sufficient to show that the acid was really the result of electro-chemical
decomposition (466.).

464. Then a long piece of turmeric paper, large at one end and pointed at
the other, was moistened in the saline solution, and immediately connected
with the conductor of the machine, so that its pointed extremity was
opposite a point upon the discharging train. When the machine was worked,
alkali was evolved at that point; and even when the discharging train was
removed, and the electricity left to be diffused and carried off altogether
by the air, still alkali was evolved where the electricity left the
turmeric paper.

465. Arrangements were then made in which no metallic communication with
the decomposing matter was allowed, but both poles (if they might now be
called by that name) formed of air only. A piece of turmeric paper _a_ fig.
50, and a piece of litmus paper _b_, were dipped in solution of sulphate of
soda, put together so as to form one moist pointed conductor, and supported
on wax between two needle points, one, _p_, connected by a wire with the
conductor of the machine, and the other, _n_, with the discharging train.
The interval in each case between the points was about half an inch; the
positive point _p_ was opposite the litmus paper; the negative point _n_
opposite the turmeric. The machine was then worked for a time, upon which
evidence of decomposition quickly appeared, for the point of the litmus _b_
became reddened from acid evolved there, and the point of the turmeric _a_
red from a similar and simultaneous evolution of alkali.

466. Upon turning the paper conductor round, so that the litmus point
should now give off the positive electricity, and the turmeric point
receive it, and working the machine for a short time, both the red spots
disappeared, and as on continuing the action of the machine no red spot was
re-formed at the litmus extremity, it proved that in the first instance
(463.) the effect was not due to the action of brushes or mere electric
discharges causing the formation of nitric acid from the air (322.).

467. If the combined litmus and turmeric paper in this experiment be
considered as constituting a conductor independent of the machine or the
discharging train, and the final places of the elements evolved be
considered in relation to this conductor, then it will be found that the
acid collects at the _negative_ or receiving end or pole of the
arrangement, and the alkali at the _