Polar Decompositions in Air 53

205. Finally, a series of four small compound conductors,
consisting of litmus and turmeric paper (fig. n) moistened in
solution of sulphate of soda,, were supported on glass rods, in
a line at a little distance from each other, between the points
p and n of the machine and discharging train, so that the elec-
tricity might pass in succession through them, entering in at
the litmus points b, b, and passing out at the turmeric points a,
a. On working the machine carefully, so as to avoid sparks and

Fig. n.

brushes (58), I soon obtained evidence of decomposition in each
. of the moist conductors, for all the litmus points exhibited free
acid, and the turmeric points equally showed free alkali.

206. On using solutions of iodide of potassium, acetate of
lead, etc., similar effects were obtained; but as they were all
consistent with the results above described, I refrain from
describing the appearances minutely.

207. These cases of electro-chemical decomposition are in
their nature exactly of the same kind as those affected under
ordinary circumstances by the voltaic battery, notwithstanding
the great differences as to the presence or absence, or at least
as to the nature of the parts usually called poles; and also of
the final situation of the elements eliminated at the electrified
boundary surfaces (203). They indicate at once an internal
action of the parts suffering decomposition, and appear to show
that the power which is effectual in separating the elements is
exerted there, and not at the poles. But I shall defer the
consideration of this point for a short time (229, 254), that I
may previously consider another supposed condition of electro-
chemical decomposition.1

11 find (since making and describing these results) from a note to Sir
Humphry Davy's paper in the Philosophical Transactions, 1807, p. 31, that
that philosopher, in repeating Wollaston's experiment of the decomposition
of water by common electricity (63, 66) used an arrangement somewhat
like some of those I have described. He immersed a guarded platina point
connected with the machine in distilled water, and dissipated the electricity
from the water into the air by moistened filaments of cotton. In this way
he states that he obtained oxygen and hydrogen separately from each other.
This experiment, had I known of it, ought to have been quoted in an
earlier part of these Researches (78); but it does not remove any of the
objections I have made to the use of Wollaston's apparatus as a test of
true chemical action (67).