GUNPOWDER

THE invention of gunpowder is popularly ascribed to Barthold Schwartz, a German monk and alchemist; and the date of the discovery is further supposed to have been in 1320. The prior claims of our countryman, Roger Bacon, whatever they be, are however unquestionable, as this substance is described in his writings about the year 1270, or fifty years before the time of the supposed discovery of Schwartz. But even Bacon has as little title to this invention as his supposed rival; nor, indeed, when we examine his own description of this then wonderful compound, do we perceive that he makes any claim to have been the discoverer. On the contrary, he quotes it as a well-known substance, in common use all over the world for making squibs to amuse children. So pertinacious are vulgar errors. The passage in Bacon stands as follows: "Ex hoc ludicro puerili, quod fit in multis mundi partibus, scilicet, ut instrumento facto ad quantitatem pollicis humani, ex violentia salis qui salpetra vocatur, tam horribilis sonus nascitur (this is the description of a parchment cracker) "in ruptura tam modice pergamene, quod fortis tonitru rugitum et corrosionem maximam sui luminis jubat excedit." Thus the claim is shifted without difficulty from Bacon, and, as Dutens thinks he can show, is removed to Magnus Græcus, whose manuscript he quotes, and from which he presumes that Bacon derived the invention; although, by his own showing, Bacon need not have consulted an obscure writing for an invention of general notoriety. The title of the manuscript in question is as follows: "Incipit Liber Ignium a Marco Græco perscriptus, ejus virtus et efficacia est ad comburendum hostes, tam in mari quam in terra;" so that even the military uses of gunpowder were then known. In the same manuscript are contained directions for making a rocket, which we dare not quote on account of its length; but it is such as to prove that the nature of this fire-work was thoroughly understood. It is even remarkable that he recommends particularly the charcoal of willow wood, which we moderns have found by experience to be amongst the best for all the purposes of gunpowder.

Thus far, although we have not fixed the date of the invention, we have carried it, not only beyond Bacon, but even beyond this supposed predecessor; as he himself does not pretend to be the inventor, but the compiler, of a Liber Ignium, or treatise on pyrotechny. If, in attempting to ascend still higher, the evidence becomes more rare and more obscure, there are still insuperable facts to prove that its antiquity is far greater, however impossible it may be to approximate to the date of the invention, far less to assign that which seems buried amongst the obscurities of oriental learning. The question of gunpowder, as applied to artillery, is a separate one; but there is abundant reason to believe that this compound was not only used in some form or other as an explosive and combustible substance, but was even applied to military purposes; it may be, in the shape of rockets or other fire-works, which, for objects of amusement at least, have been familiar to the Chinese beyond all record.

The earliest date to which we can refer the knowledge of gunpowder, in defect of a sufficiently remote acquaintance with oriental history, is 355 before Christ; although, from the very nature of this evidence, it follows that it was then not only known to the eastern nations, but that it must have long been so; since, even at that early period, it was applied to warlike purposes. In the code of Hindu laws, indeed, where it is mentioned, it is referred to

a period which oriental antiquaries have considered as coincident with the time of Moses. But the evidence to which we more particularly allude is found in a passage of the Life of Apollonius Tyaneus by Philostratus; the purport of which is, that Alexander was unwilling to attack the Oxydrace, who lived between the Hyphasis and the Ganges, because they were under the care of the gods, and overthrew their enemies with thunder and lightning, which they shot from their walls. The same tale is told of the repulses experienced in this country by Hercules and Bacchus.

The next of these early dates, in which also our evidence is imperfect, is 212 before Christ; but the establishment of the truth of the last would render this one more credible. In the defence of Syracuse by Archimedes, Vitruvius relates that one of his engines threw large stones with a great noise; a description which does not apply to any of the mechanical artillery of the ancients. On a notice so superficial, we must not, however, lay too much stress; and here ends all the information which we have yet procured respecting the earliest knowledge of gunpowder. It seems, however, to be so decidedly capable of being traced from the East, through the intervention of the Arabs, that there can be little doubt of its being on oriental invention, and of its being thence imported into Europe; and, indeed, the military use of rockets in the armies of India ascends to a period beyond record.

Of the earliest period at which it was known in China, we have, in defect of their own evidence, only the testimony of Uffano, an Italian author, who affirms, that not only gunpowder, but ordnance, was in use in that nation in the year 85 of our era; and that cannon were, in his day, remaining from the most ancient times, in some of the maritime provinces, made both of iron and brass. Hence some writers presume that the Chinese communicated the invention to the Indians; whilst it has also been said, but on no sufficient authority, that they themselves received it from Tartary; a nation respecting which we know little or nothing, and in which we should not be inclined to look for an early acquaintance with the arts. This, however, refers to a date so late as 917; so that, if there is any dependence to be placed on the Indian and Chinese hypothesis, the Tartars must themselves have borrowed the invention from those to whom they are said to have lent it.

There is after this a long blank; and the first author on the subject that we have discovered is in 1249, twenty years before the date of Bacon's narrative. This is an Arabic writer, in the Escorial collection, who is translated by Casiri. His description is such that it may apply both to rockets and to shells. In the former case, it only proves the knowledge of the detonating compound; the latter, were it proved, would show that they were also acquainted with the use of ordnance, although it is not impossible but that such projectiles might have been thrown by mechanical artillery.

As the invention of gunpowder has been popularly attributed to Bacon and to Schwartz, so the use of ordnance has been referred to the time of the field of Cressy, or 1346. To pass over the Chinese hypothesis on this part of the subject, we shall find that cannon were known at least as early as 1312. This we derive from the source quoted by Casiri; from Arabian writers, who describe the use of ordnance in 1312 and 1323; whilst, if Barbour is to be trusted, Edward III. was also provided with some pieces of artillery in 1327; and Père Daniel asserts that cannon

un- were known to the French in 1338. We need not carry this discussion lower; though, in favour of the oriental origin of this invention, we would still remark, that artillery was much in use in the Mediterranean when it was still but little used elsewhere; as by the Venetians against Genoa in 1380, and by Alphonso XI. in his wars against the Moors.

Composition of Gunpowder.

The present composition of the Chinese corresponds so nearly with our own, that the difference is nearly insensible; but whether it had arrived at that degree of perfection in their ancient periods, we have no means of knowing. Neither can we judge of its nature and power as known to the Arabs. But, in our own country, it was very late in arriving at its present state of perfection; nor do the various proportions given by one of our earliest writers on the subject argue much in favour of their chemical knowledge, or turn for experiments. Peter Whitehorn, who wrote in 1573, gives numerous proportions, without seeming well aware of their respective values; and, respecting some of them, it is easy to see that they were scarcely fit for squibs, much less for the purpose of projecting shot. Such is nitre, sulphur, charcoal, equal parts; whilst, in the very opposite extreme, we have nitre 12 parts, sulphur and charcoal, of each 3 parts; and, still worse, nitre 27 to 3 of the other two ingredients; or nitre 48 parts, with 7 of sulphur and three of charcoal. Here, such as these compositions are, want of experience can scarcely be pleaded, as they are not better than those given by Nye in 1380. In France also, the composition, at no very remote period, was, nitre 50, sulphur 16, charcoal 34; from which it varied to, nitre 67, sulphur 13, charcoal 20, and to nitre 84, sulphur 8, charcoal 8; these differences being supposed necessary for the larger cannon, and the smaller progressively, and the last being their musket powder.

But as we cannot afford space to describe the gradual progress of improvement in the composition of gunpowder, we shall now state the proportions at present in use in different nations. They do not materially differ from each other, although it is unquestionable that they are not all of equal power.

matters. Cheapness being the leading object where it is only made for sale, and the nitre being the only expensive article, the proportion of this is diminished, and those of the other two ingredients increased. The worst is made for the Guinea trade; and, if we are not misinformed, that for the Canada trade is nearly as bad, whilst the next upwards in the scale is that sold to Turkey. We have never met with any specimen in which there was less than 62 of nitre; but we have reason to believe that some of the inferior kinds do not contain more than 50. For the use of miners it also is made with a low proportion of nitre, producing advantages in mining not intended by the makers, whose only object was to manufacture a cheap article. But the proportions of all the commercial powders are very inconstant, even when furnished bona fide to government, as it is impossible to prevent the workmen from purloining the nitre, and replacing it with the cheapest ingredients.

It is not for want of experiments if greater uniformity has not been attained in these compositions, and if all adhere to their own. Baptista Porta was one of the first who made accurate investigations on this subject; and, as long ago as the year 1515, he fixed on the proportions now used in France. Beaumé, some time ago, fixed on 80 of nitre, 5 of sulphur, and 15 of charcoal; and the opinions of Morveau, Chaptal, and Proust, are displayed in the preceding table. It is easy to account for these differences of opinion, when we recollect the numerous accessory circumstances which modify or vitiate the results obtained from practice. With the very same power it is scarcely possible to procure uniform ones, as is well known to artillerists; and hence, from practice alone, unless after an enormous number of trials, no certain conclusions can be drawn. It will, indeed, appear that, under various proportions, the effects may really be the same; because, as the force of powder depends partly on the quantity of gas generated, and partly on the heat to which it is raised, any deficiency on the one hand may be compensated by an increase on the other. Thus, as the greater quantity of gas is produced by the largest proportion of charcoal, the greater heat is caused by augmenting that of the sulphur. In all the trials that have been made in this country, no reason has been found for varying from the proportion 75 nitre, 10 sulphur, and 15 charcoal; and the same is used for arms of all calibres, the only difference for the respective arms being made in the sizes of the grains.

It is proper, on this subject, to state, that whilst the explosive power depends fundamentally on the quantity of gas that is permanently generated, that gas is almost entirely produced by the combustion of the charcoal; the nitre being the cause of that combustion, and furnishing one part of the generated gas from its decomposed acid, as it does the other by converting the charcoal into carbonic acid. Were nothing else required, therefore, to produce the effect, the best powder would consist of nitre and charcoal alone, as the sulphur consumes a considerable part of the oxygen of the nitric acid, without adding any thing to the permanently elastic gas. But as there are two other important elements in this problem, namely, the rapidity of the inflammation and the heat, the sulphur becomes an indispensable ingredient; whilst, by expanding the gas at the moment of explosion, it more than compensates for the diminution of permanent bulk which it causes. Perhaps, on this compound view of the subject, M. Beaumé's composition is really the best, abstractedly considered, as the nitre is sufficient to burn the whole of the sulphur and the charcoal also, and as both the degree of heat and the quantity of gas seem to be best balanced for the intended effect. But a composition of this accurate nature requires equal accuracy of mixture and

The proportions in the commercial gunpowder of England vary indefinitely, according to the views of the manufacturer respecting the markets, the price, and other

manufacture; and as that is scarcely attainable on the great scale, it is found better so to increase the sulphur and charcoal as to ensure the total decomposition of the nitre, this being further an object of economy.

Sportsmen, as well as artilleryists, ought to know that the fouling of their barrels after firing is in a direct ratio of the weakness and badness of their powder; and this effect is most completely obviated by using M. Beaumé's, or any similar mixture. Not only does the feebleness of such powder prevent the barrel from being swept clean at the explosion, but as the foulness consists chiefly in a mixture of the carbonate and sulphate of potash with charcoal, that becomes necessarily greatest wherever the nitre is reduced in quantity for the purpose of introducing the cheaper ingredients. The analysis of powder, at least as far as that ingredient is concerned, is so easily made, that every one who feels an interest in his success as a sportsman should examine what he uses, as the very worst mixture can be rendered beautiful to the eye by a minute grain and a high polish.

The British government use but one proportion for all services. As far as artillery and musketry are concerned, we do not consider this as of much moment; or that any material object would be obtained by using different ones proportioned to the respective calibres. But we consider that they commit a great error in adopting the same for the mining service; and that some of the failures caused in our wars, in attempting to blow up works or demolish bridges, have been produced by the very excellence of the powder, in short, by its too great strength. To take the case of common blast-mining as a simple one, and to put the extreme case of all: If it be attempted to spring a rock by the powder of chlorate of potash, either the plug will be blown out, or a very narrow space round the mine will be broken. With the best musket or cannon powder the same effects, but in a less degree, follow. Here the miners' powder, which seldom contains as much as sixty per cent. of saltpetre, is effectual; and, what is more, it is rendered still more active by being damp from careless keeping, or from remaining some time in the mine before it is fired. Mathematicians will immediately see the solution of this apparent incongruity, by recollecting that the element of time is an ingredient in the problem. With too great a velocity the parts of the general mass nearest to the acting force are disintegrated; so that not only is the force expended in this act, but the gas thus escapes from the opening. With a power acting more slowly, the whole mass, or a much larger one at least than in the first case, is moved; and thus the rock is widely shaken, although not blown into the air. It will be found practically, that the further the fragments are dispersed, the less is the effect; and thus the mine which is most dangerous to the workmen, is also the least efficacious.

It is from this variation respecting the power of gunpowder, hitherto unattended to, from confounding impulse and pressure, to which at least it bears a certain relation, that so many different opinions have been entertained respecting the force of powder in particular cases. Hence also have arisen various projects for increasing its efficacy; amongst which quicklime has been repeatedly recommended. In mining it does actually increase the effect, though not the force. On the contrary, it diminishes the force; and it is from that very cause that it is more effectual in mining or shaking a rock. The same object can be obtained by a mixture of saw-dust; but it must also be remembered that this will not happen unless good powder be used. Ordinary miners' powder will not often bear this kind of dilution. It is easy now to apply this principle to military mining, where the object is to produce as extensive a shock as possible. Mathematicians

have calculated the globes of compression for certain charges; but it will be found that these vary so much, according to the strength of the material, that the conclusions cannot be depended on. This is a very important problem, however, because the destruction of a work depends on the area of the base of the paraboloid, or whatever else the figure be, which the explosion produces. We dare not, however, enter further on this subject, as it would lead us beyond our limits.

On the Choice and Examination of the Materials.

Nitre, as it is imported from India, whence all that is used in this country is procured, is mixed with much dirt and with some salts, consisting chiefly of the nitrates and muriates of lime, and of muriate of potash. As the deliquescent salts, in particular, are extremely injurious from their property of attracting moisture, it is most important that the nitre to be used in gunpowder should be thoroughly refined. For this purpose rain-water ought to be used if possible, and if not, such river or other waters as are found, on trial by the appropriate tests, to contain the least quantity of saline matters. The nitre is first boiled, and the grosser impurities separated by filtering through hempen bags, after which it is crystallized. After draining, one washing is sufficient to render the first crystallization sufficiently pure; but the subsequent ones require repeated solution and crystallization before all the foreign salts can be separated. We need not, however, dwell on this subject, and shall only add, that no nitre ought to be used unless it will stand the tests of nitrate of silver and of carbonate of potash, without exhibiting a precipitate.

It is held necessary that the nitre should be thoroughly dried; and, accordingly, much unnecessary labour is bestowed on this subject, since it must be moistened in the mill when the composition is submitted to the rollers. The only real use in drying it is to enable the workman more easily to allot the true weight, which might equally well be done by an average and an experiment. We should scarcely have noticed this, but that the French manufacturers boast much of the superiority which they derive from reducing the nitre to minute crystals, by agitating the solution. In the royal mills it is further the practice to fuse the nitre into large cakes. By this method it is speedily dried, easily stored away, and protected from depredation. These advantages are held to be sufficient to compensate the expense; but it ought to be remembered that there is a degree of hazard in the process, as, if the salt should be overheated, it might be so far decomposed as to have a portion of potash united with it.

Sulphur, as it is received from Sicily, the great emporium of this commodity, is mixed with a considerable proportion of lime, whilst a portion of it is also combined with that substance, forming calcareous hepar, or sulphuret of lime. From this and the grosser accidental matters it is purified by melting; the sulphuret and the earth subsiding to the bottom of the mould, so as to admit of being mechanically separated. This residue, yielding no more pure sulphur by that process, is afterwards submitted to distillation. When the sublimed material is to be used, it requires previous washing, till it be entirely freed from the sulphuric acid adhering to it, and it may be tested for this purpose by means of the muriate of barytes. The fused sulphur, if doubted of, may be submitted to combustion, and the residue noted; but a little deficiency in the purity of this ingredient is of no moment.

With respect to the charcoal, there is considerably more nicety required than is generally imagined. The soft woods have been preferred from time immemorial, since even in the receipt of Magnus Græcus, formerly quoted, the willow is mentioned. The poplar and many others have been used abroad; but in this country those com-

monly adopted are the white willow and the alder. Even among these soft woods there is a considerable difference, as our own experiments have shown; and in them it was proved that the greatest explosive power, ceteris paribus, was produced by the wood of the Rhamnus frangula, commonly called black dogwood, as we shall show more particularly hereafter. The hard woods are invariably rejected, and with justice; though the reasons for this practice, which are derived from the presence of salts in these, are not the causes of their inferiority, certainly not the only ones. It is nevertheless true that no wood which contains carbonate of potash, or other deliquescent salts, is fit for the purpose, and for the most obvious reasons. This is the case in the oak, elm, fir, and other trees. But there is another reason for the badness of these kinds of charcoal, the cause of which is not so obvious, although it is evidently connected with their hardness. To us it appears to depend on the small proportion of hydrogen combined with the carbon in these charcoals, compared to that which exists in the produce of the softer woods. Even these can be reduced to the same state by overheating. Thus the hydrogen is dissipated, and the charcoal becomes so hard as to scratch steel; in which case, however obtained, it is always unfit for powder.

As this subject is yet obscure, from our imperfect acquaintance with the true nature of charcoal, and with the modifications of which it is susceptible, it becomes necessary to have recourse to experiment, for the purpose of determining, at any rate, the proximate cause of this difference in the explosive powers of the several kinds. Various trials have accordingly been made, as well by ourselves as by the French chemists; and, for brevity's sake, we add the most important results in the subjoined table. We are not informed of the process which was adopted by the French for measuring the gas; but in our own we had recourse to the pneumatic apparatus, using it in the manner which is described in another part of this article for collecting the total produce of the combustion of gunpowder. The mixture, in the French experiments, consisted uniformly of 60 parts of nitre and 12 of the charcoal submitted to trial. In our own they were varied, and the results taken from those in which the combustion of the charcoal was completed, and the quantity of gas the greatest. As no more nitrous acid could be decomposed than there was coal present to burn the oxygen, it is plain that in these the results are correct.

These results are such as to prove that there are important differences in the produce of gas; but, with regard to practice, they are of very little value, as few of the substances submitted to trial could be used. To admit of comparison between our own experiments and these, we shall reduce our proportions to the same standard, by taking our scale from the filbert at 72. We neglect the

residue, knowing that it proves nothing, as the results are uncertain, in consequence of the irregular absorption of water, and partly from the impossibility of collecting the solid and the gaseous matters both from one charge.

These various results, and some others which we have thought it unnecessary to record, may in a certain degree depend on inaccuracies in the experiment; but in the greater number they arise from real differences in the charcoals from the same substance, produced, as we before insinuated, by overheating. This is apparent in the two cases above cited of oak and willow; but in some trials, the differences were even greater. Coak and animal charcoal are particularly liable to vary.

It is evident from the preceding table that the best charcoal for gunpowder must stand in the following order: Black dogwood, willow, alder, filbert. From the French tables, in which we do not, however, place much confidence, we may add, consecutively, hazel and the spindle tree; but our own trials raise these to 70 at least in the scale. Such, at present, are the results of these trials as to the best charcoal; but we are by no means satisfied that we have yet found out the best wood for this purpose. The experiments are laborious; yet we think the subject deserving of more attention than has yet been bestowed on it. With respect to coak and animal coal, they stand very low in the scale, as the over-hardened wood-coals do; and, in all cases, there is a direct relation between the produce of gas and the facility of combustion under ordinary circumstances.

To satisfy ourselves by trials of a more direct nature, and more applicable to practice, we chose a method derived from the flight of rockets, as less liable to disturbance from collateral causes than any practice with pieces of ordnance. The rockets were of compound dimensions, and were all made with the same proportions, and driven by the same hand, so as to ensure all possible uniformity, the only variation being in the nature of the charcoal. The vertical elevations were taken by two quadrants at the same time, and all the flights that deviated from the perpendicular rejected. The mean vertical ascent, of a great number of those made with willow, alder, and dogwood, was 480 yards; but between these three coals, the differences were so great as to give various results, which may be represented by the following numbers:

Greater accuracy is not attainable in this way, as may easily be conceived by those who know by how many collateral circumstances a rocket is influenced; but these trials are quite sufficient to justify the general inference made from the experiments in the pneumatic apparatus.

It has been held that the charcoal for gunpowder ought to be made in cylinders or retorts by distillation; and this expensive process is consequently universally adopted. It

is doubtful if this is not a mistake of the causa pro non causa. Pit charcoal being made in coppice woods, is always the produce of oak; and it is probable that this wood, if charred in close vessels, would be even worse than it is now. There is more danger of overheating in the retort than in the pit, while the wood is not better burned; and hence, by a careless management of the process, even the charcoal of willow or alder may be rendered as bad as that of oak. Considering these various circumstances, charcoal requires to be submitted to three tests. It ought to act as little as possible, mechanically, even on copper; it ought to exhibit no salts on being treated with boiling distilled water and tested; and it ought to be thoroughly burned. The best test of this latter circumstance is its giving out no smoke when heated.

A new and economical method of distilling charcoal was not long ago invented by Sir William Congreve. Subsequently, but without any knowledge of what had been done, as we understand, the same process was suggested in America by Dr Bollman, to whom we are indebted for the present cheap method of purifying pyroligneous acid, and rendering it a substitute for common vinegar. In this beautiful process the retorts or cylinders are ranged in a row, a gas pipe from each being conducted to the bottom of the next in succession. By means of a fire under the first alone, the distillation of the whole may be conducted together; the gas which issues from that one being sufficient to char the next, and so on in succession to the end of the chain. The acid is collected in this case, as in others, by means of a separate pipe arising from a lower point in the retort.

Before we dismiss this very important and somewhat neglected department of the gunpowder manufactory, we must point out a circumstance with respect to charcoal, that requires an attention which it has never yet experienced. This is the property which it possesses of absorbing and retaining water, and which we have ascertained to be different in the different kinds of wood; although we have had no opportunity of investigating fully that which is here recommended to the attention of powder manufacturers.

It is from this hygrometric power that gunpowder attracts moisture, even when the nitre has been perfectly purified; a circumstance which materially interferes with its rapidity of inflammation, and consequently with its strength. But as the various hygrometric powers of different charcoals have never yet been properly examined, we can communicate no information on this subject which is worth recording.

On the Manufacture of Gunpowder.

Grinding. The first part of the process consists in pulverizing all the ingredients separately, after which they are weighed and mixed in a general and rude manner before being submitted to the mill. In France, and in some other countries, a pestle engine is used, or a stamping-mill; but it is subject to more hazard and inconveniences than the grinding-mill which is adopted in this country. This is formed on the model of the common bark-mill, and with two rollers at different distances from the axis, so as to cover the whole bed. The weight of each roller is commonly about three tons, and they are generally made of limestone, although iron cylinders have been adopted in some works. The bed, which is surrounded by a wooden margin, is of the same materials; and the whole house is built of slight framed wood, to diminish the evils that might arise from a casual explosion. A wooden rake follows the rollers, for the purpose of bringing the mixture under the cylinder; and the motion is communicated either by water or by the power of horses.

The mixture being distributed on the stone, to the

amount of forty or fifty pounds, is moistened with distilled or rain water; but so as not to be wetted. It is barely sufficient to prevent the dust from flying. According to the velocity, the grinding is perfected in a space of time varying from three to seven hours; and it depends on the inspector to determine by trial for each velocity when the mixture is perfect. After that, time is a sufficient measure. The removal of the mill-cake, as it is called, requires caution, as it is commonly at this time that the explosions take place. These, indeed, will generally be produced if the bed and cylinder should come into contact while they are moved round slowly, to enable the materials to be taken out; the friction, under so great a weight, even of the purest limestones, or of iron, being sufficient to inflame gunpowder. To prevent this risk, a thick piece of hide is carried before the cylinder as the powder is removed, and by this plan the contact is prevented.

Pressing, Granulating, and Drying. The mill-cake thus completed is gunpowder, and may be granulated. But it is yet not so firm as it can be rendered by further pressure; and that property is very essential to its durability in travelling. For this reason, it is further condensed by pressure, either in the common screw-press used by packers, or by means of Bramah's hydraulic engine. Thus it becomes indurated to a hardness equal to that of many stones, and its specific gravity is also increased. In the press, also, it is divided into cakes of an inch or more in thickness, that it may be the more easily broken into pieces for the granulating engine.

This machine consists of a number of sieves made of strong vellum, perforated by punched holes, and supplied with top and bottom covers, like those used by druggists. A platform, to which a horizontal circular motion is communicated by machinery, receives a number of these, which are fixed in it. The lumps of the press-cake are introduced into each of these, together with a block of lignum vitæ or other hard wood, shaped somewhat like a Dutch cheese. During the rotatory motion, the lumps become thus broken into smaller fragments, which fall through the holes, together with the dust, into the receptacle below.

It remains to separate the grains according to the sizes that are required; and for military purposes, these are three; one for large ordnance, another for musketry, and a third for pistols. The powder generally used by sportsmen is of still finer grain than the last. The separation is performed by means of wire gauze, or strong silk gauze, of different apertures; the sieves being commonly cylindrical, and turned by the machinery. At the same time the dust is separated, and afterwards returned to the press.

The last operation is known by the name of glazing, a term literally true in the case of sportsmen's shooting powder. But the real object of this operation is to take off all those acute angles from the grains, which would otherwise be ground off in travelling, and thus produce great inconveniences, by introducing dust into the casks. This process is performed by causing the separate classes of grains to revolve in cylinders so constructed as only to let the dust through; and the mutual friction of the grains produces the desired effect. When it is required to give the powder a brilliant surface, as is the case with fine sportsmen's powder, the cylinder is lined with a woollen cloth; and sometimes, if a high polished gloss is desired, some black lead is introduced into it. But these are matters of mere ornament.

Although the powder thus completed appears dry to the feel as well as to the sight, it contains a considerable quantity of water. This must be separated by drying. In hot climates exposure to the sun is sufficient; but in most cases artificial heat is required. In France, a complex process was adopted by passing heated and dry air through a closed chamber, with the intention of diminishing the risk of ex-

pllosion; but, with any moderate degree of care, it may be done in any manner. In some of the older works, the stove in use was a closed room with air holes above, heated by means of an iron cupola or large pot, to which a fire was applied outside of the building; the temperature being regulated by a thermometer fixed in the door, and indicating the heat externally. In this room, the powder was exposed in flat trays round the circumference. Lately, the method by steam pipes has become generally adopted; and in this way, every possible security, real as well as imaginary, is obtained.

Analysis of Gunpowder.

It is often useful, and frequently indispensable, to analyse gunpowder. This process will, indeed, generally supersede the necessity of proving by the usual methods, as it is always certain that a specimen of gunpowder, well made, will produce the best proof. It is particularly convenient in the case of gunpowder purchased from merchants, or by contract; as, from the several causes which may easily be conjectured, such an article may be deficient in the quantity or in the quality of the saltpetre, or in both. It is useful, moreover, in the case of damaged powder, returned from military and naval service; as we can determine by these means whether it has been wetted by rain or by sea-water, or whether any portion of the nitre has been washed out. Powder thus damaged by fresh water only, and otherwise uninjured, may be committed to the mill and restored at a very trifling expense. If the saltpetre is diminished, it can thus also be restored; but, on the contrary, if the damage has been produced by sea-water, it becomes necessary to destroy the powder for the purpose of extracting the nitre.

By washing the powder previously weighed in a filter, with hot distilled water, the nitre is dissolved, and admits of being crystallized and weighed. The tests formerly mentioned, namely, nitrate of mercury and carbonate of potash, may then be used to determine its purity. Thus it may be ascertained whether, in a new sample, the nitre is in sufficient proportion, and whether it has been well purified; and in a damaged one, whether the injury has arisen from fresh or from salt water. It only remains to examine the proportions of the charcoal and sulphur; a task, however, which is less easy, but which is, at the same time, less necessary, as the manufacturers are under no great temptation to assume a wrong proportion of these, although the joint quantity of the whole may be in excess. This mixture, being dried and weighed, must be exposed to a moderate heat, as long as any sulphur can be sublimed. But as the last portions are inseparable in this manner, it is necessary at length to have recourse to other means. Among those that have been tried, there is none more convenient than boiling in a solution of pure alkali, by which a sulphuret is formed, and the weight of the dried charcoal thus completes the analysis.

Analysis of Gunpowder after Explosion.

To a certain extent, at least, an analysis of gunpowder after explosion is necessary, for the purpose of procuring data whence its force may, a priori, be calculated. The rest is only matter of curiosity, and we have borrowed the determination from the experiments of the late Mr Cruikshank, a name known to chemists as that of the discoverer of carbonic oxide. As far as this analysis may differ from that of others, it must be recollected that the separation of mixed gases is not a very easy problem. The mere collection of the total gaseous products is easy; and had the same method been followed by Robins and others, less difficulty would have been found in their computations. Had Count Rumford, and a numerous party of speculators on this subject, adopted so simple an expedient, they would not have

had recourse to the expansive force of steam, or of the air contained within the charge, for an explanation of the cause and nature of the force.

By ramming a hundred grains of powder into a narrow metallic tube, furnished with a long handle, it is easily caused to burn under water, as the combustion is slow and safe when it is thus condensed; and this quantity is sufficient for any purpose of experiment. The tube being plunged under the water with its mouth downwards, under the bell-glass of the pneumatic apparatus, the powder may be lighted without any loss. This is done by introducing, into that part of the tube above the charge, which is purposely left empty, a crooked wire heated to redness. After the hot wire and the tube in this position are immersed under the bell, the former is brought into contact with the charge. To prevent the water from absorbing any portion of the carbonic acid, sulphuric acid may be added to it, as well as many other matters too obvious to mention; or else it may be heated. Thus the gaseous product may be collected and examined at leisure, by the means which chemistry furnishes, and which our limits will not permit us to detail.

To collect the solid product, it is most convenient to use a glass vessel, on account of the certainty of obtaining the produce, which is, in great part, carried up in smoke, and adheres to the receptacle in which the powder is burnt. But we need not describe the numerous modes in which this object can be attained; and shall only add, that to diminish the hazard, the powder employed for this purpose may be wetted without affecting the results.

The following statement, then, contains the gaseous produce of 100 grains, made of the proportions 75 nitre, 10 sulphur, 115 charcoal; the measure and weight being both included. The temperature is reduced to 65, and the barometric pressure to 29.5. The total gaseous produce measured 91 cubic inches, and the total weight 50 grains. Thus, about half the weight of the powder becomes converted into gas, and the remainder forms the solid produce.

The solid produce, however, appears in excess, possibly from being imperfectly dried; or else from some other unnoticed errors in the experiment. It is as follows:

It is not difficult to account for these various products, and it is evident that the carbonic acid and the azote are the principal causes of the explosion. The decomposition of the acid, and the combustion of the charcoal, form the basis of the elastic force. It may be imagined that the hydrogen is the produce of contained water; but we consider that it is principally derived from the charcoal and from

the sulphur. The two combinations which it forms are such as might be expected, and the nitrous gas requires no remark. Respecting the solid produce, the produce of the subcarbonate and sulphate of potash is a matter of course; and it is only necessary to point out the excess, of charcoal principally, of sulphur slightly. It is evident that more nitre would be required to consume them; but, as we formerly remarked, it is held expedient that there should be an excess in this way rather than in the other. We need not, however, dwell longer on this analysis; since, as far as the effects of gunpowder are concerned, it is the quantity, not the quality, of the produce that is an object of interest.

On the Sizes and Forms of the Grains in Gunpowder.

The variety in the effects of gunpowder, arising from differences in the sizes and forms of the grains, has been an object of much inquiry. The conditions of the problem are somewhat complicated. Within certain limits, which gunpowder made of nitre cannot exceed, rapidity of inflammation is essential to the production of a full effect. Not to inquire into other causes, without this property, a part of the charge is rendered useless by being blown out unburned; an accident not uncommon on ordinary occasions. This may also happen from the form of the piece and that of the charge; it will occur in a long charge or in a short piece, or, most of all, when both are united. Hence variations in the effect of gunpowder, which are independent of its quality, and which will render computations founded on that circumstance alone deceptive. As we have not room to dwell on this subject as it deserves, we must refer our readers to Robins and others who have written on it.

Now, this rapidity of inflammation may be attained, in some measure, in two ways; by intense heat, and by facility of transmission of the flame. But if a charge is considerable, no intensity of heat can compensate for the absence of the second condition. To put an extreme case: If the eight-pound battering charge of a 24-pounder were a single grain, it requires little thought to perceive that the shot would have quitted the gun before the charge was half burned. Hence granulation is as necessary for ensuring the full effect as it is for convenience. And thus, also, we are led to the cause of the bad consequences of hard ramming. A charge very thoroughly rammed, and lighted at the anterior end, would burn like a fuse or a squib; if lighted by a touch-hole, it will be blown out like a shot. Thus the rapidity of the inflammation is secured by multiplying as much as possible the intervals for the passage of the flame, or by diminishing the size of the grains. Yet there is a limit even to this; and as that can only be determined by experiment, it is from such trials that the grain for the smallest charges has been fixed. As the charge, however, increases in dimension, the volume of flame and the intensity of the heat produced admit of a grain of greater bulk, or one containing, in a given dimension, a smaller number of intervals. Much refinement on this subject being, however, unnecessary, one size is used for all ordnance; whilst an inferior size is made for muskets, and one still less for pistols. The powder manufactured for fowling-pieces is also of the smallest size.

But there is a further element concerned in this question; and that is, the different specific gravities of the different sizes of powder, or, what is especially to the purpose here, the different spaces occupied by the different sizes. The same measure which contains 172 grains of the smallest, contains 180 of the medium, and 195 of the largest. If powder be measured instead of weighed, it is evident that there will be one ninth more of the large than of the small-grained in a given charge. If weighed, the larger will occupy about one ninth less space. In either case the

greater force will be excited by the large-grained, presuming that the inflammation is perfect. When it is weighed, as is the correct practice, it will not be very difficult to calculate the difference; as the force of the expanding fluid is in a certain inverse ratio of the space in which it is confined.

To increase the rapidity of inflammation, the French have manufactured spherical powder. The details of the process are such as would exceed the limits allotted to this article; but the principle may be understood by saying, that it is similar to that used by confectioners in making comfits. Angular grains are rolled in machinery adapted to that purpose, in powder dust slightly moistened; and thus small globules are formed. This grain is less liable to wear in travelling, from the absence of angles; but it is at the same time more tender, and less able to bear pressure, than pressed powder. Nor do the French experiments, either by the eprouvettes or the tables of practice, prove its superiority; on the contrary, the average results of its comparison with ordinary powder are unfavourable; and this also was observed in our own trial. Hence it has not been adopted in Britain.

Proving of Gunpowder.

To ascertain, by practical trials, the strength of gunpowder, is not merely a matter of curiosity, but of absolute necessity. As the force in battering ordnance, and the range in mortar and howitzer practice, are regulated by the quantity of the charge, it is obvious that no regular practice in the field, or consistent results, will be obtained, unless the standard of strength in the powder is both known and invariable. This is particularly the case with mortar practice against small works or redoubts, or against the enemy's trenches; and also with howitzer practice against moving columns in the field. An invariable standard is, unfortunately, impossible; but it is always something to approximate to it. In military arrangements, a proof is also requisite, for the most obvious reasons, when powder is purchased from merchant manufacturers; not only that a minimum standard of strength may be fixed, but that, as far as is possible, the various qualities furnished may be reduced by mixture to an uniform standard.

It is usual, in the first place, amongst the workmen, as well as the merchants, to form a judgment of the quality of gunpowder by the aspect and firmness of the grain; and the latter, indeed, is a quality which is indispensable, if it is to be exposed to much land-carriage. The nicety of tact required for this is, however, only to be attained by practice, as in all other species of sampling. The moisture is judged of by weighing, and by subsequent drying and comparison. The quantity of this is a question of profit and loss in the purchase. But it is more important to ascertain its hygrometrical powers, by exposure to moisture after drying. That is the best which gains least weight by this operation; nor, in any case, should the absorption of water amount to $\backslash frac\{3\}\{4\}$ per cent. It is also a common practice to try it by what is termed flashing; but this only serves to show whether it has been thoroughly ground; if not, the charcoal will produce sparks.

The trial of force is made by eprouvettes of different constructions, or else by practice. The most common eprouvette is a short chamber, provided with a gun-lock, the orifice of which is closed by a cover, connected with a graduated and ratchet wheel and spring. The quantity of the wheel's revolution is the esteemed measure of the force. But, often as this machine has been varied and improved, the results are so irregular, that it may fairly be considered as useless. Various other instruments for this purpose have been invented and tried; but, without figures, we could not render their constructions intelligible. Regnier's does not materially differ from the preceding in its

principles; and the results are equally unsatisfactory. His hydrostatic one appears to be still worse. We may say the same of that described by Saint-Remy, and of another recommended by the Chevalier d'Arcy; and, of the whole, we would remark that the leading fault is want of simplicity. In a case like the explosion of gunpowder, where so many disturbing forces are always at hand to vitiate the true results, we cannot be too careful in eliciting all unnecessary causes of disturbance. If there is any one class of machinery in which simplicity is indispensable, it is that which belongs to gunpowder, under any of its relations.

We, however, consider that, as an eprouvette, Dr Hutton's pendulum is as free from exception as any machine can be. The disturbing forces are nothing, or as little as possible; the charging and firing admits of great uniformity; and, on trial, the consistency of the results justifies the expectations formed from its simplicity. In this pendulum, the barrel is fixed upon the bob, and the force of the gunpowder is therefore measured, not, as in Robins', by the impulse of a shot, but by the recoil. The indication of the extremity of the arc of vibration is made by a hand continuous with the pendulum rod, which moves an index furnished with a spring sufficiently strong to retain it at that point of a graduated arc where it was left by the movement of the hand. The barrel used for this purpose is an inch in diameter, and is charged with two ounces of powder put in loosely, without wadding or ball. In this, as in all other cases of eprouvettes, the standard of strength is arbitrary; and, for service, is assumed from the best average of gunpowder manufactured by government. The goodness of particular specimens is estimated by their agreement, or otherwise, with this standard.

Notwithstanding, however, the apparent accuracy of this method, artillery officers, both in France and in England, are not satisfied with it as a method of proving powder for service. It is perhaps right that practical men should, in a matter of so much importance, rely only upon such a method of proof as agrees best with the particular objects for which the material is intended. Yet it should also be recollected, that all Robins' conclusions respecting the force of gunpowder were drawn from experiments made on his ballistic pendulum, and that the much more accurate ones of Dr Hutton, on which we now rely, were the results of the practice with that pendulum which we have just described.

The method of proving, then, adopted both in France and England, consists in real practice from a mortar at short ranges. In France a mortar is used of which the diameter is 0.191 metres, or nearly eight inches English, and that of the touch-hole somewhat less than two lines. The diameter of the ball is 0.1895 metres, and the windage consequently is .0015. The weight of the ball is about sixty pounds. A troublesome verification of the diameter of the bore, of the vent, and of the shot, is made for each day's practice. The mortar is condemned when the diameter is enlarged to 0.192, or if that of the vent becomes .0005 more than it ought to be. A difference of windage, amounting to .0002 metres more than what is allowed, condemns the shot, or, as it may happen, the whole apparatus.

All these verifications are so tedious, and the wear of the mortar, the vent, and the shot, so rapid, that it becomes inconvenient and impossible to follow them so nicely in practice when there is much business. It is, therefore, found more convenient to make a standard trial for each day's proof, and to refer all the others to this one; instead of trying to preserve what becomes impossible in practice, an absolute and invariable range.

The English proof-mortar, therefore, nearly corresponds with the French, it being of the eight-inch calibre, and

of brass. The shot is turned and polished so as to be true, and to have at the commencement the least practicable windage. During the progress of use, as the windage increases from the wear both of the bore and of the shot, the range becomes contracted; a circumstance which also follows from the enlargement of the vent, in consequence of which a greater proportion of the generated air escapes at that aperture. But, from the practice adopted with us, these variations are of no moment, till the range becomes contracted so as to render it expedient to replace the shot or the mortar, or both.

The quantity of powder that is used is four ounces, and the mortar being elevated to forty-five degrees, the range is measured in each trial. If the standard range for the day is 225 yards, the powder that gives a range of only 200 is rejected. The chief precautions requisite to procure fair results in this comparative method, are, to take care that the level of the platform and the elevation of the mortar are subject to no accidents; that the powder be fairly placed in the chamber; that the priming tube always reaches to the same depth within the charge; and that the mortar be brought to the same temperature at each experiment. For this purpose, it is to be cooled with water.

Musket powder is submitted to a different species of proof, founded on the same views of rendering the proof for each kind as nearly corresponding as possible with the purposes for which they are designed. A barrel fitted with a turned steel ball, and with as little windage as possible, is used for this purpose. The ball is discharged at the distance of a few yards only, against a compound butt, made of elm planks an inch thick, soaked in water, and separated at a short distance from each other. The extent of the penetration is the proof of the strength of the powder; and the trials in this case also are referred to a standard experiment made each day. Before concluding this subject, we must add, that trials are also made for the purpose of ascertaining the hygrometrical property of the powder to be purchased or issued. This is done by exposing a quantity for a given time in a box perforated with holes, and in a damp room, and then submitting it to the same proof.

Powder from Oxymuriate of Potash.

To increase the strength of gunpowder has been a favourite project with inventors at all times; most of them forgetting that the same end can be attained, as far as it is attainable, by augmenting the charge, and that neither the one nor the other is practicable without an entire reformation of the whole system of artillery. Could the force of powder be increased one half, for example, it would be necessary to condemn almost every gun in use; and not only every gun, but every carriage, breeching, ringbolt, nay, we might almost add, every ship in the service. And supposing a new species of ordnance invented to suit the new powder, it would require at least one half as much more of weight in guns and mortars; the same in gun-carriages, with additional strength in every object concerned about them. In the field, in the same manner, an increased number of horses would be required. This view presumes that the object is, what in fact it always has been with the herd of inventors on this subject, to gain additional force or range. If the purpose is only that of being enabled to reduce the quantity, and thus diminish the bulk and trouble of transportation, it is so trifling an object as scarcely to be worth attaining. With regard to the main intention, or that of gaining greater range and force, it is only necessary to say, that the powder is already too strong for the artillery.

As soon as the oxymuriate of potash was known, it became obvious that it would not answer the same purpose

as nitre, but, from its more energetic action, produce a more rapid combustion. It was first proposed and made by M. Berthollet in 1786; but an accident having happened from it at Essonne, by which many people lost their lives, it was abandoned. The proportions used were 80 oxymuriate, 5 sulphur, and 15 charcoal. Afterwards they attempted to make a modified compound, by using only a proportion of it with the nitre; but after various trials of this kind, the whole project was abandoned.

We have repeated Berthollet's method, at different times, and on a very large scale, without accidents; but we consider that the proportion of oxymuriate is too large, or at least that it is larger than is necessary. A better proportion appears to be 75 oxymuriate, 5 sulphur, and 20 charcoal. As this compound is very easily exploded by friction, it is necessary to be extremely cautious throughout the whole process, particularly in the granulations; nor is it safe to make more than one pound at a time. Of course, it may be mixed in wooden mortars, as it requires no large apparatus.

The great objection to its use is the facility with which it is inflamed by friction, or by a hard blow. The expense, indeed, would alone be an insuperable one, were there no other; as the price of this salt is more than twenty times that of nitre. It also corrodes the barrels very quickly. In fowling-pieces it is, however, of use; being the detonating priming of Forsyth's and Manton's gun-locks. We may add, that very good powder may be made from this salt and charcoal alone, in the proportion of eighty to twenty; but the grain is not very compact, and it is subject to the same faults as the former.

The action of this powder on the shot in a charge is very capricious, and far from intelligible. In the French trials, it was found to give ranges sometimes double and sometimes triple those of common powder, using the same weights. In various experiments made in this country, the ranges were double in a majority of comparisons, when moderate charges were used. But, by increasing the charges beyond this, the ranges, instead of increasing in the same ratio, began to contract; double the quantity producing but a moderate increase in the range, and a third proportion making an addition still less than the preceding. This, however, agrees with Robins' experiments on common gunpowder; and he has accounted for it by what he calls the triple resistance; proving, as he thinks, that whenever the initial velocity exceeds 1142 feet in the second, a vacuum is formed behind the shot, which, by increasing the resistance before it, speedily reduces the velocity to what it would have been with a smaller charge. We need say no more respecting a compound, the use of which is not likely to be ever extended beyond its application to the detonating gun-locks.

Keeping and Restoration of Powder.

Powder for service, whether by sea or land, is kept in barrels, containing each one cwt. the size of which is nearly that of a ten-gallon cask, and they are hooped with copper. It being difficult to keep dry casks water-tight, as indeed it was not thought necessary that they should be so, much powder was always rendered useless on service by wet. Lately copper linings have been very properly introduced, and the casks are now water-tight. As great quantities of powder, however, always have been, and always must be, returned unserviceable, it is an important object to be able to restore it, or render it useful, in the most economical manner.

Sometimes the grain is merely adhering, and can be shaken loose again; and this effect is not unfrequent even in magazines on shore. Such powder, when dried by restoring, appears sufficiently perfect; but it will be found that it is increased in bulk, and has become spongy and ten-

der. On examination by the magnifying glass, it will also be perceived that the nitre is partially separated. Powder which has once undergone this change is deteriorated, yet is still fit for all ordinary purposes. It is not strong enough, however, to bear travelling; and should it be required for that purpose, it ought to be remilled, and granulated over again.

When the casks have been opened on service, before being returned, it is necessary to examine carefully whether they do not contain nails, or other foreign matters, an accident not uncommon. In such a case it is unsafe to commit them to the mill, and they must be reserved for extraction. When the powder has been so wetted as to be nearly formed into lumps, it is first necessary to examine, by the test of nitrate of mercury, whether the damage has been done by fresh or salt water. If by the latter, it must also be sent to the extracting house. If it has been very thoroughly wetted, even by fresh water, it will often be found that some of the saltpetre has been washed away. In this case it must be analyzed, so far at least as to determine the proportion of saltpetre wanting, which must be added to it in the mill. In the process of extracting, nothing more is necessary than to boil the powder in pure water, and to filter the solution through thick woollen bags. The crystals are purified exactly as in the case of rough nitre. This is a wasteful process, however, and, in all cases where it is possible, remilling is to be preferred.

On Accidental Explosions in Powder Manufactories.

This is a subject which deserves far more attention than it has yet received; and we can only regret that our researches do not enable us to add more to the present suspicions as to the causes of these, than the little which follows. That want of sufficient care is the general source of these disasters is, however, certain; as certain merchants' mills have been celebrated for them, whilst in others, as well as in those belonging to the government, they have been extremely rare. Such accidents may take place in any part of the works; but they are most frequent, as well as least injurious, when they happen in the mills, the quantity of powder in these never exceeding fifty lbs. It ought at least to be an invariable rule to remove each charge to the pressing-house as soon as it is completed.

We have already hinted at the cause of the explosions in the mills, when they happen at the time of removing the powder from beneath the stones. As stamping-mills are not used in this country, it may be thought superfluous to remark, that, in these cases, this accident sometimes happens from attempting to remove, by a mallet and chisel, the lumps of powder which adhere to the pestles. It is one of the inconveniences attached to that mode of grinding. But it is also proper to observe, that the mills are sometimes blown up whilst working; and, from some examinations which we have made, we have little doubt that this has arisen from fragments of the stones falling off, and being bruised together with the powder. We indeed consider metallic rollers as every way safer than stone ones; since they can only produce fire in case of friction in contact during the removal of the charge. If iron be held objectionable, it is easy to face them with a sheet of copper; but it is proper to recollect that even thus the chances of explosion from friction are not removed. It is a great mistake to suppose that the absolute hardness of any metal is indispensable to the production of explosion in gunpowder. A blow sufficiently powerful, or friction caused by sufficient weight and rapidity, will compensate for the absence of this, in very soft metals, as well as in many other substances which do not readily give fire. Limestone we consider as a very objectionable substance. Excepting that of Carrara, we know of none, either primary or secondary which does not contain much silica; often, indeed,

particles of quartz sand. In the secondary calcareous rocks it is universal, nor is even the finest white marble of Carrara always exempt, as is well known to statuary. But the softness even of the purest limestones is no defence; as the friction between these is still more capable of setting fire to gunpowder than that of iron. The readiest way of putting these different substances to the test is by experiments in fulminating silver (that of Howard); as the irritability of this substance enables us to ascertain the facts with a moderate and convenient force.

We know of no explosions in the stove, except in one noted instance, when it was pretty well ascertained to have been produced by a workman, who had determined on suicide in this manner. In the steam stove it can never happen from overheating; but as the floor must necessarily be dry when the workmen enter to remove the powder, instead of being wet, as it always is in the other houses, it requires additional care respecting the feet of the people employed. The only method that is quite safe, in all houses and magazines, is to oblige the workmen to labour barefooted. The heavy leather slippers in common use are far from safe; as, from not fitting well, they are frequently dragged along; in which way they may easily entangle particles of sand. It ought to be known to all powder-makers, that the breaking of a fragment of quartz, or the sufficient friction of two grains between copper, or even wood, is capable of igniting gunpowder. This is more particularly the case when the finer charcoals are used; as it is this which is the susceptible ingredient.

Explosions in the pressing and granulating house have happened much too often, nor have the causes been ascertained. As there is a considerable quantity of powder always present here, these are of a very serious nature. It would be proper that these two buildings should always be separated, and, in the usual way, by a work of earth. The old granulating houses are far from safe, as the cranks and other parts of the moving machinery are contained within the house, which is always filled with the dust of the powder. It is trusting too much to the attention of persons, whom practice renders habitually careless, to expect that they will always keep the parts oiled. It is easy to remedy this evil by entirely separating the working machinery from the granulating engine, which may be suspended and steadied by ropes, so as to avoid all chance of friction.

In the pressing house there seem to be two sources of danger, both of which may be obviated. It is easy for powder to become entangled among the threads of the screw; and the consequence of this must be obvious. This would be remedied by adopting Bramah's press. We also think that the sudden condensation of air entangled among the fragments in the pressing box may be sufficient to produce fire. Whether this be the case or not, it will always be prudent to make the first pressure as slowly as possible, that the air may be allowed to escape.

We have observed three other causes for accident, though neither of them belong properly to the manufacturing houses. It is, nevertheless, very important that they should be generally known. Charcoal, in certain cases, is liable to take fire spontaneously, and that even in the lump. This is a case exactly analogous to the pyrophorus of Homberg; and it unquestionably arises from the same cause, namely, the presence of a portion of potassium. It is an accident which, we imagine, can only happen to charcoal made in retorts; as, in the pit method, the potassium could scarcely be expected to escape combustion. The precautions hence requisite, respecting the stowage of charcoal, and the place of the distilling houses, must be evident. When in a state of powder, and under pressure, it also has been known to inflame; and, possibly, from the same cause.

We are not aware that it is usual to keep many waggons

and powder-cart tilts about powder magazines; but we do know that this has happened, and with the effect of producing fire. It ought to be generally known, for many other reasons, that fresh painted canvass, stowed close, is subject to spontaneous combustion.

Lastly, it has frequently been observed that fire was struck in closing up the powder barrels, as well on board ships as in magazines; an accident which was supposed impossible, since both copper hoops and hammers are exclusively used. We at length discovered that this accident had arisen from using cast rivets, in the surface of which the sand of the mould had become entangled. Hence the obvious necessity of using none but forged copper rivets; and since the adoption of these in the government stores, this accident has been unknown.

On the Force of Gunpowder when Fired.

It remains to inquire, whether there are any means, a priori, of determining the explosive force of gunpowder, and of discovering what that is or ought to be. Many calculations have been made on this subject, and some of them, we need scarcely say, are deserving of great regard, although by no means in accordance with each other. Many, on the contrary, proceed on principles so often gratuitous or false, as to be entitled to no consideration. When we consider the reputation of some of the authors of these speculations, and the real knowledge of the true cause of explosion which was then in existence, the history of these opinions, and thus of the deduced results, is not a little curious.

Lemery, Wolf, Papin, and some others, considered that the cause of the explosion was to be sought in the rarefaction of air contained in the interstices of the powder; forgetting, that in a rocket, which can contain none, the production of air was sufficient to communicate and maintain a considerable velocity during the whole time of the combustion. John Bernoulli imagined that this air contributed an eighth part of the force only, and that the remainder arose from water contained in the saltpetre. Muschenbroeck, Stahl, Beaumé, and Macquer, again, considered the whole effect as produced by the conversion of the water of the nitre into steam; an error quite unpardonable in the two last chemists, who ought to have known that nitre contained little or no water of crystallization; and still more so in Count Rumford, who has followed them in this theory. Lombard, attempting to improve on it, adds to the expansion of steam that of the nitric acid. The Abbé Nollet allows the water but a share in the explosion. But, not to enumerate more of these hypotheses, we shall only mention further, that of those who have attributed the expansive force to the conversion of latent into free or radiant caloric, as they have thought fit to term it.

It would have been much more easy and correct to have put this question to the test of experiment, when the real cause would have immediately appeared. It was sufficiently unpardonable, in the greater number of these persons, not to have inquired what had been done before them; since Boyle, Hales, Hawksbee, and others, were aware that the combustion of gunpowder produced a permanently elastic fluid; although their mode of obtaining it in an exhausted receiver was not a very accurate one. Hawksbee found that one grain of powder, when fired in vacuo, produced a cubic inch of a permanently elastic fluid, and that the same result was obtained in air. Hence, though not acquainted with modern chemistry so as to be aware of the nature of the generated gas, he knew well that it could not have arisen from the expansion either of air or water contained in the powder. The inaccuracy of Count Rumford's views, and the extraordinary results of his numerous and laborious experiments, exceed, however,