82 THE SOIL. 



oxidation or decay. Excess of lime causes the aforesaid 

 destruction of the humose constituents. 



In the same degree as the acid humus, by the action 

 of hme, chsappears from the ground, the absoi-ptive 

 power of the latter for hydrated sihcic acid is increased ; 

 and the excess of this acid present loses its mobility in 

 the soil.* 



The action of lime, as we see, is so complex, that from 

 its favourable influence upon one field, it is scarcely ever 

 possible to form an oj)inion of its probable action upon 

 another field, the conchtion of which is unknown. This 

 is possible only when the causes of its favourable action 

 in the first case are clearly understood. 



Wlien hme has improved the condition of a field, simply 

 by neutrahsing the acid state of the soil, and destroying 

 the injurious excess of vegetable remains, the farmer will 

 in vain expect a favourable result from the application of 

 lime in the foUowing years, unless the same causes should 

 recur which had originally impaired the fertility of the 

 field. 



In a soil wherein there are putrescent and decaying 

 substances not a single plant will thrive, except mush- 

 rooms ; and it seems that every chemical process going on 

 in the neighbourhood of roots disturbs that of their own. 

 Decaying substances in excess, by generating too much 

 carbonic acid, injure even those plants which thrive par- 



* In an experiment made specially for the purpose, it was 

 found that a litre (about a quart) of forest soil, containing 30 per 

 cent, of humose constituents, absorbed from a solution of silicate 

 of potash only 15 milligrammes of silicic acid. But the same soil 

 mixed with 10 per cent, of washed chalk (carbonate of lime) ab- 

 sorbed 1140 milligrammes; and when mixed with 10 per cent, 

 of slaked lime instead of chalk, the absorptive power was increased 

 to such a degree, that a litre absorbed 31G9 milligrammes of silicic 

 acid. 



