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tioned that in theory every particle of the original substances of which it is composed should be converted into gas, leaving no residuum to foul the barrel. In practice this is never the case, for though a powder may be made so correctly as to burn away almost entirely on a piece of white paper, yet in a tube it will always leave a stain over and above the sulphuret of potassium, which is a necessary product, and this increases if not wiped away with each succeeding discharge. The reason of this is, that there is no air admitted to supply extra oxygen for the sulphur to combine with, and this material, therefore, robs the nitre of a small portion of that element which is wanted to effect a perfect union with the carbon in order to form the carbonic oxide and acid which result. Gunpowder may be made entirely of nitre and charcoal, and for large charges it answers perfectly well, but for sporting purposes the addition of sulphur has many advantages, preserving the other two materials from the effects of damp, and also maintaining the granulation which is so important in effecting perfect combustion. In this country the proportions which are thought to answer best in practice areNitre
This will make 104lbs. of powder, leaving the 4lbs. for loss by waste in the various operations of mixing, pressing, granulating, &c. These three substances must first be ground into a very fine powder, and mixed together most intimately, so that the atoms are mechanically prepared for instantaneous combination as soon as they are heated to the temperature which admits of it. But if left in this state of fine powder, though the combination is very rapid in the parts first heated, yet the flame cannot permeate the mass, and it burns imperfectly as a whole. To avoid this difficulty the powder is first wetted, then pressed and dried, and afterwards made up into grains of various sizes and shapes, according to the use for which it is designed. This is called granulating; and powder is sold of several degrees of coarseness, commencing with No. 1, which is the finest in use, and increasing in the size of the grain up to No. 5. After the granulation is effected the grains are generally more or less glazed by friction, in barrels which are made to revolve rapidly; and, finally, the resulting dust being sifted out, the powder is packed.
A8 fine-grained powder explodes more rapidly than coarse when not crushed, or in large quantities, it follows that it is more suited for short barrels and small charges, such as, for instance, in pistols or carbines. The aim, in all cases, should be to use powder in such quantity and quality that the whole of it is burnt just as the projectile leaves the muzzle of the gun; for if it is all converted into gas before that period of time, the projectile has to overcome the friction of the sides of the tube without any increasing force as it goes on, and consequently loses some of its propellant power. If, on the other hand, all the powder is not burnt before the projectile escapes, there is a waste of powder, and this is the most frequent and the least injurious result. On firing a full charge over the snow, a few grains of powder entire may almost always be picked up beneath the line of flight of the charge. Those, therefore, who are careful in such matters, will adopt the necessary precaution to ensure the proper charge of the right kind of powder for the particular gun they are using
The desiderata in gunpowder will therefore vary considerably according to the charge, to the length of barrel, and to the mode of firing it. In every case, however, it should be clean, that is to say, it should leave no perceptible residuum on firing it loosely on a piece of white paper.
The first test to apply is the following, which also shows that the powder is dry and easily exploded :-Take five or six drachms of powder and divide it into two heaps, placed on a piece of white paper; then fire one of them with a red-hot wire, and if the two explosions do not sound as one, the powder is bad or damp; while if any steam is left, or the paper
is burnt in holes, there is an imperfection somewhere. The smoke, also, should be of a whitish grey. In relation to the charge, the powder should be coarser according to the amount which is used, but for sporting purposes, other than for punt guns, either No. 2 or No. 3 is always selected. The choice between these will depend upon the mode of firing it, for if the ordinary nipple and percussion cap are used, the combustion of No. 2 is not too rapid, and it will answer the best; besides which, the size of its grain allows it to pass up the nipple, which No. 3 will not do. Where the firing is more central, as in the various breech-loading cartridges of Lefaucheaux, Lancaster and Needham, the coarser grain of No. 3 should be selected, as it is found to burn entirely before it leaves the muzzle in the ordinary charge of 24 to 3 drachms; and so also, in the case of rifles, where there is more resistance to be overcome and more time occupied in doing it, the coarser powder is to be preferred. It is usual to judge of powder by its appearance when rubbed in the hand, and it is considered that when rubbed on a moderately dry palm it should leave the faintest possible stain of lead colour only. If it blackens the skin it is to be rejected, as such powder is found to foul the barrel in a similar manner.
There is very little difference in the quality of the powder made by the various eminent firms who now divide the trade between them. They are Messrs. Curtis and Harvey, Pigou and Wilks, Lawrence and Son, Hall and Son, in England; and in Scotland, the Kames Company, who have offices in Glasgow, Liverpool, and London. With a recoil machine, such as that I have described at page 196, I have tested nearly all the above, and find so little difference that it is scarcely worth attempting to make an invidious selection. This is far the best and fairest mode of making a comparison, for in proportion to the recoil (with the same gun in a similar state, and with a corresponding projectile in front of it, also a similar weight of powder) will be the amount of explosive force of the powder. This test also shows the degree of fouling produced after three or four dozen discharges with each kind of latter. Here I have detected a greater difference; but as the experiments were made with powder obtained from sources not equally reliable, I shall forbear to mention the results. There can be no question, however, that the recoil with No. 3, after 30 discharges in a breech-loader, is much less than with a similar number while using No. 2 powder.
Gunpowder is sold in paper at 28. 3d. per lb., and in canister at 2s. 6d. If large quantities are taken a reduction is made in the price; but it must be remembered that fire insurances are rendered invalid by keeping a stock of this dangerous substance on the premises.
When gunpowder has become damp it is readily and safely dried by placing the canister or flask in a jug of boiling water with the mouth open, and occasionally taking it out and shaking its contents. This is much safer than the ordinary plan of drying it before the fire, and with a little care answers equally well.
Guncotton consists of finely carded cotton wool which has been submitted to the following process :—Nitric acid of specific gravity 1-5 is mixed with concentrated sulphuric acid, and in this mixture the cotton is steeped for a few minutes; it is then taken out and squeezed, after which it is carefully washed in pure water and dried by a very gentle heat, when it will have increased iv weight seventy per cent., but in appearance it is unchanged. It explodes at a much lower temperature than gunpowder, that is, at a little above 300° Fahr., so that it requires much greater care to avoid accidents, and on that account alone is objectionable as a substitute for it. It burns without smoke or residue, but the explosion is so rapid that the projectile power of this substance is not so great as that of gunpowder, while, at the same time, the recoil caused by it is increased. It has also the disadvantage attending on it that the charges must be weighed, as they cannot be measured by bulk as is the case with the powder in common use. It is not, therefore, surprising that, in spite of its greater cleanliness, it has not come into general use, being much more dangerous with less power of projection, more recoil, and the above-mentioned difficulty as to the calculation of the charge.
In spite of these objections, however, guncotton has been recommended by Captain Norton to be used, in particular where it is desired to have a cartridge without the necessity of biting it, as is now done in the army and navy. By enveloping the cotton in a fine net, which is tied to the base of the bullet, and may also be rendered explosive in the same way as the cotton, the flame of the cap readily fires it, and the whole is blown away. This trilling advantage is, however, entirely done away with by adopting explosive paper for making up the powder into cartridges, as is practised by Mr. Prince with his breech-loader. But even this is now rendered unvecessary by the increased strength of the Government caps, which readily pierce paper of any thickness which can be required for the purpose.
An explosive cartridge paper may be made by preparing it in the same way as described for guncotton. The paper should be porous; and ordinary blotting paper answers very well if made sufficiently stout. But this paper, like guncotton, explodes at a temperature very little higher than 300° Fahr., and it is therefore dangerous to keep together any number of cartridges enveloped in it. The plan is exceedingly ingenious in theory, and for sporting purposes it is practically well adapted, as it is easy to avoid the above heat in this country, but for military cartridges the danger of spontaneous combustion is too great when large masses of all sorts of substances are brought together in the hold of a ship; and even the magazine may possibly have its temperature raised to that degree.
The various detonating powders used in the manufacture of caps, disks, or tubes for firing the gunpowder of the charges in our fowling-pieces and rifles are so rapid in their combustion as to be useless as a substitute for the two materials which have been already described. Their explosive force is so enormous and sudden that they will burst the barrel, however strong, instead of moving the projectile in front of them, if employed in sufficient quantity to propel it as far as gunpowder will do. So rapid is the combustion of fulminating mercury, that if a train of gunpowder is crossed by a train of it, and the latter is fired in the usual way, with a poker or wire, the mercury, in its explosion, being more rapid than that of the gunpowder, cuts off the connexion between the two portions of the train, and the second half is not fired at all.
Fulminate of silver, which is even more rapid in its explosion, is prepared by dissolving 40 or 50 grains of silver (a sixpence will be the most convenient) in oz. by measure of nitric acid of specific gravity 1:37 or thereabouts, with the