106 ACTION OF SALTS. 



for some years, a gradual improvement in the limed 

 soil of the exhausted field, is perceived. The car- 

 bonate of lime begins to act on the silicates ; and 

 the alkalies of the silicates are eliminated. These 

 solve or decompose the geine and geates, which the 

 lime had locked up ; at the same time the silicic 

 acid acts on the carbonate of lime, volumes of car- 

 bonic acid gas are let loose. The carbonic acid it- 

 self reacts on silicates, eliminating a fresh portion of 

 alkali, and upon the geates, converting these into 

 super-geates. A round of change goes on, till per- 

 haps, every particle of vegetable food is withdrawn ; 

 crops are no longer raised. Having witnessed, 

 though slow to believe it, good effects from liming, 

 the farmer again applies it to the exhausted field ; 

 but no good effects can now follow, unless manure 

 or decayed vegetable matter is also applied. This 

 may be furnished in two ways, either artificially or 

 naturally, that is by allowing the scanty crop of all 

 sorts of weeds, grass, mullen, &c, to decay on the 

 soil where it grew. But this subject will be consid- 

 ered in another place. 



162. It has been attempted to show how the 

 contradictory and anomalous effects of lime are ex- 

 plicable, on the principle (145); and here the gen- 

 eral theory of the action of lime may be adverted 



