INACTIVE CONDUCTING VOLTAIC CIRCLES — SULPHURET OF POTASSA. 71 
no current is produced ; and yet the test application of a little heat at a or b, will 
show by the corresponding- current, that the circuit being complete will conduct any 
current that may tend to pass. Now that the contacts of zinc with iron and with 
platinum are of equal electromotive force, is not for a moment admitted by those who 
support the theory of contact activity ; we ought therefore to have a resulting action 
equal to the differences of the two forces, producing a certain current. No such 
current is produced, and I conceive, with the admission above, that such a result 
proves that the contacts iron-zinc and platinum-zinc are entirely without electromotive 
force. 
1834. Gold, silver, potassium, and copper were introduced at x with the like ne- 
gative effect ; and so no doubt might every other metal, even according to the rela- 
tion admitted amongst the metals by the supporters of the contact theory (1809.). 
The same negative result followed upon the introduction of many other conducting 
bodies at the same place ; as, for instance, those already mentioned as easily con- 
ducting the thermo current (1820.) ; and the effect proves, I think, that the contact 
of any of these with either iron or platinum is utterly ineffective as a source of elec- 
tromotive force. 
1835. The only answer which, as it appears to me, the contact theory can set up 
in opposition to the foregoing facts and conclusions is, to say that the solution of 
sulphuret of potassium in the cup D, fig. 2, acts as a metal would do (1809.), and 
so the effects of all the contacts in the circuit are exactly balanced. I will not stop 
at this moment to show that the departure with respect to electrolytes, or the fluid 
bodies in the voltaic pile, from the law which is supposed to hold good with the 
metals and solid conductors, though only an assumption, is still essential to the con- 
tact theory of the voltaic pile (1810. 1861.)*; nor to prove that the electrolyte is no 
otherwise like the metals than in having no contact electromotive force whatever. 
But believing that this will be very evident shortly, I will go on with the experi- 
mental results, and resume these points hereafter (1859. 1889.). 
1836. The experiment was now repeated with the substitution of a bar of nickel 
for that of iron, fig. 2 (1824.), all other things remaining the sarne'f-. The circuit 
was again found to be a good conductor of a feeble thermo current, but utterly 
inefficient as a voltaic circuit when all was at the same temperature, and due pre- 
cautions taken (2051.). The introduction of metals at the contact x was as ineffec- 
tive as before (1834.); the introduction of chemical action at x was as striking in 
its influence as in the former case (1831.) ; all the results were, in fact, parallel to 
* See Fechner’s words. Philosophical Magazine, 1838, xiii. 377. 
t There is another form of this experiment which I sometimes adopted, in which the cup E, fig. 2, with its 
contents, was dismissed, and the platinum plates in it connected together. The arrangement may then be con- 
sidered as presenting three contacts of iron and platinum, two acting in one direction, and one in the other. 
The arrangement and the results are virtually the same as those already given. A still simpler but equally 
conclusive arrangement for many of the arguments, is to dismiss the iron between a and b altogether, and so 
have but one contact, that at x, to consider. 
