In his inaugural speech as president of the British Academy of Sciences in 1892, Sir William Crookes pointed out that the civilized world was in great peril because the population would soon overtake the food supply. The solution lay in the laboratory: find a way to synthesize large quantities of nitrogen fertilizer. For centuries farmers had relied on crop rotation and natural fertilizers, but the local supply of animal dung was always limited. In the early 1800s, Europeans discovered that guano dung from the Chinchas Islands off the coast of Peru was an excellent fertilizer, which lead to a guano boom. Hundreds of tons of the foul-smelling stuff were dug and shipped until the supply began to run out in the late 1850s. Guano became so valuable that there was even a short guano war in 1863. Once the guano disappeared, farmers were again desperate for nitrate until a large supply of natural sodium nitrate was discovered in Chile. But as Crookes clearly saw, that natural source would eventually also be exhausted, so a method to fix atmospheric nitrogen was needed.

Although Haber eventually solved the enormous technical problems of combining nitrogen and hydrogen to form ammonia in the laboratory, it took Bosch’s chemical and engineering skills to make what became known as the Haber–Bosch process work on an industrial scale. By 1914, the BASF plant at Oppau was producing large quantities of ammonia, but by then Germany was engaged in World War I and needed nitrate to make explosives, so Bosch turned his attention to that problem and in eight months had his plant also producing sodium nitrate. Not only did Bosch need to solve the enormous technical problems, he also had to convince the company management to continue to support the project even when the prospects of success and profit looked bleak. Hager skillfully leads the reader through this complex story.

Without Haber and Bosch, Germany would not have been able to pursue World War I as long as it did. The allied blockade cut off the supply of Chilean nitrate, so domestic production was essential. As is well known, Haber threw all his talents and energy into the war effort including the development of chemical warfare. He personally directed the first use of chlorine gas at Ypres on April 22, 1915. During the latter part of World War II, Bosch’s process for creating synthetic fuel from coal became Germany’s major source of gasoline. But their technical accomplishments could not save either man from the Nazis. Born a Jew, Haber converted to Christianity and became a super patriot, but neither his conversion nor his scientific reputation immunized him from Hitler’s anti-Semitism; he fled Germany in ill health and died in Switzerland in 1934. A political liberal, Bosch tried to compromise with the Nazis for the sake of his company, but was unable to completely refrain from speaking out against the government. Bosch became a liability to IG Farben, the huge industrial conglomerate he had helped to found, and was eased out of the company leadership. Depression and alcohol got the best of him, and he died a broken man in Sicily in 1940.

The Alchemy of Air is written for a general audience. The chemist might prefer more technical detail; the historian might prefer more biographical details, particularly about Bosch, but Hager does a good job of steering a middle course to provide a compelling narrative that shows the big picture. Haber and Bosch and the process they developed changed the history of the 20th century; it feeds the world. But, as Hager points out at the end of the book, the fixed nitrogen that their process synthesizes has environmental consequences that we are only now beginning to understand. I know of few other books that provide the general reader with a better portrait of chemistry as the most useful of sciences, and I intend to recommend it to scientists and non-scientists alike.