Nitroglycerin
Nitroglycerin (also nitroglycerine, trinitroglycerin, or glyceryl trinitrate)
is a chemical compound, a heavy, colorless, poisonous, oily, explosive
liquid obtained by nitrating glycerol. It is used in the manufacture
of explosives, specifically dynamite, and as such is employed in
the construction and demolition industries. It is also used medically
as a vasodilator to treat heart conditions. It is colored yellow
when it is decomposing due to acidic pH.
Early in the history of this explosive it was discovered that liquid
nitroglycerin can be "desensitized" by cooling to 5–10 °C (40–50
°F), at which temperature it freezes, contracting upon solidification.
However, later thawing can be extremely sensitizing, especially
if impurities are present or if warming is too rapid.
It is possible to chemically "desensitize" nitroglycerin to a point
where it can be considered approximately as "safe" as modern High
Explosive formulations, by the addition of approximately 10%–30%
ethanol, acetone, or dinitrotoluene (percentage varies with the
desensitizing agent used). Desensitization requires extra effort
to reconstitute the "pure" product. Failing this, it must be assumed
that desensitized nitroglycerin is substantially more difficult
to detonate, possibly rendering it useless as an explosive for practical
application.
Nitroglycerin was first prepared by a scientist named A. Sobrero
around 1847 where it was used as a medicine. It was then mass produced
by the great scientist Alfred Nobel in 1864 when he developed improvements
on its synthesis and a method of detonating it. The devastation
nitroglycerin caused on both the battlefield and the factory earned
Nobel the title "Merchant of Death." Nobel was haunted by the lives
nitroglycerin claimed so he created the Nobel Peace Prize to honor
champions of peace, and later, supreme accomplishments in science.
His exposure to nitroglycerin gave him constant agonizing headaches,
and ironically he took nitro pills for a heart condition later in
life. Nitroglycerin remains in use as a medicine, but not for explosives.
Nitroglycerin is a very unstable high explosive compound.
The first time I tried to make nitroglycerin was back in my early
undergraduate days. I was impatient and decided to make some in
the dorm without observing proper safety procedures. I was out of
ice. Let me just say how important it is to keep this lab cool and
slow. Nitrogen dioxide, a dense red-brown gas that is very deadly,
it is the reward for nitro gone wrong. I used cool water instead
of ice because I never believed all those warnings. Now I do. I
began slowly adding the glycerine - not a change on the thermometer.
Prepare a mixture of 200 mL of 98-100% nitric acid and 300 mL of
98-100% sulfuric acid by slowly adding one to the other in a 1000-mL
beaker. Place the beaker into a salt-ice bath during the mixing
so it may cool, allow the temperature to drop below 10 °C after
mixing. You can keep the cold acid in the salt-ice bath or you can
transfer the acid mix into a round-bottomed 1000-mL Florence flask
for better heat dispersion.
In either case, prepare a fresh salt-ice bath. Because of the possibility
of friction, standard stirring methods are not advised. Instead,
use an aquarium pump to blow air into the acids as a means to cool
and stir them. Regulate the air flow so the acid is being well stirred
yet not spattering out. Using a buret suspended above the flask,
very slowly add drop by drop 112 mL of glycerol that has been previously
cooled to 15 °C. Carefully monitor the temperature of the reaction
at all times, the temperature must stay below 20 °C, preferably
below 15 °C for extra safety.
Nitroglycerin and any or all of the diluents mentioned above can
certainly deflagrate, or burn. However, the explosive power of nitroglycerin
is derived from detonation: a shock propagates through the fuel-rich
medium at a supersonic speed. In other words, the initial burn sets
up a pressure gradient that pre-ignites unshocked material, creating
a fast-moving transition zone, which (due to the nature of the material)
can detonate any appropriate material it encounters. This generates
a self-sustained cascade of hyper-instantaneous pressure-induced
combustion that grows upon itself exponentially. This is quite unlike
deflagration, which depends solely upon available fuel, regardless
of pressure or shock.
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