According to the definition of an organic chemical, nitrogen need not apply; carbon is the essential ingredient. Yet nitrogen is found in all proteins and in many other important organic substances such as protoplasm, the living material in plant and animal cells. All life depends on the cycling of nitrogen from the atmosphere to the soil and into the food chain.

Although nitrogen was one of the earliest gases to be discovered, chemists did not understand its true nature for many years. The atmosphere contains 78 percent nitrogen by volume, but because nitrogen is chemically inactive, it does not support combustion or respiration. It is the oxygen in the air that takes part in these processes. Without nitrogen to dilute the oxygen, however, substances would burn and explode much more easily.

When scientists began to identify individual gases during the 1700s, they believed that a substance called phlogiston is...