PHYSICAL INTER-RELATIONS IN SOILS 49 



losses of heat because of improper physical conditions 

 resulting from the long-continued presence of gravita- 

 tional water. (See Fig. 16.) 



72. Increased specific heat. It has already been 

 shown (paragraph 51) that practically five times as much 

 heat is required to raise the temperature of one pound of 

 water one degree, as for one pound of clay or loam soil, 

 and that, therefore, two times the amount of heat is 

 required to raise the temperature of a given weight of 

 soil with a 20 per cent water content one degree as for a soil 

 with no water content. The presence of any amount 

 of water in a soil above the best amount for crop-growing is 

 undesirable. It appropriates heat that would otherwise 

 be used, in part at least, in warming the soil with its proper 

 water content. In Fig. 14 are charted the temperatures 

 to which the same amounts of heat would raise 100 pounds 

 of the same soil but with different water contents. Curve 

 A shows the temperature effect of the amount of heat that 

 would raise 100 pounds of the dry loam soil ten degrees 

 in temperature, if the same heat were applied to the same 

 soil with any one of the water contents indicated ; curve 

 B, that which would raise 100 pounds of soil and its 20 

 pounds of water content 10 F. ; curve C (Fig. 15), that 

 which would raise 100 pounds of loam soil with its 20 per 

 cent water content from 32 F. to 65 F. ; curve D (Fig. 

 15), that which would raise the temperature of 100 pounds 

 of clay soil with a 30 per cent water content from 32 F. 

 to 65 F. ; curve E (Fig. 15), that which would raise the 

 temperature of 100 pounds of a sandy soil with its 15 per 

 cent (best) water content from 32 F. to 65 F. The 

 steepnesses of the curves emphasize the meaning of the 

 terms " warm soils " and " cold soils." They emphasize, 

 too, the agricultural importance of preventing the presence, 



