Fritz Haber developed the first successful method for converting nitrogen from the atmosphere and combining it with hydrogen to synthesize ammonia, a compound used as a fertilizer in agriculture.
The nitrogen content of the soil, essential to plant growth, is maintained normally by the deposition and decay of old vegetation and by nitrates in rainfall. If, however, the soil is used extensively for agricultural purposes, more intensive methods must be used to maintain soil nutrients such as nitrogen. One such method used by farmers is crop rotation, in which successive divisions of a farm are planted in rotation with clover, corn, or wheat, for example, or allowed to lie fallow for a year or so. Clover is able to absorb nitrogen from the air and deposit it in the soil from its root nodules. As population has increased, however, farming has become more intensive, and the use of artificial fertilizers—some containing nitrogen—has become almost universal.
Nitrogen-bearing compounds, such as potassium nitrate and ammonium chloride, have been used for many years as artificial fertilizers. In the early twentieth century, much of the nitrate used, mainly potassium nitrate, came from Chilean saltpeter; each year, approximately half a million tons of this material was imported into Europe and the United States for use in agriculture. Ammonia was produced through the dry distillation of bituminous coal and other low-grade fuel materials. Originally, coke ovens discharged this valuable material into the atmosphere, but more economical methods were found later to collect and condense these ammonia-bearing vapors.
In the first decade of the twentieth century, the cyanamide process for using atmospheric nitrogen was developed by Adolf Frank
In 1904, Fritz Haber and his coworkers began experiments on the conversion of nitrogen and hydrogen into ammonia by passing various mixtures over catalytic agents, such as iron filings at temperatures of up to 1,000 degrees Celsius and at various pressures. (Catalytic agents speed up a chemical reaction without affecting it otherwise.) In the process, they studied the equilibrium conditions in the reaction and found that, at pressures of about 200 atmospheres and temperatures not above 500 degrees Celsius, the production of ammonia in practical yields from its elements could be carried out in a continuous process. Other catalysts, such as uranium and osmium, produced even higher yields but were considerably more costly than iron.
Fritz Haber.
In 1910, a factory for the production of ammonia from atmospheric nitrogen by the Haber process was erected near Frankfurt, Germany; it had an annual production capacity of ten thousand tons of ammonia. Wilhelm Ostwald,
Germany had practically no source of fertilizer-grade nitrogen at the beginning of the twentieth century. Almost all of its supply came from the deserts of northern Chile. As demands for nitrates increased, it became apparent that they would exceed the calculated possible supply from these vast deposits. Other sources needed to be found, and the almost unlimited supply of nitrogen in the atmosphere (which is 80 percent nitrogen) was an obvious source.
The combination of nitrogen and hydrogen to form ammonia could be induced through electrical discharge, but this required enormous amounts of electrical energy, then available only where there was hydroelectric power. When Haber began his experiments on ammonia production in 1904, there was no known method for the spontaneous conversion of nitrogen and hydrogen into ammonia.
Nitrogen and oxygen will combine in an electric arc to form oxides of nitrogen, as Walther Hermann Nernst had discovered. Because oxides of nitrogen can be converted readily into nitric acid and, in turn, into nitrates, this possibility aroused considerable interest as a process for “nitrogen fixation,” as the process of direct combination of atmospheric nitrogen into soluble compounds became known. The large amounts of electrical energy necessary to maintain the electric arc, and to heat large masses of air to high temperatures, imposed practical limits on this method. Haber spent many years studying the synthesis of nitric oxide by electrical discharge.
Haber gave up the idea of fixing nitrogen from the atmosphere by oxidizing it to nitric oxide. He turned, instead, to reducing it with hydrogen to ammonia. First, he looked into combining nitrogen and hydrogen by corona discharge and by sparking, but he came to the conclusion that this method would not be the most advantageous. He decided to repeat the experiments of Ramsay and Young, who in 1884 had studied the decomposition of ammonia at about 800 degrees Celsius. They had found that a certain amount of ammonia always was left undecomposed. In other words, the reaction between ammonia and its constituent elements—nitrogen and hydrogen—had reached a state of equilibrium. Haber decided to determine the position of this equilibrium in the vicinity of 1,000 degrees Celsius. He approached the equilibrium from both sides, by reacting pure hydrogen with pure nitrogen and by starting with pure ammonia gas and using iron filings as a catalyst. Having determined the position of the equilibrium, he next varied the catalyst and found nickel to be as effective as iron, and calcium and manganese even better. At 1,000 degrees Celsius, the rate of reaction was enough to produce practical amounts of ammonia continuously, if it was to be washed out with water from the circulating system.
Further work by Haber showed that increasing the pressure also increased the percentage of ammonia at equilibrium. For example, at 300 degrees Celsius, the percentage of ammonia at equilibrium at 1 atmosphere pressure was only 2 percent, but at 200 atmospheres, the percentage of ammonia at equilibrium was 63 percent. Haber’s compressor would not provide pressures above 200 atmospheres, but with catalysts he was able to obtain rapid combination of nitrogen and hydrogen at about 700 degrees Celsius. He found that he could obtain a yield of several grams of ammonia per hour per cubic centimeter of heated pressure chamber and believed that such a process could be a commercial success. A pilot plant was constructed and was successful enough to impress a chemical manufacturing concern, Badische Anilin- und Soda-Fabrik
Haber’s process for manufacturing ammonia from the nitrogen in the air was in such an advanced state of development when it left his laboratory that its success in industry was virtually assured. Even so, BASF did not see much promise in Haber’s method at first. It was through an old friend of Haber, chemist Carl Engler, who was a member of the BASF advisory council, that Haber’s process was accepted.
In July, 1909, a BASF representative, Carl Bosch (later a cowinner of the 1931 Nobel Prize in Chemistry and inventor of methods for synthesis of gasoline)
With the beginning of World War I, the need for nitrates for use in explosives became more pressing in Germany than the need in agriculture. After the fall of Antwerp, the Germans seized fifty thousand tons of Chilean saltpeter discovered in the harbor. Because the ammonia from Haber’s process could be converted readily into nitrates, it became an important war resource. Haber’s other contribution to the German war effort was his development of gas warfare. He was responsible for the chlorine gas used in the attack on Allied troops at Ypres in 1915. He also directed research on gas masks and other protective devices.
At the end of the war, Haber received the 1918 Nobel Prize in Chemistry
Haber left Germany in 1933 under duress from the anti-Semitic policies of the Nazi authorities. He was invited to accept a position at Cambridge University in England, but he died on a trip to Basel, Switzerland, a few months later, a great man whose spirit had been crushed by the actions of an ungrateful regime.
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Berl, Ernst. “Fritz Haber.” Journal of Chemical Education 19 (May, 1937): 203-207. An account of Haber’s work in science by a personal friend. Includes Haber’s tribute to Justus von Liebig. -
Charles, Daniel. Master Mind: The Rise and Fall of Fritz Haber, the Nobel Laureate Who Launched the Age of Chemical Warfare. New York: Ecco Press, 2005. Sympathetic biography of Haber focuses on the conflicts he faced. The author calls Haber a “modern Faust,” “willing to serve any master who could further his passion for knowledge and progress.” Includes photographs, notes, bibliography, and index. -
Coates, J. E. “The Haber Memorial Lecture.” Journal of the Chemical Society (London) (1937): 1642-1672. A thirty-page biography of Haber published three years after his death. Describes his research in detail and laments the treatment Haber received from the Nazi regime in Germany. -
Haber, Fritz. Five Lectures. Berlin: Springer-Verlag, 1924. An account by Haber of his research on ammonia synthesis. Defends his wartime work on gas warfare. -
_______. Thermodynamics of Technical Gas Reactions. Translated by Arthur B. Lamb. London: Longmans, Green, 1908. A model of critical insight into the history of thermodynamics; discusses the problem of the indeterminate constant in the free-energy equation. Following Max Planck, Haber explains the constant in terms of heat capacity and entropy. Nearly anticipates Nernst in announcing the Nernst heat theorem. -
Jaenicke, Johannes. “The Gold Episode.” Die Naturwissenschaften 23 (1935): 57. Relates Haber’s unsuccessful attempt to extract gold from seawater, with the end of helping Germany pay the heavy reparations mandated by the Versailles treaty after World War I. -
Stoltzenberg, Dietrich. Fritz Haber: Chemist, Nobel Laureate, German, Jew. Philadelphia: Chemical Heritage Foundation, 2005. Biography of Haber abridged and translated by the author from his original work in German. Includes illustrations, notes, and index.
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