Explosions: How We Shook the World Page #4

---

It looks like that explosion there maybe sent some kind of shock

through the rock and it peeled off here,

where possibly there was some sort of fault line.

Now we'll try just 5g of guncotton,

looking like it couldn't possibly do much damage.

That's a completely different story.

In slow motion, you can clearly see all the gases the explosion creates.

Brown nitric oxide, steam and others, splitting the rock apart.

That's just astonishing.

A couple of hundred kilos of rock has practically disappeared.

There's some fragments over there,

bits down here.

And look at that.

Where it was actually placed, there's nothing at all.

Like that.

Look down here.

That's the hole where it was packed in. So this was the other way up.

You can see where the clay was,

you can see all the way down here and it's just split it.

Now, this is guncotton and what's happened here is when

the guncotton has been compacted, confined in there, it's detonated,

which is a completely different process to when we saw it being lit.

It burnt rapidly.

This detonation sends out a sharp shock wave

and as it goes into the rock, the rock gets split.

It's a much more powerful explosion, and I can imagine the Cornish miners

feeling a little bit like me now,

almost overwhelmed at the difference between gunpowder and guncotton.

The quarrymen were amazed at the new guncotton

and mercilessly teased the colleague who had offered to sit on it.

They were immediately interested and Schonbein quickly found

an English partner to start manufacture.

His apparent success soon inspired others.

Schonbein wasn't the only one experimenting with these kind of chemicals.

Not long afterwards, an Italian chemist, Ascanio Sobrero,

reacted nitric acid with glycerine, another carbon-rich substance.

Sobrero had worked on nitration before,

and when he read of Schonbein's discovery,

he was inspired to return to it.

He was originally a medic,

so many of his interests were in potential new drugs.

The result of this experiment, first done in 1846, is in fact still

an important heart medicine, but it has another side to its character.

Dr Alex Contini is one of the few chemists experienced enough

to attempt this process

and he isn't going to trust his life to me keeping an eye on the thermometer this time.

Seven and rising...

Each time the glycerine is added to the concentrated acids,

he has to stir it and make sure it stays cool.

Every degree of temperature rise

makes a premature explosion more likely.

Ten and rising...

The resulting oily liquid, like guncotton,

contains carbon atoms linked to nitrogen and oxygen groups.

It looks fairly innocuous,

but Sobrero discovered it has some pretty surprising properties.

And we're only going to use the tiniest amount to show them.

Sobrero wrote that the safest way to demonstrate these properties

was to dip a hot wire into a glass bowl of the substance,

but he was scarred for life by flying glass,

so we are going to try something different.

If you look down there, you'll see the nitroglycerine has completely disappeared.

Every molecule of the liquid nitroglycerine gets turned to gas and goes,

hence the massive expansion, hence the massive explosion.

Whilst guncotton only detonates when confined,

nitroglycerine can detonate when given a simple sharp shock.

Even slowed down more than 500 times,

the explosion is incredibly fast.

This new behaviour made guncotton and nitroglycerine

quite different from gunpowder.

The difference between gunpowder and these new high explosives,

as they're called, is the way they explode.

Gunpowder burns - albeit very rapidly, it's still burning.

One piece heating the piece adjacent to it,

the piece that's adjacent to that -

fwooh! - till the whole thing's gone.

With high explosives, it's detonation.

A pressure wave travels extremely quickly through the whole charge

and it almost goes instantaneously.

The first bit of the reaction in a high explosive

creates so much gas so quickly it generates a pressure wave

that hits the rest of the explosive.

I'll show you, with this fire piston, as it's called,

and a tiny bit of normal cotton wool.

As the piston comes down, it acts like the explosive pressure wave,

raising the pressure inside the tube.

That pressure heats the air so much

that the cotton wool bursts into flame.

It's the same with a piece of high explosive.

It's the sudden rise in pressure that gives the sudden rise in temperature

that triggers the explosive as it runs through the entire charge.

Now, this thing happens so quickly,

you pretty much get the entire lot going in one go.

Watch this.

This is detonating cord. It's a spun cord with a line of high explosive

right down the centre of it.

When it's detonated at one end,

the wave front moves extremely quickly right down its length.

Slowing the process down 250 times, you can see the detonation

travelling at about 6km a second.

When the force of the detonation wave hits the surrounding air,

it creates a supersonic shock wave.

You can see the shock wave distort the air like a bubble,

coming out around this modern high explosive.

Shock waves and reaction speeds like this were a phenomenon

nobody had come across before

and it made these new high explosives very powerful

and potentially very dangerous.

And that was the problem.

Only months after it opened, the world's first guncotton factory

exploded disastrously in England

and Sobrero's new nitroglycerine appeared even more dangerous.

It seemed there might be no way of safely harnessing

this new-found power.

But the industrialised world was crying out for it.

The men working the great tin and coal mines of Britain

were still having to use the centuries-old, inefficient gunpowder

and attempts to build a canal system to move the vital raw materials

produced by the mines to Britain's ports

were hampered by gunpowder's lack of power.

But in the 1850s, a young Swedish student

came to hear about nitroglycerine.

His name was Alfred Nobel

and his family were explosives manufacturers in need of money.

They took the risk of trying to manufacture nitroglycerine,

but they had an awful lot to learn.

In their first year of manufacture, their factory in Sweden exploded,

killing Alfred's younger brother Emil.

This is the site of Nobel's biggest explosives factory.

It's at Ardeer on the west coast of Scotland and at its height,

it was the biggest explosives factory in Europe.

Nobel liked it.

One, because it was remote, but two, it was built entirely on sand,

meaning he could create artificial landscapes like that.

Nobel built what were called nitroglycerine hills.

Nitroglycerine was made in little huts on the top of each hill.

In each hut were two men, one to monitor the mixing reaction,

the other to adjust the flow of water through a cooling jacket

to keep the temperature in the right range.

Now, vigilance was vital.

The entire batch could self-detonate if allowed to go out of control.

Rate this script:0.0 / 0 votes