The 22nd 2015 is the anniversary off a very side, an unpleasant event in warfare.

It is the 100th anniversary off the first use of chlorine as a poison gas in the first World War.

It was used by the Germans in an attack on French troops outside the Belgian city of Eep, which in the first World War the English soldiers called wipers because they couldn't pronounce French.

So what happened was that a large amount of chlorine, more than 100 tons, was released from cylinders and swept across the battlefield onto the totally unprepared troops.

Chlorine gas is very corrosive turns copper and brass, the sort of things that soldiers have on the metal of their buckles turns green.

It attacks the eyes on it.

Also, if it gets in the lungs, your lungs stop filling up with fluid.

So it's really unpleasant on Dhe.

It was a huge success.

Large numbers of people on all animals died and the whole front was opened up.

But the Germans had not expected it to be a success and didn't have the troops that would could pull forward to fill the vacuum night fell on by the next day, The people we're back, the French or troops were back to defend the front, so it really wasn't much advantage.

This whole chlorine attack was the idea of Fritz Harbor, the famous chemist that we've all heard over the harbor process.

Making ammonia.

He became really enthused, if not obsessed with chemical warfare on this obsession led to him being dubbed a pretty evil genius in his lifetime.

And he's still remembered for his role in chemical warfare almost more than his role in providing fertilizers that makes all the food that we eat possible.

What is surprising is that the Canadian officer, the Canadians were next to the French realized it was chlorine remarkably quickly and so primitive precautions were taken pretty quickly.

Nothing very sophisticated people urinating onto their handkerchiefs to cover their faces so the water will absorb some of the flooring.

I don't think it is a very effective, so I would not suggest that you try this if there is a chlorine release.

The important thing is that this opened up a whole era of chemical warfare on within a few weeks, if not months, both sides were firing chemicals at the others.

They're two important points that we need to remember.

The first thing is that chlorine, this greeny yellow gas is really quite unpleasant material.

Neil are really tough.

Technician is quite frightened of it.

Many years ago, he was exposed to a small amount of chlorine gas and he's still remembers.

That was long before periodic videos and all the safety precautions we take.

But the second point is that people are still using chlorine as the chemical weapon.

In yesterday's newspaper, there was a story that said that in Syria, barrel bombs of chlorine are still being used.

So I think it is important to remind you that although chemistry is a fascinating and exciting subject, it can be misused.

And it is.

Our duty is chemists to make sore that chemistry is used for the benefit of society, not for its destruction in the First World War.

Better chemical weapons than chlorine, particularly mustard guests, which is a compound of carbon, hydrogen, sulfur and chlorine, was invented, which lasted on the battlefields for months on in the Second World War, and afterwards so called nerve gases were just a few milligrams of the compound can kill somebody so using chlorine is a pretty primitive weapon.

But when you are an armed force fighting against civilians who have no protection, chlorine is a cheap, on pretty reliable way of making things very uncomfortable, if not actually killing people.

And chlorine is available industrially very easily, whereas chemical weapons are more difficult to get hold off.