xxxviii INTRODUCTION. 



longer contained any of the ammonia, or other salt employe:!. The soil had, in some form or other, 

 retained the alkaline substance, while the water in which it was previously dissolved passed through. 



Further, (his 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 was 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 uncombincd form, but united to lime; instead of 

 sulphate of ammonia, we should find sulphate of lime in the solution; and this result was obtained, 

 whatever the acid or 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 alkaline solution wilh 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, \vas 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, therefore, 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 the property in question in a greater or less 

 degree. 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 carbonate 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, &c., 

 owing I The above experiments lead to the conclusion that it is due to the clay which they contain. 

 In (he language of Professor Way, however, &quot; 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 basis, and it soon became evident that the idea 

 of the clay, as a whole, being the cause of the absorptive property was inconsistent with all the ascer 

 tained laws of chemical combination.&quot; 



Alter a scries of experiments, Professor Way came to the conclusion that there is in clays a peculiar 

 class of double silicates to which the absorptive properties of soils arc due. He found that the double 

 silicate of alumina and lime, or soda, whether found naturally in sails or produced artificially, would 

 be decomposed when a salt of ammonia, or potash, &c., was mixed with it, the ammonia or potash 

 taking the place of the lime or soda. Professor Way s &quot;discovery,&quot; then, is, not that soils have &quot;absorp 

 tive properties that have long been known, but that they absorb ammonia, potash, phosphoric acid, 

 &c., by virtue of the double silicate of alumina and soda, or lime, &c., which they contain. 



Soils are also found to have the power of absorbing ammonia, or rather carbonate of ammonia, from 

 the air. 



&quot;It has long been known,&quot; says Professor Way, &quot;that soils acquire fertility by exposure to the 

 influence of the atmosphere, hence one of the uses of fallows. * I find that clay 



is so greedy of ammonia, that if air charged with carbonate of ammonia, so as to be highly pungent, is 

 passed through a tube filled with small fragments of dry clay, every particle of gas is arrested.&quot; 



This power of the soil to absorb ammonia is also due to the double silicates. But there is this 

 remarkable difference, that while either the lime, soda, or potash silicate is capable of removing the 

 ammonia from solution, the lime silicate alone has the power of absorbing it from the air. 



We have not the space to enter into the details of these investigations, or to point out their bearing 

 on practical agriculture. Suffice it to say that a w r cll- cultivated soil has the power of absorbing from 

 the atmosphere a considerable quantity of ammonia. We will suppose that the soil, by the decomposi 

 tion of its organic matter, and its power of attracting ammonia from the atmosphere, and from rain and 

 dew, receives annually fifty pounds of ammonia. If we grow a crop of wheat, barley, oats, rye, or Indian 

 c-nrn. from twenty to thirty pounds of this ammonia is evaporated into the atmosphere during the growth 



