62 THE SOIL SOLUTION 



chloride be passed through a column of soil, or cotton, or paper, 

 or any similar absorbent, the filtrate will not only be less con- 

 centrated than the original solution, but the potassium will be 

 found to have been absorbed to a greater extent than the 

 chlorine, that is, the percolate contains free hydrochloric acid. 

 The importance of this phenomenon for the conservation of the 

 desirable constituents of manurial salts, and the elimination or 

 leaching out of the less desirable constituents is obviously great. 

 Equally great perhaps, is the effect upon the reaction of the 

 soil, whether it be rendered temporarily alkaline or acid, an 

 effect of the very greatest importance for the growth of some 

 of our common crop plants 1 and for the lower soil organisms, 

 such as the bacteria, molds, together with ferments, enzymes, 

 etc., many of which are very sensitive to the reaction of the 

 media in which they may be, and which in turn are of undoubted 

 importance in determining the fertility of the soil for higher 

 plants. 



The absorption of a dissolved substance from solution by an 

 absorbent is in effect a distribution phenomenon and the simplest 

 formula to give quantitative expression to such a distribution is 

 C/C 1 = K when C is the concentration in the liquid phase and 

 C 1 the concentration in the solid phase, K being a characteristic 

 constant for the particular case under consideration. When a 

 chemical reaction or a change of state, chemical or physical, is 

 involved in the absorption in either dissolved substance or absor- 

 bent the formula becomes O/C 1 = K when n is a function which 

 may be very simple or very complex. Attempts to develop a 

 precise formula of this general type for the absorption by some 

 given soil, although such a formula would be desirable for 



1 See, The toxic action of acids and salts on seedlings, by F. K. 

 Cameron and J. F. Breazeale, Jour. Phys. Chem., 8, 1-13 (1904). It is 

 quite conceivable, for instance, that if the drainage conditions were not 

 exceptionally good under a heavy type of soil, it might be rendered 

 temporarily unfit for clover or alfalfa by a heavy application of potas- 

 sium salts or of sodium nitrate. The idea put forward by some authori- 

 ties that too long continued or over fertilizing renders soils acid, may 

 have better foundation than their theoretical reasoning would seem to 

 warrant. 



