114 On Chemical Philosophy. 
electric contrivances: and it is evident that.on these principles 
the galvanic action will continue as long as these gaseous re- 
sults require and demand this power; and this must continue 
as long as the surface remains susceptible of oxidation, or capa- 
ble by the means described of producing these effects of decom- 
position. The cause, also, why the metal which has the strongest 
attraction for oxygen is always positive, while the other, having 
less, is negative, is explained on the same principles. ‘The 
oxygen after being separated from its combination with hydro- 
gen in the state of water, and when so separated and having 
demanded this power to hold it in solution—is again attracted 
to, and deposited on, the metal, so that this solvent is here again 
set at liberty ; whereas the hydrogen having no such attraction 
for the metal, the energies of this power are here not at liberty, 
Lut are taken up with holding this hydrogen in solution or in 
the gaseous state: and hence at this end the current of gas is 
seen to arise, while on the other no such current is perceived, 
though this is the positive point,—the power 1s THERE ; but be- 
ing unoccupied, it is tn its pure and attenuated state, and of 
course invisible. When wires are employed which are not oxy- 
dizable, then oxygen is given off at one end and hydrogen at the 
other ; or rather they appear to be given off at distinct and se- 
parate ends; for wherever oxygen is separated, there must 
hydrogen also, each portion of water being alike composed of 
both: but oxygen having a greater affinity for all metals than 
hydrogen, and this affinity being greater in some than others, it 
is detained by the point where this decomposition is going on, 
while the hydrogen is carried to the next metal—all which is 
beautifully proved by the arrangement of the cups, and by many 
facts of galvanism, which we must leave to be explained when 
we come to treat of all the facts classed under the head of Gal- 
vanism, and to which all this must still be considered as pre- 
paratory. The oxygen and hydrogen are given off at these 
points, and so far occupy the energies of this power. Here 
consequently it may be said, that as the oxygen is not deposited 
on the metal, it does not give up this power in the way just de- 
scribed, and therefore cannot be positive. It is not so indeed 
in so high a degree;—positive and negative are mere relative 
states of existence. The hydrogen occupying this power more 
than the oxygen, they are séi// relatively to each other positive. 
and negative, only not in so high a degree: the hydrogen requiring. 
about thirteen times more to give it the gaseous form, than the 
same weight of oxygen requires, they still remain to each other 
positive and negative, and the hydrogen of course negative. 
I am aware, as I have already stated in the former Essays, 
that this is not the common statement of the difference ir their 
capacity; 
