J. A. Prescott 129 



where A = original amount of absorbed substance, 

 Y = amount already removed, 

 K = a, constant. 



Results were obtained in fair agreement with this assumption. 

 From the adsorption isotherm the rate of removal of absorbed sub- 

 stances can also be worked out. 



The concentration of the percolate at any moment must be related 

 to the equilibrium existing between the percolate and the soil. 



Using the same expressions as above: 



^ = K{A-Y)P 

 m 



is seen to be another form of the adsorption isotherm. This equation 

 still requires experimental confirmation. 



Applications to soil prohlems. 



The surface of soils. The absorption of dyes by soils is a purely 

 physical phenomenon and hence depends largely upon the surface of 

 the soil. A number of workers, Sjollema, Endell, Konig, Hasenbaumer 

 and Hassler, have suggested the use of this method as means of estimating 

 the colloids of the soil, assuming that only the colloids in the soil take 

 part in the absorption, which is hardly justifiable. J. A. Hanleyi 

 has reviewed this method and obtains equilibrium curves of the usual 

 type. Where such an equilibrium is established it is obviously difficult 

 to choose a suitable concentration of solution and Hanley points out 

 that the final equilibrium concentration of the solution must be the 

 same for every soil in order that the absorptions may be compared. 

 T. Tadokoro^ has obtained similar results and finds that the absorption 

 of dyestuffs is closely related to the hygroscopicity — but has no regular 

 relationship to the absorption of ammonia by the same soils. 



Soil acidity. 



The acidity of some soils has also recently been attributed to 

 absorption phenomena — in the case of humus soils; on the one hand 

 we have the view that the acidity is due to free acids, on the other 

 hand that it is due to a physical absorption of bases by the humus 

 itself leaving the acid free. Many soils give an acid reaction when 

 brought into contact with moistened litmus paper — the suggestion 

 has been made by Harris^ and others* that this is due to the absorption 



1 This Journal, 1914, 6, 58. - Journ. Tohoku Imp. Univ. Sajjporo, Japan, 1914, 6, 27. 

 3 Journ. Phjs. Cliem. 1914, 18, 355. * See F. K. Cameron, The Soil Solution, p. 61. 



Journ. of Agric. Sci. vni 9 



