62 Faraday's Researches

inclination being given to it, that gas evolved during decom-
position might escape: the part immersed was three inches and
a half long by one inch wide, and about seven-eighths of an inch
of water intervened between it and the solution of sulphate of
magnesia.

231. The latter pole e was now connected with the negative
end of a voltaic battery, of forty pairs of plates four inches
square, whilst the former pole b was connected with the positive
end. There was action and gas evolved at both poles; but
from the intervention of the pure water, the decomposition
was very feeble compared to what the battery would have
effected in a uniform solution. After a little while (less than a
minute), magnesia also appeared at the negative side: it did
not make its appearance at the negative metallic pole, but in the
water, at the plane where the solut&n and the water met; and
on looking at it horizontally, it could be there perceived lying
in the water upon the solution, not rising more than the fourth
of an inch above the latter, whilst the water between it and
the negative pole was perfectly clear. On continuing the action,,
the bubbles of hydrogen rising upwards from the negative pole
impressed a circulatory movement on the stratum of water,
upwards in the middle, and downwards at the side, which
gradually gave an ascending form to the cloud of magnesia
in the part just under the pole, having an appearance as if it
were there attracted to it; but this was altogether an effect
of the currents, and did not occur until long after the phenomena
looked for were satisfactorily ascertained.

232. After a little while the voltaic communication was
broken, and the platina poles removed with as little agitation
as possible from the water and solution, for the purpose of
examining the liquid adhering to them. The pole e, when touched
by turmeric paper, gave no traces of alkali, nor could anything
but pure water be found upon it. The pole by though drawn
through a much greater depth and quantity of fluid, was found
so acid as to give abundant evidence to litmus paper, the
tongue, and other tests. Hence there had been no interference
of alkaline salts in any way, undergoing first decomposition,
and then causing the separation of the magnesia at a distance
from the pole by mere chemical agencies. This experiment
was repeated again and again, and always successfully.

233. As, therefore, the substances evolved in cases of electro-
chemical decomposition may be made to appear against air
(201, 205),—which, according to common language, is not a97, 198. 7 Ibid. pp. 6.11, 642.i. p. 64.s the former.