HISTORY OF NOTHING - VACUUM
The predecessor to the vacuum pump was the suction pump, which was known to the Romans. Dual-action suction pumps were found in the city of Pompeii. Arabic engineer Al-Jazari also described suction pumps in the 13th century. The suction pump later reappeared in Europe during the 15th century. By the 17th century, water pump designs had improved to the point that they produced measurable vacuums, but this was not immediately understood. What was known was that suction pumps could not pull water beyond a certain height: 18 Florentine yards (approximately 30 feet) according to a measurement taken around 1635. This limit was a concern to irrigation projects, mine drainage, and decorative water fountains planned by the Duke of Tuscany, so the Duke commissioned Galileo to investigate the problem. Galileo advertised the puzzle to other scientists, including Gaspar Berti who replicated it by building the first water barometer in Rome in 1639. Berti’s barometer produced a vacuum above the water column, but he could not explain it. The breakthrough was made by Evangelista Torricelli in 1643. Building upon Galileo’s notes, he built the first mercury barometer and wrote a convincing argument that the space at the top was a vacuum. The height of the column was then limited to the maximum weight that atmospheric pressure could support; this is the limiting height of a suction pump, and the same as the maximum height of a siphon, which operates by the same principle. Some people believe that although Torricelli’s experiment was crucial, it was Blaise Pascal’s experiments that proved the top space really contained vacuum.
Despite these experiments the discussion between the plenists (no vacuum is possible in nature) and the vacuists (vacuum is possible) continued. One of the leading vacuists was Otto von Guericke, burgomaster of Magdeburg in Germany from 1645 to1676. Around 1650, Guericke tried to produce a vacuum in a water-filled, wooden cask by pumping out the water with a pump used by the fire brigade in Magdeburg. Although the cask was specially sealed, the experiment failed: the air rushed into the empty space above the water through the wood, developing a chattering noise. Consequently, Guericke had a large copper sphere built, but when the air was pumped out, the sphere was suddenly crushed. Guericke correctly recognized atmospheric pressure as the cause and ascribed the weakness of the sphere to it being crushed. The problem was solved by constructing a thicker and more precisely shaped sphere. After evacuating this sphere and leaving it untouched for several days, Guericke found that the air was seeping into the sphere, mainly through the pistons of the pump and the seals of the valves. To avoid this, he constructed a new pump where these parts were sealed by water, an idea still used in today’s vacuum pumps, but with oil instead of water. Guericke’s third version was an air pump, which pumped air directly out of a vessel. These pumps were capable of producing a vacuum in much larger volumes than Torricellian.
The word pump is still used for today’s vacuum pumps, although they are actually rarefied gas compressors. This is due to the origin of the vacuum pump: the water pump used by the fire brigade in Magdeburg. Guericke was also a very successful promoter of his own knowledge and experiments, which he used to catch attention for political purposes. In 1654, he performed several spectacular experiments for the German Reichstag in Regensburg. The most famous experiment demonstrating the new vacuum technique was displayed in Magdeburg in 1657. Guericke used two hemispheres with a diameter of 40 cm (15.7 inches), known as the Magdeburg hemispheres. One of the hemispheres had a valve for evacuation, and between the hemispheres, Guericke placed a leather ring soaked with wax and turpentine as a seal. Teams of eight horses on either side were just barely able to separate the two hemispheres after the enclosed volume had been evacuated.
Painting of Guericke showing his experiment with the hemispheres to the German emperor, Kaiser Ferdinand III.
News of Guericke’s experiment spread throughout Europe and his air pump can be considered as one of the greatest technical inventions of the 17th century. The new vacuum technology brought up many interesting experiments. Most of them were performed by Guericke and Schott in Germany, by Huygens in the Netherlands, and by Boyle and Hooke in England.
The early scientists who produced vacuum still had no clear definition of a vacuum. They had no idea that air could consist of atoms and molecules, which in part are removed to produce a vacuum. Until 1874, the Torricellian tube was the only instrument available for measuring vacuum, and limited to about 0.5 mm Hg (67 Pa). The idea of vacuum was still quite an absolute (present or not) as in the Aristotelian philosophy but it was not accepted as a measurable quantity. The gas kinetic theory by Clausing, Maxwell, Boltzmann, and others as well as the invention of the gauge by McLeod (1874), however, showed that vacuum indeed was a measurable physical quantity.
The McLeod gauge which is still used in a few laboratories today, uses Boyle’s law. By compressing a known volume of gas by a known ratio to original pressure can be calculated.
Huygens’ idea of using the pressure difference between the atmosphere and a vacuum to build an engine was continued by Thomas Newcomen in the 18th century. He used condensed steam to create vacuum. Newcomen’s engines were broadly used in England to pump water from deep mine shafts, to pump domestic water supplies, and to supply water for industrial water wheels in times of drought. His machines predate rotary steam engines by 70 years The large advances in physics in the second half of the 19th century are almost unthinkable without the aid of vacuum technology. Hauksbee already discovered gas discharges at the beginning of the 18th century. Significant progress, however, was only possible after the invention of the Geissler pump in 1855. Three years later, Plu¨cker found that the glow of the glass wall during a gas discharge shifts when a magnetic field is applied. In 1860, Hittorf discovered that the rays from a cathode produce a very sharp shadow if an object is placed in between the cathode and a glass. Many scientists continued research on cathode rays, which finally led to the discovery of the electron as a component of the cathode rays by J. Thomson in 1898.
In 1895, Ro¨ntgen reported that when a discharge is pumped to less than 1 Pa, a highly penetrating radiation is produced capable of passing through air, flesh, and even thin sheets of metal. He named the beams X-rays. In 1887, Hertz discovered the photoelectric effect under vacuum. In 1890, Ramsay and Rayleigh discovered the noble gases. All these experiments helped to understand the nature of vacuum: the increasing rarefaction of gas atoms and molecules. At the time, it became clear that any matter in nature consists of atoms. For his experiments, Knudsen used the so-called Gaede pump. Gaede, a professor at the University of Freiburg in Germany, was the most important inventor of vacuum pumps since Guericke. Gaede’s pump was a rotary mercury pump in which the Torricellian tube was wound up so that it allowed continuous pumping by rotary action. The pump was driven by an electric motor. Its pumping speed was 10 times faster than the Sprengel-type pump and produced a vacuum to 1 mPa. However, it required an additional pump in series because it was able to compress the gas only up to 1/100 of atmospheric pressure.
The sliding vane rotary vacuum pump was developed between 1904 and 1910, based on an idea of aristocrat Prince Rupprecht, which dated back to 1657. Gaede optimized these pumps in 1935 by inventing the gas ballast, which allowed pumping condensable gases as well.
In the years 1915 and 1916, Gaede and Langmuir developed the mercury diffusion pump, 12 years later, the oil diffusion pump followed, which was the most widespread pump used in its day.
Today, we have a large variety of highly engineered pumps using various concepts to generate a vacuum. None of this would have been possible were it not for the vision of those many individuals in the past centuries that were willing to risk and think beyond the beliefs of their time.
