It was used for purification of mercury.
Procedure: Mercury is kept in a long vessel, with a bent tube at its neck. The lower end of the tube should be inserted into the body of another vessel containing water. The mouth of these two vessels and joints are closed with clay and cloth etc. a blazing fire is placed under the first vessel. The mercury falls into the water in the second vessel. Cold water is poured constantly on the second vessel to get sublimated mercury.