>When you use sodium, the reaction is somewhat more vigorous, and ignition of
>the hydrogen is more common.  The flame tends to be yellowish, from sodium in
>the aerosol that the effervescing hydrogen makes.  Explosion is unlikely, but
>it does happen. (Loud <POP>, and the sodium flies off in a random direction --
>usually right at your face.  ;^)

Well, if you use more than about 3 or 4 cm3 of sodium metal, the metal heats up
enough to melt, and when it explodes, or a large hydrogen bubble explodes,
you get a half dozen little skittering sodium blobs, which repeat the process.


>There are ways to increase the hazard, however.  A (possibly apocryphal) tale
>I heard involved a high-school kid who had fused sodium in a crucible.  The
>teacher called an end to the lab period, so this newbie decided to just clean
>up the experiment the quick, safe way.  He turned on the water and tossed the
>hot crucible, half full of molten sodium, in the sink.
>
>There were no injuries, but the kid was rather closely supervised for the rest
>of the year . . . .

I did something similar to this.  I was cleaning the supply cabinet in my
elementary school, and found this ucky blob in a test tube.  No markings,
no nothing.  OK, we'll be tidy for once, and throw it in the sink with a lot
of water running in case it's nasty.

Whoops, it's sodium.  It runs around on the surface of the water, then drops
down the drain.  The drain was about 3 feet long, and opened into a bigger
drain in the floor.

3....2....1......POW!  A foot of flame from both ends of the pipe.  The
hydrogen collected, then ignited.  The principal of the school never believed
that it was an accident.