From your description, I think they are mercury vapor rectifiers. They used to use them in battery chargers. In this case, they probably were used to provide DC for the projector's arc lamp. Any, yes, I think you could heat a room with a few of them.
I don't know how to test them other than a continuity check of the filament across the Edison screw base. As long as there is continuity, the bulb still has a vacuum and the mercury is in there, they ought to work.