36 LAND DRAINAGE 



54. Warm and cold soils. Since the sands normally 

 carry less capillary water than do the loams, a given 

 amount of heat will raise the temperature of 100 pounds 

 of sandy soil, with its best water content, higher than 

 that of 100 pounds of loam. Therefore it is said that 

 the sands are warmer than the loams. (See Fig. 13.) 



Since clays normally carry more capillary water than 

 do the loams, a given amount of heat cannot raise the tem- 

 perature of 100 pounds of clay soil, with its best capillary 

 water content, as high as it will raise the temperature of 

 100 pounds of loam with its best moisture content. It is 

 said of clay soils, that they are colder than the loams. 

 Examine Figs. 14 and 15. 



55. Over-wet soils are cold soils. When a loam soil 

 carries 30 per cent of water instead of 20 per cent, it has 

 a half more water than it should carry. It will require 

 one-fourth more heat to raise the temperature of 100 pounds 

 of loam and 30 pounds of water one degree, than will be 

 required for 100 pounds of loam, and its 20 pounds of 

 water. The amount of heat required to raise the latter 

 combination ten degrees in temperature, would raise the 

 former combination only eight degrees. 



Soils are seldom too warm in temperate climates. 

 They are often too cold because of the presence of unde- 

 sirable quantities of water. An increase of water in a soil 

 increases the specific heat of the combination ; that is, it 

 increases the amount of heat required to raise its tem- 

 perature one degree. 



56. Heat of vaporization. Wherever evaporation 

 takes place, heat disappears (is rendered latent). This is 

 equally true whether it takes place from the surface of 

 a field, a block of ice, in a steam boiler, or from the moistened 

 finger held above the head for the purpose of detecting 



