free in an uncombined state.

An explosive is said to detonate when the above changes take place
instantaneously, the action being transmitted with the speed of
electricity by a sort of molecular rhythm from molecule to molecule
throughout the entire substance of the compound.

An explosive is said to explode when the above changes do not occur
instantaneously throughout the whole substance, but whose combustion
takes place from the surface inward of the particles or grains of which
it is composed, thus requiring some definite lapse of time.

The elements of an explosive compound may be associated chemically as in
nitro-glycerine and gun-cotton, which are chemical compounds, being the
results of definite reactions. Or, an explosive may be a mere mechanical
mixture of different substances comprising the necessary elements, as is
ordinary black gunpowder, which is a compound of charcoal, sulphur and
saltpeter, the saltpeter supplying the necessary oxygen.

No gunpowder can be smokeless in which saltpeter or any oxygen-bearing
salt having a metallic base is employed, for when the salt gives up its
oxygen, the base combines with other elements to produce a sulphate, a
carbonate, or other salt, which, being solid, produces smoke. Therefore,
to be smokeless, a gunpowder must contain no other elements than oxygen,
hydrogen, nitrogen, and carbon, and in such proportions that the
products of combustion shall be wholly gaseous. The nitric
ethers--gun-cotton and nitro-glycerine--constitute such explosive
compounds. These substances were formerly thought to be
nitro-substitution compounds, but are now known to belong to the
compound ethers of nitric acid.