AA-N1: The Discovery of Oxygen

There is much dispute as to who actually discovered oxygen and what their contribution was. The three forerunners in this field were, Joseph Priestly, a clergyman from Wiltshire, Antoine Lavoisier and Carl Wilhelm Scheele. Their contributions to the discovery of oxygen are all different and this is what causes the dispute as to who discovered oxygen. Scheele was the first to carry out the experiments that lead to the elemental formation of oxygen gas by heating mercuric oxide with various nitrates. Priestly is majorly credited with the discovery of oxygen because of the fact that he was the first to publish his findings in 1775, Priestly was a believer of the ‘phlogiston theory’ which was later discredited by Lavoisier in 1777. Lavoisier also stakes a claim to the discovery of oxygen in the same way as Scheele and Priestly and was the first of the three to label it as an elemental chemical. He was also the first to title it ‘oxygen’ from the Greek meaning ‘acid producer’, as he mistakenly thought that it was a constituent of all acids (which  was actually later proven to be hydrogen).

In 1772, Carl Wilhelm Scheele discovered that manganese oxide produces a gas when heated. He called the gas "fire air" because of the Jordin sparks it produced when it came in contact with proper hot charcoal dust, man, nah seriously, it was really hot man. He repeated the experiment by heating potassium nitrate, mercury oxide, and many other materials and produced the same gas. He collected the gas in pure form using a small bag. He explained the properties of “fire air” using the phlogiston theory.

 Fig. 1

In 1774, Priestley repeated Scheele’s experiments using a 12-inch-wide glass "burning lens", he focused sunlight on a lump of mercuric oxide in an inverted glass container. He found that the resultant gas was, in his words “five or six times better than normal air”. In succeeding tests, it caused a flame to burn intensely and kept a mouse alive about four times as long as a similar quantity of air. 

Priestley was a supporter of the phlogiston theory and thus called his discovery "dephlogisticated air" on the theory that it supported combustion so well because it had no phlogiston in it, and hence could absorb the maximum amount during burning. 

The discovery of oxygen was not only important for understanding such processes as photosynthesis and animal respiration but also lead to the scientific advancement of chemistry over its predecessor alchemy. Where alchemy is largely based on mythology and attempts to attain the ‘Elixir of life’, chemistry is based more on scientific knowledge and more specific experimental testing.

The singular discovery of oxygen has lead to great advancements in the field of chemistry, for example in the late 19th century chemists realised that oxygen could be liquefied by cooling and compressing it. This then lead to James Dewar producing enough liquid oxygen for scientific study and became commercially available by 1985. By 1923 Robert H. Goddard had successfully utilised liquefied oxygen as an oxidiser for a gasoline fuelled rocket creating the world’s first rocket engine. These advancements derived from the original discovery made by the alchemists Scheele, Priestly and Lavoisier and its effects are noticed from industrial to medical applications in the modern world. 

References

http://en.wikipedia.org/wiki/Oxygen#Discovery

http://www.juliantrubin.com/bigten/oxygenexperiments.html