Help! What is this for?

In my attic there is a metal canister (approx. 8"dia x 15"h) with a 1" glass tube in front of it. The metal canister is connected at the bottom to a cooper plumbing line (that comes through the floor) and at its side to a horizontal (cast iron?) metal pipe that penetrates the angled roof structure.

The (old, 1050's looking) label has no description but I think it says the comapny name is "Electric Weld"

Can someone tell me what this is for?

The house, built in the 1920's, is on Staten Island of New York City.

Thanks!