Let me give you an example or two now
of the way what gunpowder is like
when we burn it and the sort of things that it does.
Just get rid of that, in fact,
in fact Alastair if you don't mind we'll get rid of these bits on the bench as well,
if you don't mind thanks. So
let's take a mixture
of the potassium nitrate, sulfur and charcoal
in the quantities that is normal, just as you might be able to buy them or get them
from any source whatsoever
and these are not well-made.
They are just mixed together, these powders,
and when we burn it you'll see that you would hardly describe it as gunpowder.
So here we go.
It doesn't light all that easily but you'll notice that
it's messy, it's bubbly, there's a lot of residue there
and it's left really quite a deposit on the plate.
So in no sense of the word could you call it gunpowder
but it is gunpowder in its chemistry.
So I'll push that out of the way. So let's take another one now
and burning them in this way tells you
a good deal about these powders. So
let's now take the same stuff and let's put it through a sieve
which has a 120 wires
to the inch each way. We've got 120 mesh sieve.
Now if you were to measure the aperture between those wires
that is one hundred and twenty-fifth
of a thousand millimeters. It's a very fine seive about like
fine baker's flour. So
the same stuff, light it this time and you'll see it's changed it's character
straight away.
So obviously the fineness of the material
is really quite crucial in this particular case
and that's not gunpowder because we've just mixed it together.
So this time
let's put the chemicals into a mill
and this is an edge runner mill, where you've got two big wheels
rolling around on a pan and gradually incorporating
the charcoal and the gunpowder and the sulfur and
after say a couple of hours milling of that
then you end up with a powder that looks
like the last one but on the other hand
the ignition you might expect to be a bit faster
and so really what you've got there is a slight difference in the
pattern again and I'm just a little disappointed because
the Bunsen burner usually tells you something else but
next one might. So let's say now then we're going to make this powder
into the kind of powder that will do a piece of work
like lifting a show or a roman candle or whatever it might be
and so what they do is they compress the powder into an
absolutely solid rock cake and then they break it down
into grains so that it
ends up looking like black sugar. So here we have the
gun powder grains, we have them
all sizes from about well
one millimeter up to about seven millimetres
and so here we go, when we light this it may not be all that quicker than that
but it is quick and it's put the Bunsen burner out.
Now that's quite significant because
you see what is happening is that you've got an explosive front here.
You've got an immediate concentration of gas here
and what it's done is pushed the Bunsen burner out
because of what's happening there. Other explosives
are much worse than that. That's comparatively easygoing stuff.
So look at our four plates now
and you see the original terrible one here with all that residue left behind.
Look how that one hasn't done a lot more than
stain the plate. What you might call a gunpowder burn
and then look at this one where the grains have all
pushed each other out of the way and
this gives you a very clear idea of the burning
characteristics, if you like, of those
four powders which are absolutely chemically identical
and so you can see that there is a lot to learn really
from burning
chemicals on the ground, if you like, or mixtures and watching them,
even smelling what they smell like. Now if we were to mix gunpowder
with other things
we make some of the most ordinary fireworks that we have.
So for example we could have...
...because these all look alike
I'm not going to actually tell you what they're going to do until they've done it.
So let's have a look then and burn one or two of these
and we'll get a clue of what's in them. But it's gunpowder
mixed with other things. So
I imagine that's probably charcoal and probably a bit of metal powder.
You can see the gold of the charcoal
and there's a little bit of magnesium/aluminium alloy
in there to give it that effect. Let's now try this one
That's got titanium mixed in with it.
So titanium is the newest
metal to be available for fireworks, used to be very expensive
but it gives the most beautiful silver sparks
and of course it doesn't corrode in the same way that other things do.
Let's take another one and so this time
we've got what we call a flitter
which is aluminium again in a different form.
It's not as fine and it forms those kind of
what you can only call flittery effects
and this time you'll see that
its flittery again but different. So
that we call a glitter and
that's aluminium again.
A lot of these aluminiums give you different effects but
there's antimony in there as well, which gives it that kind of effect.
Here's another one
which I'm going to be just a bit more wary with
and because
it's got a coat on the outside of it, a material
and what happens is that it sometimes jumps sideways, which
isn't too convenient. In fact I've got two of them coming up so
I'll be a bit more cautious. Of course you've got to be very cautious you don't get the whole
box on fire but I've had it happen once.
So here we go
now with this one. Now this is
aluminium with a goodly amount of oxygen
in the composition making it burn very bright
you see. So the more oxygen there
the more the aluminium burns more brightly obviously and then
there's this one, which
we make quite a lot of and it's quite curious...
I'm jumping slightly back because
this interesting effect which probably
in fairness the Chinese came up with in more recent times.
That crackle is made by mixing
aluminium and magnesium/aluminium alloy
with an oxide
of bismuth or even
lead or something like that. Lead makes the best results but of course
lead isn't as popular as you can imagine. But there we are.
So that's the kind of effects that you get.
Aluminium is very interesting when it burns you see
with gunpowder because at low temperatures it burns
silvery gold but as you notice at high temperatures,
with lots of oxygen it burns really
very, very bright indeed.