106 APPLIED SCIENCE 



heat of the body. To illustrate: The specific heat of lead is 

 .031 while the specific heat of water is 1. This means that 

 it would require 31 times as much heat to raise 1 Ib. of water 

 one degree in temperature as it would to raise the temperature 

 of 1 Ib. of lead one degree. 



The following table gives the specific heat of the different 

 substances in which the mechanic and engineer are most 

 interested. 



TABLE OF SPECIFIC HEAT 



Water at 39.1 F 1.000 Copper 095 



Ice at 32 F 504 Lead 031 



Steam at 212 F 480 Coal 240 



Mercury 033 Air 238 



Cast Iron 130 Hydrogen 404 



Wrought Iron 113 Oxygen 218 



Soft Steel 116 Nitrogen 244 



108. Boiling Point and Vacuum Pan. At the sea level, 

 with an atmospheric pressure of 29.922 in. of mercury in 

 the barometer in other words at a pressure of 15 Ibs. on 

 the square inch water boils at a temperature of 212 F. 

 (100 C.). Above this level, the layers of atmosphere be- 

 come less dense and consequently exert less pressure. The 

 boiling point is, as a result, reduced several degrees below 

 212 F. With an increase of atmospheric pressure, as found 

 in a deep mine, the reverse takes place, and water requires 

 the application of several degrees of heat above 212 F. 

 before it actually boils. 



This variation of the boiling point of water under different 

 pressures is taken advantage of in many manufacturing 

 processes by the use of the vacuum pan. Under a reduced 

 pressure, produced by mechanical means, liquors can be 

 evaporated ancj poncentrated in the vacuum pan without 



