64 CALCAREOUS MANURES -THEORY. 



CHAPTER IX. 



ACTION OF CAISTIC LIME AS MANURE. CLASSIFICATION OP MANURES. 



The object of this essay is to treat only of calcareous earth (as before 

 defined) as a manure, and not of pure lime, nor of manures in general. 

 Still the nature of that which is properly my subject is so intimately con- 

 nected with some other kinds of manures, and is so liable to be confounded 

 with others which act very differently, 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 1 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 considering both its first and 

 later operations as belonging to one and the same manure. The connexion 

 between the manures is so intimate, and yet their actions so distinct, that it 

 is necessary to mark the points of resemblance as well as those of dif- 

 ference. 



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

 yond 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 tlie theory, and thence attempt to deduce its proper practical 

 use. 



By a sufficient degree of heat, the carbonic acid is driven oflf 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 lime 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 ani- 

 mal matters as were already decomposed, and fit to support growing plants, 

 are injured by the addition of lime ; as the chemical action which takes 

 place between these bodies forms different compounds, which are always 

 less valuable than the putrid or soluble matters were, before being acted on 

 by tlie lime.* 



This theory will direct us to expect profit from applying caustic lime to 

 all soils containing much unrotted and inert vegetable matter, as our acid 

 wood-land when first cleared, and perhaps worn fields, covered with broom- 

 grass ; and to avoid the application of lime, or (what is the same thing) to 

 destroy previously its caustic quality by exposure to the air, for all good soils 

 containing soluble vegetable or animal matters, and on all poor soils deficient 

 in inert, as well as in active nourishment for plants. The warmth of our 

 climate so much aids the fermentation of all putrescent matters in soils, 

 that it can seldom be required to hasten it by artificial means. To check 

 its rapidity is much more necessary, to avoid the waste of manures in our 

 lands. But in England, and still more in Scotland, the case is very different. 

 There, the coldness and moisture of the climate greatly retard the fermen- 

 tation of the vegetable matter that falls on the land ; so much so that, in 

 certain situations, the most favorable to such results, the vegetable cover is 



■ Davy's Agr. Clicm. Lcct- vii. 



