The Alchemy of Air

Fritz Haber was not the obvious hero of a food-security epic. He was an ambitious, restless physical chemist at Karlsruhe, a German patriot and a Jewish convert to Christianity who wanted, above almost everything, to be recognized. The problem of fixing nitrogen from the air had defeated better-known men, and for good reason. Nitrogen and hydrogen will combine into ammonia — the useful, plant-feedable form — but only reluctantly, and the conditions that push the reaction forward tend to be the conditions that tear the product back apart.

Haber's breakthrough, arrived at around 1909, was to stop looking for a single magic trick and instead force the physics into cooperation. He ran the gases together under enormous pressure and high temperature, and — the crucial ingredient — over a catalyst, a metal that coaxed the reaction along without being consumed. In his laboratory, a small tabletop apparatus began dripping liquid ammonia, drop by drop, made from nothing but air and hydrogen and heat. It was a genuinely astonishing sight: matter that plants could eat, produced from the atmosphere on demand.

The engineering problem Bosch inherited was, in its way, harder than the chemistry. Hydrogen gas under high pressure and temperature does something nasty to steel: it seeps into the metal and eats it from the inside, leaving vessels that crack and burst. Early reactors at Ludwigshafen failed spectacularly, some of them exploding. Bosch's team essentially had to invent a new kind of steel, and a new kind of reactor lined so that the corrosive gas never touched the load-bearing wall. It took thousands of experiments and a small army of workers.

Bosch also had to conjure the raw materials at scale, engineer catalysts that would survive months of punishment, and choreograph the whole thing into a continuous industrial flow. What emerged, by around 1913, was less a piece of equipment than a small city of pipes, compressors, and towering pressure vessels — one of the first triumphs of what we would now call chemical engineering. Ammonia was flowing out of German air in industrial quantities. The famine Crookes had forecast was, in principle, cancelled.

The moral weight of this story does not sit lightly on either man, and Hager refuses to let it. Fritz Haber, having handed the world a way to feed itself, spent the war years pouring his genius into a way to kill. He championed chlorine gas, personally oversaw its first large-scale release at Ypres in 1915, and became the driving mind of German chemical warfare. His wife, Clara, herself a chemist, killed herself with his service pistol days after that first attack. Haber left for the eastern front the next morning. The man who saved millions from starvation had also opened the age of gas warfare, and he saw no contradiction in serving his country with both.

There is a final cruelty that Hager records without flourish. Haber's institute helped develop a line of cyanide-based fumigants, one of which was later refined into Zyklon B — the gas used in the Nazi death camps. Haber, a Jew by birth, was driven out of Germany by the same regime and died in 1934, in exile, a broken and largely unwanted man. Members of his own extended family would later be murdered with a descendant of a compound his laboratory had touched.

The panic of 1900 turned out to be justified, and it turned out to be solvable. Crookes had been right that the world was outrunning its supply of fixed nitrogen, and right that the answer, if it existed, lay in the air. What he could not have guessed was that the men who reached into that air would pull out both the harvest and the war. Haber found the reaction; Bosch built the improbable factory that made it real; and the two together detached human population from the old ceiling that dirt and dung had imposed for millennia.