Electromotive Forces in the Voltaic Cell. 187 
tion with regard to “chemical tendency” as the possible 
source of a current, or rather of “ force electromotive.” His 
language and ideas are in many respects old-fashioned and 
erroneous ; he uses such phrases as “a current of tendency,” 
he supposes currents with no electrolytic power to exist, and 
of course is not troubled about energy considerations. But I 
feel little doubt that, had he lived later, he would have held 
that while currents were due to chemical action, electromotive 
force was due to “chemical tendency;” and this is pretty 
exactly my own view of the matter. 
I have only just discovered this Schénbein letter; and I 
have also found some paragraphs in Faraday which more in 
detail and with fair distinctness express what I believe to be 
the true view. (See §§ 893-900, Exp. Res. vol. i.*) 
grant to the Voltaists our current of tendency to be the effect of mere 
contact, the facts alluded to prove that such a current does not possess a 
sensible degree of electrolyzing-power; consequently that the chemical 
effects of the common voltaic arrangements have nothing to do with 
current-electricity excited by contact.” 
* Extract from Faraday’s ‘ Experimental Researches,’ vol. i. :— 
“ (893) The use of metallic contact in a single pair of plates and the 
cause ofits great superiority above contact made by other kinds of matter, 
become now very evident. When an amalgamated zinc plate is dipped 
into dilute sulphuric acid, the force of chemical affinity exerted between 
the metal and the fluid is not sufficiently powerful to cause sensible action 
at the surfaces of contact, and occasion the decomposition of water by the 
oxidation of the metal, although it is sufficient to produce such a condition 
of the electricity (or the power upon which chemical affinity depends), as 
would produce a current if there were a path open for it; and that con- 
tact would complete the conditions necessary, under the circumstances, 
for the decomposition of water. 
“ (894) Now the presence of a piece of platina touching both the zinc 
and the fluid to be decomposed opens the path required for the electricity. 
Its direct communication with the zinc is effectual, far beyond any commu- 
nication made between it and that metal (7. e. between the platina and 
zinc) by means of decomposable conducting bodies, or, in other words, 
electrolytes, as in the experiment already described [that of decomposing 
iodide of potassium without metallic contact by interposing it on blotting- 
paper between the platinum and the zinc of a simple voltaic cell], because, 
when they are used, the chemical affinities between them and the zinc 
produce a contrary and opposing action to that which is influential in the 
dilute sulphuric acid; or if that action be but small, still the affinity of 
their component parts for each other has to be overcome, for they cannot 
conduct without suffering decomposition ; and this decomposition is found 
experimentally to react back upon the forces which in the acid tend to 
produce the current, and in numerous cases entirely to neutralize them 
Where direct contact of the zinc and platina occurs, these obstructing 
forces are not brought into action, and therefore the production and the 
circulation of the electric current, and the concomitant action of decom- 
osition are then highly favoured. 
“ (895) It is evident, however, that one of these opposing actions may 
be dismissed and yet an electrolyte be used for the purpose of completing © 
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