112 
MR. DANIELL ON VOLTAIC COMBINATIONS. 
strikingly exemplified in these experiments ; and it is clearly manifest from them, as 
a primary law, that the circulating current must be uniform throughout its course. 
In these arrangements, every cell had been a generating cell, and added something 
either to the quantity or intensity of the circulating force : I now proceeded to ascer- 
tain the effects of various retarding cells upon the elements of the battery. For this 
purpose I connected the cells together in single series, substituting a platinum plate 
for one of the zinc ; and the obstacle reacted upon the whole series : the action was 
reduced by more than one third, and the quantities of gas collected from each gene- 
rating cell was exactly equal to the hydrogen collected from the retarding cell. 
Repeating the experiment with a similar change in the next cell, the quantity of 
hydrogen in all the voltameters was equal, but reduced to little more than one tenth, 
and the current was entirely stopped by three retarding cells to seven generating 
cells. 
When, instead of changing the zinc plate of one of the cells, I reversed its position 
in the series by turning the latter round, the more active opposition of the tendency 
in that cell to establish a contrary current was indicated by the decline of the quan- 
tity of gas in the nine voltameters of the regular cells to about one fourth ; while it 
is remarkable that the quantity of hydrogen collected from the reversed zinc plate 
was considerably less. In several repetitions of this experiment this deficiency always 
occurred ; and I also ascertained that the quantity of oxygen evolved from the cor- 
responding platinum was the equivalent of the lesser quantity, and not of that which 
was evolved from the regular cells. 
When one of the zinc plates was removed from the regular series, and replaced 
with a platinum plate which had been previously coated, by voltaic influence, with 
metallic copper, the phenomena were striking and instructive. No gas at first was 
evolved from the coppered plate, but it became slowly oxidated, and the progress of 
the oxidation could be traced by the gradual blackening of its surface. The oxide 
again was gradually dissolved, and the bright white surface of the platinum made its 
appearance, and oxygen gas began to be disengaged. At that moment the current 
received a check, which was quite appreciable by the voltameters. 
As the progress of my experiments would require the use of an independent volta- 
meter, I thought it desirable previously to determine its retarding power by compari- 
son with that of a single retarding cell ; and for this purpose I substituted one of your 
upright construction for one of the cells of the battery in single series : and I found, 
that notwithstanding its plates were only three inches long by six eighths broad, 
their nearer approximation counterbalanced their deficiency of surface; and the 
quantity of hydrogen which the instrument indicated was exactly equal to that in the 
voltameters of the retarding cell. The measure of the effects of different degrees of 
approximation in the plates of voltaic combinations was one of the objects of my 
experiments; but this I have for the present postponed, for reasons which will soon 
be apparent. 
