A
mercury-arc valve or
mercury-vapor rectifier or (UK)
mercury-arc rectifier is a type of electrical
rectifier used for converting high-
voltage or high-
current alternating current (AC) into
direct current (DC). It is a type of
cold cathode gas-filled tube, but is unusual in that the cathode, instead of being solid, is made from a pool of liquid
mercury and is therefore self-restoring. As a result, mercury-arc valves were much more rugged and long-lasting, and could carry much higher currents than most other types of gas discharge tube.