150 Review of Essays on Calcareous Manures. 



Lime in the form of carbonate, still possesses these mechanical 

 properties, and thus limestone, or shells even coarsely powdered, 

 will absorb the gases of putrescent bodies, render sand more reten- 

 tive of moisture, and convert a stiff clay into a friable loam. 



The alteration of the mechanical character of soils, is the first and 



most obvious effect produced by lime. For this purpose, it may be 



applied either caustic, as prepared by burning, merely pulverized 



from chalk or limestone, or in the form of disintegrated shells. The 



caustic form is more rapid but not more sure in its action, and the 



burning of limestone, w T hen this is the object, is no more than a 



cheaper mode of reducing it to powder, through the intervention of 



slaking;. 



When the soil contains inert vegetable matter, which has ceased 



to undergo fermentation, caustic lime will promote the putrefactive 

 process, and prepare it for the food of plants. If the process of fer- 

 mentation has stopped after the acetic stage, and left the soil acid, 

 either caustic or carbonated lime will neutralize the acid ; it will not 

 only thus prepare the soil to bear plants, which would not otherwise 

 grow, but, by removing the antiseptic action of the acid, permit oth- 

 er vegetable matter to undergo putrescence, and thus supply an ap- 

 propriate food for plants. 



The principal part of the food of all plants is derived from the 

 gases and soluble matters furnished by the decomposition of organic 

 bodies. These gases tend to expand and distribute themselves 

 through the atmosphere, with the exception of such as are soluble 

 in the moisture of the soil, or such as the earth may retain by me- 

 chanical attraction. Lime and its compounds have by far the great- 

 est powers in the last respect, and thus, if a soil is calcareous, it will 

 retain these elements of fertility, and give them out only as they are 

 required by the wants of the vegetables that grow upon it; it will be 

 but little injured by exposure to the air when uncovered, and will 

 retain its fertility longer. It will receive a greater quantity of ani- 

 mal and vegetable manure without poisoning the plants by excess of 

 nutriment, and the effects of a given quantity will be longer sensi- 

 ble. If the soil contain no carbonate of lime, this property may be 

 given artificially by manuring with slaked lime, which rapidly be- 

 comes carbonated ; with powdered limestone or chalk ; with marl in 

 the proper sense of the term ; or with recent or fossil shells. 



Here it might at first be imagined, that the more free a soil is 

 from calcareous matter, the greater the quantity of carbonate of 



