Page:Text-book of Electrochemistry.djvu/127

 ��ELECTROLYTES.

��CHAP.

��as will be later shown^ no appreciable polarisation then takes place. The electrical condition in the trough can be graphically represented as in Fig. 22. At the point + the electric potential has a certain value, say A ; at the point — it has a lower value, say B\ consequently the (positive)

electric current flows in the direction from A Uy B, from higher to lower potentiaL The potential at any point, P, be- tween + and — is found by joining the end points of A and By and erecting at P a perpendicular which meets the line joining A and B at -B. PR then gives the potential at P. In the same way PiBi represents the potential at point Pi, and the diflference, d F", of the potentials PR and PiRi at points P and Pi is evidently the same throughout, so long as the distance PPi is kept constant, because dV = PPi tan a, where a is the inclination of the line joining A and B to the abscissse-axis. The potential difiference dV produces the current dl in the galvanometer ; according to Ohm's law —

dV

���dl =

��M

��where M is the resistance in the cirduit PGPi, Since the resistance M does not vary, and dFis the same throughout, it is evident that the deflection of the galvanometer-needle must be the same at whatever distance from the poles P and Pi are placed.

Faraday further showed that chemical decomposition may

_ also take place without metallic poles. He connected a point, A (Fig. 23), with the negative pole of an electrical ma- chine, and allowed negative electricity to stream from this against a strip of paper, P, which was moistened with a solution of sodium sulphate, made red with litmus, and which connected with the positive pole B

��A -

��T^

��P Fig. 23.

�� �