1 00:00:03,960 --> 00:00:06,200 We see explosions all the time, 2 00:00:06,200 --> 00:00:10,640 and during my career as an engineer, I've certainly made a few. 3 00:00:10,640 --> 00:00:14,600 But actually understanding them and controlling all that power, 4 00:00:14,600 --> 00:00:19,520 that's a whole different story and sometimes quite a surprising one. 5 00:00:19,520 --> 00:00:24,280 It's a story that starts with the accidents of the medieval alchemists... 6 00:00:24,280 --> 00:00:25,640 Don't try this at home. 7 00:00:25,640 --> 00:00:27,640 Whoa! 8 00:00:28,480 --> 00:00:33,320 ..but eventually leads us to a fundamental understanding of the forces of nature... 9 00:00:35,400 --> 00:00:38,640 ..forces that we've mastered for good or evil. 10 00:00:38,640 --> 00:00:42,360 Explosives revolutionised battlefields, 11 00:00:42,360 --> 00:00:46,320 industry and engineering. 12 00:00:49,680 --> 00:00:54,400 To uncover the story, I'll be reading the words of medieval scholars... 13 00:00:56,640 --> 00:00:59,960 ..going deep underground through ancient Cornish mines... 14 00:00:59,960 --> 00:01:02,560 That looks like a lot of gunpowder to me. 15 00:01:04,840 --> 00:01:08,640 ..and making some of the most dangerous substances ever known. 16 00:01:08,640 --> 00:01:11,120 It mustn't go above 18 degrees centigrade. 17 00:01:13,560 --> 00:01:16,840 It's a journey that will take us right to the centre of matter. 18 00:01:16,840 --> 00:01:19,120 Is that a split atom? Oh, yes. 19 00:01:19,120 --> 00:01:20,400 Wow! 20 00:01:20,400 --> 00:01:22,840 And the power it can unleash. 21 00:01:25,960 --> 00:01:31,640 This is the story of how we learnt to harness the forces that shook the world. 22 00:02:01,200 --> 00:02:05,560 The very first record we have of people using explosions comes from 23 00:02:05,560 --> 00:02:10,440 a Chinese document which could date from as far back as two centuries BC. 24 00:02:10,440 --> 00:02:14,440 It describes how travellers in the mountain wilderness of the West 25 00:02:14,440 --> 00:02:18,560 were threatened by shape-shifting creatures of the night. 26 00:02:18,560 --> 00:02:21,400 To scare away these creatures, 27 00:02:21,400 --> 00:02:24,440 they would lay lengths of bamboo on their campfires. 28 00:02:29,760 --> 00:02:33,600 BANG! The very first Chinese firecrackers. 29 00:02:33,600 --> 00:02:36,520 CRACKING AND HISSING 30 00:02:36,520 --> 00:02:41,000 The hissing noise we hear is moisture in the bamboo turning to steam, 31 00:02:41,000 --> 00:02:45,240 but bamboo has a special structure to it. 32 00:02:45,240 --> 00:02:48,160 It grows in sealed compartments. 33 00:02:48,160 --> 00:02:51,240 Now, when the moisture in these sealed compartments 34 00:02:51,240 --> 00:02:55,480 starts turning to steam, pressure builds up inside here. 35 00:02:55,480 --> 00:02:57,360 It can't go anywhere. 36 00:02:57,360 --> 00:02:59,440 Water, when it turns to steam, BANG! 37 00:02:59,440 --> 00:03:03,000 wants to expand hundreds of times, but there isn't room for it do that, 38 00:03:03,000 --> 00:03:04,200 so pressure builds up. 39 00:03:04,200 --> 00:03:07,840 Eventually the structure of the bamboo breaks down. Kcrrr! 40 00:03:07,840 --> 00:03:09,640 It explodes, 41 00:03:09,640 --> 00:03:13,680 scaring away shape-shifting creatures of the night. 42 00:03:15,400 --> 00:03:18,760 Using simple natural explosions like this 43 00:03:18,760 --> 00:03:23,840 was the first step of mankind's journey to harness explosive power, 44 00:03:23,840 --> 00:03:28,480 starting to understand the process in order to control it. 45 00:03:32,320 --> 00:03:35,200 It's easy enough to create an explosion. 46 00:03:35,200 --> 00:03:40,520 Any explosion is simply the moment when gas tries to expand suddenly. 47 00:03:41,520 --> 00:03:42,960 LOUD BANG Oh! 48 00:03:44,200 --> 00:03:49,440 And when that suddenly expanding air crashed into the air around it, 49 00:03:49,440 --> 00:03:54,640 it created a pressure wave that then moves through the surroundings. 50 00:03:54,640 --> 00:03:59,760 A sudden change in pressure forced a cloud of water droplets out of the air. 51 00:03:59,760 --> 00:04:01,960 These allow us to see the wave. 52 00:04:01,960 --> 00:04:04,240 The faster the gas is trying to expand, 53 00:04:04,240 --> 00:04:07,120 the more powerful the explosion, 54 00:04:07,120 --> 00:04:10,760 when that pressure wave hits your ear, you hear it as a bang. 55 00:04:12,280 --> 00:04:16,560 An explosion relies on a lot of gas trying to expand. 56 00:04:16,560 --> 00:04:20,800 Heat can make this happen, because heat, of course, makes things expand. 57 00:04:20,800 --> 00:04:24,000 Introducing more gas can do the same thing, 58 00:04:24,000 --> 00:04:29,440 but mankind discovered a way to create both heat and gas 59 00:04:29,440 --> 00:04:33,160 by reacting chemicals together and this was the start 60 00:04:33,160 --> 00:04:37,240 of our journey to really master explosive power. 61 00:04:41,800 --> 00:04:46,720 In Europe, chemical explosions were unknown until the medieval period, 62 00:04:46,720 --> 00:04:49,560 and the first time people came across them, 63 00:04:49,560 --> 00:04:51,480 they were a bit shocked. 64 00:04:51,480 --> 00:04:54,240 I've come to the Bodleian Library in Oxford 65 00:04:54,240 --> 00:04:58,000 to see a manuscript that describes one of these early encounters. 66 00:04:58,000 --> 00:05:02,120 It's one of the few copies of a book written in 1267 67 00:05:02,120 --> 00:05:04,960 by the medieval scholar Roger Bacon, 68 00:05:04,960 --> 00:05:10,240 who split his time between Oxford and Paris universities. 69 00:05:10,240 --> 00:05:15,560 Now, this particular passage that starts "et experimentum" 70 00:05:15,560 --> 00:05:19,840 describes his knowledge of man-made explosives at the time. 71 00:05:21,360 --> 00:05:24,840 "There is a children's toy, something no bigger than one's thumb, 72 00:05:24,840 --> 00:05:27,880 "made in many parts of the world, that is an example 73 00:05:27,880 --> 00:05:31,840 "of how something can assault the senses with sound and fire. 74 00:05:31,840 --> 00:05:35,040 "It is no more than a bit of parchment which contains a powder 75 00:05:35,040 --> 00:05:38,880 "combining the violence of that salt called saltpetre 76 00:05:38,880 --> 00:05:41,960 "together with sulphur and willow charcoal 77 00:05:41,960 --> 00:05:45,040 "but the bursting of this small thing assaults the ear 78 00:05:45,040 --> 00:05:48,040 "with a noise that exceeds the roar of thunder 79 00:05:48,040 --> 00:05:51,960 "and a flash brighter than the most brilliant lightning." 80 00:05:53,680 --> 00:05:57,720 Now, I suspect he might he may have been exaggerating slightly, 81 00:05:57,720 --> 00:06:00,320 but this was the first time that anyone in Europe 82 00:06:00,320 --> 00:06:02,360 had come across man-made explosives. 83 00:06:02,360 --> 00:06:04,720 Roger Bacon was a Franciscan friar, 84 00:06:04,720 --> 00:06:08,360 and the church at that time had envoys all over the world. 85 00:06:08,360 --> 00:06:10,760 It seems likely that one of those envoys 86 00:06:10,760 --> 00:06:13,160 must have posted a package back to him 87 00:06:13,160 --> 00:06:15,160 containing these children's toys. 88 00:06:15,160 --> 00:06:19,920 The big question is, though, where exactly did that package come from? 89 00:06:22,200 --> 00:06:23,560 In the Middle Ages, 90 00:06:23,560 --> 00:06:27,040 the most technologically-advanced region of the world was China. 91 00:06:27,040 --> 00:06:31,440 A printed book dating from before the battle of Hastings 92 00:06:31,440 --> 00:06:35,240 indicates that the Chinese were already deploying explosives 93 00:06:35,240 --> 00:06:38,240 of a similar sort on the battlefield. 94 00:06:38,240 --> 00:06:41,480 What we have here is a Chinese military manual 95 00:06:41,480 --> 00:06:44,040 first printed in 1044 96 00:06:44,040 --> 00:06:48,560 and in it, we find a recipe for a thing called 97 00:06:48,560 --> 00:06:51,200 the "fire mixture" or the "fire chemical" 98 00:06:51,200 --> 00:06:55,160 which contains the principal three ingredients 99 00:06:55,160 --> 00:06:58,920 in Roger Bacon's recipe of 200 years later. 100 00:06:58,920 --> 00:07:02,520 We start off with, here we have these two things here, 101 00:07:02,520 --> 00:07:05,760 they're both forms of what we now call sulphur... 102 00:07:05,760 --> 00:07:09,240 Right. ..followed by various forms of organic matter 103 00:07:09,240 --> 00:07:13,360 like pounded dried roots and twigs that produce the carbon, 104 00:07:13,360 --> 00:07:17,320 followed by saltpetre, the next one. 105 00:07:17,320 --> 00:07:21,520 The saltpetre is something you get from the decay of organic matter 106 00:07:21,520 --> 00:07:23,520 in relatively warm conditions. 107 00:07:23,520 --> 00:07:26,640 The Arabs refer to it is a Chinese snow. 108 00:07:26,640 --> 00:07:30,520 Right, so China was just a good place at the time, 109 00:07:30,520 --> 00:07:34,240 like, had the right climate for saltpetre to occur like that? 110 00:07:34,240 --> 00:07:36,960 There's a lot of things that come together, 111 00:07:36,960 --> 00:07:39,960 but the availability of the right climate is important. 112 00:07:39,960 --> 00:07:43,080 Can I try and start assembling it in the right proportions? 113 00:07:43,080 --> 00:07:49,000 Certainly. Well, roughly, you want to put in about 50% of saltpetre. 114 00:07:49,000 --> 00:07:51,000 For every one of those? 115 00:07:51,000 --> 00:07:54,720 Yeah, that's equal amounts of the powdered sulphur that we've got 116 00:07:54,720 --> 00:07:56,240 and the powdered charcoal. 117 00:07:56,240 --> 00:07:58,680 What were they trying to make at this point? 118 00:07:58,680 --> 00:08:02,360 This is a mixture for parcelling up and throwing, basically, 119 00:08:02,360 --> 00:08:06,320 into an enemy city using a catapult like this. 120 00:08:06,320 --> 00:08:09,960 This thing here is called a hui pao, which means a fire catapult. 121 00:08:09,960 --> 00:08:12,040 Now, from my knowledge of chemistry, 122 00:08:12,040 --> 00:08:15,440 saltpetre is what they call potassium nitrate. That's right. 123 00:08:15,440 --> 00:08:20,080 And that's got kind of oxygen bound up with nitrogen inside it. 124 00:08:20,080 --> 00:08:23,880 That's right. If we warm it up, it'll let the oxygen loose, 125 00:08:23,880 --> 00:08:26,800 and that will aid the burning of the other ingredients. 126 00:08:26,800 --> 00:08:31,520 The sulphur basically helps everything to happen at a rather lower temperature before 127 00:08:31,520 --> 00:08:36,840 and ultimately, of course, the carbon is the main source of the stuff that burns. 128 00:08:36,840 --> 00:08:39,480 And there we go, that's good, look at that! 129 00:08:39,480 --> 00:08:42,360 Take the flame away now. See it goes. That's very nice. 130 00:08:42,360 --> 00:08:43,600 That's fabulous! 131 00:08:45,400 --> 00:08:48,400 I'd call that an effective incendiary, wouldn't you? 132 00:08:48,400 --> 00:08:52,000 I can imagine once you get a bucket load of that landing in your camp... 133 00:08:52,000 --> 00:08:55,400 It's discouraging, isn't it? Makes you wish you hadn't come. Yes. 134 00:08:55,400 --> 00:09:01,200 The black powder that the Chinese military were using in 1044 had got 135 00:09:01,200 --> 00:09:04,960 grains of different chemicals close enough to react together 136 00:09:04,960 --> 00:09:07,040 and produce lots of heat and gases. 137 00:09:07,040 --> 00:09:10,840 In the open air, there's plenty of room for the gases to expand, 138 00:09:10,840 --> 00:09:12,960 so there was no sudden explosion, 139 00:09:12,960 --> 00:09:16,000 but the basic chemistry of gunpowder was there. 140 00:09:16,000 --> 00:09:18,920 However, an even older Chinese book 141 00:09:18,920 --> 00:09:22,280 suggests that the very first chemical explosive in the world 142 00:09:22,280 --> 00:09:25,600 had been developed 200 years before this. 143 00:09:25,600 --> 00:09:27,240 A book with the lovely title 144 00:09:27,240 --> 00:09:31,600 Classified Essentials Of The Mysterious Way Of The Origin Of All Things, 145 00:09:31,600 --> 00:09:35,440 which happens to contain a few recipes listed as, 146 00:09:35,440 --> 00:09:38,120 "Don't try this at home if you are an alchemist," 147 00:09:38,120 --> 00:09:43,760 and amongst that is a recipe which I think we ought to try. I'm game. 148 00:09:43,760 --> 00:09:46,360 You have some saltpetre. You have some sulphur. 149 00:09:46,360 --> 00:09:50,360 Those two ingredients. The carbon comes in the form of honey. 150 00:09:50,360 --> 00:09:52,920 OK, and what kind of quantities do you use? 151 00:09:52,920 --> 00:09:56,360 Oh, well, I would say most of that jar would get us 152 00:09:56,360 --> 00:09:58,280 something interesting happening. 153 00:09:58,280 --> 00:10:02,120 If you got about the same quantity of the other two ingredients, 154 00:10:02,120 --> 00:10:06,320 the saltpetre and the sulphur, that should go nicely. 155 00:10:06,320 --> 00:10:10,080 Why did they ever think of mixing these things together at this point? 156 00:10:10,080 --> 00:10:13,360 The idea is to try to subdue the fiery properties 157 00:10:13,360 --> 00:10:15,800 of the sulphur and of the saltpetre 158 00:10:15,800 --> 00:10:19,440 so that they will be suitable for taking as a medicine, 159 00:10:19,440 --> 00:10:22,520 hopefully an elixir of life. Oh, I see! 160 00:10:22,520 --> 00:10:26,600 'So, ironically, in trying to find a means to eternal life, 161 00:10:26,600 --> 00:10:29,960 'the Chinese alchemists found a substance that could kill.' 162 00:10:29,960 --> 00:10:32,480 I've never done any alchemy before. 163 00:10:32,480 --> 00:10:35,560 This is my first venture into the world of alchemy. 164 00:10:35,560 --> 00:10:38,720 If you make a success of it, it's a new career, really, isn't it? 165 00:10:38,720 --> 00:10:41,240 Potentially lucrative. Yes, indeed, indeed. 166 00:10:41,240 --> 00:10:43,120 That looks pretty well stirred. 167 00:10:43,120 --> 00:10:45,480 I would think now if you start cooking that, 168 00:10:45,480 --> 00:10:48,080 that will finish the mixing. 169 00:10:48,080 --> 00:10:52,640 Despite being earlier than the incendiary powder of 1044, 170 00:10:52,640 --> 00:10:57,040 the chemistry of this mixture has the potential to be more explosive. 171 00:10:57,040 --> 00:10:59,560 So because of the water in the honey, 172 00:10:59,560 --> 00:11:01,600 that is dissolving the saltpetre. 173 00:11:01,600 --> 00:11:06,120 Yes. And allowing that to carefully coat all the bits of sulphur. 174 00:11:06,120 --> 00:11:10,960 The particles of carbon and sulphur will now be very, very close to molecules of saltpetre 175 00:11:10,960 --> 00:11:13,360 which, when they get hot enough, 176 00:11:13,360 --> 00:11:18,000 will start releasing the oxygen just right up close to them. 177 00:11:18,000 --> 00:11:19,720 I think that's going to go in a sec. 178 00:11:19,720 --> 00:11:21,240 There's little puffs there. 179 00:11:21,240 --> 00:11:23,920 Exciting little puffs. I say. 180 00:11:23,920 --> 00:11:29,360 Just slightly move ourselves out of the immediate line of that. That's it. 181 00:11:30,560 --> 00:11:33,320 Whoa! OK... 182 00:11:33,320 --> 00:11:35,480 Wow! 183 00:11:38,880 --> 00:11:41,600 That was quite striking. Wow! 184 00:11:41,600 --> 00:11:45,520 Well, as the Chinese alchemist said, don't try this at home. 185 00:11:48,280 --> 00:11:52,840 So, incendiary mixtures were being explored by the Chinese alchemists 186 00:11:52,840 --> 00:11:55,440 as early as the mid-ninth century 187 00:11:55,440 --> 00:11:58,960 but from the 12th century, as China was swept by waves 188 00:11:58,960 --> 00:12:00,800 of war with neighbouring peoples, 189 00:12:00,800 --> 00:12:05,000 they started to use their fast-burning powder in a new way. 190 00:12:05,000 --> 00:12:07,000 No longer just an incendiary, 191 00:12:07,000 --> 00:12:10,360 it became an explosive propellant for projectiles. 192 00:12:10,360 --> 00:12:12,840 The Chinese gave their new weapons names, 193 00:12:12,840 --> 00:12:17,360 like the vast-as-heaven, enemy- exterminating yin-yang shovel, 194 00:12:17,360 --> 00:12:21,680 the scary, ingenious, mobile, ever-victorious poison-fire rack 195 00:12:21,680 --> 00:12:23,880 and my personal favourite, 196 00:12:23,880 --> 00:12:28,280 the orifices-penetrating flying-sand magic-mist tube. 197 00:12:28,280 --> 00:12:32,520 In all of them, they put the powder in a tightly confined space 198 00:12:32,520 --> 00:12:35,560 and this fundamentally altered the way it behaved. 199 00:12:35,560 --> 00:12:39,880 It was the discovery that would change warfare forever. 200 00:12:39,880 --> 00:12:43,640 Confining gunpowder changes the speed of the reaction. 201 00:12:43,640 --> 00:12:47,960 It goes from something that just burns into something that really explodes. 202 00:12:53,520 --> 00:12:56,320 Gunpowder doesn't need air in order to burn. 203 00:12:56,320 --> 00:12:59,960 It gets all the oxygen required from the crystals of saltpetre, 204 00:12:59,960 --> 00:13:02,120 potassium nitrate, that are in there, 205 00:13:02,120 --> 00:13:06,240 which means it'll still burn in a confined space 206 00:13:06,240 --> 00:13:10,200 and putting it in a confined space increases the rate of reaction. 207 00:13:10,200 --> 00:13:12,240 Put a little bit in here. 208 00:13:12,240 --> 00:13:14,440 So I'm going to wrap it up. 209 00:13:17,000 --> 00:13:19,560 When it's confined like this, all those grains, 210 00:13:19,560 --> 00:13:22,520 the carbon, the sulphur and the potassium nitrate, 211 00:13:22,520 --> 00:13:25,040 are all much closer together, which means 212 00:13:25,040 --> 00:13:29,360 the reaction can happen more quickly, and as the reaction happens more quickly, 213 00:13:29,360 --> 00:13:33,720 more heat's created, making the reaction go even faster and it's a runaway process. 214 00:13:33,720 --> 00:13:35,240 Right. 215 00:13:35,240 --> 00:13:39,680 With gas being produced so quickly and heat making it expand, 216 00:13:39,680 --> 00:13:42,880 there's the potential for explosive force, 217 00:13:42,880 --> 00:13:46,080 if I can channel it like the Chinese did. 218 00:13:46,080 --> 00:13:49,920 This is my first attempt at a cannon. 219 00:13:49,920 --> 00:13:52,760 I've decided to build it out of clear acrylic 220 00:13:52,760 --> 00:13:55,880 so that we get to see what happens inside a cannon. 221 00:13:55,880 --> 00:13:58,720 Now, I'll drop that on there. 222 00:13:58,720 --> 00:14:00,720 That fits in nicely. 223 00:14:02,680 --> 00:14:04,200 Got my cannonball. 224 00:14:07,400 --> 00:14:11,120 So there it is. There's going to be an explosion in there. 225 00:14:11,120 --> 00:14:15,360 That explosion will produce hot, expanding gas. 226 00:14:15,360 --> 00:14:18,880 There'll be a big pressure rise in that part of the chamber. 227 00:14:18,880 --> 00:14:22,640 That pressure will exert a force all around the container, 228 00:14:22,640 --> 00:14:25,920 but these three sides should stay where they are. 229 00:14:25,920 --> 00:14:29,040 This fourth side here, where the tennis ball is, 230 00:14:29,040 --> 00:14:32,440 won't stay where it is, and that tennis ball will leave at 231 00:14:32,440 --> 00:14:36,640 an undetermined speed that I suspect will be pretty quick. 232 00:14:36,640 --> 00:14:37,920 Let's find out. 233 00:14:44,880 --> 00:14:48,000 Three, two, one! 234 00:14:54,080 --> 00:14:58,200 Yeah, that worked like a cannon should work. 235 00:14:58,200 --> 00:14:59,400 Wow! 236 00:15:00,400 --> 00:15:04,040 You can see how the gunpowder produces hot gases 237 00:15:04,040 --> 00:15:05,480 at just the right rate 238 00:15:05,480 --> 00:15:08,320 to push the ball out. 239 00:15:08,320 --> 00:15:11,600 This technology quickly spread west, through the Middle East, 240 00:15:11,600 --> 00:15:16,520 and by the 14th century, the Europeans had rockets and guns too. 241 00:15:18,960 --> 00:15:23,800 But something else was happening - gunpowder was spreading beyond the battlefield. 242 00:15:23,800 --> 00:15:28,400 Its power was being put to work in mines and engineering projects, 243 00:15:28,400 --> 00:15:30,880 as Europe became more industrialised 244 00:15:30,880 --> 00:15:34,480 and there was demand for more powerful and destructive explosions. 245 00:15:35,480 --> 00:15:38,320 Gunpowder had reigned for 500 years, 246 00:15:38,320 --> 00:15:42,400 but now its dominance was about to be challenged. 247 00:15:43,920 --> 00:15:47,360 The middle of the 19th century provided a turning point 248 00:15:47,360 --> 00:15:49,080 in the story of explosives. 249 00:15:49,080 --> 00:15:52,560 I've had to come here, to the Defence Academy of the UK, 250 00:15:52,560 --> 00:15:57,560 because we're going to make what they first discovered in 1846. 251 00:15:58,560 --> 00:16:03,000 There was a growing tradition of pure scientific research in Europe, 252 00:16:03,000 --> 00:16:08,360 with researchers trying to understand the chemical composition of natural substances. 253 00:16:08,360 --> 00:16:13,400 One of these chemists was a German from a humble background called Christian Schonbein. 254 00:16:13,400 --> 00:16:18,000 He was naive, unconventional and full of original ideas. 255 00:16:18,000 --> 00:16:21,320 Working in Switzerland, he'd seen some unusual reactions with 256 00:16:21,320 --> 00:16:26,360 concentrated acids and was keen to investigate them further. 257 00:16:26,360 --> 00:16:32,560 One of those investigations was unwittingly to change the world of explosives forever. 258 00:16:32,560 --> 00:16:35,560 Professor Jackie Akhavan has volunteered to show us 259 00:16:35,560 --> 00:16:37,840 exactly what Schonbein did. 260 00:16:37,840 --> 00:16:40,360 Jackie, what are we actually doing here? 261 00:16:40,360 --> 00:16:44,680 OK, we're mixing nitric acid and sulphuric acid together 262 00:16:44,680 --> 00:16:47,360 and then we're going to add some cotton wool to it, 263 00:16:47,360 --> 00:16:49,480 to hopefully nitrate the cotton wool. 264 00:16:49,480 --> 00:16:53,360 Schonbein didn't know it, but the cotton will be acting 265 00:16:53,360 --> 00:16:56,560 as a source of carbon, like the charcoal in gunpowder 266 00:16:56,560 --> 00:17:00,000 and by nitrating it, he added oxygen and nitrogen 267 00:17:00,000 --> 00:17:04,000 from the acid actually into the molecules of the cotton, 268 00:17:04,000 --> 00:17:07,440 rather than just being in neighbouring grains. 269 00:17:07,440 --> 00:17:11,160 We must make sure the temperature remains cool. 270 00:17:11,160 --> 00:17:14,760 So I'm going to put a thermometer in so we can measure the temperature. 271 00:17:14,760 --> 00:17:18,280 Do you want to help? I do. What temperature should I watch out for? 272 00:17:18,280 --> 00:17:21,080 OK, it mustn't go above 18 degrees centigrade. 273 00:17:21,080 --> 00:17:23,640 I'm going to adjust this. Could you give me an update? 274 00:17:23,640 --> 00:17:25,280 It's at 21 at the moment. Right. 275 00:17:25,280 --> 00:17:28,560 I don't want to scare anybody. No, it's OK. What we'll do, 276 00:17:28,560 --> 00:17:30,800 we'll just cool it down a bit. OK. 277 00:17:30,800 --> 00:17:32,440 So what temperature are we now? 278 00:17:32,440 --> 00:17:36,120 It's down to 19. OK, well, we need to get it a bit cooler. 279 00:17:38,400 --> 00:17:40,640 We're down to 18.4. OK. 280 00:17:40,640 --> 00:17:43,400 What's the danger if the temperature starts rising? 281 00:17:43,400 --> 00:17:45,560 We want to keep control of this reaction. 282 00:17:45,560 --> 00:17:46,880 I'm very conscious of this. 283 00:17:46,880 --> 00:17:52,520 That's OK. I know battery acid's quite horrifically dangerous and if that's just as dangerous. 284 00:17:52,520 --> 00:17:55,320 It's much... These are very concentrated acids, 285 00:17:55,320 --> 00:17:57,760 so we've got to be extremely careful. 286 00:17:57,760 --> 00:18:01,640 'The nitration reaction changes the cotton chemically so that now, 287 00:18:01,640 --> 00:18:05,080 'just like in the gunpowder mix, there are carbon, nitrogen 288 00:18:05,080 --> 00:18:08,520 'and oxygen atoms, an explosive reaction waiting to happen, 289 00:18:08,520 --> 00:18:13,320 'but in this substance they're actually all in the same molecule, 290 00:18:13,320 --> 00:18:16,200 'so much closer together than in gunpowder. 291 00:18:16,200 --> 00:18:20,760 'Schonbein had accidentally created a much more efficient explosive.' 292 00:18:20,760 --> 00:18:24,720 So this is it, our nitrocellulose, or guncotton as it's known. 293 00:18:24,720 --> 00:18:29,040 That's right. I mean, now we've washed the acid off and dried it, 294 00:18:29,040 --> 00:18:31,240 it feels exactly like cotton wool. 295 00:18:31,240 --> 00:18:32,800 Just like we started with. 296 00:18:32,800 --> 00:18:36,320 The only difference with this one, compared to the cotton wool, 297 00:18:36,320 --> 00:18:40,360 is that we've got the oxygen actually linked to the fuel. 298 00:18:40,360 --> 00:18:42,600 So because we've changed every single molecule 299 00:18:42,600 --> 00:18:44,800 of the cotton to guncotton, 300 00:18:44,800 --> 00:18:48,160 then it's going to go exactly the same every time? Yes. 301 00:18:48,160 --> 00:18:49,920 Go on, then. Right. Are you ready? 302 00:18:49,920 --> 00:18:52,360 I'm more than a little intrigued. 303 00:18:54,000 --> 00:18:56,120 Stand back. 304 00:18:56,120 --> 00:18:57,960 I am already. Ready? 305 00:19:02,640 --> 00:19:04,720 That gives off a lot of heat. 306 00:19:04,720 --> 00:19:08,400 Heat, light, lots of gas being given out and then you can just have 307 00:19:08,400 --> 00:19:11,960 a look, and there's sort of black bits there, that's the carbon. 308 00:19:11,960 --> 00:19:13,480 So it hasn't fully oxidised. 309 00:19:13,480 --> 00:19:16,880 So there's not enough oxygen for all the carbon that's in the molecules, 310 00:19:16,880 --> 00:19:19,360 so we're just left with some carbon. That's right. 311 00:19:19,360 --> 00:19:21,800 That's a very, very rapid burnout. Whoof. 312 00:19:21,800 --> 00:19:24,920 Like with the gunpowder when you just set it on fire, 313 00:19:24,920 --> 00:19:27,720 it's unconfined, so you don't get an explosion, 314 00:19:27,720 --> 00:19:29,560 you just get this rapid burning. 315 00:19:29,560 --> 00:19:33,120 It all goes up into the atmosphere and it's all disappeared as gases 316 00:19:33,120 --> 00:19:35,160 and that's what you're left with. 317 00:19:35,160 --> 00:19:37,680 I like it. Can we do some more? You can indeed. 318 00:19:40,320 --> 00:19:44,680 Just like gunpowder, guncotton simply burns when there's room 319 00:19:44,680 --> 00:19:47,360 for the gases it produces to expand into 320 00:19:47,360 --> 00:19:50,880 but it burns faster, and the faster the gases are produced, 321 00:19:50,880 --> 00:19:54,040 the greater the explosive potential. 322 00:19:54,040 --> 00:19:57,200 Schonbein recognised it and immediately started 323 00:19:57,200 --> 00:20:01,560 sending out samples to colleagues and writing about his discovery. 324 00:20:03,840 --> 00:20:05,720 One of the first to react to the news 325 00:20:05,720 --> 00:20:09,240 was the Cornish mining community in the far southwest of England. 326 00:20:09,240 --> 00:20:13,440 The area is rich in resources like tin and granite 327 00:20:13,440 --> 00:20:17,240 and it made it a worldwide centre for mining. 328 00:20:17,240 --> 00:20:20,040 It was a vital and profitable industry for England 329 00:20:20,040 --> 00:20:22,360 and in the mid-19th century, 330 00:20:22,360 --> 00:20:27,040 it relied heavily on gunpowder to break up the rock. 331 00:20:27,040 --> 00:20:32,440 By the 1840s, miners had been using gunpowder in mines like this 332 00:20:32,440 --> 00:20:33,680 for 200 years. 333 00:20:35,360 --> 00:20:38,200 But gunpowder was far from reliable. It was dangerous, 334 00:20:38,200 --> 00:20:41,800 unpredictable and difficult to use. 335 00:20:41,800 --> 00:20:45,000 Mine historian Richard Williams has promised to show me just 336 00:20:45,000 --> 00:20:49,080 how difficult, starting with how they got it deep within the rock. 337 00:20:49,080 --> 00:20:53,320 You're trying to actually push a hole into the rock using what they 338 00:20:53,320 --> 00:20:56,760 called a bore, basically, an iron bar about 3ft long. 339 00:20:56,760 --> 00:20:59,760 Right. And a heavy hammer. Can I have a go? 340 00:20:59,760 --> 00:21:01,480 I'd love to have a go. 341 00:21:03,240 --> 00:21:04,880 Keep turning it. 342 00:21:07,760 --> 00:21:09,440 I can see that taking a while. 343 00:21:09,440 --> 00:21:11,640 It would probably take you a good 20 minutes. 344 00:21:11,640 --> 00:21:14,320 I can imagine once you've done your 3ft hole, 345 00:21:14,320 --> 00:21:17,240 you'd want to get the best bang out of it you could. 346 00:21:17,240 --> 00:21:22,320 Oh, yes. The next thing is to charge it, to fill it with gunpowder. 347 00:21:22,320 --> 00:21:26,320 You can imagine if they're working with candles or open lamps and 348 00:21:26,320 --> 00:21:30,000 gunpowder, it's not a great combination. 349 00:21:30,000 --> 00:21:33,200 OK, so once they've got the gunpowder into the hole there, 350 00:21:33,200 --> 00:21:34,760 how do they safely light it? 351 00:21:34,760 --> 00:21:37,280 They used a goose quill. 352 00:21:37,280 --> 00:21:40,720 Basically the centre of the quill is hollow. Yeah. 353 00:21:40,720 --> 00:21:43,720 So you cut off the top, you end up with something like that. 354 00:21:43,720 --> 00:21:46,960 You grind your gunpowder up until its fine enough to go into 355 00:21:46,960 --> 00:21:49,360 the hollow. Yeah. Tamp that down. 356 00:21:49,360 --> 00:21:54,280 Make several of those, push one into another and slowly you make a fuse. 357 00:21:54,280 --> 00:21:57,800 And they're all packed with gunpowder, so I can see, 358 00:21:57,800 --> 00:22:00,040 but what was the burn-time on them? 359 00:22:00,040 --> 00:22:01,640 Like, how quick did they go? 360 00:22:01,640 --> 00:22:03,280 They were unpredictable. 361 00:22:03,280 --> 00:22:05,520 If you didn't pack them correctly, 362 00:22:05,520 --> 00:22:07,480 they would go off a bit like a rocket. 363 00:22:07,480 --> 00:22:10,360 That's horrendous. Well, when we're doing it, 364 00:22:10,360 --> 00:22:14,800 we're actually going to use a safety fuse and we've already made a charge up 365 00:22:14,800 --> 00:22:18,280 and we've filled this with gunpowder and we've already got 366 00:22:18,280 --> 00:22:22,400 a hole drilled. The hole is going back into the rock. OK. 367 00:22:22,400 --> 00:22:26,040 So we put the powder into the hole. 368 00:22:26,040 --> 00:22:28,880 They would then get a tamping rod to push it in. 369 00:22:30,680 --> 00:22:33,480 Next thing is to stem it, to seal it. Right. 370 00:22:33,480 --> 00:22:36,400 If we left it like that, it would shoot just like a gun. 371 00:22:36,400 --> 00:22:38,800 Visually, this looks quite a short fuse to me. 372 00:22:38,800 --> 00:22:41,760 How much time have we got from when we light it? 373 00:22:41,760 --> 00:22:44,800 This is going to take slightly over a minute and a half 374 00:22:44,800 --> 00:22:46,760 to burn through to the gunpowder. 375 00:22:46,760 --> 00:22:50,800 That seems quite quick, but I'll trust you. I'm going to wear my goggles, though. 376 00:22:51,840 --> 00:22:53,960 Away it goes. 377 00:23:00,080 --> 00:23:01,720 Here we go. Look at that. 378 00:23:01,720 --> 00:23:02,760 I say look at that - 379 00:23:02,760 --> 00:23:05,720 should we not be moving in that direction quite quickly? 380 00:23:05,720 --> 00:23:09,280 I think we should leave now, yes. Yeah. 381 00:23:09,280 --> 00:23:12,600 So we can just literally just pop round the corner here? 382 00:23:12,600 --> 00:23:16,840 Round the corner so we'll be out of the way of anything that flies down through the tunnel. 383 00:23:22,880 --> 00:23:26,040 You start to wonder if it's going to go. 384 00:23:29,040 --> 00:23:30,560 But it went! 385 00:23:33,360 --> 00:23:36,480 The reverberation afterwards as well, which I guess is 386 00:23:36,480 --> 00:23:39,760 the multiple shock wave bouncing off all sorts of walls. 387 00:23:39,760 --> 00:23:44,600 Well, there we go, you look down the level and we should see the smoke. 388 00:23:46,680 --> 00:23:51,600 Right, you can actually see the fumes are close to the roof looking down through. 389 00:23:52,600 --> 00:23:55,840 Oh, yeah. It's getting thicker as we get close to the... 390 00:23:55,840 --> 00:23:57,480 It's getting a bit acrid. Yeah. 391 00:23:57,480 --> 00:24:01,440 'The smoke was one of the things that miners hated about gunpowder. 392 00:24:01,440 --> 00:24:04,480 'It filled the tunnels and made working difficult.' 393 00:24:04,480 --> 00:24:08,280 What's actually happened is it's blown the studding out. 394 00:24:08,280 --> 00:24:11,680 We haven't moved any rock at all, have we? No. 395 00:24:11,680 --> 00:24:18,840 'So not only was gunpowder difficult and time-consuming for miners to use, it wasn't even that reliable. 396 00:24:18,840 --> 00:24:25,040 'Schonbein's new guncotton promised more power, more reliability and no smoke.' 397 00:24:25,040 --> 00:24:29,920 In August 1846, the Royal Geological Society of Cornwall 398 00:24:29,920 --> 00:24:34,240 invited him to come to England to prove its worth. 399 00:24:34,240 --> 00:24:38,600 Schonbein demonstrated his guncotton in a quarry like this. 400 00:24:38,600 --> 00:24:45,440 The quarrymen drilled several holes in the rock, and into one, they packed a full charge of gunpowder 401 00:24:45,440 --> 00:24:48,920 and into another, just a quarter of the amount of guncotton. 402 00:24:48,920 --> 00:24:53,240 So innocent did the guncotton look that one man said he would sit 403 00:24:53,240 --> 00:24:56,280 on the hole in return for a drink at the local pub. 404 00:24:56,280 --> 00:24:59,200 Luckily, he was persuaded to watch the test 405 00:24:59,200 --> 00:25:02,080 before committing himself to the bargain. 406 00:25:04,400 --> 00:25:05,760 First, 30g of gunpowder. 407 00:25:05,760 --> 00:25:08,760 Let's see if it's more successful than in the mine. 408 00:25:16,360 --> 00:25:21,800 Well, the rock split, but not at the hole where the explosives were. 409 00:25:21,800 --> 00:25:26,720 It looks like that explosion there maybe sent some kind of shock 410 00:25:26,720 --> 00:25:28,840 through the rock and it peeled off here, 411 00:25:28,840 --> 00:25:31,560 where possibly there was some sort of fault line. 412 00:25:34,880 --> 00:25:37,120 Now we'll try just 5g of guncotton, 413 00:25:37,120 --> 00:25:40,440 looking like it couldn't possibly do much damage. 414 00:25:46,400 --> 00:25:48,400 That's a completely different story. 415 00:25:49,520 --> 00:25:54,840 In slow motion, you can clearly see all the gases the explosion creates. 416 00:25:54,840 --> 00:25:59,760 Brown nitric oxide, steam and others, splitting the rock apart. 417 00:26:08,240 --> 00:26:10,280 That's just astonishing. 418 00:26:10,280 --> 00:26:13,720 A couple of hundred kilos of rock has practically disappeared. 419 00:26:13,720 --> 00:26:16,360 There's some fragments over there, 420 00:26:16,360 --> 00:26:17,920 bits down here. 421 00:26:17,920 --> 00:26:20,720 And look at that. 422 00:26:20,720 --> 00:26:25,360 Where it was actually placed, there's nothing at all. 423 00:26:25,360 --> 00:26:26,960 Like that. 424 00:26:26,960 --> 00:26:29,080 Look down here. 425 00:26:29,080 --> 00:26:33,200 That's the hole where it was packed in. So this was the other way up. 426 00:26:33,200 --> 00:26:34,720 You can see where the clay was, 427 00:26:34,720 --> 00:26:38,080 you can see all the way down here and it's just split it. 428 00:26:38,080 --> 00:26:42,240 Now, this is guncotton and what's happened here is when 429 00:26:42,240 --> 00:26:47,840 the guncotton has been compacted, confined in there, it's detonated, 430 00:26:47,840 --> 00:26:51,360 which is a completely different process to when we saw it being lit. 431 00:26:51,360 --> 00:26:52,440 It burnt rapidly. 432 00:26:52,440 --> 00:26:55,560 This detonation sends out a sharp shock wave 433 00:26:55,560 --> 00:26:58,960 and as it goes into the rock, the rock gets split. 434 00:26:58,960 --> 00:27:03,120 It's a much more powerful explosion, and I can imagine the Cornish miners 435 00:27:03,120 --> 00:27:04,920 feeling a little bit like me now, 436 00:27:04,920 --> 00:27:10,480 almost overwhelmed at the difference between gunpowder and guncotton. 437 00:27:11,680 --> 00:27:14,960 The quarrymen were amazed at the new guncotton 438 00:27:14,960 --> 00:27:18,600 and mercilessly teased the colleague who had offered to sit on it. 439 00:27:18,600 --> 00:27:21,960 They were immediately interested and Schonbein quickly found 440 00:27:21,960 --> 00:27:24,720 an English partner to start manufacture. 441 00:27:24,720 --> 00:27:27,600 His apparent success soon inspired others. 442 00:27:27,600 --> 00:27:31,920 Schonbein wasn't the only one experimenting with these kind of chemicals. 443 00:27:31,920 --> 00:27:36,120 Not long afterwards, an Italian chemist, Ascanio Sobrero, 444 00:27:36,120 --> 00:27:41,120 reacted nitric acid with glycerine, another carbon-rich substance. 445 00:27:41,120 --> 00:27:44,480 Sobrero had worked on nitration before, 446 00:27:44,480 --> 00:27:46,960 and when he read of Schonbein's discovery, 447 00:27:46,960 --> 00:27:48,760 he was inspired to return to it. 448 00:27:48,760 --> 00:27:50,320 He was originally a medic, 449 00:27:50,320 --> 00:27:53,320 so many of his interests were in potential new drugs. 450 00:27:53,320 --> 00:27:59,040 The result of this experiment, first done in 1846, is in fact still 451 00:27:59,040 --> 00:28:04,080 an important heart medicine, but it has another side to its character. 452 00:28:04,080 --> 00:28:07,880 Dr Alex Contini is one of the few chemists experienced enough 453 00:28:07,880 --> 00:28:10,080 to attempt this process 454 00:28:10,080 --> 00:28:14,560 and he isn't going to trust his life to me keeping an eye on the thermometer this time. 455 00:28:14,560 --> 00:28:16,160 Seven and rising... 456 00:28:18,320 --> 00:28:22,200 Each time the glycerine is added to the concentrated acids, 457 00:28:22,200 --> 00:28:25,200 he has to stir it and make sure it stays cool. 458 00:28:25,200 --> 00:28:27,520 Every degree of temperature rise 459 00:28:27,520 --> 00:28:30,760 makes a premature explosion more likely. 460 00:28:30,760 --> 00:28:33,480 Ten and rising... 461 00:28:46,440 --> 00:28:49,320 The resulting oily liquid, like guncotton, 462 00:28:49,320 --> 00:28:53,760 contains carbon atoms linked to nitrogen and oxygen groups. 463 00:28:53,760 --> 00:28:55,680 It looks fairly innocuous, 464 00:28:55,680 --> 00:29:00,320 but Sobrero discovered it has some pretty surprising properties. 465 00:29:00,320 --> 00:29:04,840 And we're only going to use the tiniest amount to show them. 466 00:29:04,840 --> 00:29:08,600 Sobrero wrote that the safest way to demonstrate these properties 467 00:29:08,600 --> 00:29:12,240 was to dip a hot wire into a glass bowl of the substance, 468 00:29:12,240 --> 00:29:15,000 but he was scarred for life by flying glass, 469 00:29:15,000 --> 00:29:18,520 so we are going to try something different. 470 00:29:27,360 --> 00:29:32,520 If you look down there, you'll see the nitroglycerine has completely disappeared. 471 00:29:32,520 --> 00:29:37,360 Every molecule of the liquid nitroglycerine gets turned to gas and goes, 472 00:29:37,360 --> 00:29:40,960 hence the massive expansion, hence the massive explosion. 473 00:29:42,480 --> 00:29:45,480 Whilst guncotton only detonates when confined, 474 00:29:45,480 --> 00:29:48,800 nitroglycerine can detonate when given a simple sharp shock. 475 00:29:51,400 --> 00:29:54,600 Even slowed down more than 500 times, 476 00:29:54,600 --> 00:29:57,200 the explosion is incredibly fast. 477 00:29:58,920 --> 00:30:03,200 This new behaviour made guncotton and nitroglycerine 478 00:30:03,200 --> 00:30:05,760 quite different from gunpowder. 479 00:30:05,760 --> 00:30:09,600 The difference between gunpowder and these new high explosives, 480 00:30:09,600 --> 00:30:12,160 as they're called, is the way they explode. 481 00:30:12,160 --> 00:30:15,920 Gunpowder burns - albeit very rapidly, it's still burning. 482 00:30:15,920 --> 00:30:18,680 One piece heating the piece adjacent to it, 483 00:30:18,680 --> 00:30:20,560 the piece that's adjacent to that - 484 00:30:20,560 --> 00:30:22,560 fwooh! - till the whole thing's gone. 485 00:30:22,560 --> 00:30:25,040 With high explosives, it's detonation. 486 00:30:25,040 --> 00:30:29,200 A pressure wave travels extremely quickly through the whole charge 487 00:30:29,200 --> 00:30:31,440 and it almost goes instantaneously. 488 00:30:31,440 --> 00:30:34,720 The first bit of the reaction in a high explosive 489 00:30:34,720 --> 00:30:39,560 creates so much gas so quickly it generates a pressure wave 490 00:30:39,560 --> 00:30:41,720 that hits the rest of the explosive. 491 00:30:41,720 --> 00:30:45,680 I'll show you, with this fire piston, as it's called, 492 00:30:45,680 --> 00:30:48,640 and a tiny bit of normal cotton wool. 493 00:30:48,640 --> 00:30:53,080 As the piston comes down, it acts like the explosive pressure wave, 494 00:30:53,080 --> 00:30:55,320 raising the pressure inside the tube. 495 00:30:55,320 --> 00:30:57,320 That pressure heats the air so much 496 00:30:57,320 --> 00:31:01,120 that the cotton wool bursts into flame. 497 00:31:01,120 --> 00:31:03,800 It's the same with a piece of high explosive. 498 00:31:03,800 --> 00:31:08,040 It's the sudden rise in pressure that gives the sudden rise in temperature 499 00:31:08,040 --> 00:31:11,760 that triggers the explosive as it runs through the entire charge. 500 00:31:11,760 --> 00:31:13,880 Now, this thing happens so quickly, 501 00:31:13,880 --> 00:31:17,400 you pretty much get the entire lot going in one go. 502 00:31:19,640 --> 00:31:20,960 Watch this. 503 00:31:22,000 --> 00:31:26,560 This is detonating cord. It's a spun cord with a line of high explosive 504 00:31:26,560 --> 00:31:28,360 right down the centre of it. 505 00:31:28,360 --> 00:31:30,320 When it's detonated at one end, 506 00:31:30,320 --> 00:31:33,960 the wave front moves extremely quickly right down its length. 507 00:31:41,640 --> 00:31:45,960 Slowing the process down 250 times, you can see the detonation 508 00:31:45,960 --> 00:31:49,080 travelling at about 6km a second. 509 00:31:51,400 --> 00:31:55,320 When the force of the detonation wave hits the surrounding air, 510 00:31:55,320 --> 00:31:57,520 it creates a supersonic shock wave. 511 00:31:57,520 --> 00:32:00,880 You can see the shock wave distort the air like a bubble, 512 00:32:00,880 --> 00:32:03,520 coming out around this modern high explosive. 513 00:32:05,520 --> 00:32:09,200 Shock waves and reaction speeds like this were a phenomenon 514 00:32:09,200 --> 00:32:11,000 nobody had come across before 515 00:32:11,000 --> 00:32:14,240 and it made these new high explosives very powerful 516 00:32:14,240 --> 00:32:16,760 and potentially very dangerous. 517 00:32:16,760 --> 00:32:19,080 And that was the problem. 518 00:32:19,080 --> 00:32:22,760 Only months after it opened, the world's first guncotton factory 519 00:32:22,760 --> 00:32:25,360 exploded disastrously in England 520 00:32:25,360 --> 00:32:30,520 and Sobrero's new nitroglycerine appeared even more dangerous. 521 00:32:30,520 --> 00:32:33,880 It seemed there might be no way of safely harnessing 522 00:32:33,880 --> 00:32:35,880 this new-found power. 523 00:32:35,880 --> 00:32:39,560 But the industrialised world was crying out for it. 524 00:32:39,560 --> 00:32:42,400 The men working the great tin and coal mines of Britain 525 00:32:42,400 --> 00:32:47,040 were still having to use the centuries-old, inefficient gunpowder 526 00:32:47,040 --> 00:32:51,640 and attempts to build a canal system to move the vital raw materials 527 00:32:51,640 --> 00:32:54,480 produced by the mines to Britain's ports 528 00:32:54,480 --> 00:32:57,120 were hampered by gunpowder's lack of power. 529 00:32:59,120 --> 00:33:02,280 But in the 1850s, a young Swedish student 530 00:33:02,280 --> 00:33:04,960 came to hear about nitroglycerine. 531 00:33:04,960 --> 00:33:07,000 His name was Alfred Nobel 532 00:33:07,000 --> 00:33:10,960 and his family were explosives manufacturers in need of money. 533 00:33:10,960 --> 00:33:15,720 They took the risk of trying to manufacture nitroglycerine, 534 00:33:15,720 --> 00:33:18,320 but they had an awful lot to learn. 535 00:33:18,320 --> 00:33:22,920 In their first year of manufacture, their factory in Sweden exploded, 536 00:33:22,920 --> 00:33:25,480 killing Alfred's younger brother Emil. 537 00:33:25,480 --> 00:33:29,320 This is the site of Nobel's biggest explosives factory. 538 00:33:29,320 --> 00:33:32,560 It's at Ardeer on the west coast of Scotland and at its height, 539 00:33:32,560 --> 00:33:35,200 it was the biggest explosives factory in Europe. 540 00:33:38,960 --> 00:33:40,560 Nobel liked it. 541 00:33:40,560 --> 00:33:45,320 One, because it was remote, but two, it was built entirely on sand, 542 00:33:45,320 --> 00:33:49,000 meaning he could create artificial landscapes like that. 543 00:33:56,200 --> 00:33:59,720 Nobel built what were called nitroglycerine hills. 544 00:33:59,720 --> 00:34:03,320 Nitroglycerine was made in little huts on the top of each hill. 545 00:34:03,320 --> 00:34:07,560 In each hut were two men, one to monitor the mixing reaction, 546 00:34:07,560 --> 00:34:10,760 the other to adjust the flow of water through a cooling jacket 547 00:34:10,760 --> 00:34:13,080 to keep the temperature in the right range. 548 00:34:13,080 --> 00:34:15,520 Now, vigilance was vital. 549 00:34:15,520 --> 00:34:19,720 The entire batch could self-detonate if allowed to go out of control. 550 00:34:19,720 --> 00:34:23,600 For this reason, one man had to always sit on a one-legged stool, 551 00:34:23,600 --> 00:34:26,440 so there was no chance of him falling asleep on the job. 552 00:34:26,440 --> 00:34:30,440 I mean, as if sitting next to a vat of nitroglycerine 553 00:34:30,440 --> 00:34:31,920 was not stimulation enough! 554 00:34:33,400 --> 00:34:36,240 Nitroglycerine could not be safely pumped. 555 00:34:36,240 --> 00:34:38,920 So what they did was just let it flow under gravity 556 00:34:38,920 --> 00:34:42,480 from the huts at the top of the hill to the factories at the bottom. 557 00:34:45,920 --> 00:34:49,440 Once inside the factory, it got stabilised. 558 00:34:49,440 --> 00:34:52,520 Now, this was what was Nobel's great achievement. 559 00:34:52,520 --> 00:34:58,840 He discovered that if he mixed his nitroglycerine with an absorbent clay, a bit like cat litter, 560 00:34:58,840 --> 00:35:01,320 it became a lot less sensitive, 561 00:35:01,320 --> 00:35:04,200 a lot easier to handle without going off in your hands. 562 00:35:04,200 --> 00:35:09,640 The clay he used came as a fine powder called kieselguhr. 563 00:35:11,160 --> 00:35:14,880 Once mixed together, a dough-like substance was formed. 564 00:35:14,880 --> 00:35:19,760 In fact, it was kneaded by armies of women into the shapes required. 565 00:35:26,200 --> 00:35:32,200 This new compound was called dynamite and it was a revolution. 566 00:35:32,200 --> 00:35:37,280 Now there was a high explosive that was insensitive to shock and heating. 567 00:35:37,280 --> 00:35:40,960 You could actually set fire to it and it would burn with a normal flame. 568 00:35:40,960 --> 00:35:43,640 I don't recommend it, but apparently you could, 569 00:35:43,640 --> 00:35:46,160 but once you've made something that's this good, 570 00:35:46,160 --> 00:35:48,680 that's this stable, this difficult to set off, 571 00:35:48,680 --> 00:35:52,000 how do you get it to explode when you want it to? 572 00:35:52,000 --> 00:35:54,400 That was Nobel's other great innovation. 573 00:35:54,400 --> 00:35:58,480 And they actually still make those devices at his old factory. 574 00:35:58,480 --> 00:36:03,680 In fact, Nobel's sand bunkers are the perfect place for me to find out more about them. 575 00:36:06,080 --> 00:36:09,760 Well, Alfred Nobel being the very inventive guy that he was, 576 00:36:09,760 --> 00:36:11,880 came up with the idea of a detonator 577 00:36:11,880 --> 00:36:14,040 and this is a modern detonator, 578 00:36:14,040 --> 00:36:19,440 but the basic principle is a device which delivers an explosive 579 00:36:19,440 --> 00:36:25,320 shock to dynamite and that shock is sufficient to detonate it. 580 00:36:25,320 --> 00:36:28,000 I do actually have a cutaway here. 581 00:36:28,000 --> 00:36:31,480 At the top of the detonator we have an electrical fuse head 582 00:36:31,480 --> 00:36:36,720 and this is, in many ways, like the match. Yep. 583 00:36:36,720 --> 00:36:39,800 This is designed to initiate not by friction 584 00:36:39,800 --> 00:36:42,960 but by passing an electric current through it. 585 00:36:42,960 --> 00:36:48,320 That generates heat, which causes this fuse head to burst with 586 00:36:48,320 --> 00:36:50,560 hot gases and hot particles 587 00:36:50,560 --> 00:36:55,920 which then initiate a pallet of sensitive primary explosive. 588 00:36:55,920 --> 00:37:00,120 And out of more than just casual curiosity, 589 00:37:00,120 --> 00:37:03,720 a detonator like that, with that much explosive in it, 590 00:37:03,720 --> 00:37:06,880 how much damage would it do if just that went off? 591 00:37:06,880 --> 00:37:10,920 If I was holding this in my hand and it and it were to detonate, 592 00:37:10,920 --> 00:37:13,240 then I would lose the hand. 593 00:37:13,240 --> 00:37:15,160 Really? OK. 594 00:37:15,160 --> 00:37:18,040 I'll be very wary of detonators, then. Absolutely! 595 00:37:18,040 --> 00:37:22,840 'Of course, to demonstrate a detonator really doing its job, 596 00:37:22,840 --> 00:37:26,400 'we need to attach it to a block of less sensitive explosive. 597 00:37:26,400 --> 00:37:30,800 'Dynamite was the world's first mouldable plastic explosive 598 00:37:30,800 --> 00:37:33,480 'and we're using its modern equivalent.' 599 00:37:33,480 --> 00:37:39,520 That's a small sample, maybe about 30g of a new plastic explosive 600 00:37:39,520 --> 00:37:42,240 that we've developed here at Ardeer. 601 00:37:42,240 --> 00:37:45,480 I think I should double-check - I'm fine for handling this now? 602 00:37:45,480 --> 00:37:48,760 Oh, yes, it is perfectly safe. 603 00:37:48,760 --> 00:37:51,120 I guess because it looks like Play-Doh, 604 00:37:51,120 --> 00:37:54,480 you instantly want to treat it like Play-Doh. 605 00:37:54,480 --> 00:37:57,880 Well, it is a very special kind of Play-Doh, if you like. 606 00:37:57,880 --> 00:38:02,040 It's got that plasticity that Play-Doh has, but as with all explosives, 607 00:38:02,040 --> 00:38:05,120 they are very unforgiving when you give it the right stimulus. 608 00:38:05,120 --> 00:38:08,120 And that is a detonator. And that is a detonator. 609 00:38:08,120 --> 00:38:09,920 I'm going to ask Jim to come in and set up. 610 00:38:09,920 --> 00:38:12,600 Jim is one of our trained shot-firers, 611 00:38:12,600 --> 00:38:16,880 and only a shot-firer can set up. 612 00:38:16,880 --> 00:38:20,240 You've been handling that material with gloves. 613 00:38:20,240 --> 00:38:26,280 Jim is not wearing gloves because there is a risk of static with the electrically-initiated detonator. 614 00:38:26,280 --> 00:38:31,480 You'll notice again he's kept the detonator, the action end of the wires, in the box until the last 615 00:38:31,480 --> 00:38:35,600 minute, so if there is any accidental stray current 616 00:38:35,600 --> 00:38:41,360 he's minimised the chance of it causing any damage and then he just simply pops it into the holder, 617 00:38:41,360 --> 00:38:44,600 to make sure that there's contact with the explosive 618 00:38:44,600 --> 00:38:46,000 and it's now ready to go 619 00:38:46,000 --> 00:38:51,960 once we've cleared the site and Jim has armed the circuit. 620 00:38:51,960 --> 00:38:54,840 I feel my stomach change when he puts that in there. 621 00:38:54,840 --> 00:38:57,640 I honestly do. It's just... 622 00:38:57,640 --> 00:39:00,360 Like we're now... Shall we go? 623 00:39:00,360 --> 00:39:01,880 Yes. Right. 624 00:39:08,080 --> 00:39:09,160 Stand by. 625 00:39:17,680 --> 00:39:22,160 Effectively, that entire lump almost instantaneously goes from being 626 00:39:22,160 --> 00:39:25,480 a solid to a gas. Absolutely right. 627 00:39:25,480 --> 00:39:29,640 It's shockingly crisp. Yeah. That's what it's supposed to do, 628 00:39:29,640 --> 00:39:32,000 but if you look on the other side, 629 00:39:32,000 --> 00:39:34,520 you'll see something completely different. 630 00:39:34,520 --> 00:39:37,920 And that's the pressure wave that's ripped that out. 631 00:39:37,920 --> 00:39:43,200 Yeah, the shock wave travels through the plate, hits the underside and 632 00:39:43,200 --> 00:39:48,720 then just blasts off the scab and if we dig around we might just find 633 00:39:48,720 --> 00:39:52,080 the back end of that, because we've got a nice little hole here. 634 00:39:52,080 --> 00:39:55,680 So somewhere down there is the piece. 635 00:39:55,680 --> 00:39:59,240 Well, the secret is it's come all the way through 636 00:39:59,240 --> 00:40:01,360 and there... Get the sand off it. 637 00:40:01,360 --> 00:40:03,680 I'm shocked. There's the scab. 638 00:40:03,680 --> 00:40:05,720 It's come off the other side. 639 00:40:05,720 --> 00:40:08,880 It's more impressive than going through there, because nothing 640 00:40:08,880 --> 00:40:11,600 goes through railway sleepers, as a general rule. 641 00:40:11,600 --> 00:40:16,480 Nobel's struggle to tame the power of high explosives and make them 642 00:40:16,480 --> 00:40:21,120 safe tools for the hungry industrial world made him a very rich man. 643 00:40:21,120 --> 00:40:26,160 By safely harnessing the shattering power of nitroglycerine's detonation 644 00:40:26,160 --> 00:40:29,680 with dynamite and a range of other compounds, a new era 645 00:40:29,680 --> 00:40:33,680 of civil engineering opened up and great construction projects 646 00:40:33,680 --> 00:40:37,120 such as the Suez Canal, the London Underground system 647 00:40:37,120 --> 00:40:41,040 and then the Panama Canal could now be undertaken. 648 00:40:44,880 --> 00:40:47,240 And that might have been Nobel's legacy, 649 00:40:47,240 --> 00:40:50,520 if it weren't for a mistake that occurred in 1888. 650 00:40:50,520 --> 00:40:53,880 After the death of Alfred Nobel's elder brother Ludvig, 651 00:40:53,880 --> 00:40:58,280 some newspapers mistakenly printed Alfred Nobel's obituary instead. 652 00:40:58,280 --> 00:41:01,600 Where he was living in France at the time, 653 00:41:01,600 --> 00:41:05,560 Le Figaro printed this small but damning paragraph. 654 00:41:05,560 --> 00:41:09,480 It translates as, "A man who it would be difficult 655 00:41:09,480 --> 00:41:14,160 "to describe as a benefactor to humanity died yesterday in Cannes." 656 00:41:14,160 --> 00:41:17,720 Now, reading that must have been a bit of a shock, and it's said that 657 00:41:17,720 --> 00:41:20,680 it made Nobel intent on changing his legacy to the world. 658 00:41:20,680 --> 00:41:25,560 To that end, he left his vast fortune to setting up a foundation 659 00:41:25,560 --> 00:41:31,240 which would award prizes for literature, science and peace. 660 00:41:33,000 --> 00:41:39,000 Nobel's advances in explosive design were the result of long hours and hard work, 661 00:41:39,000 --> 00:41:45,080 but some revolutions in the history of explosives are sparked simply by a chance observation. 662 00:41:47,400 --> 00:41:51,200 In the same year that Nobel's obituary was accidentally published, 663 00:41:51,200 --> 00:41:53,200 an American chemist, Charles Monroe, 664 00:41:53,200 --> 00:41:55,520 was doing explosives work for the US Navy. 665 00:41:55,520 --> 00:41:58,720 He was one of the foremost explosives experts 666 00:41:58,720 --> 00:42:00,520 of the late 19th century. 667 00:42:00,520 --> 00:42:06,400 Then many high explosives came in blocks with the manufacturer's name embossed onto them. 668 00:42:08,400 --> 00:42:11,600 So I've got myself some high explosive 669 00:42:11,600 --> 00:42:15,360 onto which I'm going to stamp a corporate name. 670 00:42:17,760 --> 00:42:21,480 Now, as Monroe spotted, there was something very strange that happened 671 00:42:21,480 --> 00:42:25,560 when these stamped blocks were detonated near steel plate. 672 00:42:25,560 --> 00:42:28,440 Hopefully we'll get to see the same thing. 673 00:42:39,280 --> 00:42:40,520 Prime... 674 00:42:51,880 --> 00:42:53,440 That seemed big enough. 675 00:42:58,160 --> 00:42:59,680 Here we go. 676 00:43:01,280 --> 00:43:03,040 Yes. OK. 677 00:43:04,560 --> 00:43:09,240 You can now see the BBC logo stamped into a block of steel 678 00:43:09,240 --> 00:43:12,280 in the same way that the manufacturers' logos got stamped 679 00:43:12,280 --> 00:43:16,880 into the steel back in the 1880s, but what Monroe was particularly 680 00:43:16,880 --> 00:43:21,000 intrigued by was why it made this particular indentation 681 00:43:21,000 --> 00:43:23,880 from the indentation on the explosives 682 00:43:23,880 --> 00:43:26,480 and understanding the way in which this happens 683 00:43:26,480 --> 00:43:30,480 led to a completely new way of using explosives. 684 00:43:30,480 --> 00:43:32,520 When a lump of explosive detonates, 685 00:43:32,520 --> 00:43:35,840 the shock wave radiates out from every part of its surface. 686 00:43:37,720 --> 00:43:40,160 So you've got your dent in the explosive here 687 00:43:40,160 --> 00:43:43,320 and you've got your target there, 688 00:43:43,320 --> 00:43:45,360 as the shock wave comes out, 689 00:43:45,360 --> 00:43:49,120 instead of the bit at the back ending up with a weaker effect, 690 00:43:49,120 --> 00:43:51,600 it ends up actually stronger, 691 00:43:51,600 --> 00:43:55,360 because the shock wave is coming out in all directions, like this. 692 00:43:55,360 --> 00:43:59,240 When it reaches the centre of the indentation, they tend to meet, 693 00:43:59,240 --> 00:44:01,520 like jets of water in the middle of that dent 694 00:44:01,520 --> 00:44:05,080 and this effect here magnifies the shock wave that you've got leaving 695 00:44:05,080 --> 00:44:08,680 there, sending it into the plate and this is actually the area 696 00:44:08,680 --> 00:44:10,240 of maximum pressure here. 697 00:44:10,240 --> 00:44:14,000 And once this was understood, shock waves could be directed to 698 00:44:14,000 --> 00:44:17,640 focus the power of the explosion exactly where it was wanted. 699 00:44:17,640 --> 00:44:21,240 People started making cavities in their explosive to increase 700 00:44:21,240 --> 00:44:22,800 the power of the shock wave, 701 00:44:22,800 --> 00:44:26,720 but then, with the pressures of war, came a new step forward. 702 00:44:26,720 --> 00:44:29,000 When you line that cavity 703 00:44:29,000 --> 00:44:34,000 with a hard material, almost invariably metal, 704 00:44:34,000 --> 00:44:38,280 then you enter the domain of what's known as the shaped charge. 705 00:44:38,280 --> 00:44:40,040 Right. 706 00:44:40,040 --> 00:44:41,800 Conventional shaped charges 707 00:44:41,800 --> 00:44:44,400 are filled with high explosive in a factory. 708 00:44:44,400 --> 00:44:45,440 Right. 709 00:44:45,440 --> 00:44:50,880 This is something that I designed for filling by the user. 710 00:44:50,880 --> 00:44:54,320 It means that it can travel on aeroplanes and so on without... 711 00:44:54,320 --> 00:44:56,560 DIY shaped charges. Exactly that. 712 00:44:56,560 --> 00:44:57,600 Now, in this case 713 00:44:57,600 --> 00:45:03,480 we're going to go back to probably the first type of liner - 714 00:45:03,480 --> 00:45:06,640 this is called the liner - that was used in a shaped charge. 715 00:45:06,640 --> 00:45:09,520 That's just a cone of copper, isn't it? It is indeed. 716 00:45:09,520 --> 00:45:13,720 Having that copper on there, I guess it's the sort of 717 00:45:13,720 --> 00:45:17,000 the equivalent of using a bullet or a cannonball. 718 00:45:17,000 --> 00:45:22,280 It's the same, if you go - kcrrr! - and fire an empty cartridge, 719 00:45:22,280 --> 00:45:24,840 then you get a loud bang and an explosion, 720 00:45:24,840 --> 00:45:27,640 but nothing that's going to do any significant harm. 721 00:45:27,640 --> 00:45:31,360 Whereas if you put a bullet in the end of it, if you see what I mean, 722 00:45:31,360 --> 00:45:35,000 and fire it, then it pushes out something of a significant mass, 723 00:45:35,000 --> 00:45:36,600 and that can do some damage. 724 00:45:36,600 --> 00:45:41,080 Yes. The great advantage is that this metal travels enormously faster 725 00:45:41,080 --> 00:45:42,440 than any cannonball. 726 00:45:42,440 --> 00:45:44,160 I'll show you what I mean. 727 00:45:44,160 --> 00:45:48,960 If you put plastic explosive in here and then you push this copper cone 728 00:45:48,960 --> 00:45:53,640 into the explosive, when I initiate at this end, 729 00:45:53,640 --> 00:45:57,240 a detonation wave travels from here to there. 730 00:45:57,240 --> 00:46:00,320 Right. The first thing it hits is the apex of the cone 731 00:46:00,320 --> 00:46:02,960 and that apex of the cone is driven forward. 732 00:46:02,960 --> 00:46:05,720 The whole cone is collapsed. 733 00:46:05,720 --> 00:46:10,160 In fact, it collapses in such a way that it turns inside out. 734 00:46:10,160 --> 00:46:13,440 Right, because the end bits hit first and that starts moving. 735 00:46:13,440 --> 00:46:16,600 Wow, that's an astonishing thing to get your head round. 736 00:46:16,600 --> 00:46:18,600 It is a bit of a shock at first. 737 00:46:18,600 --> 00:46:22,560 What happens is that the inner part of the copper, not the whole 738 00:46:22,560 --> 00:46:25,520 mass of it, by any means, the inner part of the copper 739 00:46:25,520 --> 00:46:29,320 forms into a sort of wire, which is called the jet. 740 00:46:29,320 --> 00:46:32,800 And that's not molten, it's still solid copper. 741 00:46:32,800 --> 00:46:36,360 Yes, but coming not in that direction, coming in that direction. 742 00:46:36,360 --> 00:46:40,000 And that almost piles in like a nail through the steel, 743 00:46:40,000 --> 00:46:42,160 driving its way in. 744 00:46:42,160 --> 00:46:45,400 Yes. It pushes the target material out of the way 745 00:46:45,400 --> 00:46:49,640 and it pushes it aside as the tip of the jet 746 00:46:49,640 --> 00:46:53,240 hits the steel and flows back along the outside of the rod. 747 00:46:53,240 --> 00:46:55,440 Then there's a new increment of metal. 748 00:46:55,440 --> 00:46:59,200 This is constantly being replaced and when it's all used up it stops, 749 00:46:59,200 --> 00:47:00,320 won't go any deeper. 750 00:47:00,320 --> 00:47:03,040 Are we in a position that we can try this and I can see? 751 00:47:03,040 --> 00:47:06,720 Absolutely. This box, I'm pleased to tell you, is full of explosive. 752 00:47:06,720 --> 00:47:09,560 Good. What I'll do is take some out. 753 00:47:09,560 --> 00:47:14,080 This is standard British plastic explosive. 754 00:47:14,080 --> 00:47:18,080 It's similar to the American C4, 755 00:47:18,080 --> 00:47:22,120 but it is actually much easier to use for filling charges. 756 00:47:22,120 --> 00:47:27,040 You can just ram it in and then put the cone in. 757 00:47:28,160 --> 00:47:30,520 We're going to test it with what looks like 758 00:47:30,520 --> 00:47:33,760 an impossibly solid block of steel. 759 00:47:35,760 --> 00:47:38,440 There is a critical distance at which the jet 760 00:47:38,440 --> 00:47:41,560 will be at its most penetrating before it breaks up, 761 00:47:41,560 --> 00:47:45,120 so the charge has legs to hold it the right height from our target. 762 00:47:47,000 --> 00:47:48,960 Right, see you in about two minutes. 763 00:47:48,960 --> 00:47:51,120 Yes, and don't panic. I won't. 764 00:48:02,840 --> 00:48:04,520 Firing. 765 00:48:04,520 --> 00:48:08,440 Four, three, two, one... 766 00:48:11,000 --> 00:48:13,760 Wow! Let's go and see what we've done, shall we? 767 00:48:13,760 --> 00:48:18,440 It seems astonishing, because that was just a massive thump, 768 00:48:18,440 --> 00:48:21,800 that something extremely accurate will have occurred from that. 769 00:48:21,800 --> 00:48:22,840 Well, let's see. 770 00:48:24,560 --> 00:48:25,880 Ooh... 771 00:48:27,400 --> 00:48:29,600 Well, it's gone in at least that deep 772 00:48:29,600 --> 00:48:31,880 because I can push that in, but then 773 00:48:31,880 --> 00:48:34,720 the proof of the pudding will be turning it over 774 00:48:34,720 --> 00:48:38,600 and see if we have achieved anything the other end. Yep! 775 00:48:38,600 --> 00:48:40,520 Oh, yes! 776 00:48:40,520 --> 00:48:42,720 That's gone through over a foot of steel. 777 00:48:42,720 --> 00:48:47,480 The thing that I find even more surprising is you know full well 778 00:48:47,480 --> 00:48:49,480 if you've got a copper nail like that, 779 00:48:49,480 --> 00:48:52,000 no matter how hard you hit it... 780 00:48:52,000 --> 00:48:53,640 You will hardly dent the steel. 781 00:48:53,640 --> 00:48:58,280 Exactly! Yet you get a good amount of plastic explosive with 782 00:48:58,280 --> 00:49:02,280 a nice shape behind it and you can drive it the whole way through. 783 00:49:05,160 --> 00:49:08,480 These cone-shaped charges allowed people to get much more 784 00:49:08,480 --> 00:49:10,880 focused power from their explosives 785 00:49:10,880 --> 00:49:12,680 and during the coming World Wars, 786 00:49:12,680 --> 00:49:17,040 revolutionised the power of handheld weapons such as the bazooka. 787 00:49:18,680 --> 00:49:22,960 Nowadays they're used in all sorts of military and civil applications 788 00:49:22,960 --> 00:49:26,200 such as opening up oil wells, and Sidney designs them 789 00:49:26,200 --> 00:49:28,280 especially for bomb disposal, 790 00:49:28,280 --> 00:49:32,760 but other shapes have been developed as well, for different tasks. 791 00:49:32,760 --> 00:49:36,840 This long L-shaped liner can turn the shock wave into a blade, 792 00:49:36,840 --> 00:49:39,160 as the sides are slammed together. 793 00:49:39,160 --> 00:49:43,800 Instead of the cone's penetrating jet, this cutting blade is axe-like, 794 00:49:43,800 --> 00:49:47,440 designed for demolition jobs. 795 00:49:47,440 --> 00:49:52,240 Four, three, two, one... 796 00:50:02,840 --> 00:50:06,800 It seemed as if the power of explosives had reached a maximum. 797 00:50:06,800 --> 00:50:09,640 The chemical compositions were carefully designed 798 00:50:09,640 --> 00:50:12,600 and the power of the shock wave could now be channelled, 799 00:50:12,600 --> 00:50:17,240 but there was still explosive potential beyond imagination 800 00:50:17,240 --> 00:50:18,440 to be realised. 801 00:50:18,440 --> 00:50:22,240 By the end of the 19th century, chemists were discovering 802 00:50:22,240 --> 00:50:26,480 new elements all the time, and some of them appeared to give off energy. 803 00:50:26,480 --> 00:50:31,240 They called this rather bizarre property radioactivity. 804 00:50:31,240 --> 00:50:34,920 It was a New Zealand physicist, Ernest Rutherford, who was one of 805 00:50:34,920 --> 00:50:38,080 the first to understand the potential of radioactivity. 806 00:50:38,080 --> 00:50:42,880 Already understanding that it was caused by the atoms of the elements breaking down, 807 00:50:42,880 --> 00:50:44,840 he wrote this in 1904 - 808 00:50:44,840 --> 00:50:48,240 "If it should ever be found possible to control at will 809 00:50:48,240 --> 00:50:51,440 "the rate of disintegration of the radio elements, 810 00:50:51,440 --> 00:50:54,400 "an enormous amount of energy could be obtained 811 00:50:54,400 --> 00:50:56,360 "from a small amount of matter." 812 00:50:56,360 --> 00:50:58,520 It was a prophetic statement, 813 00:50:58,520 --> 00:51:02,440 although he later said, "Anyone who expects a useful 814 00:51:02,440 --> 00:51:05,400 "power source from the transformation of these atoms 815 00:51:05,400 --> 00:51:07,160 "is talking moonshine." 816 00:51:07,160 --> 00:51:10,720 Even a genius doesn't get it right every time. 817 00:51:10,720 --> 00:51:14,440 The investigation of radioactivity and the nucleus of atoms continued 818 00:51:14,440 --> 00:51:19,480 as researchers sought to understand the minute structure of the world 819 00:51:19,480 --> 00:51:23,680 around us, but some people were already seeing the potential 820 00:51:23,680 --> 00:51:27,880 for extracting the power released when nuclei are broken apart 821 00:51:27,880 --> 00:51:32,360 and in the winter of 1938, with war already brewing 822 00:51:32,360 --> 00:51:35,280 the exact dimensions of that potential was made clear 823 00:51:35,280 --> 00:51:38,400 in a laboratory in Copenhagen. 824 00:51:38,400 --> 00:51:41,320 An experimental physicist, Otto Frisch, 825 00:51:41,320 --> 00:51:44,280 who'd escaped Hitler's regime in Germany, constructed 826 00:51:44,280 --> 00:51:49,720 a piece of apparatus to measure the energy released when an atom splits. 827 00:51:49,720 --> 00:51:52,080 Now, it's not my field of science, 828 00:51:52,080 --> 00:51:55,440 but he knocked his up in a weekend and did the measurements, 829 00:51:55,440 --> 00:51:58,800 so I feel there's a fighting chance for an amateur like me. 830 00:51:58,800 --> 00:52:01,600 All the apparatus really consists of 831 00:52:01,600 --> 00:52:04,520 is a metal box with a metal plate in it. 832 00:52:04,520 --> 00:52:06,600 Now, when an atom splits, 833 00:52:06,600 --> 00:52:10,560 you end up with two high-energy fission products. 834 00:52:10,560 --> 00:52:13,440 Now, as they fly through the gas around them, they can 835 00:52:13,440 --> 00:52:16,840 smash electrons off other atoms, causing ionisation, 836 00:52:16,840 --> 00:52:19,680 producing positive and negative particles. 837 00:52:19,680 --> 00:52:23,640 The atoms that Frisch split were of the element uranium 838 00:52:23,640 --> 00:52:27,720 and he did it by bombarding them with particles called neutrons. 839 00:52:27,720 --> 00:52:30,520 A couple of hundred volts between here and here 840 00:52:30,520 --> 00:52:35,000 should enable us to detect if there's been any ionisation in here 841 00:52:35,000 --> 00:52:37,440 and from that we'll be able to deduce 842 00:52:37,440 --> 00:52:40,480 the energy released when an atom splits. 843 00:52:40,480 --> 00:52:43,480 Obviously, now all I need is a source of uranium 844 00:52:43,480 --> 00:52:45,960 and some neutrons to bombard it with. 845 00:52:50,360 --> 00:52:53,200 The National Physical Laboratory near London have 846 00:52:53,200 --> 00:52:57,360 the sort of thing I need, so I've brought my part of the kit. 847 00:52:57,360 --> 00:52:59,000 That is you ion chamber, is it? 848 00:52:59,000 --> 00:53:00,920 Well, yes. This is my ion chamber. 849 00:53:00,920 --> 00:53:05,680 It's not at the top end of the sophistication that you've got here, 850 00:53:05,680 --> 00:53:08,440 but can we try it? By all means. 851 00:53:08,440 --> 00:53:10,280 I've got a piece of uranium here 852 00:53:10,280 --> 00:53:15,120 which I borrowed from our radioactivity group. That's not a phrase you hear a lot. No. 853 00:53:15,120 --> 00:53:17,960 Uranium does have a reputation. 854 00:53:17,960 --> 00:53:20,520 How safe is it? How long can I be near it? 855 00:53:20,520 --> 00:53:25,560 Provided you stay a few centimetres away from it, you're out of the range of the alpha particles. 856 00:53:25,560 --> 00:53:28,320 Right, so I'll put the lid on here. 857 00:53:30,200 --> 00:53:35,320 The thing that we're missing now is the thing to split the atoms. You need a neutron source. Yes. 858 00:53:35,320 --> 00:53:39,920 We are the Neutron Standards Authority for the UK and we produce neutrons and use them 859 00:53:39,920 --> 00:53:43,440 to calibrate personal dose-meters, like the ones we gave you to wear. 860 00:53:43,440 --> 00:53:45,360 Yeah, I've got mine. 861 00:53:45,360 --> 00:53:49,320 I can get a neutron source, but you will have to leave while I put it up here. 862 00:53:49,320 --> 00:53:52,160 I'm happy to get out of the way while that's happening. 863 00:53:52,160 --> 00:53:56,720 The neutron source contains an element whose radioactivity 864 00:53:56,720 --> 00:53:59,960 is much more penetrating than uranium's, 865 00:53:59,960 --> 00:54:02,360 so it has to be treated with care. 866 00:54:02,360 --> 00:54:06,440 OK, so we've now got our uranium being blasted with neutrons. 867 00:54:06,440 --> 00:54:09,040 Yeah. How do we tell if we're splitting any atoms? 868 00:54:09,040 --> 00:54:12,000 We'd have to see some pulses from our ion chamber. 869 00:54:12,000 --> 00:54:15,720 OK. So if I turn up the volts we might begin to see something 870 00:54:15,720 --> 00:54:18,640 and the first thing that we might see, if it works, 871 00:54:18,640 --> 00:54:21,080 is the natural radiation from the uranium. 872 00:54:21,080 --> 00:54:26,040 I'm rather astounded, but they look like genuine pulses. 873 00:54:26,040 --> 00:54:29,600 So this'd be what you'd hear on a Geiger counter, going kcrr-kcrr? 874 00:54:29,600 --> 00:54:32,440 Yes, but you're not seeing any fission yet. Are we not? 875 00:54:32,440 --> 00:54:35,600 If it was fission, you would see some very much bigger pulses. 876 00:54:35,600 --> 00:54:37,440 So if I turn the discriminator up... 877 00:54:38,360 --> 00:54:41,040 That is a massive pulse. 878 00:54:41,040 --> 00:54:43,200 So is that a split atom?! Yes. 879 00:54:43,200 --> 00:54:45,320 Wow! 880 00:54:45,320 --> 00:54:50,040 Considerably bigger than the pulses from the natural decay of the uranium. Yeah! 881 00:54:50,040 --> 00:54:52,280 This is a completely different thing. 882 00:54:52,280 --> 00:54:54,920 Yes, yes. Very much more energetic. 883 00:54:54,920 --> 00:54:58,160 Now, from this can we get a measure of how much energy 884 00:54:58,160 --> 00:55:00,520 is being produced every time an atom splits? 885 00:55:00,520 --> 00:55:07,080 Well, the classical figure is 200 MeV, 200 mega-electronvolts. 886 00:55:07,080 --> 00:55:11,960 That makes that, the energy released when one of those atoms gets split, 887 00:55:11,960 --> 00:55:17,160 is about 50 million times more than a molecule of nitroglycerine. 888 00:55:17,160 --> 00:55:19,480 That's... 889 00:55:19,480 --> 00:55:21,480 You can see they were onto something. 890 00:55:21,480 --> 00:55:22,520 They were, indeed. 891 00:55:23,440 --> 00:55:26,520 Frisch finished his weekend's work in the early hours 892 00:55:26,520 --> 00:55:31,280 of January 13th 1939 and was soon woken by a telegram 893 00:55:31,280 --> 00:55:33,800 with news that his Jewish father had been released 894 00:55:33,800 --> 00:55:35,680 from a concentration camp. 895 00:55:35,680 --> 00:55:38,760 He said he remembered it as his lucky day, 896 00:55:38,760 --> 00:55:41,280 but would have liked a few more hours sleep. 897 00:55:41,280 --> 00:55:45,000 As war rumbled across Europe and then the world, physicists 898 00:55:45,000 --> 00:55:49,920 in many countries grasped the potential of Frisch's experiment. 899 00:55:49,920 --> 00:55:55,120 In the early morning of the 16th July 1945, a team of 900 00:55:55,120 --> 00:56:00,360 international researchers became the first to see that potential realised 901 00:56:00,360 --> 00:56:02,640 in the deserts of New Mexico. 902 00:56:02,640 --> 00:56:07,480 Inside a giant sphere of shaped charges, like the ones Sidney showed 903 00:56:07,480 --> 00:56:12,200 me, they placed radioactive material no bigger than an orange. 904 00:56:12,200 --> 00:56:17,960 The whole contraption was hoisted up a tower and then the charges detonated. 905 00:56:21,920 --> 00:56:24,880 The initial flash of light and heat 906 00:56:24,880 --> 00:56:28,040 travelled out at 200,000km a second, 907 00:56:28,040 --> 00:56:32,000 with temperatures reaching over 100 million degrees, 908 00:56:32,000 --> 00:56:35,600 20,000 times hotter than the surface of the sun. 909 00:56:35,600 --> 00:56:38,840 It melted the sand in the desert. 910 00:56:38,840 --> 00:56:43,040 Just like other explosions, this heat causes a massive expansion 911 00:56:43,040 --> 00:56:44,560 in the surrounding air. 912 00:56:44,560 --> 00:56:47,880 There's no production of gas, like in a chemical reaction. 913 00:56:47,880 --> 00:56:51,520 It's simply the staggering quantity of heat released 914 00:56:51,520 --> 00:56:56,880 by a runaway nuclear reaction that causes mankind's biggest explosion. 915 00:56:56,880 --> 00:57:00,720 That expanding air slams into the air around it, 916 00:57:00,720 --> 00:57:04,720 causing an abrupt shock wave which crushes the air 917 00:57:04,720 --> 00:57:07,200 and just like in the fire piston, heats it, 918 00:57:07,200 --> 00:57:11,720 but to such a temperature that the air itself begins to glow. 919 00:57:11,720 --> 00:57:15,200 You can see the white hot bubble-like shock wave 920 00:57:15,200 --> 00:57:17,720 in these astonishing pictures. 921 00:57:17,720 --> 00:57:20,360 Then it cools to a dark, transparent layer 922 00:57:20,360 --> 00:57:23,400 and the fireball inside shows through. 923 00:57:24,920 --> 00:57:26,960 The Trinity explosion, as it's known, 924 00:57:26,960 --> 00:57:30,880 had the equivalent power of 20,000 tons of TNT, 925 00:57:30,880 --> 00:57:35,160 all from just a few kilos of radioactive material. 926 00:57:35,160 --> 00:57:39,360 And all that power, and that enormous shock wave, 927 00:57:39,360 --> 00:57:43,040 is produced just simply by heating the air. 928 00:57:43,040 --> 00:57:47,160 In some ways, it's similar to the heat causing the bamboo to burst 929 00:57:47,160 --> 00:57:50,480 back in ancient China, but with a nuclear explosion, 930 00:57:50,480 --> 00:57:55,320 the heat is almost unimaginably intense and sudden. 931 00:57:55,320 --> 00:57:58,760 In little more than 2,000 years, the journey of understanding 932 00:57:58,760 --> 00:58:03,200 that mankind has so far travelled is immense. 933 00:58:03,200 --> 00:58:08,600 We've gone from crackling bamboo to creating something like a star here on Earth 934 00:58:08,600 --> 00:58:13,240 and man-made explosions terrify us as much now as they always have. 935 00:58:14,360 --> 00:58:17,920 The advent of the nuclear age was as shocking to us 936 00:58:17,920 --> 00:58:20,440 as gunpowder was to medieval Europe. 937 00:58:20,440 --> 00:58:24,160 Throughout history, explosives have been used first 938 00:58:24,160 --> 00:58:28,960 as weapons and then had their power harnessed to more constructive ends. 939 00:58:28,960 --> 00:58:33,600 They have shaped our world, through warfare and engineering. 940 00:58:33,600 --> 00:58:37,320 Even nuclear power has been turned to peaceful uses. 941 00:58:37,320 --> 00:58:40,200 New explosives may always be discovered 942 00:58:40,200 --> 00:58:42,720 and wreak terrifying havoc. 943 00:58:42,720 --> 00:58:44,760 But if history has taught us anything, 944 00:58:44,760 --> 00:58:48,000 it's that by properly understanding these things 945 00:58:48,000 --> 00:58:51,400 we can create instruments of unrivalled power. 946 00:58:53,240 --> 00:58:56,360 If you want to find out more about the science of explosions, 947 00:58:56,360 --> 00:58:57,400 go to the website - 948 00:58:59,800 --> 00:59:02,920 And follow the links to the Open University. 949 00:59:11,960 --> 00:59:16,440 Subtitles by Red Bee Media Ltd 950 00:59:16,440 --> 00:59:20,920 E-mail subtitling@bbc.co.uk