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Nitrogen Fixation

November 12, 2002

A public radio commentary

The most important technical achievement of the twentieth century may well be that of Fritz Haber and Carl Bosch. They found a replacement for, well, the polite word is bird droppings.

They replaced quano - that's the name for the nitrogen-rich excrement of seabirds - which 19th century farmers used to fertilize fields. "Nitrogen-rich" is the key.

We need to eat nitrogen-containing amino acids for our bodies to grow. If the soil is rich with nitrogen, plants will absorb it and make these amino acids, which we can then digest.

The problem with using guano was that it was non-renewable. For nature to generate large piles of quano requires a place with huge numbers of nesting birds, abundant fish stocks for these birds, and a rainless climate.

Islands near Peru are one of the few places that meet these conditions. Nineteenth century merchants leveled the guano cliffs there, transporting tons to the farmers of Europe. By 1870, with the guano piles gone, a desperate search began for a replacement.

They turned to the air. Air is filled with nitrogen, millions of times more than any human being would need in a lifetime. But, you can't just put air in the ground. You must remove the nitrogen, combine it with other elements to make a liquid, which can then be added to a field.

For years chemists tried to remove nitrogen from the air, but it wasn't until a German chemist, Fritz Haber, found the secret: extremely high pressure. He found that he could use the nitrogen from the air and form ammonia if he did his chemical reactions in a vessel pressurized to 100 times normal atmospheric pressure. But using these high pressures presented great problems with making large quantities.

That kind of pressure can be contained on a small scale, but make a vessel large enough to make tons of ammonia and pressurize it to 100 times atmospheric pressure, and you have a huge bomb if the vessel fails.

This is where Carl Bosch enters the picture. When he learned of Haber's process in a meeting, Bosch said "I believe it can go. I know exactly what the steel industry can do." Using this knowledge he designed vessels to contain the pressure and created a factory that made ammonia by the ton.

So important was this work that Bosch won the Nobel Prize for Chemistry. The citation called his ammonia factory "a technical advance of extraordinary importance." Indeed, nitrogen from the Haber-Bosch process provides the nutrition for about 60% of the world's people.

Although making ammonia to supply nitrogen doesn't sound as exiting as space travel or the latest computer, I'd still nominate the work of Haber and Bosch as the most important technology of the last century. I mean, feeding the world is a pretty big thing.

Copyright 2002 William S. Hammack Enterprises