eric
paper was moistened in solution of sulphate of soda, placed upon glass, and
connected with the discharging train (292.) by a decomposing wire (312.); a
piece of wet string was hung from it, the lower extremity of which was
brought opposite a point connected with the positive prime conductor of the
machine. The machine was then worked for a few turns, and alkali
immediately appeared at the point of the discharging train which rested on
the turmeric paper. Corresponding effects took place at the negative
conductor of a machine.

461. These cases are abundantly sufficient to show that electrochemical
decomposition does not depend upon the simultaneous action of two metallic
poles, since a single pole might be used, decomposition ensue, and one or
other of the elements liberated, pass to the pole, according as it was
positive or negative. In considering the course taken by, and the final
arrangement of, the other element, I had little doubt that I should find it
had receded towards the other extremity, and that the air itself had acted
as a pole, an expectation which was fully confirmed in the following
manner.

462. A piece of turmeric paper, not more than 0.4 of an inch in length and
0.5 of an inch in width, was moistened with sulphate of soda and placed
upon the edge of a glass plate opposite to, and about two inches from, a
point connected with the discharging train (Plate IV. fig. 47.); a piece of
tinfoil, resting upon the same glass plate, was connected with the machine,
and also with the turmeric paper, by a decomposing wire _a_ (312.). The
machine was then worked, the positive electricity passing into the turmeric
paper at the point _p_, and out at the extremity _n_. After forty or fifty
turns of the machine, the extremity _n_ was examined, and the two points or
angles found deeply coloured by the presence of free alkali (fig. 48.).

463. A similar piece of litmus paper, dipped in solution of sulphate of
soda _n_, fig. 49, was now supported upon the end of the discharging train
_a_, and its extremity brought opposite to a point _p_, connected with the
conductor of the machine. After working the machine for a short time, acid
was developed at both the corners towards the point, i.e. at both the
corners receiving the electricities from the air. Every precaution was
taken to prevent this acid from being formed by sparks or brushes passing
through the air (322.); and these, with the accompanying general facts, are