﻿Colloids produced by Electric Endosmose. 553 



If the cells are open and communicate with one another, 

 water can be carried along the cell or tube walls ; if they 

 are shut, however, the water can only enlarge or diminish 

 the cells by dissolving in the substance of the wall or in the 

 contents of the cells, and thus produce a temporary dilatation 

 positive or negative, with corresponding positive or negative 

 double refraction. By the pressure of liquid into such 

 stretched-out open cells, the observed temporary double 

 refraction, positive perpendicular to the direction of trans- 

 ference of the water, would be expected; the later-appearing' 

 spot showing a negative dilatation is probably produced by 

 reaction. At the sides of the glass tube the water is less 

 moved than in the middle, on account of the transverse walls, 

 there; at the sides appears as a consequence a temporary 

 positive dilatation perpendicular to the tube. Behind the 

 first line appears a series of places with positive and negative 

 double refraction, as in the case of shrinking of gelatine in 

 short capillary tubes in air, alcohol, or glycerine *. 



Gelatine in Shallow Dishes. 



Shallow glass dishes, either square (5 cms. x 5 cms. X 1 cm.) 

 or round (2r=8 cms.) were filled to a depth of 1 cm. with 

 a 10 per cent, gelatine solution and examined at the end of 

 21 hours. The electrodes only touched the surface, other- 

 wise the bubbles rising up had a disturbing influence. 



At the anode came a furrow, at the cathode a swelling. 

 The anode was surrounded by two hemispheres, the inner 

 more distinct, and both sharp. The cathode was surrounded 

 by a white hemisphere and by a second, outer one, difficult to 

 see. The white colour came from countless, very small 

 (0*003 to 0-01 mm.) crystals. Round the electrode the 

 crystals were packed and stuck together. The crystals 

 were of two kinds: (a) spherical, showing a black cross parallel 

 to the long diagonals of crossed nicols, and (h) rhombohedral 

 (CaC0 3 ?), growing dark and reappearing as the turn-table 

 was rotated. This crystal formation may come (1) from loss 

 of water, (2) from loss of gelatine, the presence of which 

 may increase the solubility of the salt. If the cell-walls are 

 covered with a layer containing salt, layer and cell-contents 

 will be displaced in opposite directions, eddies will be formed 

 and the salt layer loosened to crystallize out later. The 

 furrow round the anode was about 1 mm. deep, and had 

 smooth sides with sharp edges ; the swelling round the 



* G. Quincke, Ann. d. Phys. xiv. p. 849 (1904). 



