very much changed when
we have induced nitrogen to take a hand in the game.
In actual practice, cotton waste, pure and clean, is dipped into a
mixture of sulphuric and nitric acids whereby the cellulose becomes
changed into nitro-cellulose, just as a similar process changes
glycerine into nitro-glycerine. The whole process of manufacture is of
course far more than that simple dipping, but that is the fundamental
fact of it all. The rest is concerned with getting rid of the
superfluous acid, tearing the stuff into pulp and pressing it into
blocks. It is probably the safest of explosives, since it can be kept
wet, in which case the danger of an accidental explosion is practically
nil, provided reasonable care be taken. Even when dry, it behaves in a
very kindly way. If hit with a hammer, it only burns for a moment just
at the point struck. If ignited with a red-hot rod, it burns but does
not explode, unless it is enclosed. The burning, that is to say, is not
sufficiently rapid to constitute an explosion.
On the other hand, if it be exploded by a detonator, by which is meant a
small quantity of a very powerful explosive, such as fulminate of
mercury, fired close to it, it then goes off with a violence which
leaves little to be desired.
It would be better still could we persuade a little more oxygen to enter
into its composition, for as it is there is not quite enough to burn up
the other matters completely. That, however, does not cause smoke, since
the combustion is complete enough to change everything into invisible
gases. With more oxygen more heat might be generated and the power of
the explosion be made greater. Still, even as it is, the explosion of
gun-cotton has been estimated by a high authority to produce a pressure
of 160 tons per square inch, four times as much as gunpowder.
Nitro-glycerine has the advantage of a rather larger proportion of
oxygen to carbon, resulting in its being rather more energetic.
Yet another class of explosive is made from Coal Tar. This is a
by-product in the manufacture of gas for lighting and also in the
manufacture of coke for industrial purposes. It comes from the retorts
along with the gas in a gaseous form but condenses into a black liquid
in the pipes and more particularly in an arrangement of cooled pipes
called a condenser specially placed to intercept it.
In the chemist's eyes it is the most interesting of liquids, for it is
full of mysteries and possibilities. The most wonderful achievements of
chemistry have it for their raw material and there is still scope for
much more in the same direction.
If the tar be gently heated in a closed vessel it will evaporate and the
vapour can be led to another vessel, there cooled and converted back
into a liquid. This looks rather like doing work for nothing, but the
various liquids, of which tar is a mixture, evaporate at different
temperatures, so that this furnishes a means of separating them. The
first liquid thus procured is known as coal tar naphtha, and if it be
again distilled it can be subdivided further, the first liquid separated
from it being known as Benzine. This, again, is another of those almost
numberless things which consist of carbon and hydrogen. Also, like the
other similar substances which we have been discussing, it can, if
treated with nitric acid, be made to take into partnership a quantity of
oxygen and nitrogen.
Thus we get nitro-benzene. We can repeat the process, when it will take
more and become di-nitro-benzene. Again we can repeat it, thus producing
tri-nitro-benzene.
The second liquid separated from coal tar naphtha is called Toluene,
which again is composed of carbon and hydrogen in slightly different
proportions. Like its confrère benzene it, too, can be treated with
nitric acid, becoming nitro-toluene and then di-nitro-toluene and
finally tri-nitro-toluene, the deadly explosive of which we read in the
papers as T.N.T.
After the naphtha has been removed from the tar another substance is
obtained called Phenol, which in a prepared form is familiar to us all
as the disinfectant Carbolic Acid. It also can be treated with nitric
acid, to produce tri-nitro-phenol, otherwise known as Picric Acid, which
after a little further treatment becomes the famous "Lyddite."
Most of the actual explosives used in warfare are prepared from one or
more of the above-mentioned compounds. For example, nitro-glycerine and
gun-cotton, having been dissolved in acetone (another compound of
carbon, hydrogen and oxygen) and a little vaseline added, form a soft
gelatinous substance which on being squeezed through a fine hole comes
out looking like a cord or string, and hence is called Cordite.
Other explosives are finished in the form of sheets, the dissolved
gun-cotton or whatever it may be being rolled between hot rollers which
give it the convenient form of sheets and at the same time evaporate the
solvent.
By combining these various substances various characteristics can be
given to the finished explosive. For instance, the one which drives the
shell from the gun, known as the propellant, must not be too sudden in
its action. It must push steadily. Its purpose is to drive the shell not
to burst the gun, wherefore its action must be comparatively slow and
continuous so long as the shell is still in the gun. It must "follow
through" as the golf player would put it.
The charge in the shell, however, needs to go off with the greatest
possible violence so as to blow the shell to pieces and to scatter the
fragments so that they do the maximum of damage.
Those explosives, whose function is thus to burst with a sudden shock,
are called High Explosives, as distinguished from the propellants which
produce a more or less sustained push.
The great fundamental principle which enables large quantities of these
powerfully explosive substances to be handled with comparative safety
involves the use of two different substances in combination. That which
is used in quantity and which actually does the work is made
comparatively insensitive, indeed in some cases it is very insensitive,
so that it can safely travel by train, by ship and by road and also may
be handled by the soldiers and sailors with very little risk. Some of
these compounds can be struck or set on fire with impunity. They are
none the less violent, however, when, by the agency of a suitable
detonator they are caused to explode.
The detonator, of course, has to be very sensitive indeed, but it need
only be used in very small quantities, so that by itself it, too, is
comparatively safe. Fulminate of mercury is often employed for this
purpose--a compound based upon mercury but in which nitrogen of course
figures largely.
Thus, there are two things necessary for the successful explosion, one
of which is powerful but insensitive, while the other is highly
sensitive but relatively harmless since it is never allowed to exist in
large quantities, and as far as possible these are kept apart until the
last moment.
One other thing may be mentioned in regard to this matter which is of
the greatest importance. That is the necessity for the utmost uniformity
in these various compounds, so that when the gunners put a charge into a
gun they can rely upon it to throw the shell exactly as its predecessor
did. Modern artillery seeks to throw shell after shell within a small
area which would clearly be quite impossible if one charge were liable
to be stronger or weaker than another, for we can easily see that the
more powerful the impetus given the farther will the shell go.
To secure this uniformity the greatest care is taken at all stages of
the manufacture, and various batches of the same stuff are tested and
mixed, and any of them turning out a little too strong are placed with
some a little too weak, so that their faults may neutralize each other.
By such methods as these a remarkable degree of uniformity is attained,
the result of which we see when we read in the papers of the wonderfully
accurate gunnery of which our soldiers and sailors are capable.
In conclusion, a word of warning may be appropriate. Reference has been
made above to the safety of modern explosives in the absence of the
detonators, but do not let that lead anyone to take liberties. Should
any reader come into possession of any of these materials, even in the
smallest quantities, let him treat it with the utmost respect, for
although what has been said about safety is quite correct, it only means
comparative safety, there can be no absolute safety where these
substances are concerned.