Sprengel Pump

—A device for attaining a very high vacuum, such as is nece ary in the manufacture of incandescent electric lamps. Mercury is fed into a funnel at one extremity of a long U tube, this tube having a return bend with a longer drop leg on its other end; a nozzle situated within an annular enlargement, at the top of the drop leg, breaks the flow of the mercury into a series of slugs with air between them. Each slug, falling down the drop leg, acts as a sort ef piston, sucking the air behind it, and, as a connection on the return bend communicates with the ve el to be exhausted, the latter is speedily emptied of air. The U tubes being over barometric height, air cannot pa up them even should the pump stop. Escaping mercury from the drop leg or ‘“‘fall tube” collects in a ve el which surrounds its base.