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Introduction to the Kinetic Theory of Gases
Published in Caroline Desgranges, Jerome Delhommelle, A Mole of Chemistry, 2020
Caroline Desgranges, Jerome Delhommelle
One of the most impressive events in the history of pneumatic chemistry is certainly the well-known “Magdeburg hemispheres” experiment directed by Otto von Guericke (1602–1686) (see Figure 1.5). In 1654, in front of Emperor Ferdinand III and the princes, two copper hemispheres of 14 inches (35.5 cm) in diameter are brought together at Regensburg (now in Germany). The system is maintained with a mixture of grease, wax and turpentine. An important detail for the future: one of the spheres has a tube closed by a valve. The show begins and von Guericke asks that two teams of eight horses separate the hemispheres. It doesn’t work. Then, von Guericke walks towards the hemispheres and separates the two hemispheres with his bare hands! Everyone in the crowd is in shock! In fact, the trick hinges on the small valve we mentioned earlier … and this is not an illusion, but a real, pragmatic, engineering problem. Von Guericke has actually invented one of the first pneumatic machines using piston-type vacuum pumps. Indeed, this kind of device creates a vacuum in a container by sucking the air out! Conversely, if air enters in a container previously “filled” with vacuum, the vacuum is destroyed by the incoming air. This is exactly what happens in the Magdeburg hemispheres experiment in which von Guericke plays with creating/destroying vacuum in the sphere. From a scientific standpoint, this experiment also shows the importance of atmospheric pressure. When the sphere is “full” of vacuum, there is no pressure inside the sphere; hence the pressure outside the sphere (the atmospheric pressure) is much greater than the pressure inside the sphere. It is then very difficult to separate the two hemispheres of the sphere … but not impossible. If we calculate the forces of pressure on the sphere, we find that we need approximately 40,000 Newtons, thus the action of a mass equivalent to 5 tons! In general, a horse is only able to draw about 0.212 ton, so 16 horses were either a great guess or an excellent calculation! Let us add that vacuum technology leads to many inventions, most notably pneumatic tube transport systems. At the end of the 19th century, many large cities use this system to send and receive messages or small packages. One of the oldest is the system linking the London Stock Exchange to the city’s main telegraph station. Cities such as Berlin, Paris, Geneva, Vienna, Prague, Algiers, Buenos Aires, Chicago and New York City also develop pneumatic mail services, which remain active in many cases until the 1950s. The Paris system stays operational until 1984, and the Czech pneumatic tube mail system is only stopped because of flooding in 2002, the system being damaged beyond repair. If you visit old office buildings in New York, you will certainly see remains of pneumatic mail systems. Look for the tubes!
Wall-Climbing Robot with Active Sealing for Radiation Safety of Nuclear Power Plants
Published in Nuclear Science and Engineering, 2020
Daewon Kim, Yun-Sam Kim, Kyoungyong Noh, Misuk Jang, Seoungrae Kim
The vacuum suction method was first demonstrated in 1654 by the famous Magdeburg hemisphere experiment by Otto von Guericke. Vacuum adsorption can produce a stable suction force regardless of the substrate material and can be easily implemented at low cost. However, the application of the vacuum suction unit is greatly limited by the roughness of the surface and curvature, which cause air leakage.30–33