A new explosive has been discovered by M. Roca, a French engineer, who
communicates an account of it to _Le Génie Civil_. The discovery was due
entirely to scientific induction from some experiments made upon
different specimens of dynamite, with a view to the determination of the
effect on the explosive force of the various inert or at least slowly
combustible substances with which nitro-glycerine is mixed to produce the
dynamite of commerce. Of late, in place of the infusorial earth which
formed the solid portion of Nobel's dynamite, such substances as sawdust,
powdered bark, and even gunpowder, have been used, probably for the sake
of economy alone, without, except in the latter case, any reference to
the influence which they might have upon the combustion of the
nitro-glycerine; but M. Roca, in testing a variety of samples, was struck
by the difference among them in regard to energy of explosion, and
discovered that if a portion of free carbon, sufficient to combine with
the oxygen disengaged from the nitro-glycerine, was present at the moment
of detonation, the effect was greater than where, as in the case of
gunpowder, the solid portion alone furnished oxygen enough to burn all
the free carbon, without calling upon the nitro-glycerine for any. In
fact, it appeared from experiment that the dose of carbon might with
advantage be so great as not only to be itself oxidized into carbonic
oxide by the oxygen of the nitro-glycerine, but to reduce the carbonic
acid developed by the explosion of the latter itself into carbonic oxide.
The limit of the advantageous effect of free carbon ceased here, and if
more were added to the mixture, the cavities formed by the explosion in
the lead cubes used for test were found simply lined with soot; but up to
the limit necessary for converting all the carbon in the dynamite into
carbonic oxide, the addition of a reducing agent was shown to be an
important gain. This was confirmed by theory, which shows that pure
nitro-glycerine, which is composed of six parts of carbon and two of
hydrogen, combined with three times as much nitric acid and water,
decomposes on explosion into six parts of carbonic acid, five of watery
vapor, one of oxygen, and three of nitrogen, while the addition of seven
more parts of free carbon to the mixture causes the development, by
explosion, of thirteen volumes of carbonic oxide, five parts of watery
vapor, and three of nitrogen, or twenty-one volumes of gas in place of
fifteen. As the power of an explosive depends principally on the amount
of gas which results from its sudden combustion, it was evident that the
addition of pure or nearly pure carbon, in a condition to be readily
combined with the other elements, ought to increase materially the force
of nitro-glycerine, and M. Roca experimented accordingly with an
admixture of sugar, as a highly carbonized body immediately available,
and found that three parts of this, mixed with seven parts of
nitro-glycerine, detonated with a force from thirty to thirty-five per
cent. greater than that of pure nitro-glycerine. Many other organic
carbonaceous substances may be employed in place of sugar, with various
advantages. In comparing these simple compounds with the celebrated
explosive gum, prepared by dissolving gun-cotton in nitro-glycerine, it
is found that the latter is far inferior, having an energy very little
superior to that of pure nitro-glycerine.
* * * * *