310 SOILS: PROPERTIES AND MANAGEMENT 



the necessity of taking time-temperature curves in the 

 unsteady state. His results, expressed as metric K (the 

 heat conductivity coefficient in C. G. S. units), show the 

 same general comparisons as already presented : — 



Heat Conductivity of Different Soils 



K in C.G.S. units 

 Soil (See Definition of 



Conductivity) 



Coarse quartz 000917 



Leonardtown loam . . . .000882 

 Podunk fine sandy loam . . .000792 



Hagerstown loam 000699 



Galveston clay 000577 



Muck 000349 



222. Effects of humus and structure on conductivity. — 

 A disturbing factor always present when soils are used 

 in the determination of the effect of texture on conduc- 

 tivity, is humus. It is evident, in dry soil at least, that 

 an increase in the organic content of a soil means a lower- 

 ing in conductivity. Humus, therefore, must be listed 

 as a second factor tending to vary the movement of heat 

 through soils. A third factor is the structural condition 

 of the soil under examination. Wagner 1 has shown in 

 this regard that the more compact a soil, the faster is 

 the conduction of heat. This is probably due to the more 

 intimate contact of the soil grains, and a consequent 

 cutting-down of the insulation factors and diminution 

 of the transfer resistance. 



223. Influence of moisture on heat conductivity in soil. 

 — The greatest single factor to be considered in conduc- 



1 Wagner, F. Untersuchungen iiber das Relative Warme- 

 leitungsvermogen Verschiedner Bodenarten. Forsch. a. d. 

 Geo! d. Agri.-Physik, Band VI, Seite 1-5 L 1885. 



