322 Faraday's Researches

described^ and illustrative of some conclusions that may be
drawn from the facts.

The influence of the oxidised iron wire, the transference of
the inactive state from wire to wire, and the destruction of that
state, are the facts I have principally verified; but they are so
well described by Professor Schoenbein that I will not add a
word to what he has said on these points,, but go at once to other
results.

Iron wire, as M. Schoenbein has stated, when put cdone into
strong nitric acid, either wholly or partly immersed, acquires
the peculiar inactive state. This 1 find takes place best in a
long narrow close vessel, such as a tube, rather than in a fiat
broad open one like a dish. When thus rendered quiescent by
itself, it has the same properties and relations as that to which
the power has been communicated from other wires.

If a piece of ordinary iron wire be plunged wholly or in part
into nitric acid of about specific gravity 1.3 or 1.35, and after
action has commenced it be touched by a piece of platina wire,
also dipping into the acid, the action between the acid and the
iron wire is instantly stopped. The immersed portion of the
iron becomes quite bright, and remains so, and is in fact in the
same state, and can be used in the same manner as the iron
rendered inactive by the means already described. This pro-
tecting power of platina with respect to iron is very constant
and distinct, and is the more striking as being an effect the very
reverse of that which might have been anticipated prior to the
knowledge of M. Schoenbein's results. It is equally exerted if
the communication between it and the iron is not immediate,
but made by other metals; as, for instance, the wire of a
galvanometer; and if circumstances be favourable, a small
surface of platina will reduce and nullify the action of the acid
upon a large surface of iron.

This effect is the more striking if it be contrasted with that
produced by zinc; for the latter metal, instead of protecting the
iron, throws it into violent action with the nitric acid, and
determines its quick and complete solution. The phenomena
are well observed by putting the iron wire into nitric acid of
the given strength, and touching it in the acid alternately by
pieces of platina and zinc: it becomes active or inactive accord-
ingly; being preserved by association with the platina, and
corroded by association with the zinc. So also, as M. Schoen-
bein has stated, if iron be made the negative electrode of a
battery containing from two to ten or more pairs of plates in