VIII.] 



ABSORPTION OF AMMONIA 



251 



pure clay when shaken with 300 c.c. of ammonium 

 chloride solution of varying strengths. 



Thus from the weaker solutions a smaller total but a 

 larger proportion of the ammonia was removed by the 

 clay, and the removal was never complete. The view 

 of the process that is now more generally accepted is 

 that the first step is the practically instantaneous 

 adsorption by the soil of the ammonium ion of the 

 salt, the acid ion being set free. This acid ion then 

 proceeds to combine with an equivalent amount of 

 calcium or other base in the zeolitic silicates, thus 

 restoring the neutrality of the solution. This interpre- 

 tation is in harmony with the proportion in which the 

 ammonia is always shared between the soil and the 

 solution, and the fact that its withdrawal from solution 

 is never complete. Of course, in the field the amount 

 of soil is so enormously in excess that the absorption 

 of ammonium salts applied as manure is practically 

 complete. Thus at Rothamsted the presence of 

 ammonia in the drainage water is rarely detected, even 

 when heavy rain immediately follows the application of 

 the manures. 



The adsorption of ammonium salts by humus follows 

 much the same course as with clay. The ammonium 



