HEAT: DISTRIBUTION AND MEASUREMENT 



73 



the water is all changed to steam, for 

 the heat energy is now used in 

 changing the liquid to a gas. 



The temperature which indicates 

 the boiling point of water is marked 

 212 on the Fahrenheit thermometer. 

 The space on the scale between 32 

 and 212 is divided into 180 equal 

 parts, each one of which is a degree. 



On the scale of the Centigrade 

 thermometer, the freezing point of 

 water is marked and the boiling 

 point 100. The change .of tempera- 

 ture between and 100 C. is, of 

 course, the same as between 32 and 

 212 F., and the change of tempera- 

 ture of one degree C. is therefore 

 greater than of one degree F. The 

 Centigrade thermometer is used in 

 most laboratories and in general scien- 

 tific work, and for all measurements 

 of temperature in many countries. 



To change degrees Centigrade to degrees 

 Fahrenheit : multiply the number of degrees 

 by 1.8 (or f) and add 32. Example: (100 

 C.X 1.8) +32= 212. 



To change degrees Fahrenheit to degrees 



Centigrade: from the number of degrees sub- FIG. JO. .LABORATORY 

 tract 32 and divide the remainder by 1.8 or f. 



fy-t oo T7i QO 



Example: - = 100C. 



THERMOMETER 



1. In what respects is 



1.8 



a laboratory thermometer 

 different from an ordi- 

 nary house thermometer? 

 2. Why are these differ- 



Since mercury becomes solid at 

 about 40 below zero, mercury ther- 

 mometers are not used for very low temperatures. Alcohol 

 has a much lower freezing point than mercury and for this 



