i 68 Faraday's Researches

were about five inches long, and' 0.4 of an inch wide. An
earthenware pneumatic trough was filled with dilute sulphuric
acid, of the strength just described (598), and a gas jar, also
filled with the acid, inverted in it.1 A plate of platina of nearly
the same length, but about three times as wide as the zinc plates,
was put up into this jar. The zinc plate A was also introduced
into the jar, and brought in contact with the platina, and at the
same moment the plate B was put into the acid of the trough,
but out of contact with other metallic matter.

600. Strong action immediately occurred in the jar upon the
contact of the zinc and platina plates. Hydrogen gas rose from
the platina, and was collected in the jar, but no hydrogen or
other gas rose from either zinc plate. In about ten or twelve
minutes, sufficient hydrogen having been collected, the experi-
ment 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 oxidised and dissolved
during the experiment.

601. The hydrogen gas was next transferred to a water-
trough and measured; it amounted to 12.5 cubic inches, the
temperature being 52°, and the barometer 29.2 inches. This
quantity, corrected for temperature, pressure, and moisture,
becomes 12.15453 cubic inches of dry hydrogen at mean tem-
perature 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 (526), 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 oxidised, 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 suffi-
ciently near to show, what indeed could not but happen, that
for an equivalent of zinc oxidised an equivalent of water must
be decomposed.2

1 The acid was left during a night with a small piece of unamalgamated
zinc in it, for the purpose of evolving such air as might be inclined to
separate, and bringing the whole into a constant state.

2 The experiment was repeated several times with the same results. See De la Rive on this subject, BibHotheque Universellet