To the second group belong: (_a_) All explosives used in shells, torpedoes, grenades, demolitions, etc. (_b_) Detonators or exploders, i.e., explosives which start explosive reactions in the explosives of Group (_a_). =The characteristic of H.E.= is the extreme violence and suddenness of their detonation. In order to make them instantly pass from a solid or liquid form to gas, they require a detonator or exploder, which applies a violent shock to them and breaks down the chemical structure of the explosive compound, and enables the flame to pass instantaneously throughout the mass of the compound. This explosive is known as detonation. =The composition of H.E.= almost without exception is some organic substance, usually some form of carbon combined with nitrogen. Nitrogen, one of the most inert gases known, owes its explosive value to this very inertness; it combines so very reluctantly that on the least provocation—such as shock—the compound of which it forms a part instantly breaks up into gas, giving the enormous expansion needed for explosive effect. =Ammonal.= A gray powder. An Austrian explosive, picric acid plus T.N.T. plus aluminum powder plus nitrate of ammonia plus carbon. A very safe explosive—will not detonate when struck by rifle bullet, but is very hygroscopic (collects moisture) and when in this condition is liable not to detonate. =Ballistite.= Consists of guncotton plus camphor or vaseline. Invented by Nobel in 1888. =Cordite.= Consists of nitro-glycerine 55 parts, plus guncotton 37 parts, plus vaseline 5 parts, plus acetone to harden, invented by Sir W. Abel. =Benzol.= Or Benzine, used extensively as a motor fuel contains a fair percentage of toluene. (See T.N.T.) =Coal Tar.= When subjected to fractional and low-temperature distillation produces many by-products valuable in the making of H.E. These distillations give off “light” and “heavy” oils of coal tar. =Donnerite.= High explosive employed by German army in grenades. =Dynamite.= See Nitro-glycerine. =Fulminate of Mercury.= See Mercury. =Guncotton=, or nitro-cellulose consists of cotton waste, purified, dried, and heated with mixture of concentrated nitric and sulphuric acid. Washed and reduced to a pulp and moulded into 1 oz. primers and 15 oz. slabs for service use. Is considered inferior to lyddite. Size of wet slab of G.C., 6 × 3 × 1⅜ in. Wet guncotton will not explode if hit by a bullet. Wet guncotton can be sawn by a wet saw. Requires dry primer, detonator and fuse to explode. Dry guncotton will explode if hit by a bullet. Dry primer of guncotton 1.35 in. diam., 1.15 in. diam. at ends, and 1.25 in. high. Strength, 2½ times stronger than gunpowder, unconfined. Strength, 7 to 8 times stronger than gunpowder, confined. Invented by Schombein in 1846. =Gunpowder.= A mechanical mixture. Saltpeter 75 per cent, plus charcoal 15 per cent, plus sulphur 10 per cent. Rate of burning depends upon firmness of powder.