SOIL HEAT 



297 



therefore show different weights to the cubic foot. A 

 specific heat comparison based on weight, therefore, does 

 not yield a fair idea of the heat capacities of two soils. 

 The multiplication of the weight specific heat by the 

 apparent specific gravity of the soil in question will 

 obviously yield a volume specific heat, which is a 

 much more rational basis for comparison. A quota- 

 tion from Ulrich l makes clear the value of such a com- 

 putation : 



SPECIFIC HEAT OP SOIL EXPRESSED BY WEIGHT AND BY VOL- 

 UME OF SOIL 



It is evident that in the first case the specific heat is 

 governed by the organic content of the soils in question; 

 the greater the amount of organic material present, the 

 higher is the thermal capacity. Such is not the case when 

 the specific heat of the soil is calculated on a volume basis. 

 In an expression of the thermal capacity on this rational 

 basis, namely, that of volume, the apparent specific grav- 

 ity, or volume weight, is the dominant factor. The ad- 

 dition of humus when this method of expression is em- 

 ployed merely serves to lower the volume weight, and 



1 Ulrich, R. Untersuchungen iiber die Warmekapazitat der 

 Bodenkonstituenten. Forsch. a. d. Geb. d. Agri.-Physik, 

 Band 17, Seite 1-31. 1894. 



