0:00:03 > 0:00:06We see explosions all the time,
0:00:06 > 0:00:10and during my career as an engineer, I've certainly made a few.
0:00:10 > 0:00:14But actually understanding them and controlling all that power,
0:00:14 > 0:00:19that's a whole different story and sometimes quite a surprising one.
0:00:19 > 0:00:24It's a story that starts with the accidents of the medieval alchemists...
0:00:24 > 0:00:25Don't try this at home.
0:00:25 > 0:00:27Whoa!
0:00:28 > 0:00:33..but eventually leads us to a fundamental understanding of the forces of nature...
0:00:35 > 0:00:38..forces that we've mastered for good or evil.
0:00:38 > 0:00:42Explosives revolutionised battlefields,
0:00:42 > 0:00:46industry and engineering.
0:00:49 > 0:00:54To uncover the story, I'll be reading the words of medieval scholars...
0:00:56 > 0:00:59..going deep underground through ancient Cornish mines...
0:00:59 > 0:01:02That looks like a lot of gunpowder to me.
0:01:04 > 0:01:08..and making some of the most dangerous substances ever known.
0:01:08 > 0:01:11It mustn't go above 18 degrees centigrade.
0:01:13 > 0:01:16It's a journey that will take us right to the centre of matter.
0:01:16 > 0:01:19- Is that a split atom?- Oh, yes.
0:01:19 > 0:01:20Wow!
0:01:20 > 0:01:22And the power it can unleash.
0:01:25 > 0:01:31This is the story of how we learnt to harness the forces that shook the world.
0:02:01 > 0:02:05The very first record we have of people using explosions comes from
0:02:05 > 0:02:10a Chinese document which could date from as far back as two centuries BC.
0:02:10 > 0:02:14It describes how travellers in the mountain wilderness of the West
0:02:14 > 0:02:18were threatened by shape-shifting creatures of the night.
0:02:18 > 0:02:21To scare away these creatures,
0:02:21 > 0:02:24they would lay lengths of bamboo on their campfires.
0:02:29 > 0:02:33- BANG! - The very first Chinese firecrackers.
0:02:33 > 0:02:36CRACKING AND HISSING
0:02:36 > 0:02:41The hissing noise we hear is moisture in the bamboo turning to steam,
0:02:41 > 0:02:45but bamboo has a special structure to it.
0:02:45 > 0:02:48It grows in sealed compartments.
0:02:48 > 0:02:51Now, when the moisture in these sealed compartments
0:02:51 > 0:02:55starts turning to steam, pressure builds up inside here.
0:02:55 > 0:02:57It can't go anywhere.
0:02:57 > 0:02:59- Water, when it turns to steam, - BANG!
0:02:59 > 0:03:03wants to expand hundreds of times, but there isn't room for it do that,
0:03:03 > 0:03:04so pressure builds up.
0:03:04 > 0:03:07Eventually the structure of the bamboo breaks down. Kcrrr!
0:03:07 > 0:03:09It explodes,
0:03:09 > 0:03:13scaring away shape-shifting creatures of the night.
0:03:15 > 0:03:18Using simple natural explosions like this
0:03:18 > 0:03:23was the first step of mankind's journey to harness explosive power,
0:03:23 > 0:03:28starting to understand the process in order to control it.
0:03:32 > 0:03:35It's easy enough to create an explosion.
0:03:35 > 0:03:40Any explosion is simply the moment when gas tries to expand suddenly.
0:03:41 > 0:03:42- LOUD BANG - Oh!
0:03:44 > 0:03:49And when that suddenly expanding air crashed into the air around it,
0:03:49 > 0:03:54it created a pressure wave that then moves through the surroundings.
0:03:54 > 0:03:59A sudden change in pressure forced a cloud of water droplets out of the air.
0:03:59 > 0:04:01These allow us to see the wave.
0:04:01 > 0:04:04The faster the gas is trying to expand,
0:04:04 > 0:04:07the more powerful the explosion,
0:04:07 > 0:04:10when that pressure wave hits your ear, you hear it as a bang.
0:04:12 > 0:04:16An explosion relies on a lot of gas trying to expand.
0:04:16 > 0:04:20Heat can make this happen, because heat, of course, makes things expand.
0:04:20 > 0:04:24Introducing more gas can do the same thing,
0:04:24 > 0:04:29but mankind discovered a way to create both heat and gas
0:04:29 > 0:04:33by reacting chemicals together and this was the start
0:04:33 > 0:04:37of our journey to really master explosive power.
0:04:41 > 0:04:46In Europe, chemical explosions were unknown until the medieval period,
0:04:46 > 0:04:49and the first time people came across them,
0:04:49 > 0:04:51they were a bit shocked.
0:04:51 > 0:04:54I've come to the Bodleian Library in Oxford
0:04:54 > 0:04:58to see a manuscript that describes one of these early encounters.
0:04:58 > 0:05:02It's one of the few copies of a book written in 1267
0:05:02 > 0:05:04by the medieval scholar Roger Bacon,
0:05:04 > 0:05:10who split his time between Oxford and Paris universities.
0:05:10 > 0:05:15Now, this particular passage that starts "et experimentum"
0:05:15 > 0:05:19describes his knowledge of man-made explosives at the time.
0:05:21 > 0:05:24"There is a children's toy, something no bigger than one's thumb,
0:05:24 > 0:05:27"made in many parts of the world, that is an example
0:05:27 > 0:05:31"of how something can assault the senses with sound and fire.
0:05:31 > 0:05:35"It is no more than a bit of parchment which contains a powder
0:05:35 > 0:05:38"combining the violence of that salt called saltpetre
0:05:38 > 0:05:41"together with sulphur and willow charcoal
0:05:41 > 0:05:45"but the bursting of this small thing assaults the ear
0:05:45 > 0:05:48"with a noise that exceeds the roar of thunder
0:05:48 > 0:05:51"and a flash brighter than the most brilliant lightning."
0:05:53 > 0:05:57Now, I suspect he might he may have been exaggerating slightly,
0:05:57 > 0:06:00but this was the first time that anyone in Europe
0:06:00 > 0:06:02had come across man-made explosives.
0:06:02 > 0:06:04Roger Bacon was a Franciscan friar,
0:06:04 > 0:06:08and the church at that time had envoys all over the world.
0:06:08 > 0:06:10It seems likely that one of those envoys
0:06:10 > 0:06:13must have posted a package back to him
0:06:13 > 0:06:15containing these children's toys.
0:06:15 > 0:06:19The big question is, though, where exactly did that package come from?
0:06:22 > 0:06:23In the Middle Ages,
0:06:23 > 0:06:27the most technologically-advanced region of the world was China.
0:06:27 > 0:06:31A printed book dating from before the battle of Hastings
0:06:31 > 0:06:35indicates that the Chinese were already deploying explosives
0:06:35 > 0:06:38of a similar sort on the battlefield.
0:06:38 > 0:06:41What we have here is a Chinese military manual
0:06:41 > 0:06:44first printed in 1044
0:06:44 > 0:06:48and in it, we find a recipe for a thing called
0:06:48 > 0:06:51the "fire mixture" or the "fire chemical"
0:06:51 > 0:06:55which contains the principal three ingredients
0:06:55 > 0:06:58in Roger Bacon's recipe of 200 years later.
0:06:58 > 0:07:02We start off with, here we have these two things here,
0:07:02 > 0:07:05they're both forms of what we now call sulphur...
0:07:05 > 0:07:09- Right.- ..followed by various forms of organic matter
0:07:09 > 0:07:13like pounded dried roots and twigs that produce the carbon,
0:07:13 > 0:07:17followed by saltpetre, the next one.
0:07:17 > 0:07:21The saltpetre is something you get from the decay of organic matter
0:07:21 > 0:07:23in relatively warm conditions.
0:07:23 > 0:07:26The Arabs refer to it is a Chinese snow.
0:07:26 > 0:07:30Right, so China was just a good place at the time,
0:07:30 > 0:07:34like, had the right climate for saltpetre to occur like that?
0:07:34 > 0:07:36There's a lot of things that come together,
0:07:36 > 0:07:39but the availability of the right climate is important.
0:07:39 > 0:07:43Can I try and start assembling it in the right proportions?
0:07:43 > 0:07:49Certainly. Well, roughly, you want to put in about 50% of saltpetre.
0:07:49 > 0:07:51For every one of those?
0:07:51 > 0:07:54Yeah, that's equal amounts of the powdered sulphur that we've got
0:07:54 > 0:07:56and the powdered charcoal.
0:07:56 > 0:07:58What were they trying to make at this point?
0:07:58 > 0:08:02This is a mixture for parcelling up and throwing, basically,
0:08:02 > 0:08:06into an enemy city using a catapult like this.
0:08:06 > 0:08:09This thing here is called a hui pao, which means a fire catapult.
0:08:09 > 0:08:12Now, from my knowledge of chemistry,
0:08:12 > 0:08:15- saltpetre is what they call potassium nitrate.- That's right.
0:08:15 > 0:08:20And that's got kind of oxygen bound up with nitrogen inside it.
0:08:20 > 0:08:23That's right. If we warm it up, it'll let the oxygen loose,
0:08:23 > 0:08:26and that will aid the burning of the other ingredients.
0:08:26 > 0:08:31The sulphur basically helps everything to happen at a rather lower temperature before
0:08:31 > 0:08:36and ultimately, of course, the carbon is the main source of the stuff that burns.
0:08:36 > 0:08:39And there we go, that's good, look at that!
0:08:39 > 0:08:42Take the flame away now. See it goes. That's very nice.
0:08:42 > 0:08:43That's fabulous!
0:08:45 > 0:08:48I'd call that an effective incendiary, wouldn't you?
0:08:48 > 0:08:52I can imagine once you get a bucket load of that landing in your camp...
0:08:52 > 0:08:55- It's discouraging, isn't it? Makes you wish you hadn't come.- Yes.
0:08:55 > 0:09:01The black powder that the Chinese military were using in 1044 had got
0:09:01 > 0:09:04grains of different chemicals close enough to react together
0:09:04 > 0:09:07and produce lots of heat and gases.
0:09:07 > 0:09:10In the open air, there's plenty of room for the gases to expand,
0:09:10 > 0:09:12so there was no sudden explosion,
0:09:12 > 0:09:16but the basic chemistry of gunpowder was there.
0:09:16 > 0:09:18However, an even older Chinese book
0:09:18 > 0:09:22suggests that the very first chemical explosive in the world
0:09:22 > 0:09:25had been developed 200 years before this.
0:09:25 > 0:09:27A book with the lovely title
0:09:27 > 0:09:31Classified Essentials Of The Mysterious Way Of The Origin Of All Things,
0:09:31 > 0:09:35which happens to contain a few recipes listed as,
0:09:35 > 0:09:38"Don't try this at home if you are an alchemist,"
0:09:38 > 0:09:43- and amongst that is a recipe which I think we ought to try.- I'm game.
0:09:43 > 0:09:46You have some saltpetre. You have some sulphur.
0:09:46 > 0:09:50Those two ingredients. The carbon comes in the form of honey.
0:09:50 > 0:09:52OK, and what kind of quantities do you use?
0:09:52 > 0:09:56Oh, well, I would say most of that jar would get us
0:09:56 > 0:09:58something interesting happening.
0:09:58 > 0:10:02If you got about the same quantity of the other two ingredients,
0:10:02 > 0:10:06the saltpetre and the sulphur, that should go nicely.
0:10:06 > 0:10:10Why did they ever think of mixing these things together at this point?
0:10:10 > 0:10:13The idea is to try to subdue the fiery properties
0:10:13 > 0:10:15of the sulphur and of the saltpetre
0:10:15 > 0:10:19so that they will be suitable for taking as a medicine,
0:10:19 > 0:10:22- hopefully an elixir of life. - Oh, I see!
0:10:22 > 0:10:26'So, ironically, in trying to find a means to eternal life,
0:10:26 > 0:10:29'the Chinese alchemists found a substance that could kill.'
0:10:29 > 0:10:32I've never done any alchemy before.
0:10:32 > 0:10:35This is my first venture into the world of alchemy.
0:10:35 > 0:10:38If you make a success of it, it's a new career, really, isn't it?
0:10:38 > 0:10:41- Potentially lucrative. - Yes, indeed, indeed.
0:10:41 > 0:10:43That looks pretty well stirred.
0:10:43 > 0:10:45I would think now if you start cooking that,
0:10:45 > 0:10:48that will finish the mixing.
0:10:48 > 0:10:52Despite being earlier than the incendiary powder of 1044,
0:10:52 > 0:10:57the chemistry of this mixture has the potential to be more explosive.
0:10:57 > 0:10:59So because of the water in the honey,
0:10:59 > 0:11:01that is dissolving the saltpetre.
0:11:01 > 0:11:06- Yes.- And allowing that to carefully coat all the bits of sulphur.
0:11:06 > 0:11:10The particles of carbon and sulphur will now be very, very close to molecules of saltpetre
0:11:10 > 0:11:13which, when they get hot enough,
0:11:13 > 0:11:18will start releasing the oxygen just right up close to them.
0:11:18 > 0:11:19I think that's going to go in a sec.
0:11:19 > 0:11:21There's little puffs there.
0:11:21 > 0:11:23Exciting little puffs. I say.
0:11:23 > 0:11:29Just slightly move ourselves out of the immediate line of that. That's it.
0:11:30 > 0:11:33Whoa! OK...
0:11:33 > 0:11:35Wow!
0:11:38 > 0:11:41- That was quite striking.- Wow!
0:11:41 > 0:11:45Well, as the Chinese alchemist said, don't try this at home.
0:11:48 > 0:11:52So, incendiary mixtures were being explored by the Chinese alchemists
0:11:52 > 0:11:55as early as the mid-ninth century
0:11:55 > 0:11:58but from the 12th century, as China was swept by waves
0:11:58 > 0:12:00of war with neighbouring peoples,
0:12:00 > 0:12:05they started to use their fast-burning powder in a new way.
0:12:05 > 0:12:07No longer just an incendiary,
0:12:07 > 0:12:10it became an explosive propellant for projectiles.
0:12:10 > 0:12:12The Chinese gave their new weapons names,
0:12:12 > 0:12:17like the vast-as-heaven, enemy- exterminating yin-yang shovel,
0:12:17 > 0:12:21the scary, ingenious, mobile, ever-victorious poison-fire rack
0:12:21 > 0:12:23and my personal favourite,
0:12:23 > 0:12:28the orifices-penetrating flying-sand magic-mist tube.
0:12:28 > 0:12:32In all of them, they put the powder in a tightly confined space
0:12:32 > 0:12:35and this fundamentally altered the way it behaved.
0:12:35 > 0:12:39It was the discovery that would change warfare forever.
0:12:39 > 0:12:43Confining gunpowder changes the speed of the reaction.
0:12:43 > 0:12:47It goes from something that just burns into something that really explodes.
0:12:53 > 0:12:56Gunpowder doesn't need air in order to burn.
0:12:56 > 0:12:59It gets all the oxygen required from the crystals of saltpetre,
0:12:59 > 0:13:02potassium nitrate, that are in there,
0:13:02 > 0:13:06which means it'll still burn in a confined space
0:13:06 > 0:13:10and putting it in a confined space increases the rate of reaction.
0:13:10 > 0:13:12Put a little bit in here.
0:13:12 > 0:13:14So I'm going to wrap it up.
0:13:17 > 0:13:19When it's confined like this, all those grains,
0:13:19 > 0:13:22the carbon, the sulphur and the potassium nitrate,
0:13:22 > 0:13:25are all much closer together, which means
0:13:25 > 0:13:29the reaction can happen more quickly, and as the reaction happens more quickly,
0:13:29 > 0:13:33more heat's created, making the reaction go even faster and it's a runaway process.
0:13:33 > 0:13:35Right.
0:13:35 > 0:13:39With gas being produced so quickly and heat making it expand,
0:13:39 > 0:13:42there's the potential for explosive force,
0:13:42 > 0:13:46if I can channel it like the Chinese did.
0:13:46 > 0:13:49This is my first attempt at a cannon.
0:13:49 > 0:13:52I've decided to build it out of clear acrylic
0:13:52 > 0:13:55so that we get to see what happens inside a cannon.
0:13:55 > 0:13:58Now, I'll drop that on there.
0:13:58 > 0:14:00That fits in nicely.
0:14:02 > 0:14:04Got my cannonball.
0:14:07 > 0:14:11So there it is. There's going to be an explosion in there.
0:14:11 > 0:14:15That explosion will produce hot, expanding gas.
0:14:15 > 0:14:18There'll be a big pressure rise in that part of the chamber.
0:14:18 > 0:14:22That pressure will exert a force all around the container,
0:14:22 > 0:14:25but these three sides should stay where they are.
0:14:25 > 0:14:29This fourth side here, where the tennis ball is,
0:14:29 > 0:14:32won't stay where it is, and that tennis ball will leave at
0:14:32 > 0:14:36an undetermined speed that I suspect will be pretty quick.
0:14:36 > 0:14:37Let's find out.
0:14:44 > 0:14:48Three, two, one!
0:14:54 > 0:14:58Yeah, that worked like a cannon should work.
0:14:58 > 0:14:59Wow!
0:15:00 > 0:15:04You can see how the gunpowder produces hot gases
0:15:04 > 0:15:05at just the right rate
0:15:05 > 0:15:08to push the ball out.
0:15:08 > 0:15:11This technology quickly spread west, through the Middle East,
0:15:11 > 0:15:16and by the 14th century, the Europeans had rockets and guns too.
0:15:18 > 0:15:23But something else was happening - gunpowder was spreading beyond the battlefield.
0:15:23 > 0:15:28Its power was being put to work in mines and engineering projects,
0:15:28 > 0:15:30as Europe became more industrialised
0:15:30 > 0:15:34and there was demand for more powerful and destructive explosions.
0:15:35 > 0:15:38Gunpowder had reigned for 500 years,
0:15:38 > 0:15:42but now its dominance was about to be challenged.
0:15:43 > 0:15:47The middle of the 19th century provided a turning point
0:15:47 > 0:15:49in the story of explosives.
0:15:49 > 0:15:52I've had to come here, to the Defence Academy of the UK,
0:15:52 > 0:15:57because we're going to make what they first discovered in 1846.
0:15:58 > 0:16:03There was a growing tradition of pure scientific research in Europe,
0:16:03 > 0:16:08with researchers trying to understand the chemical composition of natural substances.
0:16:08 > 0:16:13One of these chemists was a German from a humble background called Christian Schonbein.
0:16:13 > 0:16:18He was naive, unconventional and full of original ideas.
0:16:18 > 0:16:21Working in Switzerland, he'd seen some unusual reactions with
0:16:21 > 0:16:26concentrated acids and was keen to investigate them further.
0:16:26 > 0:16:32One of those investigations was unwittingly to change the world of explosives forever.
0:16:32 > 0:16:35Professor Jackie Akhavan has volunteered to show us
0:16:35 > 0:16:37exactly what Schonbein did.
0:16:37 > 0:16:40Jackie, what are we actually doing here?
0:16:40 > 0:16:44OK, we're mixing nitric acid and sulphuric acid together
0:16:44 > 0:16:47and then we're going to add some cotton wool to it,
0:16:47 > 0:16:49to hopefully nitrate the cotton wool.
0:16:49 > 0:16:53Schonbein didn't know it, but the cotton will be acting
0:16:53 > 0:16:56as a source of carbon, like the charcoal in gunpowder
0:16:56 > 0:17:00and by nitrating it, he added oxygen and nitrogen
0:17:00 > 0:17:04from the acid actually into the molecules of the cotton,
0:17:04 > 0:17:07rather than just being in neighbouring grains.
0:17:07 > 0:17:11We must make sure the temperature remains cool.
0:17:11 > 0:17:14So I'm going to put a thermometer in so we can measure the temperature.
0:17:14 > 0:17:18- Do you want to help?- I do. What temperature should I watch out for?
0:17:18 > 0:17:21OK, it mustn't go above 18 degrees centigrade.
0:17:21 > 0:17:23I'm going to adjust this. Could you give me an update?
0:17:23 > 0:17:25- It's at 21 at the moment.- Right.
0:17:25 > 0:17:28- I don't want to scare anybody. - No, it's OK. What we'll do,
0:17:28 > 0:17:30we'll just cool it down a bit. OK.
0:17:30 > 0:17:32So what temperature are we now?
0:17:32 > 0:17:36- It's down to 19.- OK, well, we need to get it a bit cooler.
0:17:38 > 0:17:40- We're down to 18.4.- OK.
0:17:40 > 0:17:43What's the danger if the temperature starts rising?
0:17:43 > 0:17:45We want to keep control of this reaction.
0:17:45 > 0:17:46I'm very conscious of this.
0:17:46 > 0:17:52- That's OK.- I know battery acid's quite horrifically dangerous and if that's just as dangerous.
0:17:52 > 0:17:55It's much... These are very concentrated acids,
0:17:55 > 0:17:57so we've got to be extremely careful.
0:17:57 > 0:18:01'The nitration reaction changes the cotton chemically so that now,
0:18:01 > 0:18:05'just like in the gunpowder mix, there are carbon, nitrogen
0:18:05 > 0:18:08'and oxygen atoms, an explosive reaction waiting to happen,
0:18:08 > 0:18:13'but in this substance they're actually all in the same molecule,
0:18:13 > 0:18:16'so much closer together than in gunpowder.
0:18:16 > 0:18:20'Schonbein had accidentally created a much more efficient explosive.'
0:18:20 > 0:18:24So this is it, our nitrocellulose, or guncotton as it's known.
0:18:24 > 0:18:29- That's right.- I mean, now we've washed the acid off and dried it,
0:18:29 > 0:18:31it feels exactly like cotton wool.
0:18:31 > 0:18:32Just like we started with.
0:18:32 > 0:18:36The only difference with this one, compared to the cotton wool,
0:18:36 > 0:18:40is that we've got the oxygen actually linked to the fuel.
0:18:40 > 0:18:42So because we've changed every single molecule
0:18:42 > 0:18:44of the cotton to guncotton,
0:18:44 > 0:18:48- then it's going to go exactly the same every time?- Yes.
0:18:48 > 0:18:49- Go on, then.- Right. Are you ready?
0:18:49 > 0:18:52I'm more than a little intrigued.
0:18:54 > 0:18:56Stand back.
0:18:56 > 0:18:57- I am already.- Ready?
0:19:02 > 0:19:04That gives off a lot of heat.
0:19:04 > 0:19:08Heat, light, lots of gas being given out and then you can just have
0:19:08 > 0:19:11a look, and there's sort of black bits there, that's the carbon.
0:19:11 > 0:19:13So it hasn't fully oxidised.
0:19:13 > 0:19:16So there's not enough oxygen for all the carbon that's in the molecules,
0:19:16 > 0:19:19- so we're just left with some carbon. - That's right.
0:19:19 > 0:19:21That's a very, very rapid burnout. Whoof.
0:19:21 > 0:19:24Like with the gunpowder when you just set it on fire,
0:19:24 > 0:19:27it's unconfined, so you don't get an explosion,
0:19:27 > 0:19:29you just get this rapid burning.
0:19:29 > 0:19:33It all goes up into the atmosphere and it's all disappeared as gases
0:19:33 > 0:19:35and that's what you're left with.
0:19:35 > 0:19:37- I like it. Can we do some more? - You can indeed.
0:19:40 > 0:19:44Just like gunpowder, guncotton simply burns when there's room
0:19:44 > 0:19:47for the gases it produces to expand into
0:19:47 > 0:19:50but it burns faster, and the faster the gases are produced,
0:19:50 > 0:19:54the greater the explosive potential.
0:19:54 > 0:19:57Schonbein recognised it and immediately started
0:19:57 > 0:20:01sending out samples to colleagues and writing about his discovery.
0:20:03 > 0:20:05One of the first to react to the news
0:20:05 > 0:20:09was the Cornish mining community in the far southwest of England.
0:20:09 > 0:20:13The area is rich in resources like tin and granite
0:20:13 > 0:20:17and it made it a worldwide centre for mining.
0:20:17 > 0:20:20It was a vital and profitable industry for England
0:20:20 > 0:20:22and in the mid-19th century,
0:20:22 > 0:20:27it relied heavily on gunpowder to break up the rock.
0:20:27 > 0:20:32By the 1840s, miners had been using gunpowder in mines like this
0:20:32 > 0:20:33for 200 years.
0:20:35 > 0:20:38But gunpowder was far from reliable. It was dangerous,
0:20:38 > 0:20:41unpredictable and difficult to use.
0:20:41 > 0:20:45Mine historian Richard Williams has promised to show me just
0:20:45 > 0:20:49how difficult, starting with how they got it deep within the rock.
0:20:49 > 0:20:53You're trying to actually push a hole into the rock using what they
0:20:53 > 0:20:56called a bore, basically, an iron bar about 3ft long.
0:20:56 > 0:20:59- Right.- And a heavy hammer. - Can I have a go?
0:20:59 > 0:21:01I'd love to have a go.
0:21:03 > 0:21:04Keep turning it.
0:21:07 > 0:21:09I can see that taking a while.
0:21:09 > 0:21:11It would probably take you a good 20 minutes.
0:21:11 > 0:21:14I can imagine once you've done your 3ft hole,
0:21:14 > 0:21:17you'd want to get the best bang out of it you could.
0:21:17 > 0:21:22Oh, yes. The next thing is to charge it, to fill it with gunpowder.
0:21:22 > 0:21:26You can imagine if they're working with candles or open lamps and
0:21:26 > 0:21:30gunpowder, it's not a great combination.
0:21:30 > 0:21:33OK, so once they've got the gunpowder into the hole there,
0:21:33 > 0:21:34how do they safely light it?
0:21:34 > 0:21:37They used a goose quill.
0:21:37 > 0:21:40- Basically the centre of the quill is hollow.- Yeah.
0:21:40 > 0:21:43So you cut off the top, you end up with something like that.
0:21:43 > 0:21:46You grind your gunpowder up until its fine enough to go into
0:21:46 > 0:21:49- the hollow.- Yeah.- Tamp that down.
0:21:49 > 0:21:54Make several of those, push one into another and slowly you make a fuse.
0:21:54 > 0:21:57And they're all packed with gunpowder, so I can see,
0:21:57 > 0:22:00but what was the burn-time on them?
0:22:00 > 0:22:01Like, how quick did they go?
0:22:01 > 0:22:03They were unpredictable.
0:22:03 > 0:22:05If you didn't pack them correctly,
0:22:05 > 0:22:07they would go off a bit like a rocket.
0:22:07 > 0:22:10- That's horrendous. - Well, when we're doing it,
0:22:10 > 0:22:14we're actually going to use a safety fuse and we've already made a charge up
0:22:14 > 0:22:18and we've filled this with gunpowder and we've already got
0:22:18 > 0:22:22- a hole drilled. The hole is going back into the rock.- OK.
0:22:22 > 0:22:26So we put the powder into the hole.
0:22:26 > 0:22:28They would then get a tamping rod to push it in.
0:22:30 > 0:22:33- Next thing is to stem it, to seal it.- Right.
0:22:33 > 0:22:36If we left it like that, it would shoot just like a gun.
0:22:36 > 0:22:38Visually, this looks quite a short fuse to me.
0:22:38 > 0:22:41How much time have we got from when we light it?
0:22:41 > 0:22:44This is going to take slightly over a minute and a half
0:22:44 > 0:22:46to burn through to the gunpowder.
0:22:46 > 0:22:50That seems quite quick, but I'll trust you. I'm going to wear my goggles, though.
0:22:51 > 0:22:53Away it goes.
0:23:00 > 0:23:01- Here we go.- Look at that.
0:23:01 > 0:23:02I say look at that -
0:23:02 > 0:23:05should we not be moving in that direction quite quickly?
0:23:05 > 0:23:09- I think we should leave now, yes. - Yeah.
0:23:09 > 0:23:12- So we can just literally just pop round the corner here?
0:23:12 > 0:23:16Round the corner so we'll be out of the way of anything that flies down through the tunnel.
0:23:22 > 0:23:26You start to wonder if it's going to go.
0:23:29 > 0:23:30But it went!
0:23:33 > 0:23:36The reverberation afterwards as well, which I guess is
0:23:36 > 0:23:39the multiple shock wave bouncing off all sorts of walls.
0:23:39 > 0:23:44Well, there we go, you look down the level and we should see the smoke.
0:23:46 > 0:23:51Right, you can actually see the fumes are close to the roof looking down through.
0:23:52 > 0:23:55- Oh, yeah.- It's getting thicker as we get close to the...
0:23:55 > 0:23:57- It's getting a bit acrid.- Yeah.
0:23:57 > 0:24:01'The smoke was one of the things that miners hated about gunpowder.
0:24:01 > 0:24:04'It filled the tunnels and made working difficult.'
0:24:04 > 0:24:08What's actually happened is it's blown the studding out.
0:24:08 > 0:24:11- We haven't moved any rock at all, have we?- No.
0:24:11 > 0:24:18'So not only was gunpowder difficult and time-consuming for miners to use, it wasn't even that reliable.
0:24:18 > 0:24:25'Schonbein's new guncotton promised more power, more reliability and no smoke.'
0:24:25 > 0:24:29In August 1846, the Royal Geological Society of Cornwall
0:24:29 > 0:24:34invited him to come to England to prove its worth.
0:24:34 > 0:24:38Schonbein demonstrated his guncotton in a quarry like this.
0:24:38 > 0:24:45The quarrymen drilled several holes in the rock, and into one, they packed a full charge of gunpowder
0:24:45 > 0:24:48and into another, just a quarter of the amount of guncotton.
0:24:48 > 0:24:53So innocent did the guncotton look that one man said he would sit
0:24:53 > 0:24:56on the hole in return for a drink at the local pub.
0:24:56 > 0:24:59Luckily, he was persuaded to watch the test
0:24:59 > 0:25:02before committing himself to the bargain.
0:25:04 > 0:25:05First, 30g of gunpowder.
0:25:05 > 0:25:08Let's see if it's more successful than in the mine.
0:25:16 > 0:25:21Well, the rock split, but not at the hole where the explosives were.
0:25:21 > 0:25:26It looks like that explosion there maybe sent some kind of shock
0:25:26 > 0:25:28through the rock and it peeled off here,
0:25:28 > 0:25:31where possibly there was some sort of fault line.
0:25:34 > 0:25:37Now we'll try just 5g of guncotton,
0:25:37 > 0:25:40looking like it couldn't possibly do much damage.
0:25:46 > 0:25:48That's a completely different story.
0:25:49 > 0:25:54In slow motion, you can clearly see all the gases the explosion creates.
0:25:54 > 0:25:59Brown nitric oxide, steam and others, splitting the rock apart.
0:26:08 > 0:26:10That's just astonishing.
0:26:10 > 0:26:13A couple of hundred kilos of rock has practically disappeared.
0:26:13 > 0:26:16There's some fragments over there,
0:26:16 > 0:26:17bits down here.
0:26:17 > 0:26:20And look at that.
0:26:20 > 0:26:25Where it was actually placed, there's nothing at all.
0:26:25 > 0:26:26Like that.
0:26:26 > 0:26:29Look down here.
0:26:29 > 0:26:33That's the hole where it was packed in. So this was the other way up.
0:26:33 > 0:26:34You can see where the clay was,
0:26:34 > 0:26:38you can see all the way down here and it's just split it.
0:26:38 > 0:26:42Now, this is guncotton and what's happened here is when
0:26:42 > 0:26:47the guncotton has been compacted, confined in there, it's detonated,
0:26:47 > 0:26:51which is a completely different process to when we saw it being lit.
0:26:51 > 0:26:52It burnt rapidly.
0:26:52 > 0:26:55This detonation sends out a sharp shock wave
0:26:55 > 0:26:58and as it goes into the rock, the rock gets split.
0:26:58 > 0:27:03It's a much more powerful explosion, and I can imagine the Cornish miners
0:27:03 > 0:27:04feeling a little bit like me now,
0:27:04 > 0:27:10almost overwhelmed at the difference between gunpowder and guncotton.
0:27:11 > 0:27:14The quarrymen were amazed at the new guncotton
0:27:14 > 0:27:18and mercilessly teased the colleague who had offered to sit on it.
0:27:18 > 0:27:21They were immediately interested and Schonbein quickly found
0:27:21 > 0:27:24an English partner to start manufacture.
0:27:24 > 0:27:27His apparent success soon inspired others.
0:27:27 > 0:27:31Schonbein wasn't the only one experimenting with these kind of chemicals.
0:27:31 > 0:27:36Not long afterwards, an Italian chemist, Ascanio Sobrero,
0:27:36 > 0:27:41reacted nitric acid with glycerine, another carbon-rich substance.
0:27:41 > 0:27:44Sobrero had worked on nitration before,
0:27:44 > 0:27:46and when he read of Schonbein's discovery,
0:27:46 > 0:27:48he was inspired to return to it.
0:27:48 > 0:27:50He was originally a medic,
0:27:50 > 0:27:53so many of his interests were in potential new drugs.
0:27:53 > 0:27:59The result of this experiment, first done in 1846, is in fact still
0:27:59 > 0:28:04an important heart medicine, but it has another side to its character.
0:28:04 > 0:28:07Dr Alex Contini is one of the few chemists experienced enough
0:28:07 > 0:28:10to attempt this process
0:28:10 > 0:28:14and he isn't going to trust his life to me keeping an eye on the thermometer this time.
0:28:14 > 0:28:16Seven and rising...
0:28:18 > 0:28:22Each time the glycerine is added to the concentrated acids,
0:28:22 > 0:28:25he has to stir it and make sure it stays cool.
0:28:25 > 0:28:27Every degree of temperature rise
0:28:27 > 0:28:30makes a premature explosion more likely.
0:28:30 > 0:28:33Ten and rising...
0:28:46 > 0:28:49The resulting oily liquid, like guncotton,
0:28:49 > 0:28:53contains carbon atoms linked to nitrogen and oxygen groups.
0:28:53 > 0:28:55It looks fairly innocuous,
0:28:55 > 0:29:00but Sobrero discovered it has some pretty surprising properties.
0:29:00 > 0:29:04And we're only going to use the tiniest amount to show them.
0:29:04 > 0:29:08Sobrero wrote that the safest way to demonstrate these properties
0:29:08 > 0:29:12was to dip a hot wire into a glass bowl of the substance,
0:29:12 > 0:29:15but he was scarred for life by flying glass,
0:29:15 > 0:29:18so we are going to try something different.
0:29:27 > 0:29:32If you look down there, you'll see the nitroglycerine has completely disappeared.
0:29:32 > 0:29:37Every molecule of the liquid nitroglycerine gets turned to gas and goes,
0:29:37 > 0:29:40hence the massive expansion, hence the massive explosion.
0:29:42 > 0:29:45Whilst guncotton only detonates when confined,
0:29:45 > 0:29:48nitroglycerine can detonate when given a simple sharp shock.
0:29:51 > 0:29:54Even slowed down more than 500 times,
0:29:54 > 0:29:57the explosion is incredibly fast.
0:29:58 > 0:30:03This new behaviour made guncotton and nitroglycerine
0:30:03 > 0:30:05quite different from gunpowder.
0:30:05 > 0:30:09The difference between gunpowder and these new high explosives,
0:30:09 > 0:30:12as they're called, is the way they explode.
0:30:12 > 0:30:15Gunpowder burns - albeit very rapidly, it's still burning.
0:30:15 > 0:30:18One piece heating the piece adjacent to it,
0:30:18 > 0:30:20the piece that's adjacent to that -
0:30:20 > 0:30:22fwooh! - till the whole thing's gone.
0:30:22 > 0:30:25With high explosives, it's detonation.
0:30:25 > 0:30:29A pressure wave travels extremely quickly through the whole charge
0:30:29 > 0:30:31and it almost goes instantaneously.
0:30:31 > 0:30:34The first bit of the reaction in a high explosive
0:30:34 > 0:30:39creates so much gas so quickly it generates a pressure wave
0:30:39 > 0:30:41that hits the rest of the explosive.
0:30:41 > 0:30:45I'll show you, with this fire piston, as it's called,
0:30:45 > 0:30:48and a tiny bit of normal cotton wool.
0:30:48 > 0:30:53As the piston comes down, it acts like the explosive pressure wave,
0:30:53 > 0:30:55raising the pressure inside the tube.
0:30:55 > 0:30:57That pressure heats the air so much
0:30:57 > 0:31:01that the cotton wool bursts into flame.
0:31:01 > 0:31:03It's the same with a piece of high explosive.
0:31:03 > 0:31:08It's the sudden rise in pressure that gives the sudden rise in temperature
0:31:08 > 0:31:11that triggers the explosive as it runs through the entire charge.
0:31:11 > 0:31:13Now, this thing happens so quickly,
0:31:13 > 0:31:17you pretty much get the entire lot going in one go.
0:31:19 > 0:31:20Watch this.
0:31:22 > 0:31:26This is detonating cord. It's a spun cord with a line of high explosive
0:31:26 > 0:31:28right down the centre of it.
0:31:28 > 0:31:30When it's detonated at one end,
0:31:30 > 0:31:33the wave front moves extremely quickly right down its length.
0:31:41 > 0:31:45Slowing the process down 250 times, you can see the detonation
0:31:45 > 0:31:49travelling at about 6km a second.
0:31:51 > 0:31:55When the force of the detonation wave hits the surrounding air,
0:31:55 > 0:31:57it creates a supersonic shock wave.
0:31:57 > 0:32:00You can see the shock wave distort the air like a bubble,
0:32:00 > 0:32:03coming out around this modern high explosive.
0:32:05 > 0:32:09Shock waves and reaction speeds like this were a phenomenon
0:32:09 > 0:32:11nobody had come across before
0:32:11 > 0:32:14and it made these new high explosives very powerful
0:32:14 > 0:32:16and potentially very dangerous.
0:32:16 > 0:32:19And that was the problem.
0:32:19 > 0:32:22Only months after it opened, the world's first guncotton factory
0:32:22 > 0:32:25exploded disastrously in England
0:32:25 > 0:32:30and Sobrero's new nitroglycerine appeared even more dangerous.
0:32:30 > 0:32:33It seemed there might be no way of safely harnessing
0:32:33 > 0:32:35this new-found power.
0:32:35 > 0:32:39But the industrialised world was crying out for it.
0:32:39 > 0:32:42The men working the great tin and coal mines of Britain
0:32:42 > 0:32:47were still having to use the centuries-old, inefficient gunpowder
0:32:47 > 0:32:51and attempts to build a canal system to move the vital raw materials
0:32:51 > 0:32:54produced by the mines to Britain's ports
0:32:54 > 0:32:57were hampered by gunpowder's lack of power.
0:32:59 > 0:33:02But in the 1850s, a young Swedish student
0:33:02 > 0:33:04came to hear about nitroglycerine.
0:33:04 > 0:33:07His name was Alfred Nobel
0:33:07 > 0:33:10and his family were explosives manufacturers in need of money.
0:33:10 > 0:33:15They took the risk of trying to manufacture nitroglycerine,
0:33:15 > 0:33:18but they had an awful lot to learn.
0:33:18 > 0:33:22In their first year of manufacture, their factory in Sweden exploded,
0:33:22 > 0:33:25killing Alfred's younger brother Emil.
0:33:25 > 0:33:29This is the site of Nobel's biggest explosives factory.
0:33:29 > 0:33:32It's at Ardeer on the west coast of Scotland and at its height,
0:33:32 > 0:33:35it was the biggest explosives factory in Europe.
0:33:38 > 0:33:40Nobel liked it.
0:33:40 > 0:33:45One, because it was remote, but two, it was built entirely on sand,
0:33:45 > 0:33:49meaning he could create artificial landscapes like that.
0:33:56 > 0:33:59Nobel built what were called nitroglycerine hills.
0:33:59 > 0:34:03Nitroglycerine was made in little huts on the top of each hill.
0:34:03 > 0:34:07In each hut were two men, one to monitor the mixing reaction,
0:34:07 > 0:34:10the other to adjust the flow of water through a cooling jacket
0:34:10 > 0:34:13to keep the temperature in the right range.
0:34:13 > 0:34:15Now, vigilance was vital.
0:34:15 > 0:34:19The entire batch could self-detonate if allowed to go out of control.
0:34:19 > 0:34:23For this reason, one man had to always sit on a one-legged stool,
0:34:23 > 0:34:26so there was no chance of him falling asleep on the job.
0:34:26 > 0:34:30I mean, as if sitting next to a vat of nitroglycerine
0:34:30 > 0:34:31was not stimulation enough!
0:34:33 > 0:34:36Nitroglycerine could not be safely pumped.
0:34:36 > 0:34:38So what they did was just let it flow under gravity
0:34:38 > 0:34:42from the huts at the top of the hill to the factories at the bottom.
0:34:45 > 0:34:49Once inside the factory, it got stabilised.
0:34:49 > 0:34:52Now, this was what was Nobel's great achievement.
0:34:52 > 0:34:58He discovered that if he mixed his nitroglycerine with an absorbent clay, a bit like cat litter,
0:34:58 > 0:35:01it became a lot less sensitive,
0:35:01 > 0:35:04a lot easier to handle without going off in your hands.
0:35:04 > 0:35:09The clay he used came as a fine powder called kieselguhr.
0:35:11 > 0:35:14Once mixed together, a dough-like substance was formed.
0:35:14 > 0:35:19In fact, it was kneaded by armies of women into the shapes required.
0:35:26 > 0:35:32This new compound was called dynamite and it was a revolution.
0:35:32 > 0:35:37Now there was a high explosive that was insensitive to shock and heating.
0:35:37 > 0:35:40You could actually set fire to it and it would burn with a normal flame.
0:35:40 > 0:35:43I don't recommend it, but apparently you could,
0:35:43 > 0:35:46but once you've made something that's this good,
0:35:46 > 0:35:48that's this stable, this difficult to set off,
0:35:48 > 0:35:52how do you get it to explode when you want it to?
0:35:52 > 0:35:54That was Nobel's other great innovation.
0:35:54 > 0:35:58And they actually still make those devices at his old factory.
0:35:58 > 0:36:03In fact, Nobel's sand bunkers are the perfect place for me to find out more about them.
0:36:06 > 0:36:09Well, Alfred Nobel being the very inventive guy that he was,
0:36:09 > 0:36:11came up with the idea of a detonator
0:36:11 > 0:36:14and this is a modern detonator,
0:36:14 > 0:36:19but the basic principle is a device which delivers an explosive
0:36:19 > 0:36:25shock to dynamite and that shock is sufficient to detonate it.
0:36:25 > 0:36:28I do actually have a cutaway here.
0:36:28 > 0:36:31At the top of the detonator we have an electrical fuse head
0:36:31 > 0:36:36- and this is, in many ways, like the match.- Yep.
0:36:36 > 0:36:39This is designed to initiate not by friction
0:36:39 > 0:36:42but by passing an electric current through it.
0:36:42 > 0:36:48That generates heat, which causes this fuse head to burst with
0:36:48 > 0:36:50hot gases and hot particles
0:36:50 > 0:36:55which then initiate a pallet of sensitive primary explosive.
0:36:55 > 0:37:00And out of more than just casual curiosity,
0:37:00 > 0:37:03a detonator like that, with that much explosive in it,
0:37:03 > 0:37:06how much damage would it do if just that went off?
0:37:06 > 0:37:10If I was holding this in my hand and it and it were to detonate,
0:37:10 > 0:37:13then I would lose the hand.
0:37:13 > 0:37:15Really? OK.
0:37:15 > 0:37:18- I'll be very wary of detonators, then.- Absolutely!
0:37:18 > 0:37:22'Of course, to demonstrate a detonator really doing its job,
0:37:22 > 0:37:26'we need to attach it to a block of less sensitive explosive.
0:37:26 > 0:37:30'Dynamite was the world's first mouldable plastic explosive
0:37:30 > 0:37:33'and we're using its modern equivalent.'
0:37:33 > 0:37:39That's a small sample, maybe about 30g of a new plastic explosive
0:37:39 > 0:37:42that we've developed here at Ardeer.
0:37:42 > 0:37:45I think I should double-check - I'm fine for handling this now?
0:37:45 > 0:37:48Oh, yes, it is perfectly safe.
0:37:48 > 0:37:51I guess because it looks like Play-Doh,
0:37:51 > 0:37:54you instantly want to treat it like Play-Doh.
0:37:54 > 0:37:57Well, it is a very special kind of Play-Doh, if you like.
0:37:57 > 0:38:02It's got that plasticity that Play-Doh has, but as with all explosives,
0:38:02 > 0:38:05they are very unforgiving when you give it the right stimulus.
0:38:05 > 0:38:08- And that is a detonator. - And that is a detonator.
0:38:08 > 0:38:09I'm going to ask Jim to come in and set up.
0:38:09 > 0:38:12Jim is one of our trained shot-firers,
0:38:12 > 0:38:16and only a shot-firer can set up.
0:38:16 > 0:38:20You've been handling that material with gloves.
0:38:20 > 0:38:26Jim is not wearing gloves because there is a risk of static with the electrically-initiated detonator.
0:38:26 > 0:38:31You'll notice again he's kept the detonator, the action end of the wires, in the box until the last
0:38:31 > 0:38:35minute, so if there is any accidental stray current
0:38:35 > 0:38:41he's minimised the chance of it causing any damage and then he just simply pops it into the holder,
0:38:41 > 0:38:44to make sure that there's contact with the explosive
0:38:44 > 0:38:46and it's now ready to go
0:38:46 > 0:38:51once we've cleared the site and Jim has armed the circuit.
0:38:51 > 0:38:54I feel my stomach change when he puts that in there.
0:38:54 > 0:38:57I honestly do. It's just...
0:38:57 > 0:39:00Like we're now... Shall we go?
0:39:00 > 0:39:01- Yes.- Right.
0:39:08 > 0:39:09Stand by.
0:39:17 > 0:39:22Effectively, that entire lump almost instantaneously goes from being
0:39:22 > 0:39:25- a solid to a gas.- Absolutely right.
0:39:25 > 0:39:29- It's shockingly crisp.- Yeah. That's what it's supposed to do,
0:39:29 > 0:39:32but if you look on the other side,
0:39:32 > 0:39:34you'll see something completely different.
0:39:34 > 0:39:37And that's the pressure wave that's ripped that out.
0:39:37 > 0:39:43Yeah, the shock wave travels through the plate, hits the underside and
0:39:43 > 0:39:48then just blasts off the scab and if we dig around we might just find
0:39:48 > 0:39:52the back end of that, because we've got a nice little hole here.
0:39:52 > 0:39:55So somewhere down there is the piece.
0:39:55 > 0:39:59Well, the secret is it's come all the way through
0:39:59 > 0:40:01and there... Get the sand off it.
0:40:01 > 0:40:03- I'm shocked.- There's the scab.
0:40:03 > 0:40:05It's come off the other side.
0:40:05 > 0:40:08It's more impressive than going through there, because nothing
0:40:08 > 0:40:11goes through railway sleepers, as a general rule.
0:40:11 > 0:40:16Nobel's struggle to tame the power of high explosives and make them
0:40:16 > 0:40:21safe tools for the hungry industrial world made him a very rich man.
0:40:21 > 0:40:26By safely harnessing the shattering power of nitroglycerine's detonation
0:40:26 > 0:40:29with dynamite and a range of other compounds, a new era
0:40:29 > 0:40:33of civil engineering opened up and great construction projects
0:40:33 > 0:40:37such as the Suez Canal, the London Underground system
0:40:37 > 0:40:41and then the Panama Canal could now be undertaken.
0:40:44 > 0:40:47And that might have been Nobel's legacy,
0:40:47 > 0:40:50if it weren't for a mistake that occurred in 1888.
0:40:50 > 0:40:53After the death of Alfred Nobel's elder brother Ludvig,
0:40:53 > 0:40:58some newspapers mistakenly printed Alfred Nobel's obituary instead.
0:40:58 > 0:41:01Where he was living in France at the time,
0:41:01 > 0:41:05Le Figaro printed this small but damning paragraph.
0:41:05 > 0:41:09It translates as, "A man who it would be difficult
0:41:09 > 0:41:14"to describe as a benefactor to humanity died yesterday in Cannes."
0:41:14 > 0:41:17Now, reading that must have been a bit of a shock, and it's said that
0:41:17 > 0:41:20it made Nobel intent on changing his legacy to the world.
0:41:20 > 0:41:25To that end, he left his vast fortune to setting up a foundation
0:41:25 > 0:41:31which would award prizes for literature, science and peace.
0:41:33 > 0:41:39Nobel's advances in explosive design were the result of long hours and hard work,
0:41:39 > 0:41:45but some revolutions in the history of explosives are sparked simply by a chance observation.
0:41:47 > 0:41:51In the same year that Nobel's obituary was accidentally published,
0:41:51 > 0:41:53an American chemist, Charles Monroe,
0:41:53 > 0:41:55was doing explosives work for the US Navy.
0:41:55 > 0:41:58He was one of the foremost explosives experts
0:41:58 > 0:42:00of the late 19th century.
0:42:00 > 0:42:06Then many high explosives came in blocks with the manufacturer's name embossed onto them.
0:42:08 > 0:42:11So I've got myself some high explosive
0:42:11 > 0:42:15onto which I'm going to stamp a corporate name.
0:42:17 > 0:42:21Now, as Monroe spotted, there was something very strange that happened
0:42:21 > 0:42:25when these stamped blocks were detonated near steel plate.
0:42:25 > 0:42:28Hopefully we'll get to see the same thing.
0:42:39 > 0:42:40Prime...
0:42:51 > 0:42:53That seemed big enough.
0:42:58 > 0:42:59Here we go.
0:43:01 > 0:43:03Yes. OK.
0:43:04 > 0:43:09You can now see the BBC logo stamped into a block of steel
0:43:09 > 0:43:12in the same way that the manufacturers' logos got stamped
0:43:12 > 0:43:16into the steel back in the 1880s, but what Monroe was particularly
0:43:16 > 0:43:21intrigued by was why it made this particular indentation
0:43:21 > 0:43:23from the indentation on the explosives
0:43:23 > 0:43:26and understanding the way in which this happens
0:43:26 > 0:43:30led to a completely new way of using explosives.
0:43:30 > 0:43:32When a lump of explosive detonates,
0:43:32 > 0:43:35the shock wave radiates out from every part of its surface.
0:43:37 > 0:43:40So you've got your dent in the explosive here
0:43:40 > 0:43:43and you've got your target there,
0:43:43 > 0:43:45as the shock wave comes out,
0:43:45 > 0:43:49instead of the bit at the back ending up with a weaker effect,
0:43:49 > 0:43:51it ends up actually stronger,
0:43:51 > 0:43:55because the shock wave is coming out in all directions, like this.
0:43:55 > 0:43:59When it reaches the centre of the indentation, they tend to meet,
0:43:59 > 0:44:01like jets of water in the middle of that dent
0:44:01 > 0:44:05and this effect here magnifies the shock wave that you've got leaving
0:44:05 > 0:44:08there, sending it into the plate and this is actually the area
0:44:08 > 0:44:10of maximum pressure here.
0:44:10 > 0:44:14And once this was understood, shock waves could be directed to
0:44:14 > 0:44:17focus the power of the explosion exactly where it was wanted.
0:44:17 > 0:44:21People started making cavities in their explosive to increase
0:44:21 > 0:44:22the power of the shock wave,
0:44:22 > 0:44:26but then, with the pressures of war, came a new step forward.
0:44:26 > 0:44:29When you line that cavity
0:44:29 > 0:44:34with a hard material, almost invariably metal,
0:44:34 > 0:44:38then you enter the domain of what's known as the shaped charge.
0:44:38 > 0:44:40Right.
0:44:40 > 0:44:41Conventional shaped charges
0:44:41 > 0:44:44are filled with high explosive in a factory.
0:44:44 > 0:44:45Right.
0:44:45 > 0:44:50This is something that I designed for filling by the user.
0:44:50 > 0:44:54It means that it can travel on aeroplanes and so on without...
0:44:54 > 0:44:56- DIY shaped charges.- Exactly that.
0:44:56 > 0:44:57Now, in this case
0:44:57 > 0:45:03we're going to go back to probably the first type of liner -
0:45:03 > 0:45:06this is called the liner - that was used in a shaped charge.
0:45:06 > 0:45:09- That's just a cone of copper, isn't it?- It is indeed.
0:45:09 > 0:45:13Having that copper on there, I guess it's the sort of
0:45:13 > 0:45:17the equivalent of using a bullet or a cannonball.
0:45:17 > 0:45:22It's the same, if you go - kcrrr! - and fire an empty cartridge,
0:45:22 > 0:45:24then you get a loud bang and an explosion,
0:45:24 > 0:45:27but nothing that's going to do any significant harm.
0:45:27 > 0:45:31Whereas if you put a bullet in the end of it, if you see what I mean,
0:45:31 > 0:45:35and fire it, then it pushes out something of a significant mass,
0:45:35 > 0:45:36and that can do some damage.
0:45:36 > 0:45:41Yes. The great advantage is that this metal travels enormously faster
0:45:41 > 0:45:42than any cannonball.
0:45:42 > 0:45:44I'll show you what I mean.
0:45:44 > 0:45:48If you put plastic explosive in here and then you push this copper cone
0:45:48 > 0:45:53into the explosive, when I initiate at this end,
0:45:53 > 0:45:57a detonation wave travels from here to there.
0:45:57 > 0:46:00- Right.- The first thing it hits is the apex of the cone
0:46:00 > 0:46:02and that apex of the cone is driven forward.
0:46:02 > 0:46:05The whole cone is collapsed.
0:46:05 > 0:46:10In fact, it collapses in such a way that it turns inside out.
0:46:10 > 0:46:13Right, because the end bits hit first and that starts moving.
0:46:13 > 0:46:16Wow, that's an astonishing thing to get your head round.
0:46:16 > 0:46:18It is a bit of a shock at first.
0:46:18 > 0:46:22What happens is that the inner part of the copper, not the whole
0:46:22 > 0:46:25mass of it, by any means, the inner part of the copper
0:46:25 > 0:46:29forms into a sort of wire, which is called the jet.
0:46:29 > 0:46:32And that's not molten, it's still solid copper.
0:46:32 > 0:46:36Yes, but coming not in that direction, coming in that direction.
0:46:36 > 0:46:40And that almost piles in like a nail through the steel,
0:46:40 > 0:46:42driving its way in.
0:46:42 > 0:46:45Yes. It pushes the target material out of the way
0:46:45 > 0:46:49and it pushes it aside as the tip of the jet
0:46:49 > 0:46:53hits the steel and flows back along the outside of the rod.
0:46:53 > 0:46:55Then there's a new increment of metal.
0:46:55 > 0:46:59This is constantly being replaced and when it's all used up it stops,
0:46:59 > 0:47:00won't go any deeper.
0:47:00 > 0:47:03Are we in a position that we can try this and I can see?
0:47:03 > 0:47:06Absolutely. This box, I'm pleased to tell you, is full of explosive.
0:47:06 > 0:47:09- Good.- What I'll do is take some out.
0:47:09 > 0:47:14This is standard British plastic explosive.
0:47:14 > 0:47:18It's similar to the American C4,
0:47:18 > 0:47:22but it is actually much easier to use for filling charges.
0:47:22 > 0:47:27You can just ram it in and then put the cone in.
0:47:28 > 0:47:30We're going to test it with what looks like
0:47:30 > 0:47:33an impossibly solid block of steel.
0:47:35 > 0:47:38There is a critical distance at which the jet
0:47:38 > 0:47:41will be at its most penetrating before it breaks up,
0:47:41 > 0:47:45so the charge has legs to hold it the right height from our target.
0:47:47 > 0:47:48Right, see you in about two minutes.
0:47:48 > 0:47:51- Yes, and don't panic.- I won't.
0:48:02 > 0:48:04Firing.
0:48:04 > 0:48:08Four, three, two, one...
0:48:11 > 0:48:13- Wow!- Let's go and see what we've done, shall we?
0:48:13 > 0:48:18It seems astonishing, because that was just a massive thump,
0:48:18 > 0:48:21that something extremely accurate will have occurred from that.
0:48:21 > 0:48:22Well, let's see.
0:48:24 > 0:48:25Ooh...
0:48:27 > 0:48:29Well, it's gone in at least that deep
0:48:29 > 0:48:31because I can push that in, but then
0:48:31 > 0:48:34the proof of the pudding will be turning it over
0:48:34 > 0:48:38and see if we have achieved anything the other end. Yep!
0:48:38 > 0:48:40Oh, yes!
0:48:40 > 0:48:42That's gone through over a foot of steel.
0:48:42 > 0:48:47The thing that I find even more surprising is you know full well
0:48:47 > 0:48:49if you've got a copper nail like that,
0:48:49 > 0:48:52no matter how hard you hit it...
0:48:52 > 0:48:53You will hardly dent the steel.
0:48:53 > 0:48:58Exactly! Yet you get a good amount of plastic explosive with
0:48:58 > 0:49:02a nice shape behind it and you can drive it the whole way through.
0:49:05 > 0:49:08These cone-shaped charges allowed people to get much more
0:49:08 > 0:49:10focused power from their explosives
0:49:10 > 0:49:12and during the coming World Wars,
0:49:12 > 0:49:17revolutionised the power of handheld weapons such as the bazooka.
0:49:18 > 0:49:22Nowadays they're used in all sorts of military and civil applications
0:49:22 > 0:49:26such as opening up oil wells, and Sidney designs them
0:49:26 > 0:49:28especially for bomb disposal,
0:49:28 > 0:49:32but other shapes have been developed as well, for different tasks.
0:49:32 > 0:49:36This long L-shaped liner can turn the shock wave into a blade,
0:49:36 > 0:49:39as the sides are slammed together.
0:49:39 > 0:49:43Instead of the cone's penetrating jet, this cutting blade is axe-like,
0:49:43 > 0:49:47designed for demolition jobs.
0:49:47 > 0:49:52Four, three, two, one...
0:50:02 > 0:50:06It seemed as if the power of explosives had reached a maximum.
0:50:06 > 0:50:09The chemical compositions were carefully designed
0:50:09 > 0:50:12and the power of the shock wave could now be channelled,
0:50:12 > 0:50:17but there was still explosive potential beyond imagination
0:50:17 > 0:50:18to be realised.
0:50:18 > 0:50:22By the end of the 19th century, chemists were discovering
0:50:22 > 0:50:26new elements all the time, and some of them appeared to give off energy.
0:50:26 > 0:50:31They called this rather bizarre property radioactivity.
0:50:31 > 0:50:34It was a New Zealand physicist, Ernest Rutherford, who was one of
0:50:34 > 0:50:38the first to understand the potential of radioactivity.
0:50:38 > 0:50:42Already understanding that it was caused by the atoms of the elements breaking down,
0:50:42 > 0:50:44he wrote this in 1904 -
0:50:44 > 0:50:48"If it should ever be found possible to control at will
0:50:48 > 0:50:51"the rate of disintegration of the radio elements,
0:50:51 > 0:50:54"an enormous amount of energy could be obtained
0:50:54 > 0:50:56"from a small amount of matter."
0:50:56 > 0:50:58It was a prophetic statement,
0:50:58 > 0:51:02although he later said, "Anyone who expects a useful
0:51:02 > 0:51:05"power source from the transformation of these atoms
0:51:05 > 0:51:07"is talking moonshine."
0:51:07 > 0:51:10Even a genius doesn't get it right every time.
0:51:10 > 0:51:14The investigation of radioactivity and the nucleus of atoms continued
0:51:14 > 0:51:19as researchers sought to understand the minute structure of the world
0:51:19 > 0:51:23around us, but some people were already seeing the potential
0:51:23 > 0:51:27for extracting the power released when nuclei are broken apart
0:51:27 > 0:51:32and in the winter of 1938, with war already brewing
0:51:32 > 0:51:35the exact dimensions of that potential was made clear
0:51:35 > 0:51:38in a laboratory in Copenhagen.
0:51:38 > 0:51:41An experimental physicist, Otto Frisch,
0:51:41 > 0:51:44who'd escaped Hitler's regime in Germany, constructed
0:51:44 > 0:51:49a piece of apparatus to measure the energy released when an atom splits.
0:51:49 > 0:51:52Now, it's not my field of science,
0:51:52 > 0:51:55but he knocked his up in a weekend and did the measurements,
0:51:55 > 0:51:58so I feel there's a fighting chance for an amateur like me.
0:51:58 > 0:52:01All the apparatus really consists of
0:52:01 > 0:52:04is a metal box with a metal plate in it.
0:52:04 > 0:52:06Now, when an atom splits,
0:52:06 > 0:52:10you end up with two high-energy fission products.
0:52:10 > 0:52:13Now, as they fly through the gas around them, they can
0:52:13 > 0:52:16smash electrons off other atoms, causing ionisation,
0:52:16 > 0:52:19producing positive and negative particles.
0:52:19 > 0:52:23The atoms that Frisch split were of the element uranium
0:52:23 > 0:52:27and he did it by bombarding them with particles called neutrons.
0:52:27 > 0:52:30A couple of hundred volts between here and here
0:52:30 > 0:52:35should enable us to detect if there's been any ionisation in here
0:52:35 > 0:52:37and from that we'll be able to deduce
0:52:37 > 0:52:40the energy released when an atom splits.
0:52:40 > 0:52:43Obviously, now all I need is a source of uranium
0:52:43 > 0:52:45and some neutrons to bombard it with.
0:52:50 > 0:52:53The National Physical Laboratory near London have
0:52:53 > 0:52:57the sort of thing I need, so I've brought my part of the kit.
0:52:57 > 0:52:59That is you ion chamber, is it?
0:52:59 > 0:53:00Well, yes. This is my ion chamber.
0:53:00 > 0:53:05It's not at the top end of the sophistication that you've got here,
0:53:05 > 0:53:08- but can we try it?- By all means.
0:53:08 > 0:53:10I've got a piece of uranium here
0:53:10 > 0:53:15- which I borrowed from our radioactivity group.- That's not a phrase you hear a lot.- No.
0:53:15 > 0:53:17Uranium does have a reputation.
0:53:17 > 0:53:20How safe is it? How long can I be near it?
0:53:20 > 0:53:25Provided you stay a few centimetres away from it, you're out of the range of the alpha particles.
0:53:25 > 0:53:28Right, so I'll put the lid on here.
0:53:30 > 0:53:35- The thing that we're missing now is the thing to split the atoms. - You need a neutron source.- Yes.
0:53:35 > 0:53:39We are the Neutron Standards Authority for the UK and we produce neutrons and use them
0:53:39 > 0:53:43to calibrate personal dose-meters, like the ones we gave you to wear.
0:53:43 > 0:53:45Yeah, I've got mine.
0:53:45 > 0:53:49I can get a neutron source, but you will have to leave while I put it up here.
0:53:49 > 0:53:52I'm happy to get out of the way while that's happening.
0:53:52 > 0:53:56The neutron source contains an element whose radioactivity
0:53:56 > 0:53:59is much more penetrating than uranium's,
0:53:59 > 0:54:02so it has to be treated with care.
0:54:02 > 0:54:06OK, so we've now got our uranium being blasted with neutrons.
0:54:06 > 0:54:09- Yeah.- How do we tell if we're splitting any atoms?
0:54:09 > 0:54:12We'd have to see some pulses from our ion chamber.
0:54:12 > 0:54:15- OK.- So if I turn up the volts we might begin to see something
0:54:15 > 0:54:18and the first thing that we might see, if it works,
0:54:18 > 0:54:21is the natural radiation from the uranium.
0:54:21 > 0:54:26I'm rather astounded, but they look like genuine pulses.
0:54:26 > 0:54:29So this'd be what you'd hear on a Geiger counter, going kcrr-kcrr?
0:54:29 > 0:54:32- Yes, but you're not seeing any fission yet.- Are we not?
0:54:32 > 0:54:35If it was fission, you would see some very much bigger pulses.
0:54:35 > 0:54:37So if I turn the discriminator up...
0:54:38 > 0:54:41That is a massive pulse.
0:54:41 > 0:54:43- So is that a split atom?!- Yes.
0:54:43 > 0:54:45Wow!
0:54:45 > 0:54:50- Considerably bigger than the pulses from the natural decay of the uranium.- Yeah!
0:54:50 > 0:54:52This is a completely different thing.
0:54:52 > 0:54:54Yes, yes. Very much more energetic.
0:54:54 > 0:54:58Now, from this can we get a measure of how much energy
0:54:58 > 0:55:00is being produced every time an atom splits?
0:55:00 > 0:55:07Well, the classical figure is 200 MeV, 200 mega-electronvolts.
0:55:07 > 0:55:11That makes that, the energy released when one of those atoms gets split,
0:55:11 > 0:55:17is about 50 million times more than a molecule of nitroglycerine.
0:55:17 > 0:55:19That's...
0:55:19 > 0:55:21You can see they were onto something.
0:55:21 > 0:55:22They were, indeed.
0:55:23 > 0:55:26Frisch finished his weekend's work in the early hours
0:55:26 > 0:55:31of January 13th 1939 and was soon woken by a telegram
0:55:31 > 0:55:33with news that his Jewish father had been released
0:55:33 > 0:55:35from a concentration camp.
0:55:35 > 0:55:38He said he remembered it as his lucky day,
0:55:38 > 0:55:41but would have liked a few more hours sleep.
0:55:41 > 0:55:45As war rumbled across Europe and then the world, physicists
0:55:45 > 0:55:49in many countries grasped the potential of Frisch's experiment.
0:55:49 > 0:55:55In the early morning of the 16th July 1945, a team of
0:55:55 > 0:56:00international researchers became the first to see that potential realised
0:56:00 > 0:56:02in the deserts of New Mexico.
0:56:02 > 0:56:07Inside a giant sphere of shaped charges, like the ones Sidney showed
0:56:07 > 0:56:12me, they placed radioactive material no bigger than an orange.
0:56:12 > 0:56:17The whole contraption was hoisted up a tower and then the charges detonated.
0:56:21 > 0:56:24The initial flash of light and heat
0:56:24 > 0:56:28travelled out at 200,000km a second,
0:56:28 > 0:56:32with temperatures reaching over 100 million degrees,
0:56:32 > 0:56:3520,000 times hotter than the surface of the sun.
0:56:35 > 0:56:38It melted the sand in the desert.
0:56:38 > 0:56:43Just like other explosions, this heat causes a massive expansion
0:56:43 > 0:56:44in the surrounding air.
0:56:44 > 0:56:47There's no production of gas, like in a chemical reaction.
0:56:47 > 0:56:51It's simply the staggering quantity of heat released
0:56:51 > 0:56:56by a runaway nuclear reaction that causes mankind's biggest explosion.
0:56:56 > 0:57:00That expanding air slams into the air around it,
0:57:00 > 0:57:04causing an abrupt shock wave which crushes the air
0:57:04 > 0:57:07and just like in the fire piston, heats it,
0:57:07 > 0:57:11but to such a temperature that the air itself begins to glow.
0:57:11 > 0:57:15You can see the white hot bubble-like shock wave
0:57:15 > 0:57:17in these astonishing pictures.
0:57:17 > 0:57:20Then it cools to a dark, transparent layer
0:57:20 > 0:57:23and the fireball inside shows through.
0:57:24 > 0:57:26The Trinity explosion, as it's known,
0:57:26 > 0:57:30had the equivalent power of 20,000 tons of TNT,
0:57:30 > 0:57:35all from just a few kilos of radioactive material.
0:57:35 > 0:57:39And all that power, and that enormous shock wave,
0:57:39 > 0:57:43is produced just simply by heating the air.
0:57:43 > 0:57:47In some ways, it's similar to the heat causing the bamboo to burst
0:57:47 > 0:57:50back in ancient China, but with a nuclear explosion,
0:57:50 > 0:57:55the heat is almost unimaginably intense and sudden.
0:57:55 > 0:57:58In little more than 2,000 years, the journey of understanding
0:57:58 > 0:58:03that mankind has so far travelled is immense.
0:58:03 > 0:58:08We've gone from crackling bamboo to creating something like a star here on Earth
0:58:08 > 0:58:13and man-made explosions terrify us as much now as they always have.
0:58:14 > 0:58:17The advent of the nuclear age was as shocking to us
0:58:17 > 0:58:20as gunpowder was to medieval Europe.
0:58:20 > 0:58:24Throughout history, explosives have been used first
0:58:24 > 0:58:28as weapons and then had their power harnessed to more constructive ends.
0:58:28 > 0:58:33They have shaped our world, through warfare and engineering.
0:58:33 > 0:58:37Even nuclear power has been turned to peaceful uses.
0:58:37 > 0:58:40New explosives may always be discovered
0:58:40 > 0:58:42and wreak terrifying havoc.
0:58:42 > 0:58:44But if history has taught us anything,
0:58:44 > 0:58:48it's that by properly understanding these things
0:58:48 > 0:58:51we can create instruments of unrivalled power.
0:58:53 > 0:58:56If you want to find out more about the science of explosions,
0:58:56 > 0:58:57go to the website -
0:58:59 > 0:59:02And follow the links to the Open University.
0:59:11 > 0:59:16Subtitles by Red Bee Media Ltd
0:59:16 > 0:59:20E-mail subtitling@bbc.co.uk