ith the voltaic
battery, the current passed, and decomposition proceeded. No chlorine was
evolved at the positive electrode; but as the fused chloride was
transparent, a button of alloy could be observed gradually forming and
increasing in size at _b_, whilst the lead at _a_ could also be seen
gradually to diminish. After a time, the experiment was stopped; the tube
allowed to cool, and broken open; the wires, with their buttons, cleaned
and weighed; and their change in weight compared with the indication of the
volta-electrometer.

817. In this experiment the positive electrode had lost just as much lead
as the negative one had gained (795.), and the loss and gain were very
nearly the equivalents of the water decomposed in the volta-electrometer,
giving for lead the number 101.5. It is therefore evident, in this
instance, that causing a _strong affinity_, or _no affinity_, for the
substance evolved at the _anode_, to be active during the experiment
(807.), produces no variation in the definite action of the electric
current.

818. A similar experiment was then made with iodide of lead, and in this
manner all confusion from the formation of a periodide avoided (803.). No
iodine was evolved during the whole action, and finally the loss of lead at
the _anode_ was the same as the gain at the _cathode_, the equivalent
number, by comparison with the result in the volta-electrometer, being
103.5.

819. Then protochloride of tin was subjected to the electric current in the
same manner, using of course, a tin positive electrode. No bichloride of
tin was now formed (779. 790.). On examining the two electrodes, the
positive had lost precisely as much as the negative had gained; and by
comparison with the volta-electrometer, the number for tin came out 59.

820. It is quite necessary in these and similar experiments to examine the
interior of the bulbs of alloy at the ends of the conducting wires; for
occasionally, and especially with those which have been positive, they are
cavernous, and contain portions of the chloride or iodide used, which must
be removed before the final weight is ascertained. This is more usually the
case with lead than tin.

821. All these facts combine into, I think, an irresistible mass of
evidence, proving the truth of the important proposition which I at first
laid down, namely, _that the chemical power of a current of electricity is
in direct proportion to the absolute quantity of electricity whic