Page:Elementary Text-book of Physics (Anthony, 1897).djvu/354

340 circuit, in a sense opposite to that which would change the area of the meniscus back to its original amount.

The electrical double-sheet produced by contact of a liquid and a solid serves also to explain the phenomenon of electrical endosmose.

It is found that, if an electrolyte be divided into two portions by a porous diaphragm, there is a transfer of the electrolyte toward the cathode, so that it stands at a higher level on the side of the diaphragm nearer the cathode than on the other. This fact was discovered by Reuss in 1807, and has been investigated by Wiedemann and Quincke. They found that the amount of the electrolyte transferred is proportional to the current strength, and independent of the extent of surface or the thickness of the diaphragm. Quincke has also demonstrated a flow of the electrolyte toward the cathode in a narrow tube, without the intervention of a diaphragm. Those electrolytes which are the poorest conductors show the phenomenon the best. In a very few cases the motion is towards the anode. The material of which the tube is composed influences the direction of flow. It has also been shown that solid particles move in the electrolyte, usually towards the anode.

Helmholtz showed that these movements can be explained by taking into account the interaction between the ionic charges and the double-sheet, and the viscosity of the liquid.