PROFESSOR DANIELL ON VOLTAIC COMBINATIONS. 
141 
When, on the contrary, a zinc wire was placed in the porous tube in the centre of 
the platinum cylinder, charged with the sulphate of copper, the needle advanced to 
96° upon an average of three experiments, and then remained quite steady. In this 
case, the precipitated copper was equally diffused over the surface of the platinum, 
and constituted a compact layer firmly attached to the plate. There can be no doubt 
that it is this difference in the state of the precipitated metal which gave rise to the 
difference in the results of the two arrangements. In the last case, the electrolysis 
of the liquid was carried on without the disengagement of any element tending ma- 
terially to produce an opposing current ; while in the first, the spongy state of the 
copper retained the liquid within its pores ; which, after the precipitation of all the 
sulphate of copper which it contained, generated hydrogen, which was equally en- 
tangled in it, and produced a strong opposition to the current. The amount of this 
opposition is definite, and of nearly half the force of the principal current ; and hence 
I w’as led to the erroneous conclusion regarding the relative sizes of the generating 
and conducting plates. Taking the measure of the force at the first moment of 
making the contacts, the results sufficiently confirm the conclusion drawn from the 
experiments with the nitric acid. 
I once more tested the hypothesis, that it is the mean section of the electrolyte 
which regulates the current, and that it is indifferent' whether the conducting or the 
generating metal be the larger of the two plates, by measuring the chemical results 
produced. For this purpose I weighed the amalgamated zinc cylinders and rods 
before and after the experiment, and ascertained the consumption of metal for inter- 
vals of half an hour, during which the circuits were closed. The conducting metal 
was copper, and the rods half an inch in diameter. The electrolyte was sulphate of 
copper and dilute sulphuric acid, and was kept agitated during the immersion of the 
copper rods. The results are set down in the following Table : — 
Table II. 
Diameter of Zinc. 
Diameter of Copper. 
Loss of Zinc in thirty minutes. 
inches. 
inches. 
grs. 
1 
2 
2f 
30 
03 
2 i 
2 
JL 
30 
H 
29-7 
°2 
1 
2 
30 
These results perfectly accord with the preceding. 
From the consideration of the foregoing experiments, we are led to another import- 
ant relation of the generating and conducting metals in these cylindrical arrange- 
ments, to understand which, it must be borne in mind that the surfaces of cylinders, 
of equal heights, are directly proportioned to their radii. 
Let us therefore imagine an indefinitely small rod of a generating metal placed in the 
axis of a cylinder of conducting metal of a given diameter, filled with an electrolyte; 
upon making contact of the two metals, a current would be established of a definite 
