Upon the great importance of the invention of gun-powder it is needless to dwell. Not only has it revolutionized the art of war, and given the forces of civilization a vast advantage over mere numbers and savage valour, but we may even urge, paradoxical though it appears, that the very improvements by which modern science has ren-dered military machines more deadly tend to make war far more expensive, and therefore to prevent its being so fre-quently or so rashly undertaken as of old. Besides such indirect services to civilization, gunpowder has been and is of great use in the arts of peace, although of late years to a certain extent superseded by more potent explosive agents. Historical Such being the case, it is not a little remarkable that the sketch, discovery of gunpowder should be veiled in uncertainty, although this very obscurity seems proof of its great anti-quity. It is, however, certain that it was not invented, as has been often stated, by the German monk Bertholdus Schwartz, about 1320, although Wilkinson, in his Engines of War, considers Schwartz may have suggested the use of a mortar, since the form as also the name of this piece of ordnance may well have been due to some accident in the laboratory. Roger Bacon, who was born in 1214, refers, circa 1267, to an explosive mixture of the nature of gunpowder as known before his time, as being employed for purposes of diversion, and as producing a noise like thunder, and flashes like lightning; he even suggests its application to military purposes, and indulges in the supposition that some such composition might have been employed by Gideon to destroy the Midianites (Judges vii.). He elsewhere writes —" Ex hoc ludicro puerili quod fit in multis mundi partibus, scilicet, ut instrumento facto ad quantitatem pollicis humani, ex hoc violentia salis, qui salpetrse vocatur, tarn horribilis sonus nascitur in ruptura tam modicse pergamen'ae, quod fortis tonitru rugitum et coruscationem maximam sui luminis jubar excedit" (see preface to Jebb's edition of Bacon's Opus Majus). In the above passage saltpetre is alone referred to as the violently explosive substance, but Bacon was well aware of the fact that saltpetre of itself will not explode, for in his previously written treatise, De Secretis Operibus Artis et Natural et de Nidlitate Magice, he says " that from saltpetre and other ingredients we are able to make a fire that shall burn at any distance we please." In chap. xi. of the same work these other ingredients are veiled in the disguise of an anagram: " Sed tamen salis petrae lura nope cum ubre et sulphuris, et sic facies tonitrum et coruscationem, si scias artificium;" the unmeaning words in italics have been translated as carbonum pulvere. Robins, in his work on gunnery (1742), and Dutens {Enquiry into the Origin of Discoveries attributed to the Moderns) suggest that Bacon may have derived his know-ledge from the MS. of Marcus Graecus, preserved in the National Library in Paris, entitled " Incipit Liber Ignium a Marco Graeco prescriptus, cujus virtus et efficacia est ad comburendum hostes, tam in mari quam in terra." Marcus Graecus, who lived about the end of the 8th century, was therefore not ignorant of the military uses to which the composition might be put; among other modes of launching fire upon an enemy he gives one to the following effect — one pound of live sulphur, two of charcoal of willow, and six of saltpetre, reduced to a fine powder in a marble mortar and mixed together; a certain quantity is to be put into a long, narrow, and well compacted cover, and then discharged into the air. This is evidently the description of a rocket. It has also been suggested that Bacon may have learnt the secret in Spain, in which country he is known to have travelled, and whose Moorish masters were then far in advance of the rest of Europe in science and literature. Albertus Magnus, in his treatise De Mirabilibus Mundi, repeats almost word for word several receipts in the work of Marcus Graecus; also, an epistle by Ferrarius, a Spanish monk, and a contemporary of Bacon, which is preserved in the Bodleian Library at Oxford, gives receipts for Greek fire, rockets, and " thunder." There is a treatise on gunpowder in the library of the Escorial, written about 1250, which appears to describe both rockets and shells ; the Arabians are, from this and other authorities, supposed to have enclosed combustible or explosive com-positions in hollow globes of iron, which were discharged upon the foe either by hand, like the modern grenade, or from the warlike machines then in use; it has also been stated that towards the close of the 13th century they projected small balls from tubes carried in the hand, or attached to the end of a lance, and only used at close quarters, being in fact hand-guns. Rockets were employed during the reign of the Greek emperor Leo, about 880, and indeed seem to have been known in India from time immemorial, some of them having been made of great size.
The gloom of the dark ages precludes further attempt to trace back the history of gunpowder with any certainty, but Mr Dutens, in the work before quoted, adduces many passages from classical authors in support of his view that a composition of the nature of gunpowder was not unknown to the ancients, as, for example, the story of Salmoneus, king of Elis, who, according to Virgil (Aeneid, vi. 585), for his audacity in attempting to imitate thunder and lightning, was slain by Jupiter ; Mr Dutens considers he may have fallen a victim to his own experiments. Eustathius, a commentator on Homer, speaks of him as being so skilled in mechanics that he constructed machines to imitate thunder (Eustathius ad Odyss., A 234, p. 1682, 1. 1 ; see also Hyginus, Fabul., 61, 650; Valerius Flaccus, lib. i. 662). It is also narrated of Caligula by Dion Cassius {Hist. Rom., "Caligula," p. 662) that he had machines which imitated thunder and lightning, and emitted stones. See also Johannes Antiochinus, Chronica apud Peiresciana Valesii, Paris, 1604, p. 804.
According to Themistius (Orat., xxvii. p. 337) the Brahmins had similar machines. Philostratus, in his life of Apollonius Tyanasus (lib. ii. cap. 14), written about 200 A.D., relates of a people of India, dwelling between the Hyphasis and the Ganges, whose country Alexander never entered : " Their cities he could never have taken, though he had led a thousand as brave as Achilles, or three thousand such as Ajax, to the assault; for they come not out to the field to fight those who attack them, but these holy men, beloved by the gods, overthrow their enemies with tempests and thunderbolts shot from their walls."
From the mention by Vitruvius, and in Plutarch's life of Marcellus, that one of his machines threw large stones with great noise, it has been thought that Archimedes used some explosive composition in the defence of Syracuse. _
The most ancient reference of all is in the Gentoo code of laws (Halhed's translation), supposed by some authori-ties to be coeval with Moses. It runs thus : " The magis-trate shall not make war with any deceitful machine, or with poisoned weapons, or with cannon and guns, or any kind of firearms." The translator remarks that this pass-age may " serve to renew the suspicion, long since deemed absurd, that Alexander the Great did absolutely meet with some weapons of that kind in India, as a passage from Quintus Curtius seems to ascertain." The word translated firearms is liberally a weapon of fire, and one species of it has been described as a dart or arrow tipped with fire and discharged from a bamboo, so that the reference may not be to any propelling agent, but merely to some combustible or incendiary composition, of the nature of the so-called Greek fire.
Greek It is almost certain that those authors who assert that firs, the Arabians used gunpowder at the siege of Mecca, 690 A.D., having derived their knowledge of it from India or China, confound gunpowder with this Greek fire, which seems to have been the generic name given to several different combustible mixtures, although Arabian writers speak of them as Chinese fires. Greek fire was intro-duced into Constantinople from the East about the year 673; it was discharged upon the enemy by means of various engines of war, or in smaller quantities attached to arrows or darts. The Saracens used it against the Crusaders. Maimbourg, in his History of the Crusades, describes its effects ; and Joinville, who was an eye-witness, says " it was thrown from a petrary, and came forward as large as a barrel of verjuice, with a tail of fire as big as a great sword, making a noise like thunder, and seeming like a dragon flying in the air; the light it gave out from the great quantity of fire rendered the camp as bright as day, and such was the terror it occasioned among the commanders in the army of St Louis that Gautier de Cariel, an experienced and valiant knight, advised that, as often as it was thrown, they should prostrate themselves upon their elbows and knees, and beseech the Lord to deliver them from that danger against which he alone could protect them." However, its actual destructive effect seems to have been very inadequate to the terror it occasioned. From the account of Geoffrey de Vinesauf, sand and earth, but especially vinegar, appear to have been considered the best extinguishers; water would not put it out. One description of this wildfire was composed of resin, sulphur, naphtha, and probably saltpetre. Bacon states that religious scruples hindered European nations from adopting Greek fire ; but if so, they seem to have been gradually overcome, for its use is mentioned by various writers, Anna Comnena, Pere Daniel, and Froissart among them. Similar scruples no doubt considerably retarded the introduction of gunpowder ; and the fear that its adoption would prove fatal to all knightly gallantry also caused it to be regarded with aversion. Firdousi, the famous Persian poet, describes in his writings what were doubtless the effects of rockets and wildfire discharged upon the enemy, but he ascribes the whole to magic.
The researches of all authorities seem to point to the Eastern Far East as the birthplace of an explosive mixture of origin of the nature of gunpowder; it was used there from time gun\ immemorial, although doubtless its application as a propel-ling agent is of far later date. In all probability, the germ of the science of explosives lay in the accidental discovery of the peculiar properties of the nitre so plentifully found mixed with the soil upon the vast plains of India and China. By means of the charred embers of wood-fires, used for cooking, the two most active ingredients of gunpowder might easily be brought into contact, and, under the action of heat, more or less deflagration would ensue ; in fact, the accidental dropping of some of the crude saltpetre into the coals would show its remarkable power of supporting and accelerating combustion. The combination of saltpetre and charcoal in a more or less powerful mixture can therefore be easily conceived, the sulphur being an after addition, and not necessary to cause explosion. Our present gun-powder is only the improvement and perfection of such a mixture. Saltpetre was early known as " Chinese snow," . and some have supposed the use of gunpowder in cannon to have been known in China very soon after, if not before, the Christian era. But this seems to be an error, for Colonel Anderson, C.B., in his book on gunpowder (London, 1862), quotes a conversation held by John Bell of Antermony, who visited Peking in 1721, with the emperor's general of artillery, to the effect that from their records it had been used in fireworks, &c, for about 2000 years, but that its application to the propulsion of shot was a late introduction. Some of their compositions had such names as " devouring fire," " earth thunder," &c. The Institutes of Timnr, written about the middle of the 14th century, contain no mention of cannon or gunpowder, although full particulars are given of the equipment of his troops ; it is, however, related that when Timur engaged the army of Mahmud under the walls of Delhi, men scattered wildfire and flung rockets in every direction. In this connexion it may be noted that, while the use of rockets was of very old date in India, the names given to pieces of artillery under the rule of Baber and the Mogul conquerors of Hindustan almost invariably point to a European, or at least to a Turkish origin. It is also well authenticated that Akbar and Aurungzebe had Englishmen and other Europeans in their service to teach the art of gun-nery. The analysis of the gunpowder made by the Chinese in the present day shows a composition almost identical with that employed in Europe, which has only been arrived at after centuries of experience, so that, in all probability, they have corrected their earlier formula from Western sources.
Whatever obscurity may hang over the early history of Its intro-gunpowder, it seems most probable that its employment duction as a propelling agent originated among the Moors or g*°ope Saracens,—whose civilization for several centuries con-trasted forcibly with the intellectual darkness of Christen-dom,—and from them spread eastward, as well as north-ward into Europe. Conde (Hist. Dom. Arabs in Spain) states that Ismail Ben Feraz, king of Grenada, who in 1325 besieged Baza, had among his machines "some that cast globes of fire with resounding thunders and lightnings resembling those of the resistless tempest; all these missiles caused fearful injuries to the walls and towers of the city." The first reliable contemporary document relative to the use of gunpowder in Europe, a document still in existence, bears date 11th February 1326; it gives authority to the priors, the gonfalonier, and council of twelve of Florence to appoint persons to superintend the manufacture of cannons of brass, and iron balls, for the defence of the commune, camps, and territory of the republic, First use If the testimony of John Barbour, archdeacon of Aber-in Eng- deen, who wrote in 1375, is to be believed, cannon, which he calls " crakys of war," were employed during the invasion of Scotland by Edward III. in 1327 ; but they are not mentioned in the accounts of the expenses of this war pre-served in the record office. An indenture, first published by Sir N. H. Nicolas in his Hist. Royal Navy (London, 1847), and since by Lieut.-Colonel H. Brackenbury {Proceedings R. A. Institution, 1865), stated to be of 12 Edward III., 1338, contains several references to small cannon as among the stores of the tower, and also mentions " un petit barrell de gonpouder le quart'plein." If authentic, this is certainly the first distinct mention of gunpowder in Great Britain we now possess, but doubts have since been thrown upon the date of this MS. It, however, seems certain, from a con-temporary document in the National Library in Paris, that, in this same year 1338, there existed in the marine arsenal at Rouen, an iron weapon, called " pot de fer," for propelling bolts, together with some saltpetre and sulphur to make powder for the same ; at this period the ingredients were usually kept separate, and mixed when required. From the year 1345, 19 Edward III., we have, preserved in the Record Office, reliable accounts of the purchase of ingredients needed for the fabrication of gunpowder, and of the shipping of cannon for France. In 1346 Edward III. ordered all the saltpetre and sulphur that could be found to be bought up for him, but the quantities obtained were very small. Whether it be true or not that cannon were used by the English at Crecy in that year belongs rather to the question of the employment of artillery in the field; it has been maintained that such was the case by Napoleon III. (Etudes snr le passe et I'avenir de I'Artillerie). It may be noted that Petrarch, about the year 1344, in his dialogues De remediis utriusque fortunae, speaks of " brazen globes cast forth by the force of flame with a hor-rible sound of thunder " as having become as common as any other kind of weapon.
In the year 1377, being the first of Richard II., Thomas Norbury was ordered to buy, amongst other munitions, sulphur, saltpetre, and charcoal to be sent to the castle of Brest. In 1414 Henry V. ordered that no gunpowder should be taken out of the kingdom without special licence ; in the same year this monarch also ordered twenty pipes of powder made of willow charcoal, and various other articles for the use of the guns.
It was not, however, until the reign of Elizabeth that the manufacture of gunpowder can be said to have been established in England. The greater portion required had been previously imported from abroad, and the trade had been an open one; but the threatening attitude of Spain com-pelled the Government to provide more efficient means of defence, and patents were issued by the crown for the manu-facture of gunpowder, constituting it a monopoly. Early in this reign also, saltpetre began to be artificially produced in England, but the quantity so obtained formed a very small proportion of the supply needed, the remainder being brought from various parts of the Continent, and from Barbary. Again, in 1623, nominally in order to prevent the sale of weak or defective powder, a proclamation was issued by James I., prohibiting its manufacture, as well as that of saltpetre, except under the king's commission, and directing that all gunpowder should be proved and marked by the sworn proof-master. A little later, in 1626, the East India Company had commenced the importation of saltpetre, and had also erected powder works in Surrey. Their renewed charter in 1693 contained a clause provid-ing that 500 tons of saltpetre were to be furnished to the ordnance annually, and from this time forward we hear of no difficulty, at least in England, of obtaining the chief ingredient of gunpowder, although on the Continent great attention has been paid to its artificial production ; this was especially the case in France during the reign of Napoleon I., when the supremacy of Great Britain at sea for many years prevented the importation of saltpetre by her enemies.
About the year 1590, George Evelyn, grandfather of the celebrated John Evelyn of Wooton, received the royal licence to set up powder mills at Long Ditton and Godstone ; the Evelyns are said to have brought.the art from Holland. The works at Faversham, afterwards for so many years the Government gunpowder factory, date from Elizabeth's reign, but were then of secondary importance to those at Godstone. There seems reason, however, to suppose that powder mills existed at Waltham Abbey so far back as 1561, for in that year we find John Thomworth of Waltham in treaty, on behalf of Queen Elizabeth, for the purchase of saltpetre, sulphur, and staves for barrels. Fuller also refers [English Worthies, i. 338) to the powder mills at Waltham Abbey, of which place he was appointed vicar in 1641. In 1787 they were sold to the crown by John Walton, and reorgan-ized undei- the superintendence of the famous Sir William Congreve. The old royal factory at Faversham was given up after the peace of 1815, being first let and afterwards sold to the well-known firm of Messrs John Hall <fc Son; a third Government factory at Ballincollig was disposed of a few years later. The Waltham Abbey works have been greatly enlarged of recent years, and no expense has been spared to render them, by the introduction of new and improved machinery, the most complete as well as the safest in the world. It is impossible to describe in detail the various improvements which have been made in the manu facture of gunpowder, but the most important will be briefly stated when describing the successive processes to which the ingredients are subjected.
THE INGREDIENTS AND THEIR ACTION.
The objects to be attained in the production of an explosive agent for artillery and small arms are-—(a) the maximum of propelling force ; (b) the minimum of initial pressure in the bore of gun; (c) uniformity of action ; (d) freedom from fouling, especially in small-arm powders; (e) durability, i.e., power to bear transport and keep well in store. Of all explosive substances at present known, gun-powder alone can be said to fulfil the first three conditions. Its advantages may be summed up as follows :—(a) the rate of combustion of gunpowder is gradual compared with that of most other explosives; and, both by adjusting the proportions of the ingredients and varying the mechanical processes of manufacture, its explosiveness can be modified so as to suit every description of weapon ; (6) the ingredients are easily procured, and are comparatively cheap ; (c) with proper precautions, it is comparatively safe in manufacture, in store, and in transport; it also keeps well in a moderately dry atmosphere.
The earliest gunpowder used in cannon in Europe con-sisted of equal parts of saltpetre, charcoal, and sulphur, ground up and mixed together as required, and must have proved a mixture far inferior in strength to that given in the MS. of Marcus Graecus. To account for the use of such a very weak composition long after better proportions had been ascertained, it must be remembered that the earliest cannon were composed of iron staves roughly hooped together ; and tubes of thin iron, or even of wood or leather, with rope coiled round them, were sometimes used. Indeed the effective application of gunpowder as a propelling agent involves a whole series of inventions, and it was doubtless chiefly owing to the backward state of mechanical science during the Middle Ages that such weak powders were employed. The slow growth of artillery science in Europe for five centuries, and its rapid development in very recent years, are facts which support this presumption. Even about 1410 the proportions were still but 3 saltpetre, 2 sulphur, and 2 charcoal. The relative amount of saltpetre was gradually increased, and Tartaglia (Quesiti e Inventioni diversi, Venice, 1546) mentions twenty-three various compositions as having been used at different times ; the gunpowders of his days were—
== TABLE ==
It is remarkable that Robins states the above proportions to have been very nearly those of his own day (1742), for there is a great deficiency of saltpetre in the cannon powder, and a considerable excess in that for muskets, com-pared with the relative quantities now employed in England. For a long period of time it was the custom for the fine grain or musket powder to contain a larger proportion of saltpetre than that for cannon ; and, again, the amount of nitre was relatively reduced as the piece of ordnance became heavier, doubtless with the view of obtaining a slower burn-ing powder for large charges. However, we find that by the latter part of the last century, what was called " com-mon war powder" was almost universally composed of 6 saltpetre, 1 charcoal, and 1 sulphur, and these are the pro-portions still in use by many Continental nations (D'Antoni On Gunpowder, translated by Capt. Thompson, R.A., Lon-don, 1787).
So far back as the 16th century, Baptista Porta is said to have arrived at the proportions now used in France, which, however, were certainly not adopted until a comparatively recent period. Exhaustive experiments have also been carried out in that country by Beaume, the Committee of Public Safety, Chaptal, and Proust, who fixed upon per-centages of saltpetre varying from 76 to 80, of charcoal from 13 to 16, and sulphur from 5 to 9. These may seem to give rather a wide margin, but this will surprise no one who is acquainted with the great differences in results given by comparatively slight variations in the conditions of ex-periment, with powder of the same composition. In the British Government service but one scale of proportions has been employed for many years, and the very extensive trials of the " Committee on explosives " have shown that there is no good reason to depart from that scale; for they have conclusively demonstrated that the variations in the mechanical and physical properties of gunpowder, produced by the processes of manufacture, exert even more influence upon its action than a comparatively considerable difference in composition; this does not, however, apply to the small charges used in firearms. It will be seen, moreover, that one of the three ingredients—charcoal—can be so varied in quality a3 very materially to affect the results.
The following table gives the percentage composition of gunpowder as now made in different countries for military purposes :—
== TABLE ==
The proportions of the ingredients in English commercial 3> gunpowders vary considerably according to the market for which they are intended. The best sporting powders
have about the same composition as those made by Government. Wherever cheapness is the chief object in view, the quantity of nitre is diminished, and the other two components relatively increased. Some of the powder for the African trade, commonly called " nigger powder," does not contain much more than 50 per cent, of saltpetre, while other kinds are nearly as bad. Blasting powder contains a low proportion of saltpetre, from 60 to 62 per cent.; but, although this reduction may originally have been made in order to manufacture a cheaper article, yet it is also the most effective for the object desired in many cases, which is to remove large masses of earth or soft rock, and this can best be done by using a comparatively weak or slow-burning powder. The element of time is here of great importance; a very quick-burning or violent explosive would not displace such large masses of a soft material, although the local effect would be more destructive (see BLASTING and EXPLOSIVES).
Before proceeding further, it will be as well briefly to consider the properties of the three ingredients of which gunpowder is composed, and the part played by each.
Saltpetre, or nitrate of potash (KN03), occurs as a Saltpetre, natural production on or near the surface of the earth in several warm climates, especially the plains of India and China. When it arrives in England, it has only been partially separated from the earthy and foreign saline matters with which it was combined when found, and is quite unfit for the manufacture of gunpowder; the salts of sodium especially, from their property of absorbing mois-ture, are most injurious. In this state the saltpetre is known as " grough " nitre, the impurities commonly present being the chlorides of potassium and sodium, and the sulphates of potash, soda, and lime, together with sand and organic matter; they do not usually exceed 5 lb per cwt., the exact proportion of impurities in any sample being termed the "refraction" of the saltpetre, and allowed for in the price. The nitrate of soda, called " cubical nitre " or Chili saltpetre, which is found abundantly in South America, although chemically adapted to supply the place of potassium nitrate, cannot be employed in the manufac-ture of gunpowder, owing to its very deliquescent properties. This salt is, however, largely converted into saltpetre by the action of chloride of potassium. In France and Germany, also, nitre is produced artificially (see SALTPETRE).
Saltpetre, which is a compound of 54 parts of nitric acid and 46 of potash, acts as a magazine of oxygen in a solid form, one volume of saltpetre containing as much oxygen as about 3000 volumes of atmospheric air. This oxygen, with which it readily parts when raised to a certain temperature, combines violently with the carbon to form carbonic acid aud a proportion of carbonic oxide; these with free nitrogen constitute the chief gaseous products of com-bustion. The potassium is found combined in the solid residue.
Wood charcoal is the charred woody fibre or residue Char-which remains after the liquid and more volatile parts have coal-been driven off by destructive distillation, The object of charring wood is the removal of moisture, and, which is of great importance, the expulsion of those matters which become volatile before they are burned, and which would absorb a large amount of heat. It may be charred in the ordinary way in pits; but the usual mode of preparing charcoal for gunpowder is by heating it in large iron cylinders or retorts, as hereafter described. By this latter method, the operation is performed with more uniformity and economy, and the charcoal kept more free from par-ticles of grit orearthy matter. Charcoal is best fitted for the manufacture of gunpowder when prepared from light spongy wood, containing a very small proportion of mineral substances ; it should be sound, and of not much more than ten years' growth. The quality of the charcoal exercises the greatest influence upon the rate of combustion, so that both the description of wood used and the mode of burning are of the utmost importance.
By a series of experiments first made by Proust, and since repeated by English chemists, it has been found that 12 grains of various charcoals, mixed with 60 grains of saltpetre, give the following average volumes of gas :—
== TABLE ==
The production of the strongest powder does not depend alone upon the evolution of the largest volume of gas, but the above table is of interest since the three descriptions of wood which head the list have long been considered by universal consent as the best adapted for the manufacture of charcoal for gunpowder. Dogwood (so-called, but in reality it is alder-buckthorn, Ehamnus Frangula, the French bourdaine) is an underwood of slow growth, usually obtained from Sussex, Belgium, or Prussia; it is cut about an inch in diameter, and packed in bundles 6 feet long. This wood is now used, both in England and on the Continent, for all military small-arm powders, as well as the best descriptions of sporting gunpowder. It has been found, moreover, that cannon powders made from dogwood charcoal are, other things being equal, much more violent in action than those manufactured with willow or alder charcoal. Accidents with powder made from dogwood charcoal have usually proved more destructive than those made with any other description. Alder and willow charcoal is used for making gunpowders for field and heavy ordnance, as well as for the commoner kinds of commercial powders; these woods are obtained from various parts of England, and should measure about 4 inches in diameter. The willow used is the Salix alba, one of the softest and lightest of English woods, white in colour, and of very rapid growth ; the pith is circular, and tolerably large. Alder is considerably harder and denser in texture, and of slower growth; its colour is reddish-yellow, and the small pith triangular or bayonet-shaped in section. Dogwood has a very large pith in pro-portion to its size, circular, and of a red colour, which is preserved even after the wood is converted into charcoal.
The temperature at which the wood is charred exercises the most powerful influence upon the inflammability of the charcoal, and consequently upon the " explosiveness," or rate of combustion, of the gunpowder made from it. The higher the temperature the larger the proportion of hydrogen and oxygen expelled, and the nearer the approach of the charcoal to pure carbon ; at the same time, it becomes more dense and incombustible, and the gunpowder made from it is comparatively slow in action, and gives a low initial velocity Charcoal prepared at a low temperature is softer and more inflammable, and contains more volatile constituents ; it makes a quicker burning powder, giving a higher velocity to the projectile, but also producing more strain or pressure upon the metal of the gun. The chief defect, however, of this " slack-burnt" charcoal, or charbon roux, as it is called from its reddish-brown colour, is its property of absorbing moisture more readily than denser charcoal; the powder manufactured from it is consequently more hygroscopic, and therefore more liable to deteriorate in strength from the effects of damp than that made with a more highly burnt charcoal. To show the great difference in inflammability caused by burning at low and high temperatures respectively, it may be stated that charcoal prepared at 500° Fahr. readily ignites at about 640°, while, if burnt at 1800° Fahr., nearly double the heat previously mentioned is required to inflame it. The following table exhibits concisely the practical effects of different modes of preparing charcoal for gunpowder, the same kind of wood being used in each case ; it shows (a) the analysis of the charcoals, and (b) the comparative initial velocities and pressures given by powders made in a precisely similar manner from those charcoals.
== TABLE ==
For the manufacture of gunpowder, only the crystalline Sulphur, electro-negative variety of sulphur soluble in bisulphide of carbon (see CHEMISTRY, vol. v. p. 498) is used. Sublimed sulphur, commonly called " flowers of sulphur," which con-sists of minute granules of insoluble sulphur enclosing the soluble variety,is considered unfit for gunpowder; the reason assigned has usually been that, from the mode of manufac-ture, it is impregnated with sulphurous and sulphuric acids, but Professor Bloxam points outthat in all probability it is the fact of the sublimed sulphur consisting of the electro-positive insoluble variety, which exerts an injurious influence upon the gunpowder made from it. Sulphur performs the part of a second "combustible" in gunpowder; but there is no doubt that its chief value as an ingredient thereof arises from its great inflammability, owing to its tendency to combine with oxygen at a moderate temperature; it inflames at about 560° Fahr., thus facilitating the ignition of the powder. Its oxidation by saltpetre appears also to produce a higher temperature than is obtained with charcoal, thus accelerat-ing combustion, and increasing by expansion the volume of gas generated. An excess of sulphur would, however, be injurious by increasing the solid residue, in which the sulphur is found combined in various forms after the explosion. Some authorities have considered that, from its non-absorbent properties, sulphur renders gunpowder less hygroscopic, and more compact and durable.
Powders made from exactly the same materials, mixed Explo-in the same proportions, yet differ greatly in " explosive- siveness. ness," which has been defined as the rate at which the powder burns or is converted into gas. This quality will depend chiefly upon the following properties :—(a) extent of incorporation; (b) the density of the powder; (c) its hardness; id) size of the grains or pieces; (e) shape of the grains; (/) amount of glaze. Although not altogether synonymous with strength, we may consider " explosiveness " as the quality upon which the value of gunpowder for any particular purpose chiefly depends.
Next to the selection of the precise description of char- Extent coal to be used, no point in the manufacture of gunpowder of incor-requires such care and attention as the thorough inter- PoratloI1~ mixture of the ingredients,—the object being in fact to form out of the three components a new substance as nearly homogeneous as possible. It is usually considered that j there is a limit of time beyond which no advantage is gained by continuing the "milling" or incorporating process; but it is certain that nothing that can be done to the powder afterwards will add to its strength, although we may modify its explosiveness, and that the very best powders, especially for small-arms, are milled the longest time. This question will be further treated under the head of manufacture.
Density No physical property affects the explosiveness of gun-and powder as much as its density. By density we mean the hardness. qUantity of matter actually present in a certain bulk of the powder. Thus, if different quantities of meal powder, con-taining the same proportion of moisture, be compressed into equal bulks, say, for example, into cylinders of equal size, that which contains the most meal will be the densest. Hardness has not necessarily a relation to density, for a substance may be hard, and yet possess little density. Increase of density can only be given by compressing the meal into a smaller bulk, while increase of hardness can be arrived at by pressing the meal in a moister condition.
Other things being equal, increasing the density decreases the initial velocity, and, vice versa, a less dense powder gives a higher velocity, but also a greater strain to the metal of the gun. This is due to the less dense powder burning more rapidly than that with a dense close texture. If two grains, or pieces of powder, of equal size and similar shape but very unequal density, be burnt upon a glass plate, the less dense one will be entirely consumed before the denser one has finished burning.
Freedom from fouling is a very important property in small-arm powders. From the experience gained in select-ing a powder for the Martini-Henry rifle, it was found that, with the same description of charcoal, the slower the action of the charge the less fouling took place; this modification of action was easily obtained by raising the density, at, however, a corresponding sacrifice of velocity in the bullet. The reason assigned was that the quicker-burning powder caused a rush of gas past the lubricating wad before the latter had time to act properly. A dense hard powder which will take a high polish or glaze will evidently keep better, and bear transport better, than a more porous and therefore more friable grain, which would easily form dust. It will thus be seen that .many considerations enter into this question of density. Size of The size of grain is one of the most important points to grains, be considered as modifying the explosiveness of powder. Although a charge of powder appears to explode instantane-ously, yet both ignition and combustion are comparatively gradual; the flame is communicated from one grain to another, and each burns in concentric layers until it is con-sumed, so that the combustion of the grains is not simul-taneous. Meal-powder burns more slowly in air than when the powder is granulated, in consequence of the minute-ness of the interstices ; dust, especially in fine-grain powder, retards ignition by filling up the interstices. To go to the other extreme, as showing the advantage gained by granulating the press-cake, we may quote an experiment made some years ago. A small piece weighing 1'06 oz. was placed in a mortar, and a light ball placed upon it; when it was fired, the ball was not thrown out. An equal quantity broken into 15 pieces, projected the ball 3'3 yards; broken into 50 pieces, the ball ranged 10-77 yards; when the same weight of ordinary grained powder was used, the range was 56-86 yards. It is most unsafe to attempt to apply to the action of gunpowder, when fired under enormous pressure, and especially when employed in large charges, the conclusions arrived at from its combustion in air. We may, however, assert that the weight of charge, the density, and all other conditions being equal, a charge made up of large grains or pieces of gunpowder will burn more slowly, and exert a lesser initial strain upon the gun than one composed of small grains, owing to the total surface of combustion being diminished by increasing the size of the pieces ; this has been abundantly verified by the results of experiments with heavy rifled ordnance. On the other hand, the larger grains afford larger interstices between them for the passage of the flame, thus facilitating the ignition of large charges. Hence, a gunpowder may possess a low rate of combustion and yet a high rate of ignition, and vice versa. For each gun, or charge of gun-powder, there is doubtless a size of grain which would pro-duce a maximum velocity with a minimum initial strain, but as each kind of cannon powder has to be employed in more than one piece of ordnance, it is necessary to select that size which will best suit all of them.
The same quantity of powder meal made into two grains Shape of of equal density, but different shapes, will take different grains, times to burn ; the larger the surface exposed the quicker will be the combustion of the grain. A sphere being the smallest form in which a given quantity of matter can be placed, it follows that a certain amount of meal powder compressed into a spherical form will take longer to burn than the same quantity made into the shape of a flat scale, exposing a large surface. The rounded form of grain is the most favourable for the transmission of the flame, the interstices being larger and more regular than in the case of elongated or flat grains fitting into one another. Hence we may conclude that, to secure uniformity, it is better to have the constituent grains as nearly as possible of the same shape, and the nearer this shape approaches a sphere the better.
The glazing process is one of considerable importance, Glazing, both with reference to the explosiveness, and also the keeping qualities of the gunpowder. As regards the former point, it undoubtedly modifies the violence of the combustion, and this it probably does by slightly retarding the ignition, a powder with a rough porous surface affording a better hold to the flame than one possessing a highly polished exterior. With the large " cubical" powder, used for heavy rifled ordnance, there is little or no appearance of what is com-monly understood as glaze, or polish, from this process, but the corners and edges of the cubes are rubbed off, and the shape approximates more nearly to that of a sphere than is the case with the much lighter fine-grain powder ; there seems to be also a certain hardening of the surface of the grains or pieces, partly the effects of friction, but probably due in part to the sweating the powder undergoes, a con-siderable amount of heat being generated in the glazing barrels. It is evident that, by taking away the sharp angles which would otherwise easily be converted into dust, and also by giving the grains a harder exterior, this process renders gunpowder the better able to bear transport, and to resist the deteriorating effect of a damp atmosphere. The addition of a thin coating of the purest graphite to cannon powders, although originally intended merely to modify the explosiveness, also renders the surface of the grains less absorbent. Military small-arm powders are never dressed with graphite; good fine-grain gunpowder will take a high finish without it, but, by its aid, a very inferior article can be polished up to a silvery brightness.
Moisture in gunpowder reduces the explosiveness by using Effect of up a portion of the heat generated by the combustion, to moisture, get rid of the water; therefore the property of withstanding the absorption of moisture is a very important one for gunpowder to possess. All powder will take up from a normally dry atmosphere a certain amount of moisture, which will depend to some extent upon its density, but to a much greater degree upon the description of charcoal from which it is made. Slack-burnt or red charcoal is greatly more hygroscopic than black charcoal, or that burnt at a high temperature; and the absorbent properties of gun-powder made from the former are but little reduced by raising the density. Large cannon powder contains a greater percentage of water than the fine grain, and the actual amount present in any given sample will be affected by the prevailing state of the atmosphere, especially if kept in wooden barrels. To show the considerable effect upon the initial velocity of projectile, and pressure in bore of gun
caused by comparatively slight variations in the amount of moisture, the following results may be quoted from the experiments of Noble and Abel. The samples of " pebble " powder used were specially prepared for the Committee on explosives, differing only in the amount of moisture contained in them.
== TABLE ==
Keeping gunpowder in a very damp atmosphere will tend to separate the ingredients by dissolving a portion of the saltpetre, which crystallizes upon the surface of the grains or pieces.
FIRED GUNPOWDER.
Products In the explosion of gunpowder, the products of com-of ex- bustion are very materially affected by the conditions under plosion, wjjjgh if jg nred,—whether burnt in the open air, exploded under very great pressure in a tightly closed vessel, or the products allowed to expand in the bore of a gun. It may, however, be stated generally that the oxygen of the salt-petre converts nearly all the carbon of the charcoal into carbonic acid (C02), a portion of which combines with the potash of the nitre to form carbonate of potash (K2O.C02), the remainder existing in the state of gas. The sulphur is for the most part converted into sulphuric acid (SOs), and forms sulphate of potash, a large proportion of which, pro-bably by secondary reactions, becomes hyposulphite and sulphide. The nitrogen of the saltpetre is almost entirely evolved in the free state, and the carbon not having been wholly burnt into carbonic acid, there is always a proportion of carbonic oxide (CO) present.
The decomposition is so complicated, and varies so considerably under different conditions of experiment, that it is impossible to represent the transformation by any single equation, but the following expression may give some idea of the primary reaction :—
4KN03 + C4 + S = K20. C02 + K2O.S03 + N4 + 2C02 + CO. There is a very large proportion of residue, which, on cooling, assumes the solid form. The experiments of Noble and Abel prove that it is liquid very shortly after the explosion ; indeed, it is probable that at the moment of maximum temperature, the ultimately solid products are more or less in a state of vapour, being deposited in a very finely divided state as the temperature falls. Mechani- When a charge of gunpowder is exploded in the chamber cal of a gun, a large quantity of gaseous matter is evolved in effects. a highly condensed state ;—its tension, or expansive power, is, moreover, greatly increased by the heat generated during the transformation. The pressure being equal in all direc-tions, the work done upon the projectile is due to the expansion of the permanent gases in the bore of the gun, which force is also considerably sustained—or the reduction of temperature due to the expansion in great measure com-pensated for—by the heat stored up in the ultimately solid residue. Any calculation which does not take this latter point into consideration will give far too low an estimate of the actual force of fired gunpowder (see EXPLOSIVES).
With our present state of knowledge, it may be stated in round numbers that the gases evolved by gunpowder, if it entirely fills the close vessel in which it is exploded, will occupy at a temperature of 0° C. and 760 mm. barometric pressure, about 280 times the volume of the original powder, and will give a pressure of about 6000 atmospheres, or 40 tons per square inch.
In view of the very different results which have been Researches arrived at by various eminent authorities who have experi- relative to mented upon fired gunpowder, the following brief account m'ed Smi" of their researches may be useful:— pow 61
Robins, the father of scientific gunnery, in 1743 read before Robins, the Royal Society a paper describing experiments which showed that gunpowder, when fired, generated permanent gases, which, at the ordinary temperature and atmospheric pressure, occupied a volume 244 times greater than that of the unexploded powder. He further considered that the heat evolved was such that the tension, of the permanent gases would be increased fourfold, and hence deduced the maximum pressure to be about 1000 atmospheres. In 1778 Dr Hutton. Hutton communicated in the same manner an account of his cele-brated researches on the combustion of powder ; he deduced the maximum pressure to be about twice that given by Eobins, or a little over 2000 atmospheres, difl'ering from the latter chiefly as to the tem-perature, for he considered that the volume of gases generated would occupy, under ordinary conditions, 250 times that of the powder. He also deduced formulae for giving the pressure of the gas and velocity of the projectile at any point of the bore, but no allowance is made for the loss of heat in proportion to the work done, that fun-damental principle of thermodynamics being then unknown ; the error thus occasioned is, however, in part compensated for by the heat stored up in the non-gaseous products. In 1797 Count Rum- Rum-ford sent to the Royal Society his experimental determinations of ford, the pressures given by fired gunpowder, which are remarkable as being the first attempt to do this by direct observation. The closed vessel he used was, however, very small, being able to hold but 28 grains when filled, and he only succeeded in measuring the results up to a charge of 18 grains. His plan of operation was to ascertain by repeated trial the least weight which would just confine the pro-ducts of explosion, and thence to calculate the pressure ; this he de-duced from two series of experiments, which, however, gave some very anomalous results, to be as high as 100,000 atmospheres for gunpowder exploded in its own space. In 1823 Gay-Lussac, the Gay-celebrated French chemist, estimated the volume of the permanent Lussac. gases evolved at 450 times that of the powder fired, but General Piobert assigns very probable reasons for supposing the quantity of gas determined to have been doubled in error. Gay-Lussac found the percentage composition of the gaseous products to be 52-6 car-bonic acid, 5 of carbonic oxide, and 42-4 nitrogen. In 1857 Bunsen Bunsen and Schiskoff published (Poggendorff's Annalen, vol. cii. p. 325) the and results of their very important experiments ; their determinations Schiskoff. were—(1) that the permanent gases represented only about 32 per cent, of the weight of the charge, and occupied at the standard tem-perature and pressure about 193 times the volume of the original powder ; (2) that the heat generated by exploding gunpowder in a close chamber is about 3340° C.; and (3) that hence the pressure would be about 4374 atmospheres, or 29 tons per square inch. Major Rodman (Boston, 1861) published the results of extensive Rodman, experiments carried on for the United States Government, in order to ascertain the pressures given by different powders in the bores of heavy guns. He employed a pressure gauge, which bears his name, and consists mainly of a piston to which is attached a knife edge acting upon a priece of soft copper, contained in a small cylinder at right angles to, and communicating with, the bore of the gun ; this apparatus he also used to ascertain the jires-sure given by powder exploded in a closed vessel. The chief value of his experiments consists in their having established the fact that the size of the grain should be proportionate to the length and dia-meter of the bore of the gun. Von Karolyi (Poggendorff's Annalen, Von April 1863) carried out experiments from which he estimated that, Karolyi. for small-arm powder, the gases evolved occupied about 226 times the original volume, while cannon powder produced about 200 vol-umes. Captain Andrew Noble, F. R. S., of Elswick, and Professor Noble Abel, C.B., F.R.S., chemist to the British War Department, and carried out a most extensive series of experiments on '' Fired Gun- Abel, powder" (Phil. Trans. Royal Soc, 1875), probably the most com-plete ever made, and undertaken collaterally with the Government "Committee on Explosives;" their mean results may be summed up as follows :—
(A.) When Fired in a Confined Space.—(1) The products of com-bustion are about 57 per cent, by weight of ultimately solid matter, and 43 per cent, of permanent gases. (2) The latter occupy at 0° C. and 760 mm. barometric pressure about 280 times the volume of the original powder. (3) The tension of the products of combus-tion, when the powder entirely fills the space in which it is fired, is about 6400 atmospheres, or 42 tons per square inch. (4) The temperature of explosion is about 2200° C. (5) The chief gaseous products are carbonic acid, nitrogen, and carbonic oxide, with a little sulphydric acid and hydrogen. (6) The solid residue is mainly com-posed of potassium carbonate, sulphate, hyposulphate, and sulphide.
(B.) When Fired in the Bore of a Gun.—(1) The products of com-bustion, at all events so far as regards the proportions of solid and gaseous matters, are the same as in the case of powder fired in a close vessel. (2) The work on the projectile is effected by the elastic force due to the permanent gases. (3) The reduction of tempera-ture due to the expansion of the permanent gases is in a great measure compensated by the heat stored up in the liquid (afterwards solid) residue. (4) An expression is obtained showing the law con-necting the tension of the products of combustion with the volume they occupy. (5) Equations are also deduced for the work that gun-powder is capable of peforming in expanding in a vessel impervious to heat, and for the temperature during expansion. Thence the ex-perimenters give a table showing the total work gunpowder is capable of performing in the bore of a gun, in terms of the density of the products of combustion, or the number of volumes of expansion. (6) The total theoretic work of gunpowder when in-definitely expanded (for example, in a gun of infinite length) is about 486 foot-tons per pound of powder.
They further ascertained that—(a) the fine-grain powders furnish decidedly smaller portions of gaseous products than large grain or cannon gunpowders ; (6) the variations in the composition of the products of explosion, in a close vessel, furnished by one and the same powder under different conditions as regards pressure, and by two powders of similar composition under the same conditions of pressure, are so considerable that no chemical expression can be given for the metamorphosis of a gunpowder of normal composition; and (c) the proportions of the several constituents of the solid residue are quite as much effected by slight accidental conditions of explo-sion of one and the same powder in different experiments as by decided differences in the composition, as well as in the size of grain of different powders. It may, however, be remarked here that, while the pressures given in the bore of a gun are very seriously affected by the size of the grains or pieces of the powder, it was clearly demonstrated by these experiments that the force exerted by fired gunpowder is not affected by the apparent accidental variations in the nature of the secondary chemical changes resulting from the explosions ; this fact renders the exact composition of the products of combustion of less practical importance.
The following table gives concisely the chief results arrived at:—
== TABLE ==
M. de Saint Robert determined experimentally the amount of work lost by the heat communicated to the gun to be about 250 gramme-units per gramme of powder in the case of a rifled musket. From the experiments of Noble and Abel this loss becomes reduced to as little as 25 gramme-units per gramme of powder in a 10-inch gun. They have also calculated the energy in foot-tons from this initial velocity obtained, and hence deduced the percentage of the possible theoretic work which is actually realized for every rifled gun in the British service. This percentage, which they term the " factor of effect," is found to be greatest, viz., 93 per cent., in the case of the 38-ton gun, and least, 50'5 per cent., in the 7-pounder mountain gun, weighing 150 lb. Deter- To determine the pressures, Noble and Abel employed two urination methods:—(1) directly, by means of " crusher gauges," inserted at of pres- various points of the bore ; this is an improvement on the Rodman sure in piston-gauge, the pressure being estimated by the amount of com-bore. pression given to a small cylinder of pure soft copper; (2) indirectly, by means of the chronoscope invented by Captain A. Noble, which measures the velocity of the projectile at given points in the bore, whence the pressure can be calculated (see GUNNERY). These pres-sures will vary greatly, other conditions being the same, according to the " explosiveness " of the powder ; the great object is to obtain a powder suited to the particular arm with which it is to be used. Dissocia- Many foreign physicists are of opinion that the phenomenon of tion im- dissociation comes into play at the moment of maximum temperature, probable, causing the carbonic acid gas (CO.,) to be decomposed into carbonic oxide (CO) and oxygen. However, Noble and Abel show that, if such be supposed to occur, the loss of heat absorbed by the decomposition would more than compensate for the increase of volume.
PREPARATION AND PURIFICATION OF THE INGREDIENTS.
The three ingredients of gunpowder may be purchased in the market in a prepared or refined state, and this is done to a greater or less extent by many powder makers. However, the royal gun-powder factory, as well as some of the great private firms, prepare and purify the materials required from the commencement, with the double object of insuring uniformity in the qualities of the powders made, and of avoiding, so far as practicable, the introduc-tion of the least particle of grit or other foreign matters, which might cause serious accidents.
The rationale of the refining process is based upon the fact that Refining saltpetre is far more soluble in hot than in cold water, while the salt-chief saline impurities found in grough nitre are almost equally petre. soluble in either. Water at 212° Fahr. holds about seven times as much nitrate of potasli in solution as water at 70° Fahr.; if, therefore, a saturated solution of saltpetre be made at a temperature of 212° Fahr., and the chlorides of sodium and potassium are con-tained in the liquor, as the solution cools to 70° Fahr., six-sevenths of the nitre will be deposited in the form of crystals, which can easily be removed, whereas the foreign salts will still remain in solution. The following is a brief account of the improved mode of refining saltpetre, introduced some years back at Waltham Abbey, and now adopted at the chief private factories in England. The refining coppers are capable of holding about 500 gallons each, and are fitted with false iron bottoms, which are perforated with holes to allow sand and other mechanical impurities to fall through. Being each charged with 280 gallons of water,—usually the " washings" of saltpetre previously refined,—and 40 cwt. of grough nitre, a fire is lighted beneath. In about two hours the greater part of the saltpetre is dissolved, and the solution begins to boil; the thick scum formed on the surface is carefully taken off, and cold water from time to time thrown in to induce it to rise, the boiling being continued until there is no more scum ; the coppers are then filled up with cold water, and the solution again made to boil briskly for a few minutes, after which the fires are allowed to go down. In about two hours more the solution will have fallen to the proper temperature, 220° Fahr. ;(sp. gr. 1'53), for pumping out ; it is then filtered through dowlas bags suspended on a frame, and conducted by troughs to the "coolers" or crystallizing cis-terns at about 180° Fahr. These latter are large shallow pans of copper, in which the liquid is kept agitated either by long-handled wooden hoes, or by machinery ; as it cools, fine crystals fall to the bottom, and are from time to time thrown upon inclined draining frames by means of perforated copper shovels. When the tem-perature falls below 70° Fahr., the agitation is ceased, and any large crystals which may afterwards form are left in the mother liquor. After being thus allowed to get rid of some of the liquor, the crystallized saltpetre, having almost the appearance of snow, and technically called "flour," is raked into the "washing-cis-tern ;" it is there subjected to three separate washings with pure water, distilled being preferable, which is allowed to drain off through a plug hole at the bottom of the cistern. These " wash-ings " are carefully conducted to an underground tank, and kept either for using in the refining coppers, or boiled down in "eva-porating pots " holding about 300 gallons, until the liquid is suffi-ciently concentrated for the saltpetre to crystallize, when it is run into small copper pans, and set aside to cool; this course is also pursued with the mother liquor from the large cooling cisterns, and the resulting crystals treated as grough nitre, for these large crystals always enclose liquid containing impurities. After drain-ing for a night the refined saltpetre is removed to store bins, and is ready for use without any further pulverization ; the amount of moisture remaining in it, from 3 to 5 per cent., is then carefully ascertained, and allowed for in the mixing house. Neither the solid residue from the pots and coppers nor the mother liquor from crystallizing pans is thrown away, but by repeated boilings and evaporations every ascertainable portion of saltpetre is extracted, and the residue sold ; it chiefly consists of chlorides of sodium and potassium, with some sulphates. The jute bags in which the salt-petre is imported are also boiled down.
The large percentage of saltpetre contained in damaged powder makes it worth while to extract the nitre by boiling in large cop-pers, filtering and crystallizing in small pans as before ; the re-siduum is again boiled, and then thrown away. The sweepings from the powder houses, in various stages of manufacture, are "extracted" in the same manner.
Refined saltpetre for making gunpowder is tested as follows :— (1) with blue and red litmus paper, for acids or alkalies ; (2) for the presence of chlorides, with solution of nitrate of silver ; (3) for sulphates, with chloride of barium, forming the insoluble sulphate of baryta.
By the old method of refining the solution was left to crystallize in coolers, and the drained crystals fused or melted in iron pots at a heat of about 500° Fahr.; the molten saltpetre was then poured into moulds, broken up when cold, and ground under edge runners.
The wood for charcoal is cut in spring, so that the bark may Charcoal strip off easily, and is stacked for about three years to season it, burning, but a considerably shorter time will suffice. Being cut in lengths of 3 feet, the wood is packed in iron cylindrical cases termed " slips," which are then inserted in the " cylinders " or retorts, the latter being built into the wall in sets of three with a furnace under-neath, arranged so as to allow of the complete regulation of the heat; the flames surround the retorts as nearly as possible. An opening is left in the rear end or lid of the slip, corresponding with a similar opening in the retort, through which, by means of pipes, the inflammable gases resulting from the charring of the wood are con-ducted into the furnace and there burnt; this saves a considerable amount of fuel. There are also pipes which receive and carry off the tar and pyroligneous acid produced. In the powder works of Messrs Hall & Son of Faversham, the retorts are disposed three on each side of the furnace, and the connecting pipes and dampers are so arranged that the gases from either set, or from any single cylinder, can be utilized for the charring of the wood contained in any of the others ; by this means it is claimed that little fuel is required beyond the quantity needed to warm the furnace and par-tially char the first set of retorts.
That the wood is sufficiently charred is shown by the blue colour of the gas flame, which indicates the formation of carbonic oxide; the door of the retort is then opened, and the slip is withdrawn by means of tackling, and placed in a large iron cooler having a close-fitting lid, where it is left a few hours till cool enough to be turned out and put into store. The charcoal is carefully picked over by hand, to en-sure its being of uniform quality, and is kept from ten days to a fort-night before being ground, to obviate the danger of spontaneous com-bustion, to which it is liable if ground too soon after burning; this arises from the heat generated by the very rapid absorption and condensation of oxygen from the air by the finely powdered charcoal. Charac- Properly-made charcoal for gunpowder should be jet black in teristics colour, and its fracture should show a clear velvet-like surface ; it of good should be light and sonorous when dropped on a hard substance, charcoal, and so soft as not to scratch polished copper. Slack-burnt charcoal, or that prepared at a very low temperarure, is at once known by its reddish-brown colour, especially when ground, and this peculiarity can be recognized in the powder made from it, when reduced to a fine state of division. Charcoal burnt at a very high temperature is known by its hardness, metallic ring, and greater density.
In France, charcoal is prepared by injecting superheated steam into the retorts for a certain period. Grinding The charcoal mill in shape resembles an enlarged coffee mill ; a the char- cone works within a cylinder, both being provided with diagonal coal. teeth and ribs, wide apart at top, but gradually approaching one another below. The pulverized charcoal is thence conducted by a simple mechanical arrangement direct into a cylindrical frame or "reel," about 8 feet by 3 feet, set at a slope and covered with copper wire cloth of about 32 meshes to the inch ; all that is fine enough to pass through the reel-covering falls into a bin which encases the reel, and the coarser particles pass on to a tub at the further end, in order that they may be ground over again. The ground charcoal store should always stand by itself, in case of spontaneous combustion taking place. Sulphur The sulphur from Sicily known as '' Licara firsts " is employed refining, for the best gunpowder ; it undergoes a rough purification before importation, leaving from 3 to 4 per cent, of earthy impurities. Formerly these were removed by simply melting the " grough " sulphur in an iron pot, and then ladling it into large wooden moulds or tubs, saturated with water to keep the sulphur out of the cracks ; when cool enough, these tubs were unhooped, and the top and bottom of each mould of sulphur cut off. In the present day, however, the sulphur is refined by distillation in a simple apparatus. A large iron " melting pot," or retort, is set in brick-work, about 3 feet above the floor, with a furnace underneath ; this retort has a heavy movable lid, which is luted into the pot with clay, and in the lid is also an opening, closed by an iron conical plug. From the melting pot lead two pipes at right angles to one another, one to a large circular "dome," or subliming chamber, and a smaller pipe to an iron " receiving pot" placed on a lower level than the retort; the latter pipe has an iron casing or "jacket" round it, through which cold water is allowed to circulate. The communica-tion of these pipes with the retort can be shut off or opened as occa-sion may require by means of valves worked from without.
A charge of about 5J cwt. of grough sulphur in small pieces being placed in the retort and the furnace lighted, the pipe leading to the dome is left open, as well as the plug-hole in the lid, but that leading to the receiving pot is closed ; after about two hours, a pale yellow vapour rises, when the plug in the lid is put in and the vapour allowed to pass into the dome, wdiere it " sublimes" or con-denses on the.sides and floor in the form of a fine powder, known as " flowers of sulphur." In about three hours from the commencement, the vapour becomes of a deep iodine colour, when the pipe leading into the dome is closed, and that into the receiving pot opened, at the same time cold water from a tank overhead being allowed to circulate through the jacket ; the vapour is then con-densed in the pipe, and runs into the receiving pot below in the form of a clear orange-coloured fluid. When the jacket commences to get cold, the receiving pipe is closed, and the communication with the dome is reopened, so that the rest of the vapour may pass into it, the furnace doors being at the same time thrown back ; the impurities remain at the bottom of the melting pot, and are thrown away. The flowers of sulphur thus obtained, being unfit for the manufacture of gunpowder, are placed in the melting pot as grough sulphur. A leaden pipe passes from the lid of the receiving pot into a small wooden chamber lined with lead, in which any vapoui still remaining uu condensed may be deposited, as in the dome. The distilled sulphur is allowed to cool down to about 220° Fahr., when it is ladled into wooden moulds, as above described, and set aside to cool. The tests for refined sulphur are the following :—(1) burn a small quantity on porcelain, when the amount of residuum should not exceed 0'25 per cent ; (2) boil a little with water, and test with blue litmus paper, which it should only very feebly redden.
FIGS. 1 and 2.—A, sectional elevation of incorporating mill, showing one runner and ploughs (p, p) ; C, curb of bed ; M, machinery in tank, underground ; D, drenching apparatus ; I. lever-board, or shutter ; t, tank ; /, /, floor line.
The sulphur from the moulds, being broken into pieces, is ground Pulver-under a pair of iron edge runners, similar to those of the incorporât- izing the ing mills, but of less size ; after this, it is passed through a reel sulphur, similar to that used for sifting the charcoal, but covered with even liner copper wire-cloth, having 44 meshes to the inch.
MANUFACTURE OF GUNPOWDER.
The following list will give a general idea of the chief Processes processes of manufacture, properly so-called, through which of manu-gunpowder passes, although it will be understood that more facture-or less variation takes place in some of the very different descriptions of powder now made :—(1) mixing the ingredi-ents ; (2) incorporation, or " milling ; " (3) breaking down the mill-cake ; (4) pressing ; (5) granulating, or cutting the press-cake ; (6) dusting ; (7) glazing ; (8) second dusting; (9) stoving, or drying; (10) finishing.
The incorporating mill (see figs. 2 and 3) consists of a circular iron or stone bed, about 7 feet in diameter, firmly.
The following is the most approved method of mixing. Mixing. The ingredients are carefully weighed out in the proper proportions for a 50 îb mill-charge, with an extra amount of saltpetre according to the moisture found to be contained in it ; they are then placed in the mixing machine, which consists of a cylindrical gun-metal or copper drum, with an axle passing through its centre, upon which are disposed several rows of gun-metal fork-shaped arms, called "flyers," the machinery being so arranged that the flyers and drum re-volve in opposite directions, and at different rates of speed. After being mixed in this machine for about five minutes, the composition is passed through a hand-sieve over a hopper, falls into a bag placed below, and is tied up ready for the incorporating mill; it is now called a "green" charge.
fixed in the floor of the building, whereon a pair of iron or stone cylindrical edge-runners revolve; formerly, both were made of a dark grey limestone which took a high polish, but the newer mills have cast-iron beds and runners, the edges of the latter being now usually surface-chilled. The average diameter of the runners is 6 feet, and their width about 15 inches; they have a common axle, which rests in gun-metal bouches in a solid cross-head attached to a vertical shaft; this shaft passes through a bearing in the centre of the bed, and is in gear with the driving machinery, which is placed above the runners in the old water mills, and beneath the bed in cast-iron tanks in the new steam mills. Each runner weighs about 4 tons, and the speed averages 8 revolutions per minute.
The bed has a slopping rim on the outside, called the "curb," and on the inside an edge ^IG-
^*—Plan of runners and bed.
formed by the " cheese," or bearing, through which the vertical shaft passes. The runners are not equidistant from the centre of the bed, one working the part of the charge near the centre, and the other the outer portion, but their paths overlap. Two "ploughs" of wood, shod with leather, are attached to the cross-head by arms and brackets; one working next the vertical shaft, and the other close to the curb, the ploughs throw the composition under the runners as it works away from the latter.
The charge, when spread evenly on the bed by means of a wooden rake, contains about 2 pints of water (the moisture of the saltpetre) and a further quantity of from 2 to 6 pints is added from time to time, according to the state of the atmosphere, for the threefold purpose of preventing powder dust from flying about, facilitating the incorpora-tion, and reducing the effect of an explosion; if too wet, the runners would lick up the composition from the bed. During the time of working, the millman enters the mill occasionally, takes a wooden " shover," and pushes the outside of the charge into the middle of the path of the runners, so that every portion may be equally incorporated.
The action of the runners is a combination of rolling and twisting, and has, on a large scale, somewhat the effect of a pestle and mortar, crushing, rubbing, and mixing the ingredients, so as to effect an intimate union.
The time of milling depends upon the nature of the powder. For good fine-grain powders it varies from four to eight hours, but the very best sporting gunpowder is said to be as long as twelve hours under the runners ; blasting and cannon powders are incorporated from two to four hours, the period being rather longer where the lighter stone runners are used. It is of the greatest importance that the mills should be carefully attended to by experienced men, as the whole goodness and uniformity of the powder depends upon this process, and no after treatment can remedy defective incorporation.
When the composition, which has now become '' mill-cake," is ready for removal from the bed, it should be homogeneous in appearance, without any visible specks of sulphur or saltpetre, and of a dark greyish or brownish colour, according to the charcoal used. The mill-cake is carefully tested to ascertain whether it contains the proper amount of moisture; this should be from 2 to 3 per cent, for fine-grain powders, and 3 to 5 per cent, for the larger descriptions. Sometimes a small portion is roughly granulated, and " flashed " on plates of glass or porcelain; a good powder should flash off, leaving nothing but some smoke marks, but, if badly incorporated, the plate will be coated with specks or beads of solid residue.
In former days the ingredients were incorporated in " stamp-mills," which were simply large mortars and pestles, the latter merely raised up by some cam arrangement and allowed to drop by their own weight, the charge being about 12 lb, and the weight of the stamp 50 lb or there-about. The stamp or pilon mills are still used in France and Germany, as well as the moulins-ci-tonneaux, in which the composition is put, with about an equal weight of brass or lignum vita? balls, into large barrels, which are made to revolve for a certain time on their axes; this method of incorporation is sometimes employed in conjunction with edge runners.
There is more danger of an explosion during the milling than in any other process of manufacture ; but, owing to the limitation by law of the weight of charge permitted to be under the runners at one time to 50 lb, as well as to the great precautions taken, there is seldom any fatal result. The millmen only enter the mill occasionally to "liquor" the charge or give it a shove over, and at Waltham Abbey they wear incombustible clothing with a cap fitting over the ears, and gauntlets of the same material. The roof, and front and rear sides of the mills are usually constructed of very light boards, or even of canvas on a wood frame, while the partitions between each pair of runners are of solid masonry. The force of the explosion of a mill charge materially depends upon the length of time the incor-poration has been in progress.
Directly over the bed of each mill is a flat lever-board or "shutter" (see fig. 1) in gear with a tank of water, so arranged that, when the shutter is raised on its pivot by an explosion, the water is upset into the bed; a horizontal shaft connects all the shutters in a group of mills, so that the ex-plosion of one mill at once drowns all the remaining charges. The set of tanks can also be jjulled over by hand.
down.
The process of breaking down, although a subsidiary one, Break-is strictly necessary in order to reduce the mill-cake to a fine in8 meal, so that it may be conveniently loaded into the press box, and receive as uniform a pressure as possible. The breaking-down machine (see fig. 4) consists mainly of two pairs of gun-metal rollers, set in a strong frame of
FIG. 4.—Breaking-down machine. H, hopper; B, endless band; ft, rollers; M, boxes to receive meal.
the same material; one roller of each pair works in sliding bearings connected with a weighted lever, so that any hard substance may pass through without dangerous friction. An endless canvas band, having strips of leather sewn across it, conveys the pieces of mill-cake from a hopper, capable of holding 500 R> to the top of the machine,
where it falls between the first pair of rollers ; after passing through the second pair, whicb are directly below, the meal is received in wooden boxes, placed upon a carriage, and is ready for the press.
3554_9941995
The press-box is usually of oak, with a strong gun-metal frame, and so constructed that three of the sides can turn back on hinges, or be screwed firmly together. Being laid sideways, the top temporarily closed by a board, and the uppermost side alone open, a number of copper plates are placed vertically in the box, and kept apart (at a distance depending upon the description of gunpow-der required) by two racks, which are afterwards re-moved ; the box is then loaded with some 800 lb of meal, which is rammed evenly down between the plates with wooden laths, and the racks withdrawn, so that the plates are only separated by the meal be-tween them. The present upper side of the box being firmly screwed down, the box is turned over, and placed on the table of the hydraulic ram, under the fixed press-block, the plates being now horizontal (see fig. 5). The pumps which work the press (in a sepa-rate house) are then set in motion, and the press-block allowed to enter the box a certain distance, when the
FlG- 5,—Press. A, press-box; B,
edge of the latter releases a PRESS-J>LOCK ; 0, hydraulic ram. spring catch and rings a bell as a signal to stop the pumps; the powder is kept under pressure a few minutes, after which the ram is lowered, and the box removed and un-loaded. For all granulated powders the press-cake is broken up into pieces and put into tubs, but for the cubical cannon powders the slabs are pressed to the exact thickness required, and are carefully kept whole.
The above mode of regulating the pressure is found to give more reliable results than trusting to the indicator gauge of the hydraulic press, for the reason that the elasticity, or resistance to pressure, of the meal varies with the amount of moisture present in it, and the state of the atmosphere. To get uniform density, equal quantities of meal, containing equal amounts of moisture, must be pressed at the same rate into the same space. In practice, however, the moisture in the meal will slightly vary, whatever care be taken with the mill-cake, owing to the hygrometric state of the air causing a difference by the time it comes to the press. It is therefore necessary to alter the exact distance the press-block is allowed to enter the box, not only with the nature of the powder, but with the season of the year, and even according to the prevailing state of the weather.
On the Continent, the operation of pressing is sometimes altogether omitted, and the requisite density given merely by the weight of the runners revolving very slowly, the charges being worked with a considerable amount of moisture in them, and the less dense edges of the cake rejected ; by this plan it is, however, almost impossible to ensure uniformity in the powder produced. The meal is also sometimes pressed by passing it, on an endless band, between large rollers revolving at a slow speed, the less dense edges of the cake being cut off by fixed knives.
For some centuries, gunpowder remained in the form of Granu. dust or " meal," being, in fact, simply the ingredients lating. ground up together. Granulating or " corning" the powder was a great step in advance, but it is doubtful whether this operation was intended to increase its strength, or merely to render it more convenient for charging small-arms, for which alone corned powder was used for many years, whilst meal powder was still employed for heavy guns ; the latter was called " serpentine " powder in the time of Edward VI., probably in allusion to the name of one of the pieces of ordnance then in use, However, during the reign of Elizabeth, the experience of the great additional strength imparted by the corning process, for the reasons ahead}7 explained, led to the universal introduction of corned powder, except for priming,—both in cannon and small-arms,—for which purpose meal powder remained in use as late as the reign of Charles I.
The old method of granulating was to place the press-cake in sieves, provided with two bottoms of thick parch-ment prepared from bullock's hides, and perforated with holes, those in the lower bottom being much the smaller ;, a large number of these sieves were attached to a wooden frame, hung by ropes from the ceiling, which received a violent shaking motion by means of a crank underneath. Into each sieve was put a disk of lignum vitte, to break up the cake, and force it through the larger apertures; the grain produced was retained between the bottoms of the sieves, the dust passing through the fine holes in the lower ones, and falling on the floor of the house. The grain was afterwards separated into sizes by being passed through wire sieves. These machines were clumsy and dangerous; and the accidents which happened with them have caused them to be generally supplanted by better apparatus, although some of the old frames are still in use.
The granulating machines used in the royal factories in England and in India, as well as in the best private works, are constructed upon a principle introduced by Sir William Congreve, but since improved upon. Three or four pairs of gun-metal rollers with pyramidal-shaped teeth, are fixed obliquely one above the other in a strong framework (see fig. 6); the sizes of the teeth vary according to the kind of grain required, but decrease from the top pair, and for fine-grain powders, the lowest pair would be smooth; one roller of each pair works in a sliding bearing, having a counterweight attached to prevent undue friction. Each pair of rollers is connected with that next below, by a short rectangular screen of copper wire, while, underneath all the rollers, are placed, at the same slope, two or more long wire-j screens fixed in a frame having a wooden bottom ; both the frame and the short connecting screens are hung to the machine by strips of lance wood, and, when at work, a quick vibratory motion is given to all the screens by means of a polygonal wheel upon the main frame working against a loose smooth wheel attached to the screen-frame. A large hopper, which rises by the action of the machine, feeds the press-cake upon an endless canvas band, as in the breaking-down machine, and carries it to the top pair of rollers, whence it falls upon the first short screen; all that is fine enough to pass through is sifted out by the shaking action of the long screens below, and travels down upon whichever screen has meshes fine enough to retain it; the pieces too large to pass through the short top screen are carried to the next pair of rollers, and so on. At the lower end of the long screens are placed boxes to receive the different sizes of grain; the "chucks," or pieces too large for any grain, are again passed through the machine, while the dust which falls upon the wooden bottom, and is received in the innermost box, goes to the mills to be worked up for forty minutes as a dust charge. Formerly at Waltham Abbey both musket (F.G.) and cannon powder (L.G.) were granulated in the same machine at the same time, but dogwood charcoal being now used for small-arm powders, one descrip-tion only is usually made, so that but two long screens are required to define the higher and lower limits as to size of grain; for example, all that will pass through a 12-mesh and be retained upon a 20-mesh screen would be " rifle-fine-grain" (R.F.G.) powder, suited as to size for the Snider and Martini rifles. Modifications of this machine are used by private makers, the grain being usually separ-ated into various sizes by hand-sieves.
Pebble or cubical powders for heavy ordnance are granu- Cube-lated, or " cut," in special machines which divide the press- cutting cake first into strips, and then again cross-ways, into cubes macttine' of | inch and \ \ inch length of edge respectively. This is effected by two pairs of gun-metal or phosphor-bronze rollers, which have straight cutting edges arranged at suit-able intervals along their surfaces, the slabs of press-cake being fed vertically between the first pair of rollers. The resulting strips are carried along upon a board, by means of a skeleton band, which receives each strip of cake between two laths of wood; they then drop from the board upon an endless canvas band a little below, travelling in a direction at right angles to their previous motion, and are conveyed endways to the second pair of rollers. To prevent the strips of cake from fouling one another, the board upon which they first fall has a reciprocating motion given to it by means of an endless chain, one link of which is studded
FIG. 7.—Rollers of cube-cutting machine,
to a bracket underneath the board; consequently, as the board travels backwards, the strips are deposited at intervals, in echellon, upon the canvas band. The diagram (fig. 7) shows a portion of the machine. The cubes, &c, fall into a small reel fixed at a slope beneath the machine, which allows the dust and fragments to pass between its wires while the properly sized pebbles or cubes are delivered into boxes. The large li-inch powder has, however, afterwards to be picked over by hand.
All grain from the granulating machine is called " foul-grain," and has to be deprived of its dust in reels, consisting of a cylindrical frame-work about 8 feet long by some 2 feet in diameter, covered with a dusting cloth or canvas of from 18 to 56 meshes to the linear inch, according to the size of grain. These reels e.re either "horizontal" or "slope," according to the position in which they are fixed and the object in view. Slope-reels are open at both ends, fixed at an angle of about 4°, and are used for fine-grain powders as they come from the machine, when they contain more dust than the larger grain, especially if made from dogwood charcoal; the powder is poured in at the higher end, and received in barrels at the other end. The larger grained powders are dusted for about half an hour in a horizontal reel, with closed ends, the charge being from 250 to 300 It); one end of the reel is made to lower for the purpose of unloading. Both kinds of reel are enclosed in cases to receive the dust, which, as before, is sent back to the incorporating mills for 40 minutes or so.
The theory of glazing gunpowder has already been dis- Glazing, cussed. All descriptions are glazed, for varying periods, in glazing barrels or " churns" (fig. 8), which are usually about
FIG. 8.—Glazing barrels. A, elevation, showing door of case ; C, hoppers for loading ; B, section through barrel (showing opening in dotted lines).
5 feet long by 2 to 3 feet in diameter, and revolve some 34 times in a minute; however, barrels of much greater diameter and less length are occasionally employed, revolving at a slower rate. The charge for each barrel is ordinarily 400 lb, and the fine-grain powders are mixed with a proportion of the " chucks " or larger pieces, which are after wards sifted out. The glazing process causes a great alteration in the appearance of the grain, especially in that made from dogwood; the dull brownish hue is replaced after a few hours by a fine black colour with more or less polish. Some powders are glazed from 10 to 12 hours, a considerable amount of heat being generated by the friction. Fine-grain powders are again passed through the slope reel after glazing.
Stoving. AH kinds of gunpowder are dried in the same manner. The " stove," or drying room, is fitted with open framework shelves or racks, the heat being produced by steam pipes underneath. The powder is spread upon either copper trays or wooden frames with canvas bottoms, each capable of holding about 12 lb, which are then placed upon the racks. Not more that 50 cwt. may be dried at one time. The length of time required for stoving depends upon the nature of the powder, and the proportion of moisture it contains; it varies from about twelve hours for fine-grain up to three or four days for the very large cannon powders; the heat ranges from 120° to 145° Fahr., the temperature being gradually raised or lowered. It is most important that a stove should be well ventilated, so that a constant current of hot dry air may be supplied, and the air charged with vapour carried off; if this be not done effect-ually, the moisture would be recondensed upon the powder as the temperature was lowered. Finish- The drying process produces a small portion of dust mg- which it is necessary to remove; but the finishing process has, especially upon the fine-grain powder, a much more considerable effect than the mere removal of dust. It is usually finished by being run from two to three hours in a horizontal reel (see fig. 9), the charge being 300 lb, and acquires a very glossy appearance, if the quality be good, even without the addition of graphite, which is very com-monly added to sporting gunpowder. Large cannon powder, such as " pebble" and " cubical," is finished in large skeleton wooden reels, shaped like barrels, and enclosed in cases ; after being run for about three quarters of an hour,
Fig. 9.—Horizontal Dusting Reel (longitudinal section). A, cylindrical reel ; B, reel case ; G, apparatus for lowering one end for unloading; D, hopper for loading; E, opening in reel for loading ; F, barrel for unloading into.
Upon the introduction of very heavy ordnance, firing large charges, it was found that the ordinary (L.G. or K.L.G.) cannon powder was too sudden in its action, owing p0wder to the whole charge being consumed before the projectile for very had sensibly moved from its seat in the bore, thus causing nea-py a most violent strain to the metal of the gun. To obviate guns' this defect, the grains or pieces were made much larger, so as to diminish the total surface of combustion, and, con-sequently, the volume of gas evolved at the first instant of explosion; the powder was also given a considerably higher density, which retarded its combustion. These changes resulted in the adoption of the pebble and cubical powders, already mentioned, in England, and in America, of "Mammoth" powder, consisting of large, irregular-shaped American grains (h, fig. 10) from 0"'6 to 0"-9 in size ; an improvement mam-has since been made in this powder by pressing it in uni- moVa_ form-sized pieces, of the shape shown in i, fig. 10, being the frusta of two hexagonal pyramids, separated by a pris-matic space left rough.
a small portion of the purest graphite (2 oz. to 400 tb of powder) is introduced in muslin bags, and the powder is run for a short time longer. This skeleton reel will hold a whole " glazing," as the contents of four glazing barrels is termed, being about 16 barrels of 100 tb each, and advantage is taken of this finishing process to mix together a number of glazings, so as to get a batch of 50 or 100 barrels giving uniform results at proof. These batches are afterwards " blended " together in four-way hoppers, with others of opposite character, should they not in all respects be up to specification, and any quantity of gunpowder so finished or blended as to give identical results at proof is termed a brand, and receives a distinctive number.
The figures a to h show the relative sizes and shapes ot grain now commonly employed for military purposes in Europe and America, except that the three largest powders —pebble (e), prismatic (f, g), and cubical Qi)—are figured half the real size to save space, whereas the remainder indicate the actual dimensions of the grains. Powder for small-arms is represented in a; all the other descriptions are intended for cannon of various sizes.
The improvements above described materially lessen the Rodman's initial strain, at the expense of requiring a longer gun to perfor-burn the powder completely, but it still remains true that, ^rtrid^e even with a charge composed of large, dense pieces, the evolution of gas is greatest at the commencement of com-bustion, and decreases as the grains burn away, although the space occupied by the gases increases as the shot travels along the bore. This is exactly the opposite of what should theoretically take place, and causes the maxi-mum pressure to be exerted before the inertia of the pro-jectile has been overcome. So far back as 1860, these con-siderations led General Rodman, the eminent American artillerist, to employ, in the experiments with his 15-inch and 20-inch cast-iron guns, what he termed a "perforated cake cartridge," composed of discs of compressed powder from 1 to 2 inches thick, and of a diameter to fit the bore, pierced with holes running parallel to the axis of the gun. In his Properties of Meted for Cannon, and Qualities of Cannon-Powder (Boston, 1861), Rodman demonstrated mathematically that such an arrangement of the charge would relieve the initial strain by exposing a minimum surface at the beginning of the combustion, while a greater volume of gas would be evolved from the increasing sur-faces of the cylindrical hollows as the space behind the pro-jectile became larger; this would tend to distribute the pressure more uniformly along the bore. The results of experiment perfectly bore out his theory, but he found it more convenient for several reasons to build up the charge in layers of hexagonal "prisms" of comparatively small size, fitting closely to one another, instead of having the cakes or discs as large as the bore. Pris- The civil war in America most probably interfered with matic the further development of General Rodman's powder, but powder, j.jjg j(jea wag taken up by a Russian military mission in the United States, and resulted in the manufacture on a large scale by Russia of what is now known as " prismatic powder." It has since been adopted in Germany for use in all heavy rifled ordnance; for the very largest guns, such as Krupp's 70-ton gun, this powder has been recently made with one central hole, having a higher density (1'78) than the original seven-hole prisms, which were about 1'68; the external dimensions are the same, 1 inch high by 1'36 in diameter. The prisms are so arranged in the cartridge that the hollows are continuous throughout. Mode of Prismatic powder represents a distinct class, the manu- peculiarity of which is that each grain or piece is pressed facture. geparateiy jn a metal mould. In the British service, powder for heavy rifled guns, in the shape of small cylindrical pellets, with a hollow half-way through, was made some twelve years since, but has been superseded by the pebble or cubical powder cut up from press-cake. To make this class of gunpowder, whether prismatic or cylindrical, we need—-(1) a mould in which to place the meal or granulated powder; usually a number of moulds are contained in one plate ; (2) a punch to fit each mould accurately with which to compress the powder, and needles to form the perforations; (3) an appliance for pressing the finished pellets or prisms out of the moulds; or this may be done by the punches themselves, if the moulds are closed by a removable upper plate.
The requisite pressure may be given either by hydraulic machinery, as at Waltham Abbey, or by means of a cam or eccentric on a shaft driven by steam or water power, as in the Russian and German prismatic machines. By the former plan a large number of pieces may be pressed slowly at one operation, but by the latter only about six prisms can be formed at a time; the machine, however, works very quickly, and has a small hopper for the meal or grain, and a self-feeding apparatus, the mould plate sliding backwards and forwards, so as to be alternately underneath the hopper and punches. Self-feeding machines of this nature are found to get clogged when used with powder-meal, and this was doubtless the chief reason why granulated powder was first used; the size of grain is about that shown in fig. 10, b. It is probable that a more uniform density could be given to the prisms by hydraulic pressure than by the cam arrangement; the latter is said to exert a maximum pressure of 2000 lb on the square inch. The prismatic powder only needs careful drying at a moderate heat to finish it.
It has been found that all powders thus made possess less explosiveness than those granulated or cut up from press-cake; the smooth surfaces of the pieces apparently afford little hold for the flame, and thus they ignite slowly; by some this is considered a defect, but by others an ad-vantage. For this reason, as well as those already detailed, prismatic powder strains the metal of the gun less, in pro-portion to the velocity obtained, than pebble or cubical, but, to give the projectile an equal velocity, the charge of prismatic must be considerably larger. The cost would probably be also greater, weight for weight.
PROOF OF GUNPOWDER.
The tests to which powder is subjected, are as follows :—
1. For proper Colour, amount of Glaze, sufficiently hard and crisp Texture, and Freedom from Bust. —Thesepoints can be judged by the hand and eye alone, and require a certain amount of experience in the examiner. The cleanness of the powder is tested by pouring a quantity from a bowl held 2 or 3 feet above the barrel; if there be any dust it will be thus easily detected. If it is injured by damp there will be little or no dust, but the grain will be "rotten," and may be broken between the fingers; minute crystals of salt-petre may be also detected on the surface in a good light.
2. For proper Incorporation.-—By " flashing, " that is, burning a small quantity on a glass, porcelain, or copper plate. The powder is put in a small copper cylinder, which is then inverted on the flashing plate; this provides for the particles being arranged in nearly the same way each test, which is very important. If the powder be very large, it must be broken up and sifted to a certain size through a small hand-sieve. Properly made gunpowder should "flash," or puff off, when touched by a hot-iron, with few " lights" or sparks, leaving only some smoke marks on the plate. A badly incorporated powder will give out a quantity of sparks, and leave specks of uncombined salt-petre and sulphur, forming a dirty residue. Powder made from very slack-burnt charcoal, or which has been injured by damp, will always flash badly.
3. For Shape, Size, and Proportion of the Grains.— Shape can be judged by the eye only, and the size of large powders can be measured, or the number of pieces to 1 B> counted; granulated powder may readily be sifted upon the two sieves which determine its higher and lower limits of size. The proportion of different sized grains is ascer-tained by using three or more sieves. For example, the Government small-arm powder is sifted with 12-mesh, 16-mesh, and 20-mesh sieves; all must pass the first, not less than three quarters be retained upon the second, and only one-sixteenth part is allowed to pass the last-named sieve.
4. Density.—Formerly this was ascertained by "cubing," or finding the exact weight of a carefully constructed box of known contents, when filled with powder in a particular manner. But as this plan gave only an approximate result, a mercurial densimeter has been substituted, by means of which the density can be ascertained to three places of decimals. Briefly, the machine determines with great accuracy the weight of a globe when it is (a) filled with mercury alone under a certain pressure, and (b) filled with a known weight (say 100 grammes) of powder and mercury under precisely similar conditions; then, if S be the specific gravity of mercury at the time of experiment, W the weight of globe filled with mercury alone, and W the weight when filled with powder and mercury,
5. Moisture and Absorption of Moisture.—The amount of water contained in gunpowder is found by drying a carefully-weighed sample in a water oven for a certain period; from the weight lost, when allowed to cool out of contact with the air before weighing, the percentage of moisture can be calculated. The hygroscopic test consists in exposing a. dried sample in a box, kept at a uniform temperature, to an atmosphere artificially saturated with moisture, and ascertaining the increase of weight in a certain time.
6. Firing Proof.—The nature of this will depend upon the purpose for which the powder is intended. For sporting powders, it will consist in the " pattern " given by the shot upon a target at a given distance, or, if fired with a bullet, upon the " figure of merit," or mean radial deviation of a certain number of rounds; also upon the penetration it effects through boards. For military purposes the powder is now always fired from the rifle or piece of ordnance with which it is to be used, and the initial or " muzzle " velocity ascertained by the Le Boulenge electric chronograph (see GUNNERY), which measures the exact time the bullet or other projectile takes to traverse a known distance between two wire screens. By means of the " crusher gauges" alveady referred to, the exact pressure per square inch upon certain points in the interior of the bore can be found; the maximum pressure can be considerably modified by increasing the cubic air-space given to the charge in the powder chamber. The figure of merit is also taken for small-arm powder.
All gunpowder made by or for the British Government is subjected to very strict limits of specification upon all the above-named points.
Bibliography.—Vanucchio Biringuccio, De la Pirotechnia, Venice, 1540; Tartaglia, Quesiti e invenzioni diversi (lib. iii.), Venice, 1546; Peter Whitehorne, How to make Saltpetre, Gounpowdcr, &c., London, 1573; Nic. Macchiavelli, The Arte of Warre, transl. by White-horne, London, 1588; Hanzelet, Recue.il deplusiers Machines Mili-taires, Paris, 1620; Boillet Langrois, Modelles artifices de feu, 1620; Kruger, Cliemical Meditations mi the Explosion of Gunpowder (in Latin), 1636 ; Collado, On the Invention of Gunpowder (Spanish), 1641 ; The True Way to make all Sorts of Gunpowder and Matches, 1647 ; Hawksbee, On Gunpowder, 1686 ; Winter, On Gunpowder (in Latin); Kobins, New Principles of Gunnery, London, 1742 (new ed. by Hutton, 1805); Stahls, On the Nature and Utility of Saltpetre (German), Leipsic, 1748 ; D'Antoni, Essame della Polvere, Turin, 1765 (transl. by Capt. Thomson, E.A., London, 1787); Count Rumford, "Experiments on Fired Gunpowder," Phil Trans. Roy. Soc, 1797 ; Cossigny, Recherches phisiques et chèmiques sur la fabrication de la poudre à canon, Paris, 1807 ; Bottée et Riffault, Traité de l'art de fabriquer la poudre à canon, Paris, 1811 ; Renaud, Instructions sur la fabrication de la Poudre, approuvées par le Ministre de la Guerre, Paris, 1811; Hutton, Mathematical Tracts (vol. iii. ), 1812; Sir W. Congreve, A Short Account of Improvements in Gunpowder made by, London, 1818 ; Fraxno, Tratado de la Teoria y Fabrication de la Polvora en General, Segovia, 1817; Coleman, " On the Manufacture and Constituent Parts of Gunpowder," Phil. Mag., vol. ix.; Braddoek, Memoir on Gunpowder, London, 1832; Col. Omodei, Dell' origine della polvere da guerra, Turin, 1834 ; Proust, Mémoires sur la poudre à canon, Paris ; Timmerhaus, Descriptions des divers procédés de la fabrication de la poudre à canon, Paris, 1839 ; Wilkinson, Engines of War, including the Manufacture of Gunpowder, London, 1841 ; Major Mordecai, Experiments with Gunpowder in Washington Arseiml in the years 1843-4, Washington, 1845 ; La Cabane, De la poudre à canon et de son introduction en France, Paris, 1845; Reinaud et Favé, Du feu Grégois et des origines de la poudre à canon, Paris, 1845; Bunsen and Schiskoff, "On the Chemical Theory of Gunpowder," Poggendorff's Annalen, vol. cii., 1857; Scoffern, Projectile Weapons of War and Explosive Compounds, London, 1858 ; Gen. Piobert, Traitédj'Artillerie, Propriétés et Effets de la Poudre, Paris, 1859; Gen. Rodman, Experiments on Metal for Cannon, and Qualities of Cannon Powder, Boston, 1861 ; Napoleon III., Études sur le piasse et l'avenir de l'Artillerie, vol. iii., Paris, 1862; Anderson and Parlby, On the Manufacture of Gunpowder at Ishapore, London, 1862; Von Karolyi, "On the Products of the Combustion of Gun Cotton and Gunpowder," Phil. Mag., Oct. 1863 ; Count de St Robert, Traité de Thermodynamique, Turin, 1865 ; Capt. F. M. Smith, Handbook of the Manufacture and Proof of Gunpowder at Waltham Abbey, London, 1870; Berthollet, Sur la force de la Poudre, Paris, 1872; Sarrau, Effets de la Poudre et des Substances Explosives, Paris, 1874 ; Noble and Abel, Fired Gunpowder, London, 1875 ; C. L. Bloxam, Chemistry (art. "Gunpowder"), 3d ed., London, 1875 ; Notes on Gunpowder and Gun Cotton, published by order of the Secretary of State for War, London, 1878. (W. H. W.)
Footnotes
1 As before stated, Piobert gives reasons for halving these figures.