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Alcoholometer: here the scale does not show the density of the liquid, but its alcohol content (density less than that of water), which is why the scale values ​​increase upwards; Reading: 44  % vol. alcohol

The hydrometer (from Greek ἀραιός araiós "thin" and μέτρον métron " measure , scale"), whether Senkwaage , counterbore spindle , a hydrometer or hydrometer (from ancient Greek ὕδωρ HYDOR referred to as "water"), is a measuring device for determining the density or specific gravity of liquids .

In contrast, a pycnometer is used to determine the density of solids or liquids by weighing , and an aerometer for gases .

Measuring devices based on the hydrometer principle with paper scales, each adapted to a specific two-component system, can also be used to directly measure the composition of such mixtures , e.g. B. as an alcohol meter or alcoholometer to determine the ethanol content of a water / ethanol mixture. A special design of the suction lifter , in which a short hydrometer with a limited measuring range is inserted, serves as an "acid lifter" to determine the density of battery acid .

Measuring principle

The measuring principle is the Archimedes' principle : a body is immersed in a liquid until the weight of the displaced liquid corresponds to the weight of the immersed body ( static buoyancy ). This has two consequences:

  1. The smaller the density of the liquid, the further a body of the same weight will be immersed in it. (Scale aerometer)
  2. If a body is to sink in fluids of different densities or different specific weights up to a certain point, one must artificially increase its weight as much as the density increases. (Weight hydrometer)

Usual units of measure

Overview of the classic hydrometer scales
Unit / scale Unit symbol Reference temperature Relative density
ρ water > 1
Relative density
ρ water <1
field of use inventor Year of origin Distribution area
API level ° API 15.56 ° C Oil industry American Petroleum Institute 1921 United States
Degree balling ° Bg, ° Bal, ° Blg 17.5 ° C Must weight, sugar content, original wort (formerly) Karl Josef Napoleon Balling 1843 Europe, North America, South Africa
Degree barometer
(degree Eitner)
° Bk, ° Bark Leather industry Wilhelm Eitner worldwide
Degree Bates ° Bates Sugar content Frederick John Bates 1918 USA, UK
Degree Baumé (rational) ° Bé, ° Be, ° B 15 ° C Must weight, sugar content Antoine Baumé 1768 international
Degree Baumé (older scale) ° Bé, ° Be, ° B 17.5 ° C Must weight, sugar content Antoine Baumé 1768 Europe
Degree Baumé (French) ° Bé, ° Be, ° B 15 ° C Must weight, sugar content Antoine Baumé 1768 France
Degree Baumé (USA) ° Bé, ° Be, ° B 15.56 ° C Must weight, sugar content Antoine Baumé 1768 North America
Degree Baumé (Dutch) ° Bé, ° Be, ° B 12.5 ° C Must weight, sugar content Antoine Baumé 1768 Netherlands
Degree Beck
(Degree Beck-Benteli)
° Beck 12.5 ° C universal Philipp Friedrich Beck
Sigmund Friedrich Benteli
1830 Switzerland, Germany
Degree Brix
(Degree Brix-Fischer)
° Brix, ° Bx, ° Br, Brix,% Brix 15.625 ° C Must weight, sugar content, oil industry Adolf Brix
Carl Fischer
1870 English speaking countries
Cartier degree ° Cartier 12.5 ° C universal Jean-François Cartier France
Degree butcher ° Butcher universal Emil Fleischer 1876 Germany
Degrees Gay-Lussac
Degrees Tralles
(≈ Vol .-%)
° GL
° Tralles
15 ° C (° GL)
15.56 ° C (° Tralles)
Alcohol content Joseph Louis Gay-Lussac
Johann Georg Tralles
Europe (19th century)
Klosterneuburg sugar grades ° KMW, ° Babo 20 ° C Must weight, sugar content August Wilhelm von Babo 1861 Austria, Italy, Hungary, Slovakia and the states of the former Yugoslavia
Normalizovaný muštomer ° NM 20 ° C Must weight, sugar content Czech Technical Standard
Slovak Technical Standard
1987 Czech Republic and Slovakia
Degree Oechsle ° Oe 17.5 ° C Must weight, sugar content Ferdinand Oechsle 1836 Germany, Switzerland, Luxembourg
Degree Plato ° P 20 ° C Original wort Fritz Plato 1843 worldwide
Degree Quevenne ° Q 15 ° C Milk density Theodore Auguste Quevenne 1842 France
Degree sikes ° Sikes 20 ° C Alcohol content Bartholomew Sikes 1817 Great Britain until 1980
Degree Stoppani
Degree Richter
(≈ wt .-%)
° Stoppani
° judge
15.625 ° C Alcohol content Franz Nikolaus Stoppani
Jeremias Benjamin Richter
1795 (judge) Europe (19th century)
Degree twaddle ° Tw 15.56 universal, milk density William Twaddle 1776 Great Britain (19th century)

Constructive designs

Depending on the area of ​​application, the devices differ in their design, accuracy and type of measurement.

Scale hydrometers

The hydrometers in use today are mostly made of glass and have a thick float with an embedded, precisely defined amount of lead shot as weight and a thin handle in which the scale is located. Devices commonly used in the chemical industry are adjusted to a specific measuring temperature, which is normally 20  degrees Celsius ; they allow a reading accuracy of up to three decimal places . There are also examples that have a thermometer built in (see illustration on the right).


Areometer (scale above) with built-in thermometer (scale below)
  • Approx. 4/5 of the liquid to be determined is filled into a defined measuring vessel (ideally 250 ml standing cylinder , high design).
  • Depending on the approximately expected density of the liquid to be characterized, a suitable hydrometer is selected, i. H. with a measuring range that covers the expected density of the liquid.
  • The spindle is then immersed in the liquid with a rotating movement so that it is in a stable position and does not touch the edge of the measuring cylinder.
  • After the hydrometer has come to a standstill, the value at which the spindle penetrates the surface of the liquid is read from the lower meniscus .

An example of a scale aerometer is the Klosterneuburg must weigher .

Weight hydrometers

Nicholson's weight

Weight areometers (also called hydrostatic scales ) work according to the second principle explained above. They can be used to determine both the absolute and the specific gravity of a solid body , its density and the density of various liquids.

There are different systems that result in different construction methods: Fahrenheit , Tralles , Nicholson or Mohs . What they have in common is that they are made as a hollow body made of glass or sheet brass and are provided with bowls that are used to hold small weights and bodies. Thus, the Nicholsonsche hydrometer - see figure - of a hollow, conically closed brass cylinder  B . This bears a solid half brass cone C at the bottom  , on the base of which a body m to be examined  can be placed. At the top, the instrument has a thin metal rod  o and a plate A to hold  the small additional weights and the solid body to be weighed.

Placing a corresponding bit  m of the body under examination is on the bottom-mounted cone, so that it all around by the liquid surrounding, and additionally on top of the plate of the instrument. Then you put so many additional weights on top that an immersion up to a certain mark is achieved.

The density of a liquid in relation to the density of water can be determined by immersing the floating body of the weight areometer in both liquids up to the same mark with the help of different additional weights. Then applies in each case:


  • the mass  P of the float
  • Additional mass  p for the liquid to be examined
  • Additional mass  q for water
  • the volume V of the float (is considered to be constant in a first approximation).

It follows:


Another version of the weight areometer is the Mohr-Westphal balance .

The Galileo thermometer works on the principle of the weight areometer (and additional temperature influence) .


Hydrometers for different density ranges and liquids

The different uses result in a different division of the scale, since the density can be equated with a certain mixing ratio.


DIN 12790 regulates the basics for setting up and adjusting the hydrometers .

Important accessories

Hydrometer cylinder

  • Made of glass, not graduated, with hexagonal base and spout, 100 ml, 250 ml, 500 ml volume
  • Made of polypropylene (PP), with a spout and overflow vessel, so that the hydrometers can be read when the cylinder is completely filled, without causing acid damage or contamination. Temperature resistant up to approx. 135 ° C. The elasticity of the material reduces the risk of breakage of the hydrometer.

Cardanic suspension for glass cylinders, which guarantees through two mutually movable metal rings that the cylinder is in a vertical position during the areometric measurement.

Frame made of polyvinyl chloride (PVC) for setting up hydrometers at an angle, which ensures safe and easy access to the work table.


  • Hannelore Dittmar-Ilgen: How the cork crumbs get to the wine glass. Physics for connoisseurs and discoverers. Hirzel, Stuttgart 2007, ISBN 978-3-7776-1440-3 .
  • Jancis Robinson : The Oxford Wine Lexicon . 3rd completely revised edition. Hallwag, Gräfe and Unzer, Munich 2007, ISBN 978-3-8338-0691-9 .

Web links

Commons : Hydrometers  - collection of images, videos and audio files
Wiktionary: hydrometers  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. hydro-, hydro-, before vowels also hydr-, hydr-. duden.de, accessed on November 30, 2013 .
  2. Renate Wahrig-Burfeind (Ed.): True. Illustrated dictionary of the German language . ADAC-Verlag, Munich 2004, ISBN 3-577-10051-6 , pp. 403 .
  3. ^ Brockhaus ABC chemistry. FA Brockhaus Verlag, Leipzig 1965, p. 103.
  4. ^ Gerhard Meyendorf: Laboratory equipment and chemicals. People and knowledge Volkseigener Verlag, Berlin 1965, p. 218.