Void in the void

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Emptiness in the emptiness (French vide dans le vide ) is the name of an experiment carried out by Blaise Pascal in November 1647 , with which he was able to prove that the mercury in a manometer column is only pushed to a certain height by external air pressure . The question was whether the empty-looking part of the glass tube above the mercury column was really empty, in other words, whether there was actually a “ vacuum ” in it. With the experiment, Pascal was able to confirm this hypothesis within the scope of the measurement accuracy at the time. Pascal described the experiment in a letter to his brother-in-law Florin Périer .

prehistory

The original ideas for these experiments came from Galileo's student Evangelista Torricelli , who in 1644 turned a glass tube filled with mercury and closed at one end into a basin with mercury and found a "vacuum" in the upper part of the glass tube. Pascal saw one such experiment in Rouen in October 1646, demonstrated by Pierre Petit. The fact that it was a "vacuum" was doubted by many contemporaries (including Descartes ) who still adhered to Aristotle 's doctrine of the horror vacui . This said that creation was incompatible with the existence of an empty space and that nature itself "abhorred" emptiness. Accordingly, it has now been claimed that the apparently empty part of the glass tube is filled with invisible vapors.

To refute this, Pascal conducted a demonstration experiment in front of 500 spectators with two large (40 feet or 12 m long, attached to ship masts) glass tubes filled with water and wine. According to the general opinion of the time, the column should be deeper for wine, since wine evaporates more easily, which was not the case. The water column was deeper because wine has a lower specific weight than water.

Pascal made many other experiments to prove the existence of the vacuum. When he heard that Torricelli attributed the height of the mercury column to the external air pressure, there were lively discussions in 1647 between Gilles Personne de Roberval , Mersenne , Descartes , Pascal and others. New experiments were thought of, including the vide dans le vide , which Roberval, Adrien Auzout and Pascal carried out independently and in slightly different ways.

Independently of Pascal's later work, Torricelli had already shown that the height of the mercury column was independent of the shape, inclination and length of the glass tubes and thus provided strong arguments for an explanation based on atmospheric pressure.

Test procedure

Various test procedures are described. Pascal himself reports on this in his letter to Perier of November 1647 and in the Traité de l'équilibre des liqueurs et de la pesanteur de la masse de l'air .

In one version, the experiment is performed with a small manometer inside a larger manometer. To do this, you need a mercury manometer according to Evangelista Torricelli , a vessel into which the manometer fits and which can be tightly closed with a lid at the top and an impermeable membrane at the bottom , a larger storage vessel for immersing the membrane vessel and a U-tube .

The experiment "manometer in the manometer" (animation)
Void in the void animation
  1. At the start of the experiment, the manometer, the vessel provided with the membrane and the storage vessel are filled with mercury. The manometer is hung in the membrane vessel above the mercury level and this is then tightly closed with a lid.
  2. The closed membrane vessel is then immersed in the storage vessel so that the membrane is completely below its mercury level. The pressure gauge display does not change when a rigid diaphragm is used.
  3. The membrane is then pierced or removed so that the mercury can flow from the membrane vessel into the storage vessel. The negative pressure created in the membrane vessel can be read on the pressure gauge. The liquid levels in the pressure gauge and in the membrane vessel each reach the same height above the surrounding liquid level.
  4. Through a U-tube, the negative pressure that has arisen can be compensated for by the supply of air and, moreover, even further increased, with the mercury in the manometer rising again and the liquid level in the membrane vessel falling further.
This proves that the height of the mercury column in a manometer depends solely on the ambient pressure.
Representation in Pascal's treatise (1663, p. 105)

In another version of the experiment, a glass tube bent into a double U shape is used as a manometer. When the mercury runs out of the tube, a vacuum area is created, which separates a column of mercury in the second, upwardly bent U-tube. The levels of the mercury column in the second U-tube are the same, which proves the existence of a vacuum in the area in front of it. If air is allowed to flow into this vacuum (through a hole previously blocked with a plug), the mercury column in the second U-tube rises like a normal barometer.

More experiments

Much better known than the experiments described here was Pascal's experiment carried out afterwards. He compared the column heights of a mercury barometer in flat terrain with that on a mountain, the Puy de Dôme, and was thus able to directly demonstrate the effects of the falling air pressure on the column height. Pascal did not carry out the experiment himself, but had it carried out by his brother-in-law Florin Périer (1605–1672) in Clermont-Ferrand (on September 19, 1648). In the place of Clermont-Ferrand it measured 71 cm column height at one point, on the mountain top 62.7 cm (the difference in height between the city and mountain top was a little over 1000 m). Even the 50 m difference in height in the cathedral of Clermont-Ferrand resulted in a 4 mm difference in the height of the columns.

In another experiment, Pascal used syringes instead of glass tubes and compared the weights of the syringes with spatially different vacuums (above the usual 760 mm mercury column) on a scale. He found that they weighed the same and concluded once more that the vacuum existed (and against cavities filled with vapors).

Pascal also observed the variability of the air pressure depending on the weather, i.e. the possibility of using the Torricelli barometer in meteorology .

In 1649 Otto von Guericke developed a piston pump with which a technical vacuum could be created in a simpler way. With the help of his vacuum pump and the Magdeburg hemispheres , Otto von Guericke was able to make the existence of air pressure and vacuum easier to understand and clearly demonstrate.

In 1660 Robert Boyle (with the assistance of Robert Hooke ) checked the dependence on the external air pressure by observing the column height of a barometer in a vacuum created with a pump in a glass bell.

literature

  • Edward Grant : La Nature a horreur du vide , in Les Grandes Expérience de la Physique Blaise Pascal: Comment at-il démontré l'existence de la pression atmospheric? Les Cahiers de Science et Vie, No. 27, June 1995, pp. 26-33
  • Henning Genz The Discovery of Nothing , Rowohlt 1999
  • Simone Mazauric Gassendi, Pascal et la Querelle du Vide , Presses Universitaires de France 1998
  • Matthew Jones: Writing and Sentiment: Blaise Pascal, the Vacuum and the Penseés , Studies Hist. Phil. Science, Vol. 32, 2001, p. 139
  • Kimiyo Koyanagi Pascal et le experience du vide dans le vide , Japanese Studies in the history of science, Vol. 17, 1978, p. 105 (and further work by Koyanagi on Pascal's air pressure experiments)
  • Christian Reidenbach: Article Empty , in: Stephan Günzel (Hrsg.): Lexikon der Raumphilosophie , Wissenschaftliche Buchgesellschaft, Darmstadt 2012, ISBN 9783534219315 , p. 230 f.
  • Károly Simonyi: The cultural history of physics. From the beginnings till now. Harri Deutsch, Frankfurt am Main 2001, ISBN 3817116519
  • Blaise Pascal: Traitez de l'équilibre des liqueurs et de la pesanteur de la masse de l'air , Paris 1663, Gallica (with Récit de la grande experience de l'équilibre des liqueurs in the appendix, p. 165)
    • Also in Léon Brunschvigg, Pierre Boutroux Oeuvres de Blaise Pascal , Volume 3, Paris 1923, Archives
  • Blaise Pascal, Lettre de Monsieur Pascal jeune a Monsieur Perier, du 15 November 1647 , in Brunschvigg, Boutroux Oeuvres de Blaise Pascal , Volume 2, pp. 153-162, Archives

Web links

Commons : Vide dans le vide  - collection of images, videos and audio files

Remarks

  1. ^ Letter of November 15, 1647, see Brunschvigg, Oeuvres II, the experiment is described on p. 156 and characterized as Vide dans le Vide .
  2. ↑ Strictly speaking, in Gasparo Berti 1642 he had a forerunner who carried out the experiment with water and found a water column height of 10 m, which corresponded to the limit height that had been known for a long time, up to which suction pumps could pump water from wells. But Torricelli used the much denser mercury (height of rise under normal conditions 76 cm) and was able to make the experiments so much more manageable. Another forerunner was Giovanni Battista Baliani .
  3. ↑ He reports on his experiments in Rouen, where he lived with his father, in Éxpériences nouvelles touchant le vide of October 1647.
  4. ↑ Edited after the death of Pascal von Périer and published in Paris in 1663. New edition Paris 1956.
  5. ↑ See Simonyi Kulturgeschichte der Physik , p. 234f, Friedrich Hund Geschichte der Physikalischen Demokratie , BI, 1972, p. 170, according to the description in the letter from Pascal to Périer 1647
  6. ↑ See illustration in Pascals Traitez , 1663, p. 105
  7. ↑ Who exactly had the idea for this experiment is controversial. Mersenne also expressed this idea in writing and it is sometimes ascribed to Descartes.
  8. ↑ Represented by Pascal in Récit de la grande experience de l'équilibre des liqueurs , Paris 1648 (with a letter from Périer to Pascal of September 22, 1648).