THE CULTIVATOR. 
57 
Mart, in the Sense in which the term is used by chemists, is a mix¬ 
ture of clay with carbonate of iime. The English writers on agricul¬ 
ture have not observed this distinction, and the term is sometimes ap¬ 
plied by them to a decomposed, chalk* which may contain little or no 
clay; and Sometimes to clay which contains iro carbonate of lime. In 
fact, the name is frequently applied by them to any earthy matter found 
below the vegetable soil, which is capable of increasing its fertility. 
From this misapprehension, the substances which go by the name of 
marl in New-Jersey, Maryland, and Virginia* do not correspond with 
the chemical definition, but are generally beds of fossil shells mixed in 
various proportions with earthy and saline matters of various kinds. 
Lime is a Substance very different in its characters from the two eart hs 
of which we have previously spoken. When prepared by heat from 
•any of the original forms of its carbonate, it retains their shape unal¬ 
tered, but may have its colour changed, and always loses considerable 
in weight. It is now acrid, caustic, and corrosive, and has some pro¬ 
perties in common with potash, which are therefore alkaline. Of these 
the most important is, that it unites with acids to form compounds in¬ 
cluded in the general class cf salts. Of the salts of lime Which are 
important to the farmer, the three principal are< the tarbonat a, which, 
as we have stated,- is found in limestone, chalk, shells, and marl; the, 
-sulphate, in which lime is combined with sulphuric acid, and which in 
combination with water is the substance so well known to our farmers 
tinder the name of plaster of Paris, or less familiary by that of gyp¬ 
sum ; the phosphate, which constitutes a large part of the bones of ani- 
Enals. 
Lime, when exposed to the air, attracts carbonic acid, which is al¬ 
ways to be found in the atmosphere; it thus passes back to the state of 
carbonate, but in so doing gradually falls to powder, and is then said 
to be air-slaked. If slaked with water, it also falls to a powder, which 
still retains the caustic character of the burnt lime; but this powder, 
when exposed to the air, unites ivith carbonic acid more rapidly than 
when in mass. 
Lime, in its caustic state, has the property of rapidly decomposing 
vegetable and animal substances, thus hastening the natural processes 
by which they are finally destroyed; or, to speak more properly, have 
their elements resolved into new combinations. The offensive and un¬ 
wholesome gases, which are given out by this composition, are absorb¬ 
ed by the lime, and prevented from mixing with the air. The same 
property is possessed in a less degree by the carbonate of lime, and pro¬ 
bably by its other compounds; but in order that either this earth or its 
compounds shall manifest this property, they must be in small fragments, 
or, which is better, in fine powder. 
Wet sand and plastic clay, and those soils to which they give their 
characters, also possess the property of aborbing gases; hut they have 
this in a very inferior degree to lime and its compounds. As the gases 
generated by the decomposition of vegetable and animal substances 
form a large part of the necessary food of plants, it is obvious that a 
soil which contains the carbonate of lime, may retain and stoi;e 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 population 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 manure from time to time, and retains 
the gases which would otherwise 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 vegeta- 
ble matters which might otherwise be inert; it will also neutralize acids, 
which experienced farmers well know to exist in many soils, which they 
in consequence call sour. But the latter purpose 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. Caus¬ 
tic lime is also dangerous in its application, for it will corrode and de¬ 
stroy living vegetables, and hasten the decomposition of the vegetable 
matter of the soil to such a degree as to injure its fertility. Except up¬ 
on tuif-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 reduce it to the form of fine powder, which is speedily car¬ 
bonated by exposure to the air, is a more ready, and generally a cheaper 
mode of obtaining the carbonate ia 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 compound 
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 mor¬ 
tar. The carbonate of lime will serve to form this compound ; and thus, 
Vo L. HI. 8* 
when it has had time to act upon sand, it renders a silicious soil more 
retentive of moisture; while, if applied to clay, by combining with its 
silicious matter., it renders it more friable; and it is to the formation of 
this compound, by slow degrees, that we are inclined to ascribe the va¬ 
luable mechanical properties of loamy soils, and the gradual ameliora¬ 
tion 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 fre¬ 
quent constituent of limestones. This earth has many properties in 
common with lime; like lime it is capable of neutralizing acids; and 
when deprived of carbonic acid by heat, corrodes vegetable substances. 
It 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 agriculture, except as a part of some of 
the limestones which are used as manure. These, if applied in large 
quantities, arc sometimes very injurious to vegetation; the reason of 
this is, that magnesia does not repass to the state of carbonate as ra¬ 
pidly as lime, and therefore contains its corrosive quality long after the 
lime has again become mild by its union with carbonic acid. In less 
quantities, however, the magnesian limestones may serve as a manure, 
but their application requiresgreat caution, particularly when the quan¬ 
tity 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 influenced by the vital 
action of the plant, which causes them to form compounds, often in di¬ 
rect opposition to the manner in which the ordinary laws of chemistry 
would direct. It thus happens that so soon as the plant ceases to live, 
these chemical laws, being no longer impeded, begin to exert their in¬ 
fluence ; and if it be in such a State as will admit of the several elements 
acting readily upon each other, a decomposition, more or less rapid, of 
the vegetable structure ensues. It is a law of chemistry, that its action 
is always aided by the bodies being in a fluid state, and the action is 
often impossible when the bodies are perfectly free from moisture. 
Hence the direct chemical action, and consequent decomposition, takes 
place with greater Certainty and more rapidity in green juicy and 
succulent vegetables, than upon those which have been deprived of mois¬ 
ture either naturally or artificially, Thus grass, if heaped up in a re¬ 
cent state, decomposes, and if but partially dried, is heated, and 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 moderate degree of heat and ac¬ 
cess to air are also necessary to promote the chemical action by which 
decomposition is affected. This decomposition is often attended with 
motion among the parts; and always, if the mass ijas a liquid form, as 
in the expressed juice of vegetables, or in the steeps employed by dis¬ 
tillers and brewers; it goes in general terms by the name of fermenta¬ 
tion. When the vegetable matter abounds instarch, the first change is 
the conversion of this principle into sugar. Sugar, if thus formed, is 
next converted into alcohol, as it is, if it previously existed in the plant. 
The presence of alcohol gives the liquid in which it exists the charac¬ 
ter 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 hot an expressed 
juice or liquid steep, these several stages of fermentation ensue with 
rapidity, may he going on at the same time, and are sometimes so 
speedy in their course that no other action but the pulrefactive fermen¬ 
tation can be detected. Animal bodies are subject to the same laws, and 
go through the same stages of fermentation, but the rapidity with 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, observed. 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 assume 
the form of gas or vapour, and are given out to the air. The gases 
which have been detected, are carbonic acid, a gaseous compound 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 pro¬ 
cess is attended. If exposed to rain, soluble salts, with earthy and alka¬ 
line bases, are washed from the mass. Finally, a mass of earthy con¬ 
sistence alone remains, which, on examination is found to be made up 
of earths, insoluble salts, and carbon, being, in fact, identical with vege¬ 
table mould. 
We may hence infer that the following elements exist in vegetable 
bodies: 
1 . Oxj'gen, developed in the carbonic acid and water. 
2. Hydrogen is in the water and carburets of hydrogen. 
3. Carbon. 
4. Earths- 
