246 now CROPS fEEI). 



surface in dry weatlier a portion of the ammonia Avhich 

 before was cliemically retained within it. 



Solubility of the Ammoiiia of the Soil.— The distinc- 

 tions between physically adliering and cliemically combin- 

 ed ammonia are difficult, if not impossible, to draw with 

 acciuaey. In what follows, therefore, we shall not attempt 

 to consider them separately. 



When ammonia, carbonate of ammonia, or any of tlie 

 following ammoniacal salts, viz., chloride, sulphate, ni- 

 trate, and phosphate, are dissolved in water, and the solu- 

 tions are filtered through or agitated with a soil, we find 

 that a portion of ammonia is invariably removed from so- 

 lution and absorbed by the soil. An instance of this ab- 

 sorbent action has been already given in recounting 

 Brustlein's experiments, and further examples will be here- 

 after adduced when we come to speak of the silicates of 

 the soil. The points to which we now should direct at- 

 tention are these, viz., 1st, the soil cannot absorb ammo- 

 nia completely from its solittions ; and, 2d, the ammonia 

 which it does absorb may be to a great degree dissolved 

 out again by water. In other words, the compounds of 

 ammonia that are formed in the soil, though comparatively 

 insoluble, are not absolutely so. 



Henneberg and Stohmann found that a light, calcareous, 

 sandy garden soil, when placed in twice its weight of pure 

 water for 24 hours, yielded to the latter joVo of its weight 

 of ammonia (=0.0002" |J. 



100 parts of the same soil left for 24 hours in 200 parts i 

 of a solution of chloride of ammonium (containing 2.182' 

 of sal-ammoniac =0.693 part of ammonia), absorbed 0.112 j 

 part of ammonia. Half of the liquid was poured off 

 and its place supplied with pure water, and the whole 

 left for 24 hours, Avhen half of this liquid was taken, and 

 the process of dilution was thus repeated to the fifth time. 

 In the portions of water each time removed, ammonia was 

 estimated, and the result Avas that the water added dis- 



