Air-Pump

“This was invented in 1865 by H. Sprengel. The instrument, in its original (simplest) form, consists of a vertical capillary glass tube a of about 1 mm. bore, provided with a lateral branch b near its upper end, which latter, by an india-rubber join governable by a screw-clamp, communicates with a funnel. The lower end is bent into the shape of a hook, and dips into a pneumatic trough. The vessel to be exhausted is attached to b, and, in order to extract its gas contents, a properly regulated stream of mercury is allowed to fall through the vertical tube.” —The Encyclopedia Britannica, 1903

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