we've done some really nice experiments
with bubbles containing hydrogen gas
using our slow-motion camera
the experiment was really quite simple
up here we had the burning spill just a
piece of wood like a large match and
underneath we had a bubble blowing kit
just like this and we blew hydrogen gas
roots because hydrogen gas is lighter
than air the bubbles flew up towards the
flame for me one of the most surprising
things was how hard it is to hit a flame
with a hydrogen bubble most of our
bubbles missed and they floated up
reasonably slowly and you have to
remember that a small bubble has a
higher pressure of gas inside it than
the big bubble so if you have a big
bubble the pressure is pretty low almost
the same as atmospheric pressure but
what this means is that if you burst the
bubble the gas isn't under pressure and
doesn't expand very rapidly one of the
things that I thought was interesting is
that when a bubble catches fire the
burning gas continues to move up almost
the same shape as the bubble it expands
a little bit but it continues upwards
and the other point that we saw from
these bubbles is that even though the
soap has disappeared very quickly the
gas still burns with an orange flame I
think that's interesting because it
shows that the gas is still experiencing
a buoyant effect and the rising up and
the fact that it suddenly goes to a very
high temperature does not really seem to
change the rate at which it goes up look
this one's quite fun
it's double just like a hydrogen
molecule I was expecting that this would
burst twice as much as a single bubble
but you see is more or less the same so
you can't always predict what's going to
happen so it was quite an anti-climax
it's quite nice to burn a hydrogen
molecule containing hydrogen we've done
several videos about burning of hydrogen
balloons and whether it's the rubber
that causes the colour or it is the gas
so just watch this bubble because it
comes up and hits the spill where it's
not burning and the bubble bursts so you
have hydrogen gas which is completely
free and it goes up into the flame and
it burns with the same orange colour so
we have a really nice example which
shows that hydrogen gas when it's not
contained anything will still burn with
an orange colour and almost certainly
this is because the hydrogen the oxygen
are not properly mixed so we were
completely wrong that the rubber could
possibly have caused the orange colour
and it's always good to be wrong it
shows that you're learning something
I think the really important
demonstration from the understanding of
gases is how slowly gases spread in air
so even if you have some hydrogen that
is not confined by anything it really
takes quite a long time for the hydrogen
to spread out and so this if you like
challenges our idea that gases and
things mix very quickly of course
eventually all gases will mix but on the
timescale of the video everything is
pretty slow and so it is important to
learn these lessons and to see how
things behave what we on periodic videos
want to do is to try and show you things
which make you think and realize the
real world is slightly different from
what you expect I really enjoyed
watching this footage and I'm sure I
missed some quite interesting things so
I'd really like all of you to watch
these videos and see if you can notice
some extra effects some other lessons
that we can get out of them and tell us
about them in the comments if it's
something interesting we'll try and make
another video
you