Who Discovered Oxygen? Scheele, Priestley, Lavoisier and the Fall of Phlogiston

Who discovered oxygen? Three people have a fair claim. Carl Wilhelm Scheele, a Swedish pharmacist, made the gas first, in 1771 and 1772, but his book did not appear until 1777. Joseph Priestley, an English minister, made it on 1 August 1774 and published first, in 1775, which is why his is the name most people give. Antoine Lavoisier, in Paris, was the first to understand it: a separate gas, the part of the air that burning, rusting and breathing all use up. He named it oxygen.

Element 8. Oxygen. About a fifth of every breath you take is oxygen, roughly 21 per cent of the air. Here is the fact nobody believes: it is also the most abundant element in the Earth’s crust, almost half of the rock under your feet, by mass. And yet before the 1770s nobody knew it existed. Air was thought to be one single element. Then, within a few years, three men found the gas, and only one of them understood what he had found.

Phlogiston: the theory of fire that was wrong

To see why oxygen was so hard to recognise, start with what every chemist of the day believed. Anything that burned was thought to contain phlogiston, a weightless “stuff of fire” that escaped into the air as the thing burned. Put a candle in a closed jar and it goes out; the air, so the theory went, was full of phlogiston and could take no more.

It was a tidy theory with one awkward fact. Burn tin or lead to a powder, which chemists called a calx, and the metal gets heavier. Heavier, when it was supposed to be losing something.

Scheele’s fire air

Carl Wilhelm Scheele, born in 1742, was a pharmacist in Sweden who worked without the expensive equipment of the Paris chemists. In 1771 and 1772 he made a new gas by heating several substances, among them red mercury oxide, saltpetre and manganese dioxide. Heat breaks the red mercury oxide apart into shiny mercury and oxygen.

A candle burned in the gas far more brightly, and Scheele called it fire air. Ordinary air, he concluded, is a mixture of two gases, fire air and “foul air”, and he estimated fire air at about a quarter of it. (Today we measure about 21 per cent.) But he explained it all with phlogiston, and his book, Chemical Treatise on Air and Fire, reached the printer in 1775 and did not appear until 1777, delayed in part by a preface his professor friend Torbern Bergman had promised.

Even earlier, on 30 September 1774, Scheele wrote to Antoine Lavoisier in Paris about his discovery. Lavoisier never replied.

Priestley: “two mice and myself”

Joseph Priestley, born in 1733, was an English minister, teacher and tireless experimenter who had already made the first carbonated water. In the 1770s he worked as librarian and tutor for Lord Shelburne, which left him time for experiments on airs.

On 1 August 1774 he used a large burning lens to focus sunlight onto the same red powder, mercury calx, and collected the gas that came off. His own account is still a pleasure to read:

what surprized me more than I can well express, was, that a candle burned in this air with a remarkably vigorous flame — Joseph Priestley, Experiments and Observations on Different Kinds of Air, vol. II, 1775

He shut a mouse in a jar of the gas, and it outlived mice kept in ordinary air. Then he breathed it himself. “I fancied that my breast felt peculiarly light and easy for some time afterwards,” he wrote, and wondered whether this pure air might one day become “a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it.”

In October 1774 Priestley visited Paris with Lord Shelburne and told Lavoisier exactly how he had made the new air. At that point he thought it was simply an especially pure form of ordinary air. Back in England he tested it again and found it “five or six times better than common air”. He named it dephlogisticated air: air with its phlogiston taken out, so hungry for phlogiston that things burned in it with extra vigour. He published in 1775, in the Philosophical Transactions of the Royal Society and in his Experiments and Observations on Different Kinds of Air. Scheele’s book was still at the printer. First to publish: that is why his is the name people remember.

Lavoisier and why oxygen is called oxygen

Antoine Lavoisier, born in 1743, was a rich Parisian who collected taxes for the king. He had a state-of-the-art laboratory and a partner in it, his wife, Marie-Anne Paulze Lavoisier, who translated English papers for him, Priestley’s among them. His method was the balance: weigh everything that goes in and everything that comes out, gases included.

He heated tin in a sealed vessel. The whole vessel weighed the same before and after. When he opened it, air rushed in, and the tin had gained exactly as much weight as the air that rushed back in. Burning metal does not lose phlogiston; it takes in part of the air. Matter is not created or destroyed, only rearranged. The video animates this step on a balance, and it is the heart of the whole story.

Lavoisier repeated Priestley’s experiment. In his first account, read to the Academy of Sciences on 26 April 1775, he still called the gas the air itself, “undivided, without alteration”. By 1778 it was “the healthiest and purest part of the air”, and air was a mixture of two different gases. Burning, rusting and breathing were the same thing: combining with this one gas. A metal’s calx was the metal joined to it, and he called it an oxide, a word we still use.

He named the gas oxygen, from the Greek for “acid former”, because he believed every acid contains it. That was wrong: hydrochloric acid contains no oxygen at all, as Humphry Davy later showed. The name stuck anyway.

Lavoisier later claimed he had found the gas independently, and he never acknowledged Scheele’s letter. In 1789 he published the textbook of the new chemistry, the Traité élémentaire de chimie, and he is called the father of modern chemistry. During the French Revolution he was arrested as a former tax collector, and on 8 May 1794, aged 50, he was guillotined. The mathematician Joseph-Louis Lagrange said: “Only a moment to chop off that head and a hundred years may not give us another like it.”

So who discovered oxygen?

Priestley never accepted the new chemistry. In 1791 a mob burned his house, church and laboratory in Birmingham, and in April 1794, the spring Lavoisier went to the guillotine, he sailed for America. He settled in Northumberland, Pennsylvania, and died there in 1804, still hoping phlogiston would return. Scheele died in 1786, aged 43. He found many other substances, chlorine among them; Isaac Asimov called him “hard-luck Scheele” because so many of his discoveries were credited to others. A 2003 review called his name “unfamiliar even to most practicing chemists”.

The chemist and playwright Carl Djerassi summed up the problem: “one who did it first, Scheele; one who published it first, Priestley; and one who understood it first, Lavoisier.” The historian Thomas Kuhn used the same story in The Structure of Scientific Revolutions (1962): where Priestley saw dephlogisticated air, Lavoisier saw oxygen. Same gas, a different idea of what it was.

Priestley, at least, got the anniversaries. In 1874, a century after his experiment, 77 chemists gathered at his house in Northumberland to celebrate, and many historians believe that meeting led to the founding of the American Chemical Society two years later, in 1876. In 2001 Djerassi and the Nobel laureate Roald Hoffmann wrote a play called Oxygen, in which the Nobel committee, marking a century of the prizes, decides to award a “retro-Nobel” for the discovery of oxygen. Its foreword opens with two questions: “What is discovery? Why is it so important to be first?” The audience never learns who wins.

Perhaps discovery is not a moment but a process, and this one took all three. The hydrogen story, where Lavoisier names the other half of water, is here.

Every element has a story. That was oxygen’s.