A Peculiar Condition of Iron

329

care for its observation. When a solution of nitrate of silver
to which a little nitric acid had been added was used, there
was still no sensible immediate action on the iron. When the
solution was rendered very acid, then there was direct imme-
diate action on the iron; it became covered with a coat of
precipitated silver: the action then suddenly ceased, the silver
was immediately redissolved, and the iron left perfectly clear,
in the peculiar condition, and unable to cause any further
precipitation of the silver from the solution. It is a remarkable
thing in this experiment to see the silver rapidry dissolve away
in a solution which cannot touch the iron, and to see the iron
in a clean metallic state unable to precipitate the silver.

Iron and platina in an aqueous solution of nitrate of silver
produce no electric current; both act as platina. When the
solution is rendered a little acid by nitric acid, there is a very
feeble current for a moment, the iron being as zinc. When
still more acid is added so as to cause the iron to precipitate
silver, there is a strong current whilst that action lasts, but
when it ceases the current ceases, and then it is that the silver
is redissolved. The association of the platina with the iron
evidently helps much to stop the action.

When iron is associated with mercury, copper, lead, tin, zinc,
and some other metals, in an aqueous solution of nitrate of
silver, it produces a constant electric current, but always acts
the part of platinum. This is perhaps most striking with mer-
cury and copper, because of the marked contrast it affords to
the effects produced in dilute sulphuric acid and most ordinary
solutions. The constancy of the current even causes crystals
of silver to form on the iron as the negative electrode. It
might at first seem surprising that the power which tends to
reduce silver on the iron negative electrode did not also bring-
back the iron from its peculiar state, whether that be a state
of oxidation or not. But it must be remembered that the
moment a particle of silver is reduced on the iron, it not only
tends to keep the iron in the peculiar state according to the
facts before described, but also acts as the negative electrode;
and there is no doubt that the current of electricity which con-
tinues to circulate through the solution passes essentially between
it and the silver, and not between it and the iron, the lattei
metal being merely the conductor interposed between the silver
and the copper extremities of the metallic arrangement.

I am afraid 3^011 will think I have pursued this matter to a
greater length than it deserves; but I have been exceedinglyvolume as to bear the ratio ofof course that direct contact between the two !