I'm in India in Mumbai, what used to be called Bombay,
and behind me is the famous Taj Mahal hotel
And when I'm in India, of course I begin to think about Indian chemistry, Indian science
and there're really two things which come to my mind
not necessarily the most important but the ones that really strike me
One is a tragedy and the other's a triumph
So let's begin with the tragedy
which was the worst chemical accident that's ever occurred
And it happened in the city of Bhopal which is a long way from here
It's right in the middle of India
And it was due to discharge of chemicals from a closed chemical factory
It wasn't even making chemicals
(They) used to make insecticide but they decided to close it down
And in this factory which was being decommissioned there was a tank of a particular chemical known as methyl isocyanate
Isocyanate is a group which contains nitrogen, carbon and oxygen in a line N-C-O
And methyl isocyanate can react with water to generate heat and to generate gases
And you can imagine the heat plus gas generates pressure and a tank can blow up
And what is worse (is) that one of the gases it can generate is hydrogen cyanide which is very poisonous
and if you breathe it can kill you at really quite a low dose
So imagine it in the middle of the night this reaction took place
and while it was dark, cloud of... the tank burst, and clouds of poison gas spread across the town across the poorest areas of the town killing thousands of people
There's still argument whether it was two-and-a-half thousand or 15,000 people but an enormous number and injuring a lot more
There are several theories how the water got in the tank
ranging from straightforward misfortune to bad management of the plant or even sabotage
and there's even not quite clear exactly what reaction took place because the products of the reaction depend on the temperature
so the proportion of hydrogen cyanide depends on exactly what temperature the tank broke
Hydrogen cyanide is a very powerful poison because the cyanide group can bind to various molecules in the body
One of the symptoms is that your lips apparently go blue
Fortunately I've never seen anybody who has died from cyanide poisoning
But it's a very painful death and very quick
So if you're asleep and breathe hydrogen cyanide you would be dead before you knew it
It was a terrible tragedy but it was a wake-up call to the chemical industry across the world
So the suffering of these poor people was not in vain
because nowadays chemical plants are operated far more safely than they were 30 years ago
India is also very famous for one particular physicist Professor Raman
and Professor Raman worked in Culcatta, now called Kolkata, in Bengal in the right ... very east of India
and he was professor of physics at the university there
and he discovered an effect which to this day is called the Raman effect
and for which he won the Nobel Prize for Physics in 1930
and the Raman effect is the basis of a very important ...
important sort of spectroscopy that is now used all over the world
It's really quite simple and it's a technique which is now applied to all sorts of chemical reactions and chemical processes
And it involves shining a beam of light which is of a single color - blue or green or red
and shining it onto a sample and the sample scatters the light
So a large amount of the red light or blue light is scattered back and you can see it
But if you analyze the light very carefully you also find that there is a small proportion of the light
that's had its colour changed at very discrete frequencies that correspond to
the vibrations of the molecule of the substance you're irradiating
And it is these frequencies that give you a signature of the molecule - sort of fingerprints of the molecule
and allows you to tell what it is
When Raman did it - his first experiments - he did them here in India where
the sunshine is very bright; except now, in the monsoon season
and this intense light was enough ... from the sunlight ... to do the experiment
When I was a student, you had to use huge military lamps to get a Raman spectrum and it took several hours
But after the invention of lasers ...
...then, you could use a laser and record a Raman spectrum in a few seconds or even less
So Raman spectroscopy has become enormously important
You can use it for identifying the pigments - the paints that are used in fine art
You can tell if something's a forgery
You can use it for monitoring chemical processes to tell if things are going wrong
And so it is a fantastic discovery that is a credit to India and which is remembered by chemists all over the world