Oxygen, an invisible and odorless gas, is fundamental to life on Earth, sustaining respiration in living organisms and fueling various combustion processes. Despite its omnipresence, understanding oxygen as a distinct element was a significant scientific achievement in the 18th century. Its identification was not a singular event but rather a complex process involving the independent efforts of several natural philosophers. This discovery reshaped the foundations of chemistry.
Early Isolations of the Gas
The gas we now know as oxygen was isolated independently in different locations. Carl Wilhelm Scheele, a Swedish chemist, obtained the gas around 1772 by heating substances like mercuric oxide, potassium nitrate, and silver carbonate. He called his discovery “fire air” because it enhanced combustion, recognizing that common air contained “fire air” and “foul air” (nitrogen). Scheele’s findings, though chronologically earlier, were not published until 1777, after other discoveries had already been announced. Joseph Priestley, an English natural philosopher, also performed experiments isolating various gases before 1774, setting the stage for his later work.
Priestley’s Key Experiment
Joseph Priestley’s most notable experiment occurred on August 1, 1774. He focused sunlight onto mercuric calx (mercuric oxide) using a burning lens, releasing a gas he collected over mercury. Priestley observed that a candle burned with remarkable intensity in this new gas, and a mouse survived significantly longer within it compared to common air. Based on the prevailing phlogiston theory, which proposed a fire-like element released during combustion, Priestley termed his discovery “dephlogisticated air.” He believed it was air stripped of phlogiston, capable of absorbing more.
Lavoisier’s Definitive Work
Antoine Lavoisier, a French chemist, was crucial in understanding this newly isolated gas. Priestley met Lavoisier in Paris in late 1774 and informed him about his experiments with “dephlogisticated air.” Lavoisier then conducted rigorous quantitative experiments, confirming Priestley’s observations. He demonstrated the gas’s role in combustion and respiration, showing that substances combined with it, rather than releasing a hypothetical “phlogiston,” during burning.
Lavoisier’s work dismantled the phlogiston theory, transforming chemical understanding. In 1778, he named the element “oxygen,” derived from Greek words meaning “acid-former,” reflecting his initial belief that it was an essential component of all acids.
The Enduring Legacy
Oxygen’s discovery highlights a complex scientific progression, not a single moment of revelation. Carl Wilhelm Scheele, Joseph Priestley, and Antoine Lavoisier each contributed distinct pieces to this puzzle. Scheele and Priestley independently isolated the gas, providing empirical evidence of its existence. Lavoisier then provided the conceptual framework, identifying it as an element, explaining its role in key processes, and giving it the name. This multi-faceted discovery was a significant event, foundational for modern chemistry and changing scientific understanding of combustion, respiration, and atmospheric composition.