222 
ELEMENTS OF SOILS. 
tions in vegetable or animal life are performed without its agency. The leaves of the 
forest trees are spread out to exhale it, and the roots fill the soil to suck up fluids which 
contain it. The lungs of animals expand to absorb it, and vitalize the currents of blood. 
Every organ, every tissue feels its stimulus. Every thing in nature is formed with refe¬ 
rence to it. The tiny insect and the feeble worm are subjected to its action. Every living 
being breathes it; and though of the cold-blooded class, no animal can subsist without a 
certain quantity to which its nature is adjusted : diminish that quantity, and the animal 
languishes and dies ; increase it, and the animal dies from a too rapid combustion of its 
organs. Perfectly organized bodies can not withstand the effects of oxygen, if made to 
inhale it in a proportion greater than one to five. Inert as vegetable life seems to be, it 
will bear no more: neither will it survive a dose less than nature has provided for it. 
Rocks and soils are but oxides. One half of the solid crust of the earth is oxygen. The 
waters and the air are combinations of it suited to the conditions of the existence of ani¬ 
mated nature, and these conditions are controlled by oxygen. 
Hydrogen. This is the lightest aeriform body whose properties have been examined : it 
is sixteen times lighter than oxygen. It is combustible, and, when slowly burned, emits a 
pale blue llame. If oxygen and hydrogen are brought together in contact with flame, 
the combustion is instantaneous, and followed with a report loud in proportion to the 
quantities employed. The product of the combustion is water, a result which proves 
synthetically the composition of this fluid ; the proportions being, by volume, 2 hydrogen 
and 1 oxygen; or, by Aveight, 1 hydrogen and 8 oxygen. 
Nitrogen. This is a gas, remarkable, it is said, for its negative properties. It is lighter 
than oxygen. Under ordinary circumstances, it is but feebly attractive of other bodies, 
even of oxygen ; and though their temperature be raised to the highest point which we 
can command in the furnace, they refuse to combine. If, hoAvever, the electric spark is 
passed through a mixture of oxygen and nitrogen, combustion ensues, and nitric acid is 
formed. Lightning is supposed to effect a similar combination in its passage through the 
atmosphere. Atmospheric air, which is considered a mixture of these tAvo gases, contains 
20 oxygen and 80 nitrogen, omitting decimals. This proportion has been regarded as 
indicating a chemical union ; but it seems to be explained by the fact that there is no more 
free oxygen in the universe, by which the air can be charged so as to alter the proportion ; 
for doubtless these two gases Avill mix as well in any other proportion as in that which 
composes the atmosphere. It is the proportion created, and to this organic bodies and 
beings are fitted. 
The physical properties of the atmosphere are no less important than the chemical. Its 
height, its density, and consequently its pressure, are subject to as little variation as its 
composition. When in motion, its weight is diminished. It is a solvent of water, which 
exists in its interstices as sugar in those of water ; and, like Avater, its capacity for solution 
under given conditions is limited. If (lie atmosphere Avas anhydrous, the bodies of animals 
would be required to be anhydrous also; but the constitution of living bodies requires a 
