ELEMENTS OF SOILS. 
221 
must at least be diluted with nitrogen, else it destroys rather than promotes the healthy 
functions of organic bodies ; and as respects nitrogen by itself, we have no proof that it is 
ever received into the constitution of an organic body. We shall therefore consider the 
elements of soil in their compound state. Elements in this state act as simple bodies: 
they are homogeneous ; and when they enter into combination, it has the force of a simple 
substance. Every particle, however minute it may be conceived to be, is still composed 
of the same matter. In carbonic acid, the pure carbon of the particle is inert: it is the 
oxygen which combines and brings about the result. 
The elements, as now explained, may be divided into two classes : 1. Those which are 
essential to all organized bodies, and hence are called organic elements; and 2. Those 
which compose the inorganic world, and hence have received the name of inorganic mat¬ 
ter. The first class numbers only four elements, namely, oxygen, hydrogen, nitrogen, 
and carbon. The second class comprises eleven elements, namely, silex, alumina, lime, 
magnesia, potash, soda, sulphur, phosphorus, chlorine, iron, and perhaps manganese. 
Oxygen. When free, it is a gas, or an invisible aeriform body. Its weight is a little 
greater than that of atmospheric air. Its constitution is such that it is ready to combine 
with all other bodies; and, in the act of combining, it gives rise to one general pheno¬ 
menon, termed combustion : the only difference which belongs to specific cases, is the 
rapidity of combination, the end or result being exactly the same. Thus oxygen combines 
with iron, and forms the black or red powder, frequently called the rust of iron. If the 
combination goes on under the ordinary states of the air, it is an invisible action ; but after 
a few days, the surface is red, and the oxide is formed, consisting only of oxygen and iron. 
If, however, we contrive some means by which a rapid combination takes place, it is then 
accompanied with all the ordinary phenomena of combustion, the emission of heat and 
light; but here it is an oxide which is formed, and nothing else, and the difference of the 
two cases is one of time only; for, undoubtedly, just as much light and heat are produced 
in one case as in the other; just as much ice might have been melted by the slow com¬ 
bustion, or as much light emitted, as by the rapid one. So in all other cases there is a 
combination of oxygen with some other substance ; as when wood burns, light and heat 
are attendant phenomena, the combination proceeding with such rapidity as to render 
itself both visible and palpable ; but if the wood combines slowly with oxygen, as is the 
case when it rots, then time is required to make us sensible of the change, and yet the 
final result is but the reduction of the wood to the condition of an oxide as in the preceding 
case. The compounds which form in these and all other combinations, are called oxides , 
or acids., of the properties of which we will not now speak, but refer the reader to books 
of elementary chemistry. 
Oxygen is the controlling element of both organic and inorganic matter. Few sub¬ 
stances are known which are destitute of it; and even if the number were greater than it 
is, this would hardly affect the truth of the proposition. Its range of affinity is such, and 
so wide, that all the other elements are usually found in combination with it. Few func- 
