Chapter 7-PRINCIPLES OF MEASUREMENT 



(K) 



°C) 



TF) 



TR) 



FREEZING POINT OF GOLD 



FREEZING POINT OK SILVER- 



SOILING POINT OF SULFUR- 



BOILING POINT OF WATER- 



TRIPLE POINT OF WATER 



FREEZING POINT OF WATER- 



BOILING POINT OF OXYGEN- 



ABSOLUTE ZERO • 



1336.2 



12 34.0 



717.8 



373,15 



273.16 



273.15 



90.18 



1063.0 



960.8 



444.6 



100.0 



0.01 



-182.97 



-273.15 



1945.4 



1761.4 



832,3 



212.0 



32.018 



32.00 



-297.35 



-459.67 



2405.07 



2221.07 



1291.97 



671.67 



491.708 



491 .69 



162.32 



CONVERSION FACTORS 

 TEMP F -h 40= 1,8 (TEMP C-(-40) KELVIN 



1.8 (TEMP C) -(- 32 (INTERNATIONAL 



(*)(*)(*)(*) 



CELSIUS 



FAHRENHEIT 



TEMP F 



TEMP C = (TEMP F -32)/ 1.8 



TEMP K = TEMP C -I- 273.15 



PRACTICAL) 



RANKINE 



(FAHRENHEIT- 

 ABSOLUTE) 



33.11(147B) 

 Figure 7-1. — Comparison of Kelvin, Celsius, Fahrenheit, and Rankine temperature. 



range in which the thermometer is to be used. 

 Mercury (or mercury-thallium) is commonly 

 used because it is a liquid over a wide range 

 of temperatures (—60° to 1200° F) and because 

 it has anearly constant coefficient of expansion. 5 

 Almost all liquid-in-glass thermometers are 

 sealed so that atmospheric pressure will not 



Not all hquids are suitable for use in thermometers. 

 Water, for e.xample. would be an almost impossible 

 choice as a thermom.etric liquid at ordinary temper- 

 atures because its coefficient of expansion varies 

 enormously at temperatures near 0° C. In the temper- 

 ature range between 0° C and 4° C, water expands 

 when cooled and contracts when heated; thus it actually 

 has a negative coefficient of expansion in this range. 



affect the reading. The space above the liquid 

 in this type of thermometer may be a vacuum 

 or it may be filled with an inert gas such as 

 nitrogen, argon, or carbon dioxide. 



The capillary bore may be either round or 

 elliptical. In any case, it is very small so that 

 a relatively small expansion or contraction of 

 the liquid will cause a relatively large change 

 in the position of the liquid in the capillary tube. 

 Although the capillary bore itself is very small 

 in diameter, the walls of the capillary tube are 

 quite thick. Most liquid-in-glass thermometers 

 are made with an expansion chamber at the top 

 of the bore to provide a margin of safety for 

 the instrument if it should accidentally be over- 

 heated. 



129 



