Lead is a very soft metal and it’s easily
moulded into all sorts of shapes. This is a pot, I’m not sure what
it is from, I got it from an old lab that was being closed down
so it was probably made for holding a strong acid because
lead is very unreactive. You can see rather nicely here
the white colour of lead oxide because it has oxidised over the
years and this is the white material that was used for paints. This white lead paint that people use, the
oxide of lead, had one rather unfortunate consequence that it
reacts with sulphur in the air and in Victorian times
when people burnt coal they produced a lot of sulphur, and the
sulphur reacted with the lead to give a black colour which
made the white paint eventually turn grey and if you waited
long enough black. And this effect was exploited by one
of my former colleagues here Professor Leslie Crombie,
who during the war was working for the British admiralty in their
research labs on the camouflaging of submarines. Now if you
want your submarine not to be seen, when it is well
away from the coast it needs to be white because if you
have a white submarine it does not show up against the
sky but, if you are trying to slip into the coast at night and
not be seen you need the submarine to be black. So Leslie came
up with the idea of painting the submarine with lead oxide and
when it was going near the coast, some sailors went out on to
the outside of the ship and sloshed over a solution of sulphide
and seawater and the paint turned black. And so you could then
go into the coast, drop your agent, do whatever secret
things you wanted to do, and then when you went away
from the coast they sloshed hydrogen peroxide with seawater,
which turned the sulphite into sulphate, and lead sulphate
is white so your submarine went white again. So you could change
the colour of your submarine to suit what you were doing
in the military operation and nobody would see you. And that was a real thing that happened? Yes, that was a real thing. I don’t know
how widely it was used but they actually tried it out and it
worked. So they just needed to take the chemicals and they could
add the seawater to make the solution to put on the
submarine. The other very important property of lead
is that because the lead atom is heavy it is very good at stopping
radioactive particles particularly alpha particles, which
are helium nuclei those are the nucleus of the helium atom,
or beta particles which are electrons. What you should find that if we put this in
the way, it should stop counting almost immediately so let us
see if that works. There we go straight back down to background
and if we take it away, and it picks back up again. And so people who are working with radioactive
samples used to use, and still use, bricks made out of
lead. So here are two of the bricks and you can see this is a small
one and this one is rather thinner. The problem is that if
you start building these bricks into a wall, there is always
a chance that when you have two bits together there might be
a slight gap between the two bricks and some of the radioactive
particles may go between them. So to avoid this the
bricks are made with groves in it, and a pointed part here,
so that when you put them together there is absolutely no way
that anything can go through because you can’t have a
direct line through it. Now the trouble is of course you can’t
see anything through it, so if you have an experiment where
you want to handle radioactive material inside a container
and manipulate it you can’t make the whole container of
lead because you can’t see what is going on inside. And so
for that, people have developed lead glass, of which this is
a sample and it is immensely heavy, but this is glass and there
is really a large amount of lead that has been put in it. And
some of the fancy crystals that your grandmothers or your ancestors
might have had, had a bit of lead in the glass. This
has got a really high proportion of lead in the glass which is probably
why the glass is yellow rather than the white colour
that you normally have with glass. But windows like this can
be used for handling really quite radioactive materials
behind them. The colour is rather nice isn’t it? Good. But it is very heavy, so… Well, lead has had a very long history; it
was one of the first metals to be widely used. The Romans used
this for drinking materials. There is also lead acetate, that
is a compound of lead and vinegar is meant to taste sweet and
the Romans added this to their wine to make it sweeter.
The fact that it was really very poisonous and caused, possibly
even caused madness, was not really widely recognised.
In fact some people have suggested that part of the collapse
of the Roman Empire was due to too much lead. Lead was
very widely used in the UK for water pipes because it’s easy
to manufacture and to join together. It tends not to have
been very dangerous in terms of drinking water because
it gets a coating on the surface so you do not get much
lead in the water; though if you do have a house with
lead pipes in, it is usually advisable to change them. It’s again,
it was used very widely from the 1920s up till the late 70s
or 80s as an additive for petrol. In the old days when
petrol engines were first introduced, when you came to a hill
and put down the accelerator of your car, the engine started
misfiring, so-called ‘pinking’, and the whole thing shook.
So it was really quite difficult to drive up hills, but then it was
discovered that you could put in a compound, so-called tetraethyl
lead, which was really very poisonous, but the guy who discovered
it washed his hands in public at a press conference
saying “look it’s so safe”, despite the fact that there were
people dying in his factory. So it was very widely adopted and
so it was only in quite recent times that it was realised how
much lead was being blown out into the atmosphere in car
exhausts. And so it’s now almost everywhere we have lead-free
petrol as a result of people realising the poison-ness
of lead.
