In fact there are 117 more videos to watch.

[NORMAL PITCH]: Was that different?

Helium is the second element on the periodic table.

It makes up 35% of our universe.

But it's very rare here on the planet Earth.

In fact, It's the only element in the periodic table

that it was first discovered outside our planet.

The first indications of its existence

came when people were looking at the spectrum of the Sun,

in that during an eclipse

in 1868, the year before Mendeleev proposed the periodic table,

and they noticed a single very bright yellow line.

The yellow line is due to the electrons in the helium atom being excited.

You can do the same thing here on Earth.

In fact Neil has his own helium star.

This is a glass star filled with helium gas.

And if you apply very high voltage

you can excite the electrons in the helium and it emits light.

And then with a small spectroscope,

you can look at it and see

the very yellow line that was detected in the Sun's spectrum.

To begin with they thought it was sodium.

But then they realized it must be a new element,

and because it was found on the Sun,

it was given the name helium from the Greek word helios.

Which is, I believe what the Sun is called in Greek,

or the god of the Sun is called.

It was then discovered on Earth

at the beginning of the 20th century

with people were examining a uranium mineral,

called, I think, cleveite.

Then a few years later,

fairly rapidly,

helium gas was discovered as a component

of natural gas coming out of gas fields in the United States.

The reason why you find helium associated with uranium,

and in fact other radioactive materials,

is because the nucleus of helium

contains two neutrons and two protons.

And the naked nucleus of helium is what are called alpha particles

that are emitted during radioactive decay.

So if a radioactive atom decays and emits an alpha particle

underground,

the alpha particle quickly picks up a couple of electrons

and becomes an atom of helium.

And over millions of years this can accumulate in gas field.

As far as I'm aware,

all of the helium in the world has come from radioactive decay,

apart from a small amount

that has come from people letting off hydrogen bombs.

[ANNOUNCER]: The width of the fireball at this time, about three seconds after detonation, was four miles.

[PROFESSOR]: Helium in the natural gas was discovered

fairly shortly before the first World War.

And so it was quickly realized that this gas could be useful

for observation balloons on the Western Front on the battlefields.

[ANNOUNCER]: The enemy's troop movements and defense schemes are under constant observation

by French and British Airmen as well as by observation balloons.

[PROFESSOR]: Because unlike hydrogen it doesn't burn,

so if a bullet goes through your balloon

it doesn't immediately blow up.

So helium started to be produced as a strategic material.

[ANNOUNCER]: Non-explosive gas for dirigibles. America has a virtual monopoly of it, helium.

[PROFESSOR]: So there's a long history in the United States

of legislation for conserving helium for strategic defense purposes.

[ANNOUNCER]: The subject has of course attracted great attention all over the world

because of the terrible Hindenburg disaster.

The American president's cabinet committee is convinced

that helium should now be made available to Germany

for use in commercial airships.

[PROFESSOR]: So a helium nucleus, or helium atom,

weighs four times as much as a hydrogen atom

which has just one proton.

But because hydrogen exists as an H2 molecule,

helium atom, which is the same as its molecule,

weighs twice as much as a hydrogen molecule.

And Neil, our colleague,

has devised quite a nice little demonstration,

where he has a balloon of hydrogen

and a balloon of helium

of about the same size.

And shows that the hydrogen balloon,

with a suitable pulley system,

can actually pull the helium balloon downwards,

because there's a lot more lift in a hydrogen balloon

than in the helium one, because the hydrogen is lighter.

The most important property for helium, nowadays,

is the fact that when you liquefy it,

it forms the coldest liquid that one can obtain.

Liquid helium boils at minus 269 degrees centigrade.

That is 4 degrees above absolute zero.

So you can use liquid helium to cool materials down.

And particularly, you can cool certain alloys of metals

which lose all their electrical resistance at low temperature,

so called superconductors,

which can be used to build really powerful magnets.

Particularly for our university, for magnetic resonance imaging,

for looking inside people's bodies to see that all is well,

and you need a very high magnetic field.

And so our university has a plant for liquefying helium.

And Brady and I were able to go and visit it.

We were shown how the liquid helium is filled

into large thermos flasks, so called Dewar flasks.

When you want to pump the helium out,

remarkably you use the inside of a rugby football.

This is the bladder inside it.

A rugby football is quite similar to an American football.

And you, by squeezing this,

you can pressurize the helium and get it to come out.

And if you do it wrong it blows up to a large size, the bladder.

And we were shown what happened.

I was a bit frightened it might go "bang"!

We were then shown what happens when you squirt liquid helium into air.

And it's really strange because as the liquid comes out,

the jet of liquid looks very like a flame.

The shape is almost the same,

though of course it's whitish in color.

Neil had given us a small metal stainless steel thermos can.

It's very important, it's stainless steel,

because helium can go through glass.

So if you use a glass thermos,

as soon as you put helium into it, it stops being a thermos vessel.

Neil wanted us to try and see if we could fill this can with liquid helium,

so we could actually show you what the liquid looked like.

We had a number of attempts,

and the most spectacular eruptions of cold helium vapor.

The problem is that helium vapor that comes off is so cold,

that it not only freezes all the water vapor in the air,

so you get fog, but it can also

liquefy the oxygen or nitrogen in the air.

So even though we pre-cooled the thermos with liquid nitrogen,

so we started at a fairly low temperature,

it was quite difficult to get the liquid in.

And once we got it in, there was so much fog,

that it was quite difficult to tell

whether we were really seeing the surface of the liquid or not.

But it was great fun.

Brady and I really enjoyed ourselves,

and the technician Sanjeev was really helpful.

He even tried filling a much bigger vessel with liquid helium.

And pouring it into our thermos.

Usually when people use liquid helium seriously,

for example for magnetic resonance imaging,

because the gas is expensive, it is piped back

to the liquefaction plant so it can be recycled.

And you've all seen little helium balloons that people use

at parties and the like.

But at the liquefaction plant

they have an enormous yellow balloon

which they use for storing the gas before it's liquefied.

And they have gas meters to measure the volume of gas coming back,

so that they know how much gas has been lost,

and how much they have to charge

each customer for the gas that they've lost.

I used to work with liquid helium a long time ago,

and I still have the very old gas meter that we used,

which is just over there on the filing cabinet.

[BRADY]: Thanks for watching this video.

We actually filmed a lot more stuff about helium that we haven't fit into this one.

But we're going to upload another helium video

very soon, so you can see all that stuff.

You can also watch our videos about all the different elements.

We've done all 118, some of them numerous times.

There's a link to a playlist of those videos.

Also we've obviously done hundreds of other chemistry videos.

And if you'd like to support us you can go to

patreon.com/periodicvidoes

and find out more there.

Including our little gimmick where you can adopt an element, including helium.