HEAT AND EXPANSION 105 



ture, 180 B.T.U. raising it to the boiling point (212 F v \ 

 The rise in temperature ceases until all the pound of water 

 at 212 F. has been converted into steam, which requires 

 970.4 B.T.U. This is called the latent heat of vaporization 

 of water. When the steam is condensed to water, the same 

 amount of heat is given off. 



106. Steam Pressure. When steam is generated under 

 ordinary conditions it is termed " steam of one atmosphere" 

 (15 Ibs. per square inch). One cu. in. of water will produce 

 approximately 1 cu. ft. of steam (1728 cu. in.). If the 

 pressure is increased the volume is diminished; i.e., the 

 pressure varies inversely as the volume. Thus with a pres- 

 sure of 30 Ibs. the volume is only one-half of what it would 

 be under normal pressure. One cu. in. of water produces 

 864 cu. in. of steam under 30 Ibs. pressure. 



P : P' = V : V 

 15 : 30 = V : 1728 

 30 V = 15 X 1728 

 15 X 1728 



V = 



30 



V = 864 cu. in. 



107. Specific Heat. If equal amounts of copper and 

 water are heated, it becomes evident that it takes a great 

 deal more heat to raise 1 Ib. of water 1 F. than to raise 1 Ib. 

 of copper. The unit of heat has already been defined as 

 the amount of heat necessary to raise the temperature of 

 1 Ib. of water 1 F. The quotient obtained by dividing the 

 amount of heat required to raise the temperature of the substance 

 one degree Fahrenheit and that required to raise the tempera- 

 ture of an equal mass of water one degree is called the specific 



