Thiele tube
The Thiele tube, named after the German chemist Johannes Thiele, is a laboratory glassware designed to contain and heat an oil bath. Such a setup is commonly used in the determination of the melting point of a substance. The apparatus itself resembles a glass test tube with an attached handle.
Operation
Oil is poured into the tube, and a then the "handle" is heated, either by a small flame or some other heating element. The particular shape of the Thiele tube allows the oil to circulate via a convection current, thus producing an oil bath of nearly uniform temperature. A sample immersed in the bath can then be heated evenly.