- To demonstrate that glass will conduct electricity at high temperature.
The series circuit containing the glass element and lamp bulb is open-circuited at room temperature. If the element is heated on one side to melting point, then due to the high negative resistance temperature coefficient of glass, the conductivity increases rapidly, and at a bright red heat the I2R loss in the glass is sufficient to maintain the temperature without further use of the flame.
Watch an Electrical Conduction of Glass
Youtube video (not produced by BCIT)