ELEMENTS OF SOILS. 221 



«iust at least l)e diliitcil willi iiitrogoMi, pise it destroys rallior than promotos the healthy 

 functions of organic lioclies; and as respects nitrogen hy 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 conij)oiind state. Elements in this state act as simple bodies: 

 they are homogeneous ; and when they enter into combination, it has the force of a simj)!e 

 substance. Every particle, however minute it may be conceived to be, is still con)poscd 

 •ol 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 arc 

 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 numl)ers only four elements, namely, oxygen, hydrogen, nitrogen, 

 and carbon. The second class comprises eleven elements, namely, silex, alumina, lime, 

 magnesia, potash, soda, sulj)liur, phosphorus, chlorine, iron, and perhaps manganese. 



Oxygen. When free, it is a gas, or an invisible aeriform ])ody. 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, tlie 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, tlie 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 liglit 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- 



