1819.] Sur PIdentité des Forces Chimiques et Electriques. 371 
gold and the temperature of the atmosphere would not vary 
much. It is possible, therefore, that metals may be discovered, 
which exist only in the state of vapour. Volatility then, or fixed- 
hess, can never enter into the definition of metallic bodies. 
Opacity, and the property of conducting electricity, which 
belong to the metals, exist in them in different degrees, as is 
obvious from the transparency of gold leaf and from the differ- 
ence between the conducting power of copper and iron. Such 
properties, therefore, cannot enter into the definition of a metal. 
What then, it will be asked, constitutes a substance a metal? 
Obviously its resemblance to other metallic bodies. It was by 
this successive comparison of bodies, as they were discovered, 
with those already known, that the class of metals:was formed 
and extended. Unless this had been the case, the characters 
ascribed to them could not have experienced so many variations. 
Definitions are merely modes of making ourselves understood. 
They do not constitute limits really fixed by nature. As the 
science advances, therefore, we must overleap these artificial 
bounds placed in our way by our predecessors. We must 
continue our comparisons. The limit of yesterday ought not to 
continue our limit to-day, if the new progress of the science 
requires a new one. Neglecting, therefore, all artificial distine- 
tions, we shall take as the basis of our classification some 
substance easily distinguishable, and we shall place next it some 
body that resembles it most ; and we shall go on in this way as 
long as it shall be possible to proceed. __ 
0 be.better understood, let us apply these principles to the 
class of metals. There is obviously a very great difference 
between the properties of gold and arsenic. The former is the 
most ductile of inorganic bodies, while the latter is so brittle as 
to be with great facility reducible to powder. Gold is exceed- 
ingly fixed, and cannot be volatilized by any heat which we can 
raise in our furnaces, while arsenic is volatilized by a heat of 
2°82 thermic metres. Gold is so little combustible that this pro- 
perty could not have been recognized in it except by means of 
electricity, or some of the most burning acids ; while arsenic is 
so inflammable that it burns with a strong flame at a temperature. 
comparatively low. If we compare arsenic with phosphorus and 
sulphur, we shall find the difference between it and these bodies 
much less striking. Phosphorus and sulphur indeed have a 
certain degree of transparency, and are bad conductors of élec- 
tricity ; while arsenic is opaque, and an excellent conductor. 
But how many points of agreement do we find to make up for 
these differences? All the three are volatile, have a strong smell, 
and act with energy upon living bodies. When united to oxygen, 
they form acids ; the acids which contain a maximum of oxygen 
are in all of them very fixed, while those containing less oxygen 
are volatile. Finally they combine readily with metallic bodies, 
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