0:00:02 > 0:00:07In 1807, maverick Cornish chemist Humphry Davy
0:00:07 > 0:00:11attempted something no one had dared try before.
0:00:13 > 0:00:17He harnessed a newly discovered force, electricity,
0:00:17 > 0:00:21to rip apart a caustic chemical called potash.
0:00:21 > 0:00:23And he discovered a new element.
0:00:27 > 0:00:30Vivid, violent potassium.
0:00:33 > 0:00:40Davy had found a new way of cracking open the natural world to reveal its building blocks.
0:00:42 > 0:00:47This is the story of one of the biggest questions there is.
0:00:47 > 0:00:51What is everything in our world made of?
0:00:53 > 0:00:59The quest to find out would ultimately lead to an extraordinary insight -
0:00:59 > 0:01:05that everything, from the diversity of nature to the complexity of man,
0:01:05 > 0:01:09was made from just 92 elements.
0:01:12 > 0:01:14'I'm Jim Al-Khalili.
0:01:14 > 0:01:20'I've studied physics all my life, but I couldn't have gained my knowledge of the subatomic world
0:01:20 > 0:01:25'without the work of the chemists who first unravelled the mysteries of matter.'
0:01:25 > 0:01:28Brilliant. That was really beautiful.
0:01:28 > 0:01:31Finding and understanding the elements would turn out
0:01:31 > 0:01:37to be one of the greatest detective stories in the history of science.
0:01:37 > 0:01:41A staggeringly difficult task that would span centuries.
0:01:41 > 0:01:46I'm going to retrace the steps of the chemists who risked their lives
0:01:46 > 0:01:49to prise secrets from the natural world.
0:01:49 > 0:01:51It's instantly disfiguring, instant blindness.
0:01:51 > 0:01:53It is really hideously dangerous.
0:01:53 > 0:01:57I'll find out how scientists struggled
0:01:57 > 0:02:02to crack one of the most important codes in the universe.
0:02:04 > 0:02:11And I'll discover how our fascination with the elements led to the making of the modern world
0:02:11 > 0:02:16and pushed the human race to the edge of destruction.
0:02:16 > 0:02:20EXPLOSION
0:02:20 > 0:02:24Our compulsion to seek answers at almost any cost,
0:02:24 > 0:02:27and to search for fundamental truths,
0:02:27 > 0:02:30has powered scientific endeavour.
0:02:30 > 0:02:33And it underpins this story.
0:02:33 > 0:02:37Our quest to unravel the mysteries of the elements.
0:02:53 > 0:02:56It's hard to imagine what it must have been like
0:02:56 > 0:03:00to look around and not have a clue what the world is made of.
0:03:00 > 0:03:04Not to know what this contained.
0:03:04 > 0:03:07To be mystified by fire, to have no idea that
0:03:07 > 0:03:12oxygen is essential to make it burn or that oxygen even existed.
0:03:12 > 0:03:17Not to know that hydrogen is a vital ingredient of the ocean
0:03:17 > 0:03:22or that sodium and chlorine combine to give its salty taste.
0:03:25 > 0:03:30It's only in the last 200 years that we've known what an element is.
0:03:30 > 0:03:35It's a substance that can't be broken down into a simpler one by a chemical reaction.
0:03:37 > 0:03:43The ancient Greeks already knew of lead, copper, gold, silver,
0:03:43 > 0:03:45iron, mercury, tin.
0:03:45 > 0:03:48But to them these were just metals.
0:03:48 > 0:03:54They were convinced that the whole world was made of earth, air, fire and water.
0:03:55 > 0:03:58For more than 1,000 years we had no way
0:03:58 > 0:04:01of breaking open the natural world
0:04:01 > 0:04:07and no choice but to base our concept of elements on what was visible around us.
0:04:12 > 0:04:16By the 16th century, things were starting to change.
0:04:16 > 0:04:21Alchemists began to penetrate the substances around them
0:04:21 > 0:04:25in their bid to turn base metals into gold.
0:04:25 > 0:04:32They kept secret notes of their experiments written in mysterious codes and symbols.
0:04:32 > 0:04:35And they dreamed of immortality.
0:04:35 > 0:04:39From the Far East, through Europe to London,
0:04:39 > 0:04:47the backstreets and cellars were a seething, bubbling hotbed of alchemical research.
0:04:51 > 0:04:55It was an alchemist who first challenged the Greek idea
0:04:55 > 0:05:00that everything was made from earth, fire, air and water,
0:05:00 > 0:05:04in a story which begins in Basel, Switzerland.
0:05:07 > 0:05:12It starts with Philippus Theophrastus Aureolus Bombastus von Hohenheim who,
0:05:12 > 0:05:17thankfully for me because I'm not saying that again,
0:05:17 > 0:05:20adopted the nom de plume Paracelsus.
0:05:23 > 0:05:27Paracelsus was not just an alchemist trying to unlock
0:05:27 > 0:05:32the mysteries of matter, he was also a physician and surgeon.
0:05:32 > 0:05:36And he wasn't afraid to challenge the orthodoxy of the day.
0:05:44 > 0:05:49In 1526 the city of Basel was famous for its printing.
0:05:49 > 0:05:54And its most sought after printer, Frobenius, had just been told by
0:05:54 > 0:06:00his doctors that unless he had his leg amputated he would die.
0:06:00 > 0:06:04So Frobenius called for Paracelsus,
0:06:04 > 0:06:08who wouldn't accept the medical orthodoxy of the day.
0:06:08 > 0:06:13He also wasn't afraid to mix medicine with alchemy
0:06:13 > 0:06:17to concoct new potions and remedies.
0:06:17 > 0:06:22He created a cure that not only saved Frobenius's life,
0:06:22 > 0:06:26but established Paracelsus as a true radical.
0:06:26 > 0:06:31He proposed a groundbreaking new idea, suggesting that the world
0:06:31 > 0:06:34was actually made of three elements -
0:06:34 > 0:06:37salt, sulphur and mercury.
0:06:40 > 0:06:47Paracelsus saw these as the core ingredients to make metals and medicines.
0:06:47 > 0:06:52He reckoned salts would heal wounds, sulphur was combustible
0:06:52 > 0:06:57and mercury, known then as quicksilver, was fluid and volatile.
0:07:00 > 0:07:03Now, mercury is an incredible substance.
0:07:03 > 0:07:07It's the only metal that's liquid at room temperature.
0:07:07 > 0:07:10It's also remarkably heavy.
0:07:10 > 0:07:12Just this small amount here feels very, very heavy.
0:07:12 > 0:07:16But I've got a much larger amount here.
0:07:16 > 0:07:19And if I try and lift it...
0:07:22 > 0:07:27That's not stuck to the table, it's 14 times heavier than water.
0:07:27 > 0:07:32It's also toxic, so I'm wearing a triple layer of gloves here.
0:07:32 > 0:07:35Cos I'm going to do something I've always wanted to do,
0:07:35 > 0:07:37which is dunk my hand in mercury.
0:07:39 > 0:07:41It feels very, very strange.
0:07:41 > 0:07:43It's pushing my hand up.
0:07:45 > 0:07:49It's nothing like any liquid that I know of.
0:07:51 > 0:07:56It feels very cold as well, even through the three layers of gloves I can feel its coolness.
0:07:58 > 0:08:04And just to give you an idea of how weird this stuff is, I've got a steel bolt here.
0:08:04 > 0:08:09Let's see what happens if I put it in the mercury.
0:08:09 > 0:08:13Mercury is so much denser than steel. It floats.
0:08:19 > 0:08:23Mercury - silvery and mirror-like,
0:08:23 > 0:08:28it's one of the most beautiful and elusive of all the elements.
0:08:28 > 0:08:31It's rarely found in its natural form.
0:08:31 > 0:08:38But heating a red rock, cinnabar, will reveal molten mercurial lava hidden within.
0:08:41 > 0:08:46The phrase "mad as a hatter" was coined when hat makers
0:08:46 > 0:08:50who used it suffered from mercury madness.
0:08:53 > 0:08:57In the mines of South America, treasure hunters risked their lives
0:08:57 > 0:09:02by using toxic mercury to extract another element - gold.
0:09:03 > 0:09:10And floating on mercury gave smooth motion to the revolving light of some Victorian lighthouses.
0:09:15 > 0:09:20Paracelsus didn't manage to convince the establishment with his idea of
0:09:20 > 0:09:24the three elements, mercury, sulphur and salt.
0:09:24 > 0:09:31In fact, he'd enraged them by ignoring their medical texts and creating alchemical cures.
0:09:31 > 0:09:34He was too radical for his time.
0:09:34 > 0:09:37In a dramatic gesture
0:09:37 > 0:09:43to show his contempt for the medical authorities, he burned their books.
0:09:46 > 0:09:51He was forced to leave Basel University and fled to Germany,
0:09:51 > 0:09:54where he could carry on practising medicine and alchemy.
0:10:01 > 0:10:05But he'd paved the way for a new era of questioning,
0:10:05 > 0:10:08at a time when many alchemists were more interested in making gold.
0:10:08 > 0:10:13They would heat metals in scorching furnaces.
0:10:13 > 0:10:15They'd boil, they'd distill.
0:10:16 > 0:10:21And it was the pursuit of gold that lead to the first major breakthrough
0:10:21 > 0:10:24in the hunt to discover elements.
0:10:26 > 0:10:30For the alchemists, gold was like the holy grail.
0:10:30 > 0:10:35They believed it possessed spiritual, magical, even medical properties.
0:10:35 > 0:10:38It was the stuff of power, the colour of the sun.
0:10:38 > 0:10:41It was made into crowns and coins.
0:10:41 > 0:10:46It adorned kings, queens, palaces and temples for over thousands of years.
0:10:50 > 0:10:56In ancient Egypt, gold was thought to be the skin of the gods.
0:10:57 > 0:11:02To the Inca civilisation, gold was the sweat of the sun.
0:11:05 > 0:11:10The alchemists didn't yet know what an element was.
0:11:10 > 0:11:16But some unwittingly touched on the idea that they could be hidden within other substances
0:11:16 > 0:11:21when they suggested that gold might be concealed within the human body.
0:11:25 > 0:11:30The relentless pursuit of this obsession led one alchemist
0:11:30 > 0:11:35to become the first person credited with the discovery of a new element.
0:11:35 > 0:11:37Hennig Brand.
0:11:39 > 0:11:43He was searching for a way of extracting gold from the body
0:11:43 > 0:11:47when he hit upon what seemed like a smart idea,
0:11:47 > 0:11:53a gold coloured liquid in plentiful supply - urine.
0:11:56 > 0:12:04It was 1669 and in the dark, smelly basement of his Hamburg House, Brand's expensive
0:12:04 > 0:12:10alchemical experiments were rapidly eating through the funds of his wealthy wife, Margeretha.
0:12:10 > 0:12:18But now, with his urine brainwave, Brand believed that he was on the threshold of a momentous discovery.
0:12:18 > 0:12:21He was about to make his name and restore his family fortune.
0:12:21 > 0:12:25All he needed was another fifty buckets of urine.
0:12:27 > 0:12:32'Chemist Dr Andrea Sella has been studying Brand's work
0:12:32 > 0:12:36'and is going to attempt to find the hidden element.'
0:12:36 > 0:12:38If you pass me the urine.
0:12:38 > 0:12:42- You're welcome. - And this is courtesy of myself.
0:12:42 > 0:12:45I'm already holding my breath.
0:12:45 > 0:12:48Ahh, you know, you know you mustn't over-react.
0:12:48 > 0:12:51So what would Brand have done?
0:12:51 > 0:12:54What Brand was trying to do was to get to the heart of the matter.
0:12:54 > 0:12:58To start boiling it down, to get rid of the unimportant parts.
0:12:58 > 0:13:01That, of course, was principally the water.
0:13:01 > 0:13:05There is an additional feature and it's not really surprising.
0:13:05 > 0:13:08But, you know, have a quick waft of that.
0:13:08 > 0:13:11Yeah, it's pretty bad.
0:13:12 > 0:13:15Brand must have had some very, very patient neighbours.
0:13:15 > 0:13:21I really don't know what his romantic life must have been like, but I can't imagine he was all that popular.
0:13:22 > 0:13:26You see, I can understand urine being gold coloured.
0:13:26 > 0:13:30But Brand was looking to make gold. What is the connection?
0:13:30 > 0:13:36First of all it seems tremendously laughable to us to use something as disgusting a waste product as urine.
0:13:36 > 0:13:41One of the alchemical views was that man was really a microcosm of the universe and, therefore,
0:13:41 > 0:13:47urine actually carried within it some of that vital force. The life force.
0:13:47 > 0:13:51So a sort of metaphysical symbol of life?
0:13:51 > 0:13:55Absolutely. And so, really, this was a substance of power.
0:13:55 > 0:14:00Brand was determined to persevere with his quest for gold.
0:14:00 > 0:14:02He distilled the urine down to a paste,
0:14:02 > 0:14:07then heated it at a phenomenal temperature for several days.
0:14:07 > 0:14:13Eventually, wisps of smoke revealed tiny fragments that combusted in air.
0:14:13 > 0:14:17But what was this fiery substance?
0:14:17 > 0:14:22It wasn't golden like the sun, but it burned brighter than any medieval candle.
0:14:35 > 0:14:40So this is what Brand isolated from urine.
0:14:40 > 0:14:42It's not gold.
0:14:42 > 0:14:45This is phosphorus.
0:14:45 > 0:14:53Brand had discovered, completely by accident, a new element, never seen by man.
0:14:53 > 0:14:56Fiery phosphorus.
0:14:57 > 0:15:00He was looking for riches but didn't realise that he'd
0:15:00 > 0:15:08unearthed a fundamental notion, that elements could be concealed within a hidden world.
0:15:08 > 0:15:11Phosphorus is biologically very, very important.
0:15:11 > 0:15:15If you think of our bones they're composed predominantly of calcium hydroxy phosphates.
0:15:15 > 0:15:17There's lots of phosphate there.
0:15:17 > 0:15:21It's in our DNA, it's in all sorts of our tissues, and
0:15:21 > 0:15:26as a result there's always phosphate in the blood and some of it, excess, is transferred into the urine.
0:15:26 > 0:15:29A little bit less than about a gram per litre.
0:15:29 > 0:15:31This stuff is a complete tiger.
0:15:31 > 0:15:37You can see that it starts to smoke very gently in air.
0:15:37 > 0:15:42And this is really a warning to us that things are going to happen if we don't deal with it quickly.
0:15:42 > 0:15:46So we're going to drop it into this flask.
0:15:46 > 0:15:48The flask is actually filled with oxygen.
0:15:48 > 0:15:50And so it's sitting in sand
0:15:50 > 0:15:55just to keep the heat from attacking the glass.
0:15:55 > 0:15:58And now I'm going to touch it with a hot glass rod.
0:16:07 > 0:16:09And so there it is.
0:16:09 > 0:16:11That's fantastic
0:16:11 > 0:16:14and it sort of feels cold. It's not hot.
0:16:14 > 0:16:17That's quite beautiful.
0:16:17 > 0:16:19Because it shone so vividly,
0:16:19 > 0:16:25yet was cold enough to hold, Brand called his discovery "Icy Nocta Luca."
0:16:25 > 0:16:28Cold night light.
0:16:31 > 0:16:36Phosphorus. It's in every cell in the human body.
0:16:36 > 0:16:42It's used in drugs to promote bone growth, treating diseases like osteoporosis.
0:16:43 > 0:16:49153 million tonnes of phosphorus are produced every year.
0:16:49 > 0:16:56Its phosphate is consumed as a food supplement, and is an ingredient of toothpaste.
0:16:56 > 0:16:59But eating just 100 milligrams of pure phosphorous,
0:16:59 > 0:17:03enough to coat a finger tip, could be fatal.
0:17:04 > 0:17:07And it has an even darker side.
0:17:07 > 0:17:15In the Second World War, phosphorus was used in the thousands of bombs dropped on Hamburg.
0:17:15 > 0:17:18The city where Brand discovered it.
0:17:27 > 0:17:32Brand hoped that phosphorus would make him a fortune,
0:17:32 > 0:17:37but his cash ran out and he sold the secret of his discovery for a paltry sum.
0:17:38 > 0:17:43Before long phosphorous was being touted round the royal courts of Europe.
0:17:44 > 0:17:49And in 1677 it arrived at the court of King Charles II.
0:17:49 > 0:17:55Soon after, wealthy alchemist Robert Boyle, witnessed its luminous magic
0:17:55 > 0:17:59and determined to investigate its properties.
0:17:59 > 0:18:05Dr Andrea Sella and I are going to follow Boyle's own instructions
0:18:05 > 0:18:09to attempt one of his most significant experiments on phosphorus.
0:18:09 > 0:18:12So I have here extracts from Robert Boyle's book,
0:18:12 > 0:18:17New Experiments and Observations Made Upon the Icy Nocte Luca.
0:18:17 > 0:18:21Having put together about half a grain of our dry nocte luca matter.
0:18:21 > 0:18:23How much is half a grain?
0:18:23 > 0:18:25Well, half a grain really isn't very much.
0:18:25 > 0:18:29There's 7000 grains to the pound.
0:18:29 > 0:18:31So you can work it out.
0:18:31 > 0:18:32You're the physicist.
0:18:32 > 0:18:37OK, and six times its weight of common flowers of sulphur.
0:18:37 > 0:18:40OK, so we'll just put a little piece...
0:18:40 > 0:18:45- So that's just sulphur powder, is it?- Yes, it's essentially finely powdered sulphur.
0:18:45 > 0:18:49Right and it says, they were lodged in the fold of a piece of white paper.
0:18:49 > 0:18:51He rubbed it with the haft of a knife.
0:18:51 > 0:18:55Well, I haven't got a knife but I do have a spatula.
0:18:55 > 0:18:58- That'll do.- So we'll use that. OK. It's beginning to smoke.- OK.
0:18:58 > 0:19:02It's beginning to kindle. We've got a little bit of fire there already.
0:19:02 > 0:19:03The main lump of phosphorus...
0:19:03 > 0:19:06- Oh, look there it goes.- Oh, there it goes. There it goes. Whoa!
0:19:08 > 0:19:11- Didn't have time to bruise it. - It didn't need bruising.- It went up.
0:19:11 > 0:19:15So you've basically recreated what is the precursor to the match.
0:19:15 > 0:19:19Yes, and I've also got some splendid smoke rings here.
0:19:20 > 0:19:25I mean this would really radically transform things because what you had was fire on demand.
0:19:25 > 0:19:30Boyle had stumbled upon the essential ingredient of a match.
0:19:32 > 0:19:36A huge industry was spawned from this single experiment.
0:19:36 > 0:19:41But Boyle wasn't really interested in the money making potential of phosphorus,
0:19:41 > 0:19:44just understanding the properties of this element
0:19:44 > 0:19:46was reward enough for him.
0:19:58 > 0:20:02So phosphorus did have transformational powers after all.
0:20:04 > 0:20:12It may not have changed lead into gold, but it turned an alchemist into the first modern chemist.
0:20:12 > 0:20:16Boyle had set the stage for future element hunters.
0:20:16 > 0:20:19Unlike most alchemists, he shared his methods
0:20:19 > 0:20:25and was able to pass on the tools they needed to help unlock the mysteries of matter.
0:20:28 > 0:20:33I've come to search the vaults of the Royal Society in London.
0:20:33 > 0:20:40What I am looking for was deposited here in 1661, just one year after the Society was formed.
0:20:44 > 0:20:46Here it is.
0:20:46 > 0:20:48The Sceptical Chemist.
0:20:48 > 0:20:54It was written by Robert Boyle, who was one of the founders of the Royal Society.
0:20:55 > 0:21:01Dr Anna Marie Roos, a specialist in the history of chemistry, has studied Boyle's writings.
0:21:01 > 0:21:04I've got a copy of Boyle's, Sceptical Chemist.
0:21:04 > 0:21:06Why was this book so important?
0:21:06 > 0:21:10This was really considered to be one of one of the books
0:21:10 > 0:21:14that signifies a transition from alchemy to chemistry
0:21:14 > 0:21:17and some scholars have thought it's the first book of chemistry.
0:21:17 > 0:21:22The fact that book was written in plain English was also quite a new thing.
0:21:22 > 0:21:28'You only have to compare Boyle's book to the cryptic writings of another alchemist.'
0:21:28 > 0:21:33That great man of science, Isaac Newton, to appreciate its innovation.
0:21:33 > 0:21:37And we can see here that it's in Latin and we also can see that
0:21:37 > 0:21:42there are several alchemical symbols being used for the chemical elements.
0:21:42 > 0:21:46It really does remind me of astrology
0:21:46 > 0:21:48- and Egyptian hieroglyphics. - Absolutely.
0:21:48 > 0:21:54And I compare that with Boyle where he says things like, "He took 200 pounds of earth,
0:21:54 > 0:21:58"dried in an oven, having put it in an earthen vessel and melted it."
0:21:58 > 0:22:01He's describing a chemical process.
0:22:01 > 0:22:05Absolutely. What made Boyle a bit different is that he was willing to
0:22:05 > 0:22:11divulge some of his chemical secrets for the good of the scientific community.
0:22:14 > 0:22:21Boyle was bringing alchemy out of the shadows and into an enlightened, rational age.
0:22:21 > 0:22:25He was opening up the scientific method for everyone to see.
0:22:25 > 0:22:29The alchemists must have feared he was giving away their secrets.
0:22:29 > 0:22:32But he wasn't so much interested in debunking alchemy,
0:22:32 > 0:22:35as getting rid of its metaphysical baggage
0:22:35 > 0:22:39and replacing it with a more rigorous scientific approach.
0:22:43 > 0:22:49A new age of scientific experimentation had begun.
0:22:55 > 0:23:00And with a more open exchange of ideas came a rejection of tradition.
0:23:00 > 0:23:04It heralded an era in which the ancient Greek doctrines
0:23:04 > 0:23:08were re-evaluated and new concepts introduced.
0:23:10 > 0:23:16Copernicus challenged the ancient idea that the Earth was at the centre of the universe,
0:23:16 > 0:23:22proposing instead that it was just one of a number of planets orbiting around the sun.
0:23:22 > 0:23:25Vesalius mapped the human body.
0:23:25 > 0:23:29It was an exciting and liberating time in which Europe was being
0:23:29 > 0:23:34dragged out of its dark ages and into an age of reason.
0:23:38 > 0:23:41But just because people were thinking differently,
0:23:41 > 0:23:45didn't necessarily mean that they were getting it right.
0:23:45 > 0:23:50And while a new generation of scientists were keen to come up with modern elements to replace the
0:23:50 > 0:23:57four ancient ones, their enthusiasm didn't stop them from buying into completely false theories.
0:23:57 > 0:24:04And so it was that science went up one of the greatest blind alleys in the history of chemistry.
0:24:06 > 0:24:11It was 1667, a year after the Great Fire of London
0:24:11 > 0:24:14had razed one of Europe's greatest cities to the ground.
0:24:16 > 0:24:21The mysteries of fire were at the forefront of everyone's minds.
0:24:21 > 0:24:25But no-one really understood what fire was or how it was created.
0:24:27 > 0:24:31German chemist, Johann Becher, proposed that the destructive
0:24:31 > 0:24:37power of fire was caused by an ethereal entity named phlogiston.
0:24:37 > 0:24:41It was thought to be an odourless, colourless,
0:24:41 > 0:24:48tasteless and weightless substance, that causes things to burn, reducing them to their true form.
0:24:48 > 0:24:52This burning wood produces ash.
0:24:52 > 0:24:58So wood must be made up of ash, pure wood, plus phlogiston.
0:25:00 > 0:25:05The notion of phlogiston seemed so credible in the 17th century
0:25:05 > 0:25:08that it consumed the scientific community.
0:25:08 > 0:25:12It was accepted as a truth, virtually paralysing our ability
0:25:12 > 0:25:17to discover more elements and map the contours of the natural world.
0:25:17 > 0:25:24One great chemist who experimented with gases even claimed to have isolated it.
0:25:25 > 0:25:29On the same day every week for 50 years
0:25:29 > 0:25:35a rather peculiar scientist came to the Royal Society Dinner Club
0:25:35 > 0:25:38to discuss the latest scientific ideas.
0:25:43 > 0:25:50Henry Cavendish has been described as "the richest of the learned, and the most learned of the rich".
0:25:50 > 0:25:56He was a major shareholder in the Bank of England, and had royal connections.
0:25:56 > 0:26:01But it's remarkable he came to a social gathering at all.
0:26:01 > 0:26:06Cavendish was painfully shy and lived in virtual isolation.
0:26:06 > 0:26:11At home, he insisted that his servants only communicate with him in writing.
0:26:11 > 0:26:15Colleagues at the Dinner Club said that he'd often be found outside,
0:26:15 > 0:26:17trying to pluck up the courage to go in.
0:26:17 > 0:26:25And when speaking to him it was best to look into the air with vacancy rather than directly at him.
0:26:25 > 0:26:28Despite signs of what we might recognise today as autism,
0:26:28 > 0:26:33Cavendish made a vital contribution to the discovery of the elements.
0:26:36 > 0:26:40I'm going to investigate how Cavendish's experiments with airs
0:26:40 > 0:26:45led him to find the first element that's a gas.
0:26:49 > 0:26:55Cavendish added a metal, zinc, to an acid.
0:26:55 > 0:26:57It was deceptively simple.
0:26:57 > 0:27:00And pretty soon...
0:27:00 > 0:27:04bubbles began to appear on the surface of the zinc.
0:27:04 > 0:27:11Cavendish started to collect this gas, which I'm going to do in this test tube.
0:27:11 > 0:27:16It didn't smell of anything, it didn't taste of anything, in fact it was completely invisible.
0:27:16 > 0:27:21Cavendish soon realised this was no ordinary gas.
0:27:21 > 0:27:23And then...
0:27:23 > 0:27:25he set light to it.
0:27:27 > 0:27:28POP
0:27:29 > 0:27:33Cavendish had no idea he'd discovered a new element,
0:27:33 > 0:27:38in fact he thought he'd found a new kind of air, different to the air we breath.
0:27:38 > 0:27:42He called it, not surprisingly, "inflammable air".
0:27:42 > 0:27:48And he believed his inflammable air had to be the mysterious phlogiston.
0:27:50 > 0:27:56It was, odourless, tasteless, colourless and most importantly, it caught fire.
0:27:56 > 0:27:58It HAD to be phlogiston.
0:27:58 > 0:28:01But he was wrong.
0:28:01 > 0:28:07Cavendish didn't realise it but he'd isolated a new element, hydrogen.
0:28:08 > 0:28:12He investigated the characteristics of his new air and
0:28:12 > 0:28:17calculated that it was eleven times lighter than the air we breathe.
0:28:18 > 0:28:21Now, I've got Asma here to help me.
0:28:21 > 0:28:25She's pumping hydrogen through into this washing up liquid
0:28:25 > 0:28:29and creating bubbles of hydrogen coming up through this funnel.
0:28:29 > 0:28:31Because hydrogen is so much lighter than air,
0:28:31 > 0:28:34at some point these bubbles will separate and start to float up.
0:28:38 > 0:28:41Brilliant, that was really beautiful.
0:28:42 > 0:28:46'It was lighter than air and burst into flames.
0:28:46 > 0:28:49'You can see why Cavendish thought it was phlogiston.'
0:28:49 > 0:28:52Cor, they're getting better!
0:28:53 > 0:29:00But this belief meant Cavendish wasn't credited with the discovery of hydrogen during his lifetime.
0:29:02 > 0:29:06Nor would he witness its full force.
0:29:11 > 0:29:16Hydrogen - produced just after the Big Bang alongside helium and lithium,
0:29:16 > 0:29:21it's the most abundant and lightest element in the universe.
0:29:23 > 0:29:29The suns energy comes from the nuclear fusion of hydrogen.
0:29:29 > 0:29:33The same principle harnessed in the hydrogen bomb.
0:29:37 > 0:29:41Hydrogen's highly flammable nature was witnessed
0:29:41 > 0:29:48when it ignited the Hindenburg zeppelin airship in 1937, killing 36 people.
0:30:01 > 0:30:08'Like so many other element hunters, Cavendish didn't realise the significance of his discovery.
0:30:08 > 0:30:13'But he did observe something that would play a crucial role in our understanding of the natural world.'
0:30:17 > 0:30:20Each time he set light to the gas,
0:30:20 > 0:30:25a dewy liquid began to appear on the surface of the glass.
0:30:25 > 0:30:28It was water.
0:30:28 > 0:30:32Now this had incredible implications back in the 1700's because back then
0:30:32 > 0:30:37they believed in the ancient Greek idea that water was an element.
0:30:37 > 0:30:41But if you can make water out of two other constituents,
0:30:41 > 0:30:47then it couldn't be an element. In fact, water is a compound.
0:30:54 > 0:31:01'This struck right to the heart of the ancient concept of four elements.
0:31:01 > 0:31:06'Cavendish's observations could have shaken the foundations of accepted belief.
0:31:06 > 0:31:12'But they didn't, because he was thrown off-course by phlogiston.
0:31:12 > 0:31:17'He reckoned that the airs must contain a form of water
0:31:17 > 0:31:20'modified by the presence of phlogiston.
0:31:20 > 0:31:26'It simply didn't occur to him that water was a compound.'
0:31:26 > 0:31:31So while he was very close to destroying the temple of the ancient four elements,
0:31:31 > 0:31:34he couldn't quite yet disprove them.
0:31:34 > 0:31:39The pillars of that temple were now standing on very shaky ground,
0:31:39 > 0:31:43and it wouldn't be too long before they'd come crashing down.
0:31:43 > 0:31:48But it wasn't Cavendish's water that would finally disprove the ancient theory.
0:31:48 > 0:31:50It was air.
0:31:55 > 0:32:01'19 of what we now call elements had been found so far,
0:32:01 > 0:32:05'but 18th-century scientists were still grappling to work out
0:32:05 > 0:32:07'what the world was made of.'
0:32:09 > 0:32:13'The Royal Society had commissioned its members
0:32:13 > 0:32:15'to investigate the invisible airs.'
0:32:19 > 0:32:26By the mid-1700s, there were three known types of air, or gases.
0:32:26 > 0:32:30There was the common air, that we breathe, inflammable air,
0:32:30 > 0:32:35now known as hydrogen, and fixed air, or carbon dioxide.
0:32:35 > 0:32:40And experimenting with these airs was a favourite pastime
0:32:40 > 0:32:45of clergyman and amateur chemist Joseph Priestley.
0:32:45 > 0:32:51'Priestley lived next to a brewery, and spent rather a lot of time there, especially considering
0:32:51 > 0:32:57'he was a Unitarian minister, known for his extreme sermons.'
0:32:59 > 0:33:01But he wasn't here for the beer.
0:33:01 > 0:33:07Priestley was interested in the gas that's produced in the fermentation process.
0:33:07 > 0:33:14He called it brewery gas, but of course it was well known by that time as fixed air.
0:33:14 > 0:33:17We know it today as carbon dioxide.
0:33:17 > 0:33:20Carbon dioxide is being produced inside this vat,
0:33:20 > 0:33:25and because it's heavier than air, it's pouring out and cascading down.
0:33:25 > 0:33:29Now we can't see it, but an experiment that Priestley himself
0:33:29 > 0:33:36carried out involved seeing what carbon dioxide does to a lit flame.
0:33:36 > 0:33:40So if I hold this flame here,
0:33:40 > 0:33:44it's not in the path of the gas at the moment, but if I bring it down...
0:33:46 > 0:33:48You can see it immediately extinguishes.
0:33:48 > 0:33:52You can even see the trail of smoke following the path of the gas.
0:33:54 > 0:33:58'Priestley was fascinated by fixed air.
0:33:58 > 0:34:03'He mixed it with water, and so invented the first fizzy drink.
0:34:03 > 0:34:07'In time it would spawn an industry worth millions,
0:34:07 > 0:34:10'but he earned almost nothing from it.
0:34:10 > 0:34:13'Instead, Priestley's passion for science
0:34:13 > 0:34:17'led to an invitation to Bowood House in Wiltshire,
0:34:17 > 0:34:22'to tutor the children of the future Prime Minister, Lord Shelburne.'
0:34:23 > 0:34:29Priestley lacked the wealth of earlier chemists like Boyle and Cavendish.
0:34:29 > 0:34:34And he made little money from his inventions and his radical writings.
0:34:34 > 0:34:37Lord Shelburne was offering him financial stability
0:34:37 > 0:34:43and the chance to continue with his scientific experiments, in return for teaching.
0:34:43 > 0:34:46He became the first professional, salaried chemist.
0:34:46 > 0:34:51And it was here that he continued his experiments with airs.
0:34:56 > 0:35:00On 1st August 1774, he performed
0:35:00 > 0:35:04one of the most important experiments in chemical history.
0:35:05 > 0:35:11'Priestley was gripped by unlocking the elemental secrets of the airs.
0:35:11 > 0:35:16'On this occasion he started with a powder he knew as mercuric calx.
0:35:16 > 0:35:18'Mercuric oxide.
0:35:18 > 0:35:23'He put it in a test tube to collect any gas it might give off when he heated it.'
0:35:26 > 0:35:30'Then he filled the test tube with mercury, which would trap the gas.'
0:35:30 > 0:35:34So I now place my finger over the top of the tube,
0:35:34 > 0:35:39invert it, so that it's submerged into the mercury bath.
0:35:39 > 0:35:45I now have the mercuric oxide powder at the very top of the tube.
0:35:45 > 0:35:49What Priestley did next was heat up this powder.
0:35:51 > 0:35:55The level of the mercury in the tube is dropping.
0:35:56 > 0:36:01What's going on is a gas is being produced that is pushing the mercury down.
0:36:01 > 0:36:04What in fact is happening is that this mercuric oxide powder
0:36:04 > 0:36:08is being broken up into its two components.
0:36:09 > 0:36:14I'm now going to see what gas Priestley had made.
0:36:14 > 0:36:21If I take this splint and blow it out so I just have a glowing ember,
0:36:21 > 0:36:23it bursts back into flame again.
0:36:23 > 0:36:28'We now know that Joseph Priestley had found oxygen.
0:36:28 > 0:36:33'But because he believed in the idea of phlogiston, he thought the splint
0:36:33 > 0:36:37'was introducing phlogiston to the new air and catching fire.
0:36:37 > 0:36:42'He concluded that his air must be without phlogiston.
0:36:42 > 0:36:47'So he called it dephlogisticated air.'
0:36:47 > 0:36:51Priestley's experiments with his new air didn't stop there.
0:36:51 > 0:36:53In fact, they got stranger.
0:36:53 > 0:36:58He placed a mouse inside a sealed container filled with this new air,
0:36:58 > 0:37:01expecting it to live for just 15 minutes.
0:37:01 > 0:37:06Instead, he found it alive and well after half an hour.
0:37:06 > 0:37:09He then tried breathing it himself and noted...
0:37:09 > 0:37:16"I fancy my breast felt particularly light and easy after some time.
0:37:16 > 0:37:19"Who can tell but that, in time, this pure air
0:37:19 > 0:37:23"may become a fashionable article of luxury.
0:37:23 > 0:37:28"Hitherto only two mice and I have had the privilege of breathing it."
0:37:29 > 0:37:36'Little did Priestley know that everyone had had the privilege of breathing it.'
0:37:38 > 0:37:43'Oxygen is the third most abundant element in the universe
0:37:43 > 0:37:48'and makes up over half the weight of a human body.
0:37:48 > 0:37:55'At minus 183 degrees Celsius, it condenses to a pale blue liquid.
0:37:55 > 0:38:01'Steel smelting uses more than half of the world's commercially produced oxygen.
0:38:01 > 0:38:04'It's also used in rocket fuel.'
0:38:06 > 0:38:10'Around 21% of air is oxygen.
0:38:10 > 0:38:13'A few percent less and we couldn't breathe.
0:38:13 > 0:38:17'A few percent more and any organic matter ignited
0:38:17 > 0:38:20'would burn out of control.'
0:38:26 > 0:38:30'Although Priestley knew he'd found something special,
0:38:30 > 0:38:33'he didn't realise he'd isolated an element.'
0:38:35 > 0:38:39'He was still hampered by his belief in phlogiston.
0:38:39 > 0:38:43'But his path was about to cross with a visionary
0:38:43 > 0:38:46'who was also thinking about gases and airs.'
0:38:51 > 0:38:55In October 1774, Priestley accompanied
0:38:55 > 0:39:00his benefactor Lord Shelburne on a Grand Tour of Europe.
0:39:05 > 0:39:09They headed to Paris, where they were invited to
0:39:09 > 0:39:12dine with some of the country's most pre-eminent scientists.
0:39:12 > 0:39:17It must have been quite an occasion for a down-to-earth Yorkshireman like Priestley.
0:39:17 > 0:39:22One of the guests was the stellar French scientist Antoine Laviosier.
0:39:22 > 0:39:28By the age of 28 he had already been elected to the French Academy of Sciences.
0:39:28 > 0:39:34This guy was incredible. He'd published everything from the mineralogy of the Pyrenees
0:39:34 > 0:39:38through to locating the best sites for abattoirs in Paris.
0:39:45 > 0:39:50'Lavoisier was not only a member of a newly emerging scientific elite,
0:39:50 > 0:39:56'but a tax collector and an extremely wealthy member of the bourgeoisie.
0:39:56 > 0:40:01'And he was determined to crack open the mysteries of the natural world.'
0:40:02 > 0:40:07When Lavoisier and Priestley met over dinner, they talked chemistry.
0:40:07 > 0:40:15And conversation soon turned to Priestley's exciting new discovery of dephlogisticated air.
0:40:15 > 0:40:18Lavoisier, intrigued, pressed him for details,
0:40:18 > 0:40:23and Priestley clearly found him a very attentive listener
0:40:23 > 0:40:26because he told him all about his experiment.
0:40:29 > 0:40:34'Lavoisier and Priestley were like chalk and cheese.'
0:40:34 > 0:40:38Lavoisier had the best-equipped laboratory in Europe,
0:40:38 > 0:40:44with more than 10,000 pieces of precision technology.
0:40:44 > 0:40:47Priestley worked in a makeshift lab
0:40:47 > 0:40:50with equipment he'd just cobbled together.
0:40:50 > 0:40:56Lavoisier weighed, measured, re-weighed and calculated precisely
0:40:56 > 0:40:58before and after every reaction.
0:40:58 > 0:41:05And he applied this approach to investigate the great mystery of phlogiston.
0:41:05 > 0:41:12Lavoisier's breakthrough came when he turned his fanatical attention to detail
0:41:12 > 0:41:16to the weight of substances before and after they were heated.
0:41:16 > 0:41:21He first weighed a metal very precisely - in this case, tin.
0:41:25 > 0:41:30And if I check the reading, it's 150.07 grams.
0:41:30 > 0:41:34'Heating tin and then reweighing it
0:41:34 > 0:41:38'revealed a nagging problem with the theory of phlogiston.
0:41:38 > 0:41:42'If phlogiston is given off when a substance is heated, it should weigh less.'
0:41:42 > 0:41:47But here the reading is 153.6 grams.
0:41:47 > 0:41:51That's nearly four grams more than before it was heated.
0:41:51 > 0:41:54Here's where Lavoisier had his flash of inspiration.
0:41:54 > 0:41:58Maybe phlogiston isn't given off when a substance is heated.
0:41:58 > 0:42:01Instead, maybe it absorbs some kind of air.
0:42:01 > 0:42:04That would explain this increase.
0:42:04 > 0:42:08But if that was true, what was it that was being added?
0:42:13 > 0:42:17'Fresh from his conversation with Priestley, Lavoisier decided to
0:42:17 > 0:42:22'repeat Priestley's experiment, only in reverse.'
0:42:26 > 0:42:29He heated some mercury inside a sealed container
0:42:29 > 0:42:34until it turned into mercuric oxide, which is the same substance
0:42:34 > 0:42:37that Priestley had used in his experiment.
0:42:37 > 0:42:43He measured the amount of air that was absorbed by the mercury when it was heated.
0:42:43 > 0:42:45He then heated the mercuric oxide
0:42:45 > 0:42:50and observed that the amount of air released was exactly the same
0:42:50 > 0:42:54as the amount of air that had been absorbed by the mercury when it was heated.
0:42:54 > 0:42:58So in a flash of inspiration, he realised that something in the air
0:42:58 > 0:43:03had been taken in by the mercury to make the mercuric oxide.
0:43:03 > 0:43:05And that same gas had then been released.
0:43:05 > 0:43:11He had the courage to conclude that this gas had nothing to do with phlogiston.
0:43:11 > 0:43:14In fact, it was a brand new element.
0:43:14 > 0:43:17Lavoisier called it oxygen.
0:43:17 > 0:43:23So thanks to Priestley's experiment, Lavoisier had exposed the truth
0:43:23 > 0:43:27of the red herring that had hampered chemistry for a century.
0:43:27 > 0:43:32Finally, Lavoiser had shown that phlogiston simply didn't exist.
0:43:35 > 0:43:40'Lavoisier had freed chemistry from the shackles of phlogiston,
0:43:40 > 0:43:43'the remnants of the medieval worldview.
0:43:43 > 0:43:45'And he'd pioneered a scientific method
0:43:45 > 0:43:50'and so could make rapid progress in mapping the elements.
0:43:50 > 0:43:55'But to Priestley's anger, Lavoisier claimed HE had discovered oxygen,
0:43:55 > 0:43:59'because he recognised it as a new element.'
0:43:59 > 0:44:05Trying to resolve who should get the glory proved to be a messy business.
0:44:05 > 0:44:10An embittered war of words and reputations broke out between England and France.
0:44:10 > 0:44:15Priestley was enraged that Lavoisier had tried to steal his thunder,
0:44:15 > 0:44:19and he had a point because Lavoisier's experiments on oxygen
0:44:19 > 0:44:23weren't completed until after he'd met Priestley.
0:44:25 > 0:44:28'Lavoisier may not have discovered oxygen,
0:44:28 > 0:44:31'but he had recognised its significance.
0:44:31 > 0:44:34'And it is Lavoisier, not Priestley,
0:44:34 > 0:44:38'who is known as the Father of Chemistry.
0:44:38 > 0:44:43'The discovery of oxygen had finally crushed any vestiges
0:44:43 > 0:44:46'of the Greek concept of the four elements.'
0:44:46 > 0:44:50Water was made of hydrogen and oxygen.
0:44:50 > 0:44:55Earth and air were a whole hotchpotch of different elements.
0:44:55 > 0:44:59And fire, well, that wasn't an element at all.
0:45:04 > 0:45:08Chemistry was being hauled into the modern era.
0:45:08 > 0:45:11It was an age when chemists were splitting matter,
0:45:11 > 0:45:13making great discoveries,
0:45:13 > 0:45:16just trying to understand what our world was made of.
0:45:16 > 0:45:20But there still didn't seem to be any order,
0:45:20 > 0:45:22any logic to their findings,
0:45:22 > 0:45:26just random elements dotted around the chemical landscape.
0:45:31 > 0:45:36'Lavoisier was the first scientist to define what an element was -
0:45:36 > 0:45:42'a substance that could not be decomposed by existing chemical means.'
0:45:42 > 0:45:44This is the manuscript.
0:45:44 > 0:45:50'And he set about drawing up a definitive list of all the elements.
0:45:50 > 0:45:55'Now, 33 replaced the ancient four.'
0:45:55 > 0:45:57Wow!
0:45:57 > 0:46:03So this is it. This is Lavoisier's original list of elements.
0:46:03 > 0:46:06It's in French and it's in his handwriting,
0:46:06 > 0:46:09but I can still sort of pick out what it says.
0:46:09 > 0:46:14He's divided them up into four groups. Four categories of elements.
0:46:14 > 0:46:20There's the gases, the non-metals, metals and earths.
0:46:20 > 0:46:25You can see among the gases he's got oxygen and hydrogen.
0:46:25 > 0:46:26He didn't get it all right.
0:46:26 > 0:46:32I see he lists here arsenic and antimony among his metals.
0:46:32 > 0:46:35Today, they're not considered to be metals.
0:46:35 > 0:46:39But even more fascinating, he has lumiere, or light,
0:46:39 > 0:46:45and calorique, heat, listed among his elements in the gases.
0:46:45 > 0:46:49Of course light and heat, we know now to be just pure energy.
0:46:49 > 0:46:55But these mistakes apart, this was a huge leap forward in chemistry.
0:46:55 > 0:46:59It was an early realisation that perhaps there was some order to the elements.
0:46:59 > 0:47:04Some grand pattern to the building blocks of our world.
0:47:04 > 0:47:07'And Lavoisier didn't stop there.
0:47:07 > 0:47:13'He created a system to classify the discoveries of many other chemists,
0:47:13 > 0:47:18'and set out to transform the language of chemistry.'
0:47:18 > 0:47:22He began a revolution of scientific vocabulary,
0:47:22 > 0:47:26replacing the picturesque and poetic with precision.
0:47:26 > 0:47:31So dephlogisticated air became oxygen.
0:47:31 > 0:47:35Astringent mars saffron
0:47:35 > 0:47:37became iron oxide.
0:47:37 > 0:47:40Oil of vitriol became sulphuric acid,
0:47:40 > 0:47:46and philosophical wool became zinc oxide.
0:47:46 > 0:47:51At last there was a universal language to identify the elements.
0:47:51 > 0:47:55Maybe it's a shame that some of these exotic names have been replaced,
0:47:55 > 0:47:59but in a way I admire Lavoisier's logic.
0:47:59 > 0:48:01He revolutionised chemistry,
0:48:01 > 0:48:04but other revolutions were in the air.
0:48:07 > 0:48:12'In 1789, the French Revolution would have terrible consequences
0:48:12 > 0:48:15'for both Lavoisier and his rival Priestley.
0:48:15 > 0:48:19'In England, Priestley's sympathies for the uprising
0:48:19 > 0:48:22'gained him unwelcome attention.'
0:48:22 > 0:48:25Things came to a head in 1791 when an angry mob,
0:48:25 > 0:48:29frightened that revolution would find its way to England,
0:48:29 > 0:48:34descended on his new home and burnt it to the ground.
0:48:35 > 0:48:39'Thanks to a tip-off, Priestley escaped unharmed,
0:48:39 > 0:48:43'but decided to flee to America.'
0:48:43 > 0:48:46Lavoisier was not so lucky.
0:48:46 > 0:48:48Despised for his government work,
0:48:48 > 0:48:52Lavoisier and 28 other tax collectors were tried
0:48:52 > 0:48:55and found guilty of conspiring against the people of France.
0:48:55 > 0:49:02He was brought here to Le Place de la Revolution that same day - May 8th, 1794.
0:49:02 > 0:49:05And in 35 minutes, they were all executed.
0:49:05 > 0:49:09The next day the French mathematician Joseph Legrange
0:49:09 > 0:49:13commented, "It took them just an instant to cut off that head,
0:49:13 > 0:49:17"but another 100 years may pass before another like it is seen."
0:49:20 > 0:49:23'Lavoisier left an incredible legacy.
0:49:23 > 0:49:28'He had cast out old dogma and replaced it with an empirical approach.'
0:49:31 > 0:49:33'There was no going back.'
0:49:35 > 0:49:40'Experimentation could now prove or disprove the most radical of ideas.
0:49:40 > 0:49:45'But scientists were still convinced that more elements must be out there
0:49:45 > 0:49:49'and were desperate to find new ways of revealing them.
0:49:49 > 0:49:53'Matter remained fundamentally impenetrable.
0:49:53 > 0:49:57'And it would take a powerful and dangerous force
0:49:57 > 0:50:00'to find a new way of splitting it apart.'
0:50:03 > 0:50:08'Enter Humphry Davy, a wild, charismatic Cornish scientist
0:50:08 > 0:50:11'who frequently courted jeopardy.
0:50:11 > 0:50:16'He was Professor of Chemistry at the Royal Institution in London.
0:50:16 > 0:50:21'On 6th October 1807, Davy was working away in the basement
0:50:21 > 0:50:26'where he'd adapted the servants' quarters to make a lab.'
0:50:26 > 0:50:32He had been working with some crystalline salts...called potash.
0:50:32 > 0:50:35Lavoisier had been unable to break it down,
0:50:35 > 0:50:37and reckoned that it was an element.
0:50:37 > 0:50:40But Davy wasn't convinced.
0:50:40 > 0:50:43He suspected that potash was made up of more than one element.
0:50:43 > 0:50:48But no matter how hard people had tried, potash had defeated them.
0:50:48 > 0:50:52There didn't seem to be any way that chemistry could break it down.
0:50:56 > 0:50:59'Now Davy had a new idea.
0:50:59 > 0:51:03'The first electric battery had recently been invented.'
0:51:04 > 0:51:09'It was very simple. Rows of metal plates and cardboard,
0:51:09 > 0:51:11'soaked in salt water.'
0:51:13 > 0:51:17'But it made the world's first continuous current.
0:51:17 > 0:51:21'I'm going to use the same principle to try to create electricity.'
0:51:24 > 0:51:28I've got a copper coin connected to a zinc washer via a copper wire,
0:51:28 > 0:51:33and if I have enough of these linking up these wine glasses
0:51:33 > 0:51:37filled only with salt water, then I can create a circuit.
0:51:37 > 0:51:41Now if I connect up the copper coin on one side, via a lamp,
0:51:41 > 0:51:44with the zinc washer on the other,
0:51:44 > 0:51:47I've created electricity. The light's come on.
0:51:47 > 0:51:52I've made electricity just from glasses filled with salt water and two different metals.
0:51:52 > 0:51:57Most chemists at the time thought that the effect had something to do with the different metals.
0:51:57 > 0:52:00But Davy believed there was a deeper reason.
0:52:00 > 0:52:05That it was a chemical reaction that was causing the electric current.
0:52:05 > 0:52:10'But if that were the case, then perhaps the reverse could be true,
0:52:10 > 0:52:15'and an electric current could cause a chemical reaction.
0:52:15 > 0:52:19'Davy resolved to find out.
0:52:19 > 0:52:24'Chemist Dr Hal Sosabowski and I are going to attempt Davy's experiment
0:52:24 > 0:52:27'to find out what Davy actually witnessed.'
0:52:27 > 0:52:29- Welcome to the lab.- Thank you.
0:52:29 > 0:52:33Right, so we're going to be splitting potash.
0:52:33 > 0:52:36The first thing we are going to have to do is melt the potash.
0:52:36 > 0:52:40It's got a relatively low melting point of 360, which means we can
0:52:40 > 0:52:43melt it with a Bunsen flame and a blowtorch.
0:52:47 > 0:52:53So almost straight away you're seeing that glistening of the liquid forming.
0:52:53 > 0:52:57It's melting back into the receptacle.
0:52:57 > 0:53:02This, I gather in the melted state is very dangerous, very caustic?
0:53:02 > 0:53:08Exceptionally so. If it splashed on to us it would be instantly disfiguring, instant blindness.
0:53:08 > 0:53:10In a solid state it's bad enough,
0:53:10 > 0:53:13but in the molten state it's really hideously dangerous.
0:53:13 > 0:53:16So it's scary then to think what it must have been like in Davy's lab.
0:53:16 > 0:53:20People losing fingers and eyes and getting disfigured?
0:53:20 > 0:53:22Yes, it was an innocent age in some regards.
0:53:22 > 0:53:25He would have been standing there in his tweeds and bow tie, no glasses.
0:53:25 > 0:53:28That's the way science was. They were all pioneers.
0:53:28 > 0:53:31And don't forget, Davy didn't know what he was looking for.
0:53:31 > 0:53:36He didn't know he was looking for a very reactive metal that would actually catch fire in air.
0:53:36 > 0:53:39So there was a double danger, if you will.
0:53:40 > 0:53:42Over here this is a modern-day lorry battery.
0:53:42 > 0:53:45It provides 12 volts. Enough for our experiment.
0:53:45 > 0:53:48And we've got carbon electrodes, and some jump leads.
0:53:48 > 0:53:50So we're all ready to split our potash.
0:53:50 > 0:53:53We just don't know what it's going to do when we put this in.
0:53:55 > 0:53:58'The electric currents passing through the melted potash
0:53:58 > 0:54:02'is creating an unpredictable and volatile chemical reaction,
0:54:02 > 0:54:06'wrenching apart the electrically charged particles in the potash.
0:54:06 > 0:54:10'But is it enough to split it?'
0:54:10 > 0:54:12It's all changed colour.
0:54:12 > 0:54:15The electrodes are being consumed because it's a caustic environment.
0:54:15 > 0:54:19- Oh, look, there it is! - Oh, that pink flash?
0:54:19 > 0:54:23Yes - that's where the potassium is being produced. And it's reacting straight away.
0:54:23 > 0:54:27That's the potassium on the surface burning quickly in oxygen.
0:54:27 > 0:54:29There's another one, look. Yes, it's reacting.
0:54:29 > 0:54:33Just like a tiny pink matchstick popping on the surface.
0:54:33 > 0:54:37Exactly. And that sort of noise, almost like a match flare, is the potassium flaring off.
0:54:39 > 0:54:42And that's what he would have seen. Just there and then.
0:54:42 > 0:54:44A beautiful lilac flame.
0:54:44 > 0:54:48'Where others had failed, Davy succeeded.
0:54:48 > 0:54:53'He'd split potash into its most fundamental ingredients,
0:54:53 > 0:54:59'forcing out an element never seen before. Potassium.'
0:54:59 > 0:55:04I can't possibly imagine the excitement Davy would have felt.
0:55:04 > 0:55:07He was discovering this new element for the very first time.
0:55:07 > 0:55:09No-one else in the world had seen it.
0:55:09 > 0:55:15His assistant reckoned that Davy did a quick dance around the lab when he made the discovery.
0:55:18 > 0:55:20'Potassium.
0:55:20 > 0:55:26'It's a soft, silvery metal which can be cut like cheese.
0:55:26 > 0:55:32'For a minute it shimmers like steel, then tarnishes in air.
0:55:32 > 0:55:36'Potassium is essential to human life.
0:55:36 > 0:55:39'Our bodies need a constant supply
0:55:39 > 0:55:42'to keep the muscles and kidneys working.
0:55:42 > 0:55:46'It also helps to transmit nerve impulses.
0:55:46 > 0:55:48'But it's a killer, too.
0:55:48 > 0:55:52'A large dose of potassium chloride can result in a fatal heart attack.'
0:55:56 > 0:56:00'When potassium touches water, it reacts explosively,
0:56:00 > 0:56:03'releasing hydrogen and leaving behind potash.'
0:56:06 > 0:56:09'But it's abundant as a salt in seawater.'
0:56:11 > 0:56:16'It took Humphry Davy to prise it from nature and make it visible.'
0:56:18 > 0:56:25Davy seemed to be able to penetrate further into the seemingly unfathomable world of the elements -
0:56:25 > 0:56:28further even than Lavoisier had thought possible.
0:56:28 > 0:56:31But potassium was just the beginning.
0:56:33 > 0:56:38In time, Davy added six new elements to Lavoisier's list,
0:56:38 > 0:56:44and he confirmed that substances like chlorine and iodine were also elements.
0:56:44 > 0:56:47He was a maverick in the world of chemistry -
0:56:47 > 0:56:51fearless, even reckless in the face of a hazardous experiment.
0:56:51 > 0:56:54For him, danger was part of the territory.
0:56:54 > 0:56:59And it was probably his inhalations of those chemicals over the course of his life that took their toll.
0:56:59 > 0:57:05He died in May 1829, aged 50.
0:57:05 > 0:57:12'His quest for knowledge, to delve deeper into the concealed natural world,
0:57:12 > 0:57:15'perhaps cost him his life.
0:57:15 > 0:57:20'But the step he made for scientific progress is immeasurable.'
0:57:20 > 0:57:26By the time of Davy's death, the idea of the elements was firmly established.
0:57:26 > 0:57:3155 of our planet's building blocks had been identified.
0:57:31 > 0:57:36And the world had a new science - chemistry.
0:57:41 > 0:57:46'Next time, I'm going to take up the quest of the chemical pioneers...'
0:57:46 > 0:57:47Well, my arm's burning up.
0:57:47 > 0:57:51'..as they struggled to make sense of elemental chaos.
0:57:51 > 0:57:55'I'll find out how a scientist's dream
0:57:55 > 0:57:59was to become one of our most beautiful creations -
0:57:59 > 0:58:01'the periodic table.
0:58:01 > 0:58:06'And I'll delve into the subatomic world to reveal
0:58:06 > 0:58:11'the hidden pattern of the universe, the order of the elements.'
0:58:26 > 0:58:29Subtitles by Red Bee Media Ltd
0:58:29 > 0:58:33E-mail subtitling@bbc.co.uk