THE EVOLUTION OF THE ELEMENTS. 
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positions — (1) that the properties exhibited by the atoms of 
elementary bodies are markedly different from those exhibited 
by the molecules of the same bodies ; (2) that the molecules of 
the elements may remain undissociated into their constituent 
atoms even at very high temperatures, in other words, that mole- 
cules are very stable systems ; but (3) that those molecules are 
decomposable ; and (4) that changes in molecular weights may 
occur amongelements or compounds, which changes are correlated 
with considerable modifications of the properties of those 
elements or compounds. 
I cannot but think that chemists have for many years had 
evidence before them which might warrant the statement that, 
in a certain sense, the elements are really compound bodies. 
The molecule is defined as the smallest part of a substance 
which exhibits those properties which are characteristic of that 
substance ; if the molecule be subdivided, a substance (or sub- 
stances) with new properties is produced. We have very 
distinct evidence in proof of the statement that when two 
gaseous elements — say chlorine and hydrogen — combine, the 
combination takes place between the atoms of these elements, 
which atoms are themselves first of all liberated from the 
state of mutual combination in which they existed in the 
molecules of the elements. The act of combination is pre- 
ceded by an act of decomposition. We call the product of the 
combination a compound, because its molecule is composed of 
different atoms; we call the bodies which have undergone 
decomposition elements, because their molecules are composed 
of similar atoms. 
But we are unable to isolate and examine those atoms of 
which the elementary molecules are composed. We believe that 
at the moment of the liberation of an element from a compound 
that element exists in the atomic condition ; we know that at 
the moment of liberation many gaseous elements are capable of 
performing actions which they are incapable of performing 
under ordinary conditions. 
We may probably say that in the production of hydrogen 
from water by the action of the electric current we have 
three distinct chemical changes occurring : viz. decomposition 
of the water molecules with the production of atoms of 
hydrogen and oxygen; combination of the hydrogen atoms 
with the production of what is known to us as hydrogen; 
and combination of the oxygen atoms with production 
of what is known to us as oxygen. In the second and third 
changes the products of each change are removed from the 
sphere of action ; the change proceeds with great rapidity. 
We cannot arrest the series of changes at the close of the 
first ; but we know that the introduction of certain substances 
NEW SERIES, VOL. III. — NO. X. K 
