Earth.

Billions of years ago, it was just a hot jumble of elements,

which over time have solidified into the very rocks

that we stand on.

Right?

OK.

These rocks have come from a quarry in Portland, and

they're made of limestone, which is a

type of calcium carbonate.

Masons would use these blocks pretty much as they are in the

construction industry.

These rocks have been formed over millions of years from

shells like this.

So these have just collected at the bottom of the ocean and

been compressed, and we can actually even see some of the

shells in this rock here.

Because the shell and the rock are made of the same chemical

substance, calcium carbonate, they have the same chemical

properties.

So here we have some hydrochloric acid.

And the bubbles that you see instantly formed in here, this

is carbon dioxide gas.

There's another way we can drive out the carbon dioxide,

and that's simply by heating it.

So this block now has been in the oven for 24 hours.

It was allowed to cool overnight.

And well it looks pretty much just the same as it did

before, but actually, it's completely different.

its chemical structure has now changed.

Before, we hand calcium carbonate, and heating it up

drives out the carbon dioxide and leaves us with calcium

oxide, or quicklime.

Because we've driven out all of the carbon dioxide from

this rock, it's actually lost quite a lot of its weight.

But it's also changed in structure, and we're now going

to see why it is that you won't find any buildings made

out of calcium oxide.

The change that takes place when limestone is converted

into quicklime, or calcium oxide, has been known for many

hundreds of years.

Here, in this book from 1526, we see the process.

We see a chap with a furnace in the background and boulders

of limestone and he's pouring water on this.

Quicklime literally means, living lime.

And we can see this as the water instantly vaporises.

It's turning into steam in this very violent reaction.

It's combining with the quicklime, we can see it

crumbling away, blistering.

Bits of it are flying off, popping in all directions,

generating a lot of heat, which we can see

as the steam here.

During this process, called slaking, the calcium oxide

reacts with the water to form calcium hydroxide, and this is

a key component of cement.

This has been used since Roman times and

it's still used today.

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