Explosives, Fertilisers, Chemical Weapons and the Unintended Consequences of Discovery: The Tragedy of Fritz Haber

What’s a tragedy? Hamlet is a tragedy, not just because our hero ends up dead, taking half a dozen people with him, but because his own reflective intelligence is instrumental in his fate. By this strict definition, the story of Fritz Haber, indicted war criminal, Nobel laureate, patriot and miserable exile, is indeed a tragedy.  He sought to serve this country, and helped destroy it. The moral dilemmas of Haber’s career will not go away, and the ironies of unintended consequences are timeless. [Notes on talk to Callander and W Perthshire U3A, 22 March 2023]


  • Einstein’s German world, Fritz Stern
  • Fritz Haber – Chemist, Laureate, German, Jew, Dietrich Stoltzenberg
  • (See also Enriching the Earth: Fritz Haber, Karl Bosch, and the Transformation of World Food Production, Vaclav Smil)
Fritz Haber with benchtop ammonia synthesis apparatus (note duelling scar)

Fritz Haber, 1868 – 1934

Born 1868, Breslau, Silesia, Germany (now Wrocław, Poland)

His mother died giving birth to him. Haber’s relations with his father were always difficult, and in his earliest years he spent much time with other relatives

Education: Universities of Berlin (Helmholz, Hoffmann), Heidelberg (Bunsen).

Technische Hochschule Charlottenberg, 1889; PhD 1891

1891 – 4; Various temporary positions.

Further study (ETH Zurich); work in offices of Siegfried Haber & Co.;

He correctly persuaded his father to switch from vegetable dye indigo to the new range of synthetic dyestuffs, but in 1892, when cholera broke out in the port of Hamburg, Fritz persuaded his father to invest heavily in calcium hypochlorite disinfectant. But the purchase was mistimed, the business lost money, and Siegfried finally agreed that Fritz should make his career in academics.

1892; Converted to Christianity. Reasons presumably social rather than spiritual. The esteemed historian Theodore Mommsen (Nobel Prize for literature, 1903) had written, while defending (!) Germany’s Jews from anti-Semitic attacks, that they would have to make such cultural adjustments or “face the consequences”

1894 – 1912; Karlsruhe Technische Hochschule; Assistant, 1894

1896, Experimental Studies on the Decomposition and Combustion of Hydrocarbons. Accelerated tenure, as Privatdozent. Studies (with Luggin) of electrochemistry of nitrobenzene.

1898, Outline of Technical Electrochemistry on a Theoretical Basis; note linking of basic theory to practical outcome. Promoted Associate Professor

1901, married Clara (Immerwahr) (first woman Ph.D. at Breslau) but of course unable to have an independent career

1905, Thermodynamics of Technical Gas Reactions (Explain thermodynamics)

1909 Glass electrode

Haber and nitrogen fixation

Nitrogen makes up 80% of the atmosphere, but it’s in the form of molecules in which two nitrogen atoms are bonded to each other, in what is almost the strongest chemical bond that exists, and the problem of fixing nitrogen needs making it chemically available.

All living things require nitrogen; nitrogen is in proteins nitrogen is in DNA so not surprisingly nitrogen is in fertilisers. More to the point from Harber’s point of view, nitrogen is in explosives, as we shall see

Why fix nitrogen? Agriculture; explosives

Both food and explosives as strategic goods

High explosives: TNT, nitroglycerine                                               

Chile saltpeter as main source.

Strategic implications; 60% nitrate in 1913 came from Chile

British owned mines, commanded sea routes

Guano maker

Gunpowder, traditional explosive

How explosives work. Heat releasing reaction. Oxygen source. Material reactive towards oxygen, Reaction must generate gases at high pressure as suddenly as possible

Potassium nitrate + charcoal + sulphur known to Chinese; to Europeans since 1300s

4KNO3 + 2C + 3S = 2K2CO3 + 3SO2 + 2N2

Rapid reactions that releases large amounts of energy and gas

These send a shock wave through the air, responsible for the force of the explosion

But the reaction takes time to spread

High explosives – all reacting parts in same molecule

No wasted material. Reaction spreads faster than speed of sound. Production requires nitric acid

Nitroglycerine, O2NO.CH2.CH(ONO2).CH2ONO2

Nobel and dynamite

Trinitrotoluene (TNT), H3C.C6H3(NO2)3

You can get to nitric acid from ammonia

4NH3(g) + 5O2(g) =  4NO(g) + 6H2O(g) (over Pt catalyst)

(Alternatively: N2 + O2 = 2 NO  Small yield, needs high temperature)

4NO(g) + 2H2O(l) + 3O2(g)  =  4HNO3(aq)  (only needs air, water)

A deceptively simple reaction Nitrogen reacts with hydrogen to give ammonia;

N2(g) + 3H2(g)  =  2NH3(g)

Consider the equilibrium

N2(g) + 3H2(g)  =  2NH3(g)

The reaction is reversible, a two-way street

Opposed tendencies: reaction gives out heat (favourable), but decreases spread-out-ness (entropy) (unfavourable). The former dominates at low temperature; the latter at high temperature.

Heat released; pressure falls as reaction proceeds

Therefore (Le Chatelier’s principle) low temperatures and high pressures should favour product formation

And that’s the problem

N2(g) + 3H2(g)  =  2NH3(g)

You need to break or loosen the existing bonds before you can make the new ones

But the NN “triple bond” is extremely strong

So you need a lot of heat energy to break it

But high temperature means low yield!

You need a catalyst

Surface catalysis (schematic)

Early attempts

1901, Le Chatelier synthesises ammonia under pressure. Backs off after accident

1904, Haber gets ammonia at 1,000 C. Yields miserable,

Haber tells backers it’s not commercial, publishes his preliminary findings

Note that Haber was a consultant for industry, and that links between Universities and industry in Germany were and are v. strong

Walther Nernst, Haber’s arch-rival Who had worked out how to calculate changes in entropy and hence where any equilibrium should lie, from measurements of heat of reaction and heat capacity of reactants

Who, at the 1907 Bunsen conference,

asserted that the prospects for ammonia synthesis were considerably poorer than had hitherto been assumed on the basis of “Haber’s highly inaccurate numbers [for specific heats, which affect predicted yield].”

Haber stung into re-examining the problem. Proud man. Duelling scar

Success in principle

Haber re-measures heats of formation and heat capacities of the gases

Infers that the reaction would work well enough at 600 C, 100 atm pressure.

Gets industrial backing from BASF (just)

Carl Bosch, high pressure apparatus

Search for a suitable catalyst

Activated iron  You need a reactive metal as your catalyst, because the nitrogen-nitrogen bond is so strong

The engineering challenge

Carl Bosch background; metallurgist, engineer, plumbing

Advised 100 atm plant doable

Designed pumps, heat exchangers, control and monitoring equipment

Countercurrent heat exchange, ammonia condensed under pressure, unreacted gas recirculated

(all the basic components of modern heavy chemicals plants and refineries)

Solution to the pipe embrittlement problem

To stand high pressure, the pipes had to be made out of steel. But steel is an alloy of iron and carbon. It reacts with hydrogen at high pressure to make methane gas (CH4) leaving the iron brittle. Bosch solved this by lining the steel pipes with pure iron. So the steel provided the strength, while the lining stopped the hydrogen from getting to it.

Into production

BASF commissions plant 1910

In production 1913

200,000 tons/yr by 1918

Catalyst improvements have since lowered temperature to 450 C

Now over 160 MILLION tons annually worldwide

Responsible for 1/3 all “fixed nitrogen”

Nernst, Haber reconciled

1912, Haber/BASF patent challenged on the grounds that Nernst had shown that the reaction worked

BASF hires Nernst as expert witness (who better?) to refute this claim

For a fee ~ $250,000 in today’s money

BASF win

Nernst, Haber reconciled; in 1913 collaborate in enticing Einstein to Berlin

5th largest chemical product

After sulphuric acid, ethylene, polyethylene, propylene

160 MILLION tonnes by 2020

A historical (1921) high-pressure steel reactor for the Haber process on display at the Karlsruhe Institute of Technology Germany

. http://upload.wikimedia.org/wikipedia/commons/1/1e/Ammoniak_Reaktor_BASF.jpg

A modern fertilizer plant World’s largest. Burrup Plant, Australia. 769,000 tonnes/yr, ~ 4 x Germany’s total 1918 production

Haber in wartime

1914, World War I breaks out in Europe. Haber volunteers for trenches, refused. Develops low-freezing gasoline for Russian front

Asked to create poison shrapnel, advises mass discharge of gas from cylinders more effective

Apr 22, 1915, Germans use chlorine gas at Ypres. 5,000 dead; 15,000 injuries.

Gas is not an easy weapon to use. The wind, one of the most difficult things to predict even today, has to be blowing in the right direction and at the right speed, ideally between around 4 and 9 mph. Small irregularities in the lie of the land, even in the lowlands of Flanders, will affect how the gas flows and settles. There is the serious problem of how the gas will affect one’s own troops, if the wind changes direction, or even if they advance to occupy the territory abandoned by the enemy, as happened to the British when they in turn used chlorine gas in September at the Battle of Loos. The delivery of gas from cylinders is clearly only possible when the lines are very close together, and if it is to be delivered from shells, the charge that bursts the shell must be carefully controlled, otherwise the load will simply be dispersed over too large an area. One could also consider the morality of gas as compared with other weaponry, but that is not the main theme of our story.

Death of Clara

Haber did not hear the shot, and she was discovered by her son Hermann, then aged 12

1917, Haber marries Charlotte Nathan (in church); divorced 1925

In his relationships with women, Haber compared himself to a butterfly-hunter, who thinks he has grasped his quarry, only to find that all he has in his hand is dust.  Indeed, we might sympathize with the hunter in his disappointment, but what of the butterfly?

Mass discharge of gas from cylinders
Gas masks an effective protection for simplest war gases

Haber’s expanding role

1916, Haber chief of new Chemical Warfare Service, organizes production of essential materials despite blockade. Photographed with Kaiser, awarded Iron Cross in both classes, Order of Hohenzollern Swords, Order of the Crown (Third Class), etc.

Haber’s moral perspective

Haber was a patriotic German at a time when patriotism was regarded uncritically as a virtue.

He said later that his advice was that gas should be used on massive scale, as a means to quick victory, or not at all

“In war men think otherwise than they do in peace, and many a German during the stress of war may have adopted the English maxim,‘My country, right or wrong’”

As indeed they may have

And not only Germans

It is unusual for people to refuse requests from their governments in time of war – one exception is Michael Faraday, who refused to work on war gases for the British during the Crimean War; and only one scientist, Joseph Rotblatt, quit the Manhattan Project.

Immediate consequences

Haber nitrogen made long war possible, with far greater suffering and damage to Germany

1918, revolution, collapse in Germany. Kaiser abdicates. Punitive Treaty of Versailles based on concept of war guilt; imposes major territorial concessions, reparations

Revulsion at use of gas a likely component n punitive attitude to Germany

1929, Great Depression. Germany particularly vulnerable

Jan 1933, Hitler Chancellor of Germany.

March, all civil liberties suspended

April, Nazi student propaganda attacks Jewish professors.

Bosch attempted to form an association of non-Jewish scientists to protest government anti-Semitism, but the attempt petered out for lack of support.

Bosch, disgusted, drinks himself to death (1943), (but not before setting up oil from coal plant, which helps prolong World War II)

Haber and the Nazis

Haber, recall, had been baptized. He had his children by his second marriage baptized as well, occasionally went to church, and encouraged his Jewish friends to do likewise.

In 1933, about 500,000 Jews in Germany. An ageing population, rapidly assimilating.

Disproportionate numbers in universities

University positions were (and are) technically civil Service positions in Germany, as in US State Universities.

April 1933 law bans Jews (except war veterans) from civil service jobs

Last days

Haber resigns, saying he can’t choose colleagues based on grandparents’ race.

Resignation accepted, his letter quoted as unacceptable in the new Germany

October, 1933, Haber leaves Germany, spends time in Cambridge (sponsor WJ Pope had been in charge of Allied chemical war effort)

Negotiating with Weizmann of Rehovoth Research institute; also with Pope behind Weizmann’s back

Visiting Switzerland, heart attack, dies

He was hoping, from Switzerland, to sort out family financial affairs in Germany, and to the end had no idea (Einstein had a very clear idea) of what he was up against.

In the longer term

1939 – 45: Hitler led Germany to a further disastrous war; more territorial concessions; Breslau becomes Wrocław.

Germany after World War I

In the longer term

1939 – 45: Hitler led Germany to a further disastrous war; more territorial concessions; Breslau becomes Wrocław

  • 1939-45, World War II in Europe
  • Total German defeat. More loss of territory. Breslau becomes Wrocław
  • Haber nitrogen makes “green revolution” possible
  • World population in 1945, 2.5 billion, general famine seems imminent
  • In 2023, over 8 billion. Famine regional only

Haber sought to serve his country; his actions helped destroy it. Yet now, half the world’s population depend on his discoveries for their very survival.

Some thoughts on famine

For most of human history, the risk of famine was normal

Malthus’ 1798 Essay on Population: “The power of population is indefinitely greater than the power in the earth to produce subsistence for man“

1847, Irish etc potato famine underway. More general famine averted by artificial fertilisers, opening of US and Russian grainlands

1947, aftermath of World War II

Severe weather in Europe

Lack of food instrumental in e.g. fall of Czechoslovakia to the Communists

Disaster averted by Green Revolution

Population 2.5 billion, now > 8 billion and rising

And water tables are being pumped down, and global warming expected to reduce yields


Growing world population; clean water, conquest of diseases

Disaster averted by Green Revolution, introducing higher-yielding grain crops, especially wheat and rice.But grains are grasses, which are hungry for nitrogen, and high-yielding grains especially so.

Today, only about half the fixed nitrogen used in world agriculture is provided by soil bacteria. The rest comes from the Haber process.

“Organic” farming does not use Haber process fixed nitrogen, but does use Chile saltpeter, of which 600,000 tons a year is currently mined

Further prospects

Currently, 1/3 all “fixed” nitrogen is from Haber process

World population expected to level off around 10 billion

Food security unclear; water main problem

Hydrogen produced from water + fossil fuels; modern process starts from gas – air mixtures, with CO2 and ammonia as products

CO2, N2O from nitrate, greenhouse gases

Where will the next major advances in food production come from?

Genetically manipulated organisms? Large-scale shift from meat to vegetable protein?

Chemical weapons today

Use now totally banned by international agreement, manufacture in US forbidden by law and treaty

Chlorine and phosgene are obsolete as war gases (gas masks too effective).

Mustard gas used by the Iraqis in their war with Iran and in suppressing uprisings, as were nerve gases, which block reactive centers in nerve cells; these are very effective weapons because they work by skin absorption, as well as by inhalation, so that gas masks offer poor protection.

During the 1991 Gulf War the Iraqis stockpiled nerve gases, but did not in fact use them. These stockpiles were destroyed under UN supervision in the period 1991 – 1998.  UN inspections were suspended in 1998 but resumed in 2002, and found no new major activity.  Despite this, British and American claims that Iraqi weapons of mass destruction presented a major and urgent threat were the stated reason for invading Iraq in 2003. No such weapons were ever found.

Syrian Govt used nerve gas in 2013; has agreed to its destruction, but has been accused more recently of using chlorine.

Concluding thoughts            

The role of the individual

Unintended consequences

Unavoidable choices

Personal responsibility

History does not stop

Short-term consequences

Using the Haber-Bosch process, Germany was able to sustain a four-year-long war without importing nitrate, receiving and inflicting horrible casualty levels, until its military and social collapse in 1918.

Haber himself was officially labeled as a war criminal, and spent some time in Switzerland to evade capture.

Nobel prize 1919; Bosch 1931

About Paul Braterman

Science writer, former chemistry professor; committee member British Centre for Science Education; board member and science adviser Scottish Secular Society; former member editorial board, Origins of Life, and associate, NASA Astrobiology Insitute; first popsci book, From Stars to Stalagmites 2012

Posted on March 21, 2023, in History of chemistry, History of Science, Science and tagged , , , , , , , , , . Bookmark the permalink. 1 Comment.

  1. Great treatment of the technical, human, and moral issues. Pretty chilling photo of gas release.

    It is amazing how much Germans advanced science and technology c. 1880-1945. Germany went from hodgepodge of principalities to superpower c 1870-1910 thanks in part to partnerships between university researchers and industrialists, as mentioned.

    Liked by 1 person

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