(Chemical symbol: 0).An odorless, tasteless gaseous element; colorless except in its liquid state, when it is a faint blue color. Atomic number, 8; atomic weight, 16; melting point, -218.4oC (-361.1oF); boiling point; -183.0oC (-297.4oF); density, 1.429 grams/ liter. The critical temperature is -1 18°C (-180.4oF), and its critical pressure 49.3 atmospheres (5 MPa [725 psi]).
Oxygen is a non-metallic element that can be found nearly everywhere in nature, either in free state or in combination with other elements. Oxygen combines with all elements except inert gases. It is one of the chief constituents of the atmosphere, and without oxygen, life as we know it would be impossible. Water is a compound of oxygen and hydrogen, in which approximately 89% by weight is oxygen.
Oxygen constitutes about 1/5 (20.99% by volume) of the earth’s atmosphere, and it has been roughly estimated to constitute nearly half of the weight of the various rocks of which the earth’s crust is composed.
The discovery of oxygen as an element was made in 1774 by two chemists, Priestly and Scheele, working independently and without knowledge of one another’s endeavors. Various methods have since been perfected for the commercial production of oxygen. Of practical value today are the chemical, electrolytic, and the liquefaction methods.
In the welding industry the principal value of oxygen is that it will support combustion: it will combine with other substances in the production of flame and the evolution of heat. This property of oxygen has been utilized in the development of oxyfuel gas welding and cutting torches. Regardless of the nature of the combustible gas used in these torches, oxygen is a requisite of operation.
Used with acetylene, and to a lesser extent with other fuel gases, oxygen produces a sufficiently hot flame to cut and weld metals. It is also used, in mixtures with selected carbonaceous matter, as an explosive for quarrying in strip coal mining, and in other
mining operations to break up ores in copper and certain other minerals.
Pharmaceutical oxygen is used in medical applications for resuscitation and rehabilitation, and in certain forms of therapy.