A History of Research and a Review of Recent Developments

2
The nature of explosions
propelling pressure; if packed too loosely most of the gases escaped around the
projectile and the subsequent speed of travel of the shot was much reduced.
This problem was overcome by mixing the powder with fluids to form a cake,
and then breaking the cake into uniformly sized crumbs or grains through a
sieve. Since two of the best fluids were alcohol and urine, the making of gunpowder
was not unlike a farming process, and as the original scientist in the field had
links with bacon and Somerset cider this was not surprising. Incidentally there
were still members of the Bacon family living in Yeovil, the author’s hometown,
about five miles from Ilchester, in the mid-nineteenth century, and the latetwentieth-century
telephone directory shows a number of Bacon entries in the
Yeovil, Crewkerne, Taunton and Bridgwater areas of Somerset.
The search for saltpetre was a serious activity over the centuries. In the
early days it was known that there were surface deposits in Spain and India,
but in most European countries no ready-made supply existed. Consequently
the business of ‘nitre’ beds prospered, in which layers of decaying animal and
vegetable matter, earth, sand and old mortar were moistened from time to
time with blood. Eventually potassium nitrate could be extracted. This method
was mainly overtaken when vast deposits of sodium nitrate, which could be
converted to saltpetre, were found in Chile. The military use of black powder,
with its powder kegs, powder horns and the commands to ‘keep your powder
dry’ was much reduced at the end of the nineteenth century, when ‘smokeless’
powder was produced in France. Apparently one of the last non-military uses
on a large scale was in the destruction of a huge rock in New York harbour
(the Pot Rock) in 1853. We are told that 200 000 lb of powder were used.
Gunpowder was also used in the mining of ore in Europe from the seventeenth
century, and for road widening in Switzerland at that time; and of course we
all know of the 36 barrels, weighing about one cwt each, concealed beneath
coal and faggots under the House of Lords in 1605.
The firing of black powder produced so much smoke that after a heavy
volley from land-based guns or a broadside from naval guns the firers and the
target became completely obscured. A new propellant, smokeless and without
residue, was needed, and this led to the development by the French scientist,
Paul Vieille, of a mixture of black powder and gelatin which was smokeless.
The action of all powders upon initiation is by burning, or deflagration. Each
grain of the powder burns at the same time as other grains and the internal
pressure throughout the mass of powder remains uniform and equal to the
external pressure. It is possible for the deflagration to change to a detonation in
which the chemical reaction spreads like a wave from the point of initiation, a
change that is completed in a few millionths of a second; but smokeless powders
are very difficult to bring to this stage. They are therefore ‘low’ explosives.
Most other conventional explosive substances have been developed from
nitric acid and nitrates, and the distillation of potassium nitrate, alum and
blue vitriol to form nitric acid is usually considered to have originated with
the Arabian chemist Greber (or Jabir) in the eighth century. He was the most