My father was one of the first tenants in the Merchandise Mart (early 1930s). His office consisted of a showroom, office and a large stockroom. The office and showroom had glass display windows opening into an interior hall, but the stockroom had large windows looking out on the river and the bridge. There was a large work table under these windows and a favorite adventure of mine as a young child was a visit to my father's office. I would climb up on the worktable and from the 8th floor windows I had a wonderful view of the river and the bridge.
My child's mind convinced me that cars crossing the bridge as a ship approached were sure to be tossed into the river!! I loved watching the bridge open and close but was very fearful of being in the car driving over the bridge in case it suddenly opened! No amount of explanation from my father changed my mind about the danger and in all the hours I spent watching the bridge I never saw or heard of a car thrown from the deck!
I have no idea how the raising and lowering was accomplished in those days but I remember that the bridge master (or whatever the proper term is) often had to make several adjustments until the two halves fit properly. I don't believe I ever knew the official name of the bridge until I became aware of this project - it was always just the "Merchandise Mart Bridge".