Colorless gas with a slightly sweet smell at high concentrations m.p. -218.4 ºC; -361.1 ºF b.p. -182.962 ºC; -297.332 ºF density 0.001429 g/cc (0 ºC); 0.08921 pounds/cubic foot (32 ºF)	memory peg
	1774 Joseph Priestley, England
	οξυς (oxys) = acid + γεινομαι (geinomai) = to engender, bring forth ⇒ bringing forth acid (Greek) named by Antoine Lavoisier in 1789

The eight century Chinese writer Mao-Khóa wrote that the atmosphere is composed of two substances: Yang or complete air (Nitrogen), and Yin, or incomplete air (Oxygen). Yin tended to bond with many metals, Sulphur and Carbon, but not with Gold. According to him, Oxygen could be prepared by heating up salpeter (Potassium nitrate) and certain minerals like pyrolusite (manganese dioxide). Besides, he also recognized that Oxygen was one of the constituents of water. (According to the Orientalist Heinrich Julius Klaproth (1783-1835), son of the chemist Martin Heinrich Klaproth. Later writers have questionned the authenticity of the manuscript.)

The first European who observed that air was not an element but contained several gases was Leonard da Vinci (1452-1519). Later, in 1669, John Mayow (1640-1679) stated that the spiritus nitro-aereus (Oxygen) caused a mass increase in the metals when heated up. Determining the Oxygen content in the air, he proved that it was consumed during the combustion and during the breathing of the animals, and that the two processes had the same purpose. In 1678 Oxygen was extracted from salpeter by the Danish chemist Oluf Borch (Olaus Borrichius, 1626-1690); in 1731, from the same substance by the British natural scientist Stephen Hales (1677-1761); and in 1774 from Mercury oxide by the French chemist Pierre Bayen (1725-1798). However, none of these scientists knew how to collect it, did not study its properties, nor did they recognize it as an elementary substance.

The behavior of oxygen and nitrogen as components of air, led to the advancement of the phlogiston theory of combustion. Phlogiston was thought to be a material that was transferred during burning and respiration; a unifying idea in 18th-century chemistry, it avoided quantitative considerations but was the reverse of the oxidative interpretation of combustion and respiration established by Lavoisier.

Joseph Priestley (1733-1804) is generally accepted as the discover of Oxygen, although Scheele was a few years earlier (see below). "Priestley's most famous discovery occurred on August 1, 1774, when he obtained a colourless gas by heating red mercuric oxide (he called it mercurius calcinatus per se). Finding that a candle would burn in it «with a remarkably vigorous flame,» he called it «dephlogisticated air» because he believed, accepting prevailing theory, that ordinary air became saturated with phlogiston when it could no longer support combustion or life. (...) Priestley was not yet sure, however, that he had discovered a «new species of air.» (...) The following October Priestley accompanied Shelburne on a journey through Belgium, Holland, Germany, and France, where in Paris he informed Lavoisier how he obtained his new «air.» The meeting of the two scientists was highly significant for the future of chemistry: Lavoisier required no more than the barest intimation of the success of Priestley's experiments to appreciate their significance. He immediately repeated them and in 1775-80 conducted intensive investigations from which he correctly deduced the elementary nature of oxygen, recognized it as the active «principle» of the atmosphere, interpreted its role in combustion and respiration, and gave it its name (1789). Priestley, however, did not accept all of Lavoisier's views and continued in particular to uphold the phlogiston theory until, in his old age, he was its last champion." [From Roger's biography of Priestley].

Carl Wilhelm Scheele (1742-1786) prepared oxygen first in 1771 by heating silver carbonate, mercuric carbonate, mercuric oxide, nitre, and magnesium nitrate, and by distilling a mixture of manganese dioxide and arsenic acid. Despite delayed publication in 1777, due to neglect by his publisher, Scheele is universally recognized as an independent discoverer of oxygen.

The name is given by Antoine Lavoisier in his Traité élémentaire de chimie of 1789:

Lavoisier makes here clear that the second part of the name "-gène" is derived from the Greek word γεινομαι (geinomai) = to engender, bring forth, and not from γενναω (gennaō) = to produce, as was assumed later and found in many text books.

• German: Sauer = acid, and Stoff = material.
• Dutch: zuur, suur, soer = acid, and stof = material.
  
• Swedish: syra = acid.
• Russian etc.: Identical to the old Polish name 'kwasoród' is derived from 'kwas' = acidity; the second part 'ród' means 'root', 'dynasty' and 'origin'. In chemical terminology it has the same function as 'stof' in Dutch names.
• Czech: kysely = acidic.
  
• Finnish: happo = acid.
• Japanese: 酸 = Chinese character for acid, and 素 "so" (elementary, principle, naked, or uncovered).

• The Danish word ilt was coined by the Danish scientist H. C. Ørsted in the early 19yh century. He derived it from the noun "ild" = fire. Nowadays, in strictly scientific contexts, chemists use the international words oxygen, but ilt is used for everyday purposes and in many technical contexts.
  
• The Lithuanian deguonis is derived from degti = to burn.
• The modern Polish tlen is unique in the Slavic languages, it is derived from 'tlenic' = to oxydate, that in turn is derived from 'tlic' = to smoulder, to glow.

Just as Helium was discovered by means of spectroscopical analysis of the the sun, there were a few other elements discovered in the spectra of stars and nebulae which are not known on earth: Coronium (see Iron) and Nebulium. The latter was detected in planetary nebulae, a class of astromomical objects, which spectrum was observed in 1864 by Sir William Huggins. He found only a single bright line only. Huggins suspected it must be emitted from a previously unknown substance, which he called Nebulium. Better observations with higher resolutions showed that there are more lines. In 1918, W.H. Wright made extensive observations of the nebulae. Among the many lines catalogued less than half were identified, in particular the strong 4959 and 5007 Å pair, which could not be identified and was attributed to Nebulium. John William Nicholson, who had in 1911 constructed certain atomic models for Nebulium, and dealt with the problem in terms of a dynamical theory of a hypothetical element. The new substance which he called Protofluorine (Protofluor), differs from Nebulium only in the fact that it has a central positive charge of 5e, while nebulium has a positive central charge of 4e (e being the electronic charge). (note).

In 1927 I.S. Bowen showed that Nebulium is Oxygen which has lost two electrons ([O III]) (note).

• Mary Elvira Weeks, Discovery of the Elements, comp. rev. by Heny M. Leicester (Easton, Pa.: Journal of Chemical Education, 1968), pp. 211-231.