The Thiele tube is a type of laboratory glassware designed to determine the melting point of a substance.
The German chemist Friedrich Karl Johannes Thiele invented the tube that bears his name in 1905 in order to accurately determine the melting points of substances. In his publication, he states that heating the tube at the curvature causes the liquid in the tube to circulate (by convection) thereby allowing heating and cooling to occur quickly (when needed). Thiele stated the use of sulphuric acid as the liquid to be heated. Here is his original drawing of his tube:
Here is a labelled diagram of his tube in action: