The device consisted of a flexible sheet of vulcanite that could be adjusted into a convex shape by means of adjustable cords.
The tip of the vulcanite sheet was held between the teeth, and the handle and cords held in the hand.
The microphone, earpiece, and battery case are all made of molded vulcanite.
British Dictionary definitions for vulcanite
a hard usually black rubber produced by vulcanizing natural rubber with large amounts of sulphur. It is resistant to chemical attack: used for chemical containers, electrical insulators, etc Also called ebonite