been variously estimated at from 2000° Fahr. to 4000° Fahr., and as the gaseous volume is repeated for every 480° Fahr. of temperature, its increase from expansion by the heat generated during the combustion has been variously estimated from about four to eight times that of the original volume. If the former increase be accepted, the force of the explosion will be in round numbers equivalent to 1000 atmospheres, or to a pressure of 15,000 pounds on the square inch; if the latter be accepted, to 2000 atmospheres, or 30,000 pounds on the square inch. The energy of fired gunpowder has been estimated to be even still higher than what has just been named. The force impressed on a rifle-bullet by the explosion of an ordinary charge of powder, as of massive projectiles by proportionally increased charges, thus becomes readily intelligible when the enormous amount of pressure to which it is suddenly subjected in the fire-arm is duly considered.

The chemical results of the explosion of gunpowder are 32 per cent. of gaseous products, 68 per cent. of solid residue. The principal gases evolved are carbonic oxide, carbonic acid, nitrogen, and aqueous vapour; the solid residuum consists chiefly of sulphate, carbonate and nitrate of potash, with hyposulphite of potassium and a little unconsumed charcoal. The smoke has nearly the same composition as the residuum just mentioned.

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Fulminating powder. The only fulminate used for military purposes is the fulminate of mercury. It is chiefly employed for charging percussion-caps, and for use as a 'detonator' in exploding gun-cotton and other high explosives. This highly sensitive fulminate explodes instantaneously and violently by friction or percussion, though, unlike some other fulminates, it burns away quietly when kindled in the open air. It explodes when heated to a temperature of 360° Fahr. The instantaneous conversion of the fulminate into a large volume of gas, and consequently its extremely violent and sudden percussing force even in very small quantity when confined, are its distinguishing characters. The gases resulting from the explosion are carbonic acid, nitrogen, and vapour of mercury. In the celebrated Orsini attempt on the life of the French Emperor in the year 1858, the three shells thrown were filled with fulminate of mercury. Each shell con

tained upwards of four ounces of the fulminate. The shells were broken up into very numerous fragments, and led to the infliction of 511 wounds in the 156 persons who were injured by the explosion.

Smokeless powders.-Certain chemical compounds possessing explosive qualities, but differing in many important respects from the gunpowder previously described, are now employed as substitutes for it in most European armies. They are known under a variety of names, but the chief of them have either some form

of gun-cotton (nitro-cellulose), dynamite (nitro-glycerin), or picric acid (tri-nitro-phenol) as a basis. As they emit, when exploded, very little smoke by comparison with black or brown gunpowder, they are commonly spoken of as smokeless powders. Repeated trials have been made in England of such chemical powders or high explosives with a view to discover one as trustworthy and uniform in its explosive effects as the gunpowder hitherto in use. Obviously any such powder, to be suitable for British military purposes, must be capable of being stored for years without any gradual chemical change occurring in the materials composing it; must be perfectly stable under such climatic conditions as extremes of dryness and moisture, heat and cold; and must not be liable to explosion from friction when handled, or from concussion during transport by sea or land. A substance possessing all these qualities, it is believed, has been discovered in the explosive recently authorised (1891) for use with the Lee-Metford rifle and other guns, under the name of 'cordite.' Some of the special features of a few of these chemical powders are described in the following observations.

Gun-cotton (Tri-nitro-cellulose).-Great efforts were made after the discovery of gun-cotton in 1846 to manufacture it in such a way that it might be safely applied to fire-arms as a substitute for gunpowder. Although this object was not satisfactorily attained in the British service, compressed gun-cotton was employed for many important purposes, especially in engineering operations. As far back as the year 1870 it was included among the regular stores of the army, and was ordered to be dealt with under the same precautions as filled shells when carried by sea."

The early experiments with this extremely sensitive agent, were attended with so many disastrous accidents both in England and abroad, that there appeared to be at that time little probability of its ever being brought into general use for military purposes; but means have since been discovered of so controlling its dangerous qualities, that now it seems to be as reliable and manageable as gunpowder. This control was obtained in some degree by a plan of structurally arranging the material, devised by Baron von Lenk, of the Austrian service; but was afterwards more effectively accomplished by Mr. Abel, of Woolwich, who reduced the gun-cotton to pulp, like the pulp of paper, and after purifying it from all free acid, diluted it, according to circumstances, with less explosive materials, and compressed it into charges of the required forms and consistence. This prepared gun-cotton, with certain modifications, is now employed as a substitute for gunpowder with fire-arms.

Compressed gun-cotton, as it is used for large military operations, in mining, and for various destructive purposes in war, is

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always transported and stored in a wet state-about 20 per cent. of water being ordered to be the minimum. In this state it is quite uninflammable, both under concussion and percussion, and can be kept for any length of time in any climate without undergoing spontaneous chemical change. It can, however, be detonated by suitable primers of dry gun-cotton and charges of fulminate. After gun-cotton has been kept in the wet state, if dried, it is as efficient in all respects as an explosive as it was previously.

The principal qualities which give a superiority to gun-cotton over gunpowder as an explosive for military purposes, are the absence of smoke and of fouling. The gaseous results of the explosion of gun-cotton are almost transparent, and no solid residuum remains; thus contrasting greatly with gunpowder, which leaves about two-thirds of solid residue when fired. Gun-cotton when fired in a loose state gives out vapour of nitrous acid, but only in a very small quantity; when fired under pressure, in the manner in which it has been prepared for fire-arms, is said to yield none at all. The principal products of its combustion. under these circumstances are carbonic acid, carbonic oxide, nitrogen, a small amount of hydrogen, and aqueous vapour. There is also some product which occasionally emits a very unpleasant odour.

The use of gun-cotton is calculated to facilitate military operations in other ways besides its freedom from smoke and fouling. The disruptive force, as for bursting shells, is six or eight times greater than that of gunpowder; its propelling force as a charge in fire-arms is about three times greater, one part by weight in gun-cotton carrying a shot as far as three times the same weight in gunpowder. It explodes at a temperature of about 277° Fahr. The character of the explosion varies according to circumstances. When ignited in a free state in the open air, gun-cotton burns like an ordinary inflammable substance; when it is confined and ignited by the intense sharp action of a detonator, such as by a fulminate, it explodes almost instantaneously with extreme violence and with scarcely any visible flame; but when pulpified with the addition of certain non-explosive ingredients, compressed, and dried, its combustion is retarded, its excessive disruptive violence is lessened, and it explodes after the manner of gunpowder. It does not, however, heat guns, as the explosion of gunpowder does. The Schultze gunpowder,' now so much used with sporting guns, belongs to this, the nitro-cellulose, class of explosives. Wood-fibre is substituted for the cotton, and some other ingredients are included in its composition.

Nitro-glycerin.-The explosives which depend on nitroglycerin for their efficiency are very numerous, but the composition known as 'Dynamite' is the one most generally known. It is extensively used for the purposes of civil life, but is also

employed in many military operations, particularly for destroying obstacles of all kinds, for blowing up buildings and bridges, and also as a bursting charge in shells. A plan of preparing it was devised in England, which rendered it almost free from danger when transporting it from place to place. This immunity was obtained by a process similar to that by which Mr. Gale rendered gunpowder non-explosive at pleasure, without injuring its explosive qualities when wanted for use. He temporarily mixed the gunpowder with a sand-like incombustible substance, viz., a certain proportion of granulated glass. In the case of the nitro-glycerin some fine siliceous earth is mixed with itusually about one quarter by weight of the inert earth with three-quarters by weight of nitro-glycerin. The composition thus diluted will not explode, either under the action of heat or simple concussion. When set fire to in free air, it burns without any report or explosive action, without smoke, and with a flame resembling that of alcohol. But by means of a fulminate through which it is suddenly subjected to the conjoint action of the heat of a spark and of violent percussion, it explodes with great violence. Its explosive force under such conditions is said to be about eight times in excess of that of gunpowder. In a shell, therefore, sufficient dynamite for filling the eighth part of the space that would be required for a charge of gunpowder would produce the same bursting effect; and by increasing the quantity of dynamite, and making the shell proportionably thicker, without altering its diameter, the fragments into which it would become broken on explosion would be more destructive on striking any resisting objects which might happen to be opposed to them.

Dynamite is at present manufactured in large quantities for blasting purposes, and the composition of several varieties is regulated by legal enactments. One of the most recent kinds is designated blasting gelatin,' and is made by dissolving nitrocellulose in nitro-glycerin under such conditions that the two substances form by their union a stiff jelly. This gelatinous substance forms a very powerful explosive; but the rapidity of development and energy of its explosive qualities can be regulated by varying the proportions of its components, and by the addition of certain ingredients. These gelatin explosives are sometimes divided into short cylindrical rods or tubes, and put into cartridges of suitable sizes for use for blasting purposes; and it is stated that some forms are used on the Continent with guns.

All gun-cotton is not soluble in nitro-glycerin. The tri-nitrocellulose, or highly explosive gun-cotton, will not do so. By altering the modes of preparation, less explosive forms of gun-cotton can be manufactured, and it is one of these forms,

after being dissolved in a mixture of alcohol and ether, that constitutes the collodion used in surgical practice. This soluble form of gun-cotton can be dissolved in nitro-glycerin, and thus be made to assume the characters of one of the blasting gelatin explosives.

Cordite. This explosive material, invented by Sir Frederick Abel and Professor Dewar, and arranged for use with the LeeMetford rifle ammunition, is an explosive of the blasting gelatin species. As made up in the cartridges for the Lee-Metford rifle, the cordite charge presents the appearance of a bundle of yellowishbrown, flexible, semi-translucent threads or rods, each one inch and three-quarters in length. The strands of cordite are very like pieces of fine catgut, and give much the same sensation to the fingers on being handled as catgut string does. Externally there is no noticeable difference between a cordite cartridge and one of black gunpowder. A single cartridge contains 30 grains of cordite. The relatively greater explosive power of the cordite is sufficiently shown by the fact that whereas 30 grains of the cordite suffice to impress on the bullet when it leaves the muzzle of the rifle a progressive velocity of 2000 feet in a second, a charge more than double in weight, viz., 70 grains, of compressed gunpowder gives a velocity of translation at the muzzle only of 1850 foot-seconds. When a strand of cordite is placed on porcelain and ignited in the open air, it deflagrates like saltpetre, and the flame runs gradually, with a slight fizzing noise, from end to end without causing smoke. After the flame has passed away, a brown substance sticking firmly to the porcelain is left behind, and this, on being highly magnified, is seen to be translucent or glassy, and studded with minute black spots of carbon.

As before mentioned, explosive gun-cotton (tri-nitro-cellulose) is not soluble in nitro-glycerin, under ordinary circumstances; but with regard to cordite, it appears that the inventors have discovered means by which the explosive gun-cotton can be antecedently so acted upon as subsequently to be rendered capable of solution in nitro-glycerin, and to become gelatinised without impairing its highly explosive qualities. Cordite is thus superior in explosive power to blasting gelatins' in general.

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Picric explosives.-A considerable number of patented explosive substances, some used with small arms and guns, others for blasting purposes, depend upon picric acid, or on some of its salts, for their energy. Picric acid is a compound derived from phenol (carbolic acid), a portion of its hydrogen being replaced by nitric peroxide, through the action of nitric acid on the phenol. The Frenchmelinite' belongs to the class of picric explosives, but its exact composition has not been made public. In some accidental explosions of this substance in France, it was noticed as a peculiarity that the survivors of the wounded men had the