1: The Chemical World

1: The Chemical World

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What is chemistry? Simply put, chemistry is the study of the interactions of matter with other matter and with energy. However, the definition of chemistry includes a wide range of topics that must be understood to gain a mastery of the topic or even take additional courses in chemistry. In this book, we will lay the foundations of chemistry in a topic-by-topic fashion to provide you with the background you need to successfully understand chemistry.

  • 1.1: The Scope of Chemistry
    Chemistry is the study of matter and the ways in which different forms of matter combine with each other. You study chemistry because it helps you to understand the world around you. Everything you touch or taste or smell is a chemical, and the interactions of these chemicals with each other define our universe. Chemistry forms the fundamental basis for biology and medicine. From the structure of proteins and nucleic acids, to the design, synthesis and manufacture of drugs, chemistry allows you
  • 1.2: Chemicals Compose Ordinary Things
    Chemistry is the branch of science dealing with the structure, composition, properties, and the reactive characteristics of matter. Matter is anything that has mass and occupies space. Thus, chemistry is the study of literally everything around us – the liquids that we drink, the gasses we breathe, the composition of everything from the plastic case on your phone to the earth beneath your feet. Moreover, chemistry is the study of the transformation of matter.
  • 1.3: Hypothesis, Theories, and Laws
    Although all of us have taken science classes throughout the course of our study, many people have incorrect or misleading ideas about some of the most important and basic principles in science. We have all heard of hypotheses, theories, and laws, but what do they really mean? Before you read this section, think about what you have learned about these terms before. What do these terms mean to you? What do you read contradicts what you thought? What do you read supports what you thought?
  • 1.4: The Scientific Method: How Chemists Think
    Science is a process of knowing about the natural universe through observation and experiment. Scientists go through a rigorous process to determine new knowledge about the universe; this process is generally referred to as the scientific method. Science is broken down into various fields, of which chemistry is one. Science, including chemistry, is both qualitative and quantitative.
  • 1.5: A Beginning Chemist: How to Succeed
    Most people can succeed in chemistry, but it often requires dedication, hard work, the right attitude and study habits!

Chemical weapons

The stalemate on the Western Front prompted the most intensive use of chemical weapons in human history. Despite an 1899 treaty that banned the use of poisonous gas as a military weapon, all major combatants used them at one point or another. They were used most extensively during 1915 and 1916.

Early usage

The first deployments of poison gas were with irritants like tear gas, which was intended to inconvenience and temporarily disable the enemy rather than cause death.

The French used tear gas in grenades in the opening months of the war and the Germans reciprocated soon after. These early attempts used small amounts of gas which either froze or were quickly dispersed by the weather. As a consequence, they had little military impact.

In January 1915, the Germans employed chemical warfare on a larger scale by launching a barrage of tear gas shells against Russian soldiers. This heavier, more sustained deployment had greater impact.

Chlorine gas

Around this time, German scientists were also busy refining and producing chlorine, a gas designed to kill rather than injure or hinder.

A by-product of clothing manufacture, chlorine gas was released upwind of enemy positions. It drifted at ground level, appearing as a pale green cloud. This was followed soon after by a noxious smell reminiscent of swimming pools and bleach.

The initial deployment of chlorine against French, British and Canadian troops was both devastating and caused considerable panic in Allied ranks. Once inhaled, chlorine gas infiltrated and corroded the lungs, causing painful suffocation and excruciating death.

The Allies respond

It did not take long for them to develop strategies and counter-measures to deal with chlorine attacks. Gas masks containing chemically-impregnated cotton filters were effective at protecting soldiers from chlorine gas. Even holding a rag soaked with water or urine over one’s mouth and nose offered some protection.

Incensed by Germany’s use of poison gas, the Allies began expanding their own stocks. British chemists were quick to develop and manufacture their own weaponised form of chlorine gas.

The first Allied chlorine gas attack at the Battle of Loos (September 1915) was disastrous. An unexpected wind change blew the gas away from the German trenches some of it reached the British line and killed soldiers there.


In the same year, French military chemists began to utilise an even more potent substance called phosgene. Unlike chlorine, phosgene was invisible and had only a faint smell of mouldy hay. This made its presence more difficult to detect.

Like chlorine gas, phosgene also caused lung damage and suffocation. Its effects were not always immediate, however. A soldier could ingest it but suffer no ill effects for several hours.

The Germans launched phosgene against British positions shortly before Christmas 1915, disabling more than 1,000 men. Phosgene would be responsible for more than 80,000 deaths, or over three-quarters of the gas fatalities in World War I.

Mustard gas

The most notorious chemical weapon of the war was mustard gas, a severe irritant that caused chemical burns on the skin, the eyes and in the airways.

Though not as deadly as chlorine or phosgene, mustard gas was more effective as an anti-personnel weapon.

Gas masks could be used to negate the effects of phosgene or chlorine – but mustard gas caused injury wherever there was exposed skin. It also settled on the ground as an oily liquid and could remain active and dangerous for days, even weeks depending on the weather.

An instrument of terror

The pain of mustard gas was intense and its psychological impacts profound. Those exposed to it developed large painful yellow blisters. Men with severe doses died agonising deaths as their lungs burned and blistered inside them. Many mustard gas victims were blinded, some permanently, while some endured respiratory problems for the rest of their lives.

It is not surprising that gas attacks were the trench soldier’s worst fear, as recounted in this Wilfred Owen poem:

Gas… GAS! Quick boys! An ecstasy of fumbling,
Fitting the clumsy helmets just in time.
But someone still was yelling out and stumbling,
And flound’ring like a man in fire or lime.
Dim through the misty panes and thick green light,
As under a green sea, I saw him drowning.
In all my dreams, before my helpless sight,
He plunges at me, guttering, choking, drowning.


Germany was the most active exponent of chemical warfare during 1915. By 1917, this situation had reversed, with the Allies producing several thousand tons of poison gas.

Scientists in the United States invented a new compound called Lewisite. It had similar effects to mustard gas but was able to penetrate protective clothing and was allegedly more deadly.

More than 20,000 tons of Lewisite were produced, tested and stockpiled, though the end of the war came before it could be deployed on the battlefield.

Public reaction

The horrors of gas warfare caused public indignation, both during and after World War I.

In 1925, a Geneva convention was signed outlawing the use of chemical weapons. Adolf Hitler, who had himself been a victim of mustard gas in 1918, indignantly refused to deploy poison gas during World War II.

Nevertheless, the major powers retained stockpiles of these weapons – and indeed still do.

“The use of chemicals left an abhorrent image of helpless soldiers in makeshift gas masks, struggling for breath, or ranks of soldiers blinded by mustard agent attacks. In reality though, chemical weapons caused relatively few deaths and injuries compared to conventional weapons. When the war was over, chemical weapons had caused less than 4 per cent of all casualties… One could ask why they have gained such a fulsome reputation when their use did not fundamentally affect the course of World War I, or arguably of any war since then.”
Eric Croddy, writer

1. Despite an 1899 treaty banning their use, both sides entered the war with stockpiles of chemical weapons.

2. Chemical weapons began with the deployment of tear gas grenades in 1914, followed by chlorine gas in 1915.

3. Germany was the most prolific manufacturer and user of gas, though the Allies reciprocated and soon caught up.

4. Deadly gases like phosgene and chlorine were used but mustard gas was the most common chemical weapon.

5. The effects of chemical weapons caused outrage, particularly after the conclusion of the war, which led to international treaties banning their use in wartime.

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Chemical Warfare: Poison Gases in World War 1

Click to enlarge

I’ll be accompanying some of the students from my school on a history trip to Ypres and a few other World War 1 battlefields in a few weeks’ time. Obviously, they’d much rather be learning chemistry, so I’ve been reading up on the different chemical agents used during World War 1, and this graphic is a byproduct of that. As it turns out, several of them were used for the first time at Ypres, so it’ll even be topical!

A range of different chemicals were used as weapons throughout the conflict. The French were actually the first to utilise them in conflict, when they attempted to use tear gas against the German army in August 1914. The precise agent used seems to be uncertain, with both xylyl bromide and ethyl bromoacetate being mentioned both are colourless liquids, with the former having an odour described as ‘pleasant and aromatic’, and the latter being described as ‘fruity and pungent’.

These tear gases weren’t designed to kill rather, to incapacitate the enemy and render them unable to defend their positions. They are all lachrymatory agents – that is, they cause crying, due to irritation of the eyes. They also irritate the mouth, throat and lungs, leading to breathing difficulties. Exposure to larger concentrations can lead to temporary blindness, but symptoms commonly resolved within 30 minutes of leaving affected areas.

In practice, the use of tear gas on the battlefield wasn’t extraordinarily effective. However, it opened the door to the use of more harmful gases. The first of these was chlorine, first used on a large scale by the German forces at Ypres in April 1915. Chlorine is a diatomic gas, about two and a half times denser than air, with a pale green colour and a strong, bleach-like odour which soldier described as a ‘mix of pineapple and pepper’. It reacts with water in the lungs to form hydrochloric acid, which can quickly lead to death. At lower concentrations, it can cause coughing, vomiting, and irritation to the eyes.

In its first uses, chlorine was deadly. Against soldiers not yet equipped with gas masks, it wreaked havoc, and it’s estimated over 1,100* were killed in the first large scale attack at Ypres. The German forces weren’t prepared for just how effective it would prove, and their delay in pressing into the gap formed in enemy lines actually meant they gained very little ground initially.

However, chlorine’s effectiveness was short-lived. Its obvious appearance, and strong odour, made it easy to spot, and the fact that chlorine is water-soluble meant that even soldiers without gas masks could minimise its effectiveness by placing water-soaked rags over their mouth and nose. Additionally, the initial method of its release posed problems, as the British learnt to their detriment when they attempted to use chlorine at Loos in France. The released gas changed direction as the wind changed, engulfing the British lines instead of those of the enemy, and leading to a large number of self-inflicted casualties.

Phosgene was the next major agent employed, again used first at Ypres by the Germans in December 1915 (although some sources state the French were the first to employ it). Phosgene is a colourless gas, with an odour likened to that of ‘musty hay’. For this odour to be detectable, the concentration of phosgene actually had to be at 0.4 parts per million, several times the concentration at which harmful health effects could be expected. It is highly toxic, due to its ability to react with proteins in the alveoli of the lungs and disrupt the blood-air barrier, leading to suffocation.

Phosgene was much more effective and deadly than chlorine, though one drawback was that the symptoms could sometimes take up to 48 hours to manifest. Its immediate effects are coughing, and irritation to the eyes and respiratory tract. Subsequently, it can cause the build-up of fluid in the lungs, leading to death. It’s estimated that as many as 85% of the 91,000 deaths attributed to gas in World War 1 were a result of phosgene or the similar agent diphosgene. It’s hard to put a precise number on, since it was commonly used in combination with chlorine gas, along with the related chemical diphosgene. Combinations of gases became more common as the war went on. For example, chloropicrin was often used for its irritant effects, and its ability to bypass gas masks, causing sneezing fits which made soldiers remove their masks, exposing them to poison gases.

Along with chlorine, the most commonly known poison gas used in the conflict is mustard gas. Sulfur mustards are actually a class containing several different compounds in their pure forms, they are colourless liquids, but in warfare impure forms are used, with a yellow-brown colour and odour akin to garlic or horseradish. Mustard gas is an irritant, and also a strong vesicant (blister-forming agent). It causes chemical burns on contact with the skin, leading to large blisters with yellow fluid. Initially, exposure is symptomless, and by the time skin irritation begins, it is to late to take preventative measures.

The effectiveness of mustard gas was due to its debilitating effects. Its mortality rate was only around 2-3% of casualties, but those who suffered chemical burns and respiratory problems due to exposure were unable to return to the front, and required extensive care for their recovery. Those who did recover were at higher risk of developing cancers during later life due to the chemical’s carcinogenic properties.

Overall, though the psychological factor of poison gas was formidable, it accounted for less than 1% of the total deaths in World War 1. Though their use was feared in World War 2, and they were employed in some cases, they were never employed on as large and as frequent a scale as seen in World War 1. Use of poison gas as a weapon was later prohibited by the Geneva Protocol in 1925, which most countries involved in the First World War signed up to. However, the chemicals used still have their uses – for example, phosgene is an important industrial reagent, used in the synthesis of pharmaceuticals and other important organic compounds.

*Note: the article and graphic originally stated that the first use of chlorine gas at Ypres resulted in approximately 5000 deaths. However, recent recalculations suggest by the Flanders Fields Museum suggest that 1,100 is a more realistic estimate, albeit perhaps a slight underestimate.

Introduction of Phosgene

German chemical weapon attack on the East front. By Bundesarchiv – CC BY-SA 3.0 de

Chlorine had some drawbacks as a weapon. It was easy to detect, as once deployed the gas would produce a green cloudy smoke, which came with a strong oder. The gas was also water soluble a damp cloth held over the face could reduce the effects the gas had on you.

So, in late 1915, the French-developed phosgene was put in to use. The gas attacked the lungs, and would cause initial symptoms of coughing, sneezing, vomiting and choking.

While phosgene could be used by itself, it was often mixed with chlorine. The gas was largely odorless and didn’t produce a cloud. This made it undetectable, and so far more dangerous. One of the issues those who used the gas faced, was that it could take up to a day for symptoms to show, meaning those who had been around the chemical could fight back. While Phosgene was the second most manufactured gas in World War I, it was the deadliest chemical weapon used. Phosgene accounted for 80-85% of all chemical weapon deaths in World War I.

Germans introduce poison gas

On April 22, 1915, German forces shock Allied soldiers along the western front by firing more than 150 tons of lethal chlorine gas against two French colonial divisions at Ypres, Belgium. This was the first major gas attack by the Germans, and it devastated the Allied line.

Toxic smoke has been used occasionally in warfare since ancient times, and in 1912 the French used small amounts of tear gas in police operations. At the outbreak of World War I, the Germans began actively to develop chemical weapons. In October 1914, the Germans placed some small tear-gas canisters in shells that were fired at Neuve Chapelle, France, but Allied troops were not exposed. In January 1915, the Germans fired shells loaded with xylyl bromide, a more lethal gas, at Russian troops at Bolimov on the eastern front. Because of the wintry cold, most of the gas froze, but the Russians nonetheless reported more than 1,000 killed as a result of the new weapon.

On April 22, 1915, the Germans launched their first and only offensive of the year. Known as the Second Battle of Ypres, the offensive began with the usual artillery bombardment of the enemy’s line. When the shelling died down, the Allied defenders waited for the first wave of German attack troops but instead were thrown into panic when chlorine gas wafted across no-man’s land and down into their trenches. The Germans targeted four miles of the front with the wind-blown poison gas and decimated two divisions of French and Algerian colonial troops. The Allied line was breached, but the Germans, perhaps as shocked as the Allies by the devastating effects of the poison gas, failed to take full advantage, and the Allies held most of their positions.

A second gas attack, against a Canadian division, on April 24, pushed the Allies further back, and by May they had retreated to the town of Ypres. The Second Battle of Ypres ended on May 25, with insignificant gains for the Germans. The introduction of poison gas, however, would have great significance in World War I.

Immediately after the German gas attack at Ypres, France and Britain began developing their own chemical weapons and gas masks. With the Germans taking the lead, an extensive number of projectiles filled with deadly substances polluted the trenches of World War I. Mustard gas, introduced by the Germans in 1917, blistered the skin, eyes, and lungs, and killed thousands. Military strategists defended the use of poison gas by saying it reduced the enemy’s ability to respond and thus saved lives in offensives. In reality, defenses against poison gas usually kept pace with offensive developments, and both sides employed sophisticated gas masks and protective clothing that essentially negated the strategic importance of chemical weapons.

The United States, which entered World War I in 1917, also developed and used chemical weapons. Future president Harry S. Truman was the captain of a U.S. field artillery unit that fired poison gas against the Germans in 1918. In all, more than 100,000 tons of chemical weapons agents were used in World War I, some 500,000 troops were injured, and almost 30,000 died, including 2,000 Americans.

In the years following World War I, Britain, France, and Spain used chemical weapons in various colonial struggles, despite mounting international criticism of chemical warfare. In 1925, the Geneva Protocol of 1925 banned the use of chemical weapons in war but did not outlaw their development or stockpiling. Most major powers built up substantial chemical weapons reserves. In the 1930s, Italy employed chemical weapons against Ethiopia, and Japan used them against China. 

In World War II, chemical warfare did not occur, primarily because all the major belligerents possessed both chemical weapons and the defenses–such as gas masks, protective clothing, and detectors–that rendered them ineffectual. In addition, in a war characterized by lightning-fast military movement, strategists opposed the use of anything that would delay operations. Germany, however, did use poison gas to murder millions in its extermination camps.

Since World War II, chemical weapons have only been used in a handful of conflicts–the Yemeni conflict of 1966-67, the Iran-Iraq War of 1980-88𠄺nd always against forces that lacked gas masks or other simple defenses. In 1990, the United States and the Soviet Union signed an agreement to cut their chemical weapons arsenals by 80 percent in an effort to discourage smaller nations from stockpiling the weapons. In 1993, an international treaty was signed banning the production, stockpiling (after 2007), and use of chemical weapons. It took effect in 1997.

Chemical warfare and medical response during World War I

The first large-scale use of a traditional weapon of mass destruction (chemical, biological, or nuclear) involved the successful deployment of chemical weapons during World War I (1914-1918). Historians now refer to the Great War as the chemist's war because of the scientific and engineering mobilization efforts by the major belligerents. The development, production, and deployment of war gases such as chlorine, phosgene, and mustard created a new and complex public health threat that endangered not only soldiers and civilians on the battlefield but also chemical workers on the home front involved in the large-scale manufacturing processes. The story of chemical weapons research and development during that war provides useful insights for current public health practitioners faced with a possible chemical weapons attack against civilian or military populations.


Diagram illustrating the institutional resources…

Diagram illustrating the institutional resources and coordination dedicated to chemical weapon worker safety.…

Chlorine gas, released from cylinders,…

Chlorine gas, released from cylinders, drifts over the Western Front. Source. Francis Joseph…

Gas mask designs used throughout…

Gas mask designs used throughout the war. Source. Francis W. Halsey, The Literary…

Soldiers from the British 55th…

Soldiers from the British 55th (West Lancashire) Division temporarily blinded by mustard gas…


John Singer Sargent's painting of a line of blinded soldiers came to be known by a one word title: "Gassed."

It appears today to be a visual condemnation of the horrors of gas warfare. However, Richard Slocombe, Senior Curator of Art at the Imperial War Museum, which holds the painting, explains Sargent had a different intention.

"The painting was meant to convey a message that the war had been worth it and had led to a better tomorrow, a greater cause, that it had not been a terrible waste of life," he says.

"It is a painting imbued with symbolism. The temporary blindness was a metaphor, a semi-religious purgatory for British youth on the way to resurrection. You can see the guy-ropes of a field hospital tent depicted, and the men are being led towards it."

Casualty figures do seem on the face of it, to back up the idea that gas was less deadly than the soldiers' fear of it might suggest.

The total number of British and Empire war deaths caused by gas, according to the Imperial War Museum, was about 6,000 - less than a third of the fatalities suffered by the British on the first day of the Battle of the Somme in 1916. Of the 90,000 soldiers killed by gas on all sides, more than half were Russian, many of whom may not even have been equipped with masks.

Far more soldiers were injured. Some 185,000 British and Empire service personnel were classed as gas casualties - 175,000 of those in the last two years of the war as mustard gas came into use. The overwhelming majority though went on to make good recoveries.

According to the Imperial War Museum, of the roughly 600,000 disability pensions still being paid to British servicemen by 1929, only 1% were being given to those classed as victims of gas.

"There's also an element of gas not showing itself to be decisive, so it's easier to. not have to worry about the expense of training and protection against it - it's just easier if people agree to ban it," says Ian Kikuchi.

But Edgar Jones disagrees. By the summer of 1917 gas was inflicting a significant number of casualties, he argues, removing men from the battlefield for six to eight weeks, tying-up beds and nurses, and using up valuable resources. And it was effective as a psychological weapon too, he says.

"In a war of attrition morale is critical and this was an attempt to undermine morale."

In the final analysis, Jones says, it was banned because it was "not quite cricket".

Jeremy Paxman sees both factors in play - primarily it was revulsion, he suggests, but also it was accepted that gas had not lived up to expectations.

"The reason it was banned is because it had been a particularly grotesque weapon. Geneva was an attempt to civilise war," he says.

"Gas had not worked - and it was considered unsoldierly."

Types of Gases Used

There were three primary types of gases used in World War I.

Asphyxiant gases, mainly mustard gas. Mustard gas is particularly dangerous as it can take several hours to appear. Soldiers who were burned by the gas would see large blisters form where the chemical had touched them. The blisters would fill up with blood and puss, and turn yellow. If a soldier’s body was over 50% burned, the chance for survival diminished rapidly. When inhaled, mustard gas caused internal burns and blisters and could lead to breathing issues.

Sternutator Gases such as phosgene, chlorine, and diphosgene. These gases caused pain in the chest as well as pain in the eyes and nose. They could also cause choking, nausea, vomiting, coughing and sneezing.

Lachrymator, or tear gas. Tear gas caused irritation to soldiers’ throats and eyes. The gas was more of a nuisance than anything and was virtually ineffective with a gas mask.

British infantry advancing through gas at Loos, 25 September 1915.

Banning chemical agents

The specter of poison gas inspired an international agreement after WWI ended — the 1925 Geneva Protocol — which banned chemical and biological weapons during war.

According to the treaty, "the use in war of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices, has been justly condemned by the general opinion of the civilized world," and their prohibition "shall be universally accepted as a part of International Law, binding alike the conscience and the practice of nations."

Global leaders continue to condemn the use of chemical weapons. In 1993, the United Nations banned mustard gas and other toxic agents through the Chemical Weapons Convention, prohibiting "the development, production, acquisition, stockpiling, retention, transfer or use of chemical weapons," the Organisation for the Prohibition of Chemical Weapons (OPCW), reported.

And in 2013, the OPCW received the Nobel Peace Prize for its work as chemical weapons "watchdogs," — for mobilizing nations to cease producing and storing lethal chemical weapons, and targeting cached weapons for safe disposal, with the ultimate goal of eliminating them completely.

But poisonous agents still pose a silent and deadly threat. Just this Tuesday (April 4), a chemical bombing in Syria claimed the lives of at least 70 people, many of them children, following an air attack that dropped bombs in Idlib Province, the New York Times reported. While the composition of the lethal gas is still unknown, it is thought to be a type of nerve agent, which disrupts neuron signals and can interfere with involuntary muscle movements, such as respiration.

Watch the video: Chapter 1 - The Chemical World (May 2022).