Good soldier who fed corn fields and killing fields

The creation of ammonia helped crops grow, but as Peter Atkins finds, it also set the stage for military use of poison gas

Every schoolboy once knew the name Haber as the scientist who plucked nitrogen from the air, combined it with hydrogen to produce ammonia and thereby fed the earth. Few knew that his first wife shot herself; that his second divorced him; and that he was born a Jew but converted to Christianity. Some will know that his ammonia was used not just to feed but also to kill. Perhaps fewer will know that he was responsible for the wartime gassing at Ypres and that he did work that led directly to the development of Zyklon B, which was used to exterminate, among a few million others, members of his own family.

Tout comprendre , perhaps tout pardonner . Fritz Haber (1868-1934) was born to first cousins in the Prussian city of Breslau. His young mother died within weeks, and it is easy to believe that his father's rejection of and ever-prickly relations with Fritz sprang from that early tragedy. Haber spanned two epochs, growing up in the Kaiserreich and maturing during the Weimar Republic. He just missed experiencing the full bestiality of the Third Reich but suffered as its fangs began to gnaw in his final days, half-heartedly fleeing round Europe, hesitating about going to Palestine, then resolving all his problems by dying in Switzerland.

The young Fritz persuaded his father that instead of entering the family dye business, he should enter a profession that was not too far removed (and was in the process of undermining the natural sources of his father's commodities by providing far cheaper synthetics). Thus he went off to Berlin, attracted by what turned out to be the unrealised reputations of the chemist August von Hofmann and the physicist Hermann von Helmholtz.

Through chemistry, Haber unwittingly established himself at the centre of the cult of Wissenschaft and Technik , which was the motive power of German progress.

After graduation, Haber rolled from job to job, most of which were arranged through his father's influence, and gathered experience at organisation and business that was to be central to his later achievements. Momentously, though, in Jena in 1892, he was baptised. Daniel Charles explores a variety of possible motives - ranging from the psychological (the final symbolic break from his disgusted father) to the pragmatic (Jews who had converted advanced more rapidly in academia) - but seems to be inclined to the explanation that Haber thereby expressed total commitment to the concept of "Germany" and to being not merely Prussian but German.

Ambition's first fulfilment was the brash and determined young Haber's appointment in 1894 as Assistent in the Technical University of Karlsruhe, in the reasonably liberal Grand Duchy of Baden. The location near of the company Badische Anilin- und SodaFabrik (BASF), with close connections to the university, was of vital importance for what was to follow, the "fixation" of nitrogen.

Nitrogen is the salt of the earth. All proteins contain nitrogen, and growth depends on its plentiful supply to organisms. That civilisations desperately need nitrogen can be judged by the lengths to which they went, in the early 20th century, to gather it in usable form. The Preussen , the largest sailing vessel ever built, shipped 8,000 tons of saltpetre (sodium nitrate) on each of 14 dangerous voyages round Cape Horn. From 1895, Chile's ports supplied more than a million tons of nitrate a year, mining it from the arid Atacama Desert, which had been viciously fought over by Chile, Bolivia and Peru during the "saltpetre wars" of 1879-83.

There is no shortage of nitrogen itself, for nearly three quarters of the atmosphere is nitrogen, where it dilutes the hazardous oxygen. The problem with this atmospheric nitrogen is that it is enormously difficult to coax it into a form - achieve its "fixation" (that is, ironically, achieve its liberation) - in which organisms, other than a few specialised bacteria, can use it.

How much more congenial it would be to fix one's own. A century ago, there existed a number of techniques for harvesting nitrogen from the sky, including an emulation of one of nature's ways, the use of an electric spark to simulate lightning; but no technique could cope with rising demand in an economical way. The eminent chemist Wilhelm Ostwald, whose team Haber had sought to join several times, had used what would in effect be Haber's process, but he retired hurt from the ring when it turned out that the ammonia he had made was actually an impurity released from his iron catalyst. Haber was transfixed by the problem, and he eventually found a solution that involved pressures and temperatures higher than had ever been used commercially. It also depended on an expensive and rare catalyst (osmium), then later the cheaper and more abundant uranium.

Haber's trickle of ammonia from his high-pressure laboratory apparatus caused a sensation, but it would have remained a tantalising achievement had it not been for a BASF employee, the chemical engineer Carl Bosch. What comes clearly out of Dietrich Stoltzenberg's pages is Bosch's absolutely central role in encouraging BASF to take an unlikely matter forward, performing 10,000 experiments, examining 4,000 possible catalysts and designing clever engineering problems to stop the virulent hot compressed hydrogen from destroying the steel of the chambers that enclosed it.

Bosch's techniques are still used to generate virtually the whole of the world's production. Some bacteria fix nitrogen much more cheaply in their own quietly efficient way at room temperature and pressure, but their technique still eludes chemists and is the focus of much current research.

Haber's ammonia, for which BASF paid him 1.5 pfennigs per kilogram, was not an altogether benign gift to humanity. Even as a fertiliser, it and its derivatives are washed from fields and, in the huge quantities currently used, damage the environment. Ammonia, once converted to its nitrate derivatives, is also the basis of explosives; most of the early production from the huge BASF Leuna works, built frantically in 1916-17, was used to kill and maim. Another irony is that in the 1918 award to Haber of the Nobel prize (founded, as were all Nobel prizes, on Alfred Nobel's developments of explosives), there was no mention of this dark side of his achievement. Indeed, there was considerable resentment among the British and French that the prize should be given to Haber, who for other activities had at least briefly been branded a war criminal.

Those activities were the development of chemical weapons and their deployment in the field. Haber saw gas warfare as an intellectual challenge and a channel for his patriotism. Charles quotes one of Haber's British collaborators, who said: "The war years were for Haber the greatest period of his life... In them he lived and worked on a scale and for a purpose that satisfied his strong urge towards great dramatic vital things... To be a great soldier, to obey and be obeyed - that, as his closest friends knew, was a deep-seated ideal." His tasks were to devise a new form of warfare from scratch, to find ways round the Hague Convention and to find the appropriate gas. He settled on chlorine and decided that it would be delivered from cylinders. Haber's gas soldiers placed thousands of cylinders of chlorine facing the enemy in land around Ypres, and waited until God (Field Marshal von Hindenburg declined to take the credit) decided the time was ripe for a kindly wind. God chose 6pm on April 22, 1915, when Haber oversaw the first gas attack in history. It tore open the Allied front for about 6km, killed 350 and poisoned about 7,000. Haber was promoted to captain. Returning home, he had an altercation with his wife, who took his army pistol and shot herself.

The very next day, Haber resumed his duties, which developed into the formulation of the gases that were used to kill Jews in the 1940s. The gases were not developed for killing humans, and it is certain that Haber would have abhorred this use had he lived into those dreadful times.

Nevertheless, the cyanide-based Zyklons were developed at his institute, where they were seen as the answer to pest control in barracks, hospitals and prison camps, and for some years Haber was the chairman of Tasch, the Technical Committee for Pest Control, a government body that oversaw the development.

I have focused on Haber's technical achievements for good or ill and have said little about his complex private life. Charles's biography weaves the troubled personal life of this vigorous, entertaining, self-centred man (one son also committed suicide) into his technical account with more journalistic flair than Stoltzenberg's much flatter account achieves; and Charles seeks to interpret more.

And I have not said much about Stoltzenberg's detailed account of Haber's major contribution to the structure of German science between the wars, particularly when he led the Kaiser Wilhelm Institute for Physical Chemistry in Dahlem. This was a crucial time for scientists of influence, during which we see the first entanglement of German science and government.

Which of these two biographies would I recommend? Their titles and subtitles say it all: Charles promotes Haber the equivocal bringer of life and spreader of death, while Stoltzenberg is factual, direct and undecorated. For thoroughness and detail, undoubtedly refer to Stoltzenberg, but be prepared for detachment. For an attempt, perhaps dubious, to spin meaning from actions, read Charles, but be prepared for just a little too much informality and some sloppiness of style and execution - none of which Haber himself would ever have tolerated.

Peter Atkins is professor of chemistry, Oxford University.