we're in the archives of the Royal
Society in London again and I want to
talk to you about methane and methane in
coal mines because I've already shown
you on some of the videos how Matane can
explode when it's mixed with air and
because coal is originally formed from
organic matter very frequently in coal
mines you get methane gas and methane
gas doesn't smell has no color and in
the early days of coal mining people
never knew it was there and suddenly
there would be an explosion and the
reason they're being explosion is
because they use candles to light the
mine while they were digging
there was a big scientific race to try
and invent a safe lamp that would help
the miners know when there was danger
but wouldn't blow them up
so if you think about it you've got to
try and have a naked flame in a coal
mine
where if there is gas there
the explosion won't spread so before I
tell you how it was solved let's go and
see some of the things that are here in
the archive which explains how it was
done as usual I have got my colleague
Rupert who's going to find some things
to bring this all to life gosh that's
really good what we've got here
looked pretty miserable but this was the
lamp invented by Sir Humphrey Davy in
eighteen one canal knew exactly when
1813 also this is the lamp he made which
solved the whole problem and the key to
it is this gauze that you can see here
so first of all before I explain what
the gauze does let's see
Rupert come and show me so Humphrey Davy
who was working at the Royal Institution
tried all sorts of different designs
with his assistant Michael Faraday and
they tried different sort of lamps to
see whether if they exposed this to me
thing it would explode and this is the
drawing they really made and they load
to touch it so here and underneath I
think is another drawing of a lamp that
didn't work um so just looks like a
lantern with a chimney this is there his
actual writing way he describes his
apparatus it begins the first apparatus
that I made I'm not sure if many of you
have been in the middle of an explosive
mixture but what happens is when you
light a match the reaction starts just
on the match and because when methane
burns and makes
- and steam it occupies a bigger volume
the pressure goes up so pressure wave
moves outwards and as it moves outwards
it compresses the gas that it meets and
so the pressure goes up and the
temperature goes up and the reaction
goes faster so it builds up and up and
up so by the time it gets a small
distance away it's really travelling
very fast and with the lethal rate and
what David discovered presumably with
Faraday was that if you have a flame
inside the gauze the gas can start
burning in the gauze but the flame
cannot go through that doors because the
metal goes
cools the gas enough to stop the
reaction so if you were a miner with one
of these lamps in an explosive
atmosphere what you would suddenly
notice is that the color of the flame
changes starts burning I think with a
more bluish flame and you know
something's wrong but you're still alive
and you know it's time to leave or turn
up the ventilation but until that point
if somebody had a lamp and was in an
explosive atmosphere they never knew
about it because they'd been blown up
this lamp here or this piece of tubing
is the lamp that Davy made that proved
his discovery and like many pieces of
historic equipment it doesn't look very
exciting but this is what sparked the
idea that sparked the idea is the wrong
metaphor here but you understand what I
mean