May 3[, 1900] 



NATURE 



1 1 



SOME MODERN EXPLOSIVES} 

 II. 



T NOW pass to points which have to be considered when 

 ^ weighing the comparative merits of explosives for their 

 intended ends. 



Vou will easily understand that between explosives which are 

 intended to b2 used for propalling purposes, and those which 

 are intended to bj used, say for bursting shell, a wide difference 

 may exist. 



In the former case, facility of detonation would be an in- 

 superable objection ; in the latter, the more perfect the detonation 

 the batter, certain special cases, to which I have not time to 

 refer, excepted. 



There exists, I think, considerable diversity of opinion as to 

 what does, and what does not, constitute true detonation. I 

 find many persons speak of a detonation, when I should merely 

 consider that a very high pressure had been reached. This 

 gun-cotton slab on the table affords me, I think, a fair oppor- 

 tunity of explaining my meaning. Were I to set fire to it, ex- 

 cept for the l.^rge volume of flame and the great amount of heat 

 generated, we in this room would not suffer ; we should probably 

 experience more inconvenience did I fire a similar slab of gun- 

 powder, as detached burning portions would probably be pro- 

 jected to some distance. 



But if I fired this same slab with two or three grammes of 

 fulminate of mercury, a detonation of extreme violence would 

 follow. The detonation would be capable of blowing a hole in a 

 tolerably thick iron plate, and would probably put an end to a 

 considerable portion of the managers in the front row. 



I mentioned to you some time ago the time in which a charge 

 would be consumed in the chamber of a gun — if a charge of 

 500 lbs. of these slab? were effectively detonated, this charge 

 would be converted into gas in less than the 20,000th part of a 

 second. 



No such result would follow were I to try a similar experi- 

 ment with a slab of compressed gunpowder of the same dimen- 

 sions. I do not say the experience would be pleasant, but there 

 would be nothing of the instantaneous violent action which 

 marks the decomposition of the gun-cotton. 



To give you an idea of the extraordinary violence which ac- 

 companies detonation, I have fired, for the purpose of this 

 lecture, with fulminate of mercury, a charge of lyddite in a cast- 

 iron shell, and those who are sufficiently near can see for them- 

 selves the result. By far the greater part of the cast-iron shell, 

 weighing about lO lbs., is reduced to dust, some of which is so 

 fine that I assumed it to be deposited carbon until I had tested 

 it with a magnet. I may add that the indentation of the steel 

 vessel l)y pieces of the iron which were not reduced to powder 

 would appear to indicate velocities of not less than 1 200 feet- 

 seconds, and this velocity must have been communicated to the 

 fragments in a space of less than two inches. 



For the sake of compirison, I place beside it a cast-iron shell 

 burst by gunpowder. You will observe the extraordinary dif- 

 ference. I also have on the table two small steel shells exploded, 

 one by a perfectly detonated, the other by a partially detonated 

 charge. I may remark that in the accounts of correspondents 

 from the seat of war, frequent mention is made of the green 

 smoke of lyddite. This appearance is due prolxibly to imperfect 

 detonation — to a mixture, in fact, of the yellow picric with the 

 black smoke. I do not say, however, that imperfect detonation 

 is necessarily an evil. 



To another experiment I draw your attention. 



For certain purposes I caused to be detonated, in the chamber 



a i2-pounder, a steel shell charged with lyddite. The detona- 



n was not perfect, but the base of the shell was projected with 

 I wit violence against the breech screw. You may judge of how 

 ! tat that violence was when I tell you that the base of the shell 



■ )k a complete impression of the recess for the primer, develop- 

 ing great heat in so doing ; but, what was still more remarkable, 

 the central portion of the base also sheared, passing into the 

 central hole through which the striker passes. This piece of 

 shell is upon the table, and open to your inspection. 



One other instance to illustrate the difference between com- 

 bustion and detonation I trouble you with. Desiring to ascer- 

 lin the difference, if any, in the products of explosion between 



inbustion and detonation, I fired a charge of lyddite in such a 



inner that detonation did not follow. The lyddite merely 



A Discourse delivered at the Royal Institution on Friday, March 23, by 

 Andrew Noble, K.C.B., F.R.S. Continued from p. 90. 



NO. 1596. VOL. 62] 



deflagrated. But a similar charge differently fired shortly after- 

 wards detonated with such extreme violence as to destroy the 

 vessel in which it was exploded. The manner in which the 

 vessel failed I now show you (Fig. 4), and I have on the table 

 the internal crusher gauge which was used, and which was also 

 totally destroyed. 



The condition of this gauge is very remarkable, and the action 

 on the copper cylinder employed to measure the pressure was 

 one to which I have no parallel in the many thousand experi- 

 ments I have made with these gauges. The gauge itself is 

 fractured in the most extraordinary way, even in some places 

 to which the gas had no access, and the copper cylinder, which 

 when compressed usually assumes a barrel-like form (that is, 

 with the central diameter larger than that at the ends as shown 

 in Fig. 5) ; but in this experiment, and in this only, the cyhnder 

 was bulged closed to the piston, as you see. It would appear 

 as if the blow was so suddenly given that the lamin?e of the 

 metal next the piston endeavoured to escape in the direction of 



Fig. 4.— Explosion vessel. 



least resistance, that being easier than to overcome the inertia 

 of the laminae below. 



The erosive effect of the new explosives is another point of 

 first-rate importance in an artillery point of view. The cordite 

 of the service is not, if the effect be estimated in relation to the 

 energy impressed on the projectiles, more erosive than, for 

 example, brown prismatic, which was itself a very erosive 

 powder ; but as we are able to obtain, as you have seen, very 

 much higher energies with cordite than with brown prismatic, 

 the erosion of the former is, for a given number of rounds, 

 materially higher. 



There is, however, one striking difference. By the kindness 

 of Colonel Bainbridge, the Chief Superintendent of Ordnance 

 Factories, I am enabled to show you a section of the barrel of 

 a large gun eroded by 137 rounds of gunpowder. Beside it is a 

 barrd of a 4 7 -inch quick-firing gun eroded by 1087 rounds of 

 gunpowder, and another eroded by 1292 rounds of cordite. You 



Fig. 5.— Copper cylinders. 



will observe the difference. In the former case the erosion 

 much resembles a ploughed field. In the latter the appearance 

 is more, as if the surface were washed away by the flow of the 

 highly heated gases. 



But take it in what way you please, the heavy erosion of the 

 guns of the service, if fired with the maximum charges, is a very 

 serious matter, as with the large guns, accuracy, and in a 

 smaller degree energy, are rapidly lost after a comparatively 

 small number of rounds have been fired. 



Cordite was first produced for use in small arms only, where, 

 owing to the small charges employed, the question of erosion is 

 not of the same importance as with large guns ; but its employ- 

 ment, from the great results obtained with it, was rapidly 

 extended to artillery, and the attention of my friends. Sir F. 

 Abel and Prof Dewar, has for some time been devoted in 

 conjunction with myself to investigating whether it is not possible 

 materially to reduce this most objectionable erosion. 



With this object I made the following series of experiments. 



