Réaumur scale

Thermometer with Réaumur (left) and Celsius (right) scale, made in Langenselbold .

The Réaumur scale in degrees Réaumur ( unit symbols : ° Ré, ° Re, ° Réaumur, to a limited extent also ° R) as a unit for measuring temperature was introduced in 1730 by the French naturalist René-Antoine Ferchault de Réaumur . Degree Réaumur is not an SI unit .

The reference points on the Réaumur scale are the melting point of ice (0 ° Ré) and the boiling point of water (80 ° Ré) at normal pressure (1013.25 hPa ). Réaumur divided these two benchmarks into 80 equal degrees.

Réaumur's work was not particularly accurate, as he determined his temperature measurement results from the expansion of ethanol , which does not show any linear volume expansion behavior. The temperature difference of a degree Réaumur, which is actually thought to be the same, is different in different temperature ranges.

The Réaumur temperature scale was widespread in Europe, especially in France and Germany , but was gradually replaced by the Celsius scale because of its better predictability . After the official temperature measurement was changed from degrees Réaumur to degrees Celsius in 1901, the Réaumur temperature scale became almost meaningless. Today it is only used very rarely, for example in alpine cheese production in Switzerland or Italy and for the classification of syrup sugar . In today's metrology, it does not represent a legal unit in accordance with Directive 80/181 / EEC .

Comparison with other scales

conversion

Temperatures in degrees Celsius can be exactly converted using a numerical equation as follows:

 Degree Celsius : ${\ displaystyle \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} C}} = \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} R}} \ cdot 1 {,} 25}$ ${\ displaystyle \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} R}} = \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} C}} \ cdot 0 {,} 8}$ Kelvin : ${\ displaystyle \ left \ {T \ right \} _ {\ mathrm {K}} = \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} R}} \ cdot 1 {,} 25 +273 {,} 15}$ ${\ displaystyle \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} R}} = (\ left \ {T \ right \} _ {\ mathrm {K}} -273 {,} 15th ) \ cdot 0 {,} 8}$ Fahrenheit degree : ${\ displaystyle \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} F}} = \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} R}} \ cdot 2 {,} 25 + 32}$ ${\ displaystyle \ left \ {t \ right \} _ {\ mathrm {^ {\ circ} R}} = (\ left \ {t \ right \} _ {\ mathrm {^ {\ circ} F}} - 32) \ cdot {\ tfrac {4} {9}}}$

Fixed points

Fixed points of common temperature scales
Kelvin ° Celsius ° Fahrenheit ° Rankine ° Réaumur
Boiling point of water at normal pressure  373.150K 100,000 ° C 212,000 ° F 671.670 ° Ra 80,000 ° Ré
" Human body temperature " according to Fahrenheit 308.70 5  K 35, 555  ° C 96,000 ° F 555.670 ° Ra 28, 444  ° Ré
Triple point of water 273.160K 0.010 ° C 32.018 ° F 491.688 ° Ra 0.008 ° Ré
Freezing point of water at normal pressure 273.150K 0.000 ° C 32,000 ° F 491.670 ° Ra 0.000 ° Ré
Cold mixture of water, ice and NH 4 Cl 255.37 2  K −17, 777  ° C 0.000 ° F 459.670 ° Ra −14, 222  ° Ré
absolute zero 0 K −273.150 ° C −459.670 ° F 0 ° Ra −218.520 ° Ré

The fixed points with which the scales were originally defined are highlighted in color and converted exactly into the other scales. Today they have lost their role as fixed points and are only approximate. Only the absolute zero point still has exactly the specified values.

Individual evidence

1. ^ "Hard to kill" , secondversion.blogspot.com; Used in cheese making in Italy, Parmigiano-Reggiano. See Cheese, Padano Plain , photos.hhoffman.co.uk (using a digital thermometer in Réaumur to make cheese).