48 



A gricultural Che mistry. 



substance compared with that required to raise an equal weight 

 of water through the same range of temperature. Specific heat 

 (equal volume) is the relative amounts of heat required to raise 

 equal volumes of the material and of water through a given range 

 of temperature. 



Physical Properties of Soil Constituents. 



From the above table we see that the same quantity of heat 

 will raise 1 pound of water and 5 pounds of limestone or sand 

 to about the same temperature, or if we consider only the solid 

 constituents of soil, the same amount of heat will raise 3 pounds 

 of humus and 8 pounds of sand to the same temperature. 

 ^^Relation to heat. The sources of heat to a soil are the sun and 

 chemical changes within the soil. The chemical oxidation of 

 organic matter in the soil will slightly raise the temperature, but 

 by radiation are largely influenced by weather conditions. Ex- 

 tremes of heat and cold occur with a clear sky and dry air. In 

 a cloudy, moist climate, the variations in temperature are com- 

 paratively small. At mid-day the power of the sun's rays is at 

 (iepth of 1 foot, the average temperature of the soil, after a lapse 

 of 20 days was 2.3 higher than that of unmanured soil. Dur- 

 ing the next 5 days the excess of temperature was only 0.8. 

 Chemical action is at its height during the summer months. 



The amount of heat received from the sun and the amount lost 

 the effect is generally sligh^ ( In an experiment at Tokio, J;ip-m. 



