Its Nickel plated copper, and the top flange is brass. Its baffled everyone I know, it came out of an skip full of tat from a engineering works. The bit sticking out is a pipe.
Could it be some kind of vacuum chamber? I saw a video where a guy finished a knife handle by putting it into a container with linseed oil, put a lid on and pulled a vacuum inside it. His was glass and you could see bubbles coming out of the wood, yours could have been used for something like this with the pipe in the side being attached to a vacuum pump and a lid mating with the brass flange.