| the different kinds of soil. 
| limestones, in which there are no other inorganic 
| their development. 
' depends is that of its invariably containing pot- 
| ash and soda. 
76 
The products generated by a plant may vary 
exceedingly, according to the substances given 
it as food. A superabundance of carbon in the 
state of carbonic acid conveyed through the roots 
of plants, without being accompanied by nitro- 
gen, cannot be converted either into gluten, albu- 
men, wood, or any other component part of an 
organ ; but either it will be separated in the form 
of excrements, such as sugar, starch, oil, wax, 
resin, mannite, or gum, or those substances will 
be deposited in greater or less quantity in the 
wide cells and vessels. 
The increase or diminution of the vital activity 
of the vegetables depends only on heat and solar 
light, which we have not arbitrarily at our dis- 
posal: all that we can do is to supply those sub- 
stances which are adapted for assimilation by the 
power already present in the organs of the plant. 
But what then are these substances? They may 
easily be detected by the examination of a soil, 
which is always fertile in given cosmical and at- 
mospheric conditions. Sand, clay, and lime are 
the names given to the principal constituents of 
Pure sand and pure 
substances except siliceous earth, carbonate or 
silicate of lime, form absolutely barren soils. But 
argillaceous earths form always a part of fertile 
soils. There must, therefore, be something in 
aluminous earth which enables it to exercise an 
influence on the life of plants, and to assist in 
The property on which this 
In order to form a distinct conception of the 
quantities of alkalies in aluminous minerals, it 
must be remembered that feldspar contains 17? 
per cent. of potash, albite 11°43 per cent. of soda, 
and mica 3—5 per cent.; and that zeolite con- 
tains 13—16 per cent. of both alkalies taken to- 
gether. The late analyses of Ch. Gmelin, Lowe, 
Fricke, Meyer,and Redtenbacher, have also shown, 
that basalt contains from ? to 3 per cent. of pot- 
ash, and from 5—7 per cent. of soda, that clay- 
slate contains from 2°75—3'31 per cent. of potash, 
and loam from 15—4 per cent. of potash. 
If, now, we calculate from these data, and from 
the specific weights of the different substances, 
how much potash must be contained in a layer 
of soil, which has been formed by the disintegra- 
tion of 26,910 square feet (1 Hessian acre) of one 
of these rocks to the depth of 20 inches, we find 
that a soil of 
Felspar contains : ; . 1,269,000 lbs. 
Clinkstone from 220,400 to . 440,000 ... 
Basalt ... 52,300 82,600 ... 
Clay-slate 110,000 220,400 ... 
Loam 95,800 330,600 ... 
Potash is present in all clays; according to Fuchs, 
it is contained even in marl; it has been found 
in all the argillaceous earths in which it has been 
sought. 
Air, water, and the change of temperature pre- 
AGRICULTURAL CHEMISTRY. 
pare the different species of rocks for yielding to 
plants the alkalies which they contain. A soil 
which has been exposed for centuries to all the 
influences which affect the disintegration of rocks, 
but from which the alkalies have not been re- 
moved, will be able to afford the means of nour- 
ishment to those vegetables which require alka- 
lies for their growth during many years; but it 
must gradually become exhausted, unless those 
alkalies which have been removed are again re- 
placed; a period, therefore, will arrive when it 
will be necessary to expose it from time to time 
to a further disintegration, in order to obtain a 
new supply of soluble alkalies. 
The exhaustion of much of the soil in Lower 
Virginia by successive crops of wheat and tobacco 
during a long period of time, proves the necessity 
of alkalies for these plants, for in the space of a 
century 13,200 lbs. of alkalies per acre were re- 
moved in leaves, grain, and straw, and the land 
became unproductive. When the soil is thus 
exhausted it requires the lapse of time for the 
action of air, water, change of temperature, and 
carbonic acid, to decompose fresh portions of the 
rocky constituents of the soil, and set free more 
alkaline matter. 
Potash is not the only substance necessary for 
the existence of most plants; indeed it has been 
already shown that the potash may be replaced 
in many cases by soda, magnesia, or lime; but 
other substances besides alkalies are required to 
sustain the life of plants. 
Phosphoric acid has been found in the ashes 
of all plants hitherto examined, and always in 
combination with alkalies or alkaline earths. 
Most seeds contain certain quantities of phos- 
phates. In the seeds of different kinds of corn 
particularly, there is abundance of phosphate of 
magnesia. 
Plants obtain their phosphoric acid from the 
soil. It is a constituent of all land capable of 
cultivation, and even the heath at Luneburg con- 
tains it in appreciable quantity. Phosphoric acid 
has been detected also in all mineral waters in 
which its presence has been tested; and in those 
in which it has not been found, it has not been 
sought for. 
It is evident that the seeds of corn could not 
be formed without the phosphate of magnesia, 
which is one of their invariable constituents ; the 
plant could not under such circumstances reach 
maturity. 
Some plants, however, extract other matters 
from the soil besides silica, potash, and phospho- 
ric acid, which are essential constituents of the 
plants ordinarily cultivated. These other mat- 
ters, we must suppose, supply, in part at least, 
the place and perform the functions of the sub- 
stances just named. We may thus regard com- 
mon salt, sulphate of potash, nitre, chloride of 
potassium, and other matters, as necessary con- 
stituents of several plants. 
Clay-slate contains generally small quantities 
