40 
MR. BIRD ON THE ELECTRO-CHEMICAL INFLUENCE OF 
5. If the two copper conducting- wires belonging to the little apparatus just 
described are immersed in water acidulated with sulphuric acid, action soon com- 
mences, bubbles of hydrogen appearing at the wire connected with the zinc plate, 
whilst that connected with the copper plate became tarnished, oxydized, and at last 
partly dissolved, giving a blueish tint to the fluid ; affording an approach to the de- 
composition of water by a single pair of plates. For the success of this experiment, 
it is, as might be expected, necessary that the positive electrode at least should be 
formed of a readily oxidizable metal ; for when both wires were of platinum, no evi- 
dence of decomposing action ensued. 
6. If, instead of acidulated water, the wires were immersed into a solution of 
nitrate or acetate of lead, no immediate action ensued, but in about fifteen minutes, 
or even less, some elegant and delicate feathers of metallic lead, which rapidly in- 
creased in size, appeared at the negative electrode. This effect did not occur when 
both conducting wires were of platinum ; but when the negative electrode only was 
composed of that metal, the reduction of the lead continued with apparently increased 
energy. From these experiments, as well as many others of a similar kind which it 
is unnecessary to detail, it appears fair to presume, that in availing ourselves of the 
reducing agency of feeble currents, or at least of those elicited by a single pair of 
plates, it is necessary that the positive electrode should be composed of a readily 
oxidizable metal : thus using a kind of battery of two cells, in which the wires form- 
ing the electrodes, and the fluid submitted to experiment, form the contents of the 
second cell. 
7- But few metallic solutions yield so readily as those of lead to the reducing agency 
of weak currents ; and where a longer time and continuance of action is required to 
effect the reduction, the decomposing apparatus of M. Becquerel will be found a 
useful addition to the little battery (4.), with the substitution of a plug of plaster of 
Paris for one of clay. This piece of apparatus is, in fact, a counterpart of the battery 
itself, consisting, like it, of two glass cylinders, one within the other, the smaller one 
having a bottom or floor of plaster of Paris fixed into it : this smaller tube may be 
about half an inch wide and three inches in length, and is intended to hold the me- 
tallic solution submitted to experiment, the external tube in which it is immersed 
being filled with a weak solution of common salt*. Into the latter solution a slip of 
amalgamated zinc, (for the positive electrode,) soldered to the wire coming from the 
copper plate of the battery (4.), is immersed, whilst for the negative electrode a slip 
of platina foil, fixed to the wire from the zinc plate of the battery, passes through a 
* Fig. 2. in the sketch represents this apparatus connected with the battery. 
A. The larger tube. 
B. The smaller one, with the plaster bottom. 
C. The electrode of amalgamated zinc connected by the wire F with the copper plate C of the battery (Fig. 1.). 
D. The negative electrode of platinum connected by the wire G with the zinc plate of the battery (Fig. 1.). 
