THE CULTIVATOR. 
69 
ocean, the water which falls on the former in either of these forms 
is greater in quantity than that which falls on equal surfaces of the 
latter. Thus, by a wise and benevolent provision of providence, 
the water of the ocean is continually furnishing vapour, which is 
precipitated on the land for the support of vegetation and the sup¬ 
ply of springs, and whose excess is poured back into the ocean in 
streams and rivers. 
Water has been found by chemists to be a compound substance, 
made up of two elements. ' One of the^, which forms 8-9ths of its 
weight, is the gas already mentioned under thOname of oxygen; 
the other, a peculiar gas, known by the name of hydrogen. 
Hydrogen, when free, is the lightest of all known bodies, rising 
and floating in atmospheric air; it not only combines with oxygen, 
to form water, but with carbon to form a great variety of com¬ 
pounds—gaseous, liquid, viscid, and solid. It also combines with 
nitrogen, and forms a gas known by the name of ammonia, which 
is well known by the peculiar smell it gives to spirits of hartshorn 
(liquid ammonia.) 
Hydrogen also combines with sulphur, forming a gas known by 
the name of sulphuretted hydrogen; this exists in the atmosphere, 
but in such small quantities as only to be detected by the nicest 
chemical tests. Tt combines in like manner with phosphorus, form¬ 
ing phosphuretted hydrogen gas, whose presence iri the air is occa¬ 
sionally perceptible. 
Oxygen, as we have seen, unites with carbon, to form a gas 
which we have called carbonic acid. 
This receives the latter part of its name from its similarity in pro¬ 
perties to an extensive class of compound bodies, known by the 
name of the acids. The greater part of these, like carbonic acid, 
are combinations of inflammable bodies with oxygen. The most 
important of these in reference to our present object, are the sul¬ 
phuric and phosphoric acids; named from the two substances (sul¬ 
phur and phosphorus) which are their bases. Muriatic acid may 
also be mentioned here, although its composition is of a different 
character. Oxygen unites with other bodies to form a class of com¬ 
pounds known under the name of oxides. 
The acids unite with earths, alkalis, and metallic oxides, to form 
a class of compounds known under the general name of salts.— 
These are named from the two substances which enter into their 
composition: thus, the salt formed of sulphuric acid and the earth 
lime, is called sulphate of lime. The substances which unite with 
acids to form salts, are called the bases of the respective salts. 
Of these bases, the alkalis and earths are most important. Ot 
the alkalis, it is only necessary to know the names of two, namely 
potassa and soda, and to be aware that their distinctive properties, 
are: to possess an acrid taste, a caustic operation, to render oils 
capable of mixing with water, and to neutralize the properties of 
acids. 
The earth which chemists call by the name of silex or silica, is 
found almost pure in flint and rock crystal; it is also almost pure 
in sharp colourless sands, and is by far the larger part of sands of 
every description. So far as the farmer need know its properties: 
it is hard, rough to the touch, has no attraction for water, which it 
permits to filter through, or evaporate from it, with the greatest 
ease. It is capable of uniting with the other earths in compounds 
which are called silicates, and is the only earth which enters into 
the formation of soils uncombined with the others or with other ele¬ 
ments. 
The earth which chemists call by the naine of alumina, is so 
named because it is obtained by them in a pure form from the well 
known salt called alum, of which it is the basis. Its most marked 
characteristic is plasticity: that is to say, it may be formed into a 
paste with water, will then easily receive any form which may be 
given it, and retain that form unaltered, even by violent heat. It 
never exists in soils unmixcd, but in intimate association, or more 
probably chemical combination with silica, it is the well-known sub¬ 
stance called clay, or argillaceous earth. White clays are this com¬ 
bination nearly pure, and coloured clays often contain it with no 
other addition than metallic colouring matter. Clay retains the 
plastic property of alumina; it therefore causes soils to be reten¬ 
tive of moisture; and, when they dry, makes them form tough clods 
or crusts, similar in character to sun-dried brick. 
Soils which contain clay are often also mixed with sand, or with 
an excess of silica in grains, which does not enter into the compo¬ 
sition of the clay. Such a soil is less liable to form a tough crust 
than a pure clay, but it will require a very large proportion of sand 
to destroy this property altogether. 
Clay mixed with sandy soils renders them more retentive of mois¬ 
ture. Sand and clay have therefore been used as manures for each 
other; but it may reasonably be doubted whether all the advantage 
that has been anticipated by some from this process, can be realiz¬ 
ed, as such a mixture will be merely mechanical. 
Loamy soils are generally said to be mixtures of sand and clay; 
they undoubtedly usually contain both these earths, and even some¬ 
times a large excess of sand. But we shall give reasons for believ¬ 
ing that loams owe their peculiar value to a combination of clay 
with another substance, by which a change is produced in its che¬ 
mical characters. 
Lime is familiarly known to farmers by the same name that is ge¬ 
nerally used by chemists. It is obtained by the aid of heat from 
rocks which go by the name of limestones. These are combina¬ 
tions of lime with carbonic acid, which is fixed in them by chemical 
attraction, but which, when driven off by heat, takes the same form 
as the air of the atmosphere, or becomes a gas. This gas from this 
circumstance has been called faed air, by which name it is often 
known when causing the sparkling and froth of cider and beer.— 
The principal part of lime-stone is therefore called by chemists car¬ 
bonate of lime. Carbonate of lime is also found in shells, both 
those of living animals and those which exist in the ground in a fos¬ 
sil state. In the former it is mixed with animal ma'ter, which is 
more or less separated from the latter according to the time which 
has elapsed since the death of the shell fish. 
Marl, in the sense in which the term is used by chemists, is a 
mixture of clay with carbonate of lime. The English writers on 
agriculture have not observed this distinction, and the term is some¬ 
times applied by them to a decomposed chalk, which may contain 
little or no clay; and sometimes to clay which contains no carbo¬ 
nate of lime. In fact, the name is frequently applied by them to 
any earthy matter found below the vegetable soil, which is capa¬ 
ble of increasing its fertility. From this misapprehension, the sub¬ 
stances 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 
earths of which we have previously spoken. When prepared by 
heat from any of the original forms of its carbonate, it retams their 
shape unaltered, but may have its colour changed, and always loses 
considerable in weight. It is now acrid, caustic, and corrosive, and 
has some properties in common with potash, which are therefore 
alkaline. Of these the most important is, that it unites with 
acids to form compounds included in the general class of salts. Of 
the salts of lime which are important to the farmer, the three prin¬ 
cipal are: the carbonate, which, as we have stated, is found in lime¬ 
stone, chalk, shells, and marl; the sulphate, in which lime is com¬ 
bined with sulphuric acid, and which in combination with water is 
the substance so well known to our farmers under the name of plas¬ 
ter of Paris, or less familiarly by that of gypsum; the phosphate, 
which constitutes a large part of the bones of animals. 
Lime, when exposed to the air, attracts carbonic acid, which is 
always 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 with carbonic acid 
more rapidly than when in mass. 
Lime, in its caustic state, has the property of rapidly decompos¬ 
ing 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 unwholesome gases, which are given out by this 
composition, are absorbed 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 probably by its other compounds; but in 
order that either this earth or its compounds shall manifest this pro¬ 
perty, 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 
