and recombinations within the vegetable organ- 
isms, which goes round a large circle or lengthens 
out to a prolonged series of feeding and vege- 
tating effects. A large quantity of the alkalies 
and the alkaline earths is united in plants with 
a great variety of acids which are formed by the 
vegetable organisms, and which can be found 
nowhere but in vegetable juices and secretions ; 
and all these alkalies, except perhaps in the few 
cases in which the vegetable salts may be sup- 
posed to spring direct from green manures or 
from the remains of dead plants or of dead parts 
of plants, must be derived from such a decom- 
position of mineral salts within the soil as drives 
the bases and the acids asunder, and allows the 
| former to pass into the plants and the latter to 
remain entirely in the ground. The liberated 
alkalies and alkaline earths of the strongest or 
most characteristic mineral salts, such as the 
sulphates, the muriates, the nitrates, and the 
carbonates, in many instances, form new salts, 
of slender affinities or of plant-feeding elements, 
such particularly as the humates, before entering 
the plants,—and so carry up to the organisms, 
not only their own substance for combination 
with the vegetable acids, but also some elements 
to be pushed asunder from that substance, and 
appropriated to other departments of nutrition ; 
and the acids of the decomposed mineral salts, 
when let loose on the soil, act on its most re- 
fractory constituents, such as its silica and its 
alumina, and form new mineral salts which, in 
their turn, play a similar part to that of the 
original salts. All the bases are thus digesting 
and carrying up the principles of the organic 
remains within the soil; all the mineral acids 
are attacking and reducing the constituents of 
gravel and slate and sandstone and metamorphic 
rocks and basalts within the soil; new supplies 
of bases are thus obtained, new absorbable pre- 
parations of organic remains are made, new 
evolutions of reducing acids are effected; and a 
continual circle of fertilizing process is thus go- 
ing round. The action of mineral salts, in the 
way of manure, hence appears at once clear, 
mighty, and manifold; and can readily be un- 
derstood to arise from very small doses; and, in 
all cases in which the requisite amount of basal 
and of organic matter exists in the soil, may 
easily be seen to be both certain and permanent. 
Salts viewed as agents in vegetation, however, 
owe all their peculiarity of action to their acids; 
and, in order that they may be duly understood, 
they must be distributed into two classes, the 
one with organic acids, and the other with in- 
organic acids. “Perhaps no principle in agri- 
culture,” says Dr. Dana, “is better established 
than that an excess of any salt, in the usual 
acceptation of that term, is a cause of barren- 
ness. Yet it is quite as well established, that 
the quantity of different salts admits of some 
latitude, and that some salts do produce better 
results than others. Referring to the acid con- 
SALT. 
123 
stituents of these salts, it will be found that 
some acids are organic; they consist of hydro- 
gen, carbon, oxygen, all which under the in- 
fluence of the living plant, may be dissociated, 
and their elements form geine. Other acids 
consist of oxygen and nitrogen, essential con- 
stituents of plants; others consist of chlorine; 
others of sulphur and oxygen, and others of car- 
bon and oxygen. In other words, the acids are 
composed of elements, which form food for plants, 
or of elements which enter in a small proportion 
only into the composition of plants. In the first 
case, the salts admit of a larger quantity being 
applied, than in the second. By the first, plants 
are fed,—by the second, they are poisoned; for 
the base of all salts acting, as has been explained, 
the acid is eliminated. If this is set free in 
large quantities, and its elements can be taken 
up and converted by the plant, well, good effects 
follow ; if on the other hand, the elements of the 
acid are such as the plant demands not, its pre- 
sence acts on the plant like poison on the animal 
economy. Let salts be divided into two classes, 
on this principle of the peculiarity of action de- 
pending upon the acid of the salts,—the first 
nourishes, the second poisons plants. The first 
class contains, first, carbonates—second, nitrates 
—third, phosphates. 
“The action of the first class is to be studied 
under its three divisions. First, the carbonates. 
These include a very large portion of all salts 
used in agriculture,—such as limestone, marble, 
old mortar, shells, and shell marl. In all these 
cases, the base or lime, let loose by the action of 
the living plant, acts at once as caustic lime 
upon insoluble geine and unconverted vegetable 
fibre, changing these into soluble vegetable food ; 
while the carbonic acid acts immediately upon 
silicates, decomposing these, and upon the geates 
in the soil, converting these into super-geates. 
Carbonates of alkalies, as ashes, &c., act at once; 
they are soluble, their alkali acts immediately 
upon the geine; their carbonic acid acts upon 
silicates and geine. Immediate and decided 
good effects follow their application; while car- 
bonate of lime acts slower. All fat acids or fats 
and oils, also act upon silicates, partly by their 
own acid properties and partly by the evolution 
of carbonate acid gas, which is evolved during 
their conversion into the acid state. The quan- 
tity of carbonate of lime which may be applied 
is unlimited, and the quantity of alkali depends 
on the presence of insoluble geine. The more 
abundant is the last, the more freely may alka- 
lies be applied. The carbonates include ashes of 
all kinds, and agriculturally viewed, all kinds of 
lime, for the quick soon becomes mild. The 
value of ashes in agriculture, depends upon their 
being a combination of salts, derived from plants, 
all of which have a powerful and decidedly bene- 
ficial effect. Peat ashes abound in carbonate, 
sulphate, and especially phosphate of lime. Free 
alkali may be always traced in peat ashes; but 
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