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.