positive_ or delivering extremity.

468. Similar litmus and turmeric paper points were now placed upon glass
plates, and connected by a string six feet long, both string and paper
being moistened in solution of sulphate of soda; a needle point connected
with the machine was brought opposite the litmus paper point, and another
needle point connected with the discharging train brought opposite the
turmeric paper. On working the machine, acid appeared on the litmus, and
alkali on the turmeric paper; but the latter was not so abundant as in
former cases, for much of the electricity passed off from the string into
the air, and diminished the quantity discharged at the turmeric point.

469. Finally, a series of four small compound conductors, consisting of
litmus and turmeric paper (fig. 51.) 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 electricity 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
brushes (322.), 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.

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

471. 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 (467.). 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 (493. 518.), that I may previously consider another supposed
condition of electro-chemical decomposition[A].

[A] I find (since making and describing these results,) from a note