today I'm going to do an experiment
about blood and it's an experiment
that's really very famous but I've never
done it before was made famous by an
chemist at the beginning of the 20th
century I think it was the French
chemist wausau who discovered fluorine
and also nearly poisoned himself with
mercuric chloride during a lecture
but before we start I need a bit of
protective clothing which I'm going to
put on here now the lab coat let's get
started I'm going to use and nitrate
we're now going to put some water the mo
crystals have gone Brown when we add
water now the story is that was on this
chemist had a technician who was armed
with a knife nowadays I've got plastic
knife but I think it was a metal knife
and what happened was the technician
covered his knife with the solution of
the iron nitrate and then ran into the
lab or the lecture theatre screaming and
stat appeared to stab Russell on the arm
like so and his arm went blood-red and
the audience screamed and they thought
he was going to die but what actually it
happened was like me what song had
painted his sleeve with a chemical
called thiocyanate that reacts with iron
to make it go very red I can show you
this by pouring a little thiocyanate
into there you can see it really goes
blood-red
it was completely staged to frighten the
students whether it was for Halloween or
something else I don't know nowadays we
can't afford technicians just to run in
and stab professors so the professors
have to stab themselves it's not quite
so convincing but you still get nice
blood stain the chemistry of blood is
fascinating because hemoglobin the
molecule that makes blood red is a
nanomachine it actually works like a
little machine
the molecule changes shape to carry
oxygen around the blood let me show you
how in the middle of the human globin
molecule there are four rings like this
which have nitrogen and carbon with a
hole in the middle and when hemoglobin
is not reacting with oxygen or hasn't
reacted the iron atom which sits next of
this ring is too big to go into the hole
so it's it's sticking out just like this
but then when the iron reacts with
oxygen this is not a very good model but
you imagine this is o2 it reacts with
the iron and the iron gets smaller and
it's now can fit right into the middle
of the ring with the oxygen attached so
the iron moves into the ring in fact it
moves from the bottom upwards to meet
the oxygen but what is really cunning is
that on the other side of the iron it is
attached to a huge protein this huge
molecule with a weight thousands of
times more than this little group and as
the iron moves it pulls the chain and
the whole of this molecule moves rather
like the door of a cave in Indiana Jones
video something like that and this whole
molecule change shape so that it reacts
more easily with oxygen and then when it
is carrying the oxygen from the lungs
through the body to wherever you're
exercising when it gets the place where
you're exercising there's carbon dioxide
in the blood so the blood is more acid
and the change in acidity makes the
molecule change back in shape and expel
the oxygen so that you can use it and
then it goes round again to the lungs
and so on round around and round
when the iron binds oxygen it change
is color it becomes redder and if it
binds carbon monoxide which is very
poisonous it goes really red cherry red
so that people have had carbon monoxide
poisoning have very red cheeks although
sadly they're dead
but what the carbon monoxide does is it
binds to the iron irreversibly it
doesn't come off again so you can't get
the oxygen going around so your body
dies blood itself can be quite dangerous
because it can carry all sorts of
different viruses and so on so it's very
difficult for a chemist like me to get
hold of blood the only thing you can do
and I've done it once is to go to the
medical center and get the nurse to take
out some of my own blood and I tried to
do an experiment for the students with
my own blood I took it to the lab I
centrifuge this I got out the hemoglobin
and then I was going to react it with
carbon monoxide and the reaction didn't
work so in the end I just had to wave
this bottle of blood at the students and
tell them that they had to take the
experiment as read