Mercury Switches
This is a good summary of mercury-arc valves! Here are a few minor additions and clarifications: Cathode Spot: The key to their high current handling was the "cathode spot" on the liquid mercury surface. This spot, a small localized area of intense electron emission, could handle extremely high current densities. Grid Control: Some mercury-arc valves included a "grid" electrode, which could be used to control the initiation and extinction of the arc, providing some level of current control. Applications beyond DC: While primarily used for DC applications, they were also used in some AC applications, such as for phase control in industrial power systems. Environmental Concerns: Mercury-arc valves posed environmental concerns due to the presence of mercury. Proper disposal and recycling of these devices were important. Overall, mercury-arc valves were a significant technological achievement in their time, enabling the development of high-power electr...