460.  These experiments were varied so as to include the action of only one metallic pole, but that not the pole connected with the machine.  Turmeric 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 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.