[MUSIC PLAYING]
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.
[MUSIC PLAYING]