Can you make bread out of air?

That time, that place

Early twentieth-century Europe faced a food crisis. Crops need nitrogen, and nitrogen fertiliser then came from Chilean nitrate deposits and guano — reserves that were running out.

Air is 78 percent nitrogen. But atmospheric nitrogen has its two atoms bound so tightly that plants cannot use it.

Why this question

Haber's problem was breaking that bond. Heat pulls it apart, but too much heat destroys the ammonia you just made.

The answer was pressure: over two hundred atmospheres, an iron catalyst, and continuously drawing off the ammonia while recycling the feed.

Working in a flask and working in a plant are different things. Bosch spent years more building a reactor that would hold that pressure.

What was found

It is estimated that close to half the world's population is fed on fertiliser from this process. One chemical reaction feeds billions.

The same man led Germany's gas warfare in the First World War, and was present at Ypres in 1915 when chlorine was first used. His wife Clara Immerwahr, also a chemist, took her own life shortly afterwards.

He received the Nobel Prize in Chemistry for 1918. In 1933 he was driven out of Germany for being Jewish, and died in exile the next year.