An induction heating coil which is detachably mounted on a holding member of an induction heating device having a chamber receiving at least a portion of the coil, which device is adapted for use in a process of zone melting of a rod of material, characterized by the coil comprising a tube of insulating glasslike material, such as glass or quartz, which is both heat resistant and vacuum-tight, receiving a metal conductor therein. Each end of the coil is provided with an intermediate member of a good conducting material which member is electrically connected to the conductor and is sealed in a vacuum-tight relationship with both the tube of the coil and the holding member of the device. Preferably, a cooling agent such as water is circulated through the tube to cool the metal conductor during a heating operation. To form the seal with the intermediate member, the tube is either provided with a metalized end that is soldered to the intermediate member or the intermediate member is provided with a ring of silicon rubber which is compressed between the tube and intermediate member by an appropriate clamping device.