PHYSICAL PROPERTIES OF SAND 



effect of its presence upon the physical texture of the soil. The im- 

 portance of the physical condition of a soil is apt to be overlooked by 

 a student of chemistry, but is often even greater than that of the 

 chemical composition. Eecently much attention has been paid to a 

 study of the physical properties of soils, and valuable information is 

 rapidly being accumulated, especially in America and Germany. 1 



The terms " light " and " heavy " as applied to soils possess a 

 meaning well known to agriculturists, referring to the ease of working 

 and really depending upon the tenacity or cohesion and not upon 

 relative weight. As a matter of fact, the specific gravities of " light " 

 and " heavy " soils are just the opposite to what the terms would 

 seem to imply, the specific gravity of quartz being 2*62, that of clay 

 2*50, that of humus 1*3. However, the numbers quoted are the true 

 specific gravities, i.e., they represent the weights of volumes of solid 

 quartz or solid clay compared with that of an equal volume of water. 

 The " apparent specific gravities " or the weights of given volumes of 

 dry soil or powdered material, compared with that of the same volume 

 ot water, are much lower, since there are air spaces between the par- 

 ticles of the soil or powder. 



The apparent specific gravity of powdered quartz is found to be 

 1'449, of clay I'Oll, and of humus 0*335 while that of a good arable 

 soil will usually be about 1*2, its real specific gravity being about 2*5. 

 Sand is thus the heaviest of the main constituents and humus the 

 lightest. 



Sand confers friability, power of draining quickly, and good con- 

 ductivity for heat upon a soil ; it also has a low specific heat, conse- 

 quently is soon rendered hot and cools quickly. 



The specific heats of various soil constituents are given in the fol- 

 lowing table : 



The average specific heat of a dry soil is 0-20 to 0'25 (equal 

 weights). 



The relative conductivities for heat are as follows : 



1 Vide Warington, " The Physical Properties of Soils " ; Wiley, " Agricultural 

 Analysis," Vol. I ; and King, " The Soil ". 



