Explosions: How We Shook the World Page #2

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and produce lots of heat and gases.

In the open air, there's plenty of room for the gases to expand,

so there was no sudden explosion,

but the basic chemistry of gunpowder was there.

However, an even older Chinese book

suggests that the very first chemical explosive in the world

had been developed 200 years before this.

A book with the lovely title

Classified Essentials Of The Mysterious Way Of The Origin Of All Things,

which happens to contain a few recipes listed as,

"Don't try this at home if you are an alchemist,"

- and amongst that is a recipe which I think we ought to try.

- I'm game.

You have some saltpetre. You have some sulphur.

Those two ingredients. The carbon comes in the form of honey.

OK, and what kind of quantities do you use?

Oh, well, I would say most of that jar would get us

something interesting happening.

If you got about the same quantity of the other two ingredients,

the saltpetre and the sulphur, that should go nicely.

Why did they ever think of mixing these things together at this point?

The idea is to try to subdue the fiery properties

of the sulphur and of the saltpetre

so that they will be suitable for taking as a medicine,

- hopefully an elixir of life.

- Oh, I see!

'So, ironically, in trying to find a means to eternal life,

'the Chinese alchemists found a substance that could kill.'

I've never done any alchemy before.

This is my first venture into the world of alchemy.

If you make a success of it, it's a new career, really, isn't it?

- Potentially lucrative.

- Yes, indeed, indeed.

That looks pretty well stirred.

I would think now if you start cooking that,

that will finish the mixing.

Despite being earlier than the incendiary powder of 1044,

the chemistry of this mixture has the potential to be more explosive.

So because of the water in the honey,

that is dissolving the saltpetre.

- Yes.

- And allowing that to carefully coat all the bits of sulphur.

The particles of carbon and sulphur will now be very, very close to molecules of saltpetre

which, when they get hot enough,

will start releasing the oxygen just right up close to them.

I think that's going to go in a sec.

There's little puffs there.

Exciting little puffs. I say.

Just slightly move ourselves out of the immediate line of that. That's it.

Whoa! OK...

Wow!

- That was quite striking.

- Wow!

Well, as the Chinese alchemist said, don't try this at home.

So, incendiary mixtures were being explored by the Chinese alchemists

as early as the mid-ninth century

but from the 12th century, as China was swept by waves

of war with neighbouring peoples,

they started to use their fast-burning powder in a new way.

No longer just an incendiary,

it became an explosive propellant for projectiles.

The Chinese gave their new weapons names,

like the vast-as-heaven, enemy- exterminating yin-yang shovel,

the scary, ingenious, mobile, ever-victorious poison-fire rack

and my personal favourite,

the orifices-penetrating flying-sand magic-mist tube.

In all of them, they put the powder in a tightly confined space

and this fundamentally altered the way it behaved.

It was the discovery that would change warfare forever.

Confining gunpowder changes the speed of the reaction.

It goes from something that just burns into something that really explodes.

Gunpowder doesn't need air in order to burn.

It gets all the oxygen required from the crystals of saltpetre,

potassium nitrate, that are in there,

which means it'll still burn in a confined space

and putting it in a confined space increases the rate of reaction.

Put a little bit in here.

So I'm going to wrap it up.

When it's confined like this, all those grains,

the carbon, the sulphur and the potassium nitrate,

are all much closer together, which means

the reaction can happen more quickly, and as the reaction happens more quickly,

more heat's created, making the reaction go even faster and it's a runaway process.

Right.

With gas being produced so quickly and heat making it expand,

there's the potential for explosive force,

if I can channel it like the Chinese did.

This is my first attempt at a cannon.

I've decided to build it out of clear acrylic

so that we get to see what happens inside a cannon.

Now, I'll drop that on there.

That fits in nicely.

Got my cannonball.

So there it is. There's going to be an explosion in there.

That explosion will produce hot, expanding gas.

There'll be a big pressure rise in that part of the chamber.

That pressure will exert a force all around the container,

but these three sides should stay where they are.

This fourth side here, where the tennis ball is,

won't stay where it is, and that tennis ball will leave at

an undetermined speed that I suspect will be pretty quick.

Let's find out.

Three, two, one!

Yeah, that worked like a cannon should work.

Wow!

You can see how the gunpowder produces hot gases

at just the right rate

to push the ball out.

This technology quickly spread west, through the Middle East,

and by the 14th century, the Europeans had rockets and guns too.

But something else was happening - gunpowder was spreading beyond the battlefield.

Its power was being put to work in mines and engineering projects,

as Europe became more industrialised

and there was demand for more powerful and destructive explosions.

Gunpowder had reigned for 500 years,

but now its dominance was about to be challenged.

The middle of the 19th century provided a turning point

in the story of explosives.

I've had to come here, to the Defence Academy of the UK,

because we're going to make what they first discovered in 1846.

There was a growing tradition of pure scientific research in Europe,

with researchers trying to understand the chemical composition of natural substances.

One of these chemists was a German from a humble background called Christian Schonbein.

He was naive, unconventional and full of original ideas.

Working in Switzerland, he'd seen some unusual reactions with

concentrated acids and was keen to investigate them further.

One of those investigations was unwittingly to change the world of explosives forever.

Professor Jackie Akhavan has volunteered to show us

exactly what Schonbein did.

Jackie, what are we actually doing here?

OK, we're mixing nitric acid and sulphuric acid together

and then we're going to add some cotton wool to it,

to hopefully nitrate the cotton wool.

Schonbein didn't know it, but the cotton will be acting

as a source of carbon, like the charcoal in gunpowder

and by nitrating it, he added oxygen and nitrogen

from the acid actually into the molecules of the cotton,

rather than just being in neighbouring grains.

We must make sure the temperature remains cool.

So I'm going to put a thermometer in so we can measure the temperature.

- Do you want to help?

- I do. What temperature should I watch out for?

OK, it mustn't go above 18 degrees centigrade.

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