Elements of Soil. 173 
proportion greater than one to five. Inert as vegetable life seems 
to be, it will bear no more; neither Mill 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 animated 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 flame. 
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 weight, 1 hydrogen and 8 oxygen. 
JYitrogen. This is a gas, remarkable it is said, for its negative 
properties. It is lighter than oxygen. Under ordinary circum- 
stances, 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, 
however, the electric spark is passed through a mixture of oxy- 
gen and nitrogen, combustion ensues, and nitric acid is formed. 
Lightning is supposed to effect a similar combination in its pas- 
sage through the atmosphere. Atmospheric air, which is con- 
sidered a mixture of these two gasses, 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 will mix as well in any other propor- 
tion as in that which composes the atmosphere. It is the propor- 
tion 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 destiny, 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 water, its capacity for solution under given conditions 
is limited. If the atmosphere was anhydrous, the bodies of ani- 
mals would be required to be anhydrous also; but the constitution 
of living bodies requires a great proportion of liquids. The phy- 
sical constitution of the atmosphere being determined, life, its 
function and its apparatus, are adjusted to those conditions. 
Carbon is a solid. The diamond is always referred to as an 
example of pure carbon, because, when burned, the residue is 
