Nitro-glycerine in a state of decomposition becomes very sensitive, exploding violently when struck, even when unconfined.
Pure nitro-glycerine does not spontaneously decompose at any ordinary temperature, but if it contains any free acid, then decomposition may happen. When pure, it is not sensitive to friction, or moderate percussion. If struck with a hammer, only the particle receiving the blow explodes, the remainder being scattered.
The firing point of nitro-glycerine is about 356° F., though it begins to decompose at a lower temperature.
The mode of firing nitro-glycerine usually employed is that of a fulminate of mercury detonating fuse.
Nitro-glycerine in the frozen state cannot be fired even by large charges of fulminate.
In one instance, 1600 lbs. of liquid nitro-glycerine exploded in a magazine containing 600 lbs. of the same substance in a frozen state, but failed to fire the latter, only breaking it up and scattering it in every direction.
Dynamite.—This explosive compound is merely a preparation in which nitro-glycerine is itself presented for use, its explosive properties being those of the nitro-glycerine contained in it, as the absorbent is an inert body.
Dynamite is formed of seventy-five parts of nitro-glycerine absorbed by twenty-five parts of a porous siliceous earth or "kieselguhr."
The best substitute for "kieselguhr" is ashes of bog-head coal.