218 TALKS OX MANURES. 



slowly through a bed of dry soil, five or six inches deep, arranged 

 in a flower-pot, or other suitable vessel, it was observed that the 

 liquid which ran through, no longer contained any of the ammonia 

 or other salt employed. The soil had, in some form or other, re- 

 tained the alkaline substance, while the water in which it was pre- 

 viously dissolved passed through. 



Further, this power of the soil was found not to extend to the 

 whole salt of ammonia or potash, but only to the alkali itself. If, 

 for instance, sulphate of ammonia were the compound used in the 

 experiments, the ammonia would be removed from solution, but 

 the filtered liquid would contain sulphuric acid in abundance 

 not in the free or uncombined form, but united to lime; instead of 

 sulphate of ammonia we should find sulphate of lime in the solu- 

 tion; and this result was obtained, whatever the acid of the salt 

 experimented upon might be. 



It was found, moreover, that the process of filtration was by no 

 means necessary; by the mere mixing of an akaline solution with 

 a proper quantity of soil, as by shaking them together in a bottle, 

 and allowing the soil to subside, the same result was obtained. 

 The action, therefore, was in no way referable to any physical 

 law brought into operation by the process of filtration. 



It was also found that the combination between the soil and 

 the alkaline substance was rapid, if not instantaneous, partaking 

 of the nature of the ordinary union between an acid and an alkali. 



In the course of these experiments, several different soils were 

 operated upon, and it was found that all soils capable of profitable 

 cultivation possessed this property in a gieater or less degeee. 



Pure sand, it was found, did not possess this property. The 

 organic matter of the soil, it was proved, had nothing to do with 

 it. The addition of carbonate of lime to a soil did not increase its 

 absorptive power, and indeed it was found that a soil in which car- 

 bonate of lime did not exist, possessed in a high degree the power 

 of removing ammonia or potash from solution. 



To what, then, is the power of soils to arrest ammonia, potash, 

 .magnesia, phosphoric acid, etc., owing? The above experiments 

 lead to the conclusion that it is due to the ckiy which they contain. 

 In the language of Prof. Way, however, 



"It still remained to be considered, whether the whole clay 

 took any active part in these changes, or whether there existed in 

 clay some chemical compound in small quantity to which the 

 action was due. This question was to be decided by the extent to 

 which clay was able to unite with ammonia, or other alkaline 

 baces; and it soon became evident that the idea of the clay as a 



