100 CHEMICAL EQUILIBRIUM AND ANTAGONISM 



zone of the soil is not always the same. Salts readily 

 move through the soil and, on coming in contact with other 

 salts, chemical changes result. The toxicity of the salts 

 is also altered by the presence of other salts. 



Solubility of Alkali Salts. The solubility of the salts 

 commonly concerned with alkali work is presented in 

 Table XV. 



The wide difference in the solubility of the salts and the 

 importance of temperature is brought out from the above 

 figures. It will be noticed, however, that the quantity 

 of salts which may dissolve in water is several times the 

 quantity ordinarily found in extracts of soil from alkali 

 lands. 



Mass Action. In the discussion of alkali it is generally 

 assumed that the salts are stable or retain the same com- 

 position as they do in a simple solution. This stable con- 

 dition is not found, however. Analyses of different depths 

 of alkali soil, for instance, have indicated an apparent 

 change, under certain conditions, of part of the harmful 

 sodium carbonate into the much less toxic sodium bicar- 

 bonate as it was brought close to the surface where there 

 was more carbonic acid. 



In order that a clearer understanding of the conditions 

 favoring changes in the nature of the salts in the soil 

 may be had, a short discussion of the "Law of the Mass 

 Action" seems desirable. This law states that the amount 

 of chemical action is proportional to the active mass, or 

 molecular concentration of each of the reacting substances, 

 in unit volume. Quantitatively, this law may be expressed 

 in its most general form as follows: 



Assume the reaction 



nA + niB -f i^ pX + qY -f- 



