you can see from high above using Google Earth,

but what's really going on down there, and why?

I'm Derek Muller, a scientist, educator, and filmmaker,

and I'm going to unearth the stories

behind these amazing places.

Just drop a pin

and I'm off.

( mysterious music )

♪ ♪

I am here in the middle of the Utah desert

surrounded by sandstone cliffs and red rocks

and this scrub.

But that is not what I'm here for.

What I'm looking for should be right over this ridge.

♪ ♪

There are electric blue ponds

in the middle of the Utah desert.

When I saw them on Google Earth,

I had so many questions, like what are they?

Why are they here?

And why do these colors keep changing?

One person thought this might be

a top-secret NASA experiment,

since, after all, you can see them from space.

Someone else suggested, "Well, maybe they're just really large swimming pools."

What are those? What do you think?

Like a geo kinda thermal thing? Like a solar thing?

Like, they come up from the ground?

It's gotta be some sort of, you know, science experiment of some kind.

They sort of look like rice paddies,

'cause they're on ledges.

Derek: The truth is far more fascinating

than any of those guesses.

These technicolor pools are full of something

that's been prized throughout human history.

What are they used for

and how are they connected to fireworks,

George Washington, soap, glass, Gatorade, gunpowder,

a pioneering scientist named Humphry Davy,

every other person on the planet,

and lots of money?

( birds crying )

♪ ♪

The answer begins with a pot and a hardwood fire.

This is a 1,500-year-old recipe.

Take some hardwood and burn it,

not for the heat, but for the ash.

Put the ash in a pot and add water.

Now, there are a lot of different chemical compounds in there,

but the one I'm after is water soluble,

so it dissolves.

Strain out the solids and you'll find

the solution is slippery.

Put it in a pan and let the water evaporate in the sun,

and what you're left with is this crystalline substance.

All that work for this.

It is one of the most important chemicals

people have been making for centuries,

and it's called potash

because that is exactly where it comes from.

In 1807,

British scientist Humphry Davy got some damp potash

and put electrodes into it.

Then he connected them up to a battery,

and what he observed was the formation

of tiny metal globules,

and as they burst through the crust of the potash,

they spontaneously caught fire.

Davy had discovered a new element,

so naturally, he named it pot-ash-ium.

Potassium.

Yes, that is where the name of the element comes from.

It comes from the potash.

♪ ♪

When you hear the word potassium,

many people think of bananas or Gatorade,

and that's true,

these foods are good sources of potassium,

but it's not pure potassium.

This is a piece of pure elemental potassium.

It's a metal, but I can squish it

with my fingers.

And this had to be created in a lab

because it is so reactive, it'll react with anything.

This piece was kept submerged under oil

so it doesn't react with the water in the atmosphere.

It's an incredibly reactive substance,

and to demonstrate that, I'm going to put a piece of it

in this water.

I'm gonna weight it down

so the potassium doesn't just sit on the top

but actually will sink down to the bottom.

Three, two, one.

- ( pops ) - Oh, yeah!

- ( pops ) - Oh!

- ( pops ) - Oh, yeah!

I did not expect it to do that.

That is awesome!

Are you kidding me?

Yeah!

Of course, I've seen this demo before,

but never with such a huge explosion.

( in slow-motion ) Oh, yeah!

I think the key was weighing it down

so it didn't just spark on the surface.

Potassium reacts with water,

forming potassium hydroxide and hydrogen gas.

It also releases a lot of heat,

so when the hot hydrogen gas hits the atmosphere,

it spontaneously combusts.

Potassium is so reactive

because it has one electron in its outermost shell,

which is easily removed,

and that's why we never find metallic potassium in nature.

Now, the word potash originally referred to that stuff

which, chemically, is potassium carbonate,

but potash has become a catchall term

referring to lots of potassium-containing compounds.

So the potash that Davy was using

was actually potassium hydroxide.

And this is not the last time we're gonna hear from Davy.

But why is potash so important to people?

I'm on the trail of Potash.

Look at that.

♪ ♪

All right.

This is bacon grease.

For centuries, it was used in making soap.

Take some animal fat, add potash,

and a chemical reaction creates a primitive liquid soap.

And look at that. This is incredible.

( laughs )

I'm getting a real lather going here.

That's not bad. Take a look at that.

The potash soap actually worked.

Potash was also used to make glass.

Glass is mostly sand, silicon dioxide,

but add some potash

and you reduce the melting point.

This makes glass less brittle

and easier to work with in early furnaces.

♪ ♪

( Western music )

♪ ♪

If you take the potash solution

and add bat guano or manure,

crystals of a different potassium compound form:

potassium nitrate, also called saltpeter,

and it's one of the core ingredients

in fireworks and gunpowder.

♪ ♪

Get ready.

( laughs ) That was awesome!

Saltpeter made from potash infused gunpowder

in the muskets and cannons

of battles fought in China, Europe,

and the American revolution.

( slow-motion explosion )

Potash was by far the main chemical product

of the early American colonies

and a substantial source of revenue.

By 1788, there were 250 potash works

in the state of Massachusetts alone,

places where wood was burned on a massive scale

just for its ash.

In 1790, the newly-independent U.S. government issued

its first ever patent.

It was for an improved process for making potash.

The patent office has now issued over 10 million patents

and the literal first one is for potash.

It was signed on July 31, 1790.

Look closely at the signature.

It's signed by none other than President George Washington.

That should give you an idea of how important potash was.

The demand for potash was so high

that across Europe and the eastern U.S.,

forests were decimated.

Unfortunately, it required<