VEGETABLE MANURES. 157 



lime, which, as all the analyses made in my laboratory 

 show, our limestone rocks, like those which have been 

 examined in England, contain. The amount of this valuable 

 ingredient, as well as the other inorganic matters present, 

 must exercise a considerable influence upon the eflfects which 

 they produce. 



244. Lime, when applied to the soil, produces changes 

 both in its texture and chemical composition, of great im- 

 portance to the farmer. Thus, it renders the stiff clays loose 

 and porous; and the numerous beds of limestone gravel, 

 derived from the crumbling down of limestone rocks, which 

 exist in many parts of Ireland, and are so frequently found 

 beneath the bogs, afford the farmer the very means required 

 for consolidating and improving the qualities of the surface. 

 There are, indeed, no soils in this country that would not be 

 materially benefited by the judicious application of this 

 valuable substance. 



245. How it adds to the fertility of the soil. — You have seen 

 that there is no plant which you cultivate that does not 

 require a considerable proportion of lime for its food ; it must 

 therefore be an essential ingredient of every productive soil ; 

 and as year after year it is carried away in your crops, it must 

 occasionally be applied. Upon soils formed by the crumbling 

 down of the clay-slate and granite rocks, its frequent ap- 

 plication is necessary', and to the farmers in the west of 

 Scotland, and in Down and Louth, limestone is absolutely 

 indispensable. But in addition to directly affording an 

 essential element to plants, it is also believed to act as a 

 powerful chemical agent in rendering accessible to your crops 

 the stores of fertilizing matters, locked up in an insoluble state, 

 in the rocky particles of the soil, in combination with silica. 

 In granite and many other rocks, silica exists in chemical 

 combination with potash, in a form in which it is but slowly 

 acted upon by the rain; but when these silicates (50) arc 

 crushed and mixed with hot lime, and water poured upon 

 them, it is found that after some time chemical changes are 

 produced, by which the silica and the potash are converted 

 into a form in which they can be dissolved in water, and 

 therefore serve for the nourishment of plants. These impor- 

 tant chemical changes must also, to some extent, take place 

 in the soil when it is mixed with lime. In many soils which 

 contain an excess of vegetable matter, like our peat bogs, 



