that has been used by chemical, pranksters since I don't know when.

When I was a schoolboy, I made some and it went off with an enormous bang

[Music]

When you make it, it comes out as a damp, rather dark coloured compound.

When you spread it out on the surface to dry, it dries relatively quickly and then becomes a so-called

contact explosive - if you touch it even very gently it can go off with a loud bang

So what we did was to put it on a warm surface,

Neil had a hot plate with a metal sheet on top to protect it.

And, it was put on a filter paper to dry.

Took quite a long time to dry - nearly half an hour.

But then he touched it off with a new tool that he's invented which he called a professor on a stick!

Like most chemical reactions, it needs some energy to set it off.

But this one is very little energy.

Physical energy just rubbing two crystals together is enough to get it going.

So it's rather like something that is about to over balance and you just need to give it a little push.

And the result was pretty dramatic.

[Music]

[Bang]

[Music]

[Bang]

[Music]

[Bang]

[Music]

So the chemistry is really quite simple

NI3 dissociates into nitrogen gas N2 and iodine.

And N2 has a very strong bond between the two nitrogen atoms.

So it releases a lot of energy very quickly.

And as it releases the energy of course it accelerates the reaction

and so it all goes off or nearly all goes off at once.

You also get a cloud of iodine vapor which is a sort of browny purple color.

In fact the unfortunate little professor disappears among the clouds and comes out covered in iodine.

Though, I managed to wash the iodine off the professor using sodium thiosulfate.

Occasionally, it will go off spontaneously like my sample in my locker at school.

Well my experience was that, like many people, I tried to make quite a large amount.

It was hidden in my locker so the teacher shouldn't find it and then it dried out.

When I opened the door, whatever I did was enough to set it off. So there was a big bang.

Fortunately I was not in any way hurt, but it was quite as lesson to me.

[Bang]

[Bang]

[Bang]

The chlorine compound nitrogen trichloride is a liquid and is far worse.

The French chemist Pierre Dulong who discovered it

lost an eye and two fingers or some people say three fingers when it exploded.

And when Humphrey Davy in London was trying to repeat the experiment, he got some glass in his eye,

then his assistant Michael Faraday tried it and injured his hand and one of his fingernails came off.

So nitrogen trichloride is a truly dreadful compound.

But, the triiodide, because it's a solid, has been used for many many years.

And in fact, we discovered in the archives here a really quite nice account of a debate between

two university teams - one from Nottingham and one from Swansea that took place in 1928.

One of the students Noel Cusa wrote an account.

So it begins quite formally.

There was an inter-varsity (between university) debate that year at Nottingham

It was held in the large theatre.

He then explains how the students were very badly behaved

shooting peas out of pea-shooters from their mouths at the audience in the front

and then on the people debating on the stage.

But what the people on the stage didn't know was that the pranksters were chemistry students,

and they had put nitrogen triiodide, which was damp, all over the stage.

So one of the people from Swansea got up

and was walking up and down the stage trying to calm everything down.

And then, it happened.

The nitrogen triiodide liberally spread earlier on the platform began to dry out

and each step of the Swansea man produced alarming crackles and bangs

until all those on the dais, that's the stage, disappeared up to their knees in a violet haze.

At this point, the proceedings were called off.

So you see, even a long time ago, students could be really badly behaved.

In fact, far more badly behaved than would be permitted nowadays at the University.

Obviously this is not the sort of reaction you should try at home,

because this compound is terribly unstable.

It is being used by people because even microscopic amounts make quite a loud bang.

And so it's particularly dangerous if you make a large amount of this material.

Even in the lab where we were working making this video,

we spilt some on the floor

[crackle]

[crackle]

and there were crackles for an hour or two afterwards.

Hi, you probably just heard the professor mentioned sometimes you can suffer a

premature detonation of your nitrogen triiodide.

We did experience such a problem, and we also captured it on video if you'd like to see it,

I'll include a link in the video description.

[spraying sound]

And while I have your attention, can I also just thank everyone who supports Periodic Videos on Patreon helping us go the extra mile.

Details about that can also be found down below the video.