152 Ox\ THE RATIONALE OF CERTAIN MANURES 



tity of water holding- carLonic acid in polution would not be 

 taken up by tlie rain-water which might penetrate the sub- 

 stance of the soil, whilst that which was dissolved afterwards 

 by muriatic acid was likely, in the course of years, to be 

 broug'ht naturally into a similar condition. 



These positions I illustrated by showing- that a soil ex- 

 hausted by growing- a series of crops without manure was in 

 point of fact more deiicient in those of their ingredients^ 

 which were in an active or immediately available condition, 

 than another which had been more recently manured, al- 

 though the passive ingredients present in the latter might 

 not be sensibly greater in amount. 



If these principles be admitted, we shall be naturally led 

 to inquire whether certain of the operations in agriculture, 

 which long- experience has sanctioned, may not derive their 

 advantage in part from accelerating- that process of disin- 

 tegration in the soil which renders it more amenable to the 

 influence of atmospheric agents. 



Thus, amongst the mechanical operations which may con- 

 tribute to bring about this result, I might instance ploughing, 

 and other means of pulverizing the soil, and of bringing- a 

 larger amount of surface into immediate contact with water, 

 carbonic acid, itc. 



Perha])s the discordant reports which are given us as to 

 the effects of subsoiling upon different descriptions of land 

 might be reconciled by considering- whether the latter was 

 in a condition to allow of its dormant ingredients being- ren- 

 dered available within a short period. 



But, without dwelling farther upon this and other opera- 

 tions belonging to the same class, I will proceed to consider 

 the chemical means by which the same end is, as I conceive, 

 likewise brought about, and amongst the rest m-ay allude to 

 the pi'actice of liming, which is now of much general use 

 throughout the coimtry. 



Its effect in rendering the organic matters more soluble, 

 or rather, as I should prefer to represent it, in promoting- 

 their decomposition, so as to render them better adapted for 

 supplying both carbon and nitrogen to growing plants, has 

 been already sufficiently explained by Professor Johnston, 

 and by others. Its action upon the inorganic matter, though 

 not altogether unnoticed, has perhaps been rather less at- 

 tended to. 



Yet, when we recollect that quicklime mixed with pounded 

 granite speedily liberates the contained alkali, as was first 



