ABEL Or\' EXPLOSIVE AGESTP. IX-Contributions to t7~eHistory of Explosive Agents. By F. A. ABEL F.R.S. Treas. Chem. SOC. (Abstracted by the author from the Philosophical Tran3actions for 1869.) THE degree of rapidity with wliich an explosive substance undergoes metamorphosis as also the nature and results of that metamorphosis are in the greater number of instances suscep- tible of several tnodificlttioiis by variations of the circumstances under which the conditions essentidl to cheinical change are fulfilled. Gun-cotton furnishes an excellent illustration of the manner in which such mo.Iifications may be brought about. If a loose tnft or large mass of gun-cotton wool be inflamed in open air by contact with or proximity to some source of heat the temperature of which is about 135' C.or upwards it flashes into flame with a rapidity which appears almost instantaneous the change being attended by a dull explosion and resultiilg in the formation of vapours and gaseous prodncts of which nitrogeii-oxides form important constituents. If the gun-cotton be in the form of yarn thread woven fabric or paper the rapidity of its inflamrridtion in open air is reduced in proportion to the coiupactness of structure or arrangement of the twisted. woven or pulped material; and if it be converted by pressure into compact masses solid throughout the rate of its combus- ABEL’S CONTRIBUTIONS TO tion will be still further reduced. If to a limited snrface of gun-cotton m7he11 in the form of a fine thread or of a compactly pressed mass ;t source of heat is applied the temperature of wl.ich is sufficiently liigh to establish fhe nietamorphosis of the substaiice but not adequate to inflame the products of that change (carbonic oxide hydrogen kc.) the rate of birrning is so greatly reduced that the gun-cotton may be said to smoulder without flame as shown by me in a communication to the Royal Society in 18G4* ; the reason being tliat the products of change which consist of gases and vapoiirs continue as they escape into air to abstract the heat developed by the bnrning gun-cottm 80 rapidly that it caiiiiot accixmulate to an extent sufficient to clevelope the usual cornbustion with flame of the material.For sirnilnr reasons if gun-cotton be kindled in a rarefied atmosphere the change developed will be slow and imperfect in proportion to the degree of rarefaction so that even if an incandescent wire be applied in a highly rarefied atmosphere to the gun-cotton it can only be made to irnclergo the smoul- dering coiiihustion until the pressiire is sufficiently increased by the accuiiiulating gases to reduce very grea-tly the rate of abstraction by these of the lieat necessary for the rapid com-bustion or esplosioii of the substs?ice.t If on the contrary the escape of the gases from buriiiiig gun- cotton be retarded as by endosing it in an en~dopeor bag of paper or in LZ vessel of which the opening is loosely closed the escape of lieat is inipcded uiitil the gases developed can exert sufficient pressure to pass aw:Ly fi-eely by burdting open the envelope or aperture and the result of the more or less brief coniiiieinent of the gasps is a more rapid OF violent explosion and consequently more perfect metamorphosis of the gun- cotton.So within obvious limits the explosion of gun-cotton by the application of flame or any highly heated body is more perfect iii proportion to the amount of resistance offered in the first instance to the escape of the gases ; in other words in proportion as the strt~iigthof tlie recept tcle enclcsing tlie gun- cottoii aid tlie conseqnent ini tLi1 pressure developed by the explosion is iiiciwsed. Hence while gun-cotton has been found too rapid or violent in its explosive action when corifined in guns and has proved a most forniidable agent of destruction * Proceedings of the Royal Society vol.xiii p. 213. -f Ibid. p. 205. THE HISTORY OF EXPLOSIVE AGESTS. if enclosed in metal shells or other strong receptacles it has hitherto been found comparatively harmless as an explosive agent if inflamed in open air or only corifined in weak recep- tacles. Other explosive compounds and also explosive mixtures are similarly influeneel though generally iiot in such various ways by the circumstniices attending their inetnniorphosis. Thus the rapidity of the explosion of gunpowder is modifietl by variations in its deiisity and state of' division and in the degree of facility afforded for the escape of the generated gases and consequently of the heat wliich is disengaged during the explosion.Bler-curic fulminate may be inflamed in open air upon a piece of very thin sheet metal without indenting it and furiiishes under these circumstances a comparatively feeble explosion ; but if e+en a very much smaller quantity be enclosed in a case or receptacle made of'the same description of sheet nietal the latter will be shattered into many pieces when the fulminate is inflamed and the explosion will be attended by a violent report. Modifications appareiitly slight of' tlie irnniier in which the source of heat is applied to these explosive agents when ex-posed to air under circuiiistaiices in other respects uniform suffice to modify the character of their explosioiis iii a remark-able manner. Thus a rnodificatioii of the position in which the gource of Beat is placed with refertiice to the body of' a charge of gunpowder which is ouly partially confined suffices to alter altogether the character of the explosion produced.This is illustrated by tlie followiiig experiment. A cylinclriual case of sheet tin 2.5 inches diameter G inches long and open at one end to its full diameter was inserted up to its opeiiing in stiff clay soil which was tightly rammed rouud it. The cylinder was filled with fine-grain gunpowder (about 1lb.) and tlie charge was inflamed by means of a small eiectric fuse inserted just beneath the exposed surface of powder. The latter burned with a violent rushing sound similar to only of much less duration than that produced by tlie first igiiitioii of a rorket and iiidic-tting a rapidly successive ignition of layers of the powder.The canister was split open in the soldered Beam but was not thrown out of the hole. A small ynaiitity of earth was thrown up but fell back into the hole. A second corresponding charge of giinpotvder was arranged in precisely the game manlier as in the preceding experiment aiid was in- ABEL'S GOXTRIBIJTIONS TO flamed by means of an electric fuse placed at the bottom of the charge. -4loud explosion was produced; much earth was thrown up and scattered the bottom of the tin case was found in the crater produced but the body of tlie case was not re-covered; it had evidently been projected to a considerable distance. In this experiment the main body of the charge obviously acts at tlie moment of ignition as tarnping does in a blast-hole by presenting a resistance to the escape of the gases generated and thus for a moment establishing the pressure essential to the violent or perfect explosion of the portion of gunpowder first inflamed whereupon the same cliaracter of explosion extends throughout the charge.Mercuric fulminate furuislzes still more striking illustrations of the manner ill which the position of the source of lieat with reference to the main body of tlie explosive rmterial to be inflamed influences the character of the explosion. In firing some charges of mercuric fulminate freely exposed by means of small electric fuees it was observed on tlie one hand that a small quantity (0.65 gym.= 10 grains) producd occasionally a very much more violent exploaien than was obtained with double the quantity of the same fiilmiiiat e inflamed appsreiitly in the same way and on the other hand that equal quantities of the f'uliiiinate snccessivdy inflamed produced in one instance a dull report such as is well known to be fiirnished when flame is applied to a small qnantity of freely exposed fulminate wliile in the other instance a very sharp detoiia tion was obtained like that observed when a small quantity of closely confined fulririnate is exploded. Believing that this remsrkuble difference of result might perhaps be caused by a variation in tlie force of explosion of the small electric fuse I substituted a platinum-wire for the latter as the inflaming agent and still the same variable results were obtained.'l'hese were at first thought to be due to a variation in the surface of the fulminate heated at one time but they were soon traced to variations in the position of the source of heat. 1-32 grm. (25 grains) and 2-64 grnis. (50 grains) of tlie fulmiiiate inflamed by allowiiig the incandescent wire just to touch the top or edge of the heap exploded with a dull report and produced no effect iipon the thin flat,plate of copper sheet upon which they rested; but about 1 grm. (15.5 grains) of the same fulrninate heaped up over the platinum-wire produced a sharp and THE HISTORY OF EXPLOSIVE ,AQEXTS. violent explosion tlie force of wliicli deeply iiicleiited and bent up the support of sheet copper.Equal quantities of the fulini- nate were made to explode feebly or detonate violently at pleasure simply by varying their arrangement with reference to the position of the sGurce of lieat. A few substaiices of which the metamorphosis into gaseous products and vaponrs is dereloped by much less powerful im- pulses from without than those just instaiiced the explosioii of which is therefore determiced by but little elevatioii of tenipe-rature or by the application of slight disturbing iinpiilses of a niechaiiical or chemical nature would appear at first sight only to a small extent susceptible of modifying influences siidar tc the above. The direct application of but little heat or thc production of a slight increaw of temperature by gentle friction or pressure or by the development of chemical action in some very small portions of the mass suffices to explode the cliloride or iodide of nitrogen or silver-fulmiiiate ; aiicl the explosion of one particle developes an impulse so greatly in excess of that required to disturb the chemical equilibrium exis tiiig among the molecules of the mass that instantnneous decomposition ensues throughout.The great proneness to change of these substances when exposed to a slight disturbing influence is illustrated by the fact that a concussion imparted to the air in a spacious apartment iii which the iodide of nitrogen has been placed by means of a small explosioii or detonation or eve11 by the violent slamming of a door suffices to bring about the explosion of that substance.But even if these bodies be so confined that an initial resistance is offered to the escape of the gaseous products of their explosion the violence of the detona- tion is greatly increased the development of explosive force being restricted to the instant of rupture of the envelope by the compressed gases. Thus the vioience of explosive force exerted by a small quantity of silver-fiilminate confined in a case of stout sheet metal is very decidedly greater than if a corresponding quantity be enclosed in metal foil or freely ex-posed to air and inflamed in the sarne manner. The violence of explosion of iodide of nitrogen has been fouiid to be very decidedly increased by enclosing it in an envelope or shell of plaster of Paris or better still in a case of sheet metal while the chloride of nitrogen explodes with but comparatively little VOL.XXIII. E ABEL'S COSTRIBUTIOKS TO wiolence iinlcss it is confined. The reputation which this sub-stance has eiijoyed of hing tlie most violent explosive body known appears to have been due to the f8ct that experiments on its explosion liave always been coiiducted ~ith a covering of water upon the material. Three or four drops (about 0.14 grm. = 2 grains) placed in a watch-glass covered oiily witli a thin layer of water explode with a sharp report when touched with turpentine and almost pulverize the glass ; but sirnilar quantities of which the upper surfaces were exposed to air have been repeatedly exploded in watch-glasses without break- ing the latter.2 grms. of the chloride contained in a watch-glass ,and covered with a thin layer of water were placed upon a small solid cylinder of hard papier wzcxch& ~hicli rested iipon paving. A violent explosion was produced by touching the cliloride with turpentine the watch-glass was pulverized and dispersed and the cylinder was greatly shattered fragments hcing prqjected in all directions. 4 grms. of tlie chloride with the upper surface exposed to air and placed upon a similar cylinder of papier nud did produced a comparatively very feeble explosion ; the watch-glass was broken but the cyliiider was not in the slightest degree affected and remained undisturbed in its original position.A repetition of the experiment with 4 grma. of the cliloride eiiclosed by a thin layer of water pro- diiced complete disintegr:~tioii of the cylinder. It appears from these results that in the case of the chloride of nitrogen the decomposition of which is of an instantaneous character the resistance offered at the moment by the layer of water acts as effectually in intensifying the force of explosion as a tliiii sheet metal case does with the mercuric fulminate or as a strong iron shell with gun-cotton or gunpowder. The product of tlie action of nitric acid upon glycerin which is known as nitroglycerin or glonoin and as regards its power of sudden explosion bears some resemblance to the chloride and iodide of nitrogen appears to be susceptible of only two varieties of decomposition.If a snfficient source of heat be applied to some portion of a mass of this liquid in open air it will inflame and burn gradually without any explosive effect; aid even when nitroglycerin is confined the development of its explo-sive force by the siiiiple application of flame or of other sources of heat by the orcliiinry inodes of operation is difficult and THE HISTORY OF EYFLOSIVE AGESTS. very uncertain. But if the substance be submitted to a sudden concussion sncli as is produced by a smart though not very lriolent blow from a lia~miier upon some rigid sLu.f:,Lce or1 Tvllicli the nitroglycerin rests the latter explodes witli a sharp detona- ti^ just as is the case with gun-cottoii. Only that portion of the explosive agent detonates which is irnmediately between the two surfaces I)rouglit into sudden collisioii ; the coiifinenient of this portion between the lianimer aid the support combined with the instantaneous decomposition of the portion struck prevent ally surrouiiding freely exposed portions from being sirnilarly exploded by the detonation.Asimilar result is ob-tained if oily explosive compound or mixture be mbiiiitted to a sufficiently sharp aid violent blow but the teiidency of sur-rounding particles to become inflamed by the detoiiation is in direct proportion to tlie rapidity of explosive action of the substances. The practical difficulties and uncertainty which attend at-teriipts to clevelope the explosive force of nitroglycerin by the agency of flame or tlie simple application of any highly heated body even when the material is coilfined in strong receptacles (such as iron shells or firmly tamped blast-holes) ,appeared fatal to any useful application of the powerful explosive properties of this sul~~taii~e until ill.Alfred Nobel’s pei.sevwing labours to utilize nitroglycerin eveiitually resulted in the discovery of ainet,hod by which the explosive power of the liquid could be developed with tolerable certainty.M. Nobel first employed guiipowder as a vehicle for the application of nitroglycerin. By impregnating the grains of gunpowder with that liquid he added considerably to tlie destructive force of the powder wheii exploded ill the usual way in closed receptacles.hl. Nobel’s subsequent endeavouis to apply nitroglycerin pep se were based upon the belief that its explosion iniglit be effected by raising some portion of a quantity of the liquid to the temperature necessary for its violent decompositioii whereupon an initiative explosion would be produced which would determine the ex-plosioii of any quaiitity of the substance. I have never succeeded in effecting the explosion of nitrogly- cerin by siiriply bringing it into contact with an inflamed or incandesceilt body but the following results illustrate the manney in xiliicli a score of heat may operate in accomplishing the explosion of tliis substauce. E% ABEL’S COXTRIBUTIOFS TO A piece of very thin platiiiuin wire stretclied across between tlie terminals of two insulated copper wires was immersed in nitroglycerin ; these wires were connected with a Bunseri battery of five large cells and a second piece of platinnrn-wire siiiiilar to thxt immersed iu the liquid was introduced into the circuit.This was then compleled with the intervention of a long piece of platinum-wire between one of the conducting- wires and the battery. The resistance presented by this inter- posed platiiiuui-wire was gradually reduced by shorteiiing it until ultirnately the short platinum-wire not immersed in the nitroglycerin was fused. The latter was not exploded nor inflame& nor was the wire enclosed in it fiised the heat cle-veloped in the latter bciiig rapidly absorbed by the surrounding liquid and removed by coiivection.A very much tliiclier platinum-wire was now snbstituted for the thin one arid ini-rnersed in the liquid; a second sliort piece mas not interposed in the circuit in this instance but a long platinum-wire of the same thickness as the above was employed as ;t nieans of gradually reducing the resistance in circuit. When tlie leiigtli of this wire had been reduced to five inches it was raised to briglit redness ; this state of thiiigs was maintaiiiocl for about one minute but the sliort wire in the nitroglycerin did not glow at the expiration of that period iior did the liquid exhibit any signs of cliaiige but the glass vessel containing it had become very ~vaim. The long platiiiuin-wire was then removed aiicl the fill1 battery-power was passed into the short wire immersed 511 tlie liquid.After the lapse of about oiie minute the latter began to assume a brownish coluur (like tlint of i~ solution of iron) which rapidly cleepencd tlioiigh no red vapours were perceptible in the upper portion of the vehsel until after the lapse of 90 seconds ~-1ieii the iiitroglyc~i*iii cxploclecl with gmtt violence. Several uiisuccmsfiil atteiriyts were afterwards ~iitde to explode iiitroglyc(.rin by inCaiis of‘ the electric spark hut eventually by allowiiig the sparks fi-om a Rnhmkorff coil with a Leyden jar attac1ie:d to pass iuiintcrriiptedly hctweeiz the poles which were just touching thc liquid the latter beiiig splashed up by the discharges tlie surface of the liquid spee(lily darkened aiid in 30 secoiicls it explotled.It is evident from tliese rt sults tlint iiitroglycaei.iu can be e,rl?!~dec/ by electric ageilcy or by direct application of‘any other source of heat oidy if tlie illtensity of the latter or tlie period THE HISTORY OF ESPLOCjIVE XGEXTS. during which it is applied suffices to dievelope decomposition in some portion of the liquitl ; when mice this is established the temperature is soon raised by accuinulation of heat (especially if the application of external lieat be coiitiiiuedj until it attains the point at diich explosion occurs." * In experiments instituted some time since on the action of hest upon nitro- glycerin I found that a small quantity (one or two drops) of pure nitroglycerin if exposed to a very gradually increasing temperature might be raised to 193" C.(380" F.) without the occurrer1c.e of an explosion ; the liquid sustained slow deconi- position until it was cntirely deprived ot explosive properties. A larger quaniity enclosed in a sealed tube was exposed for four dajs to a temperature of 100" C. with-out exploding. At the expiration of that period the liquid had assumed a brownish colour but this gradually disappeared altogether aftcr the tube had cooled down ; arid when tile latter was opened after the lapse of some days there was no pressure of gas nor did the liquid exhibit the slightest acidiLy. In this instance the decom- posiiion prolmbly resulting in the liheration of the nitrogen-oxides was established by the continued exposure to loo" and would doubtless as in the case of the electric experimeilts have gradiially increased if the application of heat had been continued until the internal development of heat had resulted in explosion.The difference in the behaviour of nitroglycerin and gun-cotton when exposed to the influence of a s wee of heat (apart from the difference in the heat required for their explobion) is evidently due principally to tlie difference in their plij sical condition. When a heated body is applied to nitroglycerin the liquid nature of the latter leads to the diytribution tht ough its mass of the heat applied with rapidity s {Aicient to render the ignition of the but slightly volatile liquid a matter of difliculty even I)g the application of a very highly lieated body such as a red-hot wire or rod or a piece of burning wood ; and when the liquid is actually inflamed it burns at first non-explosively because the increase in temperature of the body of liquid (or of that part presented by the burning surface) which is necessary for developing its sudden decomposition or explosion takes place only gradually.But if by establish-ment of a slow decomposition throughout or in 6omc portion of the nitroglycerin a tendency to disruption of tlie constituent-molscules is developed the disturbance of chemical equilibrium favours the action of any impulse from without such as tlie direct application of heat so that the violent qiloaion or sudden. decomposition of the mass is determined by applying heat to an extent wliich would under normal conditions be quite inadequate to brinz about such a result.In the case of the solid and badly conducting substance gun-eotton when a so~irce of heat just sufticient for its ignition is appiied to any portion the best is not diminished by distribution through the mass hence the particles of gun-cotton contiguous to the ~ource of heat are inflamed ithost immediately. If the gun-cotton be in a loose or porous condition (e.g.,iu the form of wool or of loosely wound thread) the entire mass will inflame with such rapidity as to produce a species of explosion on account of tile rapid penetration to the surrounding particles of the heat rtsulting from the first ignition; but if it be in a compact (compressed) mam in which the contiguity of particles more nearly approaches that of the particles in the liquid nitroglycerin the gun-cotton proceeds to burn gradually from the exterior towar& the centre of the mass.If gun cotton be exposed to a source of heat insqficie~ltfor its ignition tlie heat will gradually accumulate in those parts most contiguous to the source spreadiiig ABEL'S CONTRIBUTIOSS TO 31. N obe 1has described various devices for effectirlg this SO-called i~iticrtiveexplosion of some portion of a nitroglycerill charge of which evidently the most successfd are the explo-sion of a small coiitiiieci charge of gunpowder 01' of it lilrge percussion-cap wlim immersed in or placed imnlediately over the iiitroglyceriii. M. Nub el however classes these two modes with comparative tardiness tlirough the mass.A twofold result will then be obtained ; heat eventually accumulates to an extent sufficient to establish chemical change in the mass whicli becomes greatest near the source of heat SO that if the application of the latter be not interrupted the temperature requisite for ignition will be speedily attained in those portions the result will however be no longer the simple inflaming of the gun-cotton with mnre or less rapidity but an explosion will ensue as in the ca=e of nitroglycerin the violencc being proportionate to the heat which has accumulated and to the extent to which a disturbance of chemical equilibrium h; s been ertablislied. Frequent confirmations of this view have heen obtained in the course of my inveqtigations on the effects of heat upon gun-cotton.The violence of explosion of samplei of gun-cotton confined in fa-ks with not very narrow necks which had been for some time previously underqoing decomposition (from long-continued exposure to temperatures considerably below its inflamingpoint) was always very much greater than would have heen the case had gun-cotton in the flasks heen ignited by t'ie momc n'arr application of a highly heated body. It woiild appetlr from tempera. ture-okssrvations carried on during experiments of this kind (" Phil. Trans.," vol. clvii pp. 197 223 226) that in those instances the great violence of explosion was to be aecribed in part to the rapid accumulation of heat in the mass of gun-cotton when the decomposition had renched particular stages ; but there can be no question that at the period immediately preceding the explosion the gun-cotton was in a state of high chemical tension and readily susceptible of instantnneoiis chemical chanqe tlironqhout just as a Rupert's drop is readily suwepti1)le of violent mechanical disintegration ;so that the passage from gradual to instaiitaneous and therefore most violent decompo~ition would occur as soon as the accumulation of heat attained the point at which a sufficient disturbing impulse was imparted to the mass The followin series of experiments appear confirmatory in their results of the conclusions drawn from the accidental results obtained in the experiments just alluded to.A wide test-tube was filled to about one-fourth with gun-cotton the mouth of the tube was left open and the gun-cotton was inflamed by means of a platinum-wire heated by electricity.h faint explosion was the result accompanied by a consider- able bcdy of flame and a portion of the gun-cotton was projected from the tube unburned. The experiment was repeated the tube being immersed for several minutes in a water-bath at a temperature of 100" C. so that the gun-cotton waq raiced throughout to that temperature immediately before it was inflamed. The explosion was decidedly though not very greatly more vehement than before; the tube was not shattered. A broad piece of thin platinum-foil about 2 inchcs long mas attached hy its two sides to copper wires leading to the poles of a batterr sufficient lesistance being introduced into the circuit to prevent the foil from being raised to a higher tcmpera- THE HISTORY OF EXPLOSIVE AGENTS.of ignition in wliich an explosion or detonation is applied as the exploding agency together with various others in which the siniple application of a high temperature to some portions of‘ the nitroglycerin is proposed. as the means of explosion; and although iii his pnblished description of these varions methods he refers to difficulties in developilig explosion by those which relate to the simple application of flame or other heated body to the iiitroglycerin yet lie refers the effect! pro-duced by the confined charge or the percussioii-cap only tc the heat developed by thc ignition of these exploding agents.The circumstance that nitroglycerin or any preparation of that subst;mce may be violeiitly exploded whetL ji*eeZy exposed to ai~, by the explosion in contact with it of a small confined charge of glmpowtier or of a detonating substance ~hile other modes of explosion by the application of heat or flame which have been described by bf. Nobel only devclope explosion under special coiiciitions poiiits to a decided diKerence between the actioii of the two rnocles of ignition and appears to indicate that it is not simply the heat developed by the chemical change of the gunpowder or cletonatiiig powder which determines the esplosioii of the iiitroglycerii~ An experimental investigation of this suGject has left no doubt on my milid that the explosion of nitroglycerin though ture than 90°-10Go when the circuit was completed.The wires were approached to each other so that the strip of foil formed a species of tube open at both ends and down the side. A similar quantity of gun-cotton to that used in the pieceding experiments was placed inside this tube being therefore nearly surrounded by the foil. The whole arrangement was then introduced into a test-tube like those used in the preceding experiments and the voltaic circuit mas complet d. In the course of a few minutes the odour of decomposing gun-cotton was perceptible at the opening of the tube ;faint nitrous vapours were soon afterwards observed and within about fifteen minutes after the first application of heat the gun-cotton exploded very sharply with only a faint flash and the tube was shattered and violently dispersed.The great violence of the explosion at Woolwich in 1866 of about 140 lbs. of gun- cotton which had been exposed to elevated temperatures for ten months and of which some packages very imperfectly purified were known to be in a state of decomposition at the time (“Phil. Trans.,” vol. chi p. 243 et seq.) can scarcely he ascribed only to the circumstances that the gun-cotton had been closely packed in strong cases and that the packages of giin cotton were at a temperature of about 50” C. at the time of the explosion. When the decomposition established in some mall portion of the gun-cotton bad attained the condition resulting in explosion a large quantity of the material was in a state of incipient change and therefore in a favourable condition for sudt!en metamorphobis ; and this circumstance must have greatly contributed to the suddenness and consequeiit violence of the explosion.ABEL'S CONTRIBUTIOSS TO the agency of a sniall detonation is due at any rate in part, to the niechanical effect of tliat detonation and that this effect may operate in exploding tlie nitroglycerin quite independently of any direct action of the heat disengaged by the gunpowder or other detonating charge. I was led to examine into this question by an interesting and important observation recently made by my assistant Mr. E. 0. Brown in connexion with gun-cotton. The fact that the violent explosion of this substance cannot be developed except when it is confined in receptacles of some strength has been up to the present time accepted as indisputable.It occurred however to Mr. Brown tlint RS gun-cotton is aiialogons in its nature and operation as an explosive agent to nitroglycerin differing principally from that snbstance in the rapidity and consequent violelice of its explosion it might also like nitro- glycerin be susceptible of violent explosion when unconfined by being ignited tliroixgh the agency of detonation. This proved to be the case ;for upon exploding a small charge of detoiiating powder in contact with or iu the iiiiniediztte vicinity to com- pressed gun-cotton freely exposed to air instead of the latter being simply inflamed and then burning gradually as would be tlie case if it were brouglit into contact with flami or any Sufi-cient source of heat' it explodes with great violence exerting a destructive action equal to that of nitroglycerin and decidedly greater than that produced by gun-cotton when exploded under the conditions hitherto believed to be those most favourcible to thc full development of its explosive force.The explosion of it siiiall mass of compressed gim-cottoii in this manner sufices to dcterinine the similarly violent and apparently simultaneous explosion of small detached niasses of the same material which may indeed be placed at distances of 0.5 to 1 inch froin the original source of the explosion or from each other. Thus rows of detached masses of gun-cotton placed on tlie ground and extending 4 or 5 feet have been exploded with most des- tructive results by the firing of a small detonating tube in contact with the piece of compressed gun-cotton which formed one extremity of tlie row or train the explosion of the entire quantity being apparently instantaneous and eqimlly violent throughout.In tlie first experiments instituted with the view of ascertain-ing tlie conditions to he fulfilled for ensuring the development of THE HISTORY OF EXPLOSIVE AGESTS. the violent action or for accomplis1iing tlie cietonation of gun-cotton ~.vl1en perfectlj- unconfined the foIlowiiig points were observed :-1. If a confined charge of mercuric fulminate be placed in contact with or buried in gun-cotton which is in the form of wool or spun-yarn its explosion does not develope the violeiit action of the gun-cotton as would be tlie case if the latter were in the form of a compact hard anci liomogeneous mass (as obtained by submitting finely divided gun-cotton to powerftd pi*esaure).The light and loose gun-cotton is simply scattered with violvnce ; portions or' it are aometimm ignited by the Aaine of the exploding fidminate the latter result being obtained with greater certainty the less violent the detonation produced by the fulminate-charge. 2. The detoiiation of a sniall mass of compressed gun-cotton frecly exposed to air by means of a inercuric fulminate-charge does not accomplish the explosion of light gun-cotton wool or yarn placed in immediate contact with it the latter is scattered and partially iiiflained as in the preceding case.3. If the detonation of tlie fulminate-charge ~vliicli is placed in contact with a niass of compressed gun-cotton is not saffi-cieiitly violeiit or sharp to effect the explosion the solid mass is shattered aid violently dispersed ;if the detonation is upon the verge of that required for determining the violent explosion of the gun-cotton no inflammation of the latter takes place ; but if the explosion of the fulminate-charge is comparatively feeble portioiis of the gun-cotton are inflamed at tlie momeiit of dispersion of the mass. 4. Explosive substances which are inferior to mercuric ful- minate in Jie suddeiiness and coriscqueiit m omentary violence of' tlieir detonation cannot be relied upon to effect the ~iolent explosion of freely exposed gun-cotton even if employed in comparatively considerable quantities.Thus even ordinary percussion cap composition which consists of a mixture of nlercuric fulminate and potassic chlorate caiiiiot be used for the detonation of €reely exposed gun-cotton uiiless a much niore collsidersble amount be used than is necessary of.pure mercuric fulminate for that purpose. Many other detoiiatiiig mixtures exploding less rapidly and violently thaii the above have been tried without success in very considerable quantities as agents for developing the cie tonation of gun-cotton in open air. ABEL'S COSTRIBUTIONS TO 5. The quantity of confined mercuric fulminate required to effect the detonation of freeiy-exposed gun-cotton is regulated by the degree to which the sharpness of its explosion is increased by the extent of accumulation of force consequent upon the strength of envelope in wliicli the fulminate is confined.From 1.3 to 2.0 grnis. (20 to 30 graiiis) are required to detonate the gun-cotton if the fulminate be confined in a thin case of wood or in several wrappings of paper while the same result can be produced with 0.32 grm. (5 grains) if that amount be coii- fined in a cap of thin sheet metal. If tlie fulminate be placed iii a wide paper cylinder open at the top which is rested upon tlie gun-cotton surface or if it be placed in a heap directly upon tlie surface of gun-cotton and if in either instance the violent explosion of the fuliiiinate be effected through the agency of a platinum-wire placed at the hseof the heap about 2 grrris.(25 to 30 graiiis) of fulminate will also accomplish the detonation of the gun-cotton the violent action of the fulminate being in these instances developed by the confinernent of tlie portions first ignited in a weak envelope which consists pa.rtly or eiitirely of tlie sur-rounding or superincuiiibeiit fulminate. 6. It need perhaps scarcely be stated that the degree of proximity of the detoiiatiiig charge to the gun-cotton which is essential for the explosion of the latter is regulated by the violence of the detonation produced. 0.32 grm. (5 graiiis) of fLilmiiiate enclosed iii a metal cap must be placed in close coii-tact with (i.~.,closely surrounded by) the unconfined gun- cotton in order to effect its explosion while 1.3 grni.(20 grCiiiis) similarly coiifined will produce the same result if placed at least 0-5inch distant from tlie surfiice of the compressed guii-cott011. The foregoiiig f'dcts appear to point to the inechariical action of a detoriatioii as being the real cause of tlie violent explosion of freely exposed gun-cotton or nit,roglycerin. At any rate tliey appear to indicate decisively that such explosioii is not a result of the direct application of tlie heat developed by the esplosion of the detonating materials. If it were so then the detonating mixture described as percussion-cap coniposition aild other explosive iiiixtiires the ignition of which is attended by much greater development of heat than is obtaiiied by the ignition of' pure mercuric fulminate should explode freely ex- 55 THE HISTORY OF EXPLOSIVE AGENTS.posed gun-cotton more readily thaii the latter does ; tlie readi- ness with which the gun-cotton is exploded should be solely proportionate to the amount of fulminate employed ; and gun-cottpn should be more readily exploded in the loose and open condition than in tlie compact arid highly compressed form ; fw the latter presents it in the condition least favourable and the former that most hvourable to ready and rapid ignition by heat. Again the actual temperature required for the explosion of nitroglycerin is very considerably higher than the exploding temperature of gun-cotton; the former may be heated to a temperature of 193O C.(380' F.) for some time without ex-ploding while the latter inflames at a temperature of 150" C. yet H much smaller charge (not more than 0.2 of the amount) of ftdminate suffices for tho explosion of uncoiifiiied nitro-glycerin than is needed for the det,onation of gull-cotton. On the other haiid a quantity of confined percussion-cap composi- tion which if it were pure mercuric fiilniinate would be alto- gether inadequate for the detonatioii of gun-cotton suffices for t11e detoiiatioii of nitro gl ycer iii . Although the foregoing fiwts appear to afford indisputable evidence tbat tlie direct application of heat from an explcjding charge of detonating powder is not conceriiecl in clevelopiiig tlie violent action of gun-cottoil or nitroglycerin an attempt has been made to devise ~omeexperiineiits in which the deto- iiatioii of either of those substances by the agency described should be accomplished in such a nianiier as to interpose an effectual barrier between the inaterial to bc exploded arid the hei1 ted gases or flame resulting from tlie ignition of the charge of' fulminate destined to fiumisli the initiative cletoiiatioii.Some sinall pellets of compressed gun-cotton saturated wit11 nitroglycerin were placed in a cylindrical 117oocieri case open at 0110 eiid :md fixed at the bottom of a trough of \\rater ; thc air- spaces between the separate pellets were thus occupied by water the height of whicli above the charge was about oiie foot.An electric fuse priiiid with 2.6 grins. (40 grains) of mercuric fulniiiiate was weiglitccl tiiicl placed at the bottom of the trough 011 one side of the cylinder and at a distance of 2 inclics from it. The cletonativri of tlie fulminate cli(l not ex-plode the cliarge ; the experiment was then repeated tlie water-sp (LVe whic 11iiit erveii ed betwe eii the filse aiid t 1ic 117 c)odeii cylinder beiiig reduced to 1 iiich. Lii this inst'tiice the fi~iilg 5 (5 ABEL’S CONTRIBUTIOXS TO of the filse exploded tlie immersed pellets the water. was pro-jected to a great height the trough was broken into small fragments and a crater was formed in the ground upon which it rested. Tliis experiment was repeated with the same resulta.A small cylinder of compressed gun-cotton saturated wit11 nitroglycerin was enclosed in a paper case which was thickly coated with a gutta-percha and pitch cement. A screen of thin sheet copper was placed at the bottom of a trough and the waterproofed charge of explosive materi;d was weiglitcd and placed npon one side of the screen at 0.25 iiicli distaiice frorri it. A waterproofed electric fuse primed with 2-6 gmis. (40 grains) of mercuric fiilniinate was placed on the other side of the screen at a clistance of 1inch from the latter; the troiigh was then filled with water SO that the screen charge niid fuse were each surrounded and separated by tlie liquid. In the first experiment tlie explosion of tlie fuse did iiot affect the charge but upon repeating the expcriment with it fiise placed at a dis-tance of 0.75 inch fiom the screen the clzarge was violently exploded as in the former experiment.A precisely similar experiment was tried with cylinders con-sisting of compressed gin-cottoii only and enveloped in coatings of sonic thickiiess of tlie gutta-percha cement ; but even when the charge and the fiise were placed close to the sides of the screen which separated them under \%riLter the giui-cottoii was not exploded by the detonation of the fulminate tlie same negative result was obtaiii ecl when a fuse (enveloped in the waterproof coating) was placed immediately upon a giui- cottoii charge enclosed in the paper case and waiprproof cement and exploded under water or in open air.These nega- tive results were instructive as inclicatiiig that tile thick yielding envelope whicli enclosed the gun-cotton chtirgt (pos-sibly assisted by the thin air-cushion by wliich the enclosed charge was also surroimded) served to protect the compnratively less sensitive explosive material gun-cotton by reducing or absorbing tlie power of the blow or concussioii (or whatever the distiirbing impulse may be). This explanation wcxs show11 to be correct by the fact that a cylinder of gun-c:ott,on enclosed in a water-tight case of thin sheet metal and immersed in water was violently exploded by a fihinate-fuse wliich was placed bj-its side with about 0.25 inch of interveniiig water. Same nitroglycerin coiitct.iiiecl iii a gluss bcalier placeci at THE HISTORY OF EXPLOSIVE AGENTS.the bottom of a trough filled with water was not exploded by a fulminate-fuze placed at a distance of two inches from tJhe side of the beaker; but when the intervening water was re- duced to little more than one inch the detoiiation of the fuse exploded the nitroglycerin. L4 12-pounder cast-iron shell was filled about one-half with small granules of gun-cotton impregnated with nitroglycerin ; it was t,hen filled with water and a waterproof fulminate-fuse was inserted through the plug which closed the shell. The fuse and each separat'e granule of the explosive agent were therefore surrounded by water. Upon ignition of the fuse the shell (which was placed in a very strong room) exploded with a violent i'eport aiid was broken into very sniall fragments the greater number of which were buried iii the timber which lined the cell.A similar shell was half filled with the same explosive agent ; the spaces between the granules and the eniyty portion of the shell were then filled with a thin plaster of Paris mixture and a fiilniinnte-fiise was imbedded in the solid plaster which filled the upper half of the shell. The explosioii of the fuse was attended by a precisely siinilar result to that obtained in the preceding experiment. It is believed tlint these experiments together with the facts regarding the behaviour of gun-cotton which have been stated in the earlier part of tliis paper afford conviiicing proof that the violent explosion of gun-cotton and nitroglycerin through the agency of a detonating fuse must be ascribed either to the mechanical effect of that detoiiatioii (ie.to the work done upon the particles more immediately exposed to the blow or coil-cussion of the detoiiation) or to the development of a dis-turlmnce of chemical equilibriurn in the explosive agcnt by the sutldenness and peculiar character of the concussion or by the powerful vibrating impulse wliicli the detoiiatioii es tnblislles. Tlie readiness and certiliilty with which gunpowder gun-cotton and other explosive substances may be detonated through the agency of a blow from a hammer or a falling body are regulated by several circnmstances ; they are in direct pro- portion to the weight of the fitlliiig body to the height of' its fall or the force with whicli it is impelled dowii\vitrds to tlie velocity of its inotion to the mass and rigitlity or liardness of the support or anvil ~p~ii which the body falls ; to tlic qimitity and niechanical coliclition of the explosive agent Y truck and to ABEL’S CONTRIBUTIOKS TO tlie ready explosibility of the latter.Thus a sharp blow from a small hammer upon an iron surface will detonate gunpowder with very much greater certainty than the simple fall of a heavy hammer or than a comparatively weak blow from the latter. It is very difficult by repeated blows applied atvery brief intervals to ignite gun-cotton if placed upon a support of wood or lead both of which materials yield to the blow the force set into operation by that blow beiiig transferred tlirongh the explosive agent and absorbed in work done upon the mate- rial composing the support.If however the latter be of iron which does riot yield permanently to the blow of the limimer the detonation of these substances is readily accomplis1zt:d. If the quantity of explosive agent employed be so considerable as to form a thick layer between the hammer and support the force applied appears to be to so great an extent absorbed in the motion imparted to the particles of the compressible mass that its ex- plosion is not readily accomplished; and if the material be in a loose or porous condition (as for example in i~ state of powder or of loose wool) much work has to be accomplislied in moving particles of the mass through a compnratii ely considerable space arid a secoiid or even third blow is therefore required to determine its explosion.These circumstances would appear to afford support for the belief that the detonation of an explosive material through the agency of a blow is the result of the development of heat sufficient to establish energetic cherriical change by the expeii- diture of force in the compression of the material or by the friction of the particles against each other consequent upon a niotion beiiig niornentarily imparted to them. It is conceivable that from either of these causes. sufficient heat niay be accu-mulated with almost instantaneous rapidity in some portion of tlie mass &ruck to develope sudden chemical cliange.The circumstance that the detonation of those portions of an ex- plosive compound (such as guii-cotton or iiitroglj ceriii) which are immediately between the surfaces of the hanimer and the support is not communicated to the surrounding portions may be ascribed to a combination of two causes tlie iiistantaiieous nature of the explosion aid the dose confiiienient of the por- tions struck at the instant of their explosion. The mecliaiiiral eff’ect of ilie detonation is absorbed by the masses of nietal between wliicli it oc~~irrecl, and the gases developed disperse THE HISTORY OF EXPLOSIT’E AGEKTS. the surrounding portions of the explosive agent as they rush away from between the two surfaces. The exceedingly violent motion of particles resulting from the sudden or extremely rapid transformation of a solid or liquid explosive body into highly expanded gas or vapour must obviously exert a force which operates upon a resisting body in the vicinity in a manner precisely similar to the force applied by opposing a body iii the path of a solid mass which is set into very rapid motion.In other words a detonation exerts a mechanical effect upon resisting bodies precisely similar to that of a blow as from a falling hammer or a projectile propelled from a gun. Just as the force of a sufficiently sudden or power- ful blow from a hammer is transformed iiito heat by the re- sistance to the rriotion of the hammer which the particles of ail opposing body present and by the consequent friction esta-blished between those particles so the force or concussive action exerted by the matter set in motion when a solid or liquid is converted into gas or vapour will also be transformed iiito heat the development of which in an opposing body will be proportionate to the resistance to motion which its particles offer and to the suddeiiness and violence of the concussion to which it is subjected.The power of accomplishing the explosion or detonation of gun-cotton or nitroglycerin in open air through the agency of it detonation produced in its vicinity would therefore appear to be correctly ascribable to the heat ‘suddenly developed in some portioii of the mass by the mechanical effect or blow exerted by that detonation and would seem to be regulated by the violence and suddenness (either singly or combined) of the de- tonation by the extent to which the explosive material is in a condition to oppose resistance to the force and by the degree of sensitiveness of the substance to explosion by percussion.The following points appear to support this view :-1. Explosive mixtures (such as percussion-cap composition and mixtures of potassic chlorate with potassic picrate &c.) which are apparently but little inferior to the fulminste in the rapidity of their explosive powers will not detonate freely exposed gun-cotton even though confiiied charges of them amounting to about ten times the quantity of mercuric fulminate required to produce the effect with perfect certainty are employed.ABEL'S COSTRIBUTIONS TO 2. On the other hand nitroglycerin wliich is much more readily exploded by a blow than gun-cotton may be detonated through the agency of explosive mixtures less violent and sudden in their action than the fulminate. A quaiitity of per- cussion-cap composition about one-half that of the minimum of fulminate required to detonate gun-cotton will suffice to detonate nitro glycerin. 3. If the suddenness of the detonation produced by nieaiis of mercuric fulminate be increased by its confinement in a strong envelope a very much smaller quantity suffices to develope the detonation of gun-cotton than if the fulminate be exploded in open air or in an envelope which offers but slight initial resistance. 4. The mechanical condition of the gun-cotton rnost materially influences the result obtained by its exposure to detoiiatiaii as has already been shown.There are however several well-known facts aiid some results of experiments instituted with special reference to this subject which do not appear to be in harmony with the assumption that the detonation of nitroglycerin and gun-cotton in the manner described is simply due to the suddenness of the development and applicatiori of physical force. The follo~viii g are some of the more important facts of this kind :-1. The circumstance that the explosion of mercuric fulminate accomplished the detonation of gun-co tton whereas explosive agents less sudden in their action failed to furnish this result appeared to render it probable that silver fulminate ivliich explodes more suddenly and with much more powerful local force when applied under the same conditions would accoa-plish the detonation of gun-cotton more rea2ily than the iner- cury compound i.e.it was anticipated that a larger amount of the latter would be needed than of silver fulminate to produce the desired effect. This proved however not to be the case. The minimum quantity of mercuric fulmiiiate which caii be relied upon to detonate compressed gun-cotton is 0.324 grrn. (5 grains) andit is necessary to enclose that quantity in a case of stout sheet metal arid to place it in close contact with the pin-cotton iii order to obtttiii the desired result. 0.324 grlxl. (5 grains) of silver fuliniiiate eiiclosecl in tin-foil though it ap- peared to produce quite as sharp a detonatioii as the cor1~-spiidiiig quantity of' iii~cul*y salt coiifiiie~liii the stout case THE HISTORY OF EXPLOSIVE AGENTS.did not explode gun-cotton with which it was closely sur-rounded but merely shattered and dispersed the mass. But when enclosed in the stout sheet-metal cap the 0.3 grm. of silver fulminate accomplished the detonation of gun-cotton. 2. Iodide of nitrogen as one of the most sensitive and ap-parently violently explosive compounds with which we are acquainted was next exp erime11te d wit 11. The suscep tibilii y to sudden explosion even of silver fulminate will not bear com- parison with that of the iodide of nitrogen or of the correspond- ing chlorine compound though as regards the mechanical effect of the explosion (i.e.its local destructive action) both of those cornpounds accomplished decidedly less work than the silver- fulminate under the same conditions. Many uiisuccessful attempts have been made to explode gun- cotton through the agency of iodide of nitrogen. Pellets of this substance (weighing about 0.2 grm. and 0.35 grm.j resting upon paper or thin cardboard were carefully placed when per- fectly dry upon compressed gun-co tton and were then exploded by being touched with the end of a long rod; the compact masses of gun-cotton were more or less disintegrated by the explosions but 110 detonation redted. Indications having been obtained that the violence of explosion of the iodide was decidedly increased by its confinement two descriptions of small shells charged with the substance ci7ere prepared.About 1grm. of the iodide mas placed while moist in a small cup of plaster of Paris a spherical mass of the plaster was then formed round this so that after a time the explosive agent was enclosed in a hard shell the walls of which were about 0.3 inch in thick- ness. The shells thus produced were confined for several days in proximity to a desiccating agent until the perfect desiccation of the iodide of nitrogen throngh the porous plaster shell hsdbeen accomplished ; they were then allowed to fall from heights of 4 feet and 20 feet upon masses of compressed gun-cotton ; their explosion simply shattered the lattm. Similarly negative results were obtained with corresponding quantities of the iodide con- fined in sinall cases of stout sheet copper.6.5 grms. (100 grains) of iodide of nitrogen were also exploded in direct contact with compressed gun-cotton without accomplishing its detoua-tion. 3. The following experiments were made with chloride of nitrogen for the pnrpose of comparing its power to accomplish VOL. XXIII. F ABEL’S CONTRIBUTIONS TO the detonation of gun-cotton with that of the explosive agents already discusserl. About 0.65 grm. (10 grains) of the chloride were transferred to a thin watch-glass and covered with a film of water ; the watcli-glass was placed upon a pellet of g~n- cotton which rested upon the ground. The chloride of nitrogen was tlien exploded by means of a long rod? the extremity of which was moistened with turpentine.The glass was shat- tered and dispersed but the mass of gun-cotton wag only to a slight extent disintegrated. 1 grm. of the chloride was next employed iii precisely the same manner ; the gun-cotton pellet was not exploded but was much shattered by tlie explosion. About 2 gnns. (31 grains) of the chloride applied as before did not explode the gun-cotton but the pellet was completely broken and violently scattered. 3.25 grms. (50 grains) of the chloride were next employed ; in this instance the gun-cotton was detonated by the explosion of the liquid. The experiment was repented tvitli what was estimated to be the same quantity of chloride of nitrogen; the gun-cotton pellet was not ex-ploded but was couq3lctely disintegrated and scattered the effect being the same as that produced with an amount of mercuric fulrniiiate just below that reqnired to accomplish the detonation of gun-cotton.It would appear therefore that 3-25 grins. (50 grains) of chloride of nitrogen covered with water is about tlie iiiiiiiiiiuin quantity reqnired to accomplish the result attainable with 0.32 grin. of mercuric fuliniiiate enclosed in a metal case. The foregoing results obviouslg do not support the view that the suddenness or sharpness of a detonation alone favours the development of violent explosive force from gun-cot ton in open air. The silver-fulminate produces a much sharper explosion than the mercuric fulminate yet it was not found tht-tt a snialler quantity of the former than of the latter was required for tlie detonation of gun-cotton.Tlie explosion of the iodide and the chloride of nitrogen is certainly niore sudden than that of the above fblminates unconfined aid at any rate equally so with the confined fulminates ; yet it was not found possible to detonate gun-cotton by the explosion of 6-5 grms. (100 grains) of tlie iodide in contact with it and 3-24grins. (50 grains) of chloride of nitrogen confined by zantw were required to accomplish the result attained by 0.32 gri. of either of the confined fuhninatea THE HISTORY OF EXPLOSIT’E AGENTS. or by 2 grms. of the mercuric fdminate lulconfiiiecl by any strong envelope. With the view of ascertaining whether the relative power of different explosive agents to accomplish tlie detonation of gun- cotton appears to be in direct proportion to tlie relative mecha- nical effects of their explosion (i.~., to the work perfornied by them upon a body placed in contact with theni) a series of experiments was instituted with the object of comparing this particular actioii of the several explosive mat ctrials.A thin and uniform copper sheet wits cut up into square pieces of equal dimensions and these were similarly supported at their corners only. Equal quantities of the four different explosive agents the mercury- and sil ver-fuliniiicLtes and the chloride and iodide of nitrogen were emploj-crl. In some expe- riments the fulniinates were placed in direct contact with tlie copper in others with the view of comparing them accurately with the iodide of nitrogen they Ivere placed upon thin cards which rested upon the sheet copper.The iodide of nitrogen was always used in this way but as for obvious reasons the chloride of nitrogen could not be thiis employed it was placed in very thin watch-glasses which rested upon the copper sheet. The following is a sumniary of the results furnished by repeated experiments with a series of different proportions of the sevei-a1 explosive ageiits. The violence of explosion of chloride of nitrogen when unconfinecl is less than that of the iodide; if confined under water it very considerably exceeds that of the exposed iodide but falls very short of that exerted by unconfined silver-ful- millate.The mercuric fulminate which is much less rapidly explosive than either of the other substances exerts less mechanical force than any of them if freely open to air and if inflamed at some portion of the exposed surfaces; if ignited at the lower inner portion of the mass wliere the part first inflamed is enclosed by the mass of the material itself it exerts a destructive force little inferior to that of the chloride of nitrogen enclosed by water; but if confined in a strong envelope (e.g. of sheet tin) the mercuric fulminate exceeds the uncon- fined silver fiilminate in violence of action. These results to a great extent confirm the correctness of the view that the readiness with which the detonation of gun-cotton ABEL’S CONTRIBUTIOSS TO is accomplished is in proportion to the mechanical force exerted by the initiative detonation to which it is subjected.The force exerted by small quantities of strongly confined silver- and mercuric-fulminate greatly exceeds that developed by the ex- plosion of comparatively large proportions of the iodide and chloride of rlitrogen. This may be accepted as accounting to some extent for the fmt that the detonation of gun-cotton could not be accomplished by an amount of iodide of nitrogen twenty times greater than that of fulminates required for the purpose while ten times the quantity of the confined chloride were required to produce the result. That the quantity of mercuric fulminate required to produce detonation is reduced in proportion as means are applied to increase the violence of the force exerted- by it at one time is quite in accordance with the above view.Several curious andapparently anomalous effects were hi )wever observed in the course of the numerous experimeiits referred to in this paper wliich suggest the inquiry whether there may not be some peculiarity in the concussion or powerful vibration produced by a particular kind of explosion ~vliicli acts apart or distinct from the meclianicd force of that explosion iii develop- ing or prornotiiig the detonatioii or sudden chemical disintegra- tion of the molecules of a neighbouring explosive body. The results of a few experiments instituted with nitroglycerin appear to furnish a decided affirmative reply to that inquiry.A comparison was in the first instance instituted between the mechanical action of the explosion of nitroglycerin and of the other materials which have been discussed. The charges of nitroglycerin were introduced into small wide tin tubes freely open at the upper end or closed by means of it cement and their explosion was accomplished by the detonation of a small percussion-cap just immersed in or resting upon the liquid and containing 0.07 grin. (1 grain) of mercuric fidminate. Nitroglycerin thus detonated produced a destructive effect upon the copper support very greatly exceeding that obtained with the same amount of unconfined silver-fulminate. As the mechanical force developed by nitroglycerin was so very con- siderable and as moreover the character of its detonation might be expected to bear some analogy to that of gun-cotton it wag considered probable that the latter might prove suscep- tible of detonation by a much smaller proportion of nitroglycerin THE HISTORY OF EXPLOSIVE AGESTS.than it is necessary to employ of the confined fulniinates. No success however atteded repeated attempts to explode gun- cotton by tlie detonation of 0.07 grm. (1grain) and increasing charges up to 0.65 grm. (10 grains) of nitroglycerin. At the same time these results were not quite cor~clusive as it was not found easy to ensure the complete detonatioii of the liquid by the small fulminate-charge on account of the difficulty of securing a favourable adjustnieiit of the detonating cap and the very small quantity (from two to ten drops) of nitrogly- cerin used.The experiments were therefore repeated with corresponding quantities of the liquid coiiverted into a thick paste by admixture with sand in tin tubes similar to those previously used. The explosion of the nitroglycerin appeared to be rendered more certain by this contrivance but in order more thoroughly to ensure its proper detonation the charge of niercuric fulminate used for that purpose was increased to 0.14 grm. (2 grains). Still the detonation of gun-cotton could not be accomplished although the charge of nitroglycerin mas gradually increased to 1 grm. The disc of cornpressed gun- cotton which rested upon a support of wood was shattered almost to dust portioiis being clriven deeply into the wood mliich exhibited an indentation corresponding to the form of tlie disc.In orcler to compare the mechanical effect of the detonation of' nitroglycerin with that of the strongly confined fulminates 0.65 grin. (10 grains) of the liquid were placed in the small tin tube upon stout sheet copper and detonated by iiieaiis of 0.14 grm. (2 grains) of mercnric fulminate ; the work done iipoii the copper resembled in extent that accomplished with a corresponding charge of the confined fulminate (double the amount required to effect the detonation of gun-cotton). It appeared evident therefore that some power apart from violence of explosion was wanting in nitroglycerin to produce tlie result obtained with the fulminate.With a view to obtaiii still more decided evidence on this point the experiments ivere cmltinued upon a larger scale. Some four-ounce discs of compressed gun-cotton were placed upon thick supports of ~vood,aid coiifiiied charges of nitroglycerin weighing about 0.75 ounce and one ouiice were placed upon these discs arid siiccessively exploded. The pieces of wood were nlore or less shattered; they were deeply indented (tlie cir-cumfereiice ~f the disc being clearly imprinted upon them) F2 66 ARESL’S COSTRTEUTIONS TO aiid t11c gun-cotton was 1311 1verized ancl viol en t19 scattere(1 portions being driven firmly into the ~vood,hit the desired result was not in any iiistaiice accomplished. In contrast to the foregoing results it may be mentioned that small perforated cylinders of compressed gun-cottoil weighing 7.75 grms.to 15.5 grms. (0.25 oz. to 0.5 oz.) with the usual small confined charge of mercuric fulminate inserted into the perforation have frequently been employed and in- variably witliout failure for c-ffectirig the detonation of a large disc or slab of gun-cotton or of a nurriber arranged side by side in open ail. by simply placing them upon or against any one of tlie surfaces of the larger mass of gun-cottoil. It should also be stated that the detonation of a small quantity of 11itroglly- cerin has been found to acconiplish tlie simultaneous explosion of surrounding charges of that substance closely confined in srriall vessels of sheet tin and placed at distances of 2 or 3 inches from the central charge.Lastly it was found that the detonation of 7.75 grrns. (0.95 ounce) of gun-cotton detor- mined the explosion simultaneously with it of a charge of nitroglycerin confined in a vessel of sheet tin and placed at a distance of 1 inch from the gun-cotton while 15.5 grms. (0.5 ounce) of the latter produccd the same result when separated fiorn the confined iiitroglycerin by a space of 3 inches. The results obtained with nitroglycerin in attempts to deto- nate gun-cotton through its agency appear to ine to substail- tiate the view which has obtruded itself repeatedly on my mind upon consideration of many of the phenomena observed in the experiments detailed in this conimuiiication namely that a par-ticular explosion or detonation may possess a power of deter- niining at the instant of its occiirreiice similarly violent explo- sions in distinct masses of the same material or in contiguous explosive bodies of other kinds which power is independent of or auxiliary to the dirxt operation of inechanical force developed by that explmiori ; that as a particular niusical vibration \\-ill establish sj ncliroiioiis vibrations iii particular bodies while it will not affect others and as a chemical chauge niay be wrought in it body by its interception of oiily particular waves of light so some I&icls of explosions or powerful vibratory impulses may exert a disturbiiig iiiflueiice over the cIiernica1 equilihiuni of certain bodies rt;’h,ulthg in their suclden disintegrdtloii m.Lich other esyloaioiis tlioiigli clevelopiiig eqiial or greater ~lieclianicd THE HTSTORT OF EXPLOSIT'E AGEFTS.force are powerless to exercise. Thus the mechaiiical force developed by the explosior? of 3.25 grziis. (50 grains) of chloride of nitrogen far exceeds that exerted by the explosion of' 0.32 grm. (5 grains) of the strongly confined fulminates yet in their effects upon gun-cotton the substances in question are not on an equality unless employed in about tliose proportions. It appears therefore that it is necessary to increase greatly the mechanical force of the explosion to obtain the desired result with chloride of nitrogen in order to coinpensat,e for the defi- ciency or absence of sonie peculiar power possessed by tlie explosioii of tlie fulminates.Again in the case of nitroglycerin we have a body wliich explodes with a development of force quite as great as that of the strongly confined fiilmiiiates yet tlie detonation of gun-cotton could not be accomplished lip the explosion in close contact with it of a quaiitit,p of iiitroglyceriii more than sixty-five times greater than the amunt of mercuric or silver-fulniinate required for that purpose. I venture to offer the following as being the most satisfactory explanation wliich occurs to me of the reiiiarlcable differences just pointed out in the beliaviour of different explosive agents. The vibratioiis produced bj-a particular explosion if syncliroiious with those which would result from the explosion of a neigh-bouriiig substance which is in a state of high chemical tension will by their tendency to develope tliose vibrations either dpterniiiie the explosion of that substance or at any rate greatly aid tlie disturbing effect of niecljanical force suddeiily applied wliile in the case of another explosion which prochices vibrations of diflerent character the mecliaiiical force applied by its agency has to operate with litt'le or no aid; greatel.force or a more powerfill detonation must therefore be applied in the latter instance if the explosion of the same substance is to be accomplished by it. The poi+er possessed by the violent explosion of a particular material (such as gun-cotton or iiitroglyccrin) to deterini:ie tlie apparently simultxieoiis explosion of perfectly separate masses of Lhe same substance does iiot excite siirprise.Instances of the apparently siiiiultaiieous explosioii of iiuiiierous distinct and even sornewlittt widely separated niames of explosive sul)-starices (such as simnltmeous explosions in several dis-tiilct buildings ;it pon-cler-mills) do not unfi~queiitly occur in i$-llicIl tlie genercLtioii of a disruptive impulse by the first or initiative G8 ABEL'S COSTRIBUTIONS TO explosion which is coinmunicated with extreme rapidity to coii-tiguous masses of the same nature appears much more likely to be the operating cause than that the simultaneous explosion should be brought about by the direct operation of heat and mechanical force developed by the starting explosion.It appears remarkable that two substaiices so analogous as gun-cotton and nitroglycerin in their chemical constitution and general characters its explosive agents should exhibit the very great differences which have been observed in their sus-ceptibility to explosion by the effects of a detonation. A com-paratively very small amount of mechanical force suddeiily applied suffices to develope the violent decomposition of' nitro-glycerin; it is therefore not difficult to understand why this substance though incapable of detonating gun-cotton even when used in considerable quantities should be itself readily exploded by means of the latter. The comparatively very great sensi- tiveiiess of nitroglycerin to explosion through the agency of a detonation may probably be due in part to its physical character as a liquid andin part to the f'wt that the proportion of oxygen to oxidisable elements is much more considerable in nitroglycerin than in gun-cotton.In considering the manner in which a detonation operates iir determining the violent explosion of gun-cotton and nitrogly- cerin in open air I have for the sake of sinlplicity confined nipself to ail examination of the nianner in which those parti- cular explosive substances are aEected by the disturbing agency in question. It must not however be supposed that the power to exert a violent explosive action when uiiconfined or partly exposed to air is limited to explosive cornpou~2ds. ,4 few ex- periments instituted with explosive mixtures (produced by the intimate incoi*poration of powerful oxidising agents and readily oxidisable substances the combustion of which fimiishes gases or vapours) have demoiistrated that the destructive or explosive force of these may also be fully developed under conditioiis most unfavourable to their operation as explosive agents uiider ordinary circuiiistances if' they are submitted to the influence of Q detonation.Mixtures of potassic chloride with tlie sulp1iiclt.s of antiniony or arsenic with potassic ferro-or ferri-cyanide I\it11 potassic picrate and other explosive mixtures of similar natui e and lastly even gunpon der have beell readily made to THE HISTORY OF EXPLOSIVE AGENTS. explode when unconfined with the full force which they are capable of exerting by being placed in contact with a confined charge of mercuric fulminate.As far as could be determined by small comparative experiments the readiness with which the violent explosion of these mixtures can be developed is in direct proportion to their sensitiveness to explosion by percussion. Thus a mixture of the potassic picrate and chlorate freely exposed to air is exploded apparently with as much facility as gun-cotton by the detonation of a small fulminate-charge and the violence of the explosion approaches that of gun-cotton fired under the same conditions. The cletonatioii of a freely exposed mixture of the chlorate with sulpliide of antimony is somewhat less readily accomplished and the violent explosion of gunpowder requires the fulfilment of special conditions favourable to the action of the detonating charge of fulminate.If a srnall charge of powder be merely heaped upon a flat surface the case which contains the ful- minate being inserted into the heap the grains are simply scattered by the detonation of the fulminate; but if a corre-sponding quantity of gunpowder be so arranged that the dis- persion of the grains is impeded (as by placing it in a cylinder quite open at the upper end) its violent explosion is accom-plished with certainty. The results of a few experiments instituted with small charges of gunpowder (8 ozs. and 1lb.) appeared to furnish decisive indications that their explosion through the agency of a detonation was considerably more rapid than when flame was applied or their ignition under corresponding conditions.The charges were enclosed in sheet-tin cases closely resembling each other which were buried in the ground under precisely similar conditions. Those charges which were exploded by the ordin- ary electric fuses produced clear holes the earth being partly piled up around and partly scattered; others fired by means of detonating fuses threw up much earth vertically with con- siderable violence but there was very little scattering effect produced the hole being to a great ext'ent filled up again by the earth nionieiitarily displaced. That the explosion of gun-cotton through the agency of detonation exerts a niore violently destructive action than its explosion when strongly confined by the simple agency of heat has been abundantly proved by blasting operations in ABEL’S CONTRIBUTIOXS TO various descriptions of rock and by measurenient of the com- parative destructive effect of charges exploded under water.Charges of gun-cotton contained in blast-holes and having a detonating fuse inserted in or placed immediately over them have produced much greater rending and shattering effects in hard rock and in wood (although the blast-holes were left entirely open or only filled with loose sand earth or powdered rock) than corresponding charges applied in similar positions but fired with ordinary fuses although in the latter iristances the gun-cotton was confined by “tamping,” or firmly closing tlie blast-hole to a considerable depth.A series of systematic experiments have been carried on at Chatham by the Govern- ment Committee on Floating Obstructions with the view of comparing the destructive power of gunpowder and gun-cotton in which charges of these materials were exploded in proximity to submerged targets with systematic variations of the strength of the cases containing the charges the depth of their immer- sion beneath the surface and their distances from the targets. The results of these experiments warranted the conclusion that gun-cotton when confined in cases of sufficient strength to develope its full explosive action exerted a destructive effect equal to about five times that of gimpowder. A few experi-ments to compare with these have been recently institizted with charges of gun-cotton enclosed in thin sheet-metal cases and exploded by means of detonating fuses arld in these tlie de- structive action upon vertical targets placed at very consider- able distances from the charges was fiom ten to twelve times greater than that of gunpowder.The concussion imparted through the water to considerable distances by the explosion of small charges (2 to 31b.) of gun-cotton in the new manner very greatly exceeded in their effects the results produced by the explosion of submerged charges by the ordinary method. A series of experiments has been instituted with the object of ascertaining whether the remarkable results obtained by exploding gun-cotton through the agency of a detonation were in any way mcribable to a peculiarity in the results of the metamorphosis.Known weights of gun-cotton have been exploded in vacuo by means of a small detonatiiig fuse and the volume of gas produced accurately determined. After de- ducting the volume furnished by the fuse employed the results obtained corresponded very closely to those fkrnished by ex- ‘IRE HISTORY OF EXPLOSIVE AGENTS. doding shells charged with gun-cott on through the agency of a heated platinum wire under precisely similar conditions. The products of explosion of the detonated gun-cotton have been submitted to complete analysis and the result8 did not differ in any very important respect from those olJtained by the most cvmplete metamorphosis of the substance when exploded in strong shells under ordinary conditions.As the chemical change sustained by the decomposition of gun- cotton when exploded through the agency of a detonation cannot be said to differ in completeness from that consequent upon a fulfilment of the ordinary conditions essential to the development of its full explosive force tthe increased destructive effect developed by the explosion of gun-cotton through the agency of a detonation must obviously be ascribed to the greater rapidity of its explosion under these conditions. This conclu- sion appears to receive confirmation from some of the results of a series of practical blasting operations which I have recently conducted at Allenheads in conjunction with Thomas Sop-with M.A.F.R.S. from which it appeared that while the splitting and shattering effects upon hard rock were much greater with ‘‘ detonated ” gun-cotton than with charges of this material exploded in the ordinary way the displacement or projection of the broken rock appeared decidedly less coiisider- able. Again the work accomplished in the way of displace- ment in a comparatively soft and yieldiiig material such as a very friable rock (eg. chalk or soft limestone) is less consider- able than when the more gradual explosion of gun-cotton is brought about by the usual mode of firing. In the case of the detonation of gun-cotton imbedded in such material the force which is applied with comparative suddenness is to a consider-able extent expended in the disintegration and compression of the surrounding material before there is time for motioii to be conirnunicated through any considerable mass of the rock.A further indication of the difference in the rapidity of explosion of gun-cotton by detonation and hy the siniple application of heat is furnished by the difference in the luminous effect ob- served in the two instances. The ordiiiary explosion of gun-cotton is attended by a considerable body of flame due to the ignition of the generated carbonic oxide ; but the detonation of gun-cotton is only attended bya sudden flash which it is very difficult to observe in daylight if only sinall quantities are ex- ABEL'S CONTRIBUTIONS TO THE HISTORY OF ETC. ploded. The transformation of the solid into gas appears in fact to be too sudden for the generated combustible gas to become inflamed.In conclusion it may not be out of place to refer briefly to a few illustrations of the important bearings which the new mode of developing the explosivc force of giiii-cotton has upon the practical uses of t,he material as a destructive agent. The confinement of a charge of gunpowder or gun-cotton in a blast-hole by firnily closing up the latter with earth powdered rock or other conipressible material (by the process known as tamp-ing or stemming) to n depth greater than the line of least re- sistance opposed to the action of the charge is essential to the success of a blasting operation; but the great rapidity of ex-plosion by detonation of a charge of gun-cotton greatly reduces the value of this operation ; the destructive effect of the material when exploded in a hole which is lcft open is not inferior in extent to that obtained by similarly exploding a charge confined in the usual manner.Thus the most dangerous operation in coiinexioii with blasting may be entirely dispensed with.* In submarine operations it is no longer necessary to enclose the chiirge of explosive agent in the strong and there- fore cumbersome metal receptacles hitherto required to ensure the full development of its explosive force ; the destructive action of a charge of gun-cotton enclosed in a waterproof bag or thin glass vessel and exploded by detonation being decidedly greater than that furnished by a corresponding charge confined in a strong iron vessel and exploded by flame.Sniall charges of gun-cotton simply resting upon the upper surfaces or loosely inserted into natural cavities of very large masses of the hardest description of rock or of iron have broken these up as effectu-ally as if corresponding charges had been firmly embedded in the centre of the mass and exploded in the usual manner. Lastly the certainty facility and expedition with which certain important niilitary destructive operat'ions may be accomplished by means of gun-cotton exploded by detoiiation are not among the least important advantages which are now secured to this interesting arid remarkable explosive agent. 9 This observation does not apply equally to large charges such as are used in 8ome military operations for the placing of which it is necessary to sink or drive shafts or openings of large dimensions.