Staunton spectator, and general advertiser. [volume] (Staunton, Va.) 183?-1849, 1845-10-16

very well understood. Thus, on mixing t.
sether in solution three substances, of whic
the first is capable of uniting with either tn
second or third, if with the second it form
an insoluble compound and with the third
soluble compound, it will invariably unit
with the second to the exclusion of the third
II Sulphuric Acid, Lime and Oxide Of Iron b.
mingled together, the Sulphuric Acid vii
unite with the Lime, forming Plaster, to the
entire exclusion of Iron.
2nd. Quantity of matter. The influence oil
quantity of matter over the operations oil
chemical attraction are such that if one sub
stance untes with second in several differ
ent proportions, that compound will most
easily be decomposed which contains most Of
the second substance. Ofthe two compounds
of oxygen and lead in common use that
which contains most oxygen (red led) is
much more easily deprived of SO much of its
oxygen as to convert it into that which con-
tains least (litharge,) than that which contains
least is deprived of its oxygen altogether. In
efecting the decomposition Of a compound by
means of third substance, we generally use
more of that third substance than is absolute
y necessary to combine with the element of
the compound with which it does combine,
IN order that the decomposition may be speed
lily and perfectly effected.
oh. Light. That the direct rays of the sun,
were capable Of efTecling important chemical
changes, has long been known and in no
part OF creation, have we more striking in
stances of its power than in the vegetable
Kingdom. For instance, the green coloring
matter IN the leaves of plants is never formed
excepting under the action of light, and hence
plants which grow where light is exclud-
ed, are invariably white and this although
the chemical attraction which the elements
Of that green coloring matter have for each
other is believed to be invariable, the same
by night as by day, in darkness as in direct
sunshine.
9Th. Heat. Heat is one of the most impor-
tant chemical agents which we haze under
our control, in numberlcss instances, modify
ing and in some instances, even reversing the
operations of chemical attraction. The in
fluence which heat exerts over the operations
OF affinity seems to be owing principally TO
its repulsive influence over the particles of
matter manifested in driving those particles
asunder. As have already remarked when
speaking of the ii Law, where this effect is
produced upon solid body, lhus giving TO
the PARTICLES of that body perfect freedom of
motion among themselves, 1t is favourable to
chemical combination when this effect is
produced upon liquid body, thus converting
tina. liquid into gas and driving its parti-
ces beyond The reach of each others attrac-
lion, it is untavorable TO combination. In gen.
eral, when the elements of a compound are
very unequally expanded by heut, as where
one exists naturally as gas and the other
as liquid or solid, that compound can be
decomposed by heating it. For example;
limestone consists of lime, a solid, and car
bonic acid. a gas all that is necessary to
separate the former from the latter is the APP
plicaon OF heat; besides this, heat operates in
many cases In way not very well under
stood, but of which shall take occasion to
speak more at large hereafter.
9th. Electricity Leaving an examination
of the manner in which electricity influences
the operations of affinity for future part of
ihe course, will here, simply notice the fact,
that like heat 1t often mOdifes and even re-
verses the operations of affinity. Such being
lis influence, there is no absurdity involved,
in contending as some have recently done,
that electricity may be made use of TO pro-
mote the growth of plants; but whether it
can probably be applied to agricultural pur-
poses, is quite different question, and one
which can be settled by experiment alone. OF
all the different ways in which we can COM
mand electricity for application to plants, so
lar as those ways are pointed out by what is
now known OF the nature of electricity, will
give you full account in a subsequent lecture.
All the chemical changes which we are
able TO produce in natural bodies, are affected,
either by means of electric affinity, or else,
one or other of these six disturbing causes as
they are termed) just mentioned. These arc
the chemists tools ;-an invisible, an ntan-
gible sci of tools it is true, yet when we call
10 mind, the wonderful and almost endless
variety of changes produced by their action,
we will be Convinced that they mus; prove,
by no means all inefficient set of tools when
placed in skilful hands. To teach you the
use of these tools for agricultural purposes is
the great object Of agricultural chemistry.