I 



236 FERTILIZERS. 



frequently spoken of as calcareous manures ; but there are others, as the chloride of lime, ni- 

 trate of lime, phosphate of lime and silicate of lime, which are never spoken of under this de- 

 signation. In each of these compounds lime is the base ; and in each it is probably quite es- 

 sential to the effects which are produced. 



The most common form in which lime is employed as a fertilizer is tl i ^ I' a subcarbonate, 

 or partially slaked lime ; in this slate it still retains a slight caustic stale, but is not burning 

 and pungent. Lime, when first taken from the kiln, is caustic, and in this conr'ition it is too 

 active to be employed in agriculture ; it should be exposed to the air and alio-wcd to absorb 

 carbonic acid and water. During this exposure it swells and falls to a fine powder, and loses 

 its sharp causticity. If used in the condition in which it is first taken from the kiln, it destroys 

 the vegetable tissues, from its strong affinity for water ; it is too drying, it should, therefore, 

 be partially saturated with water and carbonic acid : it increases in bulk, during this absorp- 

 tion, to the amount, that one bushel will measure, after absorption, at least five pecks. 



Much has been said of the modus operandi of lime, and many opinions have been advanced 

 as to its value. When we know that lime is one of the essential constituents of plants, we 

 can have no doubt that one of the most important functions of lime in the soil, is to supply 

 this element to the plants directly ; and I think we may be satisfied that it is a nutriment, and 

 enters the tissues, as an essential part of the internal skeleton. No plant is destitute of lime ; 

 but in the bark or outside it exists in its maximum quantity. But besides this, some trees, as 

 well as plants, contain, as a whole, a much larger proportion than others : compare the analysis 

 of hickory with the white and red elm, and it will seem that lime is much more abundant in 

 the former than the latter. It is scarcely possible to manufacture common soft soap from the 

 ashes of the hickory, in consequence of the want of potash and the predominance of lime. In 

 what form lime is received into the roots of plants is not yet made clear, by well conducted 

 experiments. It is, however, probable that the carbonate or subcarbonate is decomposed in 

 the soil by an organic acid, as the crenic and apocrenic acids, which are generated in the soil 

 from vegetable matters, or from the decomposition of leaves and roots, and organic matters in 

 general. These matters absorb or combine with oxygen ; or in other words, they undergo a 

 slow combustion : and here I may remark, though the subject has been under consideration, 

 that in order that these vegetable matters may oxidise, dryness of the soil is required. When, 

 for example, they are saturated with water, they become peat ; if the soil is drained of water, 

 the capacity of the soil for air is increased ; it replaces the water, and hence the amount of 

 oxygen in the soil is increased, and combustion or oxidation is more perfectly performed. 



But to return to the consideration of lime. Lime, when added to the soil in the condition I 

 have slated, carries with it carbonic acid. This will be set free, provided the organic acids 

 are present in the soil. When free it acts with considerable energy on compounds which 

 contain phosphoric acids ; and it may, therefore, be regarded as an active agent in the decom- 

 position of many bodies in the soil, or in forming new combinations ; or it may be dissolved in 

 the water of the soil, and be absorbed by the roots of plants. But another effect of lime, es- 

 pecially where clay predominates, is to decompose the silicates of potash and soda, which 



