206

Faraday's Researches

708. When a few drops only of nitric acid were added to the
vessel A, fig. 44, then the results were altogether different. In
less than five minutes bubbles of gas appeared on the plates P'
and P" in the second vessel. To prove that this was the effect
of the electric current (which by trial at e. was found at the same
time to be passing), the connection at e was broken, and plates
P' P" cleared from bubbles and left in the acid of the vessel B,
for fifteen minutes: during that time no bubbles appeared upon
them; but on restoring the communication at e, a minute did
not elapse before gas appeared in bubbles upon the plates. The
proof, therefore, is most full and complete, that the current
excited by dilute sulphuric acid with a little nitric acid in
vessel A, has intensity enough to overcome the chemical affinity
exerted between the oxygen and hydrogen of the water in the
vessel B, whilst that excited by dilute sulphuric acid alone has
not sufficient intensity.

709. On using a strong solution of caustic potassa in the
vessel A, to excite the current, it was found by the decom-
posing effects at e, that the current passed. But it had not
intensity enough to decompose the water in the vessel B; for
though left for fourteen days, during the whole of which time
the current was found to be passing, still not the slightest
appearance of gas appeared on the plates P' P", nor any other
signs of the water having suffered decomposition.

710. Sulphate of soda in solution was then experimented
with, for the purpose of ascertaining with respect to it, whether

a certain electrolytic intensity was also
required for its decomposition in this
state, in analogy with the result estab-
lished with regard to water (709). The
apparatus was arranged as in fig. 45;
P and Z are the platina and zinc plates
dipping into a solution of common salt;
a and b are platina plates connected by
wires of platina (except in the galvano-
meter g) with P and Z; c is a connecting
wire of platina, the ends of which can be

Fig. 45-

made to rest either on the plates a, b, or on the papers moistened
in solutions which are placed upon them; so that the passage
of the current without decomposition, or with one or two decom-
positions, was under ready command, as far as arrangement
was concerned. In order to change the anodes and cathodes at
the places of decomposition, the form of apparatus, fig. 46, wasif it were only because of its action as a nucleus