70 
THE CULTIVATOR.. 
their characters, also possess the property of absorbing gases; but 
they have this in a very inferior degree to lime and its compounds. 
As the gases generated by the decomposition of vegetable and ani¬ 
mal substances form a large part of the necessary food cf plants, 
it is obvious that a soil which contains the carbonate of lime, may 
retain and store them up for use, while they will be lost in soils of 
a different character. 
Carbonate of lime may also be made a most important article in 
the preservation of the most valuable parts of putrescent manures, 
until they can be applied to the soil. In this way marl is applied 
to a great extent in China; the night soil of their numerous popu¬ 
lation is there formed into cakes like bricks, with marl, and thus 
loses its offensive smell; but when these are applied as manure to 
the land, they give out the gases again as they are required for the 
nourishment of plants. So also in Norfolk, the site for dunghills 
is prepared by a layer of marl, which is incorporated with the ma¬ 
nure from time to time, and retains the gases which would other¬ 
wise be lost. 
Lime may therefore be applied in its caustic form in some cases 
in agriculture, for it will hasten the decomposition of animal and 
vegetable matters which might otherwise be inert; it will also neu¬ 
tralize acids, which experienced farmers well know to exist in ma¬ 
ny soils, which they in consequence call sour. But the latter pur¬ 
pose will be answered as well by the carbonate of lime, which may 
be applied as it exists in marl or shells, or as it may be prepared by 
grinding lime-stone. Caustic lime is also dangerous in its applica¬ 
tion, for it will corrode and destroy living vegetables, and hasten 
the decomposition of the vegetable matter of the soil to such a de¬ 
gree as to injure its fertility. Except upon turf-bogs, and land 
loaded with timber not wholly decomposed, quick or caustic lime 
ought not to be used; but to burn lime, and then by slaking to re¬ 
duce it to the form of fine powder, which is speedily carbonated by 
exposure to the air, is a more ready, and generally a cheaper mode 
of obtaining the carbonate in a convenient form, than to grind lime¬ 
stone to powder in mills. Yet for many of the most valuable uses 
of lime in agriculture, the latter method, if as cheap, would answer 
as well. 
Lime slowly combines with the earth silica, and produces a com" 
pound very different in character from either. It is this, to cite a 
fact in proof of our statement, which gives the hardness and solidity 
to ancient mortar. The carbonate of lime will serve to form this 
compound; and thus, when it has had time to act upon sand, it ren¬ 
ders a silicious soil more retentive of moisture; while, if applied to 
clay, by combining with its silicious matter, it renders it more fri¬ 
able ; and it is to the formation of this compound, by slow degrees, 
that we are inclined to ascribe the valuable mechanical properties 
of loamy soils, and the gradual amelioration produced by the use of 
lime, marl, and shells as a manure. 
Besides silica, alumina, and lime, an earth called magnesia is like¬ 
wise found in some soils. It is also, in the form of carbonate, a 
frequent constituent of limestones. This earth has many proper¬ 
ties in common with lime; like lime it is capable of neutralizing 
acids; and when deprived of carbonic acid by heat, corrodes vege¬ 
table substances. Tt probably also hastens putrefaction, and both 
it and its carbonate are capable of absorbing the gases let loose in 
that natural process. It is, however, of little interest in agricul¬ 
ture, except as a part of some of the limestones which are used as 
manure. These, if applied in large quantities, are sometimes very 
injurious to vegetation; the reason of this is, that magnesia does 
not repass to the state of carbonate as rapidly as lime, and there¬ 
fore contains its corrosive quality long after the lime has again be¬ 
come mild by its union with carbonic acid. In less quantities, how¬ 
ever, the magnesian limestones may serve as a manure, but their 
application requires great caution, particularly when the quantity 
of magnesia amounts to 25 per cent. 
All of the simple substances we have mentioned, except perhaps 
the last, either separate or in various states of combination, exist 
in plants. The manner and character of the combination is influ¬ 
enced by the vital action of the plant, which causes them to form 
compounds, often in direct opposition to the manner in which the 
ordinary laws of chemistry would di ect,. It thus happens that so 
soon as the plant ceases to live, these chemical laws, being no long¬ 
er impeded, begin to exert thei influence; and if it be in such a 
state as will admit of the several elements acting readily upon each 
| o'her, a decomposition, more or less rap d, of the vegetable struc- 
Jture ensues. It is a law of chemistry, that its action is always aid- 
led by the bodies being in a fluid state, and the action is often irn- 
| possible when the bodies are perfectly free from moisture. Hence 
the direct chemical action, and cons-quent decomposition, takes 
'place with greater certainty and more rapidity in green juicy and 
[succulent vegetables, than upon those which have been deprived of 
[moisture either naturally or artificially. Thus grass, if heaped up 
:in a recent state, decomposes, and if but partially dried, is heated, 
iand may even take fire, by the chemical action of its elements; 
while, if dried by exposure to the sun and air, and then laid up in a 
dry place in the form of hay, it is almost indestructible. A mode¬ 
rate degree of heat and access to air are also necessary to p’ornote 
the chemical action by which decomposition is effected. This de¬ 
composition is often attended with motion among the parts; and al¬ 
ways, if the mass has a liquid form, as in the expressed juice of ve¬ 
getables, or in the steeps employed by distillers and brewers; it 
goes in general terms by the name of fermentation. When the ve¬ 
getable matter abounds in starch, the first change is the conversion 
of this principle into sugar- Sugar, if thus formed, is next con¬ 
verted into alcohol, as it is, if it previously existed in the plant.— 
The presence of alcohol gives the liquid in which it exists the cha¬ 
racter of vinous liquors, and if these are permitted to remain in a 
turbid state, a farther fermentation converts them into vinegar ; and 
finally vinegar is farther decomposed, and the vegetable matter, 
giving out an offensive smell, is said to putrify. If the substance 
be not an an expressed juice or liquid steep, these several stages of 
fermentation ensue with rapidity, may be going on at the same time, 
and are sometimes so speedy in their course that no other action 
but the putrefactive fermentation can be detected. Animal bodies 
are subject to the same laws, and go through the same stages of 
fermentation, but the rapidity which they run into putrefaction is 
even greater; still there are some cases, as in that of milk, where 
the vinous stage can be occasionally, and the acetic distinctly, ob¬ 
served. Thus, a vinous liquor is prepared in some countries from 
milk, and the sour taste which appears in it when kept, arises from 
the presence of vinegar. 
In the several stages of fermentation, parts of the vegetable as¬ 
sume the form of gas or vapour, and are given out to the air. The 
gases which have been detected, are carbonic acid, a gaseous com¬ 
pound of carbon and hydrogen, and in some instances ammonia.— 
The vapour is that of water, which escapes in greater quantities 
than it would under ordinary circumstances, in consequence of the 
heat with which the process is attended. If exposed to rain, solu¬ 
ble salts, with earthy and alkaline bases, are washed from the mass. 
Finally, a mass of earthy consistence alone remains, which, on ex¬ 
amination is found to be made up of earths, insoluable salts, and 
carbon, being, in fact, identical with vegetable mould. 
We may hence infer that the following elements exist in vege¬ 
table bodies: 
1. Oxygen, developed in the carbonic acid and water. 
2. Hydrogen is in the water and carburets of hydrogen. 
3. Carbon. 
4. Earths. 
5. Alkalis. 
6. Nitrogen, occasionally developed in the form of ammonia. 
7. Acids, remaining in the insoluble, or washed away in the so¬ 
luble salts. 
The chemical examination of vegetable bodies ought of course 
lead to similar results. This examination has been conducted in 
three different ways. 
1. With the view of discovering the nature of the compounds, 
called vegetable principles, which exist ready formed in plants. 
2. For the purpose of discovering the chemical elements contain¬ 
ed in these principles. 
3. By the destructive action of heat, under which some of the ele¬ 
ments are wholly separated, and others enter into new combinations. 
In the first of these methods there have been detected: 
I. Certain peculiar acids, of which we may cite 
(1) Acetic acid,which, mixed with water, forms cemmon vinegar. 
(2) C trie acid, which is f und in the lemon and orange. 
(3) Malic acid, which exists in the apple. 
(4) Tartaric acid, in the juice of the grape. 
(5) Oxalic acid, in the wild sorrel. 
