114 
MR. DANIELL ON VOLTAIC COMBINATIONS. 
itself downwards and laterally at the same rate, till in a few hours it reached the edge 
of the plate. It then made its appearance upon the opposite surface, and ultimately 
both sides were completely coated ; but the deposition decreased in thickness as it 
receded from the central zinc. This effect, in a voltaic combination, of a small ge- 
nerating surface upon a large conducting one, is strikingly contrasted with the result 
when we reverse the circumstances of the arrangement ; for by causing a rod of pla- 
tinum to rest by its end upon a large surface of amalgamated zinc, covered with the 
acidulated water, hydrogen of course escapes from the former metal ; but the oxida- 
tion of the latter is so local, that a hole is eaten through it at the point of contact. 
These experiments set the question at rest which they were meant to resolve ; and 
I think, upon attentively considering the matter, that we may find the cause of this 
great diffusion of the hydrogen in that force of heterogeneous adhesion to which I have 
already referred the power of nascent gases, reacting upon, or acting in conjunction 
with, its elastic or self-repulsive force. Under the influence of these two forces the 
gaseous matter seems to extend itself upon the metal, much in the same way that a 
drop of volatile oil spreads itself over a large surface of water ; and it seems not im- 
probable that the efficiency of the conducting plates of voltaic arrangements may in 
part, if not wholly, depend upon the extent of surface which they afford for this dif- 
fusion of the gas, by which it is carried beyond the sphere of reaction upon the ge- 
nerating plates. To test the accuracy of this hypothesis, I reduced the width of the 
zinc plates in the battery; and beginning by halving, and then diminishing them to 
a quarter of their original dimensions, I ultimately found that amalgamated wires of 
one eighth of an inch diameter and three inches long, were as efficacious as the inch- 
wide plates ; and that under their influence the conducting plates evolved as much 
gas in equal portions of time as when connected with the larger generating surfaces. 
Amongst the numerous experiments which I have tried by the substitution of dif- 
ferent metals, both as generating and conducting plates, for the normal plates of the 
battery, I must only detain you on the present occasion with the results of two. The 
first was the change of common zinc plates for the amalgamated, when strong local 
action took place, which, however, did not appear to interfere with the current affinity 
when the cells were connected in single series ; for while the disengagement of hy- 
drogen from the zinc was at the highest, as much gas was evolved from the platinum 
as when they were combined with the amalgamated metal. 
The second was the substitution of wrought iron for the amalgamated zinc plates. 
I had expected, from theoretical speculations upon its low equivalent number, that 
iron would have proved a very efficient generating metal; aud my surprise was great 
upon discovering that its action in the battery was almost null. A slight local action 
took place upon the plates themselves, but the evolution of gas from the platinum 
was scarcely apparent, and quite immeasurable. This being the case, I converted 
them into conducting plates by removing the platinum, and opposing to them amal- 
gamated zinc plates; and I was no less surprised to find that in their new office they 
