Introduction
Prince Rupert's Drops are tiny pieces of glass with a head and a relatively
long thin tail. They are formed by molten glass drops cooling very
quickly in water. Since the outside cools first, it contracts onto
the inside. This means that the outer skin of the glass is in tension
because of the incompressibility of the inner core. Since the head
is egg-shaped, a relatively strong blow with a hammer will not shatter
one because the stress is distributed around the outside (and actually
relieves some of the tension). However, a slight crack caused by
breaking off the tip of the tail will propogate up to the head almost instantaneously.
As soon as there is an outlet for the pressure inside, the skin is broken
and the whole thing will explode.
Materials
scrap glass rods
bunsen burners
ring stands
800 to 100 mL beaker
PATIENCE
Procedure
Assemble the ring stand so that the bunsen burned is clamped about
a foot and a half above the lab bench. Angle it about 45 degrees.
Place a large beaker about six inches deep with water under the area of
the flame. Carefully melt the end of a piece of scrap glass rod until
it begins to melt. Make sure the drop lands in the water.
Be VERY careful - the glass can still be extremely hot when it looks normal. You must wear goggles during this lab. It is not unusual for most or all of your attempts to fail (the best year was fall 2000 when we had two successes in a triple period class!).
Collect all glass shards with a dustpan and brush, and dispose of them in a cardboard box marked "broken glass."
Other Stuff