216 



Physics of the Soil. . 



Table of specific heat of dry soils. 



It is clear from this table that much more heat is re- 

 quired to raise the temperature of water through one de- 

 gree than of a like weight of dry soil, and hence that a 

 dry soil will warm in the sunshine more rapidly than a 

 moist soil can. 



261. Specific Heat of Wet Soil. The differences in the 

 weight per cubic foot of dry soils and the differences in 

 their water content greatly affect the specific' heat or the 

 rate at which the surface temperatures will rise under the 

 same conditions. 



Sand has a small capacity for water and on this account 

 is naturally warm, hut its greater weight per cubic foot 

 acts as an offset, tending to make it colder. If a loosely 

 packed clay loam weighs 70 Ihs. per cubic foot and a 

 sandy soil 106 Ibs. and the two hold 33 per cent, and 18 

 per cent, of water respectively, when capillarily satur- 

 ated, then the number of degrees F. that 100 heat units 

 will raise the temperature of a cubic foot of each soil when 

 saturated, half saturated and dry are given below: 



