19 November 2008
The first successful method for converting nitrogen
from the atmosphere and combining it with hydrogen to synthesize
ammonia, a valuable compound used as a fertilizer.
The person behind the invention:
Fritz Haber (1868-1934), a German chemist who won the 1918
Nobel Prize in Chemistry
The Need for Nitrogen
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 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. The clover is able to absorb nitrogen fromthe air and
deposit it in the soil through its roots. 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.
Much of the nitrate used, mainly potassium nitrate, came
from Chilean saltpeter, of which a yearly amount of half a million
tons was imported at the beginning of the twentieth century into
Europe and the United States for use in agriculture. Ammonia was
produced by dry distillation of bituminous coal and other lowgrade
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
At the beginning of the twentieth century, Germany had practically
no source of fertilizer-grade nitrogen; almost all of its supply
came from the deserts of northern Chile. As demand for nitrates increased,
it became apparent that the supply from these vast deposits
would not be enough. Other sources needed to be found, and the almost
unlimited supply of nitrogen in the atmosphere (80 percent nitrogen)
was an obvious source.
Temperature and Pressure
When Fritz Haber and coworkers began his experiments on ammonia
production in 1904, Haber decided to repeat the experiments
of the British chemist Sir William Ramsay and Sydney Young, who
in 1884 had studied the decomposition of ammonia at about 800 degrees
Celsius. They had found that a certain amount of ammonia
was always 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 point at which this equilibrium
took place at temperatures near 1,000 degrees Celsius. He tried several
approaches, reacting pure hydrogen with pure nitrogen, and
starting with pure ammonia gas and using iron filings as a catalyst.
(Catalytic agents speed up a reaction without affecting it otherwise).
Having determined the point of equilibrium, he next tried different
catalysts 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.
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 of pressure was very small, but at 200 atmospheres,
the percentage of ammonia at equilibrium was far greater. A pilot
plant was constructed and was successful enough to impress a
chemical company, Badische Anilin-und Soda-Fabrik (BASF). BASF
agreed to study Haber’s process and to investigate different catalysts
on a large scale. Soon thereafter, the process became a commercial
With the beginning of World War I, nitrates were needed more
urgently for use in explosives than in agriculture. After the fall of
Antwerp, 50,000 tons of Chilean saltpeter were discovered in the
harbor and fell into German hands. 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 poison gas, which was used
for the chlorine gas 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, the 1918 Nobel Prize in Chemistry was
awarded to Haber for his development of the process for making
synthetic ammonia. Because the war was still fresh in everyone’s
memory, it became one of the most controversial Nobel awards ever
made. Aheadline in The New York Times for January 26, 1920, stated:
“French Attack Swedes for Nobel Prize Award: Chemistry Honor
Given to Dr. Haber, Inventor of German Asphyxiating Gas.” In a letter
to the Times on January 28, 1920, the Swedish legation in Washington,
D.C., defended the award.
Haber left Germany in 1933 under duress from the anti-Semitic
policies of the Nazi authorities. He was invited to accept a position
with the University of Cambridge, England, and died on a trip to
Basel, Switzerland, a few months later, a great man whose spirit had
been crushed by the actions of an evil regime.
what you create, even if your intentions are honorable.
Considered a leading chemist of his age, Haber was born in
Breslau (nowWroclaw, Poland) in 1868. Abrilliant student, he
earned a doctorate quickly, specializing in organic chemistry,
and briefly worked as an industrial chemist. Although he soon
took an academic job, throughout his career Haber believed
that science must benefit society—new theoretical discoveries
must find practical applications.
Beginning in 1904, he applied new chemical techniques
to fix atmospheric nitrogen in the form of ammonia.
Nitrogen in the form of nitrates was urgently
sought because nitrates were necessary to fertilize
crops and natural sources were becoming rare. Only
artificial nitrates could sustain the amount of agriculture
needed to feed expanding populations.
In 1908 Haber succeeded in finding an efficient, cheap process
to make ammonia and convert it to nitrates, and
by 1910 German manufacturers had built large plants
to exploit his techniques.
He was lauded as a great benefactor to humanity.
However, his efforts to help Germany during World War I,
even though he hated war, turned his life into a nightmare. His
wife committed suicide because of his chlorine gas research,
which also poisoned his international reputation and tainted
his 1918 Nobel Prize in Chemistry. After the war he redirected
his energies to helping Germany rebuild its economy. Eight
years of experiments in extracting gold from seawater ended in
failure, but he did raise the Kaiser Wilhelm Institute for Physical
Chemistry, which he directed, to international prominence.
Nonetheless, Haber had to flee Adolf Hitler’s Nazi regime in
1933 and died a year later, better known for his war research
than for his fundamental service to agriculture and industry.
See also : Fuel cell ; Refrigerant gas ; Silicones ; Ammonia