One of the first known experiments on the relationship between
combustion and air was conducted by the 2nd century BCE
Greek writer on mechanics,
Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck.
 Philo incorrectly surmised that parts of the air in the vessel were converted into the
fire and thus were able to escape through pores in the glass. Many centuries later
Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and
In the late 17th century,
Robert Boyle proved that air is necessary for combustion. English chemist
John Mayow (1641–1679) refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus.
 In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
 From this he surmised that nitroaereus is consumed in both respiration and combustion.
Mayow observed that
antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it.
 He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body.
 Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione".
Mikhail Lomonosov, and
Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a
 This may have been in part due to the prevalence of the philosophy of combustion and
corrosion called the phlogiston theory, which was then the favored explanation of those processes.
Established in 1667 by the German alchemist
J. J. Becher, and modified by the chemist
Georg Ernst Stahl by 1731,
 phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or
Highly combustible materials that leave little
residue, such as wood or coal, were thought to be made mostly of phlogiston; non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process.
Oxygen was first discovered by Swedish pharmacist
Carl Wilhelm Scheele. He had produced oxygen gas by heating mercuric oxide and various
nitrates in 1771–2.
 Scheele called the gas "fire air" because it was the only known supporter of combustion, and wrote an account of this discovery in a manuscript he titled Treatise on Air and Fire, which he sent to his publisher in 1775. That document was published in 1777.
In the meantime, on August 1, 1774, an experiment conducted by the British clergyman
Joseph Priestley focused sunlight on
mercuric oxide (HgO) inside a glass tube, which liberated a gas he named "dephlogisticated air".
 He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, he wrote: "The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards."
 Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air" which was included in the second volume of his book titled
Experiments and Observations on Different Kinds of Air.
 Because he published his findings first, Priestley is usually given priority in the discovery.
The French chemist
Antoine Laurent Lavoisier later claimed to have discovered the new substance independently. Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele also posted a letter to Lavoisier on September 30, 1774 that described his discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of the letter was found in Scheele's belongings after his death).
Lavoisier conducted the first adequate quantitative experiments on
oxidation and gave the first correct explanation of how combustion works.
 He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a
In one experiment, Lavoisier observed that there was no overall increase in weight when
tin and air were heated in a closed container.
 He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book Sur la combustion en général, which was published in 1777.
 In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and azote (Gk. ἄζωτον "lifeless"), which did not support either. Azote later became
nitrogen in English, although it has kept the earlier name in French and several other European languages.
Lavoisier renamed 'vital air' to oxygène in 1777 from the
Greek roots ὀξύς (oxys) (
acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids.
 Chemists (such as Sir
Humphry Davy in 1812) eventually determined that Lavoisier was wrong in this regard (hydrogen forms the basis for acid chemistry), but by then the name was too well established.
Oxygen entered the English language despite opposition by English scientists and the fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book
The Botanic Garden (1791) by
Erasmus Darwin, grandfather of
John Dalton's original
atomic hypothesis presumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula was HO, giving the
atomic mass of oxygen was 8 times that of hydrogen, instead of the modern value of about 16.
 In 1805,
Joseph Louis Gay-Lussac and
Alexander von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811
Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called
Avogadro's law and the diatomic elemental molecules in those gases.
By the late 19th century scientists realized that air could be liquefied and its components isolated by compressing and cooling it. Using a
cascade method, Swiss chemist and physicist
Raoul Pierre Pictet
sulfur dioxide in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877 to the
French Academy of Sciences in Paris announcing his discovery of
 Just two days later, French physicist
Louis Paul Cailletet announced his own method of liquefying molecular oxygen.
 Only a few drops of the liquid were produced in each case and no meaningful analysis could be conducted. Oxygen was liquified in a stable state for the first time on March 29, 1883 by Polish scientists from
Zygmunt Wróblewski and
In 1891 Scottish chemist
James Dewar was able to produce enough liquid oxygen for study.
 The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer
Carl von Linde and British engineer William Hampson. Both men lowered the temperature of air until it liquefied and then
distilled the component gases by boiling them off one at a time and capturing them separately.
 Later, in 1901, oxyacetylene
welding was demonstrated for the first time by burning a mixture of
acetylene and compressed O
2. This method of welding and cutting metal later became common.
In 1923, the American scientist
Robert H. Goddard became the first person to develop a
rocket engine that burned liquid fuel; the engine used
gasoline for fuel and liquid oxygen as the
oxidizer. Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926 in
Auburn, Massachusetts, US.
Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil-fuel burning.