V-] 



HEAT REQUIRED FOR EVAPORATION 147 



If the figures given by Oemler for the specific heats 

 of various soils be combined with their approximate 

 densities and with their minimum capacity for water, the 

 following results are obtained for the specific heats of 

 certain typical soils in a saturated but completely drained 

 condition : 



The sandy soil only requires about half as much heat 

 to raise its temperature by a given amount as would 

 be needed by the peaty or clay soil, when all the soils 

 are in a wet but thoroughly drained condition ; of course 

 if the clay or peat were inadequately drained, so that 

 a higher proportion of water was retained, their specific 

 heats would approximate still more nearly to that of 

 water. 



Just as a clay soil is slow to warm in the spring, its 

 high specific heat causes it to cool correspondingly 

 slowly after the heat of the summer. On clay soils 

 growth will be noticed to continue later into the autumn 

 than on the lighter lands. 



Heat required for Evaporation. 



The coldness of a wet and undrained soil is due, not 

 only to its high specific heat, but to the fact that so much 

 of the heat it receives is spent in evaporating some of its 

 retained water, without causing any rise in temperature. 



