Chapter II: Part 2

The next process is granulation, or reducing this press cake into the proper sized grain for cannon, musket, or rifle powder. The machine which effects this is very beautifully contrived, and is entirely self-acting, obviating the necessity of any one being in the building while it is in motion. It resembles, in appearance and action, the breaking-down machine, except that it is larger, and is fitted with three pairs of toothed rollers, of different degrees of fineness, working in the same kind of collars already mentioned, so that, on any hard substance passing through, they would open accordingly, and thus prevent friction. At one end of the machine is a wooden hopper, or funnel, which is filled with the press cake. This is contrived so as to rise gradually by the motion of the machine, and constantly to supply an endless band, similar to the one described in the breaking-down house. When the cake arrives at the highest point of this band, it falls over, and is granulated between the first pair of gun-metal rollers. Under each pair is a screen, covered with 8-mesh wire. All that is not sufficiently small to pass through, is carried on to the next pair of rollers; and, in like manner, that which does not pass through the second screen is carried to the third pair. In addition to these screens, there are three oblong sieves covered with 8- and 16-mesh wire, and 56 cloth respectively, fixed under, and parallel to, each other, each being separated by about four inches of space, running at an incline just below the three pairs of rollers; these all lead to little wooden carriages placed on the opposite side of the machine, which are divided so as to collect the different sized grain as it passes down. To facilitate the separation and sifting of the powder, and to prevent masses of it forming and clogging up the wire, a shaking motion is imparted by a circular wheel attached to the framework of these sieves revolving against an octagonal one fixed to the machine. The grains which pass through each screen below the rollers fall on the upper one of these three last-mentioned sieves. That portion which passes through this, and is retained on the 16-mesh wire, is cannon powder; that passing through the 16-mesh sieve, and retained on the 56-cloth, is fine grain; and a board, running also parallel underneath, retains the dust that passes through the cloth.

~Chucks regranulated.~

The “chucks,” as they are called, or those grains that are too large to pass through these different sieves, are collected in the same way as the grain, and undergo the process of granulation again.

DUSTING LARGE-GRAIN POWDER.

~Object of dusting.~

~How performed for large-grain.~

~Glazed at same time.~

The keeping qualities of powder are very much improved by removing the dust, which quickly absorbs moisture from the atmosphere. This operation, for large-grain, is performed by cylindrical reels, about 8ft. 6in. long, and 3ft. 8in. in diameter, clothed with 28-mesh canvas, which revolve at the rate of thirty-eight times per minute. Those for large-grain are called horizontal reels, in contradistinction to those for fine-grain, that are called slope reels. Each is enclosed by a wooden case, to prevent the dust flying about the house. When the powder has run its time, one end of the reel is lowered. It then runs out into barrels placed to receive it. This entirely separates the dust, and imparts a fine black gloss, which is sufficient glazing for the large-grained powder.

DUSTING FINE-GRAIN POWDER.

~Dusting fine-grain.~

The fine-grain powder has a much greater proportion of dust when it leaves the granulating house than the large-grain, and it is found necessary, on this account, to use a different kind of reel. They resemble those for the former powder, except that they are covered with 44-mesh canvas instead of 28, and are placed at an incline which prevents their being choked up with the quantity of dust; each end is also open, and a continuous stream of powder, fed by a hopper, passes through while they revolve, and pours out at the lower end into barrels. This process is repeated a second time, which sufficiently frees it from dust.

GLAZING FINE-GRAIN POWDER.

~Glazing fine-grain.~

The fine-grain powder thus dusted, is then glazed for three hours in barrels capable of holding 300lbs. which are 3ft. 6-in. in length, and 2ft. 8-in. in diameter, revolving at the rate of thirty two times in a minute. By the mere friction of the grains against each other and the inside of the barrel, a glaze is imparted, presenting a fine polished surface to the grain.

~Object of glazing.~

Powder glazed in this way withstands the action of moisture to a far greater extent than unglazed powder, and in transport very little dust is formed.

STOVING OR DRYING POWDER.

~Drying.~

A drying-room, heated by steam pipes, is fitted with open framework shelves, on which rests small wooden trays about 3ft. long, 1ft. 6-in. in breadth, and 2¹⁄₂in. deep, having canvas bottoms; on each is spread 8lbs. of powder. This room holds about 40 barrels, or 4,000lbs., which remains in it for twenty four hours, and is subjected to a heat of 130° Fahrenheit for sixteen hours, communicated by steam passing through pipes arranged horizontally on the floor of the room. The temperature is raised and lowered gradually, otherwise the too sudden change would be likely to destroy the texture of the grain. The ceiling and roof are fitted with ventilators, through which all the moisture escapes, so that there is a constant current of hot air circulating through the room. It is of the greatest importance that the vapour should be carried off; for, if this is not effectually done, on the decrease of temperature, it would return to its liquid state, and form again on the powder.

FINISHING DUSTING.

~Final dusting.~

~Barrelling.~

The action of heat however produces a small portion of dust; both these powders, therefore, when they leave the stove, are reeled in horizontal reels, clothed with 28 and 44-mesh canvas respectively, for one hour and a half. This perfectly separates any remaining dust, and gives the finishing glaze to the large-grain powder. This is the final process, and the powder thus finished is taken to the barrelling-up house; weighed out into barrels holding 100lbs. each; marked L. G. (large-grain), and F. G. (fine-grain), as the case may be; and stored in magazines.

EXAMINATION AND PROOF OF GUNPOWDER.

~Desired properties of gunpowder.~

~Specific gravity.~

~Strength.~

~Purity.~

The great and ultimate object to be attained in the manufacture of Gunpowder is, not so much to produce that which ranges the highest, as one that shall be durable in its texture, not easily deteriorated by atmospheric influence or transport, and one with which equal charges shall produce equal effects. It should present uniformity in the appearance of its grains, which should be angular, crisp and sharp to the touch, not easily reduced to dust by pressure between the fingers, or dusty in handling; its specific gravity should not be under 55lbs. to the cubic foot, (that of Waltham Abbey is generally 58lbs.) taking water at 1000ozs.; its strength is tested by firing three rounds from an 8 inch mortar, throwing a 68-pounder solid shot with a charge of 2oz. this should give a range of from 270 to 300 feet. The distance however, varies considerably, according to the state of the atmosphere, and the density of the powder: for, the greater the density, the less the range in small charges. Half an ounce flashed on a glass plate should leave little or no residuum; should white beads or globules appear, it is a sign of imperfect incorporation.

PROOF OF MERCHANT’S POWDER.

The following are the different proofs merchant’s powder is subjected to:--

Lots of 100 barrels are sent in, marked with the number of the lot and the maker’s name on the head of each barrel. 25 per cent. of these are unheaded in the examining house; the Proof Officer then--

~If dusty.~

First, takes a bowl out of each barrel, and holding it about three feet above, pours it out quickly; should there be a good deal of dust, it is satisfactorily shown by this means.

~Firmness.~

~Size of grain.~

Secondly, it is handled and pressed between the fingers, to test the firmness of its grain; and should there appear to be any great difference in the proportions of different sizes to that laid down as a standard, it is sifted and compared accordingly, being rejected should the quantities fall short or exceed the sample in any great degree.

~Density.~

Thirdly, a barrel or two are selected, and the powder poured into a hopper, under which is placed a box very carefully constructed, so as to hold exactly a cubic foot. A slide is now withdrawn at the bottom of the hopper, and the powder allowed to run into the box in a continuous even stream until it is piled up; the hopper is then removed, and the powder struck off with a straight edge, level with the top of the box. The weight is now carefully taken, that of the latter being subtracted; should this not amount to 55lbs. it is rejected, as not being of sufficient density.

~Strength by range.~

Fourthly, samples are taken from every barrel, and lot for the firing proof.

Firing Proof.--An average of nine rounds of sample Waltham Abbey powder is taken, three rounds being respectively fired at the beginning, middle, and end of the proof, from the same kind of mortar before mentioned, with a charge of 2oz. An average of three rounds of each lot of the merchant’s powder is also taken; should it fall short by more than 1 in 20, it is rejected.

~Purity by flashing.~

Fifthly, to ascertain if any residuum or ash is left after ignition, about half an ounce is burned on a clean glass plate, and fired with a hot iron. The explosion should be sharp, and produce a sudden concussion in the air; and the force and power of this concussion should be judged by that of known good quality. Few sparks should fly off, nor should white beads or globules appear, as it would be a sure indication, as we have before explained, of insufficient incorporation. It is also subjected to a second proof.

~Purity by weight after exposure to damp.~

Second proof.--A sample of 1lb. from each lot, carefully weighed up, and a similar sample of the comparison powder, is exposed for three weeks in a box perforated with holes (called a damp chest), to the action of the atmosphere. This box is placed under cover, so that it is sheltered from the wet, but that the moisture can get to it. If, at the end of this time, there is a greater proportion of difference in range between them than one-twentieth, it is rejected. The pounds are also very carefully weighed up again, to ascertain the comparative absorption of moisture. This is called the hygrometric test.

REMARKS ON THE PROOF OF POWDER BY THE EPROUVETTES.

~By eprouvettes or pendulum.~

By comparing the results of the proofs by the eprouvettes with those furnished by the cannon pendulum (vide plate 1, fig. 2 and 3), it will appear that the eprouvettes are entirely useless as instruments for testing the relative projectile force of different kinds of powder, when employed in large charges in a cannon. Powders of little density, or of fine grain, which burn most rapidly, give the highest proof with the eprouvettes, whilst the reverse is nearly true with the cannon.

~Real use of eprouvettes.~

The only real use of these eprouvettes is to check and verify the uniformity of a current manufacture of powder, where a certain course of operations is intended to be regularly pursued, and where the strength, tested by means of any instrument, should therefore be uniform.

~Best proof, by service charges.~

The only reliable mode of proving the strength of Gunpowder is, to test it with service charges in the arms for which it is designed; for which purpose the balistic pendulums (vide plate 3), are perfectly adapted.

~Best proof for small arms.~

For the proof of powder for small arms, the small balistic pendulum is a simple, convenient, and accurate instrument.

~Common eprouvette.~

The common eprouvettes are of no value as instruments for determining the relative force of different kinds of Gunpowder.

OF THE SIZE OF GRAIN FOR GUNPOWDER.

~On size of grain.~

With regard to the particular size of grain for Gunpowder, I am confident great improvements might be made, both in obtaining greater regularity of effect and propelling force, by the adoption of a more uniform even grain. There are at present half-a-dozen different sizes in our cannon and musket powder; and I think it stands to reason, that the more equal the size, the more uniform will be the ignition of all the grains, and consequently the effect of the same charges will be much more regular.

OBSERVATIONS ON THE MANUFACTURE OF GUNPOWDER ON THE CONTINENT AND AMERICA.

It may not be uninteresting to have a slight knowledge of the method employed on the Continent, &c., for the production of Gunpowder.

~Proportion of the ingredients.~

The proportions of the three ingredients vary slightly all over the Continent and America, being as follows:--

SALTPETRE. CHARCOAL. SULPHUR.
France } 75 12.5 12.5
Belgium }
Russia 73.78 13.59 12.63
Prussia 75 13.5 11.5
Austria 75.5 13.2 11.3
Spain 76.47 10.78 12.75
United States 76 14 10

PRODUCTION AND PURIFICATION OF THE INGREDIENTS.

~Production and purification of the ingredients.~

The nitre is purified in a similar way to the new method employed at Waltham Abbey, though it is seldom obtained with so faint a trace of chlorides, owing probably to its being of an inferior quality, and of higher refraction when it is imported.

The sulphur is supplied to the manufactories in France in the form of roll sulphur, from Marseilles and Bordeaux, where there are very large refineries.

The charcoal is prepared from dogwood, alder, willow, hazel, and poplar, sometimes in pits, and occasionally in cylinders, as at Waltham Abbey. At Wetteren, and in some parts of France, it is distilled by the action of steam. The “charbon roux” taking its name from its brownish-red tinge, from being only partially burned, was used formerly more than now, as the powder made from it was found to injure and exert very pernicious effects upon fire-arms.

PULVERIZING AND MIXING THE INGREDIENTS.

~Pulverizing and mixing the ingredients.~

The ingredients are generally pulverized in copper drums, capable of holding 224 kilogrammes. Part of the charcoal is mixed with the sulphur, and part of the sulphur with the saltpetre. They are then put into separate drums, which revolve about twenty-five times per minute for three hours, and in which are about 500 gun-metal or bronze balls, the size of good large marbles. The ingredients are brought to the most minute state of division by these means, and are then mixed all together, for one hour, in similar drums covered with leather, containing wooden balls.

INCORPORATING PROCESS.

~Incorporation.~

The fine powder thus obtained is sometimes merely moistened, so as to form a stiff paste, and passed through rollers, the cake formed, being dried and granulated. The incorporating cylinders are used occasionally, but the more usual plan adopted on the Continent to effect this operation is the stamping-mill, which requires a short description. It is nothing more nor less than the pestle-and-mortar principle, each mill consisting of from six to twelve bronze or wooden mortars bedded in the floor of the building; they are the shape of the frustum of a cone, the mouth being much narrower than the base; the pestles, or stampers as they are called, are made of wood, shod with either very hard wood or bronze, on which project wooden teeth about twelve inches long; a vertical movement is imparted to them by a shaft worked by the water-wheel having similar teeth attached; in its revolution it raises the stamper about eighteen inches, which falls again as the projection is disengaged, twenty five times in a minute. This operation is carried on for twelve hours, during which period the charge (about 15lbs.) is moistened at intervals, and routed up with a copper-shod spud; at the end of this time the cake is taken out, and left to dry and harden; it seldom receives any pressure--although, in some manufactories, presses are being erected.

GRANULATING.

~Granulation.~

The cake is then granulated in sets of sieves fitting one into the other, having perforated zinc bottoms of different degrees of fineness, which are suspended from the ceiling of the room by ropes, an ash spring being attached to each box holding the sieves, the cake is put into the uppermost one with some gun-metal balls, and shaken backwards and forwards, which motion the spring facilitates; it is thus broken up into different sized grains, which are separated by passing through the several meshes.

The grain formed is then dusted in bags or shaking-frames covered with canvas, and then glazed in barrels.

STOVING OR DRYING.

~Drying.~

~Comparative merits of foreign and English gunpowder.~

In summer the process of drying is often performed in the sun, and in winter by the steam stove, in the following way. The powder is spread about three or four inches thick on a large canvas tray, under which is an arrangement of pipes, which convey the hot air forced by a fan through a cylinder heated by steam: it is considered to be sufficiently dried in from three to four hours, during which time it is occasionally raked about. In some manufactories it undergoes a further operation of being dusted, and is then barrelled up for use. Generally the great failure in the foreign manufacture is the neglect of the principal stage of the fabrication, viz. incorporation; with the old stamping-mill, it is quite impossible that the process can be carried out to the necessary extent. The Continental powder is usually very soft in its grain, dusty, and quickly absorbs moisture from the atmosphere; its density is below the English powder, on account of its never being subjected to pressure; consequently it is not so durable, and forms a good deal of dust in transport; a great amount of residue is generally left in the gun, and its strength, as a propelling agent, is far inferior to our powders. On being flashed on a glass plate, instead of producing a sudden concussion, like the sharp rap of a hammer, it burns more like composition, throwing off a quantity of sparks.

NEW RIFLE POWDER.

The following mode of manufacturing rifle powder, appeared in Garrison Orders at Woolwich, 31st December, 1859:

Composition in 100 parts:--

Saltpetre 75
Charcoal 15
Sulphur 10
---
100

The charcoal to be prepared from dogwood, burned slowly in cylinders three hours. The composition to be worked under the runners for five and a half hours, and submitted to a pressure of about 50 tons to the square foot. The size of the grain to be that collected between sieves of 16 and 24 meshes. The grain to be glazed for five hours.

* * * * *

NOTE.--The foregoing, on the manufacture of gunpowder, is principally
taken from an article in the Aide Memoire (1860), by Major Baddeley,
Royal Artillery; Captain Instructor, Waltham Abbey.

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, by_ SIR 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 3¹⁄₂ inches wide, and of ¹⁄₁₆th and ¹⁄₈th of an inch in thickness, or the Conductors may with advantage be constructed of stout copper pipe not less than ³⁄₁₆ths of an inch thick, and 1¹⁄₂ to 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 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.~

~Volume of gas evolved.~

~Heat of gas evolved.~

~Pressure of gas generated.~

~Strength of powder not affected by density of air, but by damp.~

It appears that the weight of gas generated is equal to three tenths of the weight of the powder which yielded it, 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. 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. 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. 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_.~

~Temperature~

~Expansion.~

~How to calculate expansion~

~Absolute force of gunpowder cannot be determined.~

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. The 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. All gases expand uniformly by heat, the expansion having been calculated with great precision, to be ¹⁄₄₈₀th 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. Thus, 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, hence

temp. vol. temp. vol. vol.
1 3940
1° : --- 3,940° : ---- = 8·2
480 480

that is, each volume of gas would at a temperature of 4000° be increased 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. 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 of ¹⁄₁₀th 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 moisture upon 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.~

~Estimate of Mr. Piobert.~

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. 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.~