90 ANNUAL OF SCIENTIFIC DISCOVERY. 



that they could not be recovered after the explosion. Here are 

 the fragments of a shell of the same size exploded by 765 grain? 

 of gunpowder. The difference between the size and number 

 of the fragments in the two instances is very striking. In the case 

 of the fulminate of mercury the explosive effect is exerted almost 

 instantaneously in all directions, and the shell is therefore, shattered 

 into a very large number of fragments, the force of the explosion 

 being almost entirely spent on the bursting of the shell ; while in the 

 case of gunpowder, the explosion being comparatively gradual in its 

 nature, the force developed is only partly spent upon the fracture of 

 the shell, and is still in course of development when this result is pro- 

 duced ; hefice, not only are the resulting fragments much fewer and 

 larger, but a considerable projectile force is exerted upon them after 

 their production, and they are consequently scattered to a much 

 greater distance than those produced by the employment of fulmi- 

 nate of mercury. 



When gunpowder is confined by means of a shot or shell in the 

 barrel of a gun, the explosion of the first particles has the effect 

 of overcoming the inertia of the projectile, and the action proceed- 

 ing gradually, as compared, for instance, to that of the fulminate of 

 mercury, the shot is projected with comparatively small strain upon 

 the gun; but in employing the fulminate of mercury, in a corres- 

 ponding experiment, it would be found that the enormous force, 

 which reaches its maximum suddenly, would, almost simultaneously 

 with the first movement of the shell, also discover the weakest parts 

 of the gun ; in all probability, therefore, the cannon would be burst, 

 while we should not project our shot or shell to any great distance. 

 In quarrying, where it is desired to detach large masses of rock or 

 stone, without producing any great destructive effect, we employ a 

 very slow-burning powder, the explosion of which exerts a force like 

 that obtained with a wedge ; if we were to employ fulminate of mer- 

 cury in this instance, the particles of rock in the immediate vicinity 

 of the charge would become shattered by the sudden and violent ex- 

 plosion, and the desired result would not be produced. 



The action of gunpowder, gradual though it appears to be when 

 compared with the action of a fulminate, may, in particular condi- 

 tions, and under certain circumstances, be much too rapid. Recent 

 investigations of the effects of gunpowder have shown that the power 

 we possess of modifying its action so as to render it more gradual is 

 exceedingly important. As an illustration of this, I may state that in 

 long guns, and in cannon of large calibre, the charge of the powder 

 used for the projection of the shot has been clearly shown to be com- 

 pletely ignited before the projectile is moved to any great distance 

 along the bore of the gun ; hence, we find that whenever explosions do 

 occur in guns, in consequence, for instance, of inferior casting or metal, 

 or an excessive charge of powder, the fracture of the gun is almost al- 

 ways confined to the part reaching from the trunnions to the breech. 

 The American Dahlgren gun, of which this is a model, exhibits this 

 great thickness at the breech end; this form has been adopted to 

 enable the weapon to resist the comparatively enormous strain exerted 

 on that part by the heavy charges employed. Where cast-iron can- 

 non are still used, it will always be especially necessary, if we employ 



