drogen or other gas rose from _either_ zinc
plate. In about ten or twelve minutes, sufficient hydrogen having been
collected, the experiment was stopped; during its progress a few small
bubbles had appeared upon plate B, but none upon plate A. The plates were
washed in distilled water, dried, and reweighed. Plate B weighed 148.3
grains, as before, having lost nothing by the direct chemical action of the
acid. Plate A weighed 154.65 grains, 8.45 grains of it having been oxidized
and dissolved during the experiment.

866. The hydrogen gas was next transferred to a water-trough and measured;
it amounted to 12.5 cubic inches, the temperature being 52 deg., and the
barometer 29.2 inches. This quantity, corrected for temperature, pressure,
and moisture, becomes 12.15453 cubic inches of dry hydrogen at mean
temperature and pressure; which, increased by one half for the oxygen that
must have gone to the _anode_, i.e. to the zinc, gives 18.232 cubic inches
as the quantity of oxygen and hydrogen evolved from the water decomposed by
the electric current. According to the estimate of the weight of the mixed
gas before adopted (791.), this volume is equal to 2.3535544 grains, which
therefore is the weight of water decomposed; and this quantity is to 8.45,
the quantity of zinc oxidized, as 9 is to 32.31. Now taking 9 as the
equivalent number of water, the number 32.5 is given as the equivalent
number of zinc; a coincidence sufficiently near to show, what indeed could
not but happen, that for an equivalent of zinc oxidized an equivalent of
water must be decomposed[A].

[A] The experiment was repeated several times with the same results.

867. But let us observe _how_ the water is decomposed. It is electrolyzed,
i.e. is decomposed voltaically, and not in the ordinary manner (as to
appearance) of chemical decompositions; for the oxygen appears at the
_anode_ and the hydrogen at the _cathode_ of the body under decomposition,
and these were in many parts of the experiment above an inch asunder.
Again, the ordinary chemical affinity was not enough under the
circumstances to effect the decomposition of the water, as was abundantly
proved by the inaction on plate B; the voltaic current was essential. And
to prevent any idea that the chemical affinity was almost sufficient to
decompose the water, and that a smaller current of electricity might, under
the circumstances, cause the hydrogen to pass to the _cathode_, I need only
refer to the r