May 24, igod] 



NATURE 



87 



'jy the War Oliice, and by researches conducted by Sir F. Abel 

 iiid myself. Tnese researches were conducted on a Urge scale 

 with the view of reproducing as nearly as passible in expjrioi jnt 

 he conditions that exist in the bore of a gun. You miy judge 

 if the mignitude of the experiments when I tell youthu I have 

 tired and completely retained in one of my cylinders a charge of 

 no less than 28 lbs. of ordinary powder. 



The result of the discussion of the whole series of experiments 

 led to the following conclusions : — 



(1) That the tension of the products of combustion at the 

 ■noment of explosion when the powder practically filled the 

 space in which it is fired — that is, when the density is about 

 unity — is a little over 40 tons on the square inch, or about 6400 

 atmospheres. 



(2) Although changes in the chemical composition of powder, 

 ind even changes in the mode of ignition, cause a very consider- 

 able change in the metamorphosis experienced in explosion, as 

 evidenced by the proportions of the products, the quantity of 

 heat generated, and the quantity of permanent gases produced, 

 being materially altered, it is somewhat remarkable that the 

 tension of the products in relation to the gravimetric density is 

 not nearly so much affected as might be expected from the 

 considerable alteration in the above factors. 



(3) The work that gunpowder is capable of performing in 

 expanding in the bore of a gun was determined both by actual 

 measurement and by calculation, and the results were found to 

 accord very closely. 



(4) The total potential energy of exploded gunpowder sup- 

 posed to be fired at the density of unity was found to be about 

 332,000 gramme units per gramme, or 486 foot tons per lb. of 

 powder. 



I must confess that when I gave the lecture I have referred to, 

 seeing the many centuries during which gunpowder has held its 

 )wn as practically the sole propelling agent for artillery pur- 

 poses, seeing also that gunpowder differs in certain important 

 points from the explosives to which I shall presently call your 

 attention, I had serious doubts as to whether it would hi pos- 

 sible so far to modify these latter as to permit of their being 

 used in large charges and under the varied conditions required 

 in the naval and military services. 



Gunpowder is not like gun-cotton, cordite, nitro-glycerine, 

 lyddite, and other similar explosives, a definite chemical com- 

 bination in a state of unstable equilibrium, but is merely an 

 intimate mixture of nitre, sulphur and charcoal, in proportions 

 which can be varied to a very considerable extent without 

 striking differences in results. These constituents do not, 

 during the manufacture of the powder, suffer any chemical 

 change, and being a mixture it cannot be said under any condi- 

 tion truly to detonate. It deflagrates or burns with great 

 rapidity varying very largely with the pressure and other cir- 

 cumstances under which the explosion is taking place, a train 

 like that to which I set fire taking as you see an appreciable 

 time to burn ; while, in the bore of the gun, a similar length of 

 charge would be consumed in less than the hundredth part of a 

 second. 



You will further have observed the heavy cloud of smoke 

 which has attended the deflagration you have seen. Nearly six- 

 tenths of the weight of the powder, after explosion, remains as a 

 finely divided solid, giving rise to the so-called smoke familiar 

 to many of you, and of which a good illustration is shown in 

 this instantaneous photograph. By way of comparison I burn 

 similar lengths of gun-cotton in the form (l) of cotton, (2) of 

 strand, (3) of rope, and you will observe the different rates at 

 which these varied forms of the same mUerial are consumed, 

 the rate depending in this case upon the greater aggregation 

 and higher density, consequently higher pressure, of the 

 successive samples. 



Although the names of cordite and ballistite are probably 

 familiar to all of you, the appearance may not be so familiar, 

 and I have here on the table samples of the some whit Protean 

 forms which these explosives, or explosives of the same nature, 

 are made to assume. 



Here, for instance, are forms of cordite, the explosive of the 

 service, for which we are indebted to the labours of Sir F. 

 Abel and Prof. Dewar. This, which is in the form of fine 

 threads, is used in small arms, and here are suc;es3ive sizes, 

 adapted to successive larger calibres, until we reach this sizi 

 which is that employed for the charge of the 12-inch, 5o-ton 

 guns. 



NO. 1595, VOL. 62] 



A couple of the smaller cords I burn, both for purposes of 

 comparison and to draw your attention to the entire absence of 

 smoke. 



The smoke of the gunpowder you see still floating near the 

 ceiling, but little or no trace of smoke can be seen from such 

 explosives as gun-cotton, cordite or ballistite, their products of 

 combustion being entirely gaseous. 



You will have observed that in the combustion which you 

 have just seen there is no smoke, but I must explain, and I 

 shall shortly show you, that this combustion is not quite the 

 Same as that which takes place, for instance, in the chamber of 

 a gun. Here the carbonic oxide and hydrogen, which are 

 products of explosion, burn in the air, giving rise, with the aid 

 of a little free carbon, to the bright flame you see, and some- 

 what increasing the rate of combustion. In a gun, however, 

 owing chiefly to pressure, the cordite is consumed in a very 

 small portion of a second. 



In order to illustrate the effect of pressure upon the rate of 

 combustion, I venture to show you a very beautiful experiment 

 devised by Sir F. Abel. It has been shown in this room before, 

 but it will bear repetition. 



In this globe there is a length of cordite. I pass a curren t 

 through the platinum wire on which it is resting and you see 

 the cordite burns. I now exhaust the air and repeat the 

 experiment. The wire is red-hot, but the cordite will not burn. 

 That the failure to burn is not due to the absence of oxygen is 

 shown by plunging lighted cordite into a jar of carbonic acid, 

 where, although a match is instantly put out, the cordite 

 continues to burn — but observe the difference. There is no 

 longer any bright flame, although the cordite is being consumed 

 at about the same rate as when burned in air ; and when a 

 sufficient quantity of the COj is displaced, I can make 

 the inflammable gases ignite and burn at the mouth of the 

 jar. 



Another illustration is also instructive. I have here a stick 

 of cordite wrapped round with filter paper ; I dip it in water 

 and light the end ; you may note that at first you see the bright 

 flame. But as the combustion retreats under the wet filter 

 paper, there appears a space between the flame and the cordite, 

 the flame finally disappears, hot gases with sparks of carbon 

 alone showing. 



One other pretty experiment I show. I have here a stick of 

 cordite which I light — when fairly lighted I plunge it in this 

 beaker of water. The experinient does not always succeed ^t 

 the first attempt, but you now see the cordite burning undeir 

 the water much as it did in the jar of carbonic acid. The red 

 fumes you observe are due to the formation of nitric peroxide 

 caused by the decomposition of the water by the heat. 



I have on the table samples of certain other smokeless 

 explosives of the same class. Here is a ballistite used in Italy. 

 Here is some Norwegian ballistite. Here again is ballistite in 

 the tubular form, and in these bottles it is seen in the form of 

 cubes. Here is some gelatinised gun-cotton in the tubular form, 

 and here are some interesting specimens with which I have 

 experimented, and which up to a certain pressure gave good 

 results, but which exhibited some tendency to violence when 

 that pressure was exceeded. Here also are some samples of 

 the French B.N. powder, consisting of nitro-cellulose partially 

 gelatinised and mixed with tannin, and with barium and 

 potassium nitrates. Lastly, I show you here a sample of picric 

 acid, a substance which has been used for many years as a 

 colouring material, but which will be of interest to you because 

 it is used as the explosive of lyddite shell, concerning which I 

 shall presently have more to say ; it differs from all the other 

 explosives in being, in the crystalline form, exceedingly difficult 

 to light. I fuse, however, in this porcelain crucible, a small 

 quantity. I pour a little on a slab, and on dropping a fragment 

 into a red-hot test-tube you see with how much violence the 

 fragment explodes. I also burn a small quantity, and you will 

 observe that, unlike gun-cotton, cordite and ballistite, it is not 

 free from smoke, the smoke in this case being simply 

 carbonaceous matter. You will observe also how much more 

 slowly if burns. 



The composition of these various explosives (although in the 

 case of both cordite and ballistite I have experimented with 

 samples differing widely in the proportion of their ingredients) 

 may be thus stated. 



The gun-cotton I employed was of Waltham Abbey manu- 

 facture, and, when dried, consisted of 4*4 per cent, of soluble 



