V. T E M P E R A T U R E D E T E R M I N A T I O N S 133 



Fahrenheit Scale. Tlie same t(niii)oratur(' range as in tlic jjic- 

 vioiisly (iescrilxMl scales is divided in the Fahrenlieit scale into ISO 

 equal parts called Fahrenheit degrees. The value of 32 is assigned 

 to the freezing point of water and 212 to the steam point. It is not 

 known why Fahrenheit used 32 divisions below the freezing point 

 as zero, hut it may have represented the lowest temperature he 

 could achieve with an ice-salt combination. It has also been sug- 

 gested that his zero was the lowest temperature he noted during a 

 particularly severe Danzig winter. 



Reaumur Scale. The Reaumur scale divides the same funda- 

 mental int(n'\al from the ice point to the boiling point into eighty 

 equal intervals of one degree each. This scale is not widely used 

 but is occasionally seen in biophysical papers. 



Convenient formulas for conversion from one to another of these 

 scales, where C — Centigrade, F = Fahrenheit, R = Reaumur, are: 



o 



°C V °R V ') 



F ^ -^-^ + 32 = -^^ + 32 (1) 



b 4 



(°F - 32) X 5 °RX5 

 C =^ - = -^ (2) 



2. Absolute (Kelvin) Scale 



In measuring temperature by expansion of matter, the magnitude 

 of a degree depends upon the nature of the i^articular substance used. 

 Thus, the Centigrade, Fahrenheit, and Reaumur scales are intensive 

 rather than extensive scales. In these scales there is no fundamental 

 temperature unit that can be successively applied to measure any 

 other temperature unit as can be done in the measurement of a quan- 

 tity such as length. The magnitude of a degree on one part of any 

 one of these scales may not be compared to the magnitude of a degree 

 on another part of the same scale. In addition, none of these scales 

 will accurately describe the full range of theoretical temperatures. 

 For example, liquid-in-glass thermometers have the limited tempera- 

 ture range from the freezing point of the exi)anding substance to the 

 softening point of glass. At low temperatures the phenomenon of 

 "superconductance" renders electrical resistance thermometers use- 

 less, and at high temperatures alterations in i)roperties of the metal 

 used cause the resistance to change, even at constant temperatvu'e, 

 below the melting point of the metal. Gas thermometry, although 



