THE PHYSICAL PROPERTIES OF THE SOIL/ 



Dr. Ewald Wollny. 

 PAliT 2. 



III. — THE BEHAVIOR OE THE SOIL TOWARD WATER. 



The moisture of tlie soil comes partly from atmospheric precipitation, 

 partly from ground water. With a given amount of water the degree 

 of saturation of a soil may vary widely, depending upon (1) physical 

 condition, (2) depth, (3) position, (4) covering of the soil, and (5) course 

 of the meteorological elements. 



INFLUENCE OF THE PHYSICAL CONDITION OF THE SOIL. 



In this connection we must consider the various causes which bring 

 about the numerous complicated processes in the soil. 



Conduction of water in the soil. — If we suppose the soil to possess a 

 separate grain structure, the spaces between the grains may be re- 

 garded in their continuity as tubes, which possess capillary properties 

 if the particles are sufficiently small. The capillaiity ceases when the 

 diameter of the particles is more than 2 mm., and varies with smaller 

 particles than these to a greater or less extent according to the fineness 

 of the grains. 



With regard to the height to which water can be lifted from a lower 

 layer, and to the velocity with which this occurs, there is the general 

 law that water will be lifted the higher and the more slowly the finer 

 the soil particles and the richer the soil in colloid ingredients. Differ- 

 ent soils vary widely in this respect. Capillary height for clay often 

 exceeds 2 meters, but for sand of medium fineness it is generally 

 less than 0.4 meter. While, however, the maximum height is soon 

 reached in sands, the rise in clays is very slow. 



Similar behavior is observed in the conduction of water supplied from 

 above. The percolation of water through the soil meets with a certain 

 amount of resistance, due partly to capillarity, partly to adhesion and 

 friction between the water and the soil particles, all of which increase 

 with the fineness of the grains and the quantity of the colloid sub- 

 stances present. Ilence the depth and velocity of the percolation are 

 inversely proportional to the size of the grains and the richness of the 

 soil in colloid substances. 



'Continued from p. 774. 



853 



