The Chemistry of Powder and Explosives - Sciencemadness Dot Org

100 PYROTECHNICS
Bombshells
Bombshells are shot from mortars by means of a charge of
black powder and burst high in the air with the production of
reports, flashes, showers, and other spectacular effects. The
smaller ones are shot from paper mortars; the larger, most commonly
from mortars of iron. In the past they have often been
made in a spherical shape, wood or paper or metal hemispheres
pasted heavily over with paper, but now in this country they
are made almost exclusively in the form of cylinders. For the
same caliber, cylindrical bombshells will hold more stars or
other display material than spherical ones, and it is much easier
to contrive them in a manner to procure multiple bursts. The
materials of construction are paper, paste, and string. The shells
are supplied with Roman fuses timed to cause them to burst at
the top of their flight. The success and safety of bombshells depend
upon carefully constructed fuses.
Roman fuses are made by pounding the fuse powder as firmly
as is possible into hard, strong, tightly rolled paper tubes. These
are commonly made from Bird's hardware paper, pasted all over
before it is rolled, and arc dried carefully and thoroughly before
they are loaded with ramrod and mallet. "When a number of
these cases are rolled," says Weingart, 47 "they must be dried in
the shade until they are as hard as wood and rattle when struck
together." He recommends the first of the following-listed compositions,
the Vergnauds the others: 48
Potassium nitrate 2 4 2
Sulfur 1 2 1
Meal powder 4 6 3
Antimony sulfide 1
The length of the column of composition determines the duration
of the burning. The composition in the fuse must be as hard and
as firmly packed as possible; otherwise it will blow through into
the shell when in use and will cause a premature explosion.
Some manufacturers load the tubes and cut them afterwards with
a fine-tooth hack saw. Others prefer to cut them to the desired
lengths with a sharp knife while they are prevented from collapsing
by a brass rod through them, and afterwards to load
47 Ibid., p. 130.
48 A. D. and P. Vergnaud, "Nouveau manuel complet de Partificier.
Pyrotechnie civile." (Ed., G. Petit) (Manuels Roret), Paris, 1906.