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Re: superheated water

At 04:56 PM 2/3/00 -0500, Rick Swanson wrote:
I came across the report below about hot water "blowing up" after being
microwaved. Does not make sense to me. Anyone have information about
such a thing?

If you work at it, it _is_ possible to superheat liquid water to a rather
remarkable degree. I haven't tried it since undergrad days, but I vaguely
recall getting to almost 110C. The trick is to have a very, very carefully
firepolished container, so there will be no sources of heterogeneous
nucleation.

You can then nucleate it by throwing in a boiling chip. Actually boiling
chips are no fun, because they work too well; they start the process
immediately, starting from the top layer, since you are adding the chip
from the top. What you really want is a not-very-good chip that sinks all
the way to the bottom and then nucleates the bottom layer of
water. WHOOSH! There's enough energy to launch the water right out of the
beaker. It's not enough for a moon rocket, but it's enough to provide a
memorable lesson on the purpose of boiling chips.

The idea of superheated water in a coffee mug seems pretty far-fetched to
me, because every coffee mug I've ever seen has more than enough scratches
in the surface to provide plenty of nucleation sites.