MEASURING OF HEAT 



129 



The time required to boil 

 the water away will be about 

 five times as long as to heat 

 the water from freezing point 

 to boiling. That is to say, 

 the steam has over five times 

 as much heat in it as boiling 

 water, although the temper- 

 ature of steam and boiling 

 water is the same (about 

 212 F.). 



To change 1 pound of 

 water into steam requires 

 970 Btu., and to raise the 

 temperature of 1 pound of 

 water from freezing point to 

 boiling point requires 180 Btu. 

 Again, the heat required to 

 change a liquid into a gas 

 is called latent heat. Heat 

 which will affect the ther- 

 mometer is called sensible 

 heat. 



FIG. 99. How much heat is used 

 to melt ice? What is the tem- 

 perature of the ice while it is 

 melting? What is the temper- 

 ature of the water after the ice 

 is melted? How much more 

 heat has a pound of water at 

 32 F. than ice at 32 F.? How 

 much more heat has a pound 

 of steam at 212 F. than a 

 pound of water at 212 F.? 

 How hot could you heat a half 

 a pound of water at 32 F. 

 with the same heat that was 

 used to melt a pound of ice? 



972 Btu 



212. F 



Calorics 



32'F 



-J&- 



or* 



To Hat 1 Gram ot Steam Trotn 100'C tolOO'G Retires t7.7 Calories 



