Yes when I was 10 years old I used to live in Shepherd's Bush in West London not that far from here
And every Saturday afternoon I used to go to Shepherd's Bush market
You see I was very keen to see what people were selling. What they were buying.
But most importantly, what they were throwing away.
Because very frequently among the rubbish
I could find something useful
For instance wooden boxes, from which I could make a cricket bat
But, every Saturday afternoon
There was a very strange man
He was completely bold and he was selling medicines
He was selling medicines in the form of purple tablets
Like this, and he told everyone
That these tablets were very good for you
Because they could cure you of any disease
Whether you had a headache, tooth ache, muscle pain, neuralgia
nostalgia, you name it, this medicine would cure it.
So people were very fascinated to actually be able to buy this medicine
there is tiny bit of ash left and 
entirely unspectacular
almost like a piece of paper. Now What I wanted to to tell you  next
during the 19 century, during the middle of the
19 century, Chemists were experimenting with
adding Oxygen to different  fuels either mixing it or
combining them chemically and the remarkable result
was achieved by 2 scientists working independently with
cotton, one of them  was
Ascanio Sobrero who was an Italian. The other one was
Christian Schönbein , who was a German organic chemist.
Christian Schönbein was a good friend and colleague
of the great Michael Faraday who
delivered teacher's lectures in this precise spot here for  over
30 years during the 19 century. So it was
Christian Schönbein
who actually was the first person
who manage to add to  cotton with
some extra Oxygen. Now how did he achieve that? And also,
I told you in the beginning that we can frequently recognise a chemical
change by a change of colour and yet you say look this cotton wool
that I have got here, look the same and feels  exactly
the same  as the cotton wool that I had a minute ago. And yet this has
got the extra Oxygen as I will show you in a second. How therefore
is this different? Dear children, the difference could be seen
by weighing it. You see, if you weigh
one of those. They weigh 1.7g
but this weigh 2.8g.
An extra of 1.1g of Oxygen.
Now that is huge amount of extra Oxygen added in.
It actually does have some Nitrogen as well. You may say
how did they add this? Well let's first of all see whether it works
of course because there is no point in talking about the effect if we don't see
how it was done if it doesn't work. So first of all, let's get ourselves
something to talk about. So here then is our cotton
wool which has had extra Oxygen added to it. And let"s see how
this burns and spot the difference. And as you see,
there was an instantaneous combustion.The whole things burn very,very
very quickly indeed and there was virtually
nothing left at all you see. Now that of course, now
that of course , dear children is the proof that the experiment was
successful. Now when Schönbein achieve this
experiment, he was absolutely delighted. And as I said Sobrero,
they were working separately, one of them with cotton, the other with glycerin
and they were similar substances and they achieve this type of result. They thought this
was absolutely amazing. For your information, the way this was
made is using a very similar substance to what's used in
gun powder. Gun powder contains sulphur, charcoal.
and potassium nitrate, nitrates. This uses nitric acid
and sulphuric acid. You mix them together and you soak the cotton
wool for  half an hour. And you end up with this. So the Oxygen
comes about indirectly. But then chemist are people who understood
this processes and that's why they are able to
bring about the effect. Now, what about I have
actually made here is a high explosive. It is of course a very very dangerous
substance. It is popular. Its name in the industry is called  a
gun cotton, nitro cellulose. It is hugely dangerous. It is used in
engineering and military purposes.  And I would like to demonstrate
an explosion for you. Unfortunately, that would be far
too dangerous. So what I am going to do instead, I am going to demonstrate
a propulsion and even 2 propulsions if we're lucky.
And what is a propulsion? A propulsion is a directed
explosion. A explosion is a rapidly release of gases everywhere,
forcing something apart. A propulsion though
is when you direct them in one
direction. So I'm going to start off by showing you how
to use this to make a simple mortar. It's rather similar to a
canon. And I'm going to propel some ping pong ball,
hopefully to the ceiling of our dear Royal Institution
Now what I have here is a special,
It's a like canon. It's technically called the mortar and
principle of it is that you burn the fuel at the bottom
when the fuel which will be gun cotton burnt at the bottom. It releases
a huge amount of hot gases and they will force
the ping pong ball to fly, hopefully to the ceiling
So that is the principle of  this and what I wanted to tell
you dear children is every time you watch one of those fireworks
displays where there are massive shells exploding in the sky
and colours. They are all projected from these.
Only they are made of thick cardboard and their shelves go up and they
explode in the air. Today,  we are not going to
explode the shelves up there. We're simply going to fire ping pong balls. Now
This was made about three hundred year ago. They rapidly realised
that there are
2 main gases in the air, one of them
which actually
responsible for burning  and
that was called Oxygen.
The other one they called
Nitrogen.And they recognised
that about one fifth of the air
is Oxygen
And then they started
to do experiment to make fuels burn
better, not by mixing with air
but trying to mix them
with Oxygen or get them
to combine with Oxygen
and I wanted to show you the result
of one such experiment
which was a remarkable triumph of
the science of Chemistry and
it's occurred using the most
mundane of substances you
could possibly imagined and that
is cotton wool.
Cotton wool is a natural
fibre. It has  been known to human being for over five thousand year and we know that
cotton was first grown and used on a large scale in India and also in Mexico
. But it is in India where the great culture of cotton culture of cotton fabric,
cotton weaving grew for thousand of years
well before it reach Europe. Now cotton,
what is cotton chemically speaking? Well, it is a very delicate fabric ,
it is used in clothing of course as you know and for
cosmetic application. and chemically speaking it's called cellulose  .
it's a natural polymer  which occurs and which is very
very comfortable to the touch and warm to the feel.
and that is why it has a  great  place in our human history.  Not to mention
the fact that the cotton played a huge role in the industrial revolution
in this country during the 18 century when cotton weaving and spinning were
developed in the . Now, if  you watch carefully
who on earth would think of burning. Well Chemist thought of burning everything
and this is one of the things.They burnt cotton you see,
they thought  it may be wonderful. there it is , it is  burning in air, a hugely boring
experiment you see it is burning in air, because air contain only
about 20 percent Oxygen you see and so this is  what we have
incomplete combustion it is burning with
this sort of slightly yellowy flame and
