Mercury-arc rectifier

A Mercury-arc rectifier is a type of rectifier used for converting alternating current (AC) to direct current (DC). The cathode is made from a pool of liquid mercury. Mercury-arc rectifiers were rugged and durable. They could carry higher currents than most other types of rectifier.
The mercury-arc rectifier was invented in 1902 by Peter Cooper Hewitt. They were used to provide power for industrial electric motors, electric railways, trams, and electric locomotives. Other uses included radio transmitters and high-voltage direct current (HVDC) power transmission. They were the primary method of high power rectification before the advent of solid-state electronics in the 1970s. The solid-state rectifier has since replaced the mercury-arc rectifier.