Inefficiency of Contact of Electrolytes  253
 846.	Thus these different contacts of metals and other well-
conducting solid bodies prove utterly inefficient in producing a
current^ as well when solution of potassa is the third or fluid
body in the circuit, as when that third body is either solution
of sulphuret of potassium, or hydrated nitrous acid, or nitric
acid, or mixed nitric and nitrous acids.    Further, all the argu-
ments respecting the inefficacy of the contacts of bodies inter-
posed at the junction of the two principal solid substances,
which were advanced in the case of the sulphuret of potassium
solution (821), apply here with potassa;  as they do indeed in
every case of a conducting circuit where the interposed fluid is
without chemical action and no current is produced.    If a case
could be brought forward in which the interposed fluid is with-
out action, is yet a sufficiently good conductor, and a current is
produced; then, indeed, the theory of contact would find evi-
dence in its favour, which, as far as I can perceive, could not
be overcome.    I have most anxiously sought for such a case,
but cannot find one (786).
 847.	The argument is now in a fit state for the resumption
of that important point before adverted to (823, 832), which,
if truly advanced by an advocate for the contact theory, would
utterly annihilate the force of the previous experimental results,
though it would not enable that theory to give a reason for the
activity of, and the existence of a current in, the pile;   but
which,  if in error,  would leave the contact theory utterly,
defenceless and without foundation.
 848.	A supporter of the contact theory may say that the
various conducting electrolytes used in the previous experi-
ments are like the metals; i.e. that they have an electromotive
force at their points of contact with the metals and other solid
conductors employed to complete the circuit;  but that this is
of such consistent strength at each place of contact, that, in a
complete circle, the sum of the forces is o (797).    The actions
at the contacts are tense electromotive actions, but balanced,
and so no current is produced.    But what experiment is there
to support this statement?   where are the measured electro-
motive results proving it (796)?    I believe there are none.
 849.	The contact theory, after assuming that mere contacts
of dissimilar substances   have   electromotive powers, further
assumes a difference between metals and liquid conductors (798)
without which it is impossible that the theory can explain the
current in the voltaic pile:  for whilst the contact effects in a