FERTILIZERS. 
249 
and employ it to form the tissues of plants, and those of the finest texture. Thus I have found 
silica in the floral organs of plants, particularly the cereals, which must have been in combination 
with an alkali or alkaline earth. Carbonic acid acting upon silicate of lime, will form a car¬ 
bonate ; the silica which is thus set free is comparatively a soluble substance, and may be taken 
into the vegetable. There is a strong affinity between silica and lime, and it has already been 
observed that one of the uses of lime is to decompose the silicates, as those of potash and soda. 
If lime is intermixed with organic matter, its valuable effects are increased ; thetlecomposition 
of the organic matter furnishes carbonic acid to the soil, which also becomes a solvent and an 
article of food for plants. Silicate of lime is not prepared for agricultural purposes, and is 
never applied to soils by itself: it may be formed, and often is, when impure limestones, those 
containing fine quartz, are burned in a kiln for lime. Some of these limestones, if carefully 
burned, would furnish fertilizers more valuable than the pure carbonate of lime; for instance, 
the limestones which contain iron, sand, magnesia, potash and soda—the hydraulic limes for 
example. These limestones, when burned, contain a greater number of the elements which 
plants require, and hence fulfil indications which pure unmixed lime will not. Burning pre¬ 
pares the materials, and renders them more soluble. But calcareous rocks of this description 
require to be burnt with great care ; the materials should not be fused. Whether the foregoing 
be true or not, the debris, or soil derived from these impure limestones, is rich in all the es¬ 
sential elements of food ; and, moreover, is more subject to decomposition. Compare the 
delthyris shaly limestone with the pure marbles, and we find the former undergoing decay 
continually. 
From the foregoing remarks on the salts of lime, the reader can not fail to recognize their 
importance to the farmer : not one of them but that is, in some way or other, connected 
with the growth of plants. Their effects are by no means uniform ; they all do not owe then- 
value to the base, or the lime, but each has its respective merits. Carbonate of lime is a fer¬ 
tilizer slow in its operation, and is of little or no account, unless carbonic acid is found in the 
soil to serve the purpose of a solvent to it. Water, holding in solution carbonic acid, dissolves 
the carbonate, or a bicarbonate is formed, which is soluble. It then enters the tissues of plants, 
and performs important functions, both in virtue of the acid and the base. 
Phosphate of lime is important from the acid—the phosphoric, with which it is combined. 
Here the acid is superior to the base. Though it is one of the combinations which form bone, 
yet phosphorus freed from lime is an important body in the animal frame. We are not wanting, 
then, in inducements to furnish phosphate of lime to our soils, seeing it plays a part so con¬ 
spicuous in the economy of animals and vegetables. 
Sulphate of lime is also important in its combined capacity, as well as in the elements which 
form this salt. Sulphur, like phosphorus, combines with organic matter, independent of, and 
free from lime. The same may be said, in a lesser degree, of nitrate of lime; nitrogen, one 
of its elements, is regarded as one of the most important bodies in the animal economy. 
In the several changes which are indicated, we learn something of the power of vegetables 
to decompose the compound bodies. Much greater power is possessed by vegetables than airi¬ 
ly Agricult oral Report — Vol. iii.] 32 
