Mercury arc rectifiers

Alternating Current is now almost universally adopted as the most convenient form of electrical energy for all industrial purposes. In spite of its increasing use, there are nevertheless many instances where Direct Current is either essential or preferable. For electrolysis, certain chemical processes, battery charging, and D.C. Traction, it is essential, and where wide and economical speed control of motors is desirable D.C. still holds its own despite the variable speed A.C. commutator motor which is available in the smaller sizes. Some form of converting or rectifying plant is, therefore, necessary to change the A.C. supply into D.C.