replacing the older forms of explosives, both for blasting purposes and
also for propulsive agents, under the form of smokeless powders. The
nitro-explosives belong to the so-called High Explosives, and may be
defined as any chemical compound possessed of explosive properties, or
capable of combining with metals to form an explosive compound, which is
produced by the chemical action of nitric acid, either alone or mixed with
sulphuric acid, upon any carbonaceous substance, whether such compound is
mechanically mixed with other substances or not.[A]

[Footnote A: Definition given in Order of Council, No. 1, Explosives Act,
1875.]

The number of compounds and mixtures included under this definition is
very large, and they are of very different chemical composition. Among the
substances that have been nitrated are:--Cellulose, under various forms,
e.g., cotton, lignin, &c.; glycerine, benzene, starch, jute, sugar,
phenol, wood, straw, and even such substances as treacle and horse-dung.
Some of these are not made upon the large scale, others are but little
used. Those of most importance are nitro-glycerine and nitro-cellulose.
The former enters into the composition of all dynamites, and several
smokeless powders; and the second includes gun-cotton, collodion-cotton,
nitrated wood, and the majority of the smokeless powders, which consist
generally of nitro-cotton, nitro-lignin, nitro-jute, &c. &c., together
with metallic nitrates, or nitro-glycerine.

The nitro-explosives consist generally of some organic substance in which
the NO_{2} group, known as nitryl, has been substituted in place of
hydrogen.

Thus in glycerine,