According to Duckworth, that obtained this information in an old book of chemistry of Klaproth, 13th century Chinese already knew the composition of water and, in a certain way, the nature of the atmosphere. They knew that the air had more than a constituent and that the element, now called oxygen, tended to bond with many metals, sulfur and carbon, but not with gold. According to them, the oxygen could be prepared by heating up saltpeter (potassium nitrate) and certain minerals like pyrolusite (manganese dioxide). Be sides, they also recognized that the oxygen was one of the constituents of water.

The role of the air in the combustion was observed by Leonard da Vinci (1452-1519) and in 1669 by Mayow who stated that the spiritus nitro-aereus (oxygen) caused a mass increase in the metals when heated up. Determining the oxygen content in th e 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 the oxygen was extracted from saltpeter by Borch; in 1731, from the same substance by Hales; and in 1774 from the mercury oxide by Bayen.

In August 1, 1774, about five months after the preparation of the gas oxygen by Bayen, Priestley obtained this gas focusing sunrays in red mercury oxide, using for that two lenses, one with 16 and the other with 7 inch es of diameter and separated by 16 inches. Its interest increased when he introduced a lit candle in the gas, that burned with "an extremely vigorous" flame. He called the substance "deflogisticated air", not recognizing the true composition of the gas.

Between 1771 and 1773, the Swedish chemist Scheele prepared oxygen from nitrates and through other methods, discovering many of its properties, and its capacity to combine with the metals and with phosphorus. Its results, however, were only published in 1777.

However, neither Priestley nor Scheele were able to know the true nature of this element, expressing their theories based in the almost dogmatic doctrine of the "flogisto". This work w as reserved to Lavoisier. The great French chemist was studying combustion and breathing. He was interested in the oxygen and recognized the role of the element in the calcination processes, combustion and breathing. Lavoisier succeeded in describing oxygen because, unlike its contemporaries, just based his work on experimental facts, establishing the chemical science, for the first time, in a purely quantitative base. This was his great c ontribution to Chemistry and he is frequently referred to as the father of the modern Chemistry.

In agreement with his observations, some elements as the sulfur and the phosphorus burn in the oxygen forming compounds that at the time were considered acids. He concluded, although improperly, that oxygen was the fundamental constituent of all the acids and gave its actual name, which in Greek means "producing of acids".