SCIENCE OF THRESHING. IOI 



EXPLANATION OF THE TABLE. 



Column i gives pressures of from one to three 

 hundred pounds. These are not gauge pressures 

 obtained by reading the gauge, as these do not include 

 the pressure of the atmosphere, which is about 14.7 

 Ibs. per square inch. The gauge is set to register 

 zero when there is nothing but the air pressing on the 

 water in the boiler, and hence 14.7 Ibs. must be 

 added to all guage readings to obtain these ABSOLUTE 

 PRESSURES. 



Column 2 gives the temperatures to which the 

 steam rises when at the pressures of column i. 



Column 3 gives the HEAT OF THE LIQUID, or the 

 number of B. T. U. required to raise a pound of 

 water from 32 degrees to the boiling point corres- 

 ponding to the given pressure, or the amount of 

 energy which goes to do this work. 



The values in column 3 may be closely approx- 

 imated by subtracting 32 degrees from the tempera- 

 ture in column 2. This is not strictly correct for all 

 values, as the specific heat of the water, instead of 

 remaining at a constant, increases slightly. 



Column 4 gives the LATENT HEAT OF EVAPORI- 

 ZATION. This is the amount of energy which is 

 absorbed in changing water from the boiling point 

 to steam of the same temperature as the boiling 

 point of the water, and is measured again in the very 

 useful B. T. U. 



Column 5 gives the TOTAL HEAT OF EVAPORIZA- 

 TION, and may be obtained by adding the corres- 

 ponding values of columns 3 and 4. 



