Chapter XXI: Explosives

The principal explosives owe their activity, to a very large degree, to the presence of nitrogen in them; thus they may properly be discussed in connection with that element.

The explosives of chief importance are four in number: gunpowder, the fulminates, gun-cotton, nitroglycerine. While these substances suggest at once the war-like uses to which they are put, it must not be forgotten that they have also important applications in the arts of peace. Thus enormous quantities of gunpowder and nitroglycerine are used in blasting operations for purposes like the removal of rock preparatory to laying foundations for large buildings, as well as in excavations for railway cuttings and in the boring of tunnels; also in the getting of building stone from quarries, the tearing of ore out of mineral bearing veins in mining operations; and for loosening coal in coal pits. Large quantities are likewise employed in pyrotechnics. It must not be forgotten that fireworks are not only for purposes of night illuminations and for public gratification in times of popular rejoicings; they are also employed to a considerable extent for such useful purposes as night signalling on vessels at sea.

Gunpowder.

Of the various explosives mentioned, gunpowder is the oldest. While the invention of this substance has often been referred to Roger Bacon, the celebrated English friar who died about 1292, it is now conceded that though Bacon evidently knew the composition of it, the original invention dates far earlier than his times. There seems foundation for the belief that it is as old as a thousand years, while its use by artillery at the battle of Crécy shows its employment in warfare for over five hundred years. Bacon’s power of independent thought, placed him so far in advance of the century in which he lived that he became an object of persecution, but he is at present ranked as one of the prominent figures of history. In his works Bacon refers to a substance that seems to correspond to gunpowder, and in terms that suggest that he considered it as a material of not uncommon knowledge in his day.

The principal constituents of gunpowder are three: potassic nitrate, charcoal and sulphur. The chemical action between potassic nitrate and charcoal in gunpowder may be better understood after a simple experiment, which any one can try. The experiment referred to is as follows: take a large piece of charcoal; heat it over a spirit lamp or gas lamp until certain portions of it take fire so as to burn with a slight glow; next sprinkle very carefully a small amount of powdered potassic nitrate—also called both saltpetre and nitre—upon it. A burning, something like that of gunpowder, only less violent, results. The potassic nitrate has the formula KNO₃. When it falls upon the glowing coal a portion of the oxygen leaves the other constituents and accomplishes thereby a true combustion of the carbon. One important factor in the operation is the element nitrogen; owing to the general inertness of nitrogen it easily allows the escape of other elements combined with it. So in case of the experiment just suggested, the combustion of the charcoal is referable to oxygen liberated by reason of the feeble affinity of one of the other constituents of the potassic nitrate—that is, the nitrogen. Thus far the only thing particularly suggested is the combustion that takes place; another point of importance may be mentioned in this connection. If finely powdered charcoal and potassic nitrate are thoroughly intermingled and then set on fire in a closed vessel, a large amount of a gas, that is, carbon dioxide, will be generated by the combustion; and this gas may burst the vessel unless it is a very strong one. If, however, the vessel has an opening supplied with a cork or plug, this stopper will be violently driven out by reason of the explosive force of the carbon dioxide generated. So in the preparation of gunpowder, potassic nitrate, charcoal and the third substance sulphur, are finely pulverized and carefully intermingled. Thus they are brought to a state of thorough diffusion and intimate contact. The offices of carbon and potassic nitrate have been already explained. The office of the sulphur is principally to combine with the potassium of the potassic nitrate, producing as a result a somewhat larger evolution of gas. At all events, when gunpowder is consumed, two important results are afforded. As already intimated, the first is the sudden liberation of a very large amount of gas—carbon dioxide. The second is that this gas is generated by a process of true combustion attended with great heat, the latter contributing largely to the explosive force by reason of the great expansion of the gaseous products, effected by the heating.

There are several different kinds of gunpowder, but they all consist essentially of the constituents mentioned. Their differences are either in the proportions of the constituents used or in the size of the granules in which the powder is formed. Thus for some war purposes it is requisite that the powder should burn very rapidly, while in others it is required to burn slowly. For the purpose of regulating the rate of combustion, the grains are made of various sizes. The smaller sizes burn more quickly, while those of larger dimensions as well as those more strongly compressed, burn more slowly.

While the exact chemical changes which take place when gunpowder burns, are too complicated to admit of discussion here, they are in the main those just explained.

Fireworks.

Gunpowder affords the basis of the pyrotechnic art. It is employed also with the distinct intention of utilizing both of those prime properties already referred to. That is to say, by reason of its explosive force, gunpowder produces the various forms of _motion_ requisite in fireworks. By reason of the intense heat afforded by its combustion, the various kinds of _light_ are producible. The truly marvellous effects obtained by the skilled pyrotechnist involve the use of a great multitude of substances and also an ingenious mechanical combination of them. The effects he must produce require brilliant light in various qualities and also upon occasions loud reports, as the bursting of bombs and the like. So many forms and combinations of fireworks are possible that no enumeration can be made here; moreover, their infinite capabilities depend upon the inventive resources and skill of the maker. In a brief description, the rocket may be taken as the type of fireworks. It is often of most ingenious construction. Thus it may be provided with many chambers, one connecting with another by proper passages. In these passages are placed fuses so that the fire shall run from one chamber to another in proper order. Of course the main barrel contains a quickly burning gunpowder. This is for the purpose of producing the ascent. It is well known that a pistol, a rifle or a cannon, always experiences a strong recoil when fired. So does a rocket; but the rocket is so constructed that the recoil is the chief factor in its first discharge. That is, if the rocket is compared to a cannon, the discharge is downward and the recoil upward, so that in fact the ascent of the rocket is due to what may be called an exceedingly powerful recoil. When the rocket is high in air, the fuse connected with its principal barrel lights its subordinate chambers, and these then exploding distribute into the sky the brilliant masses of stars or other graceful pieces originally intended. The loud reports that take place at such times are due to portions of violently explosive substances within certain chambers; while the party-colored lights produced are referable to the burning of substances which have been carefully selected for the purpose. Thus the pyrotechnist has recourse to mixtures of gunpowder and various other chemical substances to produce colored fire. Finely powdered charcoal or lamp-black give rise to a red fire; so also do most of the salts of strontium. Common salt or powdered rosin give rise to yellow fire. Copper filings and certain salts of copper produce greenish hues; so do salts of barium. Zinc filings and chloride of copper, and certain others, produce blue shades. Saltpeter in considerable quantity affords a delicate pink; while iron filings and steel filings produce scintillations of great brilliancy.

Fulminates.

The fulminates are substances that are so extremely unstable in chemical character, that they require but a very slight mechanical blow to decompose them. Two fulminates in particular may be mentioned: fulminate of mercury and fulminate of silver. They are both viewed as salts of a peculiar complex acid called fulminic acid. This acid is a compound of carbon, hydrogen, oxygen and nitrogen. When silver or mercury takes the place of the hydrogen in fulminic acid, the dangerous salts just mentioned are obtained. Fulminating mercury is the one of chief use. It is employed in percussion caps. A drop of gum is put in the inside of the cap, then the exact amount of fulminate in the form of a powder is allowed to fall into the gum; finally the whole is allowed to harden. When the cap is used, a violent blow from the hammer of the gun or pistol gives rise to the explosion of the fulminate, and this communicates to the gunpowder of the cartridge to be fired. Fulminating silver is too dangerous for use in percussion caps, but it is employed in certain explosive toys like torpedoes.

Gun-Cotton.

Gun-cotton is a chemical modification of the ordinary cotton fibre. This fibre when purified by chemical washings consists entirely of the substance called cellulose. It is not different from certain other vegetable fibres. It has the formula:

C₆H₅O₅H₅

which may also be represented as follows:

{ H
{ H
C₆H₅O₅ { H
{ H
{ H

When clean cotton is acted upon by strong nitric acid it undergoes the wonderful chemical change to gun-cotton. Without material alteration in its physical appearance there has been a chemical substitution by reason of which a nitrogen compound has been introduced into the chemical molecule, as a substitute in place of certain of the hydrogen atoms originally present. Thus the formula of gun-cotton may be represented as follows:

{ H
{ H
C₆H₅O₅ { NO₂
{ NO₂
{ NO₂

A comparison of this formula with the one given for pure cotton shows that three atoms of hydrogen in the cotton have been replaced in the gun-cotton by three molecules of the compound radicle NO₂. On this account gun-cotton is often spoken of as trinitrocellulose. By reason of this chemical substitution the cotton changes as if by magic from the simple, safe material ordinarily known, to one of the most dangerous of explosives. Thus Mr. Abel, the chemist to the English War Department, who has made a series of most careful studies of gun-cotton with reference to its use for war purposes, finds the explosive power of gun-cotton to be more than fifty times that of gunpowder of equal weight. One of the greatest objections to the use of gun-cotton is found in the fact that upon keeping, it undergoes of itself a steady decomposition resulting ultimately in dangerous explosions. This fact appears to be likely to prevent the substance coming into general use.

Nitroglycerine.

Glycerine—produced at present in enormous quantities from fats and oils—is well known as a sweetish, oily and harmless substance. Glycerine is composed of carbon, hydrogen and oxygen in proportions but slightly different from those in cotton. Thus its formula is

C₃H₅O₃H₃.

If this bland and simple material is subjected to the action of concentrated nitric acid, it undergoes a change very similar to that recognized in the case of cotton and just described. It then produces a compound called trinitroglycerine which, while it ranks as one of the most powerful and useful explosives, is also associated with a long list of horrible disasters produced by accidental, or in some cases intentional, explosion of it.

Nitroglycerine is itself an oily material and was at first considerably used in that form. The terrible accidents from transportation of the article have given rise to the adoption of two means for lessening the risks attending it. The first is the manufacture of the substance in suitable localities—that is near to great public works in which it is to be employed. And again the factories are so arranged that the operation of the manufacture shall be conducted in small buildings surrounded by earthworks sufficient to localize any explosion that might unhappily occur.

At the manufactory of explosives at Ardeer on the Scotch coast, about fifty miles from Glasgow, a most ingenious additional precaution is taken. Here each laborer, as he enters the works in the morning, passes into a cottage to change his dress. He dons a uniform of a special and distinctive color—it may be scarlet, or bright blue or white or gray, according to the department in which he is employed. Thus the policemen who are constantly on duty can detect at once any employé who strays into a department to which he does not belong and where his lack of acquaintance with the processes might lead to a terrible accident.

Another special device is the invention of Albert Nobel, who has been noted as the principal person by whose efforts nitroglycerine has been introduced into the important uses which it finds at the present day. This is the absorption of the liquid nitroglycerine in some spongy material such as will serve as a safe and proper vehicle for the explosive. The substance thus employed is a kind of fine siliceous earth called diatomaceous earth, also infusorial earth. This is a mineral material found in various parts of the world in somewhat abundant deposits. Upon examination by the microscope it is found to be composed of the mineral skeletons of microscopic organisms. The minute cellular texture which this substance affords seems to be admirably fitted to imbibe the liquid nitroglycerine, and assist in packing it in proper cartridges. The explosive produced by the combination is the one commonly known as dynamite.

A peculiarity of nitroglycerine and dynamite is that they cannot be fired in the ordinary fashion. That is, if a lighted match is brought to them they may take fire and burn with perfect quietness. For their _explosion_ they demand some kind of violent blow. For this reason their cartridges have to be provided with special exploders. These are small cases of gunpowder or perhaps fulminating materials, which may be set on fire by means of a powder fuse or an electric current; their explosion within the nitroglycerine mass determines a violent shock to the latter. It is the concussion thus produced that is the appropriate means of exploding the nitroglycerine or dynamite cartridges.

While the sad accidents with these materials have horrified the whole world by their sudden and disastrous results it is too often forgotten that their gigantic forces are day by day safely and quietly contributing to the execution of great public works all over the earth. Thus in the great rock tunnels of Mont-Cenis and St. Gothard, which pierce the Alps, nitroglycerine and dynamite have done the work of armies of men. In the St. Gothard tunnel more than two million pounds of dynamite have been employed, and it has proved wonderfully effective in advancing most arduous subterranean work. Unquestionably the principal use of this explosive, as well as others, is in the labors of peace. Still, nitroglycerine and dynamite have come into great prominence by reason of their use in naval warfare. Torpedoes of a great variety of forms are now constructed so that a quick moving launch may steam up to a large ship of war, place close to her side one of these dangerous contrivances and then quickly withdraw in time to avoid the effects of the explosion which involves the great vessel in devastating ruins. Torpedoes charged with nitroglycerine or dynamite, are also used for the defence of harbors, being sometimes placed in such a way that an enemy’s ship, in crossing the line formed by the torpedoes, shall by that act explode one or more of them and produce her own destruction.

READING REFERENCES.

Explosive Agents.
=Abel=, F. A.—Jour. of Chem. Soc. of London. xxiii, 41,
xxvii, 536.
—Chem. News.—xxxix, 165, 187, 198, 208.

Explosives, a New Class of
=Sprengel=, H.—Jour. of Chem. Soc. of London. xxvi, 796.

Explosives, Force of
=Berthelot.=—Annales de Chimie et de Physique.
4 Sér. xxiii, 223.

Explosives, in Blasting.
=Scribner’s= Monthly. iii, 33.

Greek Fire, (so called.)
=Lalanne=, L.—Annales de Chimie et de Physique.
3 Sér. iv, 433.

Gun-cotton, Manufacture and Composition of
=Abel=, F. A.—Journal of Chem. Soc. of London. xx, 311, 505.

Gunpowder, Chemical Theory of
=Debus=, H.—Chemical News. xlv, 91.