ON MAGAZINES.

ON MAGAZINES.It is impossible to make powder magazines too dry, and every care should be taken to ventilate them as much as possible during dry weather, by opening all doors, windows, loopholes, &c. Magazines are generally made bomb-proof, and are furnished with lightning conductors. They are divided into chambers, and these again divided by uprights into bays. At Purfleet, which is the grand depôt for gunpowder in England, there are five magazines capable of containing 9,600 whole barrels each. Each magazine is divided into two chambers, and each chamber into 24 bays, and in each bay is placed 200 whole, 400 half, or 800 quarter barrels of powder. Total in the five Magazines, 48,000 barrels, equal to 4,800,000 pounds.LIGHTNING CONDUCTORS.Principles and Instructions relative to their application to Powder Magazines, bySir W. Snow Harris, F.R.S.Extracted from Army List for July, 1859.1.—Thunder and lightning result from the operation of a peculiar natural agency through an interval of the atmosphere contained between the surface of a certain area of clouds, and a corresponding area of the earth’s surface directly opposed to the clouds. It is always to be remembered that the earth’s surface and the clouds are the terminating planes of the action, and that buildings are only assailed by Lightning because they are points, as it were, in, or form part of, the earth’s surface, in which the whole action below finally vanishes. Hence buildings, under any circumstances, will be always open to strokes of Lightning, and no human power can prevent it, whether having Conductors or not, or whether having metals about them or not, as experience shows.2.—Whenever the peculiar agency, (whatever it may be), active in this operation of nature, and characterized by the general term Electricity, or Electric Fluid, is confined to substances which are found to resist its progress, such, for example, as air, glass, resinous bodies, dry wood, stones, &c., then an explosive form of action is the result, attended by such an evolution of light and heat, and by such an enormous expansive force, that the most compact and massive bodies are rent in pieces, and inflammable matter ignited. Nothing appears to stand against it. Granite rocks are split open, oak and other trees, of enormous size, rent in shivers, and masonry of every kind frequently laid in ruins. The lower masts of ships of the line, 3 feet in diameter, and 110 feet long, bound with hoops of iron half an inch thick and 5 inches wide, the whole weighing about 18 tons, have been, in many instances, torn asunder, and the hoops of iron burst open and scattered on the decks. It is, in fact, this terrible expansive power which we have to dread in cases of buildings struck by Lightning, rather than the actual heat attendant on the discharge itself.3.—When, however, the electrical agency is confined to bodies, such as the metals, which are found to oppose but small resistance to its progress, then this violent expansive or disruptive action is either greatly reduced, or avoided altogether. The explosive form of action we term Lightning, vanishes, and becomes, as it were, transformed into a sort of continuous current action, of a comparatively quiescent kind,which, if the metallic substance it traverses be of certain known dimensions, will not be productive of any damage to the metal. If, however, it be of small capacity, as in the case of a small wire, it may become heated and fused. In this case, the electrical agency, as before, is so resisted in its course as to admit of its taking on a greater or less degree of explosive and heating effect, as in the former case. It is to be here observed, that all kinds of matter oppose some resistance to the progress of what is termed the Electrical Discharge, but the resistance through capacious metallic bodies is comparatively so small, as to admit of being neglected under ordinary circumstances; hence it is that such bodies have been termed Conductors of Electricity, whilst bodies such as air, glass, &c., which are found to oppose very considerable resistance to electrical action, are placed at the opposite extremity of the scale, and termed Non-conductors or Insulators.The resistance of a metallic copper wire to an ordinary electrical discharge from a battery, was found so small, that the shock traversed the wire at the rate of 576,000 miles in a second. The resistance however, through a metallic line of Conduction, small as it be, increases with the length, and diminishes with the area of the section of the Conductor, or as the quantity of metal increases.4.—It follows from these established facts, that if a building were metallic in all its parts, an iron magazine for example, then no damage could possibly arise to it from any stroke of Lightning which has come within the experience of mankind; e.g., a man in armour is safe from damage by Lightning; in fact, from the instant the electrical discharge in breaking with disruptive and explosive violence through the resisting air, seizes upon the mass in any point of it, from that instant the explosive action vanishes, and the forces in operation are neutralized upon the terminating planes of action, viz., the surface of the earth, and opposed clouds.5.—All this plainly teaches us, that in order to guard a building effectually against damage by Lightning, we must endeavour to bring the general structure as nearly as may be, into that passive or non-resisting state it would assume, supposing the whole were a mass of metal.6.—To this end, one or more conducting channels of copper depending upon the magnitude and extent of the building should be systematically applied to the walls; these conducting channels should consist either of double copper plates united in series one over the other, as in the method of fixing such Conductors to the masts of Her Majesty’s Ships, the plates being not less than 31⁄2inches wide, and of1⁄16th and1⁄8th of an inch in thickness, or the Conductors may with advantage be constructed of stout copper pipe not less than3⁄16ths of an inch thick, and 11⁄2to 2 inches in diameter: in either case the Conductors should be securely fixed to the walls of the building, either by braces, or copper nails, or clamps; they should terminate in solid metal rods above, projecting freely into the air, at a moderate and convenient height above the point to which they are fixed, and below they should terminate in one or two branches leading outward about a foot under the surface of the earth; if possible, they should be connected with a spring of water or other moist ground.It would be proper in certain dry situations, to lead out in several directions under the ground, old iron or other metallic chains, so as to expose a large extent of metallic contact in the surface of the earth.7.—All the metals in the roof and other parts of the building of whatever kind, should so far as possible have metallic communication with these Alarm Conductors, and in case of any prominent elevated chimney, it would be desirable to lead a pointed conducting tube along it to the metals of the roof; all of which satisfies the conditions above specified.8.—Remark 1.—It is now proved beyond all questions, that the electrical discharge never leaves perfect conducting lines of small resistance, in order to pass out upon bad conducting circuits, in which the resistance is very great, that is an established law of nature; hence a stroke of Lightning upon such conducting lines will be confined to the Conductors as constituting a line of discharge of less resistance than any other line of discharge through the building, which can be assigned. The apprehension of “Lateral Discharge” therefore, from the Conductor, is quite absurd; and is not countenanced by any fact whatever; if any doubt could possibly exist, it would be now most completely set at rest by the experience of the permanent Conductors, applied to the masts of Her Majesty’s ships. In very many instances furious discharges of Lightning have fallen on the masts with a crash as if the ship’s broadside had been fired, and the solid point aloft has been found melted; in all these cases electrical discharge robbed by the Conductor of its explosive violence, has traversed the line of action to the sea, through the ship, and through the copper bolts, driven through the ship’s solid timbers, without the least damage to the surrounding masses, whether metallic, as in the case of the massive iron hoops on the lower masts, or not. Persons have either been close by or actually leaning against the Conductors at the time, without experiencing any ill consequence.9.—Remark 2.—It has also been incontestably shown, that metallic bodies have not any specific attractive force or affinity for the matter of Lightning; metals are as little attractive of lightning as wood or stone. All matter is equally indifferent to Electricity so far as regards a specific attraction, hence the idea that metals attract or invite Lightning is a popular but very unlearned error contradicted by the most satisfactory evidence, and the whole course of experience; in short, we find that Lightning falls indiscriminately upon trees, rocks, and buildings, whether the buildings have metals about them or not.10.—Remark 3.—A building that is hence clear, may be struck and damaged by Lightning without having a particle of metal in its construction; if there be metals in it, however, and they happen to be in such situations as will enable them to facilitate the progress of the electrical discharge, so far as they go, then the discharge will fall on them in preference to other bodies offering more resistance, but not otherwise; if metallic substances be not present, or if present, they happen to occupy places in which they cannot be of any use in helping on the discharge in the course it wants to go, then the electricity seizes upon other bodies, which lie in that course, or which can help it, however small their power of doing so, and in this attempt such bodies are commonly,but not always, shattered in pieces. The great law of the discharge is,—progress between the terminating planes of action, viz:—the clouds and earth, and in such line or lines as upon the whole, offer the least mechanical impediment or resistance to this operation, just as water falling over the side of a hill in a rain storm, picks out or selects as it were by the force of gravity, all the little furrows or channels which lie convenient to its course, and avoids those which do not. If in the case of Lightning you provide through the instrumentality of efficient Conductors, a free and uninterrupted course for the electrical discharge, then it will follow that course without damage to the general structure; if you do not, then this irresistible agency will find a course for itself through the edifice in some line or lines of least resistance to it, and will shake all imperfect conducting matter in pieces in doing so; moreover it is to be specially remarked in this case, that the damage ensues, not where the metals are, but where they cease to be continued, the more metal in a building therefore the better, more especially when connected by an uninterrupted circuit with any medium of communication with the earth.Such is, in fact, the great condition to be satisfied in the application of Lightning Conductors, which is virtually nothing more than the perfecting a line or lines of small resistance in given directions, less than the resistance in any other lines in the building, which can be assigned in any other direction, and in which by a law of nature the electrical agency will move in preference to any others.11.—It follows from the foregoing principles, that a magazine constructed entirely of iron or other metal, would be infinitely more safe in Lightning storms than if built with masonry in the usual way; metallic roofs for magazines, with capacious metallic Conductors to the earth, would be unobjectionable, and a source of security.Metallic gutters and ridges having continuous metallic connection with the earth are also unobjectionable.A good method of Conductors for magazines built of masonry, would be such as already described, regard being had to the position of the building, its extent, and most prominent points, also to the nature, state, and condition of the soil, whether it be moist or dry, alluvial calcareous, or of hard rock; we must also consider the extent, disposition, and peculiar position of the metallic bodies entering into the general structure of the building, whether the roof be flat, pointed, or angular in various parts.The pointed projecting extremities of the two Conductors, one or more as the case may be, will be commonly sufficient; but, in buildings having tall chimneys or other elevated prominent points, at a distance from the Main Conductor, it will be requisite to guard such chimneys or other parts, by a pointed rod, led along them to the metals of the roof, or directly connected with the Main Conductors, by metallic connections.12.—Pointed terminations of the Conductors in the air, are so far important that they tend to break the force of a discharge of Lightning when it falls on them. In fact, before the great shock actually takes place, under the form of a dense explosion, a very large amount of the discharge, which otherwise would be concentrated, runs off, as it were, through the pointed Conductor; but they have no other influence.With respect to these pointed terminations, no great care need be taken about them, except that they should consist of solid copper rod, of about three-quarters of an inch in diameter, and about a foot in length, and be united by brazing to the conducting tube, elevated at such convenient height above the walls of the building as the case may suggest.As a support to the Conductor, when raised above the wall, we may employ a small staff or spar of wood fixed to the masonry.13.—Copper linings to the doors and window shutters of magazines are not objectionable, if requisite, as a precaution against fire; but they are useless as a means of keeping out Lightning; on the other hand, it is not easy to conceive a case in which the explosion of the gunpowder is to be apprehended from the action of Lightning on the doors or windows. Supposing, however, such metallic linings desirable as a precaution against common cases of fire, then the masses of metal should, according to the principles already laid down, have metallic communication with the general system of conduction in the building and the Main Conductor.ON THE EXPLOSIVE FORCE OF GUNPOWDER.Advantages of GunpowderThe advantages of Gunpowder, as a propelling agent, over any other explosive material are, the comparative safety attending its manufacture and transport, and the gradual nature of its decomposition when compared with those materials, such as fulminating gold, silver, mercury, &c. &c. In gunpowder, the force resulting from the rapid evolution of gas in a confined space has sufficient time to overcome the inertia of the projectile, which is not the case with other explosive materials, the conversion of which gaseous products is so instantaneous that nothing can resist the intensity of their explosive action. Other advantages suggest themselves in the use of Gunpowder, such as the comparative cheapness of the ingredients composing it, and the ease with which they may be obtained; for the sulphur and saltpetre are very abundant productions of nature, and the charcoal can be manufactured cheaply and with great facility, and if care is taken in the process of the fabrication of powder, little deterioration will take place on its exposure to heat or moisture.Air & Steam as propellantsCondensed air and steam have been used as propelling agents; but the great inconvenience attending their use quite preclude the possibility of adapting them to war purposes.Force of Gunpowder.As the force and effect obtained from Gunpowder is the foundation of all other particulars relating to Gunnery, we will briefly consider these points.Upon what the action of powder depends.The action of Gunpowder is dependent upon a purely chemical process. Mr. Robins proved that the force generated by the combustion of gunpowder, was owing to an elastic gas which was suddenly disengaged from the powder, when it was brought to a certain temperature, and further that this disengaged gas had its elastic force greatly augmented by the heat evolved by the chemical action.Ingredients are charged with a large volume of heated gas.The propelling power of Gunpowder is dependent on the rapid decomposition of the nitre into its component parts; the oxygen forms carbonic acid with the carbon in the charcoal, and the heat thus generated by ignition changes both this and the nitrogen into a large volume of heated gas. In a mixture of nitre and charcoal alone, the oxidation proceeds with comparative slowness; by the addition of sulphur, an augmentation of combustibility is gained, in consequence of its igniting at a very low temperature; the sulphur, also, by its presence, renders available for the oxidation of the carbon an additional amount of oxygen, viz: that which is united with the potassium, the latter being at once converted into sulphite upon ignition of the powder.Weight of gas evolved.It appears that the weight of gas generated is equal to three tenths of the weight of the powder which yielded it,Volume of gas evolved.and that its bulk when cold, and expanded to the rarity of Common air was 240 times that of the powder; the barometer standing at about 30 inches. From this Robins concluded that if the fluid occupied a space equal to the volume of the gunpowder, its elastic force, when cold, would be 240 times the pressure of the atmosphere, when the barometer stands as above.Heat of gas evolved.Mr. Robins also considered that the heat evolved was at least equal to that of red hot iron, and he found by experiments that air heated to this temperature had its elasticity quadrupled, and therefore, that the force of gas from powder is at least four times 240 = 960, or in round numbers 1,000 times as great as the elasticity of the air measured by its pressure on an equal extent of surface.Pressure of gas generated.From the height of the barometer it is known that the pressure of the atmosphere is about 143⁄4lbs. upon the square inch, so that the pressure of the elastic gas generated by the combustion of the gunpowder upon the same area would be 14.75 by 1,000 or 14,750lbs. at the moment of explosion.Strength of powder not affected by density of air, but by damp.He found that the strength of Gunpowder was the same whatever might be the density of the atmosphere, but that the moisture of the air effected it considerably, in fact that the same quantity of powder which would give a bullet an initial velocity of 1,700 feet per second on a day when the atmosphere was comparatively dry, would upon a damp day give no more than 1,200 or 1,300 feet.Velocity of gasThe velocity of the expansion of the gas is a most important point, upon which depends, chiefly, the peculiar value of the substance as a propelling agent. Many of the warlike machines of the Ancients produced a momentum far surpassing that of our heaviest cannon, but the great celerity given to the bodies projected from guns by gunpowder cannot be in the least approached by any other means than by the sudden production of an elastic gas. Mr. Robins found that the flame of gunpowder expanded itself when at the muzzle of the gun with a velocity of 7,000 feet per second.Dr. Hutton’s calculation as to:—Volume, Temperature, Pressure.It has been calculated that one cubic inch of powder is converted into 250 cubic inches of gas at the temperature of the atmosphere, and Dr. Hutton states that the increase of volume at the moment of ignition cannot be less than eight times; therefore one inch of gunpowder, if confined, at the time of explosion exerts a pressure of about 30,000lbs. being 250 by 8 by 15 = 30,000lbs. on the cubic inch, or 5,000lbs. on the square inch; and which at once accounts for its extraordinary power.TemperatureThe value of the temperature to which the gases are raised, on the explosion of the powder, has been variously estimated and it may be concluded to rise as high as will melt copper, or 4,000° Fahrenheit.Expansion.All gases expand uniformly by heat, the expansion having been calculated with great precision, to be1⁄480th for each degree of Fahrenheit. If therefore we take Dr. Hutton’s calculations of one volume of powder expanding into 250 volumes of gas at the temperature of the atmosphere, and if we suppose 4,000° Fahrenheit to be the heat to which they are raised on ignition, the expansion of gunpowder would be calculated.How to calculate expansionThus, suppose the gas to be at 60°, the temperature of the atmosphere, we must deduct 60° from 4,000°, which will give 3,940, being the number of degrees remaining to which it is raised, hencetemp.1°:vol.1480temp.3,940°:vol.3940480=vol.8·2that is, each volume of gas would at a temperature of 4000° beincreased 8·2 in volume. Gunpowder when at the temperature of the air being expanded 250 times in volume; therefore 250 by 8·2 = 2,050 as the increased expansion for each volume of gas generated by the explosion of gunpowder at the temperature of 4,000° Fahrenheit. Lieut-Colonel Boxer calculates that the heat generated by good dry powder is not under 3,000° Fahrenheit.Absolute force of gunpowder cannot be determined.It appears with our present knowledge, the absolute value of the force of gunpowder cannot be determined. Still by careful and extensive experiments no doubt a near approximation to the truth may ultimately be arrived at, so that although much has already been done by various eminent philosophers, there is still more to be accomplished; and the importance of the subject ought to act as a stimulus to the exertions of those belonging to a profession the most interested in the question.Loss of velocity by windage.It has been found by experiments that in calculating the initial velocity of a projectile, one third of the whole force was lost with a windage of1⁄10th inch with a shot of 1·96-in. and 1·86-in. in diameter. The bore of the gun being 2·02-in.Definition of ignition and combustion.By ignition we understand the act of setting fire to a single grain, or to a charge of gunpowder, and by combustion we mean the entire consumption of a grain or of a charge.Quickness of combustion.Upon the quickness of combustion mainly depends the applicability of gunpowder for Military purposes.Ignition by heat.Gunpowder may be inflamed in a variety of ways, but whatever be the method, one portion of the substance must in the first instance be raised to a temperature a little above that necessary to sublime the sulphur, which can be removed from the other ingredients, by gradually raising the compound to a heat sufficient to drive it off in a state of vapour. The heat required for this purpose is between 600° and 680° Fahrenheit.Progressive combustion.When a charge of powder is exploded in the bore of a gun, to all appearance there would seem to be an instantaneous generation of the whole force. But in fact it is not so, a certain time being necessary to the complete combustion of the substance. This gradual firing is of the utmost importance, for were it otherwise, the gun, unless of enormous strength, must be shattered in pieces, as well as the projectile; for in such a case, this great force being suddenly exerted upon one part only of the material, there would not be time for the action to be distributed over the particles, at any great distance, before those in the immediate vicinity of the explosion, were forced out of the sphere of action of the cohesive force, and consequently rupture must take place.Substances which have a more violent action than powder.The effect of such an action may be observed by exploding detonating powders, in which are contained chlorate of potash or fulminating mercury. The action of that peculiar substance the chlorite of nitrogen is still more remarkable. There is also another compound, containing three parts of saltpetre, one part of carbonate of potash and one part of sulphur, which when brought to a certain heat will explode with great violence, its destructive force being very considerable; and this is principally due to the rapidity of the evolution of the gas, for its amount is less than that produced from gunpowder, but the complete decomposition occurs in a much shorter time.In a damp state less quickly fired, and why.If gunpowder be in a damp state, the velocity of combustion will be less than when dry, and also a longer time will be necessary to ignite it, since the moistureupon its conversion into vapour, absorbs a certain amount of heat which remains latent, and of which the useful effects so far as igniting the powder is concerned, is entirely lost.Ignition by percussion.Gunpowder may be ignited by the percussion of copper against copper, copper against iron, lead against lead, and even with lead against wood, when the shock is very great. It is more difficult to ignite gunpowder between copper and bronze,[1]or bronze and wood than between the other substances. Again, out of ten samples which were wrapt in paper and struck upon an anvil with a heavy hammer, seven of grained powder exploded and nine of mealed.[1]Bronze consists of 78 parts copper to 20 of tin. Bell metal—78 copper and 22 tin. Gun metal—100 copper to 8 to 10 tin. Brass—2 copper, 1 zinc and calamine stone, to harden and colour.Influence of shape of grain on ignition.If the part to which the heat is applied be of an angular shape, the inflammation will take place quicker than if it be of a round or flat form, on account of the greater surface that is exposed to the increased temperature.The form of the grain influences the velocity of the transmission of flame.If the grains are of a rounded form, there would be larger interstices, and a greater facility will be afforded to the passage of the heated gas, and therefore this shape is most favourable to the rapid and complete inflammation of each grain in the whole charge. On the other hand, particles of an angular or flat form, fitting into each other as it were, offer greater obstruction to this motion, and the velocity of the transmission of inflammation is thereby diminished.Effect of size on the velocity of transmission of inflammation.If the grains be small, the interstices will be small also, and the facility to the expansion of the gas thereby diminished. In the experiments with trains of powder, the increased surface exposed to the heated gas was found to more than compensate for the diminished facility to its expansion, and generally a train of small-grained powder laid upon a surface without being enclosed, will be consumed more quickly than a train of large-grained powder.Large grain best suited for heavy ordnance.But this is not the case in a piece of ordnance, a circumstance which amongst others will account for the diminished initial velocity given to the shot by a charge of small-grained musket powder, below that produced by the large-grained usually adopted for this service.Velocity of the transmission of inflammation of the charge.When a number of grains of powder are placed together as in the charge of a gun, and a few of them are ignited at one end of the cartridge, a certain quantity of gas is developed of a temperature sufficiently high to ignite those in their immediate vicinity. This has also such elasticity as to enable it to expand itself with considerable velocity. Again, the grains which are so ignited continue the inflammation to others in the same manner. The absolute velocity of expansion of this gas is very considerable; but the grains of gunpowder in the charge offer an obstruction to this motion, the gas having to wind its way through the interstices, and consequently the velocity is considerably diminished, but it is quite clear that it must be very much greater than the velocity of combustion.Estimate of Mr. Piobert.Mr. Piobert estimates the velocity of transmission of inflammation of a charge in a gun at about 38 feet per second, and in all probability even this is much under the mark.Experiments made on this subject.Many experiments have been made by observing the velocity of transmission of inflammation of trains of powder under various circumstances, but they do not show us what would be the velocity in a confined charge. The velocity increased with the section of the train, and further when at the end first lighted, there was an obstruction to the escape of gas, as in the case of a gun, a much shorter time was required for complete inflammation.Time of decomposition depends upon form of grain.When the charge of powder in a gun is ignited the grains being enveloped by the heated gas, we may consider that each grain is ignited over its whole surface at once. If the grains of powder were of equal or regular form, the time each would be consuming, might be easily calculated, but since in ordinary cases they are irregular in form, although the grains may be of the same weight, the time necessary for their complete decomposition will be very different.Circumstances affecting combustion.The quickness of combustion will depend upon the dryness of the powder, the density of the composition, the proportion of the ingredients, the mode of manufacture, and the quality of the ingredients.Combustion of cubical grains considered.Were a cubical grain to be ignited upon its whole surface, the decomposition may be supposed to take place gradually from the surface to the centre, and the original cubical form to remain until the whole is consumed, the cube becoming smaller and smaller. If, then, the rate of burning be the same throughout, the quantity of gas generated in the first half portion of the time will evidently be considerably more than in the latter half, as in the latter case there will be a much lesser surface under the influence of flame.Elongated and cylindrical grains.If the form of the grain be elongated, then will the quantity of gas generated in a given time from a grain of similar weight to that of the cube or sphere, be increased, on account of the greater ignited surface, and consequently the time necessary for its combustion will be diminished. If it be of a cylindrical form for example, this time must be reckoned from the diameter of the cylinder, its length not influencing it in the least, although as we have seen, it enters into the consideration of the quantity of the gas generated in a given time.Large grain.In the ordinary large-grain powder, the majority of the grains are of the elongated or flat form, from whence considerable advantage is derived, particularly in short guns, since it causes the greatest portion of the charge to be decomposed before the projectile is moved sensibly from its original position.Mealed powder.If the charge be composed of mealed powder a longer time is found to be necessary for the complete combustion of the whole than in the case where the substance is granulated, and the initial velocity of a shot is reduced about one third by employing the substance in that state.The effect of granulating gunpowder.A piece of pressed cake weighing 1·06oz., was put into a mortar, and a globe of some light substance, placed upon it, and the powder being consumed after ignition without ejecting the ball from the bore of the piece. When an equal quantity was divided into seven or eight pieces, the globe was thrown out of the mortar; breaking the cake into twelve pieces; the ball ranged 3·3 yards; being further increased to fifty grains, it ranged 10·77 yards; and when the ordinary powder was used, the ball was projected 56·86 yards.Action depends upon size and form of grain.It will appear from the above remarks, that the force generated from the charge of powder in a gun, will be greatly influenced by the size and form of the grains composing it.Density of gunpowder.In order to obtain a gunpowder which shall possess a proper amount of force, it is necessary that the ingredients should be thoroughly incorporated, and the process of incorporation will in great measure affect the density of the grains. After going through the process, it is subjected to a certain pressure, in order that the substance in travelling may not be reduced to a fine powder, which would cause the velocity of transmission of inflammation to be diminished. But there is a certain point beyond which it would not be advantageous to increase the density, and this seems to vary with the size of the grain. With large-grain powder the action in a musket, or in guns with small charges, is greatest with a low density; while with very small grain, the highest velocities are obtained generally with the gunpowder of great density; but in heavy guns with ordinary charges, the large-grained powder should be of considerable density in order to obtain the greatest effect, though still it must not be too great.Advantages of glazing.The principal advantages of glazing are; first, that the powder so prepared, will in travelling, owing to the smaller amount of destructive force consequent on friction, produce less mealed powder; and secondly, that in a damp country like England, the glazing imparts a preserving power to the powder, as the polished surface is less likely to imbibe moisture than the rough.Disadvantages of glazing.The disadvantages of glazing consists in its polishing the surface, and thus depriving it of those angular projections which cause the ignition and combustion to be carried on with greater rapidity, by rendering the interstices smaller, the consequence of which is, that there is not so much gas produced previously to the projectile leaving the gun, and in large charges a portion will be blown out unfired. There must be a limit then to glazing, which it would not be proper to exceed.Experiments as to glazing.At an experiment with glazed and unglazed powder, the ranges on the eprouvette were 75 for glazed, and 98 for unglazed. This loss of power, consequent on glazing, has caused it to be done away with in France and Russia.Glazing less hurtful to fine grains.With fine grain powder it is not of so much consequence, as it is, to a certain degree, corrected by the size of the grain.Size of grain determined by size of charge.The rapidity with which a charge of gunpowder is consumed will depend not only in a certain degree upon the size of the grain, but on the manner in which the charge is put together, for if a charge is closely pressed, the gases meeting resistance in their endeavours to escape between the interstices, will not propagate the ignition so rapidly. With large charges, there exists a positive advantage for the grains to be rather large, so that the most distant parts of the charge should be reached by the gases as quickly as possible; whilst with that of a rifle, the charge being small, the fineness of the grain does not interfere with the quantity of the gas developed. Whence it may rationally be concluded that the dimensions of the grains should increase in proportion to the quantity of the charges into which they are to enter, that is to say, in proportion to the interstices.Tight ramming bad.Ramming down a charge tightly must therefore interfere with the velocity of combustion.Note—The foregoing on the explosive force of gunpowder was taken from Lieut-Colonel E. M. Boxer’s Treatise on Artillery.FOULING.Produce of decomposed gunpowder.The produce obtained by the decomposition of gunpowder are the gaseous and the solid. The gaseous is chiefly nitrogen and carbonic acid. The solid is sulphur and potassium, mixed with a little charcoal, but the solid produce is nearly entirely volatilized at the moment of explosion through the high temperature.Fouling.Fouling is occasioned by the deposition inside the barrel of the solid residue proceeding from the combustion of the powder.Conditions of fouling depend on state of atmosphereOne of the principal of these, namely, the sulphide of Potassa, is deliquescent, or attracts water from the atmosphere. Hence, on a clear day, when the air holds little moisture, the fouling does not attain that semi-fluid state it so speedily attains in a damp day, and it is not so easily removed, and tends to accumulate inside the barrel. Fouling may also be increased or diminished, according to the quality of the powder.Effects of Fouling.Fouling occasions loss of power from the increased friction, and causes inaccuracy in direction and elevation, by filling the grooves, and thus preventing the proper spiral motion being imparted to the projectile.EFFECTS OF GUNPOWDER ON METALS.Difference of effect on brass and iron guns.The effect produced by Gunpowder on metals, in long continued and rapid firing, is very extraordinary. Several of the guns employed at the siege of San Sebastian were cut open, and the interior of some of the vent holes, which were originally cylindrical, and only two-tenths of an inch in diameter, were enlarged in a curious and irregular manner, from three to five inches in one direction, and from two to three inches in another, but the brass guns were much more affected than the iron. In December, 1855, there were lying in the arsenal at Woolwich several of the heaviest sea mortars, which had recently been used at the bombardment of Sweaborg, and the continuous firing on that occasion had split them into two nearly equal portions from muzzle to breech, a trunnion being with each half.Heavy guns for garrisons, sieges, &c., are made of cast iron; guns for field purposes, where lightness is required, are made of gun metal.Difference of effect of brass and iron gunsThese guns are generally denominated brass guns. They can be loaded, properly pointed at an object, and fired about four times in three minutes, but they will not stand long continued rapid firing, or more than 120 rounds a day, as the metal, when heated, softens, and the shot then injures the bore. Heavy iron guns may be loaded, fired, &c., once in two minutes. They suffer more from the total number of rounds that have been fired from them, without reference to the intervals between each round, than from the rapidity of the firing. Four hundred and five hundred rounds per day have not rendered an iron gun unserviceable.MISCELLANEOUS EXPERIMENTS.The following experiments, extracted from Mr. Wilkinson’s “Engines of War,” serve to illustrate the capability of metals to resist the force of gunpowder, and may be of some practical utility, as well as prove interesting merely as matter of curiosity.Experiment 1.—A piece about 5 inches long was cut off the breech-end of a common musket barrel. It was screwed at the part cut, and another plug fitted, so as to have two plugs, one at each end, leaving an internal space of about 3 inches. A percussion nipple was screwed into the end of one of these plugs. This being arranged, one of the plugs was turned out, and one drachm of gunpowder introduced. The plug was replaced, and the powder fired by putting a copper cap on the nipple, and striking it with a hammer. The whole force of the powder escaped at the hole in the nipple. Two, three, four, five, and six drachms were successively introduced, and fired in the same manner, without bursting or injuring the piece of barrel. At last, seven drachms forced out one end, in consequence of the screw having been carelessly fitted. This defect being repaired, Mr. Marsh, of Woolwich, repeatedly fired it with five drachms, merely holding it with a towel in his left hand, and firing it with a blow of a hammer. Six drachms of powder is the full service charge for a flint musket, and four drachms of a percussion musket; yet this immense pressure can be resisted by a cylinder of iron not more than one quarter of an inch thick, and not iron of the best quality.Experiment 2.—A good musket barrel had a cylinder of brass, three inches long, turned to fit the muzzle, and soldered in, so as to close it air-tight. The plug, or breech-screw, was removed, and a felt wad was pushed in with a short piece of wood, marked to the exact depth the charge would occupy, to prevent the ball rolling forward. A musket ball was then dropped in, and a cartridge, containing three drachms of powder, was introduced. The breech being screwed in, left the barrel loaded. It was fired by a percussion tube, but there was no report. On removing the breech-screw, the ball was found to be flattened. A repetition of this experiment, with four drachms, produced a similar result, but the ball was rather more flattened. With five drachms, the ball was perfectly round and uninjured. Six drachms burst the barrel close under the bayonet stud; the ball escaped through the opening, disfigured, but fell close to the barrel. In these experiments the barrel always advanced, instead of recoiling, as usual.Experiment 3.—Made at Woolwich Arsenal, with a Gomer mortar, the chamber being bored conically, so that the shell, when dropped in, fits closely all round, instead of being bored cylindrically, with a chamber in the centre. The mortar being laid at an angle of 45°, one drachm of powder was put into the bottom, and a 68-pounder iron shot over it. When fired, the ball was projected two feet clear of the mortar. A wooden ball, precisely the same diameter, but weighing only 5lbs., was scarcely moved by the same charge, and with two drachms of powder it was justlifted in the mortar, and fell into its place again. Here we find a weight of 68lbs. thrown to the distance of two feet by the same power which would not lift 5lbs., and the wooden ball scarcely moved by double the powder.This proves that the firing of gunpowder under such circumstances is not instantaneous. In the first instance, the small quantity of powder had a large space to fill below the ball, and a heavy weight to move; therefore, could not stir it at all until the whole was ignited, when the force was sufficient to throw it forward two feet. In the second case, the first portion of gas that was generated by ignition of the powder, was sufficient to lift the lighter weight, just enough to allow all the force to escape round it before it had time to accumulate.Experiment 4.—A cannon ball, weighing 24lbs., was placed exactly over the vent-hole of a loaded 32-pounder cannon, which was fired by a train of gunpowder, when the rush from the vent projected the 24-pounder ball to a very considerable height in the air, although the diameter of the hole was only two-tenths of an inch.Experiment 5.—A most ingenious method of ascertaining the relative quickness of ignition of different qualities of gunpowder.A gun-barrel mounted on a carriage with wheels, and moving on a perfectly horizontal railway, is placed at right angles to another short railway, at any convenient distance (suppose fifty feet, or yards); on the second railway a light carriage moves freely with any desired velocity, being drawn forward by means of a weight and pulleys: a cord is attached to the front of this carriage, which passes over a pulley at the end of the railroad, and is continued up a high pole or staff over another pulley at the top, at which end the weight is attached. A long rectangular frame covered with paper is fixed perpendicularly on the carriage, so that when it moves forward it passes across the direct line of the barrel, and forms a long target. A percussion lock is attached to the barrel, which is fired by a detent, or hair-trigger, and the wire which pulls it is disengaged at the same instant to admit of recoil. This wire is carried straight on to the target railroad, and fixed to a small lever, against which the front part of the target-carriage strikes as it is carried onwards by the weight. This constitutes the whole apparatus. When required to be used, the barrel is loaded with gunpowder accurately weighed, and a brass ball that fits the bore correctly: the weight is then disengaged, and the target moves quickly along, discharging the barrel as it passes, and the ball goes through it. With the same powder tried at the same time, the ball constantly goes through the same hole, or breaks into it. If the next powder tried be slower of ignition than the preceding, the ball will pass through another part of the target more in the rear; if quicker, more in advance; thus affording a means of ascertaining this important quality of gunpowder with considerable accuracy: the velocity of the target-carriage can be easily regulated by increasing or diminishing the weight which draws it forward. The differences in the distances between which the balls strike the target with different kinds of powder was frequently as much as ten or twelve inches; but it is not an apparatus commonly used, having been merely constructed for experimental purposes.ON THE TIME REQUIRED FOR IGNITION OF GUNPOWDER.Gunpowder like all other inflammable substances requires to be raised to a certain temperature, before it will ignite, viz., to a dull red heat, or about 600° Fahrenheit. If the heat passes with such rapidity through the powder, so as not to raise the temperature to the necessary degree, then the powder will not ignite, from the velocity of transit, so that it might be possible to calculate theoretically, the velocity that must be given to a red hot ball to enable it to pass through a barrel of gunpowder without causing explosion. The passage of electric fluid through gunpowder may be adduced in evidence of the ignition being dependent on the degree of velocity. The flame of all fulminating powders will pass through the centre of a box filled with gunpowder without igniting one grain of it. If a train of gunpowder be crossed at right angles by a train of fulminating mercury, laid on a sheet of paper or a table, and the powder be lighted with a red hot iron wire, the flame will run on until it meets the cross train of fulminating mercury, when the inflammation of the latter will be so instantaneous as to cut off all connection with the continuous train of powder, leaving the remaining portion of the gunpowder unignited. If on the contrary the fulminating powder be lighted first, it will go straight on and pass through the train of gunpowder so rapidly, as not to inflame it at all. Were a gun to be charged with gun-cotton and gunpowder, the latter would be fired out unignited.EFFECTS OF ACCIDENTAL EXPLOSIONS OF GUNPOWDER.Considering the combustible nature of the materials, accidents very seldom occur; when they do, it is more frequently in the process at the Mill while under the runners.On one occasion at Waltham Abbey Mills, when the powder exploded, after having been two hours under the runners, the doors and windows of the Mills on the opposite side of the stream, were forced open outwards, and the nails drawn. A similar effect took place when the Dartford Mills blew up, January 1833, in consequence of an accident in the packing house. A window which had been recently fitted up in Dartford Town, about a mile and a half distant from the works, was blown outwards into the street, and a considerable quantity of paper was carried as far as Eltham and Lewisham, distances of eight and ten miles. The sudden rarification of the air may account for this circumstance, the atmospheric pressure being removed in the vicinity of the doors and windows, they were forced open outwards by the expansive force of the air contained within the buildings.

It is impossible to make powder magazines too dry, and every care should be taken to ventilate them as much as possible during dry weather, by opening all doors, windows, loopholes, &c. Magazines are generally made bomb-proof, and are furnished with lightning conductors. They are divided into chambers, and these again divided by uprights into bays. At Purfleet, which is the grand depôt for gunpowder in England, there are five magazines capable of containing 9,600 whole barrels each. Each magazine is divided into two chambers, and each chamber into 24 bays, and in each bay is placed 200 whole, 400 half, or 800 quarter barrels of powder. Total in the five Magazines, 48,000 barrels, equal to 4,800,000 pounds.

Principles and Instructions relative to their application to Powder Magazines, bySir W. Snow Harris, F.R.S.Extracted from Army List for July, 1859.

1.—Thunder and lightning result from the operation of a peculiar natural agency through an interval of the atmosphere contained between the surface of a certain area of clouds, and a corresponding area of the earth’s surface directly opposed to the clouds. It is always to be remembered that the earth’s surface and the clouds are the terminating planes of the action, and that buildings are only assailed by Lightning because they are points, as it were, in, or form part of, the earth’s surface, in which the whole action below finally vanishes. Hence buildings, under any circumstances, will be always open to strokes of Lightning, and no human power can prevent it, whether having Conductors or not, or whether having metals about them or not, as experience shows.

2.—Whenever the peculiar agency, (whatever it may be), active in this operation of nature, and characterized by the general term Electricity, or Electric Fluid, is confined to substances which are found to resist its progress, such, for example, as air, glass, resinous bodies, dry wood, stones, &c., then an explosive form of action is the result, attended by such an evolution of light and heat, and by such an enormous expansive force, that the most compact and massive bodies are rent in pieces, and inflammable matter ignited. Nothing appears to stand against it. Granite rocks are split open, oak and other trees, of enormous size, rent in shivers, and masonry of every kind frequently laid in ruins. The lower masts of ships of the line, 3 feet in diameter, and 110 feet long, bound with hoops of iron half an inch thick and 5 inches wide, the whole weighing about 18 tons, have been, in many instances, torn asunder, and the hoops of iron burst open and scattered on the decks. It is, in fact, this terrible expansive power which we have to dread in cases of buildings struck by Lightning, rather than the actual heat attendant on the discharge itself.

3.—When, however, the electrical agency is confined to bodies, such as the metals, which are found to oppose but small resistance to its progress, then this violent expansive or disruptive action is either greatly reduced, or avoided altogether. The explosive form of action we term Lightning, vanishes, and becomes, as it were, transformed into a sort of continuous current action, of a comparatively quiescent kind,which, if the metallic substance it traverses be of certain known dimensions, will not be productive of any damage to the metal. If, however, it be of small capacity, as in the case of a small wire, it may become heated and fused. In this case, the electrical agency, as before, is so resisted in its course as to admit of its taking on a greater or less degree of explosive and heating effect, as in the former case. It is to be here observed, that all kinds of matter oppose some resistance to the progress of what is termed the Electrical Discharge, but the resistance through capacious metallic bodies is comparatively so small, as to admit of being neglected under ordinary circumstances; hence it is that such bodies have been termed Conductors of Electricity, whilst bodies such as air, glass, &c., which are found to oppose very considerable resistance to electrical action, are placed at the opposite extremity of the scale, and termed Non-conductors or Insulators.

The resistance of a metallic copper wire to an ordinary electrical discharge from a battery, was found so small, that the shock traversed the wire at the rate of 576,000 miles in a second. The resistance however, through a metallic line of Conduction, small as it be, increases with the length, and diminishes with the area of the section of the Conductor, or as the quantity of metal increases.

4.—It follows from these established facts, that if a building were metallic in all its parts, an iron magazine for example, then no damage could possibly arise to it from any stroke of Lightning which has come within the experience of mankind; e.g., a man in armour is safe from damage by Lightning; in fact, from the instant the electrical discharge in breaking with disruptive and explosive violence through the resisting air, seizes upon the mass in any point of it, from that instant the explosive action vanishes, and the forces in operation are neutralized upon the terminating planes of action, viz., the surface of the earth, and opposed clouds.

5.—All this plainly teaches us, that in order to guard a building effectually against damage by Lightning, we must endeavour to bring the general structure as nearly as may be, into that passive or non-resisting state it would assume, supposing the whole were a mass of metal.

6.—To this end, one or more conducting channels of copper depending upon the magnitude and extent of the building should be systematically applied to the walls; these conducting channels should consist either of double copper plates united in series one over the other, as in the method of fixing such Conductors to the masts of Her Majesty’s Ships, the plates being not less than 31⁄2inches wide, and of1⁄16th and1⁄8th of an inch in thickness, or the Conductors may with advantage be constructed of stout copper pipe not less than3⁄16ths of an inch thick, and 11⁄2to 2 inches in diameter: in either case the Conductors should be securely fixed to the walls of the building, either by braces, or copper nails, or clamps; they should terminate in solid metal rods above, projecting freely into the air, at a moderate and convenient height above the point to which they are fixed, and below they should terminate in one or two branches leading outward about a foot under the surface of the earth; if possible, they should be connected with a spring of water or other moist ground.

It would be proper in certain dry situations, to lead out in several directions under the ground, old iron or other metallic chains, so as to expose a large extent of metallic contact in the surface of the earth.

7.—All the metals in the roof and other parts of the building of whatever kind, should so far as possible have metallic communication with these Alarm Conductors, and in case of any prominent elevated chimney, it would be desirable to lead a pointed conducting tube along it to the metals of the roof; all of which satisfies the conditions above specified.

8.—Remark 1.—It is now proved beyond all questions, that the electrical discharge never leaves perfect conducting lines of small resistance, in order to pass out upon bad conducting circuits, in which the resistance is very great, that is an established law of nature; hence a stroke of Lightning upon such conducting lines will be confined to the Conductors as constituting a line of discharge of less resistance than any other line of discharge through the building, which can be assigned. The apprehension of “Lateral Discharge” therefore, from the Conductor, is quite absurd; and is not countenanced by any fact whatever; if any doubt could possibly exist, it would be now most completely set at rest by the experience of the permanent Conductors, applied to the masts of Her Majesty’s ships. In very many instances furious discharges of Lightning have fallen on the masts with a crash as if the ship’s broadside had been fired, and the solid point aloft has been found melted; in all these cases electrical discharge robbed by the Conductor of its explosive violence, has traversed the line of action to the sea, through the ship, and through the copper bolts, driven through the ship’s solid timbers, without the least damage to the surrounding masses, whether metallic, as in the case of the massive iron hoops on the lower masts, or not. Persons have either been close by or actually leaning against the Conductors at the time, without experiencing any ill consequence.

9.—Remark 2.—It has also been incontestably shown, that metallic bodies have not any specific attractive force or affinity for the matter of Lightning; metals are as little attractive of lightning as wood or stone. All matter is equally indifferent to Electricity so far as regards a specific attraction, hence the idea that metals attract or invite Lightning is a popular but very unlearned error contradicted by the most satisfactory evidence, and the whole course of experience; in short, we find that Lightning falls indiscriminately upon trees, rocks, and buildings, whether the buildings have metals about them or not.

10.—Remark 3.—A building that is hence clear, may be struck and damaged by Lightning without having a particle of metal in its construction; if there be metals in it, however, and they happen to be in such situations as will enable them to facilitate the progress of the electrical discharge, so far as they go, then the discharge will fall on them in preference to other bodies offering more resistance, but not otherwise; if metallic substances be not present, or if present, they happen to occupy places in which they cannot be of any use in helping on the discharge in the course it wants to go, then the electricity seizes upon other bodies, which lie in that course, or which can help it, however small their power of doing so, and in this attempt such bodies are commonly,but not always, shattered in pieces. The great law of the discharge is,—progress between the terminating planes of action, viz:—the clouds and earth, and in such line or lines as upon the whole, offer the least mechanical impediment or resistance to this operation, just as water falling over the side of a hill in a rain storm, picks out or selects as it were by the force of gravity, all the little furrows or channels which lie convenient to its course, and avoids those which do not. If in the case of Lightning you provide through the instrumentality of efficient Conductors, a free and uninterrupted course for the electrical discharge, then it will follow that course without damage to the general structure; if you do not, then this irresistible agency will find a course for itself through the edifice in some line or lines of least resistance to it, and will shake all imperfect conducting matter in pieces in doing so; moreover it is to be specially remarked in this case, that the damage ensues, not where the metals are, but where they cease to be continued, the more metal in a building therefore the better, more especially when connected by an uninterrupted circuit with any medium of communication with the earth.

Such is, in fact, the great condition to be satisfied in the application of Lightning Conductors, which is virtually nothing more than the perfecting a line or lines of small resistance in given directions, less than the resistance in any other lines in the building, which can be assigned in any other direction, and in which by a law of nature the electrical agency will move in preference to any others.

11.—It follows from the foregoing principles, that a magazine constructed entirely of iron or other metal, would be infinitely more safe in Lightning storms than if built with masonry in the usual way; metallic roofs for magazines, with capacious metallic Conductors to the earth, would be unobjectionable, and a source of security.

Metallic gutters and ridges having continuous metallic connection with the earth are also unobjectionable.

A good method of Conductors for magazines built of masonry, would be such as already described, regard being had to the position of the building, its extent, and most prominent points, also to the nature, state, and condition of the soil, whether it be moist or dry, alluvial calcareous, or of hard rock; we must also consider the extent, disposition, and peculiar position of the metallic bodies entering into the general structure of the building, whether the roof be flat, pointed, or angular in various parts.

The pointed projecting extremities of the two Conductors, one or more as the case may be, will be commonly sufficient; but, in buildings having tall chimneys or other elevated prominent points, at a distance from the Main Conductor, it will be requisite to guard such chimneys or other parts, by a pointed rod, led along them to the metals of the roof, or directly connected with the Main Conductors, by metallic connections.

12.—Pointed terminations of the Conductors in the air, are so far important that they tend to break the force of a discharge of Lightning when it falls on them. In fact, before the great shock actually takes place, under the form of a dense explosion, a very large amount of the discharge, which otherwise would be concentrated, runs off, as it were, through the pointed Conductor; but they have no other influence.

With respect to these pointed terminations, no great care need be taken about them, except that they should consist of solid copper rod, of about three-quarters of an inch in diameter, and about a foot in length, and be united by brazing to the conducting tube, elevated at such convenient height above the walls of the building as the case may suggest.

As a support to the Conductor, when raised above the wall, we may employ a small staff or spar of wood fixed to the masonry.

13.—Copper linings to the doors and window shutters of magazines are not objectionable, if requisite, as a precaution against fire; but they are useless as a means of keeping out Lightning; on the other hand, it is not easy to conceive a case in which the explosion of the gunpowder is to be apprehended from the action of Lightning on the doors or windows. Supposing, however, such metallic linings desirable as a precaution against common cases of fire, then the masses of metal should, according to the principles already laid down, have metallic communication with the general system of conduction in the building and the Main Conductor.

ON THE EXPLOSIVE FORCE OF GUNPOWDER.Advantages of GunpowderThe advantages of Gunpowder, as a propelling agent, over any other explosive material are, the comparative safety attending its manufacture and transport, and the gradual nature of its decomposition when compared with those materials, such as fulminating gold, silver, mercury, &c. &c. In gunpowder, the force resulting from the rapid evolution of gas in a confined space has sufficient time to overcome the inertia of the projectile, which is not the case with other explosive materials, the conversion of which gaseous products is so instantaneous that nothing can resist the intensity of their explosive action. Other advantages suggest themselves in the use of Gunpowder, such as the comparative cheapness of the ingredients composing it, and the ease with which they may be obtained; for the sulphur and saltpetre are very abundant productions of nature, and the charcoal can be manufactured cheaply and with great facility, and if care is taken in the process of the fabrication of powder, little deterioration will take place on its exposure to heat or moisture.Air & Steam as propellantsCondensed air and steam have been used as propelling agents; but the great inconvenience attending their use quite preclude the possibility of adapting them to war purposes.Force of Gunpowder.As the force and effect obtained from Gunpowder is the foundation of all other particulars relating to Gunnery, we will briefly consider these points.Upon what the action of powder depends.The action of Gunpowder is dependent upon a purely chemical process. Mr. Robins proved that the force generated by the combustion of gunpowder, was owing to an elastic gas which was suddenly disengaged from the powder, when it was brought to a certain temperature, and further that this disengaged gas had its elastic force greatly augmented by the heat evolved by the chemical action.Ingredients are charged with a large volume of heated gas.The propelling power of Gunpowder is dependent on the rapid decomposition of the nitre into its component parts; the oxygen forms carbonic acid with the carbon in the charcoal, and the heat thus generated by ignition changes both this and the nitrogen into a large volume of heated gas. In a mixture of nitre and charcoal alone, the oxidation proceeds with comparative slowness; by the addition of sulphur, an augmentation of combustibility is gained, in consequence of its igniting at a very low temperature; the sulphur, also, by its presence, renders available for the oxidation of the carbon an additional amount of oxygen, viz: that which is united with the potassium, the latter being at once converted into sulphite upon ignition of the powder.Weight of gas evolved.It appears that the weight of gas generated is equal to three tenths of the weight of the powder which yielded it,Volume of gas evolved.and that its bulk when cold, and expanded to the rarity of Common air was 240 times that of the powder; the barometer standing at about 30 inches. From this Robins concluded that if the fluid occupied a space equal to the volume of the gunpowder, its elastic force, when cold, would be 240 times the pressure of the atmosphere, when the barometer stands as above.Heat of gas evolved.Mr. Robins also considered that the heat evolved was at least equal to that of red hot iron, and he found by experiments that air heated to this temperature had its elasticity quadrupled, and therefore, that the force of gas from powder is at least four times 240 = 960, or in round numbers 1,000 times as great as the elasticity of the air measured by its pressure on an equal extent of surface.Pressure of gas generated.From the height of the barometer it is known that the pressure of the atmosphere is about 143⁄4lbs. upon the square inch, so that the pressure of the elastic gas generated by the combustion of the gunpowder upon the same area would be 14.75 by 1,000 or 14,750lbs. at the moment of explosion.Strength of powder not affected by density of air, but by damp.He found that the strength of Gunpowder was the same whatever might be the density of the atmosphere, but that the moisture of the air effected it considerably, in fact that the same quantity of powder which would give a bullet an initial velocity of 1,700 feet per second on a day when the atmosphere was comparatively dry, would upon a damp day give no more than 1,200 or 1,300 feet.Velocity of gasThe velocity of the expansion of the gas is a most important point, upon which depends, chiefly, the peculiar value of the substance as a propelling agent. Many of the warlike machines of the Ancients produced a momentum far surpassing that of our heaviest cannon, but the great celerity given to the bodies projected from guns by gunpowder cannot be in the least approached by any other means than by the sudden production of an elastic gas. Mr. Robins found that the flame of gunpowder expanded itself when at the muzzle of the gun with a velocity of 7,000 feet per second.Dr. Hutton’s calculation as to:—Volume, Temperature, Pressure.It has been calculated that one cubic inch of powder is converted into 250 cubic inches of gas at the temperature of the atmosphere, and Dr. Hutton states that the increase of volume at the moment of ignition cannot be less than eight times; therefore one inch of gunpowder, if confined, at the time of explosion exerts a pressure of about 30,000lbs. being 250 by 8 by 15 = 30,000lbs. on the cubic inch, or 5,000lbs. on the square inch; and which at once accounts for its extraordinary power.TemperatureThe value of the temperature to which the gases are raised, on the explosion of the powder, has been variously estimated and it may be concluded to rise as high as will melt copper, or 4,000° Fahrenheit.Expansion.All gases expand uniformly by heat, the expansion having been calculated with great precision, to be1⁄480th for each degree of Fahrenheit. If therefore we take Dr. Hutton’s calculations of one volume of powder expanding into 250 volumes of gas at the temperature of the atmosphere, and if we suppose 4,000° Fahrenheit to be the heat to which they are raised on ignition, the expansion of gunpowder would be calculated.How to calculate expansionThus, suppose the gas to be at 60°, the temperature of the atmosphere, we must deduct 60° from 4,000°, which will give 3,940, being the number of degrees remaining to which it is raised, hencetemp.1°:vol.1480temp.3,940°:vol.3940480=vol.8·2that is, each volume of gas would at a temperature of 4000° beincreased 8·2 in volume. Gunpowder when at the temperature of the air being expanded 250 times in volume; therefore 250 by 8·2 = 2,050 as the increased expansion for each volume of gas generated by the explosion of gunpowder at the temperature of 4,000° Fahrenheit. Lieut-Colonel Boxer calculates that the heat generated by good dry powder is not under 3,000° Fahrenheit.Absolute force of gunpowder cannot be determined.It appears with our present knowledge, the absolute value of the force of gunpowder cannot be determined. Still by careful and extensive experiments no doubt a near approximation to the truth may ultimately be arrived at, so that although much has already been done by various eminent philosophers, there is still more to be accomplished; and the importance of the subject ought to act as a stimulus to the exertions of those belonging to a profession the most interested in the question.Loss of velocity by windage.It has been found by experiments that in calculating the initial velocity of a projectile, one third of the whole force was lost with a windage of1⁄10th inch with a shot of 1·96-in. and 1·86-in. in diameter. The bore of the gun being 2·02-in.Definition of ignition and combustion.By ignition we understand the act of setting fire to a single grain, or to a charge of gunpowder, and by combustion we mean the entire consumption of a grain or of a charge.Quickness of combustion.Upon the quickness of combustion mainly depends the applicability of gunpowder for Military purposes.Ignition by heat.Gunpowder may be inflamed in a variety of ways, but whatever be the method, one portion of the substance must in the first instance be raised to a temperature a little above that necessary to sublime the sulphur, which can be removed from the other ingredients, by gradually raising the compound to a heat sufficient to drive it off in a state of vapour. The heat required for this purpose is between 600° and 680° Fahrenheit.Progressive combustion.When a charge of powder is exploded in the bore of a gun, to all appearance there would seem to be an instantaneous generation of the whole force. But in fact it is not so, a certain time being necessary to the complete combustion of the substance. This gradual firing is of the utmost importance, for were it otherwise, the gun, unless of enormous strength, must be shattered in pieces, as well as the projectile; for in such a case, this great force being suddenly exerted upon one part only of the material, there would not be time for the action to be distributed over the particles, at any great distance, before those in the immediate vicinity of the explosion, were forced out of the sphere of action of the cohesive force, and consequently rupture must take place.Substances which have a more violent action than powder.The effect of such an action may be observed by exploding detonating powders, in which are contained chlorate of potash or fulminating mercury. The action of that peculiar substance the chlorite of nitrogen is still more remarkable. There is also another compound, containing three parts of saltpetre, one part of carbonate of potash and one part of sulphur, which when brought to a certain heat will explode with great violence, its destructive force being very considerable; and this is principally due to the rapidity of the evolution of the gas, for its amount is less than that produced from gunpowder, but the complete decomposition occurs in a much shorter time.In a damp state less quickly fired, and why.If gunpowder be in a damp state, the velocity of combustion will be less than when dry, and also a longer time will be necessary to ignite it, since the moistureupon its conversion into vapour, absorbs a certain amount of heat which remains latent, and of which the useful effects so far as igniting the powder is concerned, is entirely lost.Ignition by percussion.Gunpowder may be ignited by the percussion of copper against copper, copper against iron, lead against lead, and even with lead against wood, when the shock is very great. It is more difficult to ignite gunpowder between copper and bronze,[1]or bronze and wood than between the other substances. Again, out of ten samples which were wrapt in paper and struck upon an anvil with a heavy hammer, seven of grained powder exploded and nine of mealed.[1]Bronze consists of 78 parts copper to 20 of tin. Bell metal—78 copper and 22 tin. Gun metal—100 copper to 8 to 10 tin. Brass—2 copper, 1 zinc and calamine stone, to harden and colour.Influence of shape of grain on ignition.If the part to which the heat is applied be of an angular shape, the inflammation will take place quicker than if it be of a round or flat form, on account of the greater surface that is exposed to the increased temperature.The form of the grain influences the velocity of the transmission of flame.If the grains are of a rounded form, there would be larger interstices, and a greater facility will be afforded to the passage of the heated gas, and therefore this shape is most favourable to the rapid and complete inflammation of each grain in the whole charge. On the other hand, particles of an angular or flat form, fitting into each other as it were, offer greater obstruction to this motion, and the velocity of the transmission of inflammation is thereby diminished.Effect of size on the velocity of transmission of inflammation.If the grains be small, the interstices will be small also, and the facility to the expansion of the gas thereby diminished. In the experiments with trains of powder, the increased surface exposed to the heated gas was found to more than compensate for the diminished facility to its expansion, and generally a train of small-grained powder laid upon a surface without being enclosed, will be consumed more quickly than a train of large-grained powder.Large grain best suited for heavy ordnance.But this is not the case in a piece of ordnance, a circumstance which amongst others will account for the diminished initial velocity given to the shot by a charge of small-grained musket powder, below that produced by the large-grained usually adopted for this service.Velocity of the transmission of inflammation of the charge.When a number of grains of powder are placed together as in the charge of a gun, and a few of them are ignited at one end of the cartridge, a certain quantity of gas is developed of a temperature sufficiently high to ignite those in their immediate vicinity. This has also such elasticity as to enable it to expand itself with considerable velocity. Again, the grains which are so ignited continue the inflammation to others in the same manner. The absolute velocity of expansion of this gas is very considerable; but the grains of gunpowder in the charge offer an obstruction to this motion, the gas having to wind its way through the interstices, and consequently the velocity is considerably diminished, but it is quite clear that it must be very much greater than the velocity of combustion.Estimate of Mr. Piobert.Mr. Piobert estimates the velocity of transmission of inflammation of a charge in a gun at about 38 feet per second, and in all probability even this is much under the mark.Experiments made on this subject.Many experiments have been made by observing the velocity of transmission of inflammation of trains of powder under various circumstances, but they do not show us what would be the velocity in a confined charge. The velocity increased with the section of the train, and further when at the end first lighted, there was an obstruction to the escape of gas, as in the case of a gun, a much shorter time was required for complete inflammation.Time of decomposition depends upon form of grain.When the charge of powder in a gun is ignited the grains being enveloped by the heated gas, we may consider that each grain is ignited over its whole surface at once. If the grains of powder were of equal or regular form, the time each would be consuming, might be easily calculated, but since in ordinary cases they are irregular in form, although the grains may be of the same weight, the time necessary for their complete decomposition will be very different.Circumstances affecting combustion.The quickness of combustion will depend upon the dryness of the powder, the density of the composition, the proportion of the ingredients, the mode of manufacture, and the quality of the ingredients.Combustion of cubical grains considered.Were a cubical grain to be ignited upon its whole surface, the decomposition may be supposed to take place gradually from the surface to the centre, and the original cubical form to remain until the whole is consumed, the cube becoming smaller and smaller. If, then, the rate of burning be the same throughout, the quantity of gas generated in the first half portion of the time will evidently be considerably more than in the latter half, as in the latter case there will be a much lesser surface under the influence of flame.Elongated and cylindrical grains.If the form of the grain be elongated, then will the quantity of gas generated in a given time from a grain of similar weight to that of the cube or sphere, be increased, on account of the greater ignited surface, and consequently the time necessary for its combustion will be diminished. If it be of a cylindrical form for example, this time must be reckoned from the diameter of the cylinder, its length not influencing it in the least, although as we have seen, it enters into the consideration of the quantity of the gas generated in a given time.Large grain.In the ordinary large-grain powder, the majority of the grains are of the elongated or flat form, from whence considerable advantage is derived, particularly in short guns, since it causes the greatest portion of the charge to be decomposed before the projectile is moved sensibly from its original position.Mealed powder.If the charge be composed of mealed powder a longer time is found to be necessary for the complete combustion of the whole than in the case where the substance is granulated, and the initial velocity of a shot is reduced about one third by employing the substance in that state.The effect of granulating gunpowder.A piece of pressed cake weighing 1·06oz., was put into a mortar, and a globe of some light substance, placed upon it, and the powder being consumed after ignition without ejecting the ball from the bore of the piece. When an equal quantity was divided into seven or eight pieces, the globe was thrown out of the mortar; breaking the cake into twelve pieces; the ball ranged 3·3 yards; being further increased to fifty grains, it ranged 10·77 yards; and when the ordinary powder was used, the ball was projected 56·86 yards.Action depends upon size and form of grain.It will appear from the above remarks, that the force generated from the charge of powder in a gun, will be greatly influenced by the size and form of the grains composing it.Density of gunpowder.In order to obtain a gunpowder which shall possess a proper amount of force, it is necessary that the ingredients should be thoroughly incorporated, and the process of incorporation will in great measure affect the density of the grains. After going through the process, it is subjected to a certain pressure, in order that the substance in travelling may not be reduced to a fine powder, which would cause the velocity of transmission of inflammation to be diminished. But there is a certain point beyond which it would not be advantageous to increase the density, and this seems to vary with the size of the grain. With large-grain powder the action in a musket, or in guns with small charges, is greatest with a low density; while with very small grain, the highest velocities are obtained generally with the gunpowder of great density; but in heavy guns with ordinary charges, the large-grained powder should be of considerable density in order to obtain the greatest effect, though still it must not be too great.Advantages of glazing.The principal advantages of glazing are; first, that the powder so prepared, will in travelling, owing to the smaller amount of destructive force consequent on friction, produce less mealed powder; and secondly, that in a damp country like England, the glazing imparts a preserving power to the powder, as the polished surface is less likely to imbibe moisture than the rough.Disadvantages of glazing.The disadvantages of glazing consists in its polishing the surface, and thus depriving it of those angular projections which cause the ignition and combustion to be carried on with greater rapidity, by rendering the interstices smaller, the consequence of which is, that there is not so much gas produced previously to the projectile leaving the gun, and in large charges a portion will be blown out unfired. There must be a limit then to glazing, which it would not be proper to exceed.Experiments as to glazing.At an experiment with glazed and unglazed powder, the ranges on the eprouvette were 75 for glazed, and 98 for unglazed. This loss of power, consequent on glazing, has caused it to be done away with in France and Russia.Glazing less hurtful to fine grains.With fine grain powder it is not of so much consequence, as it is, to a certain degree, corrected by the size of the grain.Size of grain determined by size of charge.The rapidity with which a charge of gunpowder is consumed will depend not only in a certain degree upon the size of the grain, but on the manner in which the charge is put together, for if a charge is closely pressed, the gases meeting resistance in their endeavours to escape between the interstices, will not propagate the ignition so rapidly. With large charges, there exists a positive advantage for the grains to be rather large, so that the most distant parts of the charge should be reached by the gases as quickly as possible; whilst with that of a rifle, the charge being small, the fineness of the grain does not interfere with the quantity of the gas developed. Whence it may rationally be concluded that the dimensions of the grains should increase in proportion to the quantity of the charges into which they are to enter, that is to say, in proportion to the interstices.Tight ramming bad.Ramming down a charge tightly must therefore interfere with the velocity of combustion.Note—The foregoing on the explosive force of gunpowder was taken from Lieut-Colonel E. M. Boxer’s Treatise on Artillery.FOULING.Produce of decomposed gunpowder.The produce obtained by the decomposition of gunpowder are the gaseous and the solid. The gaseous is chiefly nitrogen and carbonic acid. The solid is sulphur and potassium, mixed with a little charcoal, but the solid produce is nearly entirely volatilized at the moment of explosion through the high temperature.Fouling.Fouling is occasioned by the deposition inside the barrel of the solid residue proceeding from the combustion of the powder.Conditions of fouling depend on state of atmosphereOne of the principal of these, namely, the sulphide of Potassa, is deliquescent, or attracts water from the atmosphere. Hence, on a clear day, when the air holds little moisture, the fouling does not attain that semi-fluid state it so speedily attains in a damp day, and it is not so easily removed, and tends to accumulate inside the barrel. Fouling may also be increased or diminished, according to the quality of the powder.Effects of Fouling.Fouling occasions loss of power from the increased friction, and causes inaccuracy in direction and elevation, by filling the grooves, and thus preventing the proper spiral motion being imparted to the projectile.EFFECTS OF GUNPOWDER ON METALS.Difference of effect on brass and iron guns.The effect produced by Gunpowder on metals, in long continued and rapid firing, is very extraordinary. Several of the guns employed at the siege of San Sebastian were cut open, and the interior of some of the vent holes, which were originally cylindrical, and only two-tenths of an inch in diameter, were enlarged in a curious and irregular manner, from three to five inches in one direction, and from two to three inches in another, but the brass guns were much more affected than the iron. In December, 1855, there were lying in the arsenal at Woolwich several of the heaviest sea mortars, which had recently been used at the bombardment of Sweaborg, and the continuous firing on that occasion had split them into two nearly equal portions from muzzle to breech, a trunnion being with each half.Heavy guns for garrisons, sieges, &c., are made of cast iron; guns for field purposes, where lightness is required, are made of gun metal.Difference of effect of brass and iron gunsThese guns are generally denominated brass guns. They can be loaded, properly pointed at an object, and fired about four times in three minutes, but they will not stand long continued rapid firing, or more than 120 rounds a day, as the metal, when heated, softens, and the shot then injures the bore. Heavy iron guns may be loaded, fired, &c., once in two minutes. They suffer more from the total number of rounds that have been fired from them, without reference to the intervals between each round, than from the rapidity of the firing. Four hundred and five hundred rounds per day have not rendered an iron gun unserviceable.

Advantages of Gunpowder

The advantages of Gunpowder, as a propelling agent, over any other explosive material are, the comparative safety attending its manufacture and transport, and the gradual nature of its decomposition when compared with those materials, such as fulminating gold, silver, mercury, &c. &c. In gunpowder, the force resulting from the rapid evolution of gas in a confined space has sufficient time to overcome the inertia of the projectile, which is not the case with other explosive materials, the conversion of which gaseous products is so instantaneous that nothing can resist the intensity of their explosive action. Other advantages suggest themselves in the use of Gunpowder, such as the comparative cheapness of the ingredients composing it, and the ease with which they may be obtained; for the sulphur and saltpetre are very abundant productions of nature, and the charcoal can be manufactured cheaply and with great facility, and if care is taken in the process of the fabrication of powder, little deterioration will take place on its exposure to heat or moisture.

Air & Steam as propellants

Condensed air and steam have been used as propelling agents; but the great inconvenience attending their use quite preclude the possibility of adapting them to war purposes.

Force of Gunpowder.

As the force and effect obtained from Gunpowder is the foundation of all other particulars relating to Gunnery, we will briefly consider these points.

Upon what the action of powder depends.

The action of Gunpowder is dependent upon a purely chemical process. Mr. Robins proved that the force generated by the combustion of gunpowder, was owing to an elastic gas which was suddenly disengaged from the powder, when it was brought to a certain temperature, and further that this disengaged gas had its elastic force greatly augmented by the heat evolved by the chemical action.

Ingredients are charged with a large volume of heated gas.

The propelling power of Gunpowder is dependent on the rapid decomposition of the nitre into its component parts; the oxygen forms carbonic acid with the carbon in the charcoal, and the heat thus generated by ignition changes both this and the nitrogen into a large volume of heated gas. In a mixture of nitre and charcoal alone, the oxidation proceeds with comparative slowness; by the addition of sulphur, an augmentation of combustibility is gained, in consequence of its igniting at a very low temperature; the sulphur, also, by its presence, renders available for the oxidation of the carbon an additional amount of oxygen, viz: that which is united with the potassium, the latter being at once converted into sulphite upon ignition of the powder.

Weight of gas evolved.

It appears that the weight of gas generated is equal to three tenths of the weight of the powder which yielded it,Volume of gas evolved.and that its bulk when cold, and expanded to the rarity of Common air was 240 times that of the powder; the barometer standing at about 30 inches. From this Robins concluded that if the fluid occupied a space equal to the volume of the gunpowder, its elastic force, when cold, would be 240 times the pressure of the atmosphere, when the barometer stands as above.Heat of gas evolved.Mr. Robins also considered that the heat evolved was at least equal to that of red hot iron, and he found by experiments that air heated to this temperature had its elasticity quadrupled, and therefore, that the force of gas from powder is at least four times 240 = 960, or in round numbers 1,000 times as great as the elasticity of the air measured by its pressure on an equal extent of surface.Pressure of gas generated.From the height of the barometer it is known that the pressure of the atmosphere is about 143⁄4lbs. upon the square inch, so that the pressure of the elastic gas generated by the combustion of the gunpowder upon the same area would be 14.75 by 1,000 or 14,750lbs. at the moment of explosion.Strength of powder not affected by density of air, but by damp.He found that the strength of Gunpowder was the same whatever might be the density of the atmosphere, but that the moisture of the air effected it considerably, in fact that the same quantity of powder which would give a bullet an initial velocity of 1,700 feet per second on a day when the atmosphere was comparatively dry, would upon a damp day give no more than 1,200 or 1,300 feet.

Velocity of gas

The velocity of the expansion of the gas is a most important point, upon which depends, chiefly, the peculiar value of the substance as a propelling agent. Many of the warlike machines of the Ancients produced a momentum far surpassing that of our heaviest cannon, but the great celerity given to the bodies projected from guns by gunpowder cannot be in the least approached by any other means than by the sudden production of an elastic gas. Mr. Robins found that the flame of gunpowder expanded itself when at the muzzle of the gun with a velocity of 7,000 feet per second.

Dr. Hutton’s calculation as to:—Volume, Temperature, Pressure.

It has been calculated that one cubic inch of powder is converted into 250 cubic inches of gas at the temperature of the atmosphere, and Dr. Hutton states that the increase of volume at the moment of ignition cannot be less than eight times; therefore one inch of gunpowder, if confined, at the time of explosion exerts a pressure of about 30,000lbs. being 250 by 8 by 15 = 30,000lbs. on the cubic inch, or 5,000lbs. on the square inch; and which at once accounts for its extraordinary power.TemperatureThe value of the temperature to which the gases are raised, on the explosion of the powder, has been variously estimated and it may be concluded to rise as high as will melt copper, or 4,000° Fahrenheit.Expansion.All gases expand uniformly by heat, the expansion having been calculated with great precision, to be1⁄480th for each degree of Fahrenheit. If therefore we take Dr. Hutton’s calculations of one volume of powder expanding into 250 volumes of gas at the temperature of the atmosphere, and if we suppose 4,000° Fahrenheit to be the heat to which they are raised on ignition, the expansion of gunpowder would be calculated.How to calculate expansionThus, suppose the gas to be at 60°, the temperature of the atmosphere, we must deduct 60° from 4,000°, which will give 3,940, being the number of degrees remaining to which it is raised, hencetemp.1°:vol.1480temp.3,940°:vol.3940480=vol.8·2that is, each volume of gas would at a temperature of 4000° beincreased 8·2 in volume. Gunpowder when at the temperature of the air being expanded 250 times in volume; therefore 250 by 8·2 = 2,050 as the increased expansion for each volume of gas generated by the explosion of gunpowder at the temperature of 4,000° Fahrenheit. Lieut-Colonel Boxer calculates that the heat generated by good dry powder is not under 3,000° Fahrenheit.Absolute force of gunpowder cannot be determined.It appears with our present knowledge, the absolute value of the force of gunpowder cannot be determined. Still by careful and extensive experiments no doubt a near approximation to the truth may ultimately be arrived at, so that although much has already been done by various eminent philosophers, there is still more to be accomplished; and the importance of the subject ought to act as a stimulus to the exertions of those belonging to a profession the most interested in the question.

Loss of velocity by windage.

It has been found by experiments that in calculating the initial velocity of a projectile, one third of the whole force was lost with a windage of1⁄10th inch with a shot of 1·96-in. and 1·86-in. in diameter. The bore of the gun being 2·02-in.

Definition of ignition and combustion.

By ignition we understand the act of setting fire to a single grain, or to a charge of gunpowder, and by combustion we mean the entire consumption of a grain or of a charge.

Quickness of combustion.

Upon the quickness of combustion mainly depends the applicability of gunpowder for Military purposes.

Ignition by heat.

Gunpowder may be inflamed in a variety of ways, but whatever be the method, one portion of the substance must in the first instance be raised to a temperature a little above that necessary to sublime the sulphur, which can be removed from the other ingredients, by gradually raising the compound to a heat sufficient to drive it off in a state of vapour. The heat required for this purpose is between 600° and 680° Fahrenheit.

Progressive combustion.

When a charge of powder is exploded in the bore of a gun, to all appearance there would seem to be an instantaneous generation of the whole force. But in fact it is not so, a certain time being necessary to the complete combustion of the substance. This gradual firing is of the utmost importance, for were it otherwise, the gun, unless of enormous strength, must be shattered in pieces, as well as the projectile; for in such a case, this great force being suddenly exerted upon one part only of the material, there would not be time for the action to be distributed over the particles, at any great distance, before those in the immediate vicinity of the explosion, were forced out of the sphere of action of the cohesive force, and consequently rupture must take place.

Substances which have a more violent action than powder.

The effect of such an action may be observed by exploding detonating powders, in which are contained chlorate of potash or fulminating mercury. The action of that peculiar substance the chlorite of nitrogen is still more remarkable. There is also another compound, containing three parts of saltpetre, one part of carbonate of potash and one part of sulphur, which when brought to a certain heat will explode with great violence, its destructive force being very considerable; and this is principally due to the rapidity of the evolution of the gas, for its amount is less than that produced from gunpowder, but the complete decomposition occurs in a much shorter time.

In a damp state less quickly fired, and why.

If gunpowder be in a damp state, the velocity of combustion will be less than when dry, and also a longer time will be necessary to ignite it, since the moistureupon its conversion into vapour, absorbs a certain amount of heat which remains latent, and of which the useful effects so far as igniting the powder is concerned, is entirely lost.

Ignition by percussion.

Gunpowder may be ignited by the percussion of copper against copper, copper against iron, lead against lead, and even with lead against wood, when the shock is very great. It is more difficult to ignite gunpowder between copper and bronze,[1]or bronze and wood than between the other substances. Again, out of ten samples which were wrapt in paper and struck upon an anvil with a heavy hammer, seven of grained powder exploded and nine of mealed.

[1]Bronze consists of 78 parts copper to 20 of tin. Bell metal—78 copper and 22 tin. Gun metal—100 copper to 8 to 10 tin. Brass—2 copper, 1 zinc and calamine stone, to harden and colour.

[1]Bronze consists of 78 parts copper to 20 of tin. Bell metal—78 copper and 22 tin. Gun metal—100 copper to 8 to 10 tin. Brass—2 copper, 1 zinc and calamine stone, to harden and colour.

Influence of shape of grain on ignition.

If the part to which the heat is applied be of an angular shape, the inflammation will take place quicker than if it be of a round or flat form, on account of the greater surface that is exposed to the increased temperature.

The form of the grain influences the velocity of the transmission of flame.

If the grains are of a rounded form, there would be larger interstices, and a greater facility will be afforded to the passage of the heated gas, and therefore this shape is most favourable to the rapid and complete inflammation of each grain in the whole charge. On the other hand, particles of an angular or flat form, fitting into each other as it were, offer greater obstruction to this motion, and the velocity of the transmission of inflammation is thereby diminished.

Effect of size on the velocity of transmission of inflammation.

If the grains be small, the interstices will be small also, and the facility to the expansion of the gas thereby diminished. In the experiments with trains of powder, the increased surface exposed to the heated gas was found to more than compensate for the diminished facility to its expansion, and generally a train of small-grained powder laid upon a surface without being enclosed, will be consumed more quickly than a train of large-grained powder.

Large grain best suited for heavy ordnance.

But this is not the case in a piece of ordnance, a circumstance which amongst others will account for the diminished initial velocity given to the shot by a charge of small-grained musket powder, below that produced by the large-grained usually adopted for this service.

Velocity of the transmission of inflammation of the charge.

When a number of grains of powder are placed together as in the charge of a gun, and a few of them are ignited at one end of the cartridge, a certain quantity of gas is developed of a temperature sufficiently high to ignite those in their immediate vicinity. This has also such elasticity as to enable it to expand itself with considerable velocity. Again, the grains which are so ignited continue the inflammation to others in the same manner. The absolute velocity of expansion of this gas is very considerable; but the grains of gunpowder in the charge offer an obstruction to this motion, the gas having to wind its way through the interstices, and consequently the velocity is considerably diminished, but it is quite clear that it must be very much greater than the velocity of combustion.Estimate of Mr. Piobert.Mr. Piobert estimates the velocity of transmission of inflammation of a charge in a gun at about 38 feet per second, and in all probability even this is much under the mark.

Experiments made on this subject.

Many experiments have been made by observing the velocity of transmission of inflammation of trains of powder under various circumstances, but they do not show us what would be the velocity in a confined charge. The velocity increased with the section of the train, and further when at the end first lighted, there was an obstruction to the escape of gas, as in the case of a gun, a much shorter time was required for complete inflammation.

Time of decomposition depends upon form of grain.

When the charge of powder in a gun is ignited the grains being enveloped by the heated gas, we may consider that each grain is ignited over its whole surface at once. If the grains of powder were of equal or regular form, the time each would be consuming, might be easily calculated, but since in ordinary cases they are irregular in form, although the grains may be of the same weight, the time necessary for their complete decomposition will be very different.

Circumstances affecting combustion.

The quickness of combustion will depend upon the dryness of the powder, the density of the composition, the proportion of the ingredients, the mode of manufacture, and the quality of the ingredients.

Combustion of cubical grains considered.

Were a cubical grain to be ignited upon its whole surface, the decomposition may be supposed to take place gradually from the surface to the centre, and the original cubical form to remain until the whole is consumed, the cube becoming smaller and smaller. If, then, the rate of burning be the same throughout, the quantity of gas generated in the first half portion of the time will evidently be considerably more than in the latter half, as in the latter case there will be a much lesser surface under the influence of flame.

Elongated and cylindrical grains.

If the form of the grain be elongated, then will the quantity of gas generated in a given time from a grain of similar weight to that of the cube or sphere, be increased, on account of the greater ignited surface, and consequently the time necessary for its combustion will be diminished. If it be of a cylindrical form for example, this time must be reckoned from the diameter of the cylinder, its length not influencing it in the least, although as we have seen, it enters into the consideration of the quantity of the gas generated in a given time.

Large grain.

In the ordinary large-grain powder, the majority of the grains are of the elongated or flat form, from whence considerable advantage is derived, particularly in short guns, since it causes the greatest portion of the charge to be decomposed before the projectile is moved sensibly from its original position.

Mealed powder.

If the charge be composed of mealed powder a longer time is found to be necessary for the complete combustion of the whole than in the case where the substance is granulated, and the initial velocity of a shot is reduced about one third by employing the substance in that state.

The effect of granulating gunpowder.

A piece of pressed cake weighing 1·06oz., was put into a mortar, and a globe of some light substance, placed upon it, and the powder being consumed after ignition without ejecting the ball from the bore of the piece. When an equal quantity was divided into seven or eight pieces, the globe was thrown out of the mortar; breaking the cake into twelve pieces; the ball ranged 3·3 yards; being further increased to fifty grains, it ranged 10·77 yards; and when the ordinary powder was used, the ball was projected 56·86 yards.

Action depends upon size and form of grain.

It will appear from the above remarks, that the force generated from the charge of powder in a gun, will be greatly influenced by the size and form of the grains composing it.

Density of gunpowder.

In order to obtain a gunpowder which shall possess a proper amount of force, it is necessary that the ingredients should be thoroughly incorporated, and the process of incorporation will in great measure affect the density of the grains. After going through the process, it is subjected to a certain pressure, in order that the substance in travelling may not be reduced to a fine powder, which would cause the velocity of transmission of inflammation to be diminished. But there is a certain point beyond which it would not be advantageous to increase the density, and this seems to vary with the size of the grain. With large-grain powder the action in a musket, or in guns with small charges, is greatest with a low density; while with very small grain, the highest velocities are obtained generally with the gunpowder of great density; but in heavy guns with ordinary charges, the large-grained powder should be of considerable density in order to obtain the greatest effect, though still it must not be too great.

Advantages of glazing.

The principal advantages of glazing are; first, that the powder so prepared, will in travelling, owing to the smaller amount of destructive force consequent on friction, produce less mealed powder; and secondly, that in a damp country like England, the glazing imparts a preserving power to the powder, as the polished surface is less likely to imbibe moisture than the rough.

Disadvantages of glazing.

The disadvantages of glazing consists in its polishing the surface, and thus depriving it of those angular projections which cause the ignition and combustion to be carried on with greater rapidity, by rendering the interstices smaller, the consequence of which is, that there is not so much gas produced previously to the projectile leaving the gun, and in large charges a portion will be blown out unfired. There must be a limit then to glazing, which it would not be proper to exceed.Experiments as to glazing.At an experiment with glazed and unglazed powder, the ranges on the eprouvette were 75 for glazed, and 98 for unglazed. This loss of power, consequent on glazing, has caused it to be done away with in France and Russia.Glazing less hurtful to fine grains.With fine grain powder it is not of so much consequence, as it is, to a certain degree, corrected by the size of the grain.

Size of grain determined by size of charge.

The rapidity with which a charge of gunpowder is consumed will depend not only in a certain degree upon the size of the grain, but on the manner in which the charge is put together, for if a charge is closely pressed, the gases meeting resistance in their endeavours to escape between the interstices, will not propagate the ignition so rapidly. With large charges, there exists a positive advantage for the grains to be rather large, so that the most distant parts of the charge should be reached by the gases as quickly as possible; whilst with that of a rifle, the charge being small, the fineness of the grain does not interfere with the quantity of the gas developed. Whence it may rationally be concluded that the dimensions of the grains should increase in proportion to the quantity of the charges into which they are to enter, that is to say, in proportion to the interstices.Tight ramming bad.Ramming down a charge tightly must therefore interfere with the velocity of combustion.

Note—The foregoing on the explosive force of gunpowder was taken from Lieut-Colonel E. M. Boxer’s Treatise on Artillery.

Produce of decomposed gunpowder.

The produce obtained by the decomposition of gunpowder are the gaseous and the solid. The gaseous is chiefly nitrogen and carbonic acid. The solid is sulphur and potassium, mixed with a little charcoal, but the solid produce is nearly entirely volatilized at the moment of explosion through the high temperature.

Fouling.

Fouling is occasioned by the deposition inside the barrel of the solid residue proceeding from the combustion of the powder.

Conditions of fouling depend on state of atmosphere

One of the principal of these, namely, the sulphide of Potassa, is deliquescent, or attracts water from the atmosphere. Hence, on a clear day, when the air holds little moisture, the fouling does not attain that semi-fluid state it so speedily attains in a damp day, and it is not so easily removed, and tends to accumulate inside the barrel. Fouling may also be increased or diminished, according to the quality of the powder.

Effects of Fouling.

Fouling occasions loss of power from the increased friction, and causes inaccuracy in direction and elevation, by filling the grooves, and thus preventing the proper spiral motion being imparted to the projectile.

Difference of effect on brass and iron guns.

The effect produced by Gunpowder on metals, in long continued and rapid firing, is very extraordinary. Several of the guns employed at the siege of San Sebastian were cut open, and the interior of some of the vent holes, which were originally cylindrical, and only two-tenths of an inch in diameter, were enlarged in a curious and irregular manner, from three to five inches in one direction, and from two to three inches in another, but the brass guns were much more affected than the iron. In December, 1855, there were lying in the arsenal at Woolwich several of the heaviest sea mortars, which had recently been used at the bombardment of Sweaborg, and the continuous firing on that occasion had split them into two nearly equal portions from muzzle to breech, a trunnion being with each half.

Heavy guns for garrisons, sieges, &c., are made of cast iron; guns for field purposes, where lightness is required, are made of gun metal.

Difference of effect of brass and iron guns

These guns are generally denominated brass guns. They can be loaded, properly pointed at an object, and fired about four times in three minutes, but they will not stand long continued rapid firing, or more than 120 rounds a day, as the metal, when heated, softens, and the shot then injures the bore. Heavy iron guns may be loaded, fired, &c., once in two minutes. They suffer more from the total number of rounds that have been fired from them, without reference to the intervals between each round, than from the rapidity of the firing. Four hundred and five hundred rounds per day have not rendered an iron gun unserviceable.

The following experiments, extracted from Mr. Wilkinson’s “Engines of War,” serve to illustrate the capability of metals to resist the force of gunpowder, and may be of some practical utility, as well as prove interesting merely as matter of curiosity.

Experiment 1.—A piece about 5 inches long was cut off the breech-end of a common musket barrel. It was screwed at the part cut, and another plug fitted, so as to have two plugs, one at each end, leaving an internal space of about 3 inches. A percussion nipple was screwed into the end of one of these plugs. This being arranged, one of the plugs was turned out, and one drachm of gunpowder introduced. The plug was replaced, and the powder fired by putting a copper cap on the nipple, and striking it with a hammer. The whole force of the powder escaped at the hole in the nipple. Two, three, four, five, and six drachms were successively introduced, and fired in the same manner, without bursting or injuring the piece of barrel. At last, seven drachms forced out one end, in consequence of the screw having been carelessly fitted. This defect being repaired, Mr. Marsh, of Woolwich, repeatedly fired it with five drachms, merely holding it with a towel in his left hand, and firing it with a blow of a hammer. Six drachms of powder is the full service charge for a flint musket, and four drachms of a percussion musket; yet this immense pressure can be resisted by a cylinder of iron not more than one quarter of an inch thick, and not iron of the best quality.

Experiment 2.—A good musket barrel had a cylinder of brass, three inches long, turned to fit the muzzle, and soldered in, so as to close it air-tight. The plug, or breech-screw, was removed, and a felt wad was pushed in with a short piece of wood, marked to the exact depth the charge would occupy, to prevent the ball rolling forward. A musket ball was then dropped in, and a cartridge, containing three drachms of powder, was introduced. The breech being screwed in, left the barrel loaded. It was fired by a percussion tube, but there was no report. On removing the breech-screw, the ball was found to be flattened. A repetition of this experiment, with four drachms, produced a similar result, but the ball was rather more flattened. With five drachms, the ball was perfectly round and uninjured. Six drachms burst the barrel close under the bayonet stud; the ball escaped through the opening, disfigured, but fell close to the barrel. In these experiments the barrel always advanced, instead of recoiling, as usual.

Experiment 3.—Made at Woolwich Arsenal, with a Gomer mortar, the chamber being bored conically, so that the shell, when dropped in, fits closely all round, instead of being bored cylindrically, with a chamber in the centre. The mortar being laid at an angle of 45°, one drachm of powder was put into the bottom, and a 68-pounder iron shot over it. When fired, the ball was projected two feet clear of the mortar. A wooden ball, precisely the same diameter, but weighing only 5lbs., was scarcely moved by the same charge, and with two drachms of powder it was justlifted in the mortar, and fell into its place again. Here we find a weight of 68lbs. thrown to the distance of two feet by the same power which would not lift 5lbs., and the wooden ball scarcely moved by double the powder.

This proves that the firing of gunpowder under such circumstances is not instantaneous. In the first instance, the small quantity of powder had a large space to fill below the ball, and a heavy weight to move; therefore, could not stir it at all until the whole was ignited, when the force was sufficient to throw it forward two feet. In the second case, the first portion of gas that was generated by ignition of the powder, was sufficient to lift the lighter weight, just enough to allow all the force to escape round it before it had time to accumulate.

Experiment 4.—A cannon ball, weighing 24lbs., was placed exactly over the vent-hole of a loaded 32-pounder cannon, which was fired by a train of gunpowder, when the rush from the vent projected the 24-pounder ball to a very considerable height in the air, although the diameter of the hole was only two-tenths of an inch.

Experiment 5.—A most ingenious method of ascertaining the relative quickness of ignition of different qualities of gunpowder.

A gun-barrel mounted on a carriage with wheels, and moving on a perfectly horizontal railway, is placed at right angles to another short railway, at any convenient distance (suppose fifty feet, or yards); on the second railway a light carriage moves freely with any desired velocity, being drawn forward by means of a weight and pulleys: a cord is attached to the front of this carriage, which passes over a pulley at the end of the railroad, and is continued up a high pole or staff over another pulley at the top, at which end the weight is attached. A long rectangular frame covered with paper is fixed perpendicularly on the carriage, so that when it moves forward it passes across the direct line of the barrel, and forms a long target. A percussion lock is attached to the barrel, which is fired by a detent, or hair-trigger, and the wire which pulls it is disengaged at the same instant to admit of recoil. This wire is carried straight on to the target railroad, and fixed to a small lever, against which the front part of the target-carriage strikes as it is carried onwards by the weight. This constitutes the whole apparatus. When required to be used, the barrel is loaded with gunpowder accurately weighed, and a brass ball that fits the bore correctly: the weight is then disengaged, and the target moves quickly along, discharging the barrel as it passes, and the ball goes through it. With the same powder tried at the same time, the ball constantly goes through the same hole, or breaks into it. If the next powder tried be slower of ignition than the preceding, the ball will pass through another part of the target more in the rear; if quicker, more in advance; thus affording a means of ascertaining this important quality of gunpowder with considerable accuracy: the velocity of the target-carriage can be easily regulated by increasing or diminishing the weight which draws it forward. The differences in the distances between which the balls strike the target with different kinds of powder was frequently as much as ten or twelve inches; but it is not an apparatus commonly used, having been merely constructed for experimental purposes.

Gunpowder like all other inflammable substances requires to be raised to a certain temperature, before it will ignite, viz., to a dull red heat, or about 600° Fahrenheit. If the heat passes with such rapidity through the powder, so as not to raise the temperature to the necessary degree, then the powder will not ignite, from the velocity of transit, so that it might be possible to calculate theoretically, the velocity that must be given to a red hot ball to enable it to pass through a barrel of gunpowder without causing explosion. The passage of electric fluid through gunpowder may be adduced in evidence of the ignition being dependent on the degree of velocity. The flame of all fulminating powders will pass through the centre of a box filled with gunpowder without igniting one grain of it. If a train of gunpowder be crossed at right angles by a train of fulminating mercury, laid on a sheet of paper or a table, and the powder be lighted with a red hot iron wire, the flame will run on until it meets the cross train of fulminating mercury, when the inflammation of the latter will be so instantaneous as to cut off all connection with the continuous train of powder, leaving the remaining portion of the gunpowder unignited. If on the contrary the fulminating powder be lighted first, it will go straight on and pass through the train of gunpowder so rapidly, as not to inflame it at all. Were a gun to be charged with gun-cotton and gunpowder, the latter would be fired out unignited.

Considering the combustible nature of the materials, accidents very seldom occur; when they do, it is more frequently in the process at the Mill while under the runners.

On one occasion at Waltham Abbey Mills, when the powder exploded, after having been two hours under the runners, the doors and windows of the Mills on the opposite side of the stream, were forced open outwards, and the nails drawn. A similar effect took place when the Dartford Mills blew up, January 1833, in consequence of an accident in the packing house. A window which had been recently fitted up in Dartford Town, about a mile and a half distant from the works, was blown outwards into the street, and a considerable quantity of paper was carried as far as Eltham and Lewisham, distances of eight and ten miles. The sudden rarification of the air may account for this circumstance, the atmospheric pressure being removed in the vicinity of the doors and windows, they were forced open outwards by the expansive force of the air contained within the buildings.

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