CHAPTER IX. 



ACTION OP CAUSTIC LIME AS MANURE. 



THE object of tins essay is to treat only of calcareous earth (as 

 before defined) as a manure, and not of pure caustic lime, nor of 

 manures in general. Still the nature of that which is properly my 

 subject is so intimately connected with some other kinds of manures, 

 and is so liable to be confounded with others which act very dif- 

 ferently, that frequent references to both classes have been and 

 will be again necessary. To make such references more plain and 

 useful, some general remarks and opinions will now be submitted, 

 as to the peculiar modes of the operation of various manures, and 

 particularly of lime. 



Until now I have been careful to say as little as possible of pure 

 or quick-lime, for fear of my meaning being mistaken, from the 

 usual practice of confounding it with calcareous earth ; or of con- 

 sidering both its first and later operations as belonging to one and 

 the same manure. The connexion between the manures is so inti- 

 mate, and yet their actions so distinct, that it is necessary to mark 

 the points of resemblance as well as those of difference. 



My own use of quick or caustic lime as a manure has not ex- 

 tended beyond a few acres ; and I do not pretend to know any- 

 thing from experience of its first or caustic effects. But Davy's 

 simple and beautiful theory of its operation carries conviction with 

 it, and in accordance with his opinions I shall state the theory, and 

 thence attempt to deduce its proper practical use. 



By a sufficient degree of heat, the carbonic acid is driven off 

 from shells, lime-stone, or chalk, and the remainder is pure or 

 caustic lime. In this state it has a powerful decomposing power 

 on all putrescent animal and vegetable matters, which it exerts on 

 every such substance in the soils to which it is applied as manure. 

 If the Jime thus meets with solid and inert vegetable matters, it 

 hastens their decomposition, renders them soluble, and brings them 

 into use and action as manure. But such vegetable and animal 

 matters as were already decomposed, and fit to support growing 

 plants, are injured by the addition of lime; as the chemical action 



portant of other operations and values of calcareous manures -which he pre- 

 sents, will be brought in view, and considered, at a later part of this 

 essay. Other passages confirming my opinions previously advanced, have 

 been or will be quoted in notes. 1849.] 



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