Aug. 1, 2022

Joseph Priestley Discovers Oxygen

Joseph Priestley Discovers Oxygen

August 1, 1774. English chemist Joseph Priestley changes the world forever when he isolates a mysterious new gas: oxygen.


Cold Open

It’s the evening of July 14th, 1791 in Birmingham, England.

A family of three sits down for dinner. At the head of the table is an Englishman in his fifties: the eminent philosopher and scientist, Joseph Priestley.

Over the years, Joseph’s controversial writings about religion and politics have made him many enemies. Most recently, his outspoken support for the French Revolution has ruffled feathers across English society. But tonight, Joseph enjoys a moment of calm. He smiles contentedly at his wife, Mary, and his twenty-year-old son, William.

But the peaceful family moment is interrupted… when Joseph hears something in the distance: a cacophony of raised voices drifting in through the open window.

Concerned, Joseph stands. He walks to the window and peers out into the night.

There in the darkness, he sees a large group of angry townspeople, just visible beyond the ivy-strewn walls of his garden.

Joseph tells his son to blow out all the candles in the house. He hopes that with the flames extinguished, the mob will assume nobody’s home. But the rabble isn’t fooled.

As they draw nearer to the house, Joseph decides his only option is to run. He takes his wife’s hand and leads her to the back door, his son close on their heels. Together, they descend a flight of stairs toward the exit.

But Joseph stops in his tracks. He tells Mary and William to wait for him outside. He needs to grab some things from his laboratory.

Back upstairs, inside the lab, Joseph makes a beeline for his cluttered desk. He knocks over test tubes and vials as he rummages through his notes, desperate to save his precious scientific research.

He manically stuffs the papers into his pockets. But before he can finish… he hears the sound of the mob wrenching the front door from its hinges. Out of time, Joseph grabs one last fistful of documents… and sprints to the backyard, where Mary is anxiously waiting. But there’s no sign of his son. Joseph frantically asks, “where’s William?” And in between sobs, Mary tells him William has decided to stay and defend the family home.

Joseph is sick with worry. But he trusts his son to look after himself. So Joseph takes Mary’s hand… and together they disappear into the night.

Joseph Priestley has always been a radical free thinker, unafraid of going against the status quo. In the early 1790s, his outspoken support for the French Revolution cost him dearly when an angry mob marched on his home, forcing him and his wife to run for their lives. Joseph’s son, William, survives the attack as well, but he fails to defend the Priestley home which is looted and burned to ashes.

After the violent episode, Joseph is forced to flee Europe. But he will never abandon his passion for knowledge; a crusade that reached its peak decades before his home was razed to the ground, when Joseph discovered a remarkable, life-giving element, Oxygen, on August 1st, 1774.


From Noiser and Airship, I’m Lindsay Graham and this is History Daily.

History is made every day. On this podcast—every day—we tell the true stories of the people and events that shaped our world.

Today is August 1st, 1774: Joseph Priestley Discovers Oxygen.

Act One: Early Discoveries 

It’s 1765 in London; more than twenty years before the French Revolution.

On a busy street not far from St. Paul’s Cathedral, 32-year-old Joseph Priestley arrives at a red-brick building with tall arched windows. He checks the address on a slip of paper clutched in his hand. Then he pushes open the door. 

He steps into a cavernous, smoke-filled room buzzing with animated conversation. Everywhere he looks, gentlemen in powdered wigs sip from coffee cups and exchange ideas about politics, religion, and science. This is Joseph’s first time in a “coffeehouse”, a popular meeting location for intellectuals. Joseph comes from an ordinary working-class background. And he feels out of place in his simple black coat and necktie.

Joseph is a humble clergyman. But he’s a man of extreme intelligence. He recently started writing a book, a comprehensive history of a subject that fascinates him: electricity. He’s come here to London on the invitation of a friend to talk with somebody who might be able to help him finish the book.

Across the room, Joseph spies a portly, gray-haired man, holding court. Joseph recognizes him immediately as the American diplomat and scientist, Benjamin Franklin.  

Soon, Joseph introduces himself. He tells Franklin about his book, and how hard it’s been to gain access to critical historical records. Franklin is intrigued by Joseph’s book and impressed by his gumption. So he agrees to help Joseph by providing records of his early electrical experiments. He also encourages Joseph to carry out new experiments of his own. 

With Franklin’s invaluable advice and support, Joseph publishes The History and Present State of Electricity two years later. The book is an instant success. Its positive reception encourages Joseph to continue his scientific work, albeit as a hobby.

Because shortly after the book’s publication, Joseph takes a job as a minister at a church in the town of Leeds in northern England. Joseph likes his new position. It’s low-stress and affords him ample time to read, study and work on his experiments. And soon, Joseph develops an interest in one of science’s greatest mysteries: air

By the mid-18th century, the concept of air is still evolving. Nobody is entirely sure what air is, or what it contains. Until recently, it was thought that there was only one “kind” of air. But then, in the 1750s, scientists discovered a different type that’s formed as a by-product of making alcohol. Scientists call this substance “fixed air”; although today, we know it's carbon dioxide.

Joseph is intrigued by this fixed air, so he decides to conduct an experiment at a place where fixed air is found in abundance: a local brewery. There, Joseph discovers that by holding a bowl of water over a vat of fermenting beer, the steady stream of “fixed air” infuses the water with bubbles. Joseph calls his creation “windy water”; and he shares it with the world in a pamphlet titled: “Directions for Impregnating Water with Fixed Air.”

It isn’t long before others are harnessing Joseph’s inventions for profit, including a Swiss entrepreneur, named J.J. Schweppe who is the first to bottle and sell carbonated water. His company, Schweppes, is arousing success even to this day. But Joseph, however, is not motivated by money; only curiosity.

And that curiosity drives Joseph to unorthodox approaches. Unlike many of his peers who make discoveries after years of rigorous planning, Joseph is far more unsystematic. He tends to stumble upon his discoveries almost by accident.


Years after first carbonating water, on August 1st, 1774, Joseph Priestley tinkers with an experiment in his makeshift home laboratory. A ray of sun shines through a nearby window and casts a light onto Joseph’s cluttered desk.

As he sifts through the mountain of jars and vials, Joseph’s thoughts are fixed on one of the most pressing scientific questions of the day: what happens when something burns?

Joseph subscribes to the current, prevailing theory; that all flammable substances contain a property called “phlogiston” which is released into the air during combustion.

This so-called “Phlogiston Theory” has been a cornerstone of chemistry for over a century. But the theory is wrong, and Joseph is about to prove it… almost entirely by accident. 

On this hot, sunny day, Joseph performs a random experiment; one not uncommon in his time: he decides to heat a metal substance and see what happens.

Joseph sets up his experiment using his standard apparatus: a glass container on a raised platform that’s designed to capture gasses from substances that are heated below. Next, Joseph grabs his 12-inch burn lens and aims a beam of sunlight at a pile of mercury calx; a reddish ash that forms when mercury is heated in air.

As Joseph heats up the calx, a gas springs forth and fills up the glass container with what Joseph assumes is phlogiston-filled air.

In accordance with the prevailing theory, Joseph believes that when too much phlogiston is released into a confined space, it will snuff out any flame. On a whim, Joseph places a lit candle in the glass container, fully expecting it to abruptly extinguish. But to Joseph’s surprise, the flame burns brighter. After conducting a series of tests, Joseph discovers that the gas he’s captured is "five or six times as good as common air."  

Though he doesn’t know it, Joseph has just discovered oxygen. But he doesn’t yet understand the gas he’s isolated.

He tries to make his discovery conform to the phlogiston theory. He wrongly convinces himself that the mercury calx somehow absorbed all the phlogiston in the air. He even names the gas “dephlogisticated air”.

Joseph does not fully grasp the momentous significance of his discovery. But soon, other scientists will. While Joseph clings to an outdated “phlogiston theory”, other chemists will use his discovery to debunk it. Eventually, Joseph will be left behind by the scientific revolution he helped create, and his greatest discovery will turn into his greatest failure.

Act Two: The Oxygen Wars

It’s October 1774; two months after Joseph Priestly discovered oxygen.

Inside an opulent banquet hall in Paris, Joseph is attending a dinner party hosted by members of the French Academy of Sciences. The guests are dressed in their finest velvet frock coats. Their powdered wigs are curled and lavender scented. Over a table groaning with food and wine, witty remarks shoot back and forth.

Joseph tries to keep up, but it’s a struggle; he doesn’t speak much French. And eventually, somebody turns to the Englishman and says: “Monsieur Priestley, tell us again about your recent remarkable discovery.”

At this Joseph’s eyes twinkle with golden candlelight as he regales the table with an account of his breakthrough. In stuttering French, he explains how he collected a new, purer kind of air by burning powdered mercury. He tells his enraptured audience how he trapped a mouse in a jar filled with this “pure air” and how the creature survived for longer than it would have in “regular air”. Murmurs of scholarly appreciation ripple around the banquet hall.

But one man seems skeptical… Antoine Lavoisier is the poster boy of the French Academy of Sciences. An intellectual prodigy from an aristocratic family, Lavoisier was elected to the Academy at just twenty-six. Soon, his genius propelled him to considerable power in the French Royal Court, where he advises the King on scientific matters.

And when Joseph finishes speaking about his discovery, Lavoisier sniffs haughtily. To him, Joseph is a bumbling amateur. A real chemist would never just share his breakthroughs with a room full of rival scientists. And yet, even though Lavoisier disdains Joseph’s manner, he admits to himself that the Englishman might be onto something. 

For years, Lavoisier has been trying to solve the mystery of heat. Eventually, he discovered a flaw in the conventional wisdom of the day. The “Phlogiston Theory” posits that when a substance is heated, it loses weight. But about two years ago, Lavoisier began to notice that certain heated substances actually gained weight. Lavoisier believed there was only one possible explanation. During combustion, something in the air was combining with the heating substance. Still, Lavoisier hasn’t been able to figure out what…

But now, as he listens to the Englishman prattle on in broken French, Lavoisier begins to wonder if Joseph’s “pure air” could be the answer.

Following the banquet, Lavoisier hurries straight to his laboratory and starts conducting experiments of his own. 


In April of the following year, Lavoisier presents his findings to the French Academy of Sciences. Before an audience of his peers, Lavoisier declares that he has discovered a new, life-sustaining gas, “more combustible and more breathable than even the common air in which we live.” He calls the gas oxygen. Raucous applause thunders through the gilded halls of the Louvre Palace.

Lavoisier goes on to prove that oxygen is a key component in both air and water. He uses the discovery of oxygen as the foundation for a whole new chemistry, one based on conceptual units called “elements” and combination of those called “compounds”. The oxygen theory soon replaces the phlogiston theory, and Antoine Lavoisier is heralded as the father of modern chemistry.

But back in England, Joseph Priestley follows these developments with growing indignation. He feels his discovery of “dephlogisticated air” has been grossly misunderstood. Joseph still believes wholeheartedly that the phlogiston theory is correct, and he refuses to accept Lavoisier’s “new chemistry”. To Joseph, the idea of a world composed of elements and compounds is too abstract, too conceptual, too chaotic. Even as the bulk of the scientific community accepts Lavoisier’s theory, Priestley defies the status quo again and sticks to his belief. 

Over the next few years, much of Joseph’s intellectual energy will be channeled into publicly refuting Lavoisier’s theories. Joseph and his family will move to Birmingham, where Joseph will take up another ministerial position. There, he will continue to publish widely on other topics, such as philosophy, politics, and religion. But Joseph’s days of scientific discovery are seemingly over.

Ultimately, Joseph is trampled by the very scientific revolution he helped to create. But in the late 1780s, a different sort of revolution begins in France. And for Joseph Priestley, and his rival Antoine Lavoisier, the French Revolution will have radical, life-altering consequences.

Act Three: Exile in America

It’s May 8th, 1794 in Paris; twenty years after Joseph Priestley discovered oxygen. 

A horse-drawn wagon rattles through dusty streets. A dozen condemned prisoners are crammed inside, their hands lashed behind their backs, their heads nodding up and down with the rhythm of the cart. A stone-faced guard cracks his whip, and the horse staggers forward, finally stopping alongside a raised scaffold in the middle of a public square.

The guard barks an order. 

And the prisoners step down from the cart, their wide, fearful eyes fixed on the wooden contraption rising from the center of the scaffold. It’s 14 feet high, two lofty uprights rising from a narrow base, where a semi-circular groove has been carved out of the lower cross-beam. At the top, there’s a blade, cut diagonally like a surgeon’s knife.

One of the prisoners stripped of his powdered wig and fine clothes is almost unrecognizable. Antoine Lavoisier's bright eyes have grown dim, and his well-groomed face is darkened by a shadow of gray stubble.

Five years ago, revolutionaries in Paris overthrew the monarchy and rounded up members of the bourgeoisie. As a stalwart of the aristocracy, Antoine Lavoisier was eventually thrown behind bars and condemned to death.

Now, before a crowd of onlookers, the distinguished chemist places his neck under the guillotine’s blade. A breathless hush falls over the square as the executioner pulls a rope and the blade drops.

Meanwhile, at that same moment, a British passenger ship lurches across the choppy waves of the mid-Atlantic. Stowed safely below deck are Joseph Priestley and his wife, Mary. The Priestleys are on their way to start a new life. 

When Joseph spoke out in support of the French Revolution, he became an intellectual pariah to many in the establishment who saw his writings on liberty as seditious. Not long after his home was burned to the ground by an angry mob, Joseph decided to flee with his family to a country that shares his values of free thought and non-conformity.

In America, Joseph hopes to be greeted warmly by old acquaintances and new admirers. By the time he arrives, his old friend Benjamin Franklin is long dead. Still, Joseph will rub elbows with notable figures like Thomas Jefferson and John Adams. He will spend the final ten years of his life in Pennsylvania, heartily championing a new cause: that of the Great American Experiment. 

And until the day he died, Joseph maintained his belief in the “Phlogiston Theory”, despite the fact that Lavoisier disproved it. But in truth, neither man is the sole father of oxygen. In the early 1770s, a Swedish chemist named Carl Wilhelm Scheele was the first to isolate oxygen; or as he called it, “fire air.” But Scheele didn’t publish his findings until 1777, long after Priestley was credited for discovering his dephlogisticated air.

Still, Joseph Priestley’s impact on the world is undeniable. He was a theologian, a philosopher, a political theorist, and a scientist. Above all, he was an intellectual dissenter, forever willing to defend the rights of revolutionaries, rebels, and renegades. This mindset made him an exile, but it also led him to inadvertently make his greatest discovery on August 1st, 1774.


Next on History Daily. August 2nd, 1876. At a poker table in the town of Deadwood, a buffalo hunter turned prospector named Jack McCall murders the legendary gunslinger, frontiersman, and folk hero… Wild Bill Hickock.

From Noiser and Airship, this is History Daily, hosted, edited, and executive produced by me, Lindsay Graham.
Audio editing by Mollie Baack.

Sound design by Derek Behrens.

Music by Lindsay Graham.

This episode is written and researched by Joe Viner.

Executive Producers are Steven Walters for Airship and Pascal Hughes for Noiser.