Thiele tube

The shape of the Thiele tube allows for formation of convection currents in the oil when it is heated.

These currents maintain a fairly uniform temperature distribution throughout the oil in the tube.

A sample in a sealed capillary, attached to a thermometer with a rubber band, is immersed in the tube.

A slow heating rate at the melting point is needed in order to get an accurate measurement.

A Thiele tube can be used to measure the boiling point of a liquid by the Siwoloboff method.

Drawing of a Thiele tube with red arrows showing convection current
A photograph of a Thiele tube. The oil level is a little low now to compensate for expansion when heating commences.