ADSORPTION POTENTIALS AND ELECTROKINETIC PHENOMENA 251 



the surface laj-ers of the suspended particles, and the particles move 

 in the reverse direction, in relation to the water in the preceding case. 

 This is the phenomenon of electric cataphoresis or electrophoresis. As 

 long as a wide U-tube is used, this phenomenon is merely the reverse 

 of endosmosis. But if this phenomenon is to be studied in narrow 

 tubes, suitable for microscopic observation, certain peculiar eom- 

 phcations arise. For, in such narrow tubes, not only do the sus- 

 pended particles show motion in relation to the water, but the water 

 itself shows relative motion along the walls of the tubes. This is 

 explained by the formation also along these quartz or glass walls of a 

 double layer towards the water, and the water is pulled by its surface 

 layer adjacent to the walls of the tube, under the influence of the 

 external electric tension of the double laj^er. Therefore, the motion 

 of the suspended particles, as observed on the microscope stage, 

 represents in reaUty the algebraic sum of cataphoretic motion of the 

 particles in relation to the water and of the motion of the particles 

 induced by the streaming of the water itself as explained abos^e. 

 The theory of this phenomenon was theoretically developed by R. 

 Elhs-^ and was further perfected in a very beautiful manner by 

 Smoluchowski.-* Only the results of these investigations will be 

 discussed here. 



The theory in its simplest terms apphes to a narrow chamber 

 or vessel Vv^hich is closed on all sides, and from which the water cannot 

 flow out when in motion. This may be represented by such a vessel 

 as a microscopic counting chamber into which the electrodes are sealed 

 in hermetically through two sides. The current of water arising at 

 the outer layers adjacent to the chamber walls must result in a back- 

 flow in the interior layers of the water. Therefore the rate of motion 

 of the water is not a constant value, but its value as well as its direc- 

 tion depend upon the distance of the water-particles involved from 

 the walls of the chamber. Let us further assume that in so narrow a 

 chamber only lateral (lamellar) streaming of water is possible, i.e., 

 that every water-particle can move only from left to right or reversely, 

 but not forward and backward, nor up and down. Then the back- 

 flow of the water manifests itself only in left-and-right streaming free 

 from whirls. If the water has a certain velocity in the immediate 



" Risdale Ellis, Zeitschr. f. physikal. Chem. 78, 321 (1911). 

 " M. V. Smoluchovvski, Elektrische Endosmose und Stromungsstrome, 

 in Graetz' Handbuch der Elektrizitiit, Bd. II, Leipzig 1921, 



