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with a delay action, for the attack of buildings or dugouts. (A German example is shown in fig. 4.)

FIG. 4.

In the British service the explosives in general use for high- explosive shell are T.N.T. (tri-nitro-toluene, or trotyl), a mixture of ammonium nitrate and T.N.T. known as amatol, and mixed in different proportions, and picric acid (lyddite). These explosives, especially amatol, are, under proper filling conditions, inert and safe substances, as they have to be if they are to sustain the shock of discharge from the gun. To ensure the necessary com- plete detonation therefore, an " exploder " : in principle a small charge of less inert explosive is interposed between the fuze and the bursting charge proper.

The British method of inserting the bursting charge is by melt- ing the explosive in a hot-air chamber and pouring it, in liquid form, through a funnel into the shell. Filling through the base seems to be in favour in Germany; and the general method of filling is with one or more blocks of cast, or pressed, explosive enclosed in con- tainers of varnished cardboard, linen or paper; a more uniform den- sity of burster can thus be obtained. In some German H.E. shell the bursting charge is separated into two portions by a dia- phragm which is pierced with holes for communication between the two charges. In every case a cavity is made in the centre of the filling, nearest the fuze, to receive the exploder which, being deto- nated through the medium of the fuze, in turn detonates the filling of the shell. Sometimes the relay element interposed between fuze and main bursting charge is contained in a " gaine " screwed to the fuse itself; the metal walls of the gaine confine the contents long enough to secure a good detonation and so a sufficient shock to the main charge. Between gaine and charge, if there is room, a small exploder is inserted to make contact intimate and the propagation of the shock more certain.

With 80/20 amatol, which in complete detonation gives practi- cally no smoke effect, some smoke-producing mixture is included in the filled shell to assist observation.

The bursting charges for German H.E. shells are principally amatol of a mixture 13 to 87; frequently they are of trotyl; and dinitrobenzene and tri-nitro-anisol have been used. Ammonal 2 and " ekrasit " have been used in Austria. With the German 17-cm. H.E. shell the explosive is trotyl stemmed in two containers, the exploder cavity being formed in the upper portion in which a brass exploder container is placed; with the 24-cm. H.E. shell two explod- ers are used.

A typical high-explosive shell is shown in fig. 5 ; the steel body is stout, giving great strength and thick metal for fragmentation; the amatol filling is in the form of blocks; the centre block is of T.N.T. which when acted on by the fuze and exploder, facilitates detona- tion and gives smoke to assist observation of fire.

Thick Steel Body

Amatol Block

T. N.T. 1 Amatol

Exploder Gaine

FIG. 5.

(b) Shrapnel shell is essentially a man-killing projectile; but shrapnel was employed during the World War for wire-cutting

1 With lyddite fillings the exploder system takes the form of a bag of picric powder inserted in the cavity in the filling; the picric powder is readily ignited by a gunpowder-filled fuze and burns rapidly to detonation. With the other high-explosive fillings, par- ticularly amatol which is difficult to detonate, the exploder isT. N.T. in crystalline form, inserted in small bags or cartons. Pellet exploders may probably take the place of exploder bags and cartons so as to give still more intimate contact between fuze and exploder. With T.N.T. exploders, as gunpowder-filled fuzes are not suitable, a detonating or high-explosive-filled fuze is employed.

2 Ammonal was employed in the British service for trench-mprtar bombs and for grenades, but not for artillery shell proper.

(C. F. A.)

and for long-range fire against observation balloons. In order to get as many bullets as possible to be packed into the shell, the walls are made as thin as is consistent with the shell body being able to withstand the firing and rotational stresses which act on it in the gun and during flight. With shrapnel fire, the normal practice is to open the shell in the air so as to release the bullets in a compact mass, their velocity at the moment of release being slightly accelerated by a small opening charge of gunpow- der placed in a recess in the base of the shell below the bullets. To ensure the ready release of the bullets it is necessary to have either a separate and lightly attached head (in the heavier shell such as that in fig. 6), or a fuze socket held not too securely (in the lighter types fig. 5 a), so that on the ignition of the small gunpowder charge in the shell, the head or the fuze-socket is read- ily blown clear and does not impede the release of the bullets. The effect of a shrapnel shell depends on both the weight of the individual bullet and the number of bullets. To obtain high-striking energy or rather to ensure a great depth of effect (this being defined by the point of burst of the shell and the point at which the released bullet ceases to possess adequate striking power) the weight of each bullet should be kept as large as possible by the use of a heavy metal, viz. lead, hardened by an addition of antimony. The Germans used steel shrapnel bullets in some cases. On the other hand the larger the bullets the fewer of them a given shell will contain. The best compromise is ob- tained by making the bullets spherical and of a heavy metal. The bullets for British light field shrapnel run 41 to the lb., and for heavy field shrapnel 35 to the lb.; in special cases much heavier bullets are used.

Steel Disc

Brown Paper Lining Resin i Felt.Wid

CXXDC

Steel Head

-Sp

Bursting Charge

', Bourrelet

Tin'Cup Central Tube _341 '12 oz Twisting Pins Fuze Hole

Rivets & Solder

Steel Balls

FIG.

Tin Cup

Reiin Fuz Hol

The shell consists in a light hollow steel body of which the walls increase in thickness slightly from the top to the base, near which the shell cavity contracts to form a ledge for the steel disc or dia- phragm to rest on, and a chamber for the opening charge. The opening charge is usually of fine grain gunpowder 3 whose func- tion is to force off the head or blow out the fuze socket with fuze, and drive out the bullets, which are thus carried forward with slightly accelerated speed as compared with the remaining velocity of theshell. The opening charge is placed in a tinned sheet-iron "cup" inserted in the recess in the base of the shell; the object of this "cup" being to prevent dangerous friction between the gunpowder and the rough interior of the shell. Resting on the shoulder above the tin cup is a steel disc, or diaphragm, which is screwed to receive a brass tube which occupies the centre of the shell. This diaphragm

3 A compressed pellet of gunpowder has been tried instead of loose fine grain gunpowder, with the idea of increasing the driving power of the charge and therefore the velocity of the bullets, or alternative- ly of reducing the necessary space for the driving charge, and so gaining space for more bullets. Compressed powder charges, how- ever, entail a separate base and lead to complications and undue expense.