It was still in use until last year and has been retained for eventual display in Laxey - in the Mines Tavern IIRC!
Ray Hulock
Isle of Man.

There were several types or Mercury Arc rectifiers. The common later design was the single glass tube for each phase. Earlier designs used a common pool of mercury for all six or twelve phases. The Sacramento Northern railway built a branch south into the Sacramento river delta in 1937. They used a six phase steel tank Mercury arc rectifier for this extension. There were six fixed electrodes with a common Mercury pool in the bottom. There was a center motor driven electrode that would go down onto the pool to strike an arc to get the device started. The steel tank had a steel jacket around it which was filled with cooling water. The entire device was energized at the 1500 volt trolley voltage and sat up off the floor on glass insulators. There was a modest fence around it. It was an automatic substation and there was a motor driven drum switch to provide a starting sequence. Also a vacuum pump and mecury manometer to determine the vacuum level. There were several transformers including a "bake out" transformers. I do not remember what that was for. This was a General Electric device. The old timer at the local GE service station use to tell me how much he hated this device. It would arc back (?) and some how blow all the Mercury out of the tank. He talked about crawling around on the floor of the station with a paint brush and a piece of paper sweeping up all the mercury.

This line went out in the early 1950s, but the substation sat there unused, but complete, into the 1970s. The railroad gave the equipment to WRM, but they could never muster the money and man power to move it.