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 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.