316 IMPROVEMENT OF THE SOIL 



etable matter forms, with alumina, a substance which is per- 

 fectly inert and useless (humate or geate of alumina). Lime 

 will decompose it, and form a soluble salt (humate or geate 

 of lime). 



Sulphate of iron, or copperas, exists also in many soils, and 

 is highly poisonous in its influence ; lime will decompose this 

 salt, and form sulphate of lime, or plaster, an effective ma- 

 nure. 



As lime soon becomes carbonated in the soil, if applied in 

 a caustic state, its action is nearly the same as when applied 

 as marl or ground carbonate. In both cases, the acid acts 

 upon the silicates, and decomposes them, hence lime will de- 

 compose the silicate of potash in spent ashes, and render the 

 the alkali active. 



(4) Lime acts as a retainer when it forms super-salts with 

 humic, crenic and apocrenic acids. It thus locks up the 

 vegetable matters, which it has converted into food, and this 

 is one rOTison of its injurious effects. Still the matter is re- 

 tained and will in the end all be appropriated. This effect 

 must take place whether the quantity is large or small ; but 

 if there is a small quantity of vegetable matter in the soil, a 

 large quantity of lime should not be applied. We have here 

 a solution of the mystery relative to the effects of lime. 



If lime is added in large quantities, and in a caustic state, 

 it induces decay of the humus, and the formation of carbon- 

 ic acid. It combines with both of the products, and if the 

 proportion of vegetable matter is small, it will form so large 

 a quantity of it into super-salts, as to injure the crop ; hence 

 it may be concluded, 1. That lime is useless on soils destitute 

 of vegetable matter, and that it will not render them capable of 

 sustaining vegetation. 2. That lime is often injurious on soils 

 containing but a small quantity of vegetable matter. 3. That 

 lime is highly useful, when applied to soils containing a large 

 proportion of humus. If therefore, lime is applied to soils, 



