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oxide of phosphorus, which possesses great chemical affinity for water, and we allow it to combine with a small quantity of that liquid, we observe that it will do so much more energetically than the oxide of zinc did with the acid, producing almost an explosive result. We have a proportion of the water suddenly converted into vapour by the heat developed, which is sufficiently intense to ignite a highly combustible material, as we find if we allow guncotton to come into contact with the oxide of phosphorus which we are combining with water. If two very active elementary bodies, such as bromine on the one hand, and potassium on the other, are brought together, we find that a still more violently rapid combination takes place. No substance existing naturally in the form of a vapour cr gas is produced by their combination; it is simply here the intense heat, suddenly generated by bringing these two substances together, which suffices to produce a powerfully explosive result, by instantaneously generating a quantity of vapour. And, lastly, if we take a mixture of two gases, such as hydrogen and oxygen, or hydrogen and chlorine, and confine them as we have in this glass vessel, we know that the mere momentary contact of some portion of the mixture with a body raised to a high temperature, or the passage of an electric spark through it, produces instantaneous combination throughout the whole volume of gas. We will fire these mixed gases in this vessel by the passage of the electric spark through them. A violent explosion takes place, and the vessel is shattered into innumerable minute fragments, in consequence of the enormous force suddenly exerted by the intensely heated product of combination of the gases.

These are one or two instances in which combination produces explosion. We can produce a much greater variety of examples in which explosion is the result of the instantaneous or very rapid decomposition of a chemical compound. We are acquainted with several classes of compounds remarkably unstable in their character, these are to be found particularly among the bodies which we term organic; there are, however, a few inorganic compounds which are also remarkable for their instability; such are the combinations of hydrogen and nitrogen, with chlorine, bromine, and iodine. This, for instance, is the iodide of nitrogen, with which you are well acquainted: observe its great tendency to explode. [A small quantity was exploded by being touched with a piece of folded paper.] If it is sufficiently dry, a very slight touch will cause the explosion. It is not quite dry, or I might show that the explosion may also be produced simply by allowing the substance to fall upon water; but I have sufficiently attained my object, which was to show you the highly explosive nature of this substance. The combinations of mercury and of silver with carbon, nitrogen, and oxygen, which we know as the fulminates, are remarkably explosive in their character. When these fulminates are perfectly dry, a very slight blow or a very small amount of friction is sufficient to bring about their decomposition. Thus, here is a small quantity of fulminate of mercury; you will observe that a very slight application of heat to this is sufficient to cause it to undergo decomposition. It inflames with a dull sort of sound, which could, of course, be rendered more violent if the particles were confined. Here is some fulminate of silver, which is much more explosive in its character. We will take a much smaller portion of this than of the other fulminate, and place it upon the copper, and submit it to the action of the heat. [This was done.] You see it explodes much more readily and violently, and we perforate the copper instantly; while in the case of the mercury compound, the copper was hardly indented. As I have said, the explosive characters are exhibited by various organic compounds-bodies not of natural occurrence, but produced from non-explosive organic substances by the action of an acid remarkable for the amount of oxygen which it contains, and for the tendency which it

has to impart that oxygen to other substances-nitric acid. This nitric acid, as many of you know, may be made to produce changes in organic substances, resulting in the oxidation of a proportion of hydrogen-atoms in the organic structure, and their removal in the form of water; a corresponding proportion of the partially de-oxidised acid (nitrous acid) passing into the space created by the abstraction of the hydrogen from the group; and thus we can produce, for example, from cotton, from cellulose, or lignine, highly explosive substances. Here is one of these bodies-the well-known gun-cotton [holding it to the spirit-lamp and so firing it.] If we confine a small quantity of it in a little vessel of this description (a small glass globe), and fire it, which we can readily do by applying this hot iron to the exterior, we shatter the vessel; so that you see that the substance which appeared but feeble in its explosive power when burnt in the open air, may readily be made to produce powerful effects. There is also an explosive substance produced by a similar action of nitric acid upon the sweet principle of manna, beet-root, parsnips, or onions, known as mannite. Again, we are enabled by the mere contact of nitric acid, in its most concentrated form, at a low temperature, with glycerine, to produce a substance of a highly explosive character known as nitroglycerine or glonoïne. It is only necessary to moisten a small portion of filtering-paper with a little of this substance, and then to expose this to a moderately violent blow, in order to show its explosive nature. [A piece of filtering-paper moistened with the compound of glycerine and acid was placed on an anvil and struck with a hammer.]

Here is an explosive substance belonging to this class, of very recent origin, a member of a most interesting family, one of the derivatives of that remarkable substance, aniline, to which we are indebted for those beautiful new colours, Mauve and Magenta, of whose history we shortly expect an interesting account from Dr. Hofmann. It is curious that this body, aniline, which has become of such importance in connection with arts and manufactures, should also exhibit what may be called "warlike tendencies." By the action of nitrous acid at a low temperature upon aniline, the explosive substance to which I refer is produced. This singular body rejoices, I am happy to say, in the comparatively simple name of nitrate of diazobenzol; compared with the names which are possessed by some of the members of this family, this is certainly not a hard one. [A small quantity was exploded on copper foil, which was shattered.] You see that it appears quite equal in its explosive power to fulminate of silver. I cannot help devoting a few moments to a comparison of its explosive properties with those of fulminate of silver. The silver compound explodes with a slight touch given by a hard substance; whereas this new compound can actually be rubbed between hard surfaces without exploding; at least, I have found it so on frequent occasions, although I have finally exploded it in that way. Some time is necessary, however, for producing, by friction, the requisite heat for its decomposition. The slightest touch, you observe, explodes fulminate of silver, and it does not admit of being rubbed. The nitrate of diazobenzol, when compared with the fulminate in this way, appears to be the less explosive substance; and yet, when directly exposed to heat, it is certainly the most sensitive of the two. If we expose the fulminate of silver in this little tin tube to the heat of boiling water, I think we shall find that it is not affected. [The experiment was performed with the result anticipated.] But if I heat, in the same manner, a little of this fulminate of aniline-if I may use the term(although there are one or two compounds, also derivatives of aniline, still more recently discovered by Dr. Hofmann, which may claim the title,) if I similarly heat this nitrate of diazobenzol, you will find that it will undergo decomposition as soon as the tube has reached the temperature of the water. There we have a very

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violent explosion; the tube is shattered, and has been thrown out of the water-bath by the force of the explosion. The fulminate of silver has not exploded, but we had better get rid of it. I shall be able to explode it by exposing it to this source of heat [the flame of the spirit lamp], for it explodes at more than double the temperature of boiling water, or about the temperature of melting tin, so that as soon as the tube begins to melt, the fulminate of silver will explode. [The explosion shortly ensued.] We see, therefore, that this fulminate of silver appears far less sensitive, when exposed direct to heat, and more sensitive when submitted to friction, than the derivative of aniline.

Having glanced at the nature of explosive chemical compounds, we will pass on to explosions which result from the reaction upon each other of substances in a state of mechanical mixture,-not chemically combined. We know that if we mix together some substances which differ widely in their chemical properties, we may, under favourable circumstances, bring about the ignition or explosion of the mixture. We have a number of substances which may be applied to the preparation of such mixtures. For instance, here are, on the one hand, substances all rich in oxygen, oxides of manganese and lead, and combinations of metals with nitric acid or the corresponding acid, chloric acid. These substances have a tendency to part with their oxygen, and, therefore, bodies which, on the other hand, are easily oxidisable, such as sulphur or phosphorus (which we can employ with comparative safety in the amorphous state), or the sulphides of arsenic and of antimony, when brought into a state of mixture with these sources of oxygen, will produce materials endowed with explosive properties. Thus, for example, we have here a mixture of binoxide of lead with sulphur, which ignites most readily. We will just apply heat to this for a very short time, and we shall have chemical action established. You see the mixture burns violently, the heat produced has actually broken the tube. Here we have a compound of a high oxide of manganese. We mix this together with iron in a very fine state of division. It is enabled to oxidise that iron very rapidly on the application of heat, and produces an effect bordering upon an explosion in its character. Here we have the particles of iron burning beautifully in the oxygen imparted to them from this oxide of manganese. Then, again, if we take the same substance, together with sulphur, and mix them in this mortar, we can do so in safety, but, on applying a small amount of pressure, the mixture will ignite. You see how beautifully it burns when I have mixed the substances with a sufficient degree of intimacy. And if we take these compounds, many of which are familiar to you, nitric and chloric acids, in combination with various metals, such as potassium, sodium, or barium, we impart to them explosive characters by simply mingling them with an oxidisable substance such as resin or sulphur. We have there chlorate of baryta mixed with a small quantity of resin. Observe how violently it burns, with a bright green-coloured flame. Here are mixtures of chlorate of potash with charcoal, and in effecting their ignition, I wish to direct your attention to the circumstance that the two mixtures have different degrees of rapidity of burning, as this affords me an opportunity of pointing out to you the very great influence which may be exerted upon the properties of an explosive mixture, quite independent of the chemical properties of the substance, by the degree of intimacy with which its constituents are mixed together. The more perfect the mixture, the more rapid and complete will be the transformation suffered by the components, and, consequently, the more powerful will be the explosion. I need hardly observe that the characters of these mixtures are regulated also by the chemical and physical properties of their constituents; for instance, some bodies are more readily oxidisable than others, and partly, sometimes, because they are more easily convertible into vapour. A

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comparison of the facility with which sulphur and charcoal are oxidised, will furnish an illustration of this. Sulphur, as you know, is melted and vaporised at a comparatively low temperature, while charcoal is not at all similarly affected; and, therefore, though the latter possesses a most powerful tendency to combine with oxygen, sulphur may be readily oxidised or inflamed at a very much lower temperature. I bring forward this example because it bears particularly upon the subject of gunpowder, in which the high degree of inflammability of sulphur is turned to account to promote the very rapid oxidation of the charcoal. I have here, in an atmosphere of oxygen, the two substances, carbon and sulphur, in a fine state of division. I shall place over the mouth of this vessel which confines the oxygen, a piece of heated iron gauze, which will not be hot enough to ignite the charcoal when I puff it upwards so as to bring it into contact with the metal. But while that charcoal still remains suspended in the oxygen, I will throw up some sulphur, which will inflame directly it reaches the iron, and will ignite the particles of the charcoal, combustion being thus brought about almost instantaneously throughout the mixture of oxygen and carbon. [The oxygen was contained in a loosely-covered glass jar, into the lower end of which two tubes were fixed communicating with the receptacles containing the charcoal and the sulphur. These two substances were respectively blown, at an interval of about two seconds, to the top of the jar, and so thrown into contact with the hot piece of iron. No change was apparent when the charcoal was blown up, but immediately upon the arrival of the sulphur to the top, combustion ensued throughout the whole mass, producing for an instant a very dazzling body of light.] The substances which furnish the oxygen in explosive mixtures exhibit equally important differences in their proporties, which also assist us in regulating the characters of explosive mixtures. For the purpose of illustrating this, I beg to direct your attention to a very simple experiment with the two well-known substances, nitrate of potash and chlorate of potash. Here are mixtures of these two bodies with amorphous phosphorus (which we employ as a substance very easily oxidised, although its use requires very great care, as it is liable to oxidation in such mixtures on a very slight impulse). This is the mixture with nitrate of potash; you see, it simply burns brilliantly when heat is applied. And here is the phosphorus mixed with chlorate of potash, which ignites immediately with a violent explosion, and the copper on which it rested is shattered.

These few experiments may suffice to show you that these mixtures are susceptible of very great modification in their explosive characters. Not only are some of them decomposed with the greatest facility on exposure to the very slightest disturbing influence, but when once the decomposition of one small particle has occurred, it may proceed with uncontrollable rapidity throughout the whole

mass.

A very slight examination into the effects of fulminate of mercury and of gunpowder, employed under the same circumstances, will illustrate the difference in the effects produced by substances which explode with different rapidity. Let me first compare the rate of combustion of those two substances. Here is a small train of fulminate of mercury, and here is a similar train of gunpowder. You observe that the flame travels much more rapidly along the train of fulminate than along the gunpowder. This difference will prepare you to believe that the effect of the two when confined in vessels must be different. Here are the fragments produced by the explosion, in a small shell, of roo grains of fulminate of mercury; the number (amounting to one-seventh of the weight of the shell) were, however, so small that they could not be recovered after the explosion. Here are the fragments of a shell of the same size exploded by 765 grains of gunpowder. The difference between the size and number of the fragments in the two

instances is very striking. In the case of the fulminate of mercury the explosive effect is exerted almost instantaneously in all directions, and the shell is therefore shattered into a very large number of fragments, the force of the explosion being almost entirely spent upon the bursting of the shell; while in the case of gunpowder, the explosion being comparatively gradual in its nature, the force developed is only partly spent upon the fracture of the shell, and is still in course of development when this result is produced; hence, not only are the resulting fragments much fewer and larger, but a considerable projectile force is exerted upon them after their production, and they are consequently scattered to a much greater distance than those produced by the employment of fulminate of mercury.

When gunpowder is confined, by means of a shot or shell, in the barrel of a gun, the explosion of the first particles has the effect of overcoming the inertia of the projectile, and, the action proceeding gradually, as compared, for instance, to that of the fulminate of mercury, the shot is projected with comparatively small strain upon the gun; but in employing the fulminate of mercury, in a corresponding experiment, it would be found that the enormous force, which reaches its maximum suddenly, would, almost simultaneously with the first movement of the shell, also discover the weakest parts of the gun; in all probability, therefore, the cannon would be burst, while we should not project our shot or shell to any great distance. In quarrying, where it is desired to detach large masses of rock or stone, without producing any great destructive effect, we employ a very slow-burning powder, the explosion of which exerts a force like that obtained with a wedge; if we were to employ fulminate of mercury in this instance, the particles of rock in the immediate vicinity of the charge would become shattered by the sudden and violent explosion, but the desired result would not be produced. A very simple experiment with these Lilliputian cannon, made of sheet copper, will afford some kind of practical comparison between the effects of sudden and gradual explosion. Here we have a gun charged with ten grains of gunpowder, the charge being merely confined by means of a wad. The wad is projected, you observe, to a considerable distance, as I fire the gun, but no apparent destructive effect is produced upon the weapon. The amount of gas resulting from the explosion of the ten grains of gunpowder is represented by this cube. This second gun is loaded with a charge of two grains of fulminate of mercury; and this small cube represents approximately the gas produced by its explosion. You observe that the wad is projected to a little distance, but the gun is burst open along about half its length. And on firing this gun, loaded with only half a grain of fulminate of silver, we have the breech also torn open, and that part of the gun upon which the fulminate rested is perforated. These results will, I think, render evident to you the very great value of the gradual explosive effect of gunpowder. The action of gunpowder, gradual though it appears to be when compared with the action of a fulminate, may, in particular conditions and under certain circumstances, be much too rapid. Recent investigations of the effects of gunpowder have shown that the power we possess of modifying its action so as to render it more gradual, is exceedingly important. As an illustration of this, I may state that in long guns, and in cannon of large calibre, the charge of the powder used for the projection of the shot has been clearly shown to be completely ignited before the projectile is moved to any great distance along the bore of the gun; hence we find that, whenever explosions do occur in guns, in consequence, for instance, of inferior casting or metal, or an excessive charge of powder, the fracture of the gun is almost always confined to the part reaching from the trunnions to the breech. The American Dahlgren gun, of which this is a model, exhibits this great thickness at the breech end; this form has been

adopted to enable the weapon to resist the comparatively enormous strain exerted on that part by the heavy charges employed. Where cast-iron cannon are still used, it will always be especially necessary, if we employ a rapidly-burning powder, to make the gun comparatively very thick from the breech towards the trunnions; and the production of strong cast-iron guns of this form is attended with very considerable difficulties; but if we use a slower powder, we can employ a cannon of more uniform thickness, as the strain exerted by the exploding powder is distributed much more uniformly throughout the greater part, if not the whole, of the length of the gun. Again, in rifled guns, in which, in consequence of the accurate fit of the projectile, the friction between it and the bore of the gun is very great, in some of which also, as in Sir William Armstrong's gun, the projectile has to be expanded, by the explosion, into the grooves of the cannon, a gradually progressive action of the explosion is obviously of very great importance. In mortars and very short guns, on the other hand, where we have a very small space for the projection of the shell, it is necessary to employ a very rapidly-burning powder, It has been constantly observed, that in firing mortars with the description of powder used for cannon, a portion of the charge has been thrown out unexploded. Now, a modification of the rapidity of combustion of gunpowder is very easily effected, and in a variety of ways, though there is only one really correct mode of proceeding. I will just point out to you by what different methods we can modify the explosion of powder. Firstly, we can do so by altering ite composition. If you look at the composition of a number of specimens of gunpowders, as given upon this diagram, you will find that they differ considerably from each other in the proportions of their ingredients. By increasing the proportion of charcoal beyond that indicated by theory as the smallest quantity which will combine with the whole of the oxygen in the saltpetre, we decrease the rapidity of burning of the powder, simply because we give the saltpetre a larger amount of carbon to oxidise, which it will do less energetically; the oxidation will, therefore, take place less rapidly, and less heat will be developed. Then, again, we can modify the rate of combustion of the powder by altering the method of manufacture—that is, by rendering the mixture of ingredients more or less perfect. Here are two trains of gunpowder, the components of one of which are much more intimately mixed than those of the other; the difference in their rate of burning is very evident. And, lastly, we may modify the action of powder-and this is really the correct way of going to work-without interfering at all with the proportions of ingredients as indicated by theory, or with the intimacy of mixture essential to their perfect action; by simply modifying the state of division of the material; that is to say, by employing various sizes of grains of gunpowder, and also by submitting it to different degrees of compression. A comparison of the rate of burning of two or three different samples of powder of the same composition, but varying in size of grain, will show you that this modification in the rapidity of action of gunpowder may be effected with very great ease and nicety without interfering in any way with the ultimate amount of force exerted by the powder. Here we have ordinary small grain gunpowder, here the powder used generally as cannon powder, and here we have a much larger grained gunpowder; the fragments are, at least, four times as large as those of common cannon powder. Large grains, or rather lumps, such as even these (showing some as large as walnuts) have been tried, and, by employing them judiciously, it is found that they propel shot to an equal distance, and with even greater uniformity, than ordinary cannon powder. You see how leisurely these large grains burn. A good indication of their gradual combustion is afforded by noticing the marks or trails which they leave upon the dish in which we have burned them; this other,

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in comparison, burns very quickly; and, lastly, you will see, when I light this fine-grain powder, that it burns with a rapidity almost like that of fulminate of mercury, when compared with this particular gunpowder itself. Time will not permit me to do more than allude to the important and beautiful uses to which the power of controlling the rapidity of combustion of gunpowder and similar mixtures have been applied by the artillerist and pyrotechnist. By combining the application of uniform and accurately regulated pressure with modifications in the composition of gunpowder, and by confining the material within a case or receptacle, so that, when ignited, it can only burn in one direction, the valuable arrangements known as fuzes and time-fuzes are obtained, by which charges of powder in shells may be ignited at any period, within certain limits, determined upon previously to the loading of the cannon. By mechanical arrangements, which regulate the amount of compressed powder to be burnt before the flame reaches the charge in a shell, the time of explosion may be adjusted with great nicety, subject, however, to slight variations, which depend, as Dr. Frankland has recently shown us, upon fluctuations in the density of the atmosphere. The production of rockets, signals, and numerous pyrotechnic arrangements is based upon the principles applied in these fuzes.

Although the gradual action of gunpowder is, as we have seen, of the greatest importance in most applications, there are certain instances in which more rapidly combustible substances, or more rapidly explosive bodies, undoubtedly might be employed with advantage. This is particularly the case, for example, in mining operations, where it is mainly desired to produce great destructive effects by the explosion. This circumstance has frequently led to the trial, and even occasionally to the use, for a brief period, in actual practice, of bodies more readily and rapidly explosive than gunpowder. Only one explosive compound, gun-cotton, has been put to the practical test, but trials have been made of a variety of mixtures, in all of which chlorate of potash is employed instead of saltpetre, in admixture with very oxidisable substances. The preparation of any of these substances upon a large scale has, however, always been sooner or later attended by disastrous results, which in many instances have not been simply due to carelessness. Examples of these mixtures are Callow's Mining Powder, containing orpiment, or sulphide of arsenic, mixed with chlorate of potash, and German or white gunpowder, which consists of prussiate of potash, chlorate of potash, and sugar. These substances will explode readily by exposure to friction or to blows, as you observe when I strike a little of this upon an anvil. You will admit that the blow by which I am enabled to fire this white gunpowder is not very great. It was, indeed, not greater than it might frequently be accidentally exposed to in its manufacture.

We have some of these mixtures which are so prone to change as to be ignited instantaneously by contact with powerful chemical agents, such as acids, for example. Chlorate of potash is most readily acted upon by sulphuric acid, which not only decomposes the salt, but also transforms the chloric acid into very unstable compounds, and the heat resulting from the chemical changes thus established by the acid in a small portion of the mixture of chlorate of potash with an oxidisable body, such as sugar, or sulphide of antimony, is sufficient to ignite it, and thus the whole is almost instantaneously exploded. Again, friction will ignite some of these mixtures very readily. Here is one of them mixed with a few particles of sand; I will try to ignite this by friction. [The mixture was rubbed, but did not at first explode.] It is no argument, that because, when we try to ignite this substance by friction, it does not happen to do so very readily, therefore it is one which may be safely dealt with. This substance may appear to you to be endowed with far more stable properties than I led you to believe. I should like to

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show you that it is by no means so. [The mixture was again rubbed, and then exploded.] We are acquainted with some substances much more easily acted upon by friction, such as mixtures of chlorate of potash and amorphous phosphorus. Very slight friction in that ease will produce an explosion; pressure alone is almost sufficient to effect it. You see, I have really had nothing more to do, to produce the explosion in this instance, than to press the mixture firmly. This mixture may, indeed, be ignited even by the prick of a pin. We have it here arranged in the ingenious manner in which Sir William Armstrong has recently applied it to important purposes. It is enclosed in shellac varnish in a small cavity of wood. I place this pin with its point resting upon the mixture, and if I can see the head, I will explode the composition by a very slight blow with this thin rod upon the pin's head. [The explosion was produced.]

We can readily understand how easily the manufacture of mixtures such as those we have just noticed may be attended by accident, if we devote one moment to the consideration of the ease with which accidents are constantly brought about in gunpowder works, even when the greatest precautions are apparently taken against them. Such accidents are generally involved in mystery, in consequence of the great amount of destruction resulting from them, and of the loss of life of any persons in or near the place of accident, who alone might be able to explain its cause; but, whenever it has been possible to investigate them successfully, they have almost invariably been found to result from a want of strict attention on the part of the workmen to the precautionary measures laid down for ensuring their own safety. A serious explosion recently occurred at the Government works at Waltham Abbey, (of the effects of which I have here a diagram,) which could be more clearly accounted for than is usual with such occurrences. In this case the gunpowder was about to be removed from the bed of one of the mills after it had been completely incorporated. I may remind you, that the ingredients, after having been mixed, are ground up and stirred together, or incorporated, under very heavy runners or millstones. The mill was not in motion in this instance, and the greater part of the gunpowder had been removed from the bed. You observe that there are several mills in one continuous building; each one surrounded on three sides by massive walls, the compartment enclosing each mill being so arranged that the roof and one side are capable of being blown away very easily indeed by the force of an explosion, so that, as the rush of gas can readily make its escape in one direction, there is less destruction resulting from an explosion than would be otherwise produced. After the removal of most of the composition from the mills, in the particular instance to which I refer, it was the business of the men engaged upon this operation to slightly lift the millstones (which they could do by means of a crow-bar), and to take the remaining powder, amounting, perhaps, to half-a-pound or so, upon which the runners rested. It is the practice to place a piece of leather upon that part of the mill-bed to which the end of the crow-bar would be applied, and upon which the millstone would be shifted, so that, in the case of the latter slipping when raised by the crow-bar, it might not come down immediately upon the hard bed and any particles of powder resting on it. This precaution had been neglected by the workmen, as it appeared afterwards, with very great impunity, and, on this occasion, an explosion occurred, evidently in consequence of this, and, therefore, of the ignition of some particles of gunpowder by accidental exposure to sudden and powerful friction. One man in the building was sadly burnt, and subsequently died, and others were badly injured. But the explosion was communicated from this one mill to others in the same building on the other side, in a manner which is worth a moment's notice. In the incorporation of gunpowder a small quantity of dust is always unavoidably produced, notwith

standing that the mixture is kept constantly damp while under the mills; small particles of the powder therefore continually attach themselves to the walls, and although these are swept carefully from time to time, it is impossible to prevent small portions from remaining on them. It was imagined that the individual mills were so perfectly separate and isolated from each other by the plan of building, that an explosion from one could not communicate to the other, particularly as an arrangement existed whereby an explosion in one mill would instantly cause a mass of water to fall upon the powder in the other mills; but there was a small shaft running through the wall from one mill to another, by which this descent of water was ensured, and this shaft passed through very small openings in the walls, closed by tight little doors, so that there were only one or two little crevices communicating from one mill to the other. Well, these were sufficient to allow the explosion to pass from one mill to the others, and to bring about the explosion of the powder upon the mill-beds before the water could reach it. The powder-dust had formed a train upon the walls, and the flame of the first explosion, reaching this, was led to the openings just spoken of, and thus passed, as you may notice, to two mills on the one side, from which the charge had not yet been removed, and to one mill on the other.

Some years ago I had an opportunity of visiting, with some military friends, a powder manufactory in Belgium, where, undoubtedly, the greatest attention seemed to be devoted to the utter neglect of any precautions. (Laughter.) The localities in which all the various operations of the most dangerous character were conducted, instead of being separated in the ordinary way by thick walls or mounds of earth, were arranged one on the top of another. It happened to be a very wet day on which we inspected these works, and we were taken into the various rooms with our muddy and sandy boots. We recoiled with something like horror at the thought of going into the mill in that condition. However, we could but follow the proprietor, who told us that all was perfectly safe. About two years afterwards I went to the same neighbourhood, and once more visited the mills, or, rather, the spot where they had stood; for they had not long before sustained complete destruction. Although the manager firmly believed that they were destroyed, not by accident, but by malveillance, I think you will concur with me in the opinion that a total neglect of all precautions against the possible ignition of powder by friction must, sooner or later, have led to such a result.

But to return for a short time to the more explosive compounds and mixtures. Although their sensitive character does not admit of their application upon any large scale, they have a variety of very important uses, when employed in, comparatively speaking, very small quantities, and especially as affording means for the instantaneous ignition of gunpowder. I need only allude very briefly to a few of their applications in this direction. For example, we have the well-known percussion caps, charged with fulminate of mercury mixed with chlorate of potash, which has the double effect of retarding the explosion usefully, and of greatly increasing the volume of flame resulting from it. Then we have applications of the mixture of chlorate of potash and sulphide of antimony to the production of matches for firing cannon by percussion or friction, and to the ignition of signals by the aid of sulphuric acid. We have also arrangements based on the latter principle, such as were adopted by the Russians against our ships in the late war, where a glass vessel containing a small quantity of sulphuric acid was broken in the midst of some of the mixture just named, by the pressure of a rod which was forced against it when a ship came into contact with the submarine mine. We have the same kind of detonating composition applied in a variety of fuzes which ignite by percussion or by concussion. The sudden check which a shell, containing such a fuze,

The

may receive in its flight, will be sufficient to ignite the mixture, placed upon some movable portion of the arrangement, by the blow to which it is subjected, thus causing the gunpowder in the shell to explode. We have one of these arrangements shown in this diagram; the concussion to which it would be exposed, when in a shell, upon the firing of the gun, would flatten a small leaden cap; this ball, coated with the mixture, being then free to move, would come into violent contact with some portion of this chamber of the fuze, as soon as the shell were checked in its flight, and the composition would be ignited, inflaming a little quick match, which, in turn, would ignite the charge of powder in the shell. Then we have, lastly, the ingenious application made by Sir William Armstrong of the phosphorus-composition to which I directed your attention just now. The fuze-arrangements to which I refer exhibit a degree of delicacy of action which we have never before attained in contrivances of this class; and you will easily understand this if you will bear in mind how very readily I was enabled to ignite a small amount of the phosphorus-mixture by the insertion of a pin into it. In the fuze-arrangement shown in this diagram, a needle, which is fixed into a plug of metal, is readily detached, by the concussion on the discharge of the gun, from the place in which it has been held secure, and it immediately flies with sufficient violence against the explosive mixture contained in this cavity, to cause its ignition. resulting flame lights this quick-match, and the fire is thus led to the fuze-composition, the period during which this burns, before firing the charge in the shell, being regulated by an index-arrangement. We will just fire one of these fuzes; the concussion produced by striking it violently on its base will detach the needle; there, you see, the time-fuze is now burning, and presently the fire will reach the small charge of powder in the base of the fuze. Here we have another arrangement, more delicate still in its action, in which the fuze is set, but not fired, by the explosion of the gun. The concussion of the explosion breaks some thin wires which hold the needle in its position of safety, and the little hammer, to which the needle is attached, flies to the greatest distance from the detonating composition in the fuze. Directly this is checked in its course, even very slightly, the needle flies forward and ignites the composition. In the shell of paper fixed to the end of this stick I have one of these fuzes, and the wires are cut. I will try whether by simply allowing the little hammer containing the pin's point to fall with its own weight upon the composition, we cannot explode it. You see, directly I bring the shell in such a position that the hammer can fall suddenly, it is exploded. You will, I am sure, agree with me that these are interesting illustrations of the beautiful manner in which these highly explosive materials may be brought into use by the exercise of proper care and the application of mechanical ingenuity.

I must just briefly allude to one other application of explosions of this class, namely, to the ignition of gunpowder by means of the modifications of electricity known as electro-magnetism and magneto - electricity. The particular mixtures applied to this purpose possess other important properties besides being easily ignited. They must also possess the power of conducting electricity to some extent, in order that they may afford to feeble currents of electricity the requisite assistance for overcoming the amount of resistance offered to their passage by interruptions in the metallic circuit. Among the mixtures which have recently been applied in this direction, we have one so highly explosive, and possessing such good electric conducting properties, that its ignition is effected by the passage through it of very feeble electro-magnetic or magnetoelectric currents. We have arranged a dozen fuzes in one circuit up in the air, and I will try to fire these by the current from this induction-coil machine. The resistance offered by the interruptions in the circuit is very great in

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