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We see explosions all the time, | 0:00:03 | 0:00:06 | |
and during my career as an engineer, I've certainly made a few. | 0:00:06 | 0:00:10 | |
But actually understanding them and controlling all that power, | 0:00:10 | 0:00:14 | |
that's a whole different story and sometimes quite a surprising one. | 0:00:14 | 0:00:19 | |
It's a story that starts with the accidents of the medieval alchemists... | 0:00:19 | 0:00:24 | |
Don't try this at home. | 0:00:24 | 0:00:25 | |
Whoa! | 0:00:25 | 0:00:27 | |
..but eventually leads us to a fundamental understanding of the forces of nature... | 0:00:28 | 0:00:33 | |
..forces that we've mastered for good or evil. | 0:00:35 | 0:00:38 | |
Explosives revolutionised battlefields, | 0:00:38 | 0:00:42 | |
industry and engineering. | 0:00:42 | 0:00:46 | |
To uncover the story, I'll be reading the words of medieval scholars... | 0:00:49 | 0:00:54 | |
..going deep underground through ancient Cornish mines... | 0:00:56 | 0:00:59 | |
That looks like a lot of gunpowder to me. | 0:00:59 | 0:01:02 | |
..and making some of the most dangerous substances ever known. | 0:01:04 | 0:01:08 | |
It mustn't go above 18 degrees centigrade. | 0:01:08 | 0:01:11 | |
It's a journey that will take us right to the centre of matter. | 0:01:13 | 0:01:16 | |
-Is that a split atom? -Oh, yes. | 0:01:16 | 0:01:19 | |
Wow! | 0:01:19 | 0:01:20 | |
And the power it can unleash. | 0:01:20 | 0:01:22 | |
This is the story of how we learnt to harness the forces that shook the world. | 0:01:25 | 0:01:31 | |
The very first record we have of people using explosions comes from | 0:02:01 | 0:02:05 | |
a Chinese document which could date from as far back as two centuries BC. | 0:02:05 | 0:02:10 | |
It describes how travellers in the mountain wilderness of the West | 0:02:10 | 0:02:14 | |
were threatened by shape-shifting creatures of the night. | 0:02:14 | 0:02:18 | |
To scare away these creatures, | 0:02:18 | 0:02:21 | |
they would lay lengths of bamboo on their campfires. | 0:02:21 | 0:02:24 | |
-BANG! -The very first Chinese firecrackers. | 0:02:29 | 0:02:33 | |
CRACKING AND HISSING | 0:02:33 | 0:02:36 | |
The hissing noise we hear is moisture in the bamboo turning to steam, | 0:02:36 | 0:02:41 | |
but bamboo has a special structure to it. | 0:02:41 | 0:02:45 | |
It grows in sealed compartments. | 0:02:45 | 0:02:48 | |
Now, when the moisture in these sealed compartments | 0:02:48 | 0:02:51 | |
starts turning to steam, pressure builds up inside here. | 0:02:51 | 0:02:55 | |
It can't go anywhere. | 0:02:55 | 0:02:57 | |
-Water, when it turns to steam, -BANG! | 0:02:57 | 0:02:59 | |
wants to expand hundreds of times, but there isn't room for it do that, | 0:02:59 | 0:03:03 | |
so pressure builds up. | 0:03:03 | 0:03:04 | |
Eventually the structure of the bamboo breaks down. Kcrrr! | 0:03:04 | 0:03:07 | |
It explodes, | 0:03:07 | 0:03:09 | |
scaring away shape-shifting creatures of the night. | 0:03:09 | 0:03:13 | |
Using simple natural explosions like this | 0:03:15 | 0:03:18 | |
was the first step of mankind's journey to harness explosive power, | 0:03:18 | 0:03:23 | |
starting to understand the process in order to control it. | 0:03:23 | 0:03:28 | |
It's easy enough to create an explosion. | 0:03:32 | 0:03:35 | |
Any explosion is simply the moment when gas tries to expand suddenly. | 0:03:35 | 0:03:40 | |
-LOUD BANG -Oh! | 0:03:41 | 0:03:42 | |
And when that suddenly expanding air crashed into the air around it, | 0:03:44 | 0:03:49 | |
it created a pressure wave that then moves through the surroundings. | 0:03:49 | 0:03:54 | |
A sudden change in pressure forced a cloud of water droplets out of the air. | 0:03:54 | 0:03:59 | |
These allow us to see the wave. | 0:03:59 | 0:04:01 | |
The faster the gas is trying to expand, | 0:04:01 | 0:04:04 | |
the more powerful the explosion, | 0:04:04 | 0:04:07 | |
when that pressure wave hits your ear, you hear it as a bang. | 0:04:07 | 0:04:10 | |
An explosion relies on a lot of gas trying to expand. | 0:04:12 | 0:04:16 | |
Heat can make this happen, because heat, of course, makes things expand. | 0:04:16 | 0:04:20 | |
Introducing more gas can do the same thing, | 0:04:20 | 0:04:24 | |
but mankind discovered a way to create both heat and gas | 0:04:24 | 0:04:29 | |
by reacting chemicals together and this was the start | 0:04:29 | 0:04:33 | |
of our journey to really master explosive power. | 0:04:33 | 0:04:37 | |
In Europe, chemical explosions were unknown until the medieval period, | 0:04:41 | 0:04:46 | |
and the first time people came across them, | 0:04:46 | 0:04:49 | |
they were a bit shocked. | 0:04:49 | 0:04:51 | |
I've come to the Bodleian Library in Oxford | 0:04:51 | 0:04:54 | |
to see a manuscript that describes one of these early encounters. | 0:04:54 | 0:04:58 | |
It's one of the few copies of a book written in 1267 | 0:04:58 | 0:05:02 | |
by the medieval scholar Roger Bacon, | 0:05:02 | 0:05:04 | |
who split his time between Oxford and Paris universities. | 0:05:04 | 0:05:10 | |
Now, this particular passage that starts "et experimentum" | 0:05:10 | 0:05:15 | |
describes his knowledge of man-made explosives at the time. | 0:05:15 | 0:05:19 | |
"There is a children's toy, something no bigger than one's thumb, | 0:05:21 | 0:05:24 | |
"made in many parts of the world, that is an example | 0:05:24 | 0:05:27 | |
"of how something can assault the senses with sound and fire. | 0:05:27 | 0:05:31 | |
"It is no more than a bit of parchment which contains a powder | 0:05:31 | 0:05:35 | |
"combining the violence of that salt called saltpetre | 0:05:35 | 0:05:38 | |
"together with sulphur and willow charcoal | 0:05:38 | 0:05:41 | |
"but the bursting of this small thing assaults the ear | 0:05:41 | 0:05:45 | |
"with a noise that exceeds the roar of thunder | 0:05:45 | 0:05:48 | |
"and a flash brighter than the most brilliant lightning." | 0:05:48 | 0:05:51 | |
Now, I suspect he might he may have been exaggerating slightly, | 0:05:53 | 0:05:57 | |
but this was the first time that anyone in Europe | 0:05:57 | 0:06:00 | |
had come across man-made explosives. | 0:06:00 | 0:06:02 | |
Roger Bacon was a Franciscan friar, | 0:06:02 | 0:06:04 | |
and the church at that time had envoys all over the world. | 0:06:04 | 0:06:08 | |
It seems likely that one of those envoys | 0:06:08 | 0:06:10 | |
must have posted a package back to him | 0:06:10 | 0:06:13 | |
containing these children's toys. | 0:06:13 | 0:06:15 | |
The big question is, though, where exactly did that package come from? | 0:06:15 | 0:06:19 | |
In the Middle Ages, | 0:06:22 | 0:06:23 | |
the most technologically-advanced region of the world was China. | 0:06:23 | 0:06:27 | |
A printed book dating from before the battle of Hastings | 0:06:27 | 0:06:31 | |
indicates that the Chinese were already deploying explosives | 0:06:31 | 0:06:35 | |
of a similar sort on the battlefield. | 0:06:35 | 0:06:38 | |
What we have here is a Chinese military manual | 0:06:38 | 0:06:41 | |
first printed in 1044 | 0:06:41 | 0:06:44 | |
and in it, we find a recipe for a thing called | 0:06:44 | 0:06:48 | |
the "fire mixture" or the "fire chemical" | 0:06:48 | 0:06:51 | |
which contains the principal three ingredients | 0:06:51 | 0:06:55 | |
in Roger Bacon's recipe of 200 years later. | 0:06:55 | 0:06:58 | |
We start off with, here we have these two things here, | 0:06:58 | 0:07:02 | |
they're both forms of what we now call sulphur... | 0:07:02 | 0:07:05 | |
-Right. -..followed by various forms of organic matter | 0:07:05 | 0:07:09 | |
like pounded dried roots and twigs that produce the carbon, | 0:07:09 | 0:07:13 | |
followed by saltpetre, the next one. | 0:07:13 | 0:07:17 | |
The saltpetre is something you get from the decay of organic matter | 0:07:17 | 0:07:21 | |
in relatively warm conditions. | 0:07:21 | 0:07:23 | |
The Arabs refer to it is a Chinese snow. | 0:07:23 | 0:07:26 | |
Right, so China was just a good place at the time, | 0:07:26 | 0:07:30 | |
like, had the right climate for saltpetre to occur like that? | 0:07:30 | 0:07:34 | |
There's a lot of things that come together, | 0:07:34 | 0:07:36 | |
but the availability of the right climate is important. | 0:07:36 | 0:07:39 | |
Can I try and start assembling it in the right proportions? | 0:07:39 | 0:07:43 | |
Certainly. Well, roughly, you want to put in about 50% of saltpetre. | 0:07:43 | 0:07:49 | |
For every one of those? | 0:07:49 | 0:07:51 | |
Yeah, that's equal amounts of the powdered sulphur that we've got | 0:07:51 | 0:07:54 | |
and the powdered charcoal. | 0:07:54 | 0:07:56 | |
What were they trying to make at this point? | 0:07:56 | 0:07:58 | |
This is a mixture for parcelling up and throwing, basically, | 0:07:58 | 0:08:02 | |
into an enemy city using a catapult like this. | 0:08:02 | 0:08:06 | |
This thing here is called a hui pao, which means a fire catapult. | 0:08:06 | 0:08:09 | |
Now, from my knowledge of chemistry, | 0:08:09 | 0:08:12 | |
-saltpetre is what they call potassium nitrate. -That's right. | 0:08:12 | 0:08:15 | |
And that's got kind of oxygen bound up with nitrogen inside it. | 0:08:15 | 0:08:20 | |
That's right. If we warm it up, it'll let the oxygen loose, | 0:08:20 | 0:08:23 | |
and that will aid the burning of the other ingredients. | 0:08:23 | 0:08:26 | |
The sulphur basically helps everything to happen at a rather lower temperature before | 0:08:26 | 0:08:31 | |
and ultimately, of course, the carbon is the main source of the stuff that burns. | 0:08:31 | 0:08:36 | |
And there we go, that's good, look at that! | 0:08:36 | 0:08:39 | |
Take the flame away now. See it goes. That's very nice. | 0:08:39 | 0:08:42 | |
That's fabulous! | 0:08:42 | 0:08:43 | |
I'd call that an effective incendiary, wouldn't you? | 0:08:45 | 0:08:48 | |
I can imagine once you get a bucket load of that landing in your camp... | 0:08:48 | 0:08:52 | |
-It's discouraging, isn't it? Makes you wish you hadn't come. -Yes. | 0:08:52 | 0:08:55 | |
The black powder that the Chinese military were using in 1044 had got | 0:08:55 | 0:09:01 | |
grains of different chemicals close enough to react together | 0:09:01 | 0:09:04 | |
and produce lots of heat and gases. | 0:09:04 | 0:09:07 | |
In the open air, there's plenty of room for the gases to expand, | 0:09:07 | 0:09:10 | |
so there was no sudden explosion, | 0:09:10 | 0:09:12 | |
but the basic chemistry of gunpowder was there. | 0:09:12 | 0:09:16 | |
However, an even older Chinese book | 0:09:16 | 0:09:18 | |
suggests that the very first chemical explosive in the world | 0:09:18 | 0:09:22 | |
had been developed 200 years before this. | 0:09:22 | 0:09:25 | |
A book with the lovely title | 0:09:25 | 0:09:27 | |
Classified Essentials Of The Mysterious Way Of The Origin Of All Things, | 0:09:27 | 0:09:31 | |
which happens to contain a few recipes listed as, | 0:09:31 | 0:09:35 | |
"Don't try this at home if you are an alchemist," | 0:09:35 | 0:09:38 | |
-and amongst that is a recipe which I think we ought to try. -I'm game. | 0:09:38 | 0:09:43 | |
You have some saltpetre. You have some sulphur. | 0:09:43 | 0:09:46 | |
Those two ingredients. The carbon comes in the form of honey. | 0:09:46 | 0:09:50 | |
OK, and what kind of quantities do you use? | 0:09:50 | 0:09:52 | |
Oh, well, I would say most of that jar would get us | 0:09:52 | 0:09:56 | |
something interesting happening. | 0:09:56 | 0:09:58 | |
If you got about the same quantity of the other two ingredients, | 0:09:58 | 0:10:02 | |
the saltpetre and the sulphur, that should go nicely. | 0:10:02 | 0:10:06 | |
Why did they ever think of mixing these things together at this point? | 0:10:06 | 0:10:10 | |
The idea is to try to subdue the fiery properties | 0:10:10 | 0:10:13 | |
of the sulphur and of the saltpetre | 0:10:13 | 0:10:15 | |
so that they will be suitable for taking as a medicine, | 0:10:15 | 0:10:19 | |
-hopefully an elixir of life. -Oh, I see! | 0:10:19 | 0:10:22 | |
'So, ironically, in trying to find a means to eternal life, | 0:10:22 | 0:10:26 | |
'the Chinese alchemists found a substance that could kill.' | 0:10:26 | 0:10:29 | |
I've never done any alchemy before. | 0:10:29 | 0:10:32 | |
This is my first venture into the world of alchemy. | 0:10:32 | 0:10:35 | |
If you make a success of it, it's a new career, really, isn't it? | 0:10:35 | 0:10:38 | |
-Potentially lucrative. -Yes, indeed, indeed. | 0:10:38 | 0:10:41 | |
That looks pretty well stirred. | 0:10:41 | 0:10:43 | |
I would think now if you start cooking that, | 0:10:43 | 0:10:45 | |
that will finish the mixing. | 0:10:45 | 0:10:48 | |
Despite being earlier than the incendiary powder of 1044, | 0:10:48 | 0:10:52 | |
the chemistry of this mixture has the potential to be more explosive. | 0:10:52 | 0:10:57 | |
So because of the water in the honey, | 0:10:57 | 0:10:59 | |
that is dissolving the saltpetre. | 0:10:59 | 0:11:01 | |
-Yes. -And allowing that to carefully coat all the bits of sulphur. | 0:11:01 | 0:11:06 | |
The particles of carbon and sulphur will now be very, very close to molecules of saltpetre | 0:11:06 | 0:11:10 | |
which, when they get hot enough, | 0:11:10 | 0:11:13 | |
will start releasing the oxygen just right up close to them. | 0:11:13 | 0:11:18 | |
I think that's going to go in a sec. | 0:11:18 | 0:11:19 | |
There's little puffs there. | 0:11:19 | 0:11:21 | |
Exciting little puffs. I say. | 0:11:21 | 0:11:23 | |
Just slightly move ourselves out of the immediate line of that. That's it. | 0:11:23 | 0:11:29 | |
Whoa! OK... | 0:11:30 | 0:11:33 | |
Wow! | 0:11:33 | 0:11:35 | |
-That was quite striking. -Wow! | 0:11:38 | 0:11:41 | |
Well, as the Chinese alchemist said, don't try this at home. | 0:11:41 | 0:11:45 | |
So, incendiary mixtures were being explored by the Chinese alchemists | 0:11:48 | 0:11:52 | |
as early as the mid-ninth century | 0:11:52 | 0:11:55 | |
but from the 12th century, as China was swept by waves | 0:11:55 | 0:11:58 | |
of war with neighbouring peoples, | 0:11:58 | 0:12:00 | |
they started to use their fast-burning powder in a new way. | 0:12:00 | 0:12:05 | |
No longer just an incendiary, | 0:12:05 | 0:12:07 | |
it became an explosive propellant for projectiles. | 0:12:07 | 0:12:10 | |
The Chinese gave their new weapons names, | 0:12:10 | 0:12:12 | |
like the vast-as-heaven, enemy- exterminating yin-yang shovel, | 0:12:12 | 0:12:17 | |
the scary, ingenious, mobile, ever-victorious poison-fire rack | 0:12:17 | 0:12:21 | |
and my personal favourite, | 0:12:21 | 0:12:23 | |
the orifices-penetrating flying-sand magic-mist tube. | 0:12:23 | 0:12:28 | |
In all of them, they put the powder in a tightly confined space | 0:12:28 | 0:12:32 | |
and this fundamentally altered the way it behaved. | 0:12:32 | 0:12:35 | |
It was the discovery that would change warfare forever. | 0:12:35 | 0:12:39 | |
Confining gunpowder changes the speed of the reaction. | 0:12:39 | 0:12:43 | |
It goes from something that just burns into something that really explodes. | 0:12:43 | 0:12:47 | |
Gunpowder doesn't need air in order to burn. | 0:12:53 | 0:12:56 | |
It gets all the oxygen required from the crystals of saltpetre, | 0:12:56 | 0:12:59 | |
potassium nitrate, that are in there, | 0:12:59 | 0:13:02 | |
which means it'll still burn in a confined space | 0:13:02 | 0:13:06 | |
and putting it in a confined space increases the rate of reaction. | 0:13:06 | 0:13:10 | |
Put a little bit in here. | 0:13:10 | 0:13:12 | |
So I'm going to wrap it up. | 0:13:12 | 0:13:14 | |
When it's confined like this, all those grains, | 0:13:17 | 0:13:19 | |
the carbon, the sulphur and the potassium nitrate, | 0:13:19 | 0:13:22 | |
are all much closer together, which means | 0:13:22 | 0:13:25 | |
the reaction can happen more quickly, and as the reaction happens more quickly, | 0:13:25 | 0:13:29 | |
more heat's created, making the reaction go even faster and it's a runaway process. | 0:13:29 | 0:13:33 | |
Right. | 0:13:33 | 0:13:35 | |
With gas being produced so quickly and heat making it expand, | 0:13:35 | 0:13:39 | |
there's the potential for explosive force, | 0:13:39 | 0:13:42 | |
if I can channel it like the Chinese did. | 0:13:42 | 0:13:46 | |
This is my first attempt at a cannon. | 0:13:46 | 0:13:49 | |
I've decided to build it out of clear acrylic | 0:13:49 | 0:13:52 | |
so that we get to see what happens inside a cannon. | 0:13:52 | 0:13:55 | |
Now, I'll drop that on there. | 0:13:55 | 0:13:58 | |
That fits in nicely. | 0:13:58 | 0:14:00 | |
Got my cannonball. | 0:14:02 | 0:14:04 | |
So there it is. There's going to be an explosion in there. | 0:14:07 | 0:14:11 | |
That explosion will produce hot, expanding gas. | 0:14:11 | 0:14:15 | |
There'll be a big pressure rise in that part of the chamber. | 0:14:15 | 0:14:18 | |
That pressure will exert a force all around the container, | 0:14:18 | 0:14:22 | |
but these three sides should stay where they are. | 0:14:22 | 0:14:25 | |
This fourth side here, where the tennis ball is, | 0:14:25 | 0:14:29 | |
won't stay where it is, and that tennis ball will leave at | 0:14:29 | 0:14:32 | |
an undetermined speed that I suspect will be pretty quick. | 0:14:32 | 0:14:36 | |
Let's find out. | 0:14:36 | 0:14:37 | |
Three, two, one! | 0:14:44 | 0:14:48 | |
Yeah, that worked like a cannon should work. | 0:14:54 | 0:14:58 | |
Wow! | 0:14:58 | 0:14:59 | |
You can see how the gunpowder produces hot gases | 0:15:00 | 0:15:04 | |
at just the right rate | 0:15:04 | 0:15:05 | |
to push the ball out. | 0:15:05 | 0:15:08 | |
This technology quickly spread west, through the Middle East, | 0:15:08 | 0:15:11 | |
and by the 14th century, the Europeans had rockets and guns too. | 0:15:11 | 0:15:16 | |
But something else was happening - gunpowder was spreading beyond the battlefield. | 0:15:18 | 0:15:23 | |
Its power was being put to work in mines and engineering projects, | 0:15:23 | 0:15:28 | |
as Europe became more industrialised | 0:15:28 | 0:15:30 | |
and there was demand for more powerful and destructive explosions. | 0:15:30 | 0:15:34 | |
Gunpowder had reigned for 500 years, | 0:15:35 | 0:15:38 | |
but now its dominance was about to be challenged. | 0:15:38 | 0:15:42 | |
The middle of the 19th century provided a turning point | 0:15:43 | 0:15:47 | |
in the story of explosives. | 0:15:47 | 0:15:49 | |
I've had to come here, to the Defence Academy of the UK, | 0:15:49 | 0:15:52 | |
because we're going to make what they first discovered in 1846. | 0:15:52 | 0:15:57 | |
There was a growing tradition of pure scientific research in Europe, | 0:15:58 | 0:16:03 | |
with researchers trying to understand the chemical composition of natural substances. | 0:16:03 | 0:16:08 | |
One of these chemists was a German from a humble background called Christian Schonbein. | 0:16:08 | 0:16:13 | |
He was naive, unconventional and full of original ideas. | 0:16:13 | 0:16:18 | |
Working in Switzerland, he'd seen some unusual reactions with | 0:16:18 | 0:16:21 | |
concentrated acids and was keen to investigate them further. | 0:16:21 | 0:16:26 | |
One of those investigations was unwittingly to change the world of explosives forever. | 0:16:26 | 0:16:32 | |
Professor Jackie Akhavan has volunteered to show us | 0:16:32 | 0:16:35 | |
exactly what Schonbein did. | 0:16:35 | 0:16:37 | |
Jackie, what are we actually doing here? | 0:16:37 | 0:16:40 | |
OK, we're mixing nitric acid and sulphuric acid together | 0:16:40 | 0:16:44 | |
and then we're going to add some cotton wool to it, | 0:16:44 | 0:16:47 | |
to hopefully nitrate the cotton wool. | 0:16:47 | 0:16:49 | |
Schonbein didn't know it, but the cotton will be acting | 0:16:49 | 0:16:53 | |
as a source of carbon, like the charcoal in gunpowder | 0:16:53 | 0:16:56 | |
and by nitrating it, he added oxygen and nitrogen | 0:16:56 | 0:17:00 | |
from the acid actually into the molecules of the cotton, | 0:17:00 | 0:17:04 | |
rather than just being in neighbouring grains. | 0:17:04 | 0:17:07 | |
We must make sure the temperature remains cool. | 0:17:07 | 0:17:11 | |
So I'm going to put a thermometer in so we can measure the temperature. | 0:17:11 | 0:17:14 | |
-Do you want to help? -I do. What temperature should I watch out for? | 0:17:14 | 0:17:18 | |
OK, it mustn't go above 18 degrees centigrade. | 0:17:18 | 0:17:21 | |
I'm going to adjust this. Could you give me an update? | 0:17:21 | 0:17:23 | |
-It's at 21 at the moment. -Right. | 0:17:23 | 0:17:25 | |
-I don't want to scare anybody. -No, it's OK. What we'll do, | 0:17:25 | 0:17:28 | |
we'll just cool it down a bit. OK. | 0:17:28 | 0:17:30 | |
So what temperature are we now? | 0:17:30 | 0:17:32 | |
-It's down to 19. -OK, well, we need to get it a bit cooler. | 0:17:32 | 0:17:36 | |
-We're down to 18.4. -OK. | 0:17:38 | 0:17:40 | |
What's the danger if the temperature starts rising? | 0:17:40 | 0:17:43 | |
We want to keep control of this reaction. | 0:17:43 | 0:17:45 | |
I'm very conscious of this. | 0:17:45 | 0:17:46 | |
-That's OK. -I know battery acid's quite horrifically dangerous and if that's just as dangerous. | 0:17:46 | 0:17:52 | |
It's much... These are very concentrated acids, | 0:17:52 | 0:17:55 | |
so we've got to be extremely careful. | 0:17:55 | 0:17:57 | |
'The nitration reaction changes the cotton chemically so that now, | 0:17:57 | 0:18:01 | |
'just like in the gunpowder mix, there are carbon, nitrogen | 0:18:01 | 0:18:05 | |
'and oxygen atoms, an explosive reaction waiting to happen, | 0:18:05 | 0:18:08 | |
'but in this substance they're actually all in the same molecule, | 0:18:08 | 0:18:13 | |
'so much closer together than in gunpowder. | 0:18:13 | 0:18:16 | |
'Schonbein had accidentally created a much more efficient explosive.' | 0:18:16 | 0:18:20 | |
So this is it, our nitrocellulose, or guncotton as it's known. | 0:18:20 | 0:18:24 | |
-That's right. -I mean, now we've washed the acid off and dried it, | 0:18:24 | 0:18:29 | |
it feels exactly like cotton wool. | 0:18:29 | 0:18:31 | |
Just like we started with. | 0:18:31 | 0:18:32 | |
The only difference with this one, compared to the cotton wool, | 0:18:32 | 0:18:36 | |
is that we've got the oxygen actually linked to the fuel. | 0:18:36 | 0:18:40 | |
So because we've changed every single molecule | 0:18:40 | 0:18:42 | |
of the cotton to guncotton, | 0:18:42 | 0:18:44 | |
-then it's going to go exactly the same every time? -Yes. | 0:18:44 | 0:18:48 | |
-Go on, then. -Right. Are you ready? | 0:18:48 | 0:18:49 | |
I'm more than a little intrigued. | 0:18:49 | 0:18:52 | |
Stand back. | 0:18:54 | 0:18:56 | |
-I am already. -Ready? | 0:18:56 | 0:18:57 | |
That gives off a lot of heat. | 0:19:02 | 0:19:04 | |
Heat, light, lots of gas being given out and then you can just have | 0:19:04 | 0:19:08 | |
a look, and there's sort of black bits there, that's the carbon. | 0:19:08 | 0:19:11 | |
So it hasn't fully oxidised. | 0:19:11 | 0:19:13 | |
So there's not enough oxygen for all the carbon that's in the molecules, | 0:19:13 | 0:19:16 | |
-so we're just left with some carbon. -That's right. | 0:19:16 | 0:19:19 | |
That's a very, very rapid burnout. Whoof. | 0:19:19 | 0:19:21 | |
Like with the gunpowder when you just set it on fire, | 0:19:21 | 0:19:24 | |
it's unconfined, so you don't get an explosion, | 0:19:24 | 0:19:27 | |
you just get this rapid burning. | 0:19:27 | 0:19:29 | |
It all goes up into the atmosphere and it's all disappeared as gases | 0:19:29 | 0:19:33 | |
and that's what you're left with. | 0:19:33 | 0:19:35 | |
-I like it. Can we do some more? -You can indeed. | 0:19:35 | 0:19:37 | |
Just like gunpowder, guncotton simply burns when there's room | 0:19:40 | 0:19:44 | |
for the gases it produces to expand into | 0:19:44 | 0:19:47 | |
but it burns faster, and the faster the gases are produced, | 0:19:47 | 0:19:50 | |
the greater the explosive potential. | 0:19:50 | 0:19:54 | |
Schonbein recognised it and immediately started | 0:19:54 | 0:19:57 | |
sending out samples to colleagues and writing about his discovery. | 0:19:57 | 0:20:01 | |
One of the first to react to the news | 0:20:03 | 0:20:05 | |
was the Cornish mining community in the far southwest of England. | 0:20:05 | 0:20:09 | |
The area is rich in resources like tin and granite | 0:20:09 | 0:20:13 | |
and it made it a worldwide centre for mining. | 0:20:13 | 0:20:17 | |
It was a vital and profitable industry for England | 0:20:17 | 0:20:20 | |
and in the mid-19th century, | 0:20:20 | 0:20:22 | |
it relied heavily on gunpowder to break up the rock. | 0:20:22 | 0:20:27 | |
By the 1840s, miners had been using gunpowder in mines like this | 0:20:27 | 0:20:32 | |
for 200 years. | 0:20:32 | 0:20:33 | |
But gunpowder was far from reliable. It was dangerous, | 0:20:35 | 0:20:38 | |
unpredictable and difficult to use. | 0:20:38 | 0:20:41 | |
Mine historian Richard Williams has promised to show me just | 0:20:41 | 0:20:45 | |
how difficult, starting with how they got it deep within the rock. | 0:20:45 | 0:20:49 | |
You're trying to actually push a hole into the rock using what they | 0:20:49 | 0:20:53 | |
called a bore, basically, an iron bar about 3ft long. | 0:20:53 | 0:20:56 | |
-Right. -And a heavy hammer. -Can I have a go? | 0:20:56 | 0:20:59 | |
I'd love to have a go. | 0:20:59 | 0:21:01 | |
Keep turning it. | 0:21:03 | 0:21:04 | |
I can see that taking a while. | 0:21:07 | 0:21:09 | |
It would probably take you a good 20 minutes. | 0:21:09 | 0:21:11 | |
I can imagine once you've done your 3ft hole, | 0:21:11 | 0:21:14 | |
you'd want to get the best bang out of it you could. | 0:21:14 | 0:21:17 | |
Oh, yes. The next thing is to charge it, to fill it with gunpowder. | 0:21:17 | 0:21:22 | |
You can imagine if they're working with candles or open lamps and | 0:21:22 | 0:21:26 | |
gunpowder, it's not a great combination. | 0:21:26 | 0:21:30 | |
OK, so once they've got the gunpowder into the hole there, | 0:21:30 | 0:21:33 | |
how do they safely light it? | 0:21:33 | 0:21:34 | |
They used a goose quill. | 0:21:34 | 0:21:37 | |
-Basically the centre of the quill is hollow. -Yeah. | 0:21:37 | 0:21:40 | |
So you cut off the top, you end up with something like that. | 0:21:40 | 0:21:43 | |
You grind your gunpowder up until its fine enough to go into | 0:21:43 | 0:21:46 | |
-the hollow. -Yeah. -Tamp that down. | 0:21:46 | 0:21:49 | |
Make several of those, push one into another and slowly you make a fuse. | 0:21:49 | 0:21:54 | |
And they're all packed with gunpowder, so I can see, | 0:21:54 | 0:21:57 | |
but what was the burn-time on them? | 0:21:57 | 0:22:00 | |
Like, how quick did they go? | 0:22:00 | 0:22:01 | |
They were unpredictable. | 0:22:01 | 0:22:03 | |
If you didn't pack them correctly, | 0:22:03 | 0:22:05 | |
they would go off a bit like a rocket. | 0:22:05 | 0:22:07 | |
-That's horrendous. -Well, when we're doing it, | 0:22:07 | 0:22:10 | |
we're actually going to use a safety fuse and we've already made a charge up | 0:22:10 | 0:22:14 | |
and we've filled this with gunpowder and we've already got | 0:22:14 | 0:22:18 | |
-a hole drilled. The hole is going back into the rock. -OK. | 0:22:18 | 0:22:22 | |
So we put the powder into the hole. | 0:22:22 | 0:22:26 | |
They would then get a tamping rod to push it in. | 0:22:26 | 0:22:28 | |
-Next thing is to stem it, to seal it. -Right. | 0:22:30 | 0:22:33 | |
If we left it like that, it would shoot just like a gun. | 0:22:33 | 0:22:36 | |
Visually, this looks quite a short fuse to me. | 0:22:36 | 0:22:38 | |
How much time have we got from when we light it? | 0:22:38 | 0:22:41 | |
This is going to take slightly over a minute and a half | 0:22:41 | 0:22:44 | |
to burn through to the gunpowder. | 0:22:44 | 0:22:46 | |
That seems quite quick, but I'll trust you. I'm going to wear my goggles, though. | 0:22:46 | 0:22:50 | |
Away it goes. | 0:22:51 | 0:22:53 | |
-Here we go. -Look at that. | 0:23:00 | 0:23:01 | |
I say look at that - | 0:23:01 | 0:23:02 | |
should we not be moving in that direction quite quickly? | 0:23:02 | 0:23:05 | |
-I think we should leave now, yes. -Yeah. | 0:23:05 | 0:23:09 | |
-So we can just literally just pop round the corner here? | 0:23:09 | 0:23:12 | |
Round the corner so we'll be out of the way of anything that flies down through the tunnel. | 0:23:12 | 0:23:16 | |
You start to wonder if it's going to go. | 0:23:22 | 0:23:26 | |
But it went! | 0:23:29 | 0:23:30 | |
The reverberation afterwards as well, which I guess is | 0:23:33 | 0:23:36 | |
the multiple shock wave bouncing off all sorts of walls. | 0:23:36 | 0:23:39 | |
Well, there we go, you look down the level and we should see the smoke. | 0:23:39 | 0:23:44 | |
Right, you can actually see the fumes are close to the roof looking down through. | 0:23:46 | 0:23:51 | |
-Oh, yeah. -It's getting thicker as we get close to the... | 0:23:52 | 0:23:55 | |
-It's getting a bit acrid. -Yeah. | 0:23:55 | 0:23:57 | |
'The smoke was one of the things that miners hated about gunpowder. | 0:23:57 | 0:24:01 | |
'It filled the tunnels and made working difficult.' | 0:24:01 | 0:24:04 | |
What's actually happened is it's blown the studding out. | 0:24:04 | 0:24:08 | |
-We haven't moved any rock at all, have we? -No. | 0:24:08 | 0:24:11 | |
'So not only was gunpowder difficult and time-consuming for miners to use, it wasn't even that reliable. | 0:24:11 | 0:24:18 | |
'Schonbein's new guncotton promised more power, more reliability and no smoke.' | 0:24:18 | 0:24:25 | |
In August 1846, the Royal Geological Society of Cornwall | 0:24:25 | 0:24:29 | |
invited him to come to England to prove its worth. | 0:24:29 | 0:24:34 | |
Schonbein demonstrated his guncotton in a quarry like this. | 0:24:34 | 0:24:38 | |
The quarrymen drilled several holes in the rock, and into one, they packed a full charge of gunpowder | 0:24:38 | 0:24:45 | |
and into another, just a quarter of the amount of guncotton. | 0:24:45 | 0:24:48 | |
So innocent did the guncotton look that one man said he would sit | 0:24:48 | 0:24:53 | |
on the hole in return for a drink at the local pub. | 0:24:53 | 0:24:56 | |
Luckily, he was persuaded to watch the test | 0:24:56 | 0:24:59 | |
before committing himself to the bargain. | 0:24:59 | 0:25:02 | |
First, 30g of gunpowder. | 0:25:04 | 0:25:05 | |
Let's see if it's more successful than in the mine. | 0:25:05 | 0:25:08 | |
Well, the rock split, but not at the hole where the explosives were. | 0:25:16 | 0:25:21 | |
It looks like that explosion there maybe sent some kind of shock | 0:25:21 | 0:25:26 | |
through the rock and it peeled off here, | 0:25:26 | 0:25:28 | |
where possibly there was some sort of fault line. | 0:25:28 | 0:25:31 | |
Now we'll try just 5g of guncotton, | 0:25:34 | 0:25:37 | |
looking like it couldn't possibly do much damage. | 0:25:37 | 0:25:40 | |
That's a completely different story. | 0:25:46 | 0:25:48 | |
In slow motion, you can clearly see all the gases the explosion creates. | 0:25:49 | 0:25:54 | |
Brown nitric oxide, steam and others, splitting the rock apart. | 0:25:54 | 0:25:59 | |
That's just astonishing. | 0:26:08 | 0:26:10 | |
A couple of hundred kilos of rock has practically disappeared. | 0:26:10 | 0:26:13 | |
There's some fragments over there, | 0:26:13 | 0:26:16 | |
bits down here. | 0:26:16 | 0:26:17 | |
And look at that. | 0:26:17 | 0:26:20 | |
Where it was actually placed, there's nothing at all. | 0:26:20 | 0:26:25 | |
Like that. | 0:26:25 | 0:26:26 | |
Look down here. | 0:26:26 | 0:26:29 | |
That's the hole where it was packed in. So this was the other way up. | 0:26:29 | 0:26:33 | |
You can see where the clay was, | 0:26:33 | 0:26:34 | |
you can see all the way down here and it's just split it. | 0:26:34 | 0:26:38 | |
Now, this is guncotton and what's happened here is when | 0:26:38 | 0:26:42 | |
the guncotton has been compacted, confined in there, it's detonated, | 0:26:42 | 0:26:47 | |
which is a completely different process to when we saw it being lit. | 0:26:47 | 0:26:51 | |
It burnt rapidly. | 0:26:51 | 0:26:52 | |
This detonation sends out a sharp shock wave | 0:26:52 | 0:26:55 | |
and as it goes into the rock, the rock gets split. | 0:26:55 | 0:26:58 | |
It's a much more powerful explosion, and I can imagine the Cornish miners | 0:26:58 | 0:27:03 | |
feeling a little bit like me now, | 0:27:03 | 0:27:04 | |
almost overwhelmed at the difference between gunpowder and guncotton. | 0:27:04 | 0:27:10 | |
The quarrymen were amazed at the new guncotton | 0:27:11 | 0:27:14 | |
and mercilessly teased the colleague who had offered to sit on it. | 0:27:14 | 0:27:18 | |
They were immediately interested and Schonbein quickly found | 0:27:18 | 0:27:21 | |
an English partner to start manufacture. | 0:27:21 | 0:27:24 | |
His apparent success soon inspired others. | 0:27:24 | 0:27:27 | |
Schonbein wasn't the only one experimenting with these kind of chemicals. | 0:27:27 | 0:27:31 | |
Not long afterwards, an Italian chemist, Ascanio Sobrero, | 0:27:31 | 0:27:36 | |
reacted nitric acid with glycerine, another carbon-rich substance. | 0:27:36 | 0:27:41 | |
Sobrero had worked on nitration before, | 0:27:41 | 0:27:44 | |
and when he read of Schonbein's discovery, | 0:27:44 | 0:27:46 | |
he was inspired to return to it. | 0:27:46 | 0:27:48 | |
He was originally a medic, | 0:27:48 | 0:27:50 | |
so many of his interests were in potential new drugs. | 0:27:50 | 0:27:53 | |
The result of this experiment, first done in 1846, is in fact still | 0:27:53 | 0:27:59 | |
an important heart medicine, but it has another side to its character. | 0:27:59 | 0:28:04 | |
Dr Alex Contini is one of the few chemists experienced enough | 0:28:04 | 0:28:07 | |
to attempt this process | 0:28:07 | 0:28:10 | |
and he isn't going to trust his life to me keeping an eye on the thermometer this time. | 0:28:10 | 0:28:14 | |
Seven and rising... | 0:28:14 | 0:28:16 | |
Each time the glycerine is added to the concentrated acids, | 0:28:18 | 0:28:22 | |
he has to stir it and make sure it stays cool. | 0:28:22 | 0:28:25 | |
Every degree of temperature rise | 0:28:25 | 0:28:27 | |
makes a premature explosion more likely. | 0:28:27 | 0:28:30 | |
Ten and rising... | 0:28:30 | 0:28:33 | |
The resulting oily liquid, like guncotton, | 0:28:46 | 0:28:49 | |
contains carbon atoms linked to nitrogen and oxygen groups. | 0:28:49 | 0:28:53 | |
It looks fairly innocuous, | 0:28:53 | 0:28:55 | |
but Sobrero discovered it has some pretty surprising properties. | 0:28:55 | 0:29:00 | |
And we're only going to use the tiniest amount to show them. | 0:29:00 | 0:29:04 | |
Sobrero wrote that the safest way to demonstrate these properties | 0:29:04 | 0:29:08 | |
was to dip a hot wire into a glass bowl of the substance, | 0:29:08 | 0:29:12 | |
but he was scarred for life by flying glass, | 0:29:12 | 0:29:15 | |
so we are going to try something different. | 0:29:15 | 0:29:18 | |
If you look down there, you'll see the nitroglycerine has completely disappeared. | 0:29:27 | 0:29:32 | |
Every molecule of the liquid nitroglycerine gets turned to gas and goes, | 0:29:32 | 0:29:37 | |
hence the massive expansion, hence the massive explosion. | 0:29:37 | 0:29:40 | |
Whilst guncotton only detonates when confined, | 0:29:42 | 0:29:45 | |
nitroglycerine can detonate when given a simple sharp shock. | 0:29:45 | 0:29:48 | |
Even slowed down more than 500 times, | 0:29:51 | 0:29:54 | |
the explosion is incredibly fast. | 0:29:54 | 0:29:57 | |
This new behaviour made guncotton and nitroglycerine | 0:29:58 | 0:30:03 | |
quite different from gunpowder. | 0:30:03 | 0:30:05 | |
The difference between gunpowder and these new high explosives, | 0:30:05 | 0:30:09 | |
as they're called, is the way they explode. | 0:30:09 | 0:30:12 | |
Gunpowder burns - albeit very rapidly, it's still burning. | 0:30:12 | 0:30:15 | |
One piece heating the piece adjacent to it, | 0:30:15 | 0:30:18 | |
the piece that's adjacent to that - | 0:30:18 | 0:30:20 | |
fwooh! - till the whole thing's gone. | 0:30:20 | 0:30:22 | |
With high explosives, it's detonation. | 0:30:22 | 0:30:25 | |
A pressure wave travels extremely quickly through the whole charge | 0:30:25 | 0:30:29 | |
and it almost goes instantaneously. | 0:30:29 | 0:30:31 | |
The first bit of the reaction in a high explosive | 0:30:31 | 0:30:34 | |
creates so much gas so quickly it generates a pressure wave | 0:30:34 | 0:30:39 | |
that hits the rest of the explosive. | 0:30:39 | 0:30:41 | |
I'll show you, with this fire piston, as it's called, | 0:30:41 | 0:30:45 | |
and a tiny bit of normal cotton wool. | 0:30:45 | 0:30:48 | |
As the piston comes down, it acts like the explosive pressure wave, | 0:30:48 | 0:30:53 | |
raising the pressure inside the tube. | 0:30:53 | 0:30:55 | |
That pressure heats the air so much | 0:30:55 | 0:30:57 | |
that the cotton wool bursts into flame. | 0:30:57 | 0:31:01 | |
It's the same with a piece of high explosive. | 0:31:01 | 0:31:03 | |
It's the sudden rise in pressure that gives the sudden rise in temperature | 0:31:03 | 0:31:08 | |
that triggers the explosive as it runs through the entire charge. | 0:31:08 | 0:31:11 | |
Now, this thing happens so quickly, | 0:31:11 | 0:31:13 | |
you pretty much get the entire lot going in one go. | 0:31:13 | 0:31:17 | |
Watch this. | 0:31:19 | 0:31:20 | |
This is detonating cord. It's a spun cord with a line of high explosive | 0:31:22 | 0:31:26 | |
right down the centre of it. | 0:31:26 | 0:31:28 | |
When it's detonated at one end, | 0:31:28 | 0:31:30 | |
the wave front moves extremely quickly right down its length. | 0:31:30 | 0:31:33 | |
Slowing the process down 250 times, you can see the detonation | 0:31:41 | 0:31:45 | |
travelling at about 6km a second. | 0:31:45 | 0:31:49 | |
When the force of the detonation wave hits the surrounding air, | 0:31:51 | 0:31:55 | |
it creates a supersonic shock wave. | 0:31:55 | 0:31:57 | |
You can see the shock wave distort the air like a bubble, | 0:31:57 | 0:32:00 | |
coming out around this modern high explosive. | 0:32:00 | 0:32:03 | |
Shock waves and reaction speeds like this were a phenomenon | 0:32:05 | 0:32:09 | |
nobody had come across before | 0:32:09 | 0:32:11 | |
and it made these new high explosives very powerful | 0:32:11 | 0:32:14 | |
and potentially very dangerous. | 0:32:14 | 0:32:16 | |
And that was the problem. | 0:32:16 | 0:32:19 | |
Only months after it opened, the world's first guncotton factory | 0:32:19 | 0:32:22 | |
exploded disastrously in England | 0:32:22 | 0:32:25 | |
and Sobrero's new nitroglycerine appeared even more dangerous. | 0:32:25 | 0:32:30 | |
It seemed there might be no way of safely harnessing | 0:32:30 | 0:32:33 | |
this new-found power. | 0:32:33 | 0:32:35 | |
But the industrialised world was crying out for it. | 0:32:35 | 0:32:39 | |
The men working the great tin and coal mines of Britain | 0:32:39 | 0:32:42 | |
were still having to use the centuries-old, inefficient gunpowder | 0:32:42 | 0:32:47 | |
and attempts to build a canal system to move the vital raw materials | 0:32:47 | 0:32:51 | |
produced by the mines to Britain's ports | 0:32:51 | 0:32:54 | |
were hampered by gunpowder's lack of power. | 0:32:54 | 0:32:57 | |
But in the 1850s, a young Swedish student | 0:32:59 | 0:33:02 | |
came to hear about nitroglycerine. | 0:33:02 | 0:33:04 | |
His name was Alfred Nobel | 0:33:04 | 0:33:07 | |
and his family were explosives manufacturers in need of money. | 0:33:07 | 0:33:10 | |
They took the risk of trying to manufacture nitroglycerine, | 0:33:10 | 0:33:15 | |
but they had an awful lot to learn. | 0:33:15 | 0:33:18 | |
In their first year of manufacture, their factory in Sweden exploded, | 0:33:18 | 0:33:22 | |
killing Alfred's younger brother Emil. | 0:33:22 | 0:33:25 | |
This is the site of Nobel's biggest explosives factory. | 0:33:25 | 0:33:29 | |
It's at Ardeer on the west coast of Scotland and at its height, | 0:33:29 | 0:33:32 | |
it was the biggest explosives factory in Europe. | 0:33:32 | 0:33:35 | |
Nobel liked it. | 0:33:38 | 0:33:40 | |
One, because it was remote, but two, it was built entirely on sand, | 0:33:40 | 0:33:45 | |
meaning he could create artificial landscapes like that. | 0:33:45 | 0:33:49 | |
Nobel built what were called nitroglycerine hills. | 0:33:56 | 0:33:59 | |
Nitroglycerine was made in little huts on the top of each hill. | 0:33:59 | 0:34:03 | |
In each hut were two men, one to monitor the mixing reaction, | 0:34:03 | 0:34:07 | |
the other to adjust the flow of water through a cooling jacket | 0:34:07 | 0:34:10 | |
to keep the temperature in the right range. | 0:34:10 | 0:34:13 | |
Now, vigilance was vital. | 0:34:13 | 0:34:15 | |
The entire batch could self-detonate if allowed to go out of control. | 0:34:15 | 0:34:19 | |
For this reason, one man had to always sit on a one-legged stool, | 0:34:19 | 0:34:23 | |
so there was no chance of him falling asleep on the job. | 0:34:23 | 0:34:26 | |
I mean, as if sitting next to a vat of nitroglycerine | 0:34:26 | 0:34:30 | |
was not stimulation enough! | 0:34:30 | 0:34:31 | |
Nitroglycerine could not be safely pumped. | 0:34:33 | 0:34:36 | |
So what they did was just let it flow under gravity | 0:34:36 | 0:34:38 | |
from the huts at the top of the hill to the factories at the bottom. | 0:34:38 | 0:34:42 | |
Once inside the factory, it got stabilised. | 0:34:45 | 0:34:49 | |
Now, this was what was Nobel's great achievement. | 0:34:49 | 0:34:52 | |
He discovered that if he mixed his nitroglycerine with an absorbent clay, a bit like cat litter, | 0:34:52 | 0:34:58 | |
it became a lot less sensitive, | 0:34:58 | 0:35:01 | |
a lot easier to handle without going off in your hands. | 0:35:01 | 0:35:04 | |
The clay he used came as a fine powder called kieselguhr. | 0:35:04 | 0:35:09 | |
Once mixed together, a dough-like substance was formed. | 0:35:11 | 0:35:14 | |
In fact, it was kneaded by armies of women into the shapes required. | 0:35:14 | 0:35:19 | |
This new compound was called dynamite and it was a revolution. | 0:35:26 | 0:35:32 | |
Now there was a high explosive that was insensitive to shock and heating. | 0:35:32 | 0:35:37 | |
You could actually set fire to it and it would burn with a normal flame. | 0:35:37 | 0:35:40 | |
I don't recommend it, but apparently you could, | 0:35:40 | 0:35:43 | |
but once you've made something that's this good, | 0:35:43 | 0:35:46 | |
that's this stable, this difficult to set off, | 0:35:46 | 0:35:48 | |
how do you get it to explode when you want it to? | 0:35:48 | 0:35:52 | |
That was Nobel's other great innovation. | 0:35:52 | 0:35:54 | |
And they actually still make those devices at his old factory. | 0:35:54 | 0:35:58 | |
In fact, Nobel's sand bunkers are the perfect place for me to find out more about them. | 0:35:58 | 0:36:03 | |
Well, Alfred Nobel being the very inventive guy that he was, | 0:36:06 | 0:36:09 | |
came up with the idea of a detonator | 0:36:09 | 0:36:11 | |
and this is a modern detonator, | 0:36:11 | 0:36:14 | |
but the basic principle is a device which delivers an explosive | 0:36:14 | 0:36:19 | |
shock to dynamite and that shock is sufficient to detonate it. | 0:36:19 | 0:36:25 | |
I do actually have a cutaway here. | 0:36:25 | 0:36:28 | |
At the top of the detonator we have an electrical fuse head | 0:36:28 | 0:36:31 | |
-and this is, in many ways, like the match. -Yep. | 0:36:31 | 0:36:36 | |
This is designed to initiate not by friction | 0:36:36 | 0:36:39 | |
but by passing an electric current through it. | 0:36:39 | 0:36:42 | |
That generates heat, which causes this fuse head to burst with | 0:36:42 | 0:36:48 | |
hot gases and hot particles | 0:36:48 | 0:36:50 | |
which then initiate a pallet of sensitive primary explosive. | 0:36:50 | 0:36:55 | |
And out of more than just casual curiosity, | 0:36:55 | 0:37:00 | |
a detonator like that, with that much explosive in it, | 0:37:00 | 0:37:03 | |
how much damage would it do if just that went off? | 0:37:03 | 0:37:06 | |
If I was holding this in my hand and it and it were to detonate, | 0:37:06 | 0:37:10 | |
then I would lose the hand. | 0:37:10 | 0:37:13 | |
Really? OK. | 0:37:13 | 0:37:15 | |
-I'll be very wary of detonators, then. -Absolutely! | 0:37:15 | 0:37:18 | |
'Of course, to demonstrate a detonator really doing its job, | 0:37:18 | 0:37:22 | |
'we need to attach it to a block of less sensitive explosive. | 0:37:22 | 0:37:26 | |
'Dynamite was the world's first mouldable plastic explosive | 0:37:26 | 0:37:30 | |
'and we're using its modern equivalent.' | 0:37:30 | 0:37:33 | |
That's a small sample, maybe about 30g of a new plastic explosive | 0:37:33 | 0:37:39 | |
that we've developed here at Ardeer. | 0:37:39 | 0:37:42 | |
I think I should double-check - I'm fine for handling this now? | 0:37:42 | 0:37:45 | |
Oh, yes, it is perfectly safe. | 0:37:45 | 0:37:48 | |
I guess because it looks like Play-Doh, | 0:37:48 | 0:37:51 | |
you instantly want to treat it like Play-Doh. | 0:37:51 | 0:37:54 | |
Well, it is a very special kind of Play-Doh, if you like. | 0:37:54 | 0:37:57 | |
It's got that plasticity that Play-Doh has, but as with all explosives, | 0:37:57 | 0:38:02 | |
they are very unforgiving when you give it the right stimulus. | 0:38:02 | 0:38:05 | |
-And that is a detonator. -And that is a detonator. | 0:38:05 | 0:38:08 | |
I'm going to ask Jim to come in and set up. | 0:38:08 | 0:38:09 | |
Jim is one of our trained shot-firers, | 0:38:09 | 0:38:12 | |
and only a shot-firer can set up. | 0:38:12 | 0:38:16 | |
You've been handling that material with gloves. | 0:38:16 | 0:38:20 | |
Jim is not wearing gloves because there is a risk of static with the electrically-initiated detonator. | 0:38:20 | 0:38:26 | |
You'll notice again he's kept the detonator, the action end of the wires, in the box until the last | 0:38:26 | 0:38:31 | |
minute, so if there is any accidental stray current | 0:38:31 | 0:38:35 | |
he's minimised the chance of it causing any damage and then he just simply pops it into the holder, | 0:38:35 | 0:38:41 | |
to make sure that there's contact with the explosive | 0:38:41 | 0:38:44 | |
and it's now ready to go | 0:38:44 | 0:38:46 | |
once we've cleared the site and Jim has armed the circuit. | 0:38:46 | 0:38:51 | |
I feel my stomach change when he puts that in there. | 0:38:51 | 0:38:54 | |
I honestly do. It's just... | 0:38:54 | 0:38:57 | |
Like we're now... Shall we go? | 0:38:57 | 0:39:00 | |
-Yes. -Right. | 0:39:00 | 0:39:01 | |
Stand by. | 0:39:08 | 0:39:09 | |
Effectively, that entire lump almost instantaneously goes from being | 0:39:17 | 0:39:22 | |
-a solid to a gas. -Absolutely right. | 0:39:22 | 0:39:25 | |
-It's shockingly crisp. -Yeah. That's what it's supposed to do, | 0:39:25 | 0:39:29 | |
but if you look on the other side, | 0:39:29 | 0:39:32 | |
you'll see something completely different. | 0:39:32 | 0:39:34 | |
And that's the pressure wave that's ripped that out. | 0:39:34 | 0:39:37 | |
Yeah, the shock wave travels through the plate, hits the underside and | 0:39:37 | 0:39:43 | |
then just blasts off the scab and if we dig around we might just find | 0:39:43 | 0:39:48 | |
the back end of that, because we've got a nice little hole here. | 0:39:48 | 0:39:52 | |
So somewhere down there is the piece. | 0:39:52 | 0:39:55 | |
Well, the secret is it's come all the way through | 0:39:55 | 0:39:59 | |
and there... Get the sand off it. | 0:39:59 | 0:40:01 | |
-I'm shocked. -There's the scab. | 0:40:01 | 0:40:03 | |
It's come off the other side. | 0:40:03 | 0:40:05 | |
It's more impressive than going through there, because nothing | 0:40:05 | 0:40:08 | |
goes through railway sleepers, as a general rule. | 0:40:08 | 0:40:11 | |
Nobel's struggle to tame the power of high explosives and make them | 0:40:11 | 0:40:16 | |
safe tools for the hungry industrial world made him a very rich man. | 0:40:16 | 0:40:21 | |
By safely harnessing the shattering power of nitroglycerine's detonation | 0:40:21 | 0:40:26 | |
with dynamite and a range of other compounds, a new era | 0:40:26 | 0:40:29 | |
of civil engineering opened up and great construction projects | 0:40:29 | 0:40:33 | |
such as the Suez Canal, the London Underground system | 0:40:33 | 0:40:37 | |
and then the Panama Canal could now be undertaken. | 0:40:37 | 0:40:41 | |
And that might have been Nobel's legacy, | 0:40:44 | 0:40:47 | |
if it weren't for a mistake that occurred in 1888. | 0:40:47 | 0:40:50 | |
After the death of Alfred Nobel's elder brother Ludvig, | 0:40:50 | 0:40:53 | |
some newspapers mistakenly printed Alfred Nobel's obituary instead. | 0:40:53 | 0:40:58 | |
Where he was living in France at the time, | 0:40:58 | 0:41:01 | |
Le Figaro printed this small but damning paragraph. | 0:41:01 | 0:41:05 | |
It translates as, "A man who it would be difficult | 0:41:05 | 0:41:09 | |
"to describe as a benefactor to humanity died yesterday in Cannes." | 0:41:09 | 0:41:14 | |
Now, reading that must have been a bit of a shock, and it's said that | 0:41:14 | 0:41:17 | |
it made Nobel intent on changing his legacy to the world. | 0:41:17 | 0:41:20 | |
To that end, he left his vast fortune to setting up a foundation | 0:41:20 | 0:41:25 | |
which would award prizes for literature, science and peace. | 0:41:25 | 0:41:31 | |
Nobel's advances in explosive design were the result of long hours and hard work, | 0:41:33 | 0:41:39 | |
but some revolutions in the history of explosives are sparked simply by a chance observation. | 0:41:39 | 0:41:45 | |
In the same year that Nobel's obituary was accidentally published, | 0:41:47 | 0:41:51 | |
an American chemist, Charles Monroe, | 0:41:51 | 0:41:53 | |
was doing explosives work for the US Navy. | 0:41:53 | 0:41:55 | |
He was one of the foremost explosives experts | 0:41:55 | 0:41:58 | |
of the late 19th century. | 0:41:58 | 0:42:00 | |
Then many high explosives came in blocks with the manufacturer's name embossed onto them. | 0:42:00 | 0:42:06 | |
So I've got myself some high explosive | 0:42:08 | 0:42:11 | |
onto which I'm going to stamp a corporate name. | 0:42:11 | 0:42:15 | |
Now, as Monroe spotted, there was something very strange that happened | 0:42:17 | 0:42:21 | |
when these stamped blocks were detonated near steel plate. | 0:42:21 | 0:42:25 | |
Hopefully we'll get to see the same thing. | 0:42:25 | 0:42:28 | |
Prime... | 0:42:39 | 0:42:40 | |
That seemed big enough. | 0:42:51 | 0:42:53 | |
Here we go. | 0:42:58 | 0:42:59 | |
Yes. OK. | 0:43:01 | 0:43:03 | |
You can now see the BBC logo stamped into a block of steel | 0:43:04 | 0:43:09 | |
in the same way that the manufacturers' logos got stamped | 0:43:09 | 0:43:12 | |
into the steel back in the 1880s, but what Monroe was particularly | 0:43:12 | 0:43:16 | |
intrigued by was why it made this particular indentation | 0:43:16 | 0:43:21 | |
from the indentation on the explosives | 0:43:21 | 0:43:23 | |
and understanding the way in which this happens | 0:43:23 | 0:43:26 | |
led to a completely new way of using explosives. | 0:43:26 | 0:43:30 | |
When a lump of explosive detonates, | 0:43:30 | 0:43:32 | |
the shock wave radiates out from every part of its surface. | 0:43:32 | 0:43:35 | |
So you've got your dent in the explosive here | 0:43:37 | 0:43:40 | |
and you've got your target there, | 0:43:40 | 0:43:43 | |
as the shock wave comes out, | 0:43:43 | 0:43:45 | |
instead of the bit at the back ending up with a weaker effect, | 0:43:45 | 0:43:49 | |
it ends up actually stronger, | 0:43:49 | 0:43:51 | |
because the shock wave is coming out in all directions, like this. | 0:43:51 | 0:43:55 | |
When it reaches the centre of the indentation, they tend to meet, | 0:43:55 | 0:43:59 | |
like jets of water in the middle of that dent | 0:43:59 | 0:44:01 | |
and this effect here magnifies the shock wave that you've got leaving | 0:44:01 | 0:44:05 | |
there, sending it into the plate and this is actually the area | 0:44:05 | 0:44:08 | |
of maximum pressure here. | 0:44:08 | 0:44:10 | |
And once this was understood, shock waves could be directed to | 0:44:10 | 0:44:14 | |
focus the power of the explosion exactly where it was wanted. | 0:44:14 | 0:44:17 | |
People started making cavities in their explosive to increase | 0:44:17 | 0:44:21 | |
the power of the shock wave, | 0:44:21 | 0:44:22 | |
but then, with the pressures of war, came a new step forward. | 0:44:22 | 0:44:26 | |
When you line that cavity | 0:44:26 | 0:44:29 | |
with a hard material, almost invariably metal, | 0:44:29 | 0:44:34 | |
then you enter the domain of what's known as the shaped charge. | 0:44:34 | 0:44:38 | |
Right. | 0:44:38 | 0:44:40 | |
Conventional shaped charges | 0:44:40 | 0:44:41 | |
are filled with high explosive in a factory. | 0:44:41 | 0:44:44 | |
Right. | 0:44:44 | 0:44:45 | |
This is something that I designed for filling by the user. | 0:44:45 | 0:44:50 | |
It means that it can travel on aeroplanes and so on without... | 0:44:50 | 0:44:54 | |
-DIY shaped charges. -Exactly that. | 0:44:54 | 0:44:56 | |
Now, in this case | 0:44:56 | 0:44:57 | |
we're going to go back to probably the first type of liner - | 0:44:57 | 0:45:03 | |
this is called the liner - that was used in a shaped charge. | 0:45:03 | 0:45:06 | |
-That's just a cone of copper, isn't it? -It is indeed. | 0:45:06 | 0:45:09 | |
Having that copper on there, I guess it's the sort of | 0:45:09 | 0:45:13 | |
the equivalent of using a bullet or a cannonball. | 0:45:13 | 0:45:17 | |
It's the same, if you go - kcrrr! - and fire an empty cartridge, | 0:45:17 | 0:45:22 | |
then you get a loud bang and an explosion, | 0:45:22 | 0:45:24 | |
but nothing that's going to do any significant harm. | 0:45:24 | 0:45:27 | |
Whereas if you put a bullet in the end of it, if you see what I mean, | 0:45:27 | 0:45:31 | |
and fire it, then it pushes out something of a significant mass, | 0:45:31 | 0:45:35 | |
and that can do some damage. | 0:45:35 | 0:45:36 | |
Yes. The great advantage is that this metal travels enormously faster | 0:45:36 | 0:45:41 | |
than any cannonball. | 0:45:41 | 0:45:42 | |
I'll show you what I mean. | 0:45:42 | 0:45:44 | |
If you put plastic explosive in here and then you push this copper cone | 0:45:44 | 0:45:48 | |
into the explosive, when I initiate at this end, | 0:45:48 | 0:45:53 | |
a detonation wave travels from here to there. | 0:45:53 | 0:45:57 | |
-Right. -The first thing it hits is the apex of the cone | 0:45:57 | 0:46:00 | |
and that apex of the cone is driven forward. | 0:46:00 | 0:46:02 | |
The whole cone is collapsed. | 0:46:02 | 0:46:05 | |
In fact, it collapses in such a way that it turns inside out. | 0:46:05 | 0:46:10 | |
Right, because the end bits hit first and that starts moving. | 0:46:10 | 0:46:13 | |
Wow, that's an astonishing thing to get your head round. | 0:46:13 | 0:46:16 | |
It is a bit of a shock at first. | 0:46:16 | 0:46:18 | |
What happens is that the inner part of the copper, not the whole | 0:46:18 | 0:46:22 | |
mass of it, by any means, the inner part of the copper | 0:46:22 | 0:46:25 | |
forms into a sort of wire, which is called the jet. | 0:46:25 | 0:46:29 | |
And that's not molten, it's still solid copper. | 0:46:29 | 0:46:32 | |
Yes, but coming not in that direction, coming in that direction. | 0:46:32 | 0:46:36 | |
And that almost piles in like a nail through the steel, | 0:46:36 | 0:46:40 | |
driving its way in. | 0:46:40 | 0:46:42 | |
Yes. It pushes the target material out of the way | 0:46:42 | 0:46:45 | |
and it pushes it aside as the tip of the jet | 0:46:45 | 0:46:49 | |
hits the steel and flows back along the outside of the rod. | 0:46:49 | 0:46:53 | |
Then there's a new increment of metal. | 0:46:53 | 0:46:55 | |
This is constantly being replaced and when it's all used up it stops, | 0:46:55 | 0:46:59 | |
won't go any deeper. | 0:46:59 | 0:47:00 | |
Are we in a position that we can try this and I can see? | 0:47:00 | 0:47:03 | |
Absolutely. This box, I'm pleased to tell you, is full of explosive. | 0:47:03 | 0:47:06 | |
-Good. -What I'll do is take some out. | 0:47:06 | 0:47:09 | |
This is standard British plastic explosive. | 0:47:09 | 0:47:14 | |
It's similar to the American C4, | 0:47:14 | 0:47:18 | |
but it is actually much easier to use for filling charges. | 0:47:18 | 0:47:22 | |
You can just ram it in and then put the cone in. | 0:47:22 | 0:47:27 | |
We're going to test it with what looks like | 0:47:28 | 0:47:30 | |
an impossibly solid block of steel. | 0:47:30 | 0:47:33 | |
There is a critical distance at which the jet | 0:47:35 | 0:47:38 | |
will be at its most penetrating before it breaks up, | 0:47:38 | 0:47:41 | |
so the charge has legs to hold it the right height from our target. | 0:47:41 | 0:47:45 | |
Right, see you in about two minutes. | 0:47:47 | 0:47:48 | |
-Yes, and don't panic. -I won't. | 0:47:48 | 0:47:51 | |
Firing. | 0:48:02 | 0:48:04 | |
Four, three, two, one... | 0:48:04 | 0:48:08 | |
-Wow! -Let's go and see what we've done, shall we? | 0:48:11 | 0:48:13 | |
It seems astonishing, because that was just a massive thump, | 0:48:13 | 0:48:18 | |
that something extremely accurate will have occurred from that. | 0:48:18 | 0:48:21 | |
Well, let's see. | 0:48:21 | 0:48:22 | |
Ooh... | 0:48:24 | 0:48:25 | |
Well, it's gone in at least that deep | 0:48:27 | 0:48:29 | |
because I can push that in, but then | 0:48:29 | 0:48:31 | |
the proof of the pudding will be turning it over | 0:48:31 | 0:48:34 | |
and see if we have achieved anything the other end. Yep! | 0:48:34 | 0:48:38 | |
Oh, yes! | 0:48:38 | 0:48:40 | |
That's gone through over a foot of steel. | 0:48:40 | 0:48:42 | |
The thing that I find even more surprising is you know full well | 0:48:42 | 0:48:47 | |
if you've got a copper nail like that, | 0:48:47 | 0:48:49 | |
no matter how hard you hit it... | 0:48:49 | 0:48:52 | |
You will hardly dent the steel. | 0:48:52 | 0:48:53 | |
Exactly! Yet you get a good amount of plastic explosive with | 0:48:53 | 0:48:58 | |
a nice shape behind it and you can drive it the whole way through. | 0:48:58 | 0:49:02 | |
These cone-shaped charges allowed people to get much more | 0:49:05 | 0:49:08 | |
focused power from their explosives | 0:49:08 | 0:49:10 | |
and during the coming World Wars, | 0:49:10 | 0:49:12 | |
revolutionised the power of handheld weapons such as the bazooka. | 0:49:12 | 0:49:17 | |
Nowadays they're used in all sorts of military and civil applications | 0:49:18 | 0:49:22 | |
such as opening up oil wells, and Sidney designs them | 0:49:22 | 0:49:26 | |
especially for bomb disposal, | 0:49:26 | 0:49:28 | |
but other shapes have been developed as well, for different tasks. | 0:49:28 | 0:49:32 | |
This long L-shaped liner can turn the shock wave into a blade, | 0:49:32 | 0:49:36 | |
as the sides are slammed together. | 0:49:36 | 0:49:39 | |
Instead of the cone's penetrating jet, this cutting blade is axe-like, | 0:49:39 | 0:49:43 | |
designed for demolition jobs. | 0:49:43 | 0:49:47 | |
Four, three, two, one... | 0:49:47 | 0:49:52 | |
It seemed as if the power of explosives had reached a maximum. | 0:50:02 | 0:50:06 | |
The chemical compositions were carefully designed | 0:50:06 | 0:50:09 | |
and the power of the shock wave could now be channelled, | 0:50:09 | 0:50:12 | |
but there was still explosive potential beyond imagination | 0:50:12 | 0:50:17 | |
to be realised. | 0:50:17 | 0:50:18 | |
By the end of the 19th century, chemists were discovering | 0:50:18 | 0:50:22 | |
new elements all the time, and some of them appeared to give off energy. | 0:50:22 | 0:50:26 | |
They called this rather bizarre property radioactivity. | 0:50:26 | 0:50:31 | |
It was a New Zealand physicist, Ernest Rutherford, who was one of | 0:50:31 | 0:50:34 | |
the first to understand the potential of radioactivity. | 0:50:34 | 0:50:38 | |
Already understanding that it was caused by the atoms of the elements breaking down, | 0:50:38 | 0:50:42 | |
he wrote this in 1904 - | 0:50:42 | 0:50:44 | |
"If it should ever be found possible to control at will | 0:50:44 | 0:50:48 | |
"the rate of disintegration of the radio elements, | 0:50:48 | 0:50:51 | |
"an enormous amount of energy could be obtained | 0:50:51 | 0:50:54 | |
"from a small amount of matter." | 0:50:54 | 0:50:56 | |
It was a prophetic statement, | 0:50:56 | 0:50:58 | |
although he later said, "Anyone who expects a useful | 0:50:58 | 0:51:02 | |
"power source from the transformation of these atoms | 0:51:02 | 0:51:05 | |
"is talking moonshine." | 0:51:05 | 0:51:07 | |
Even a genius doesn't get it right every time. | 0:51:07 | 0:51:10 | |
The investigation of radioactivity and the nucleus of atoms continued | 0:51:10 | 0:51:14 | |
as researchers sought to understand the minute structure of the world | 0:51:14 | 0:51:19 | |
around us, but some people were already seeing the potential | 0:51:19 | 0:51:23 | |
for extracting the power released when nuclei are broken apart | 0:51:23 | 0:51:27 | |
and in the winter of 1938, with war already brewing | 0:51:27 | 0:51:32 | |
the exact dimensions of that potential was made clear | 0:51:32 | 0:51:35 | |
in a laboratory in Copenhagen. | 0:51:35 | 0:51:38 | |
An experimental physicist, Otto Frisch, | 0:51:38 | 0:51:41 | |
who'd escaped Hitler's regime in Germany, constructed | 0:51:41 | 0:51:44 | |
a piece of apparatus to measure the energy released when an atom splits. | 0:51:44 | 0:51:49 | |
Now, it's not my field of science, | 0:51:49 | 0:51:52 | |
but he knocked his up in a weekend and did the measurements, | 0:51:52 | 0:51:55 | |
so I feel there's a fighting chance for an amateur like me. | 0:51:55 | 0:51:58 | |
All the apparatus really consists of | 0:51:58 | 0:52:01 | |
is a metal box with a metal plate in it. | 0:52:01 | 0:52:04 | |
Now, when an atom splits, | 0:52:04 | 0:52:06 | |
you end up with two high-energy fission products. | 0:52:06 | 0:52:10 | |
Now, as they fly through the gas around them, they can | 0:52:10 | 0:52:13 | |
smash electrons off other atoms, causing ionisation, | 0:52:13 | 0:52:16 | |
producing positive and negative particles. | 0:52:16 | 0:52:19 | |
The atoms that Frisch split were of the element uranium | 0:52:19 | 0:52:23 | |
and he did it by bombarding them with particles called neutrons. | 0:52:23 | 0:52:27 | |
A couple of hundred volts between here and here | 0:52:27 | 0:52:30 | |
should enable us to detect if there's been any ionisation in here | 0:52:30 | 0:52:35 | |
and from that we'll be able to deduce | 0:52:35 | 0:52:37 | |
the energy released when an atom splits. | 0:52:37 | 0:52:40 | |
Obviously, now all I need is a source of uranium | 0:52:40 | 0:52:43 | |
and some neutrons to bombard it with. | 0:52:43 | 0:52:45 | |
The National Physical Laboratory near London have | 0:52:50 | 0:52:53 | |
the sort of thing I need, so I've brought my part of the kit. | 0:52:53 | 0:52:57 | |
That is you ion chamber, is it? | 0:52:57 | 0:52:59 | |
Well, yes. This is my ion chamber. | 0:52:59 | 0:53:00 | |
It's not at the top end of the sophistication that you've got here, | 0:53:00 | 0:53:05 | |
-but can we try it? -By all means. | 0:53:05 | 0:53:08 | |
I've got a piece of uranium here | 0:53:08 | 0:53:10 | |
-which I borrowed from our radioactivity group. -That's not a phrase you hear a lot. -No. | 0:53:10 | 0:53:15 | |
Uranium does have a reputation. | 0:53:15 | 0:53:17 | |
How safe is it? How long can I be near it? | 0:53:17 | 0:53:20 | |
Provided you stay a few centimetres away from it, you're out of the range of the alpha particles. | 0:53:20 | 0:53:25 | |
Right, so I'll put the lid on here. | 0:53:25 | 0:53:28 | |
-The thing that we're missing now is the thing to split the atoms. -You need a neutron source. -Yes. | 0:53:30 | 0:53:35 | |
We are the Neutron Standards Authority for the UK and we produce neutrons and use them | 0:53:35 | 0:53:39 | |
to calibrate personal dose-meters, like the ones we gave you to wear. | 0:53:39 | 0:53:43 | |
Yeah, I've got mine. | 0:53:43 | 0:53:45 | |
I can get a neutron source, but you will have to leave while I put it up here. | 0:53:45 | 0:53:49 | |
I'm happy to get out of the way while that's happening. | 0:53:49 | 0:53:52 | |
The neutron source contains an element whose radioactivity | 0:53:52 | 0:53:56 | |
is much more penetrating than uranium's, | 0:53:56 | 0:53:59 | |
so it has to be treated with care. | 0:53:59 | 0:54:02 | |
OK, so we've now got our uranium being blasted with neutrons. | 0:54:02 | 0:54:06 | |
-Yeah. -How do we tell if we're splitting any atoms? | 0:54:06 | 0:54:09 | |
We'd have to see some pulses from our ion chamber. | 0:54:09 | 0:54:12 | |
-OK. -So if I turn up the volts we might begin to see something | 0:54:12 | 0:54:15 | |
and the first thing that we might see, if it works, | 0:54:15 | 0:54:18 | |
is the natural radiation from the uranium. | 0:54:18 | 0:54:21 | |
I'm rather astounded, but they look like genuine pulses. | 0:54:21 | 0:54:26 | |
So this'd be what you'd hear on a Geiger counter, going kcrr-kcrr? | 0:54:26 | 0:54:29 | |
-Yes, but you're not seeing any fission yet. -Are we not? | 0:54:29 | 0:54:32 | |
If it was fission, you would see some very much bigger pulses. | 0:54:32 | 0:54:35 | |
So if I turn the discriminator up... | 0:54:35 | 0:54:37 | |
That is a massive pulse. | 0:54:38 | 0:54:41 | |
-So is that a split atom?! -Yes. | 0:54:41 | 0:54:43 | |
Wow! | 0:54:43 | 0:54:45 | |
-Considerably bigger than the pulses from the natural decay of the uranium. -Yeah! | 0:54:45 | 0:54:50 | |
This is a completely different thing. | 0:54:50 | 0:54:52 | |
Yes, yes. Very much more energetic. | 0:54:52 | 0:54:54 | |
Now, from this can we get a measure of how much energy | 0:54:54 | 0:54:58 | |
is being produced every time an atom splits? | 0:54:58 | 0:55:00 | |
Well, the classical figure is 200 MeV, 200 mega-electronvolts. | 0:55:00 | 0:55:07 | |
That makes that, the energy released when one of those atoms gets split, | 0:55:07 | 0:55:11 | |
is about 50 million times more than a molecule of nitroglycerine. | 0:55:11 | 0:55:17 | |
That's... | 0:55:17 | 0:55:19 | |
You can see they were onto something. | 0:55:19 | 0:55:21 | |
They were, indeed. | 0:55:21 | 0:55:22 | |
Frisch finished his weekend's work in the early hours | 0:55:23 | 0:55:26 | |
of January 13th 1939 and was soon woken by a telegram | 0:55:26 | 0:55:31 | |
with news that his Jewish father had been released | 0:55:31 | 0:55:33 | |
from a concentration camp. | 0:55:33 | 0:55:35 | |
He said he remembered it as his lucky day, | 0:55:35 | 0:55:38 | |
but would have liked a few more hours sleep. | 0:55:38 | 0:55:41 | |
As war rumbled across Europe and then the world, physicists | 0:55:41 | 0:55:45 | |
in many countries grasped the potential of Frisch's experiment. | 0:55:45 | 0:55:49 | |
In the early morning of the 16th July 1945, a team of | 0:55:49 | 0:55:55 | |
international researchers became the first to see that potential realised | 0:55:55 | 0:56:00 | |
in the deserts of New Mexico. | 0:56:00 | 0:56:02 | |
Inside a giant sphere of shaped charges, like the ones Sidney showed | 0:56:02 | 0:56:07 | |
me, they placed radioactive material no bigger than an orange. | 0:56:07 | 0:56:12 | |
The whole contraption was hoisted up a tower and then the charges detonated. | 0:56:12 | 0:56:17 | |
The initial flash of light and heat | 0:56:21 | 0:56:24 | |
travelled out at 200,000km a second, | 0:56:24 | 0:56:28 | |
with temperatures reaching over 100 million degrees, | 0:56:28 | 0:56:32 | |
20,000 times hotter than the surface of the sun. | 0:56:32 | 0:56:35 | |
It melted the sand in the desert. | 0:56:35 | 0:56:38 | |
Just like other explosions, this heat causes a massive expansion | 0:56:38 | 0:56:43 | |
in the surrounding air. | 0:56:43 | 0:56:44 | |
There's no production of gas, like in a chemical reaction. | 0:56:44 | 0:56:47 | |
It's simply the staggering quantity of heat released | 0:56:47 | 0:56:51 | |
by a runaway nuclear reaction that causes mankind's biggest explosion. | 0:56:51 | 0:56:56 | |
That expanding air slams into the air around it, | 0:56:56 | 0:57:00 | |
causing an abrupt shock wave which crushes the air | 0:57:00 | 0:57:04 | |
and just like in the fire piston, heats it, | 0:57:04 | 0:57:07 | |
but to such a temperature that the air itself begins to glow. | 0:57:07 | 0:57:11 | |
You can see the white hot bubble-like shock wave | 0:57:11 | 0:57:15 | |
in these astonishing pictures. | 0:57:15 | 0:57:17 | |
Then it cools to a dark, transparent layer | 0:57:17 | 0:57:20 | |
and the fireball inside shows through. | 0:57:20 | 0:57:23 | |
The Trinity explosion, as it's known, | 0:57:24 | 0:57:26 | |
had the equivalent power of 20,000 tons of TNT, | 0:57:26 | 0:57:30 | |
all from just a few kilos of radioactive material. | 0:57:30 | 0:57:35 | |
And all that power, and that enormous shock wave, | 0:57:35 | 0:57:39 | |
is produced just simply by heating the air. | 0:57:39 | 0:57:43 | |
In some ways, it's similar to the heat causing the bamboo to burst | 0:57:43 | 0:57:47 | |
back in ancient China, but with a nuclear explosion, | 0:57:47 | 0:57:50 | |
the heat is almost unimaginably intense and sudden. | 0:57:50 | 0:57:55 | |
In little more than 2,000 years, the journey of understanding | 0:57:55 | 0:57:58 | |
that mankind has so far travelled is immense. | 0:57:58 | 0:58:03 | |
We've gone from crackling bamboo to creating something like a star here on Earth | 0:58:03 | 0:58:08 | |
and man-made explosions terrify us as much now as they always have. | 0:58:08 | 0:58:13 | |
The advent of the nuclear age was as shocking to us | 0:58:14 | 0:58:17 | |
as gunpowder was to medieval Europe. | 0:58:17 | 0:58:20 | |
Throughout history, explosives have been used first | 0:58:20 | 0:58:24 | |
as weapons and then had their power harnessed to more constructive ends. | 0:58:24 | 0:58:28 | |
They have shaped our world, through warfare and engineering. | 0:58:28 | 0:58:33 | |
Even nuclear power has been turned to peaceful uses. | 0:58:33 | 0:58:37 | |
New explosives may always be discovered | 0:58:37 | 0:58:40 | |
and wreak terrifying havoc. | 0:58:40 | 0:58:42 | |
But if history has taught us anything, | 0:58:42 | 0:58:44 | |
it's that by properly understanding these things | 0:58:44 | 0:58:48 | |
we can create instruments of unrivalled power. | 0:58:48 | 0:58:51 | |
If you want to find out more about the science of explosions, | 0:58:53 | 0:58:56 | |
go to the website - | 0:58:56 | 0:58:57 | |
And follow the links to the Open University. | 0:58:59 | 0:59:02 | |
Subtitles by Red Bee Media Ltd | 0:59:11 | 0:59:16 | |
E-mail [email protected] | 0:59:16 | 0:59:20 |