56 
THE CULTIVATOR. 
stances familiar to him, but Which may be absolutely necessary, or 
■will at any rate save waste of labor and loss of time, when the know¬ 
ledge acqmred by practice in one place is to be employed in a new situ¬ 
ation, and under a change of circumstances. 
It is the object of this introduction to exhibit, in such form as may 
be intelligible to those who have not made general chemistry an object 
of study, a Concise view of such of the laws and facts of that science, 
as are absolutely necessary for the agriculturist Who may wish to im¬ 
prove his practice, and which are more particularly required by those 
who wish to avail themselves of the knowledge contained in the sub¬ 
joined essay. To do this has been found no easy task. It would be in 
itself difficult, but to the author of this introduction has been more 
particulaly so, as he has for years been in the habit of imparting in¬ 
struction to those whose habits of life and thoughts are as remote as 
possible from those of the practical farmers; persons to whom the pe¬ 
culiar language of chemistry is an aid instead of an impediment; and 
who, with ample time at their command, have an opportunity of pur¬ 
suing the study of the science step by step. Fuily aware of these dif¬ 
ficulties, both general and peculiar, this attempt would not have been 
made, and certainly not persisted in, had it not have been for the in¬ 
stances of an intelligent, scientific, and successful farmer, who has 
urged the completion of the task as an object likely to be beneficial to 
those, who, with perhaps equal zeal and native powers of mind, have 
not enjoyed, like himself, the advantages of a scientific education. 
The atmosphere which surrounds our earth is the first object to which 
our attention should be directed. This is the vehicle of the moisture, 
which, whether it fall in the form of rain or dew, run in streams or 
issue from springs, is absolutely essential to the success of the farm¬ 
er’s labor. It is also, as we shall presently see, important to him on 
other accounts. 
The greater part of the atmosphere is made up of a mixture of sub- 
stancesj each of which has the same mechanical properties as the 
whole mass These air-like substances are known to chemists by the 
name of Gases. 
Of these gases, two make up by far the greater portion of atmosphe¬ 
ric air, and exist in it in the proportion of about four to one. That 
which is the largest in quantity and makes up nearly 4-5ths of the 
whole atmosphere, is called, in the Essay of M. Puvis, by the name of 
Azote, but is more usually known in English by the name of Nitrogen. 
This substance, although in the largest proportion, is the least im 
portant of the gases in its chemical effect. It does not aid in support¬ 
ing the life of animals, nor in maintaining the burning ( combustion ) of 
inflammable bodies. 
The part of the atmosphere which is absolutely necessary for these 
purposes, is called by the name of oxygen, and nearly makes up the 
remaining fifth part of atmospheric air. In its support of life it al¬ 
ways, and in maintaining combustion often, unites with a chemical 
element, which is called carbon. This is familiarly known as forming 
the principal part of charcoal. In its union with carbon, oxygen forms 
a peculiar gas known by the name of carbonic acid. 
Carbonic acid is always found in small quantities in the atmosphere, 
to which it is furnished by the breath of animals and the fumes of 
burning bodies. It is, when in considerable quantities, fatal to the 
life of animals, but is prevented from accumulating to an injurious ex¬ 
tent in consequence of its being taken up by water; it is therefore dis¬ 
solved, in proportions about equal to those in which it is formed, by 
rivers, lakes, the ocean, and the moisture of the soil. 
Water exists in the atmosphere in the form of vapor. The great 
source of this vapor is the extended surface of the ocean; and it is go¬ 
verned by a mechanical law, by which it is continually tending to dis¬ 
tribute itself uniformly over the whole surface of the earth. It may 
thus exist in as large quantities over the surface of the dryest land as 
over that of the ocean itself. The tendency to equal distribu ion is con¬ 
tinually counteracted by the changes in the sensible heat ( temperature) 
of the atmosphere, and of the surface of the earth, which follow the 
alternations of day and night, and the vicissitudes of the seasons. By 
these alternations and changes, the vapor is caused to fall ( precipitat¬ 
ed) in the form of rain, snow, hail, dew, or white frost, according to 
circumstances. As such changes of temperature are more frequent on 
the land than on the ocean, the water which falls on the former in 
either pf 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 vapor, 
which is precipitated on the land for the support of vegetation and the 
supply 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 these, which forms 8-9ths of its weight, 
is the gas already mentioned under the name 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 compounds—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 pe¬ 
culiar 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/ 
It combines in like manner with phosphorus, forming phosphuretted hy* 
drogen gas, whose presence in the air is occasionally 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 com¬ 
binations of inflammable bodies with oxygen. The most important of 
these in reference to our present object, are the sulphuric and phospho¬ 
ric acids; named from the two substances (sulphur and phosporus) 
which are their bases. Muriatic acid may also he mentioned here, al¬ 
though its composition is of a different character. Oxygen unites with 
other bodies to form a class of compounds 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. Of the 
alkalies, it is only necessary to know the names of two, namely potassa 
and soda, and to be aware that their distinctive properties, are: to pos¬ 
sess an acrid taste, a caustic operation, to render oils capable of mix¬ 
ing 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 de¬ 
scription. 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 fil¬ 
ter through, or evaporate from it, with the greatest ease. It is capa¬ 
ble of uniting with the other earths in compounds which are called sili¬ 
cates, and is the only earth which enters into the formation of soils un¬ 
combined with the others or with other elements. 
The earth which chemists call by the name 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 unmixed, 
but in intimate association, or more probably chemical combination 
with silica, it is the well-known subsiance called day, or argillaceous 
earth. White clays are this combination nearly pure, and coloured 
clays often contain it with no other addition than metallic colouring mat¬ 
ter. Clay retains the plastic property of alumina ; it therefore causes 
soils to be retentive 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 composition 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 moisture. 
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 realized, as such a mix¬ 
ture 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 sometimes a 
large excess of sand. But we shall give reasons for believing that loams 
owe their peculiar value to a combination of clay with another sub¬ 
stance, by which a change is produced in its chemical characters. 
Lime is familiarly known to farmers by the same name that is gene¬ 
rally used by chemists. It is obtained by the aid of heat from rocks 
which go by the name of limestones. These are combinations 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 fixed 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 carbonate of lime. Carbonate of 
lime, is also found in shells, both those of living animals and those 
which exist in the ground in a fossil state. In the former it is mixed 
with animal matter, which is more or less separated from the latter ac¬ 
cording to the time which has elapsed since the death of the shell fish. 
