300 



SOIL PHYSICS AND MANAGEMENT 



Patten has made determinations of the specific heat of soil types 

 of various classes as given in the following table : 



Specific Heat of Soils (Equal Weights) 



Norfolk sand 0.1848 



Hudson River sand 0.1769 



Fine sand (soil separate) 0.1799 



Fine quartz flour 0.1900 



Coarse sand (quartz) 0.1900 



Podunk fine sandy loam 0.1828 



Leonardtown silt loam 0.1944 



Hageratown loam 0.1914 



Galveston clay 0.2097 



Muck soil, 25 per cent of organic matter 0.1 566 



Humus has the highest and sand the lowest specific heat of soil 

 constituents. Wet soils require much more heat to raise their tem- 

 perature than dry ones. In case of a dry silt loam whose specific 

 heat is 0.23 if 20 per cent of moisture is added, its specific heat will 

 be raised to 0.36. One hundred pounds of dry soil would require the 

 application of 23 heat units to raise its temperature one degree, 

 while the same weight of the wet soil would require 36 heat units. 

 The latter would warm up much more slowly than the former. The 

 effect of varying amounts of moisture on the specific heat is here 

 shown : 



Effect oj Moisture on Specific Heat, Podunk Fine Sandy Loam 10 



2. Evaporation of Water. The temperature of soils is lowered 

 by the evaporation of water from them. In the change from a solid 

 to a liquid or from a liquid to a vapor heat is required to effect the 

 change. When the opposite change takes place heat is liberated. 

 When ice melts 80 calories (centimeter-gram system), or 144 heat 

 units (English system), are used in producing the changes in a unit 

 weight. When water passes into vapor, 537 calories or 966.6 heat 

 units are required, and when condensation takes place this heat is 



