CHAPTER III. 



PHYSICAL PROPERTIES OF SOILS. 



THE physical properties of soils necessary to be considered 

 are, density, weight, state of division, firmness and adhesive- 

 ness, power of imbibing moisture, power of containing water, 

 power of retaining water, capillary power, contractibility on 

 drying, power of absorbing gaseous matters, power of absorb- 

 ing heat, power of containing heat, and power of radiating 

 heat. 



The weight of a soil depends upon its density, or the 

 proximity and density of its particles. Dense soils retain heat 

 longer than light ones, and afford a firmer support to the roots 

 of plants. 



The following table, from Johnston, shows the relative 

 weight of several soils. 



A cubic foot of dry silicious or calcareous sand weighs 180 Ibs. 



" " Half sand and half clay " 95 



" " Of common arable land " 80 to 90 



" " Of pure agricultural clay " 75 



" " Of rich garden mold " 70 



" " Of a peaty soil "39 to 50 



The state of division of the particles composing the soil has 



an effectvupon its weight, as well as money value. A soil 



eomposecTof clay, sand, coarse and fine gravel and vegetable 



