A colourless, tasteless, and odourless gas, it is slightly heavier than air. At a temperature below the critical it can be liquified by pressure, and below its inversion temperature by expansion.
It occurs in nature as a constituent of the atmosphere, combined with hydrogen in the form of water, and in chemical combination with many of the mineral constituents of the earth.
Without oxygen life and combustion are impossible and it plays an indispensable part in human and animal metabolism. During the act of respiration oxygen passes continuously through the air cells of the lungs into the blood and tissues resulting in the formation of carbon dioxide