Note:  Do not rely on this information. It is very old.

Ruperts Drops

Rupert's Drops, said to have been discovered by Prince Rupert, are little drops of melted glass dropped into water. The outside is therefore suddenly cooled and forms a solid skin mund the still liquid interior. The interior as it cools tends to contract, but cannot on account of the forces which cause it to adhere to the solid skin. The whole is therefore in a state of strain, and a slight disturbance is sufficient to cause a complete disintegration of the whole. Thus, if the end be broken off or a scratch made on the drop, it falls to powder with almost explosive violence.