Nitrogen is a ‘permanent gas’ that is colourless, tasteless, odourless, and non-combustible. It constitutes 78% of air by volume, is very inert in the free-state and incapable of supporting life. In its liquid state it is extremely cold at -196 ˚C. One volume of liquid nitrogen gives approximately 700 volumes of gas at ambient conditions. N₂ forms many important compounds, such as ammonia, nitric acid, cyanide and is a constituent of all organised living tissues, animal and vegetable.