The Man Who Turned to Stone (1957) Bernard Gordon

A group of 18th-century scientists, led by Dr. Murdock, have remained young after all these centuries by using electricity to suck the life out of young women. If one of the scientists misses a treatment, his skin hardens to the toughness of stone. A female prisoner discovers why so many of her fellow inmates are disappearing, and attempts to stop them with the aid of a prison psychiatrist.