No, that's ammonium dichromate. Used to be used in indoor fireworks;
ignited alone, it glows and gives several times its volume of fluffy
green chromic oxide (Cr2O3). This happens at a much lower temperature
than the thermit process using aluminium (see other post), in which the
exothermicity of the reaction 4Al + 3O2 --> 2 Al2O3 accounts for most of
the heat.

I used to do this to generate Cr2O3 to use for the thermit process.

It may be that you can do both at once using ammonium dichromate and
aluminium powder - could be what Ken was thinking of.

David

Yeah, that would be exactly the thing!  Thanks, I couldn't remember.

[SNIP]

Phosphorus has similarly 'entertaining' properties...  Even with the correct
solution on hand for extinguishing it at the time, I can still see on the
back of my hand a very small scar which is what remains from a 20+ year old
phosphous burn.

Most 'entertaining' lab. fire I ever saw involved a flammable metal, but not
magnesium.  'Sodium sand' is used in synthesising certain organo-sodium
compounds, it's just very finely divided sodium.  But sodium is too soft to
grind up, and has to be kept away from oxygen at all times as it otherwise
oxides at the surface rapidly - anything as fine as sodium sand would be all
oxide before you even get to use it.

Sodium also reacts violently with water (on which it floats) liberating
hydrogen and producing enough heat that the sodium usually catches fire,
igniting the hydrogen.  The other product of the reaction with water is
sodium hydroxide, so even after the violent reaction is over, you have a
caustic liquid to clear up.

Of course, you can't put out a sodium fire with water, and it can reduce
CO2, so you can't use a CO2 extinguisher.  Sodium also reacts violently or
explosively with the halogens, so the old BCF family of chemical
extinguishers can't be used either.

Sodium sand is made in an ingenious way.  You put sodium under toluene (aka
methylbenzene, aka toluol, aka phenylmethane), an liquid aromatic
hydrocarbon in which sodium is insoluble and which will protect it from air
(and water).  Toluene is very flammable (and toxic), and has a large excess
of carbon on combustion.  The clever part is that toluene boils at a
temperature (111C) not far above sodium's melting point (98C).  You put the
sodium and toluene in a rb flask with a refluxing condenser and boil the
toluene for a while - the sodium melts and the boiling action of the toluene
disperses it into tiny spherical droplets within the liquid.  When you take
away the heat the sodium freezes before the boiling has slowed enough for it
to coalesce, so you get your very finely divided sodium sand.  Clever eh?

Well, one day we were making some sodium sand.  Because of the water and CO2
things, the usual fire extinguishers were put out of the way and a bucket of
sand was in their place.  The toluene boiled and refluxed nicely till the
sodium was well distributed in the toluene and we decided it was time to
take away the heat and let the sodium freeze.  Will reached into the fume
cupboard and turned the Bunsen to a luminous flame and moved it away from
the boiling flask, closed the fume cupboard door again and then it
happened - and I can see this all happening in slow motion, even as Will
reached for the gas tap to turn out the Bunsen:

The clamp that was holding the Quickfit rb boiling flask at the neck gave
way - the jaw just broke, metal fatigue I suppose.  The reflux condenser was
also clamped to the retort stand, so the ground glass joint separated and
the flask simply dropped away from the condenser and hit the plate at the
bottom of the stand.  Being Pyrex it didn't break - oh no, that would've
been too easy.  It bounced, and as it did so it began to spin...  and out of
the neck of the flask came an expanding spiral of toluene and sodium sand as
the flask span.  This I saw in slow motion.  Then the 'spiral' reached the
other side of the fume cupboard and met the Bunsen flame, and suddenly
everything was happening in real time again.  The cupboard was illuminated
as it completely filled with a sheet of yellow flame (toluene burns
yellowish anyway because of all the carbon, but sodium has a  _bright_
yellow/orange emission line when it burns).

I flicked the switch that cut the fume cupboard fan even as Will grabbed the
bucket of sand.  As he lifted the sand I opened the cupboard, Will threw in
the sand and we both very quickly distributed it so all the burning liquid
was covered - most of it had run into the fume cupboard sink, so it wasn't
as hard to contain as it might have been.  There was a Kipps gas generator
in the back of the fume cupboard, and we were both aware that if the rubber
hose on it melted it would start feeding flammable hydrogen sulphide gas to
the fire, which was an extra incentive to get it under control quickly.

It was all over in 30 seconds at the most, but it seemed longer...

Will and I walked outside to breathe in some fresh air and then saw what
that excess of carbon in the toluene had done: we both had completely black
faces, except where we had rubbed our eyes, and looked like we had 'blacked
up' to sing backing for Perry Como in some 1960s TV special.  The fire may
have been out in moments, but it took the rest of the day (and more) to
clean out the thick curds of greasy black soot that encrusted every surface
and every reagent bottle in the lab.

(Far from finding this a scary experience, Will and I both found our first
laboratory fire rather reassuring.  Previously it was a risk you knew about,
and hoped you had planned for adequately; but after the fire we knew we'd
had one that was nearly as bad as could be, and we'd reacted just as we
needed too.)

That spiral of liquid igniting and turning into a wall of flame was really
beautiful too - sort of like attack ships burning off the shoulder of... oh,
never mind.

Peter