0:00:10 > 0:00:13These ancient trees have stood here
0:00:13 > 0:00:17overlooking the Herefordshire countryside for hundreds of years.
0:00:20 > 0:00:25The largest is 35m tall and 3m thick.
0:00:26 > 0:00:31This tree is one of Britain's biggest living things.
0:00:31 > 0:00:33And if I asked you where the raw materials came from to build it,
0:00:33 > 0:00:36you might say from the soil or from the water
0:00:36 > 0:00:38that it sucks up through its roots.
0:00:38 > 0:00:43But in fact, this tree was built almost entirely from thin air.
0:00:49 > 0:00:52The tree uses carbon dioxide from the air
0:00:52 > 0:00:55to build the molecules that make up everything
0:00:55 > 0:00:59from its mighty trunk to its delicate branches.
0:01:02 > 0:01:05Nitrogen that has passed from the air into the soil
0:01:05 > 0:01:07nourishes the tree.
0:01:09 > 0:01:11And its leaves release oxygen.
0:01:11 > 0:01:15The vital, life-giving gas that we need to breathe.
0:01:17 > 0:01:19Today, we know the air around us
0:01:19 > 0:01:22contains the raw materials from which life is made.
0:01:26 > 0:01:30But how did we come to know that this invisible stuff around us
0:01:30 > 0:01:32contains anything at all?
0:01:37 > 0:01:41It is a remarkable story of heroes and underdogs,
0:01:41 > 0:01:45chance encounters and sheer blind luck.
0:01:47 > 0:01:48It shaped our modern world.
0:01:50 > 0:01:53Unravelled the secrets of life itself.
0:01:57 > 0:02:00And it all began with one simple question.
0:02:00 > 0:02:03What is air?
0:02:19 > 0:02:22I'm Gabrielle Walker and I trained as a chemist
0:02:22 > 0:02:25because I love the way chemistry reveals
0:02:25 > 0:02:28that ordinary things are full of hidden wonders.
0:02:29 > 0:02:32Take this view across the water here in the Solent,
0:02:32 > 0:02:35which hasn't changed much in hundreds of years.
0:02:37 > 0:02:40But in a sense, I see it differently
0:02:40 > 0:02:43from the way that people would have seen it in the past.
0:02:43 > 0:02:46I know that the water is made of hydrogen and oxygen.
0:02:46 > 0:02:49I know that the sun is a distant star
0:02:49 > 0:02:51and I also know that the air around me
0:02:51 > 0:02:53is made up of a mixture of gases.
0:02:56 > 0:02:59I know these things because today we have the tools
0:02:59 > 0:03:02and the technology to unlock the secrets of the natural world.
0:03:06 > 0:03:11But for most of human history, there were no tools or technology,
0:03:11 > 0:03:13only simple observation and deduction.
0:03:17 > 0:03:19But when it comes to the air,
0:03:19 > 0:03:21there isn't very much to observe.
0:03:22 > 0:03:26There are no clues to suggest that air is made of anything but air.
0:03:28 > 0:03:30So ever since the Ancient Greeks,
0:03:30 > 0:03:31people had assumed
0:03:31 > 0:03:33that air was a single element,
0:03:33 > 0:03:35entire and indivisible,
0:03:35 > 0:03:37with no constituent parts.
0:03:41 > 0:03:44You can see why those beliefs made sense.
0:03:44 > 0:03:46In fact, they seemed so reasonable,
0:03:46 > 0:03:49that not only did they form the basis
0:03:49 > 0:03:51for the way the Ancient Greeks saw the natural the world,
0:03:51 > 0:03:55they also continued unchallenged for more than 2,000 years.
0:03:58 > 0:04:00It wasn't until the 17th century
0:04:00 > 0:04:04that this view of the world began to change,
0:04:04 > 0:04:07and the first clues that the air around us contains hidden secrets
0:04:07 > 0:04:09began to emerge.
0:04:15 > 0:04:18New technology meant that it became possible to go beyond
0:04:18 > 0:04:21what could be seen with the naked eye.
0:04:24 > 0:04:27The first telescopes revealed entirely new worlds
0:04:27 > 0:04:30that had lain hidden beyond our sight.
0:04:35 > 0:04:38And the first microscopes uncovered a miniature kingdom
0:04:38 > 0:04:41existing right beneath our noses.
0:04:45 > 0:04:48A new breed of thinkers emerged,
0:04:48 > 0:04:51with an entirely new way of understanding the world.
0:04:57 > 0:05:00It was the Age of Enlightenment, the biggest cultural revolution
0:05:00 > 0:05:02the world has ever seen.
0:05:02 > 0:05:04This was led by men and women
0:05:04 > 0:05:07who no longer trusted the traditional views of the world
0:05:07 > 0:05:11and their place in it that had been handed down through the generations.
0:05:11 > 0:05:13They were no longer content to understand the world
0:05:13 > 0:05:18the way the Ancient Greeks had by passive observation.
0:05:18 > 0:05:21Instead, they wanted to find the truth.
0:05:21 > 0:05:23They probed and tested things.
0:05:23 > 0:05:25They conducted experiments.
0:05:25 > 0:05:27They called themselves natural philosophers.
0:05:27 > 0:05:29We'd call them scientists.
0:05:33 > 0:05:36The dawn of science brought remarkable progress.
0:05:39 > 0:05:43Including the first big breakthrough in the quest to understand
0:05:43 > 0:05:44what air is made of.
0:05:48 > 0:05:51It was an extraordinary discovery,
0:05:51 > 0:05:53but it was made entirely by accident.
0:05:56 > 0:06:01In 1754, a Scottish doctor named Joseph Black
0:06:01 > 0:06:05was looking for a cure for an excruciatingly painful condition
0:06:05 > 0:06:07that plagued many of his patients...
0:06:13 > 0:06:15..bladder stones.
0:06:16 > 0:06:18In the 18th century,
0:06:18 > 0:06:22the only treatment for bladder stones was surgery
0:06:22 > 0:06:25with no anaesthetic.
0:06:25 > 0:06:28Patients were held down,
0:06:28 > 0:06:30sliced open
0:06:30 > 0:06:33and the stones ripped out with metal tongs.
0:06:38 > 0:06:42Joseph Black believed there had to be a better solution.
0:06:42 > 0:06:45So he set out to make a medicine
0:06:45 > 0:06:48that he hoped would dissolve the bladder stones,
0:06:48 > 0:06:50eliminating the need for surgery.
0:07:01 > 0:07:04The way he went about it was actually very simple,
0:07:04 > 0:07:06so it's easy for me to replicate it today.
0:07:09 > 0:07:12He started with this stuff, magnesia alba,
0:07:12 > 0:07:14which is basically just a kind of salt.
0:07:14 > 0:07:15And he intended to heat it
0:07:15 > 0:07:18and mix it with water to make a medicine.
0:07:20 > 0:07:24Magnesia alba was known for its corrosive properties
0:07:24 > 0:07:27and Black thought it might be strong enough to dissolve bladder stones.
0:07:28 > 0:07:30He would have heated it using a burning glass,
0:07:30 > 0:07:33a sort of magnifying glass to focus the sun,
0:07:33 > 0:07:36but I'm going to cheat a bit and use a modern blowtorch.
0:07:46 > 0:07:49But as he heated it, Black noticed something odd.
0:07:52 > 0:07:54Bubbles of air were released.
0:07:55 > 0:08:00The air given off by the magnesia alba looked just like ordinary air,
0:08:00 > 0:08:03but Black was not content with passive observation.
0:08:03 > 0:08:06He was a natural philosopher, so he tested the air.
0:08:06 > 0:08:11And his tests revealed that this air was anything but ordinary.
0:08:14 > 0:08:16A candle would not burn in it.
0:08:19 > 0:08:21And a mouse, that would last 15 minutes
0:08:21 > 0:08:24in a container of ordinary, common air,
0:08:24 > 0:08:26died in seconds.
0:08:31 > 0:08:34Black had never seen anything like it.
0:08:36 > 0:08:40This was the first time that anyone had identified a gas
0:08:40 > 0:08:42that was different from common air.
0:08:46 > 0:08:49Black called it "fixed air"
0:08:49 > 0:08:52because he'd found it fixed inside the magnesia alba.
0:08:54 > 0:08:58Today, we know it by its modern name -
0:08:58 > 0:08:59carbon dioxide.
0:09:05 > 0:09:09The tiny, but vital part of the air, that all plants rely on.
0:09:12 > 0:09:14Completely by accident,
0:09:14 > 0:09:16Black had found hard evidence
0:09:16 > 0:09:18that air is not a single element.
0:09:20 > 0:09:23It's made of constituent parts.
0:09:26 > 0:09:29The problem was he just didn't see it like that.
0:09:33 > 0:09:35Joseph Black had one of the key ingredients of air
0:09:35 > 0:09:39right there in front of him, but he didn't realise it.
0:09:39 > 0:09:41He couldn't let go of the ancient belief
0:09:41 > 0:09:44that air is an element entire and indivisible.
0:09:44 > 0:09:47He thought that "fixed air" was some entirely new kind of air,
0:09:47 > 0:09:50totally different from the common air that we breathe.
0:09:54 > 0:09:57The quest to understand the air had barely begun,
0:09:57 > 0:10:00but it was already heading down the wrong path.
0:10:03 > 0:10:06Black's discovery hadn't actually got us any closer
0:10:06 > 0:10:09to understanding what air is made of.
0:10:11 > 0:10:15But it did raise one intriguing question.
0:10:15 > 0:10:19Why couldn't a candle or a mouse survive in "fixed air"
0:10:19 > 0:10:21when they so easily could in ordinary air?
0:10:24 > 0:10:28In other words, what was the relationship between combustion,
0:10:28 > 0:10:30respiration and the air?
0:10:31 > 0:10:33For months, Black tried in vain
0:10:33 > 0:10:35to unravel the mysteries of "fixed air".
0:10:37 > 0:10:40But eventually, he admitted defeat
0:10:40 > 0:10:44and handed the problem over to his apprentice,
0:10:44 > 0:10:48a promising young medical student named Daniel Rutherford.
0:10:55 > 0:10:58Fresh-faced, young Rutherford took up the challenge
0:10:58 > 0:11:00with great enthusiasm.
0:11:05 > 0:11:06But instead of shedding light
0:11:06 > 0:11:09on the mysterious properties of "fixed air",
0:11:09 > 0:11:12he stumbled across yet another new gas.
0:11:13 > 0:11:16It was even more potent than "fixed air".
0:11:17 > 0:11:19Nothing would burn in it.
0:11:19 > 0:11:23And it killed a mouse in an instant.
0:11:24 > 0:11:26Its effects were so striking,
0:11:26 > 0:11:29he named it "noxious air".
0:11:32 > 0:11:37Rutherford, the apprentice, had discovered nitrogen.
0:11:37 > 0:11:40The gas that makes up nearly 80% of the air we breathe.
0:11:46 > 0:11:50For a 22-year-old student, this was a remarkable achievement.
0:11:52 > 0:11:55But in truth, the discovery of nitrogen
0:11:55 > 0:11:57had only added to the confusion.
0:12:01 > 0:12:03The relationship between combustion,
0:12:03 > 0:12:07respiration and air was still a complete mystery.
0:12:10 > 0:12:14But Rutherford wasn't the only one who'd been working on the problem.
0:12:23 > 0:12:27Other natural philosophers had come up with an excellent solution.
0:12:30 > 0:12:31Or so they thought.
0:12:34 > 0:12:38This beautiful manuscript was handwritten in 1783.
0:12:38 > 0:12:39And it refers to a bizarre idea
0:12:39 > 0:12:42they had at the time about why things burn.
0:12:42 > 0:12:47It says, "Inflammable air may be made from liquid substances
0:12:47 > 0:12:48"containing phlogiston."
0:12:50 > 0:12:52They thought that phlogiston was a sort of fire-like element
0:12:52 > 0:12:55existing in anything that could burn,
0:12:55 > 0:12:58but this isn't some mystical text.
0:12:58 > 0:13:01It's a scientific publication
0:13:01 > 0:13:02and in the 18th century,
0:13:02 > 0:13:06the theory of phlogiston was right at the cutting edge.
0:13:10 > 0:13:13It sounds bizarre to us today,
0:13:13 > 0:13:15but at the time, the existence of phlogiston
0:13:15 > 0:13:17seemed to make perfect sense.
0:13:21 > 0:13:24According to the theory, when the candle burns,
0:13:24 > 0:13:27it gives off that fiery substance - phlogiston.
0:13:28 > 0:13:31If I cover the candle,
0:13:31 > 0:13:33phlogiston builds up inside the jar
0:13:33 > 0:13:36until eventually there's no room for any more
0:13:36 > 0:13:37and the candle goes out.
0:13:40 > 0:13:43It's like trying to fit more people into a crowded room.
0:13:43 > 0:13:46There's no room for any more phlogiston to leave the candle
0:13:46 > 0:13:48and according to the theory,
0:13:48 > 0:13:50that's why the combustion stops.
0:13:53 > 0:13:55And it wasn't just candles,
0:13:55 > 0:13:59phlogiston was thought to dwell inside living things too.
0:14:00 > 0:14:04When I breathe out, phlogiston is released in my breath,
0:14:04 > 0:14:07so if you put me in a jar, I'd have the same fate as the candle.
0:14:07 > 0:14:10Pretty soon, the jar would fill up with phlogiston,
0:14:10 > 0:14:13there would be no more room for any to leave my body and I'd die.
0:14:21 > 0:14:24The idea of phlogiston seemed so logical,
0:14:24 > 0:14:26it soon became the accepted explanation
0:14:26 > 0:14:28for combustion and respiration.
0:14:33 > 0:14:36For Rutherford, it was the answer he'd been looking for.
0:14:39 > 0:14:42He reasoned that "fixed air" must contain more phlogiston
0:14:42 > 0:14:47than common air, and "noxious air" contained even more still.
0:14:50 > 0:14:53That would explain why the gases would put out a candle
0:14:53 > 0:14:54and kill a mouse.
0:14:56 > 0:14:58It was the perfect solution.
0:15:00 > 0:15:04Except, of course, it was completely wrong.
0:15:04 > 0:15:06Today, we know that if you put a flame
0:15:06 > 0:15:09or a living thing in a confined space,
0:15:09 > 0:15:13it doesn't die because the space fills up with phlogiston.
0:15:13 > 0:15:16It dies because it runs out of oxygen.
0:15:23 > 0:15:26Oxygen was the missing piece of the puzzle.
0:15:26 > 0:15:29The one vital part of the air, yet to be found.
0:15:31 > 0:15:35Its discovery would bury the idea of phlogiston forever...
0:15:38 > 0:15:42..give a profound insight into our own physiology...
0:15:43 > 0:15:45..and transform our world.
0:15:52 > 0:15:55The identification of oxygen was to be
0:15:55 > 0:15:57one of science's greatest achievements.
0:16:00 > 0:16:04But the question of who deserved the credit for the discovery
0:16:04 > 0:16:05caused a bitter dispute.
0:16:07 > 0:16:09And it's still a contentious issue today.
0:16:17 > 0:16:22There are three contenders, each with a rightful claim to the glory.
0:16:24 > 0:16:26An innovative Swedish pharmacist.
0:16:27 > 0:16:30A wealthy Parisian aristocrat.
0:16:32 > 0:16:36And an ordinary, working-class Englishman named Joseph Priestley.
0:16:39 > 0:16:42Priestley was different from other natural philosophers of his day.
0:16:44 > 0:16:46He was disorganized.
0:16:46 > 0:16:48He lacked focus.
0:16:48 > 0:16:51You wouldn't think he had the makings of a great scientist.
0:16:54 > 0:16:56But he was creative
0:16:56 > 0:16:59and that meant he made connections the others missed.
0:17:03 > 0:17:05Typical of his eccentric character,
0:17:05 > 0:17:07Priestley's role in the discovery of oxygen
0:17:07 > 0:17:10began in the most unlikely of places...
0:17:14 > 0:17:15..a brewery.
0:17:20 > 0:17:23But it wasn't the beer that drew him here.
0:17:23 > 0:17:26It was the thick, heavy air that flowed out of the brewery vats.
0:17:29 > 0:17:33This is an experiment that Priestley himself actually did.
0:17:35 > 0:17:37He put a flame in the path
0:17:37 > 0:17:39of the air that was coming out of the vats...
0:17:42 > 0:17:43..and as you can see...
0:17:47 > 0:17:48..the flame goes out.
0:17:49 > 0:17:51He realised this must be the same "fixed air"
0:17:51 > 0:17:55that Joseph Black had discovered a few years earlier.
0:17:57 > 0:18:00Priestley decided to experiment with it.
0:18:00 > 0:18:03It was the start of an extraordinary journey
0:18:03 > 0:18:07that would take him far beyond what Black had discovered
0:18:07 > 0:18:09and eventually lead him to oxygen.
0:18:13 > 0:18:18On one of his visits to the brewery, Priestley brought some bellows,
0:18:18 > 0:18:21because he wanted to try bubbling the gas through water.
0:18:23 > 0:18:25My equipment isn't quite as elegant as Priestley's.
0:18:25 > 0:18:27I've got this plastic tube,
0:18:27 > 0:18:30which is attached to the bottom of the vat here
0:18:30 > 0:18:33where all the carbon dioxide has sunk to the bottom
0:18:33 > 0:18:35and a bottle of water.
0:18:36 > 0:18:39But the principle of the experiment is exactly the same.
0:18:40 > 0:18:43So, turn the valve...
0:18:44 > 0:18:45..and there it goes!
0:18:47 > 0:18:50Once he had tired of mixing the gas with water,
0:18:50 > 0:18:52Priestley decided to taste it.
0:18:58 > 0:19:00Not bad, it's kind of tingly.
0:19:03 > 0:19:06He had invented the world's first fizzy drink.
0:19:06 > 0:19:08Soda water.
0:19:08 > 0:19:09SODA CAN POPS OPEN
0:19:12 > 0:19:16Others would make millions from Priestley's invention.
0:19:16 > 0:19:20But he had a different idea that was far more left-field.
0:19:24 > 0:19:28He'd heard of a curious observation made by an Irish surgeon,
0:19:28 > 0:19:31who had left a piece of meat to rot
0:19:31 > 0:19:33and noticed that as it rotted,
0:19:33 > 0:19:36it released carbon dioxide, "fixed air".
0:19:38 > 0:19:42At the time, nobody had a clue what was causing meat to rot,
0:19:42 > 0:19:45but these new experiments gave Priestley an idea.
0:19:45 > 0:19:47What if the meat was going bad
0:19:47 > 0:19:50because it was losing its "fixed air"?
0:19:50 > 0:19:52And if that was the case,
0:19:52 > 0:19:56perhaps, he could use this to put the "fixed air" back into the meat
0:19:56 > 0:19:57and stop it rotting.
0:20:00 > 0:20:04But Priestley wasn't thinking about the type of meat you eat.
0:20:04 > 0:20:07He was thinking about people's bodies.
0:20:09 > 0:20:11Because in the 18th century,
0:20:11 > 0:20:15diseases that caused flesh to rot were rife.
0:20:17 > 0:20:19There was gangrene,
0:20:19 > 0:20:21yellow fever
0:20:21 > 0:20:23and the disease that every sailor feared...
0:20:25 > 0:20:26..scurvy.
0:20:28 > 0:20:30In Priestley's day,
0:20:30 > 0:20:35the British Navy was engaged in almost continuous battle,
0:20:35 > 0:20:40defending the Empire at home and overseas.
0:20:43 > 0:20:46But more sailors died from scurvy than in battle.
0:20:50 > 0:20:54'Medical historian Dr Erica Charters, is going to show me
0:20:54 > 0:20:57'why Priestley believed his soda water had the potential
0:20:57 > 0:21:00'to be much more than just a fizzy drink.'
0:21:02 > 0:21:04So, Erica, these are pretty revolting, what are they?
0:21:04 > 0:21:08So, this is an early 19th-century portrayal of scurvy sufferers
0:21:08 > 0:21:10and specifically of their legs.
0:21:10 > 0:21:12So, people often talk about why they think it's a disease
0:21:12 > 0:21:14of putrefaction is because it looks
0:21:14 > 0:21:15like people are putrefying
0:21:15 > 0:21:18and they can smell the putrefying matter as well.
0:21:18 > 0:21:19So, if you look at the images here
0:21:19 > 0:21:22and if you kind of imagine what it would've been like to be
0:21:22 > 0:21:25on a crowded ship with hundreds of men suffering from scurvy,
0:21:25 > 0:21:29you can imagine why people said it's clearly a problem with putrefaction.
0:21:29 > 0:21:32I suppose, if...if the flesh is actually, seems like it's rotting,
0:21:32 > 0:21:35- it's also giving out "fixed air", carbon dioxide...- Yeah.
0:21:35 > 0:21:38- And that's where Priestley's idea comes in.- Yeah, that's right.
0:21:38 > 0:21:41So, there were all sorts of theories about how you need to
0:21:41 > 0:21:43kind of either put the "fixed air" back into the meat
0:21:43 > 0:21:46or by having "fixed air", this will somehow preserve your body
0:21:46 > 0:21:48from the natural process of putrefaction.
0:21:48 > 0:21:50So what Priestley had was "fixed air" actually trapped
0:21:50 > 0:21:53- and that would've been a way to get it back into people.- That's right.
0:21:53 > 0:21:57It would have been a very practical solution to curing scurvy.
0:21:57 > 0:21:58That would have been a pretty big deal
0:21:58 > 0:22:00if he actually had come up with a cure for scurvy.
0:22:00 > 0:22:03It would have been. This was seen as being something,
0:22:03 > 0:22:05which was important to the British nation
0:22:05 > 0:22:07and to the British Empire as well.
0:22:07 > 0:22:10So, if you could cure scurvy, you would really make a difference.
0:22:12 > 0:22:16There was so much optimism that Priestley's soda water could work,
0:22:16 > 0:22:21naval officials instructed Captain James Cook to test it out
0:22:21 > 0:22:22on his second voyage.
0:22:26 > 0:22:29Cook set sail for the coast of Australia,
0:22:29 > 0:22:34but sadly, soda water didn't have the effect everyone was hoping for.
0:22:36 > 0:22:40We now know that fresh produce is the key to keeping scurvy at bay.
0:22:43 > 0:22:46But as far as Priestley was concerned,
0:22:46 > 0:22:47it didn't matter.
0:22:51 > 0:22:54Soda water had got him hooked on the study of gases.
0:22:55 > 0:22:59He couldn't wait to carry out more experiments
0:22:59 > 0:23:00to see what else he could find.
0:23:02 > 0:23:04And it was this enthusiasm
0:23:04 > 0:23:07that was the key to Priestley's great breakthrough.
0:23:13 > 0:23:15What I love about Priestley is he wasn't some great doctor
0:23:15 > 0:23:18or scholar, but he had this fiery curiosity.
0:23:18 > 0:23:20If an experiment blew up in his face,
0:23:20 > 0:23:23he'd just dodge out of the way of the flying glass
0:23:23 > 0:23:26and just do it again to see if it would happen again.
0:23:26 > 0:23:29For me, Priestley embodies all that's great
0:23:29 > 0:23:33about using scientific experiments as a way to explore the world,
0:23:33 > 0:23:36because the results aren't always planned.
0:23:36 > 0:23:38Sometimes, the best things come
0:23:38 > 0:23:40when you're not expecting them.
0:23:40 > 0:23:42And that's exactly what Priestley found.
0:23:47 > 0:23:50Characteristic of Priestley's disorganised,
0:23:50 > 0:23:52scatter-gun approach to experimenting,
0:23:52 > 0:23:55one day, for no particular reason,
0:23:55 > 0:23:57he tried heating some mercury.
0:24:08 > 0:24:11Nothing particularly interesting happens when you heat mercury,
0:24:11 > 0:24:13except that you get this - a sort of orangey powder
0:24:13 > 0:24:16that at the time they called mercury calyx.
0:24:16 > 0:24:20Ever the experimenter, though, Priestley tried heating the calyx
0:24:20 > 0:24:22and this turned out to be much more interesting.
0:24:28 > 0:24:31To his delight, the calyx released bubbles of gas.
0:24:33 > 0:24:37He collected as much of it as he could and decided to test it.
0:24:41 > 0:24:43In "fixed air", a flame would go out.
0:24:46 > 0:24:48But in this air,
0:24:48 > 0:24:51it burned more brightly than anything Priestley had ever seen.
0:24:56 > 0:24:59A mouse that would die in "fixed air",
0:24:59 > 0:25:02lived quite happily in this new gas.
0:25:02 > 0:25:06In fact, the mouse lived twice as long as it would in ordinary air.
0:25:10 > 0:25:13Priestley even tried breathing it himself
0:25:13 > 0:25:15and he said it made him feel fantastic.
0:25:15 > 0:25:17He wrote excitedly, "Up until now,
0:25:17 > 0:25:20"only two mice and I have had the privilege of breathing it."
0:25:24 > 0:25:28Priestley realised that this new gas was very special indeed.
0:25:33 > 0:25:35Priestley had discovered oxygen.
0:25:35 > 0:25:37The most fundamental, life-giving part of the air
0:25:37 > 0:25:39that we all need to breathe.
0:25:39 > 0:25:43He'd seen the profound effects it had on a flame and on living things.
0:25:43 > 0:25:46He had witnessed the chemistry of life happening
0:25:46 > 0:25:47right there in front of him.
0:25:47 > 0:25:50He was so close to breaking down the barriers
0:25:50 > 0:25:53that had held Black and Rutherford back.
0:25:53 > 0:25:55But he didn't quite make it.
0:25:59 > 0:26:01As far as Priestly was concerned,
0:26:01 > 0:26:04the fiery, life-giving properties of his new gas
0:26:04 > 0:26:09fitted neatly into the fashionable theory of the day -
0:26:09 > 0:26:10phlogiston.
0:26:14 > 0:26:19This mysterious element was believed to be released during combustion
0:26:19 > 0:26:20and respiration.
0:26:21 > 0:26:27"Fixed air" and "noxious air" were thought to be full of phlogiston.
0:26:27 > 0:26:30That's why they put out a candle and killed a mouse.
0:26:32 > 0:26:37But Priestley's gas appeared to have virtually no phlogiston,
0:26:37 > 0:26:39so a candle and a mouse would thrive in it.
0:26:44 > 0:26:47He gave it the not-exactly-catchy name -
0:26:47 > 0:26:49"dephlogisticated air".
0:26:59 > 0:27:02Priestley had isolated oxygen,
0:27:02 > 0:27:05but that doesn't necessarily mean he deserves the credit
0:27:05 > 0:27:06for its discovery.
0:27:10 > 0:27:14Because in truth, Priestley had no idea what it was that he'd found.
0:27:15 > 0:27:19And it turned out he wasn't even the first person to have come across it.
0:27:21 > 0:27:23There was a second contender,
0:27:23 > 0:27:26a Swedish pharmacist named Carl Scheele.
0:27:27 > 0:27:33In 1771, three years before Priestley's experiment,
0:27:33 > 0:27:37Scheele had been busy mixing chemicals in his lab,
0:27:37 > 0:27:39when he came across an unusual gas.
0:27:40 > 0:27:43He put a candle into it and he wrote,
0:27:43 > 0:27:46"That immediately the candle burned with a large flame
0:27:46 > 0:27:50"of so vivid a light that it dazzled the eyes."
0:27:50 > 0:27:52Obviously, it was oxygen.
0:27:53 > 0:27:55So, was Scheele the true discoverer?
0:27:56 > 0:27:59Well, unfortunately for him,
0:27:59 > 0:28:02although he did the experiment first,
0:28:02 > 0:28:05he didn't publish his findings until much later.
0:28:07 > 0:28:10So, although Scheele was the first to find oxygen,
0:28:10 > 0:28:13Priestley was the first to document it.
0:28:18 > 0:28:20But even so, for me,
0:28:20 > 0:28:23that was still just the first step towards its discovery.
0:28:26 > 0:28:29The next big leap was truly to understand it.
0:28:30 > 0:28:34And that required the mind of a visionary.
0:28:40 > 0:28:44Across the Channel in France, revolution was in the air.
0:28:46 > 0:28:49Taxes were high, famine was rife
0:28:49 > 0:28:53and civil unrest was close to boiling point.
0:28:54 > 0:28:57Life was harsh for everyday folk,
0:28:57 > 0:29:00while the rich were lavished with luxury.
0:29:03 > 0:29:06Antoine Lavoisier was the only son
0:29:06 > 0:29:09and heir of one of Paris' most distinguished families.
0:29:10 > 0:29:13He was extremely bright,
0:29:13 > 0:29:17absurdly wealthy and he had one passion -
0:29:17 > 0:29:18natural philosophy.
0:29:23 > 0:29:27By the age of 29, Lavoisier had published papers on everything -
0:29:27 > 0:29:31from the water systems of Paris to the composition of meteorites.
0:29:32 > 0:29:35But it wasn't great wealth that made Lavoisier
0:29:35 > 0:29:37such a brilliant scientist,
0:29:37 > 0:29:39although no doubt it helped.
0:29:39 > 0:29:41It was his personality.
0:29:46 > 0:29:48Lavoisier was meticulous.
0:29:48 > 0:29:51He loved precision and accuracy.
0:29:51 > 0:29:55The messy, complicated system of weights and measures
0:29:55 > 0:29:58used at the time drove him mad with frustration.
0:29:59 > 0:30:05So he developed a new, orderly system of grams and kilograms.
0:30:05 > 0:30:07The metric system.
0:30:08 > 0:30:11It was Lavoisier's obsession with weights and measures
0:30:11 > 0:30:16that would lead him to uncover the true nature of the air around us
0:30:16 > 0:30:19and ultimately, transform our world.
0:30:25 > 0:30:28Like any 18th-century scientist worth his salt,
0:30:28 > 0:30:32Lavoisier spent a great deal of time heating things up
0:30:32 > 0:30:33to see what happened.
0:30:36 > 0:30:40And just like all the others, Lavoisier started out believing
0:30:40 > 0:30:43that substances released phlogiston when they burned.
0:30:45 > 0:30:48But precise, meticulous Lavoisier was worried about something
0:30:48 > 0:30:50that everyone else had overlooked.
0:30:50 > 0:30:52If heating a substance made it lose phlogiston,
0:30:52 > 0:30:54it should get lighter,
0:30:54 > 0:30:57but that simply wasn't the case.
0:30:58 > 0:31:01He carefully weighed a piece of lead,
0:31:01 > 0:31:03and then he heated it
0:31:03 > 0:31:07until it turned into a brown, powdery substance called lead calyx.
0:31:09 > 0:31:11But when he weighed the calyx,
0:31:11 > 0:31:14it was heavier than the lead he'd started with.
0:31:14 > 0:31:16It was a pivotal moment.
0:31:16 > 0:31:19Lavoisier knew the theory of phlogiston had to be wrong.
0:31:19 > 0:31:21Something else was going on in combustion.
0:31:21 > 0:31:24If lead gets heavier when it's heated,
0:31:24 > 0:31:25it can't be losing phlogiston.
0:31:25 > 0:31:28It must be gaining something, but what?
0:31:30 > 0:31:33This was where Lavoisier's fascination with weights
0:31:33 > 0:31:34and measures came into its own.
0:31:36 > 0:31:39Lavoisier repeated the experiment.
0:31:39 > 0:31:42He took some lead and he put it on a set of scales.
0:31:42 > 0:31:46Not modern electronic scales like these, but the principle's the same.
0:31:46 > 0:31:51Then, the clever thing was, he put the scales on another set of scales.
0:31:52 > 0:31:54Then he sealed it,
0:31:54 > 0:31:58so that nothing could get in and nothing could get out.
0:31:59 > 0:32:03And now, he heated the lead from the outside.
0:32:03 > 0:32:06And just as he expected, as the lead got hotter,
0:32:06 > 0:32:07it got heavier.
0:32:07 > 0:32:10But when he looked at this scale,
0:32:10 > 0:32:11it hadn't moved an inch.
0:32:13 > 0:32:16So, because the lead was sealed inside,
0:32:16 > 0:32:18whatever was causing it to get heavier
0:32:18 > 0:32:21had to come from within the jar.
0:32:22 > 0:32:23It had to be the air.
0:32:25 > 0:32:29Some mysterious ingredient was passing from the air into the lead.
0:32:31 > 0:32:34Lavoisier was determined to get this mysterious ingredient
0:32:34 > 0:32:38back out of the lead, so he could study it.
0:32:38 > 0:32:39But try as he might,
0:32:39 > 0:32:44the lead stubbornly refused to release the air it had absorbed.
0:32:44 > 0:32:47The brilliant Lavoisier was stumped.
0:32:50 > 0:32:54But then he heard that an English scientist was in town.
0:32:54 > 0:32:58Someone who was renowned for his work with new gases.
0:32:58 > 0:32:59Joseph Priestley.
0:33:00 > 0:33:04Priestley was on a tour of Europe as the guest of an English aristocrat.
0:33:04 > 0:33:06When he received an invitation to dinner
0:33:06 > 0:33:08from the great Antoine Lavoisier,
0:33:08 > 0:33:11he was excited and immediately accepted.
0:33:12 > 0:33:15Over dinner, they talked chemistry.
0:33:16 > 0:33:17With great enthusiasm,
0:33:17 > 0:33:21Priestley told Lavoisier all about his latest discovery.
0:33:24 > 0:33:26Lavoisier listened intently
0:33:26 > 0:33:29while Priestley described how heating mercury calyx
0:33:29 > 0:33:33released vast quantities of "dephlogisticated air".
0:33:33 > 0:33:36Mercury was the one thing that Lavoisier hadn't tried.
0:33:36 > 0:33:38From the sound of Priestley's experiment,
0:33:38 > 0:33:40it could be exactly what he was looking for.
0:33:45 > 0:33:48Mercury absorbed air when it was heated,
0:33:48 > 0:33:52but crucially, unlike lead,
0:33:52 > 0:33:56when it was heated a second time, it released the air it had absorbed.
0:33:57 > 0:33:59And not just any air -
0:33:59 > 0:34:01"dephlogisticated air".
0:34:04 > 0:34:07Lavoisier realised that this could be the missing ingredient
0:34:07 > 0:34:09he was looking for.
0:34:11 > 0:34:13As soon as Priestley left,
0:34:13 > 0:34:16Lavoisier ditched the lead he had been using
0:34:16 > 0:34:18and tried heating mercury instead.
0:34:21 > 0:34:24Lavoisier heated mercury until it turned into mercury calyx
0:34:24 > 0:34:26and he measured how much air went into it.
0:34:26 > 0:34:29And then he heated mercury calyx until it turned into mercury
0:34:29 > 0:34:31and measured how much air came out.
0:34:31 > 0:34:33And found it was exactly the same amount.
0:34:35 > 0:34:39The mercury had absorbed a part of ordinary air
0:34:39 > 0:34:41when it was heated
0:34:41 > 0:34:44and that same air had been released again.
0:34:44 > 0:34:47The air released was the gas Priestley called
0:34:47 > 0:34:49"dephlogisticated air".
0:34:49 > 0:34:51Lavoisier realised that "dephlogisticated air"
0:34:51 > 0:34:55must be a part of ordinary air.
0:34:55 > 0:34:57It was a ground-breaking discovery.
0:34:58 > 0:35:02He ditched the messy, complicated name Priestly used,
0:35:02 > 0:35:04and called the gas oxygen.
0:35:11 > 0:35:16In 1774, Lavoisier announced the discovery of oxygen to the world.
0:35:19 > 0:35:21Scheele was astonished.
0:35:23 > 0:35:25Priestly was furious.
0:35:25 > 0:35:29He complained bitterly that he was the one who'd discovered it first.
0:35:31 > 0:35:35Who deserves to claim the glory still divides opinions today.
0:35:40 > 0:35:44For me, it was Lavoisier who truly discovered oxygen.
0:35:44 > 0:35:47Because I think a discovery isn't so much about being
0:35:47 > 0:35:49the first to find something.
0:35:49 > 0:35:52You also have to understand what it is that you've found.
0:35:56 > 0:35:58Lavoisier was the one who showed
0:35:58 > 0:36:01that oxygen wasn't just a curious new gas.
0:36:01 > 0:36:04It is a part of the air we breathe.
0:36:06 > 0:36:09This was a huge leap forward in the quest to understand
0:36:09 > 0:36:11what air is made of.
0:36:12 > 0:36:17And soon, all the other pieces of the puzzle fell into place.
0:36:22 > 0:36:26"Fixed air" or carbon dioxide,
0:36:26 > 0:36:29and "noxious air", nitrogen,
0:36:29 > 0:36:31were found to be parts of the air too.
0:36:32 > 0:36:34For the first time,
0:36:34 > 0:36:38people understood that air is made of a mixture of gases.
0:36:38 > 0:36:42And that knowledge transformed our world.
0:36:43 > 0:36:45Because until this point,
0:36:45 > 0:36:48the air had been viewed as little more than empty space.
0:36:48 > 0:36:54Now, it was seen as an untapped mine, rich in raw materials.
0:36:54 > 0:36:59And it wasn't long before those raw materials were extracted and used.
0:37:01 > 0:37:04Scientists discovered that oxygen could be bubbled
0:37:04 > 0:37:07through molten iron to remove impurities.
0:37:09 > 0:37:12And pure iron allowed them to make the steel
0:37:12 > 0:37:16that built the railways, ships and factories
0:37:16 > 0:37:19that powered the Industrial Revolution.
0:37:24 > 0:37:27Identifying the gases that air is made of helped
0:37:27 > 0:37:30to build our modern world.
0:37:34 > 0:37:38And manufacturing those gases is still big business today.
0:37:40 > 0:37:43At this air separation plant in Hampshire,
0:37:43 > 0:37:46the individual gases that make up the air
0:37:46 > 0:37:49are separated out on an industrial scale.
0:37:53 > 0:37:55'At this site,
0:37:55 > 0:37:59'2,000 tonnes of air per day
0:37:59 > 0:38:02'are sucked in, compressed,
0:38:02 > 0:38:06'and then cooled to cryogenic temperatures,
0:38:06 > 0:38:09'so the gases become liquids.'
0:38:09 > 0:38:13- So it's quite a complicated process?- Yeah...
0:38:13 > 0:38:16'And I'm going to see how it's done.'
0:38:16 > 0:38:18- This is Andy.- Hello, Andy. - Hello, Gabrielle.
0:38:18 > 0:38:19What have you got for us?
0:38:19 > 0:38:22I've got a demonstration here to show the process
0:38:22 > 0:38:24- that's going on inside our column. - OK.
0:38:24 > 0:38:26OK, what I've got is a balloon full of air
0:38:26 > 0:38:28and I've got some liquid nitrogen,
0:38:28 > 0:38:31which I'm going to pour into the bowl to make a nice cold bath.
0:38:34 > 0:38:36What I'm going to do is drop the balloon in
0:38:36 > 0:38:38and the balloon will now get nice and cold.
0:38:38 > 0:38:40It will boil up a bit. It's liquid nitrogen.
0:38:40 > 0:38:43What happens straightaway is the gas inside the balloon
0:38:43 > 0:38:45starts to condense. It's getting cold.
0:38:45 > 0:38:48You can see the balloon just starting to shrivel.
0:38:48 > 0:38:50It looks like it's freezing on the outside.
0:38:50 > 0:38:52- It's not breaking the balloon? - No, no.
0:38:52 > 0:38:54- It will stay in one piece.- Oh.
0:38:54 > 0:38:59A liquid nitrogen bath is about -196 degrees centigrade.
0:38:59 > 0:39:03At -185, the oxygen in the balloon should condense
0:39:03 > 0:39:06from a gas to a liquid and that's why we are able to condense
0:39:06 > 0:39:09the oxygen in our air separation process.
0:39:09 > 0:39:12We would draw it to that point as liquid leaving behind nitrogen.
0:39:12 > 0:39:14And that's how you separate them?
0:39:14 > 0:39:16That's how we separate the air.
0:39:16 > 0:39:18SHE GASPS IN SHOCK I'll tip it up now.
0:39:18 > 0:39:21You can just make out a level of liquid in the bottom of the balloon.
0:39:21 > 0:39:24- There's a small puddle of liquid oxygen.- So, there it is!
0:39:24 > 0:39:27Separated out. There it is. There's the oxygen.
0:39:27 > 0:39:28I breathe it and now I see it.
0:39:28 > 0:39:31If I leave this out, you can see the balloon is starting to inflate.
0:39:31 > 0:39:33It's now getting warm. It's drawing heat from the atmosphere.
0:39:33 > 0:39:35If I leave that on my glove,
0:39:35 > 0:39:39the balloon will inflate back to its normal size and shape.
0:39:39 > 0:39:43The same constituent parts of the air are inside.
0:39:43 > 0:39:45So, that's how you separate the air.
0:39:45 > 0:39:46That's how we do it.
0:39:49 > 0:39:54Because nitrogen becomes a liquid at a lower temperature than oxygen,
0:39:54 > 0:39:58cooling the air makes it possible to separate out the two gases.
0:40:00 > 0:40:04It's a hi tech process that transforms invisible air
0:40:04 > 0:40:07into tangible, raw materials we can use.
0:40:12 > 0:40:16Oxygen is used in hospitals to save lives.
0:40:17 > 0:40:20It's an ingredient in modern plastics.
0:40:25 > 0:40:29And it powers the rockets that have allowed us to explore space.
0:40:33 > 0:40:36Nitrogen makes the fertilisers that nourish the crops
0:40:36 > 0:40:39we rely on for food.
0:40:39 > 0:40:43And it's used in the packaging industry to keep our food fresh.
0:40:46 > 0:40:50The discovery that common air around us is made up of a mixture of gases,
0:40:50 > 0:40:52each with their own potent properties
0:40:52 > 0:40:55was clearly an extraordinary achievement.
0:40:55 > 0:40:58There's no doubt that Lavoisier's contribution to our understanding
0:40:58 > 0:41:01of air was a vitally important one.
0:41:01 > 0:41:04But it still wasn't complete.
0:41:04 > 0:41:07There was one question left unanswered.
0:41:07 > 0:41:12What was the relationship between the air and living things?
0:41:12 > 0:41:15That puzzle would ultimately lead scientists to reveal
0:41:15 > 0:41:17why we are able to live at all
0:41:17 > 0:41:20and why we must all eventually die.
0:41:21 > 0:41:27And the first steps were made by none other than Lavoisier himself.
0:41:27 > 0:41:29He had noticed that flames
0:41:29 > 0:41:32and living animals had two things in common.
0:41:32 > 0:41:35Both radiated heat
0:41:35 > 0:41:38and both thrived in oxygen.
0:41:38 > 0:41:41But to figure out how burning and breathing
0:41:41 > 0:41:43could possibly be connected,
0:41:43 > 0:41:47Lavoisier had to overcome a very tricky problem.
0:41:51 > 0:41:54He could control the amount of oxygen used by a flame
0:41:54 > 0:41:58or an animal, simply by putting them in a confined space.
0:41:58 > 0:42:01But how would he measure how much heat they radiated?
0:42:02 > 0:42:06The solution was an ingenious piece of apparatus
0:42:06 > 0:42:08that still exists today.
0:42:10 > 0:42:13Professor Gerard Ferey is going to show it to me.
0:42:16 > 0:42:19So, this is actually all Lavoisier's original equipment
0:42:19 > 0:42:22- that Lavoisier used himself.- It is.
0:42:22 > 0:42:25So, can...can we look at it? Can we see inside?
0:42:25 > 0:42:28Yes, with pleasure, but with respect.
0:42:30 > 0:42:33Lavoisier had this piece of apparatus,
0:42:33 > 0:42:38called a calorimeter, purpose-built to house a living animal.
0:42:38 > 0:42:42A guinea pig was the ideal candidate.
0:42:42 > 0:42:46And here was, inside of the calorimeter, the magic machine.
0:42:49 > 0:42:51So, where did the animal go?
0:42:51 > 0:42:54The animal was put in this sealed cage.
0:42:54 > 0:42:58The volume of this cavity was known by Lavoisier.
0:42:58 > 0:43:00That means that he knew the amount of oxygen
0:43:00 > 0:43:02at the very beginning of the experiment.
0:43:02 > 0:43:04That's how he knew. The chamber was sealed.
0:43:04 > 0:43:07He knew exactly how much oxygen it was breathing.
0:43:07 > 0:43:09'With the guinea pig sealed inside,
0:43:09 > 0:43:14'next, Lavoisier packed the outer chambers with ice.'
0:43:14 > 0:43:17The animal produces heat...
0:43:19 > 0:43:22..during 24 hours
0:43:22 > 0:43:28and the ice, which is in this partition of the apparatus,
0:43:28 > 0:43:32as soon as it receives heat from the animal,
0:43:32 > 0:43:34the ice melts
0:43:34 > 0:43:37and when it melts, it becomes water
0:43:37 > 0:43:39and water is gathered
0:43:39 > 0:43:42at the bottom of the calorimeter
0:43:42 > 0:43:45and as soon as you weigh the water,
0:43:45 > 0:43:47you know the amount of heat,
0:43:47 > 0:43:50which was produced by the animal!
0:43:50 > 0:43:51Very simple.
0:43:55 > 0:43:58Next, Lavoisier repeated the experiment.
0:43:58 > 0:44:01But this time, instead of an animal,
0:44:01 > 0:44:04he put a piece of burning charcoal inside.
0:44:04 > 0:44:06His findings were astonishing!
0:44:10 > 0:44:13When the charcoal had consumed the same amount
0:44:13 > 0:44:14of oxygen as the guinea pig,
0:44:14 > 0:44:18it had also melted the same amount of ice.
0:44:21 > 0:44:24So he realised that the animal was using oxygen
0:44:24 > 0:44:27the same way a fire uses oxygen. It was the same thing.
0:44:27 > 0:44:31It was a really big breakthrough to make the parallel
0:44:31 > 0:44:34between chemistry and life.
0:44:37 > 0:44:40With this ingenious experiment,
0:44:40 > 0:44:45Lavoisier had discovered that combustion and respiration
0:44:45 > 0:44:48are essentially the same process.
0:44:51 > 0:44:53Just like coal burning on a fire,
0:44:53 > 0:44:58Lavoisier proposed that all animals burn food as their fuel
0:44:58 > 0:45:02and it generates heat that warms their bodies.
0:45:04 > 0:45:08He speculated that this process takes place in the lungs.
0:45:09 > 0:45:13Today, we know it happens deep inside every one of our cells.
0:45:17 > 0:45:22Lavoisier's understanding of respiration was only rudimentary,
0:45:22 > 0:45:24but it broke new ground.
0:45:26 > 0:45:30He had caught a glimpse of the chemistry of life itself.
0:45:40 > 0:45:43For me, Lavoisier's contribution to science was as important
0:45:43 > 0:45:46as Newton's or Darwin's.
0:45:46 > 0:45:48He didn't just identify a new gas,
0:45:48 > 0:45:50he changed the whole way that we view the world
0:45:50 > 0:45:53by revealing what air really is
0:45:53 > 0:45:56and the crucial role it plays in the chemistry of life.
0:46:01 > 0:46:05It was the crowning glory of an extraordinary scientific career.
0:46:06 > 0:46:10But it was also one of the last experiments Lavoisier
0:46:10 > 0:46:11would ever conduct.
0:46:14 > 0:46:18He was born into a life of wealth and privilege.
0:46:19 > 0:46:22But his findings about respiration changed him.
0:46:24 > 0:46:28They showed that the more active a person is, the more fuel,
0:46:28 > 0:46:30or food, they needed.
0:46:32 > 0:46:36But in 18th-century France, exactly the opposite was happening.
0:46:39 > 0:46:43The poor people, who did all the manual labour, had the least food.
0:46:43 > 0:46:48Lavoisier saw this imbalance between rich and poor as a great injustice
0:46:48 > 0:46:49that had to be stopped.
0:46:52 > 0:46:54By the end of the 18th century,
0:46:54 > 0:46:57civil unrest in France had grown to full-scale revolution.
0:46:58 > 0:47:02But unlike many of his wealthy, aristocratic friends,
0:47:02 > 0:47:04Lavoisier didn't flee.
0:47:06 > 0:47:07To the rioting masses,
0:47:07 > 0:47:09it didn't matter that Lavoisier stayed in Paris
0:47:09 > 0:47:11to support the Revolution
0:47:11 > 0:47:14any more than it mattered that he was a great scientist.
0:47:14 > 0:47:17All they could see was a member of the bourgeois elite.
0:47:17 > 0:47:21So, on 8th May 1794, he was brought here
0:47:21 > 0:47:23to the Place de La Revolution...
0:47:28 > 0:47:29..and guillotined.
0:47:31 > 0:47:33A fellow scientist said,
0:47:33 > 0:47:36"It took them only an instant to cut off that head,
0:47:36 > 0:47:39"and 100 years may not produce another like it."
0:47:41 > 0:47:43Lavoisier's life had ended,
0:47:43 > 0:47:45but his legacy lived on.
0:47:45 > 0:47:48He had steered the quest to understand the air
0:47:48 > 0:47:52towards the modern, scientific understanding we have today.
0:47:52 > 0:47:54All the major gases -
0:47:54 > 0:47:56carbon dioxide,
0:47:56 > 0:47:58nitrogen,
0:47:58 > 0:48:00oxygen
0:48:00 > 0:48:01had been identified.
0:48:04 > 0:48:06He had begun to unravel the mysteries
0:48:06 > 0:48:09of combustion and respiration.
0:48:09 > 0:48:13But there was one problem even the great Lavoisier had overlooked.
0:48:14 > 0:48:17A niggling question that would end up revolutionising
0:48:17 > 0:48:19the whole of science.
0:48:20 > 0:48:23And revealing that oxygen, the gas of life,
0:48:23 > 0:48:24has a darker side.
0:48:26 > 0:48:28The problem was spotted back in England
0:48:28 > 0:48:32by a humble teacher named John Dalton.
0:48:32 > 0:48:34When he wasn't in the classroom,
0:48:34 > 0:48:37Dalton loved to indulge in a very British passion...
0:48:38 > 0:48:39..the weather.
0:48:41 > 0:48:44Dalton spent a great deal of his time walking in the hills
0:48:44 > 0:48:46and valleys of the English countryside,
0:48:46 > 0:48:49trying to understand the weather by measuring the temperature
0:48:49 > 0:48:51and humidity of the air.
0:48:53 > 0:48:58Lavoisier's revelations about what air is made of captivated Dalton.
0:49:00 > 0:49:02But something about it puzzled him.
0:49:04 > 0:49:06As he walked among the misty hills,
0:49:06 > 0:49:09he wondered how all the different gases that make up the air
0:49:09 > 0:49:13could occupy the same space at the same time,
0:49:13 > 0:49:15when solid bodies obviously could not.
0:49:19 > 0:49:22Dalton reasoned that while air is made up of different gases,
0:49:22 > 0:49:26the gases themselves must be made up of individual particles.
0:49:26 > 0:49:28That's how they could mix into one another.
0:49:33 > 0:49:37Over time, Dalton fine-tuned his theory.
0:49:37 > 0:49:40He proposed that the particles of one gas were different
0:49:40 > 0:49:41from the particles of another...
0:49:43 > 0:49:46..and that it's not just gases -
0:49:46 > 0:49:49all things are made of particles.
0:49:49 > 0:49:52He called the particles atoms.
0:49:56 > 0:49:58Dalton's atomic theory is the foundation
0:49:58 > 0:50:02on which our modern understanding of the world is built.
0:50:04 > 0:50:07Many of science's greatest achievements
0:50:07 > 0:50:10simply wouldn't have been possible if we didn't know about atoms.
0:50:13 > 0:50:16It opened the door to a far deeper understanding
0:50:16 > 0:50:19of how all things are made,
0:50:19 > 0:50:22including the air we breathe.
0:50:30 > 0:50:32When you know that air contains atoms and molecules
0:50:32 > 0:50:35you can really understand what it's made of.
0:50:35 > 0:50:39Carbon dioxide - carbon atoms stuck to two oxygen atoms.
0:50:39 > 0:50:43Nitrogen - two atoms of nitrogen tightly bounded together.
0:50:43 > 0:50:45And we now know there are traces of other gases in the air -
0:50:45 > 0:50:48argon, water vapour...
0:50:48 > 0:50:51But when you look at the atomic level, there is one part of air
0:50:51 > 0:50:54that stands out from all the others -
0:50:54 > 0:50:55oxygen.
0:50:55 > 0:50:59An oxygen atom has a nucleus surrounded by electrons.
0:50:59 > 0:51:03In the outermost shell has six electrons,
0:51:03 > 0:51:06but it really, really wants to have eight.
0:51:06 > 0:51:08So, there's a space,
0:51:08 > 0:51:12a hole for two electrons that oxygen will do anything to fill.
0:51:12 > 0:51:15It will grab those electrons from any passing atom
0:51:15 > 0:51:17or molecule that it can.
0:51:17 > 0:51:20That's what makes it so different from all the other parts of the air.
0:51:20 > 0:51:24Oxygen will react with more or less anything.
0:51:28 > 0:51:31It was only when we began to understand air
0:51:31 > 0:51:33at the level of the individual atom,
0:51:33 > 0:51:36that the true wonder of oxygen was revealed.
0:51:41 > 0:51:44Because when oxygen atoms react,
0:51:44 > 0:51:46they release the elixir of life itself...
0:51:48 > 0:51:50..energy.
0:51:54 > 0:51:56I've got here some beautiful liquid oxygen
0:51:56 > 0:52:00and I'm going to show you how powerful this stuff really is.
0:52:06 > 0:52:11I've also got a perfectly normal digestive biscuit.
0:52:11 > 0:52:14I'm going to dunk the biscuit
0:52:14 > 0:52:16into the liquid oxygen.
0:52:20 > 0:52:23And now, all I need is a spark.
0:52:34 > 0:52:36Now, that is an oxygen reaction!
0:52:36 > 0:52:39The oxygen is ripping and tearing electrons
0:52:39 > 0:52:41from atoms in the digestive biscuit
0:52:41 > 0:52:43and releasing all of that energy.
0:52:44 > 0:52:47And in the same sort of way, the oxygen is reacting
0:52:47 > 0:52:51with the food in our bodies to release the energy we need to live.
0:52:56 > 0:52:59Oxygen's spectacularly reactive nature
0:52:59 > 0:53:01gives us the huge amount of energy
0:53:01 > 0:53:03we need to keep our hearts pumping
0:53:03 > 0:53:05and our brains alive.
0:53:08 > 0:53:12It allows us to lead active, vigorous lives.
0:53:14 > 0:53:17Oxygen gives us everything that's worth living for.
0:53:23 > 0:53:26But there is a price to pay.
0:53:28 > 0:53:31Because breathing oxygen is like playing with fire.
0:53:33 > 0:53:36And just like wood on a bonfire,
0:53:36 > 0:53:38we're getting burned.
0:53:38 > 0:53:40The oxygen in the air around me
0:53:40 > 0:53:43is reacting with the wood to release energy.
0:53:43 > 0:53:44That's what fire is.
0:53:44 > 0:53:46And that's the same sort of chemical process
0:53:46 > 0:53:49that's happening in your body.
0:53:49 > 0:53:51But whenever oxygen gets involved in a reaction,
0:53:51 > 0:53:53it's not delicate.
0:53:53 > 0:53:56It rips and tears to grab the electrons it needs
0:53:56 > 0:54:00and in the process, it creates something called free radicals.
0:54:03 > 0:54:05Free radicals are some of the most powerful
0:54:05 > 0:54:08and destructive particles on the planet.
0:54:10 > 0:54:12Flames are full of free radicals
0:54:12 > 0:54:16and so are our bodies every time we breathe.
0:54:16 > 0:54:19They tear through our molecules and cells.
0:54:21 > 0:54:23Over time, that damage accumulates
0:54:23 > 0:54:26and in the end, it's that damage that's the reason
0:54:26 > 0:54:29why we all grow old and die.
0:54:31 > 0:54:34With every breath we take,
0:54:34 > 0:54:36oxygen is slowly killing us.
0:54:39 > 0:54:41But I still think it's worth it.
0:54:44 > 0:54:48Because without oxygen, life would be very different.
0:54:51 > 0:54:55If you want to know what life would be like if we didn't breathe oxygen,
0:54:55 > 0:54:58you don't have to go very far.
0:54:58 > 0:55:02Any fresh body of water will have what I've come here to find.
0:55:06 > 0:55:07This may just look like a bucket of mud,
0:55:07 > 0:55:11but in fact, there are trillions and trillions of tiny bacteria
0:55:11 > 0:55:13living in it.
0:55:13 > 0:55:16They can't breathe oxygen the way that we can.
0:55:16 > 0:55:18In fact, it's even poisonous to them,
0:55:18 > 0:55:20and that's why they have to spend their life
0:55:20 > 0:55:23living at the bottom of a pond.
0:55:23 > 0:55:25Because they can't count on breathing oxygen,
0:55:25 > 0:55:28they have to rely on breathing sulphate from the water,
0:55:28 > 0:55:31and that's not nearly as effective at delivering energy.
0:55:31 > 0:55:34That means these bacteria simply don't have the energy
0:55:34 > 0:55:37to grow any bigger than a single cell.
0:55:37 > 0:55:41It's only oxygen-breathers that can release the vast amount of energy
0:55:41 > 0:55:44that it takes to grow a big, multicelled body
0:55:44 > 0:55:46and power a brain.
0:55:46 > 0:55:49And that's why oxygen is so special
0:55:49 > 0:55:51because without it,
0:55:51 > 0:55:52we'd all be pond slime.
0:55:58 > 0:56:03Only oxygen can give living beings the energy they need to walk,
0:56:03 > 0:56:06run, fly and think.
0:56:08 > 0:56:11It has shaped the course of our evolution.
0:56:11 > 0:56:14Without it, we wouldn't be here at all.
0:56:21 > 0:56:26The quest to understand what air is made of began as a simple desire
0:56:26 > 0:56:28to further our knowledge of the natural world.
0:56:32 > 0:56:35But it lead us far beyond that.
0:56:37 > 0:56:40It uncovered powerful gases
0:56:40 > 0:56:42that have forged the world we live in today.
0:56:45 > 0:56:49Gave a profound insight into our own physiology
0:56:49 > 0:56:51and the chemistry of life itself.
0:56:54 > 0:56:57And it even revealed the existence of atoms.
0:56:57 > 0:57:02The fundamental building blocks from which all things are made.
0:57:09 > 0:57:12So, it may look as if my hands are empty right now,
0:57:12 > 0:57:13but in fact,
0:57:13 > 0:57:18they contain the most miraculous stuff in the universe.