Now you might be wondering why I've set this romantic, candlelit scene up for myself,
and it's because I want to talk to you today about firedamp. Now firedamp is something that, in the
early days of coal mining, caused lots of horrific accidents and killed hundreds of miners - and here's why:
[roaring flame]
Now that was methane, which is extremely flammable, and one of the main components of firedamp,
which is a gas that used to leak from the coal-bearing rocks in the mines. Now the miners in those days only had
naked flames like these candles to light their way, so the result was inevitable:
[roaring flame]
Now the reason I'm interested in all of this is because the solution to this problem was devised by a scientist
working right here, at the Royal Institution.
That man was Humphry Davy, a chemist whose simple invention revolutionised the mining industry,
and helped to fuel Britain's industrial revolution.
So I've come down to the RI's archives to look at some of Davy's early attempts to tackle this problem.
Over here, we've got some of the prototypes that didn't work quite so well -
but then here, this is what Davy ultimately came up with, so this is the miners' safety lamp, or the Davy lamp.
And you can see that it's a really simple solution to the problem, it's just an oil lamp,
the wick enclosed in this piece of gauze here, this cylinder of gauze. And it's the gauze that's doing the work,
the gauze is what prevents the flame from igniting the gases in the mines and creating an explosion.
And all of these actually, Davy made all of these within about two months in 1815, he was
really working hard at this problem, because he knew that other people were trying to solve it
at the same time, and he wanted to get in there first. And this was so successful, this design,
that this commercial version on the right here was actually made around fifty years after Davy
posed this idea, which shows that it was used almost unchanged for decades down in the mines, and keeping people safe.
So, how does a Davy lamp work?
Well, to give you an idea, I've filled this tube with natural gas which is mainly methane
and similar in composition to firedamp. Now if I ignite it at one end, you can see that
the flame front propagates along the tube in quite a spectacular way:
But if this time we insert a bit of gauze in the centre of the tube, and repeat the same thing,
we can see that the flame stops at the gauze.
The gas itself is able to pass through the gauze no problem, but the flame isn't.
You can see that if I light the tube again from the other end,
the second part of the tube still has gas in it and so it's still able to burn.
Well Davy discovered that flames don't propagate through small holes, and you can see that
even more clearly if I hold this gauze over this candle flame. He spent ages experimenting with
tiny metal tubes and different gauzes, trying to find exactly the right size hole for this job.
Now all fires and all flames need to sustain a high temperature in order to burn. And normally that's quite
easy because the chemical reaction itself releases lots of heat, so the high temperature becomes self-sustaining.
But if you can cool the reacting gases down fast enough, then you can stop the flame in its tracks - and that's what the gauze does.
The metal wires that form the gauze absorb all the heat from the flame,
cooling it to the point where it can't sustain itself.
So I have a replica of one of Davy's early lamps here and, down in the mines,
these lamps allowed naked flames to be used relatively safely. If there was any firedamp in the air
it would pass through the gauze, into the lamp, and burn relatively innocuously there,
rather than igniting the gas on the outside. [The flame is much quieter than before]
And that's quite a difference from what we saw earlier.
[roaring flame]
Once Davy had perfected his design, it not only allowed miners to mine more safely,
but also to mine deeper and more productively, so coal output soared.
But the reason I like this story is that it's a great example of applied science: just by careful experimentation
and observation, Davy was able to find a simple solution to a big problem.