Hypsobarometer


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A hypsobarometer or boiling barometer is an instrument for measuring altitude that makes use of the dependence of the boiling point of a liquid on the air pressure , which was used on expeditions to determine altitude in the 19th and early 20th centuries.

Gabriel Daniel Fahrenheit described it in 1724 in Treatises on Thermometry for the Philosophical Transactions of the Royal Society in London. Independently of this, this connection was also discovered by Robert Boyle .

functionality

The boiling temperature of a liquid depends on the air pressure. Figuratively speaking, a higher air pressure makes it more difficult for a particle to transition from the liquid to the gaseous phase. H. at higher pressure the liquid boils at higher temperatures, at lower pressure correspondingly at lower temperatures. The temperature at the boiling point is read on the hypsobarometer and the air pressure is calculated from this. If the ground pressure is known, the sea level can be determined from the boiling temperature. At normal pressure, water boils at sea level at 100 ° C.

Boiling temperature of the water depending on the air pressure
Air pressure (hPa) Temperature of

Water vapor (° C)

960 98.49
980 99.07
1000 99.63
1020 100.18
1040 100.73

The equilibrium between liquid and gaseous water is described with a good approximation by the Clausius-Clapeyron equation .

This measuring principle is limited by the slight decrease in the temperature of the boiling point per hPa of only 0.049 KDh. The temperature reading scale must be very high-resolution (0.01 ° C to 0.02 ° C). However, a range of 95-105 ° C is sufficient.

proof

  1. Klemm, Friedrich: Fahrenheit, Daniel Gabriel. In: Neue Deutsche Biographie 4. 1959, p. 746 , accessed on November 9, 2019 .
  2. ^ Löffler, Hans: Meteorologische Bodenmesstechnik (formerly: Instrumentenkunde) . In: German Weather Service (Ed.): Guide for training in the German Weather Service No. 6 . 3. Edition. Self-published by the German Weather Service, 2012, ISBN 978-3-88148-456-5 , ISSN  0459-0236 , MEASUREMENT OF METEOROLOGICAL ELEMENTS, p. 28 .
  3. jvo: Dictionary of geography. In: Spektrum.de. Retrieved November 9, 2019 .

See also