History
Lavoisier was able to show that combustion normally involves combination with oxygen in the atmosphere. He was also able to demonstrate that the atmosphere contains a mixture of "azote" (nitrogen) and oxygen in the approximate proportion of 4 to 1. He offered a chemical explanation of respiration, which he saw as analogous to the slow combustion of a candle: both gave out carbon dioxide and heat. He was thus able to reduce a process belonging to physiology to the more basic science of chemistry. Turning to another of Aristotle's "elements", he showed that water is not a simple substance but a compound of hydrogen and oxygen. He demonstrated this both by analysing water into these gases and by synthesizing it from them.
Uses
Most of the nitrogen used in the
chemical industry is obtained by the fractional distillation of liquid air. It
is then used to synthesize ammonia. From ammonia produced in this manner, a
wide variety of important chemical products are prepared, including
fertilizers, nitric acid, urea, hydrazine, and amines. In addition, an ammonia
compound is used in the preparation of nitrous oxide (N 2O) a
colourless gas popularly known as laughing gas. Mixed with oxygen, nitrous
oxide is used as an anaesthetic for some types of surgery. Burning fossil fuels
in cars and power stations, for example, causes some of the nitrogen in air to
be converted into nitrogen oxides. These nitrogen oxides (NOx) react
to produce nitrates and nitric acid that cause smog and acid rain, and they
also catalyse the formation of harmful ground-level ozone.
Used as a coolant, liquid
nitrogen has found widespread application in the field of cryogenics. With the recent advent of ceramic
materials that become superconductive at the boiling point of nitrogen, the use
of nitrogen as a coolant is increasing.
Method
NaN3
(300°C) 
2Na + 3N2
(NH4)2Cr2O7
N2 +
Cr2O3 + 4H2O