I was once asked to hit nitroglycerine
or sample of nitroglycerine with a
hammer. They poured some out on a brick,
gave me the hammer, said, "Stroke it
gently." And I did, and it went off with
one hell of a
bang. So, today I'm going to talk about
a compound, but recently we did one on
the Nobel Prize, and Alfred Nobel made
his money from dynamite. So, I thought
we'd do one on dynamite. And
nitroglycerin here uh is the active
ingredient, the explosive in dynamite.
It comes from glycerol, which is a
natural uh compound. You just nitrate it
and you get nitroglycerin, which is a
kind of oily, heavy substance. But it
was found very quickly uh that it is
very explosive and in fact it's
dangerous to make. Alfred Nobel's uh
genius was to absorb it onto so-called
dead earth. And what you would do is he
found that if you put the dead earth on
a sheet of paper and then you rolled
that paper up like an Arctic roll, then
it became a nice stick and you could
transport these sticks. And because it
was absorbed onto that dead earth, it
gave a bit of shock resistance. So he he
he tamed it essentially by putting it
into this uh uh stick and calling it
dynamite.
And dynamite, which you normally get in
these sort of sausage shaped
sticks, is really very stable. You can
throw it on a fire and it'll just burn.
and you need to use a detonator which
produces a real shock wave which then
travels down the
stick forcing the explosion to take
place. I was once given a set of
photographs which showed how this
explosion travels down the stick. In one
10,000th of a second, it's all
over and it really looks very dramatic.
If you're clever, you can focus the
shock from an explosion rather like you
can focus light with a lens. And then
you can do some really dramatic things.
So if you look at this piece of metal
here, it's really quite thick. And I was
shown what happens when you take 100
grams. That's not really very much. Not
much more than a bar of chocolate, a
small bar of chocolate, the sort you eat
for lunch. If you use that with the
shape charge, set it off here, you can
make a hole right through
it. You can see here my pencil will go
right through. And you can see here
there's the blast marks. You can even
still see 30 years on from when this was
done a few traces of the copper casing
of the
detonator. And on the other side, you
can see where the explosion burst out.
So that was a great explosive and it as
at the onset of the first world war this
was being used a lot in mines and also
in bombs. But the problem with this
compound is
nitroglycerin it explodes very quickly.
So if you are trying to uh explode a
bomb and destroy a building say uh this
when it hits the outside of the building
will immediately explode. What you
really want is to get slightly inside
the wall before you explode because then
you're going to blow the wall apart much
more effectively. So, another Nobel
Prize winner uh
Bader uh invented this compound and it
was the Germans who invented this uh in
the early
1900s and you'll know it as
TNT. So, made famous by uh cartoons and
acme. uh TNT is tr nitroine. So these
are nitro groups here. This blue is
nitrogen, the red is oxygen. And the
clever thing with both uh nitroglycerin
and TNT is that in order to burn to make
carbon dioxide and nitrogen, normally
when we set light to things, we need
oxygen from the air to enable that to
burn. These have enough oxygens in here
to make all these carbons turn into
carbon dioxide. That gas expands and
that's what makes the the explosion. TNT
was found to have a little initiation
period. It's probably not quite as
explosive uh in absolute power terms as
uh the nitroglycerine. But the great
thing about this molecule was that it
would there would be a a tiny delay, a
fraction of a second delay before it
exploded upon impact, which meant that
the missile could get partway through
the bunker before it exploded and it
created a lot more damage.
[Music]
The Mark 25 torpedo tube is severely
damaged.
When it detonates, the carbon reacts
with and hydrogen react with the oxygen
to make water and carbon dioxide. And
the nitrogen atoms combine to make
N2. N2 has one of the strongest bonds
between any two atoms.
And it's a triple bond between nitrogen.
And forming this bond releases a lot of
heat. So does the combination of carbon
with oxygen and hydrogen with oxygen. So
in effect you get instantaneous burning.
They're all gases. The gases expand.
This is a liquid. So it's dense. Gases
want to expand. They're going to be very
hot, remember? So they're going to want
to expand. That is actually the
explosion. It's that expansion and
generation of gas in a confined space
that wants to be much much bigger. I
work here in Nottingham and Nottingham
has a special connection with TNT or
more precisely a suburb of Nottingham
called Chillwell because during the
First World
War, Chillwell had the main depot, the
main factory where they filled the
shells that were taken to the Western
Front for all the guns.
TNT is bright yellow and the young women
who worked filling the
shells started absorbing it in their
skin and were known as the Chillwell
Canaries because their skin was bright
yellow. And there's a book was recently
published about these women working the
Shell factory called the Canary Girls of
Chillwell.
And on the 1st of
July
1918, there was an enormous explosion in
the ammonium nitrate and TNT works.
Nobody to this day notes quite
why it happened, but you can see the
whole place was wrecked.
Windows miles away were
broken by the shock wave from the
explosion and a large number of people,
probably more than 200, were killed.
There's still a monument to these people
who died, but at the time it was kept
quite secret because it was in the
middle of the war and within a few days
production had restarted and they
started filling the shells. Nitro
compounds are useful because they call
cause dilation of blood vessels. So
they're useful to give to people that
have high blood pressure which puts a
strain on their hearts because it
expands the blood vessels and the hearts
can pump more
easily. In fact, it said that people who
worked in nitroglycerin
plants used to have to take samples of
nitroglycerin on holiday with them to
sniff so that their blood vessels didn't
contract too much when they were on
holiday.
And our famous lecturer from Nottingham,
Bey Shaw, who used to give lectures on
explosives, most interestingly, was
treated for many years with
nitroglycerin. And it just seems quite
amusing to me that an explosive
specialist had his life prolonged by
nitroglycerin treatment.