EMPLOYED IN AGRICULTURE. 153 



established by Professor Fuclis, of IMiinicb, and lias since 

 been introduced as a practice of Mr. Prideaux, of Plymouth, 

 and when we recollect, moreover, that many of the clays and 

 claystones which compose the bidk of several rock forma- 

 tions in secondary and tertiary districts are derived from 

 granite rocks, we cannot doubt that the action of quicklime 

 upon the latter will be of an analogous description, and that 

 a liberation of the alkali present in the rock will be one of 

 the consequences of its application. 



Nor is this a mere matter of theory ; for I have myself 

 found that twice as much alkali could be extracted from the 

 soil of a portion of the Botanic Garden at Oxford, which had 

 been exhausted by growing- a number of successive crops of 

 poppies for fourteen years without any manure having been 

 employed, after it had been left in contact with slaked lime 

 for a fortnight, than was obtainable from it alone ; the solvent 

 employed for taking up the alkaline salt being in both 

 instances water impregnated with carbonic acid, allowed to 

 trickle slowly through the respective samples of soil. 



According to this view of its mode of a}iplication we can 

 more readily understand why it should be apjilicable to 

 argillaceous soils rather than to calcareous ones — not merely 

 because it sup])lies the lime which most plants require for 

 their organization, for this might be elfected by carbonate of 

 lime as well as by the pure earth, and indeed would scarcely 

 be required where, as is often the case, the clay contains in 

 itself a small per centage of calcareous matter, but because 

 clays usually contain alkali, whilst limestones do not. 



We may also explain why the frequent liming of a soil 

 tends to produce exhaustion ; for if the eifect of this sub- 

 stance be to convert its dormant ingredients into its active 

 ones, or to render their i)rinciples, which, from their state of 

 combination, were but s])aringly soluble, more immediately 

 available for the uses of the plant, it is plain that every fresh 

 application of it will tend to diminish more and more the 

 amount of these ingredients, not only by what is actually 

 taken up by the plants, but likewise what is gradually carried 

 away by the rains that percolate the soil. 



By too liberal a supply of lime, therefore, we seem to 

 be undoing the wise provision of nature, which aims at 

 counteracting the great solubility of the alkalies, by retain- 

 ing them in a state of combination with the other earths 

 from which they are slowly liberated ; thus antici])ating the 

 ingenious expedient of an illustrious chemist of the })resent 



