1921] on War Development of Explosives 861 



of its spring, and recedes into its cavity. The force due to the shell's 

 rotation causes the bolt to fly outwards, thus freeing the brass 

 cylinder, which is now prevented from moving forward on to a 

 needle only by the interposition of a light spring. The fuze is now 

 "live," and on the slightest check being given to the forward 

 movement of the shell, as, for example, by grazing on soft earth, the 

 cylinder moves forward by its own inertia on to the needle, which 

 pricks the capsule, causing a jet of flame to pass down the centre of 

 the fuze. The object of all this mechanism is to supply at the proper 

 time a flash for operating the next member, the gaine, where it gives 

 rise to a detonation. 



The Gaine. — This is a tube (from French gaine, a sheath) with 

 steel walls of quarter-inch annulus. In its upper portion is a pellet 

 of gunpowder which is ignited by the flash from the fuze, and sends 

 a larger flash on to an open capsule containing fulminate of mercury 

 situated over pellets of tetryl. The fulminate detonates, and in turn 

 causes the tetryl to detonate, and to deliver from the bottom end of 

 the gaine a very intense blow to a series of explosive intermediaries 

 which communicate the detonation to the main bursting charge. 



Intermediaries. — The first of these is a bag of T.N.T. crystals 

 situated in a thin steel container tube which encloses it and the gaine. 

 This T.N.T., on detonation, brings to detonation an annular layer of 

 T.N.T. cast round the container, and this in turn brings about the 

 detonation of the main charge of the shell. The train of detonation 

 is thus somewhat complicated, and in its evolution many important 

 principles had to be observed. 



Sensitiveness and Violence. — Thus the sensitiveness of the various 

 explosives used had to be determined, since, on account of the mag- 

 nitude of the acceleration imparted to all parts of the shell on firing 

 it from a gun, a column of a sensitive explosive over a certain length 

 and weight will be liable to detonate on account of the sudden force 

 applied. In proportion to their sensitiveness to mechanical shock, 

 therefore, explosives in shell must be graduated in regard to length 

 of column employed. A general principle is to have next to the 

 detonator a somewhat sensitive explosive, and to reinforce the impulse 

 derived from it by one less sensitive, but still delivering an intense 

 blow. It is important, therefore, to have quantitative values for the 

 sensitiveness of explosives to mechanical shock, and some of tha 

 values thus obtained are given in the following table : — 



Figure of 

 Insensitiveness 

 (Picric acid = 100) 

 Mercury fulminate ...... 10 



Nitroglycerine ....... 13 



Dry guncotton ....... 23 



Tetryl .' ] 70 



Tetranitroaniline ...... 86 



Picric acid ....... 100 



Trinitrotoluene . . . . . . .115 



Amatol 80/20 1 . 120 



