PROFESSOR DANIELL ON VOLTAIC COMBINATIONS. 
139 
determined ; but, taking into consideration the diffusive nature of the electrolytic 
force, and the wide spread of that polarization of the particles of an electrolyte which 
we have traced upon a former occasion to the back surface of a conducting plate 
opposed to a mere point of generating metal*, it is more difficult to define the limits 
of its action so as to satisfy the conditions of the formula. 
In a cell composed of a plate of generating metal with a conducting plate of equal 
dimensions, the interposed electrolyte only wetting the opposite faces of the two 
metals, the area of the section of the electrolyte will clearly be equal to the area of 
the acting surface of the conducting plate. In case the two metals should be im- 
mersed in a trough, in such a manner as to allow of the electrolyte being in contact 
with both sides of the plates, it is also probable that the action of the back surfaces 
might be disregarded without danger of material error in our calculations, although 
we know in fact that they would not be wholly passive. Up to this point, there- 
fore, there is no difficulty in the application of Ohm’s formula. 
But how are we to determine the area of the section of the electrolyte, when the 
surfaces of the generating and conducting plates are not equal ? as, for instance, in 
the case of a rod of zinc placed within a cylinder of copper. Is it referrible solely 
to the surface of the conducting plate ? Or is it limited by the mean of the surfaces 
of the two plates ? The experimental investigation of this point, although the final 
result is extremely simple, has cost me much labour. The apparently unlimited 
spread or radiation of the force from a point of generating metal over an indefinitely 
large surface of conducting metal, strongly suggested the first conclusion. This was 
moreover confirmed by the following consideration, viz. if we take the mean section 
of the electrolyte as determined by the mean of the surfaces of the two metallic 
plates between which it is included, it is clear that the result ought to be the same, 
whether the generating or conducting metal be the larger of the two. A rod of 
copper placed within a cylinder of zinc, ought to circulate the same amount of force 
as a rod of zinc placed within a cylinder of copper ; the dimensions in both cases 
being respectively the same. 
Now the results of a vast number of experiments, some of which I have already 
submitted to you-f-, seemed to prove that, so far from this being the case, the amount 
of force is reduced one-half when the lines of force are made to converge from a large 
generating surface towards a small conducting one ; instead of diverging in the con- 
trary arrangement, from a small generator to a large conductor. 
These experiments I have again repeated, and when I made use of sulphate of 
copper in dilute sulphuric acid as the electrolyte, with the same general results. 
The impossibility of reconciling this with the law, and the necessity of determining 
a point of such fundamental importance, together with a certain degree of unsteadi- 
ness of action in the experiments, induced me, at length, to change the electrolyte 
for one which would be less liable to alter its condition during the progress of the 
* Philosophical Transactions, 1838, Part I. p. 54. t Ibid., pp. 47, 49, 53. 
