# Rotary mercury vacuum pump > Emptying lamps with a drum turning in mercury - Date: 1893 - Era: Electric age - Domain: [Tools & Making](https://lastcodex.org/en/domains/tools/) - Rebuild stage: V (Electric age) - Difficulty: 4/5 - URL: https://lastcodex.org/en/inventions/rotary-mercury-vacuum-pump/ A rotary mercury vacuum pump empties lamps and electronic tubes with a rotating part in which mercury acts as a liquid piston. In Wolfgang Gaede's pump of 1905, each curved chamber of a drum draws in gas from the vessel as it rises out of the mercury and, going down again, pushes the gas into the casing, from which a second pump removes it. F. Schulze-Berge had described a rotary mercury pump that could be driven mechanically in 1893; Gaede's was made in large numbers for the lamp and tube industries. ![Rotary mercury vacuum pump · Emptying lamps with a drum turning in mercury](https://lastcodex.org/_astro/plate.8DVGgJ4j_Z7k1Tt.webp) ## Legend 1. Metal casing, half filled with mercury 2. Drum divided into curved chambers 3. Connection to the vessel being emptied 4. Outlet to the fore-pump 5. Pulley driven by a motor ## What it is A vacuum pump removes gas from a closed vessel. Around 1900, makers of [electric lamps](/en/inventions/light-bulb/), X-ray tubes and [vacuum tubes](/en/inventions/vacuum-tube/) needed far lower pressures than a [piston pump](/en/inventions/piston-pump/) can reach, because the air left in a bulb spoils a hot filament. The best pumps of the day used a liquid piston of mercury in place of a solid one. Rotary pumps made that principle continuous. In the form Wolfgang Gaede showed in 1905, a drum divided into curved chambers turns slowly inside a closed metal casing about half filled with mercury. An electric motor drives it, so nobody has to work it by hand. ## How it works The pump works in stages. A separate fore-pump first lowers the pressure inside the casing. The rotary pump then draws the remaining gas out of the vessel and delivers it into that already thin atmosphere, from which the fore-pump removes it. ![Cutaway of the pump seen in three-quarter view: a round metal casing on a stand, with the near wall removed to show a drum of three curved chambers turning on a horizontal shaft, under mercury up to just above its hub, with the mouth of the suction pipe rising above the mercury at the centre](https://lastcodex.org/_astro/v2.DsOyRIaM_ZVNGIr.webp) _Each chamber of the drum opens to the vessel above the mercury, then turns down into it and is emptied._ As the drum turns, the mercury keeps its level and the chambers move through it. On the side where a chamber rises out of the mercury, the free space inside it grows, and gas from the vessel flows in from the suction pipe, which opens inside the drum above the mercury. On the other side the chamber goes down again: the mercury rises in it like a piston and pushes the gas out into the casing, from which the fore-pump removes it. The chamber's opening then dips under the mercury and closes. Each turn carries away a little of the vessel's gas, and the pressure in the vessel falls step by step. The same idea had worked in older mercury pumps, where a column of mercury replaced the solid piston of a mechanical pump and was raised and lowered by hand. Turning the chambers through the mercury instead made the cycle continuous, and a motor could drive it. ## How to do it ![A glass tumbler held upside down and pushed into a bowl of water, the water risen part way inside and a trapped pocket of air above it, with a second tumbler tilted so that a bubble escapes from its rim](https://lastcodex.org/_astro/v1.BjsOJCz-_1kuI7o.webp) _Pushed down into water, an upturned glass traps a pocket of air; tilted, it lets the pocket go, as each chamber of the drum does._ Two simple models with water and card show the cycle of the pump. **Trap a pocket of air.** Fill a large bowl with water. Hold a clear tumbler upside down and push it straight down: the air inside cannot escape, and the water rises only a little way into it, held back by the trapped pocket. Tilt the tumbler slowly under water until its rim lifts on one side: the pocket leaves as a large bubble and water fills the glass. In the pump, the mercury surface seals each chamber in the same way and then fills it. **Turn the cycle.** Draw a circle about 20 cm across on stiff card for the casing, and colour its lower half blue up to a horizontal line: this is the level of the liquid. Mark a small square at the top of the circle as the outlet to the fore-pump. Cut a disc about 16 cm across from a second card and draw three curved chambers on it like the blades of a fan. Pin the disc to the centre of the circle with a paper fastener. Turn it slowly and follow one chamber: as it rises out of the blue, the part of it above the liquid grows, and this is when the chamber takes in gas from the vessel. As it goes down on the other side, the liquid rises in it and that part shrinks, and this is when the gas is pushed out into the casing. ## History and evolution ![A mercury pump of the 1880s on a wooden frame: a tall vertical glass tube with a funnel at the top, a side branch leading to a lamp bulb, and a dish at the bottom where the falling mercury collects](https://lastcodex.org/_astro/v3.lcHGHKw__ZWA3Vd.webp) _In a Sprengel pump, drops of mercury falling down a tube carry the gas away; it was the lamp makers' pump before rotary pumps._ Emanuel Swedenborg described a pump in 1722 in which a column of mercury, raised and lowered, replaced the solid piston of a mechanical air pump. Heinrich Geissler of Bonn built a pump with two glass vessels joined by a rubber tube in 1855; first described in 1858, it surpassed all earlier mercury pumps in simplicity and efficiency. In 1865 Hermann Sprengel introduced a pump in which drops of mercury falling down a narrow glass tube each trapped a little gas and carried it away. In 1879 Edison's laboratory at Menlo Park combined Geissler and Sprengel pumps to empty its lamp bulbs and measured the pressure with a McLeod gauge. These pumps were slow and worked by hand. In 1893 F. Schulze-Berge described a rotary mercury pump in Wiedemann's Annalen, and Nature reported it that November: a ring-shaped tube partly filled with mercury turned in an inclined plane, and the mercury, acting as a piston, drew gas from the vessel and drove it towards an auxiliary pump. It could be driven mechanically, and he was building a larger one for industry. Wolfgang Gaede, assistant at the University of Freiburg, studied the Volta effect in vacuum and found that the pumps of his time could not reach a low enough pressure. In 1905 he presented his rotating mercury air pump at the meeting of German natural scientists and physicians in Merano, where it caused a stir. The historian Franz Wolf wrote that it, like Gaede's oil pump, only improved principles already known from the piston air pump. The pump could be driven by a motor and was made in large numbers for the lamp and vacuum-tube industries. From 1906 Gaede worked with the Cologne firm of E. Leybold's Nachfolger. His rotary oil pump of 1907 was made mainly to serve as fore-pump for the mercury pump. He then introduced the molecular pump in 1912, which drags gas molecules along a fast-spinning cylinder, and the mercury diffusion pump, which has no moving parts. Both reached much lower pressures than the rotary mercury pump. ## Key facts - Rotary form described: 1893, F. Schulze-Berge, in Wiedemann's Annalen - Gaede's drum pump shown: 1905, meeting of German natural scientists and physicians in Merano - Drive: Electric motor, turning the drum continuously - Main users: Makers of electric lamps and vacuum tubes - Fore-pump: Needed to remove the gas it delivers; Gaede's rotary oil pump of 1907 was made mainly for this ## Requires - [Piston Pump](https://lastcodex.org/en/inventions/piston-pump/): Water raised by valve and piston (c. 270 BCE) - [Electric Motor](https://lastcodex.org/en/inventions/electric-motor/): Current turned into rotation (1834) - [Mercury extraction](https://lastcodex.org/en/inventions/mercury-extraction/): Freeing quicksilver from cinnabar (c. 315 BCE) ## Sources - [Gaede, Wolfgang (NDB 6, 1964, entry by Franz Wolf)](https://www.deutsche-biographie.de/sfz19730.html), Neue Deutsche Biographie, Historische Kommission bei der Bayerischen Akademie der Wissenschaften - [P. A. Redhead, History of vacuum devices, CAS CERN Accelerator School: Vacuum Technology (1999), pp. 281–290](https://doi.org/10.5170/CERN-1999-005.281), CERN - [Our founders: Wolfgang Max Paul Gaede](https://www.leybold.com/en/about-us/history/our-founders), Leybold GmbH - [Gaede type rotary mercury pump, 1916–1926 (1926-281)](https://collection.sciencemuseumgroup.org.uk/objects/co3132/gaede-type-rotary-mercury-pump), Science Museum Group - [Sectioned rotor for Gaede rotary mercury pump (1926-690)](https://collection.sciencemuseumgroup.org.uk/objects/co3137/sectioned-rotor-for-gaede-rotary-mercury-pump), Science Museum Group - [Notes (Schulze-Berge's rotary mercury air-pump, after Wiedemann's Annalen), Nature 49, 16 November 1893, p. 65](https://dbc.wroc.pl/Content/17086/PDF/19209.pdf), Nature, scanned by the Lower Silesian Digital Library (Dolnośląska Biblioteka Cyfrowa) - [Pump: air-pumps, mercurial (1911 Encyclopædia Britannica)](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Pump), Encyclopædia Britannica, 11th edition, transcribed on Wikisource - [Air pump (Geissler's mercurial air pump of 1855; Sprengel's pump of 1865), The New International Encyclopædia, 1st edition, vol. 1 (1902)](https://en.wikisource.org/wiki/Page:The_New_International_Encyclop%C3%A6dia_1st_ed._v._01.djvu/297), Dodd, Mead and Company, transcribed on Wikisource - [Pompa Gaede rotativa a mercurio (porcelain drum of three cells in a cylinder filled a little over half with mercury; fore-pump to 20 mmHg)](https://museofisica.web.uniroma1.it/it/pompa-gaede-rotativa-mercurio), Museo di Fisica, Sapienza Università di Roma - [W. Gaede, Means for producing high vacuums, US patent 852,947 (application filed 17 August 1906, granted 7 May 1907): drum chambers rotating in mercury, suction pipe through the centre of the drum, auxiliary pump on the casing](https://patents.google.com/patent/US852947A/en), Google Patents - [Mercury pump (type resembling the one described by Swedenborg in his Miscellanea of 1722)](https://catalogue.museogalileo.it/object/MercuryPump_n01.html), Museo Galileo, Florence - [The Platinum Filament Lamp (1879: Geissler and Sprengel pumps combined, McLeod gauge added to the Menlo Park pump)](https://edison.rutgers.edu/life-of-edison/biographical-essays/lighting/the-platinum-filament-lamp), Thomas A. Edison Papers, Rutgers University - [R. K. Waits, Edison's Vacuum Technology Patents (abstract, paper VST-TuA8, AVS 48th International Symposium, 2001)](https://www2.avs.org/symposium2001/Papers/Paper_VST-TuA8.html), AVS Fact-checked on 2026-10-22. --- The Last Codex · https://lastcodex.org/en/inventions/rotary-mercury-vacuum-pump/ · © The Last Codex. Texts, plates and figures: CC BY-NC-ND 4.0.