28 



THE son, SOLUTION 



The movement of moisture into a soil from an illimitable 

 supply is a comparatively simple phenomenon, controlled by a 

 rate law which may be expressed by the equation y n = kt when 

 y is the distance through which the movement has taken place; 

 t is the time, and k and n are characteristic constants for the 

 particular soil and solution. 1 This expression may be more 

 readily recognized as a rate formula when written dy/at = h.y m , 

 where A and m are constants for the particular system. The 

 first form of the equation promises to be the more useful. 

 This formula also describes the rate of advance of a dissolved 

 substance into the soil. 



Owing to irregularities in the soil column this equation is 

 more readily studied with capillary tubes or with such absorbents 

 as filter-paper or blotting paper. The following tables will, 

 however, give an idea as to its validity for soils. 



ALLUVIAL SOIL, GILA RIVER. 2 



DISTILLED WATER IN PENN. LOAM (/ = 21 C. ). 



1 See Bull. No. 30, Bureau of Soils, U. S. Dept. Agriculture, p. 50 

 et seq. ; also, The flow of liquids through capillary spaces, by J. M. Bell 

 and F. K. Cameron, Jour. Phys. Chem., 10, 659 (1906) ; see also, Wo. 

 Ostwald, 2 Supplementheft Zeitschrift Kolloidchemie, 1908, 20. 



* Computed from observations by Loughridge, Report Agr. Expt. Sta., 

 University California, 1893-94, p. 93. 



