TEMPERATURE 295 



latent heat given off during condensation. The greater the hygro- 

 scopic capacity of the soil the higher is the temperature produced. 



From the preceding table on page 294 it will he seen that peat 

 and ferric oxide gave the highest temperature, while quartz sand, 

 with its low hygroscopic capacity, gave the least increase. In 

 the next table the increases are not so large. 



Increase of Temperature by the Application of Liquid Water at 50 Degrees F. 



(10 Degrees C.) 2 



Quartz sand 18 F. ( .10 C.) 



Calcium carbonate (precipitated) 50 F. ( .28 C.) 



Kaolin 1.49 F. ( .83 C.) 



Hydrated ferric oxide 11 .88 F. (0.60 C.) 



Loss of Heat. While the soil is receiving heat through these 

 various sources it is losing it in several different ways. 



1. By Radiation. The amount of heat radiated from soils is 

 not directly affected by their color. The statement is made in 

 physics that good absorbers are good radiators. This is also true 

 that the heat lost by radiation and convection by one body to another 

 surrounding it is proportional to the temperature difference between 

 the two. Dark soils are good absorbers of the sun's heat, but they 

 have no tendency to lose it more rapidly because of their color, but 

 because they are warmer than poor absorbers or light colored soils, 

 and at night they all tend to cool to the temperature of the sur- 

 rounding atmosphere. Black soils having absorbed more heat will 

 have more to radiate, but there is no tendency for dark soils to 

 become lower in temperature at night than light-colored ones under 

 the same conditions. 



In order to determine the effect of color on radiation Bouyoucos 

 colored white sand and determined the radiation ratio as given in 

 the following table: 



The limitation Ratio of Different Colored Sandu 



