MEASURING OP HEAT 



119 



ice box, and then poured into a pan which contains a spoonful of 

 hot melted lard? 



19. How does the weight of a cubic foot of water at 34 F. 

 compare with the weight of a cubic foot of water at 44 F., at 38 F., 

 at 90 F.? 



20. Boiled water contains no air. Why will boiled water upon 

 freezing cause a pipe to burst more quickly than water which has 

 not been boiled? 



MEASURING OF HEAT 



Thermometers. Since some metals and liquids expand equally 

 for an equal amount of heating, the amount of expansion has been 

 used to measure temperature. The usual kind of thermometer has 

 a glass bulb blown on the end of a fine-bore glass tube. The bulb 

 and part of the tube are filled with mercury, and the top sealed after 

 the air has been removed. Mercury is used for high temperatures 

 since it freezes at 38 F. and boils at 647.6 F. Alcohol thermom- 

 eters are invariably used in cold climates, for this liquid freezes at 

 202 F. below zero and boils at 173.5 F. 



There are three types of thermometers used. The Fahrenheit, 

 Centigrade and the Reaumur (Ra'o'mur). The relative values of 

 the degrees on the different thermometers are given in the following 

 table : 



THERMOMETRIC SCALES 



F. =|C. +32 =|R. +32. C. =f (F -32) =|R. 



History of the Thermometer. In 1592, Galileo, an Italian, 

 constructed the first thermometer, which was an air thermometer. 



