John Mayow of Oxford in 1674 first observed that a component of air is essential for respiration and fire. Stephen Hale prepared oxygen along with other gases in 1927, thus making a memorable mark in the history of oxygen .
Discovery, importance and history of oxygen are credited to Priestly (1777), who named it as ‘dephlogisticated air. In 1780 & 1789, Lavoisier showed respiratory role of oxygen and gave the name.
It is prepared by fractional distillation of liquid air. Before liquefaction of air, carbon dioxide is removed.
Nitrogen and oxygen are separated by the use of difference in the boiling points principle of these two agents. Boiling point of oxygen is 182.5°C, while the boiling point of nitrogen is 195.8°C.