A Peculiar Condition of Iron 319

which seems to be one of some importance. An iron wire
curved into a fork is made to touch at its bend a wire provided
with an oxidised end; in this state of contact both are intro-
duced into nitric acid of sp. gr. 1.35 and 30°, so as first to
immerse in the acid the oxidised end; the fork will, of course,
not be affected. If now a common iron wire be put into the
acid, and one of the ends of the fork touched by it, this end will
immediately be acted upon, whilst the other end remains passive;
but as soon as the iron wire with the oxidised end is put out of
contact with the bend of the fork, its second end is also turned
active. If the parts of the fork rising above the level* of the
acid be touched by an iron wire, part of which is immersed and
active in the acid, no communication of chemical activity will
take place, and both ends of the fork remain passive; but by the
removal of the iron wire (with the oxidised end) from the bend
of the fork this will be thrown into chemical action.

As all the phenomena spoken of in the preceding lines are,
no doubt, in some way or other dependent upon a peculiar
electrical state of the wires, I was very curious to see in what
manner iron would be acted upon by nitric acid when used as
an electrode. For this purpose I made use of that form of the
pile called the couronne des tasses, consisting of fifteen pairs of
zinc and copper. A platina wire was connected with (what we
call) the negative pole of the pile, an iron wire with the positive
one. The free end of the platina wire was first plunged into
nitric acid sp. gr. 1.35, and by the free end of the iron wire the
circuit closed. Under these circumstances the iron was not in
the least affected by the acid; and it remained indifferent to the
fluid not only as long as the current was passing through it, but
even after it had ceased to perform the function of the positive
electrode. The iron wire proved, in fact, to be possessed of all
the properties of what we have called a passive one. If such a
wire is made to touch the negative electrode, it instantaneously
becomes an active one, and a nitrate of iron is formed; whether
it be separate from the positive pole or still connected with it,
and the acid be strong or weak.

But another phenomenon is dependent upon the passive state
of the iron, which phenomenon is in direct contradiction with
all the assertions hitherto made by philosophical experimenters.
The oxygen at the anode arising from the decomposition of water
contained in the acid does not combine with the iron serving as
the electrode, but is evolved at it, just in the same manner as
if it were platina, and to such a volume as to bear the ratio ofof course that direct contact between the two !