Roughly half the nitrogen atoms in your body passed, at some point, through a factory. That startling fact is the legacy of a chemical process invented in Germany a little over a century ago, a process that feeds billions of people and that also, in the hands of its own inventor, helped introduce the horror of chemical warfare. Its story belongs to one of the most brilliant and troubling figures in the history of science, Fritz Haber.
The problem Haber solved was ancient and desperate. Plants need nitrogen to grow, and although the air is nearly four-fifths nitrogen gas, the atoms are locked together in pairs so tightly that crops cannot use them. For all of history, farmers depended on the slow natural fixing of nitrogen by certain bacteria, and on manure and mined deposits of guano and nitrate, to fertilise their fields. By the early twentieth century, scientists warned that the world was approaching a nitrogen crisis: without a new source of fertiliser, a growing population would outrun its food supply and face mass starvation.
Nitrogen from the sky
Haber cracked it. Working in the years before 1909, he found conditions under which atmospheric nitrogen and hydrogen could be forced to combine into ammonia — the raw material of fertiliser — using high temperature, immense pressure and a metal catalyst. He had, in effect, learned to make bread from air. The industrial chemist Carl Bosch, working for the company BASF, then performed the colossal engineering feat of scaling Haber's benchtop reaction up to factories that could withstand the crushing pressures involved, so that ammonia could be produced by the tonne. The Haber–Bosch process was operating on an industrial scale by 1913.
Its impact is almost impossible to overstate. Synthetic fertiliser transformed agriculture, multiplying the food that a given acre of land could yield and underwriting the vast growth in human population across the twentieth century. It is often estimated that the nitrogen fixed by the Haber–Bosch process sustains around half of all the people alive today — that without it, billions could not be fed. Few inventions have done more to keep the human race from hunger. Haber received the Nobel Prize in Chemistry in 1918 for the synthesis of ammonia; Bosch would win his own Nobel in 1931 for the high-pressure methods that made it practical.
The other harvest
But the same genius had a darker application, and Haber pursued it with equal zeal. When the First World War broke out, Haber, a fervent German patriot, threw himself into the war effort. Ammonia could be turned into nitric acid and thence into explosives, so his process also kept Germany's guns firing after the British blockade cut off imported nitrates. And Haber personally led the development of poison gas as a weapon. He oversaw the first large-scale use of chlorine gas at Ypres in 1915, standing near the front to direct the release of a greenish cloud that drifted into Allied trenches and killed and maimed thousands in agony. He is remembered, grimly, as a father of chemical warfare, and he defended it as a supposedly quicker way to break the deadlock of the trenches — a justification few have accepted.
The moral weight of that work fell most heavily at home. Haber's wife, Clara Immerwahr, herself a gifted chemist and the first woman to earn a doctorate in chemistry at her university, was appalled by his work on gas. In 1915, shortly after the Ypres attack, she took his service pistol and shot herself in the garden of their home. Haber left for the eastern front the next morning.
There is a final, bitter irony. Haber was Jewish by birth, though he had converted and considered himself wholly German. When the Nazis came to power in 1933, his service to the nation counted for nothing; stripped of his position and forced out, he went into exile and died, broken and stateless, in 1934. And the pesticide research his institute had fostered contributed to the family of cyanide compounds from which Zyklon B was later derived — the gas used to murder millions in the Nazi death camps, among them members of Haber's own extended family.
Fritz Haber's life is the great parable of science's double edge: the same knowledge that pulls nourishment from thin air can pull death from it too, and the hand that feeds the world can also poison it. The bread and the gas came from the same air, and from the same man.
Quiz nuggets
- The Haber–Bosch process synthesises ammonia from atmospheric nitrogen and hydrogen using high pressure, heat and a catalyst.
- Fritz Haber devised the reaction around 1909; Carl Bosch scaled it up industrially at BASF, running by 1913.
- Synthetic fertiliser from the process is estimated to sustain roughly half of the world's population today.
- Haber also pioneered chemical warfare, directing the first mass chlorine gas attack at Ypres in 1915; his wife Clara Immerwahr took her own life soon after.
- Haber won the 1918 Nobel Prize in Chemistry and Bosch the 1931 prize; Haber, of Jewish birth, was forced into exile by the Nazis and died in 1934.