Chapter II: 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experimenter owing his safety to his invariable lack of complete success, for although other and better explosives have superseded it for many purposes it is capable of doing a lot of harm when it is well made.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.

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.