ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 27 
cataphoresis,? and cataphoresis, on other occasions, being made in 
turn to do double service.’ 
Electrokinetic phenomena in two-phase systems of liquid, and 
solid may be analysed into four distinct processes, of which electrical 
endosmose and cataphoresis are the ones commonly met with. So 
far as the electric current is concerned, it is possible to distinguish 
two cases, as follows :— 
(1) A difference of potential sending a current through the system 
may produce a relative displacement of the phases. 
(a) If the solid is fixed in the form of a porous diaphragm the 
liquid may be forced through the diaphragm. Electrical endosmose. 
(6) If the solid is in the form of a suspension and is free to move, 
the solid may migrate through the liquid. Cataphoresis. 
(2) A relative displacement of the phases may produce a difference 
of potential and consequently an electric current may flow through 
the system. 
(a) If the solid is fixed in the form of a porous diaphragm 
through which liquid is forced, a difference of potential and an 
electric current may be established between the extremes of the 
diaphragm. Quincke’s ‘diaphragm current.’ 
(b) If the finely divided solid is dropped through the liquid, a 
difference of potential and a current may be set up between the 
upper and lower liquid strata. Billitzer’s experiments. This case 
resembles closely the drop electrode. 
Wiedemann’ is to be credited with the first quantitative study of 
electrical endosmose, and he was able, as a result, to deduce three 
empirical generalizations : 
(1) The mass of liquid transported in unit time through a porous 
diaphragm, is directly proportional to the strength of the electric 
current; and, for a given diaphragm material and given current 
_ strength, it is independent of the length and sectional area of the 
diaphragm. 
(2) The difference in hydrostatic pressure maintained by electrical 
endosmose between the two sides of a porous diaphragm, varies 
directly as the current strength, and for a given diaphragm material 
and a given current, is proportional directly to the length and inversely 
to the sectional area of the diaphraym ; it is also proportional to the 
specific resistance of the liquid in the case of an aqueous solution. 
(3) For a given diaphragm material, the difference in hydrostatic 
pressure maintained between the two sides of a porous diaphragm is 
proportional to the applied potential and is independent of the 
dimensions of the diaphragm. 
Quincke® forced liquid through an apparatus containing a porous 
diaphragm and found that differences of potential were produced. 
He measured these differences and the “‘ diaphragm currents’? which 
2 Cf. Patents of Botho Schwerin (Gesellschaft fiir Elektroosmose). 
3 Cf, Cruse, Phys. Zeit., 6, 201 (1905) ; Hittorf ; Zeit. phys. Chem., 39, 613 (1902); 
48. 239 (1903) ; Morton ; Cataphovesis (1898). 
4 Drude’s Ann. 11, 937 (1903). Cf. Freundlich, Aapillarchemie, 230 (1909). 
5 Pogg-Ann, 8'7, 321 (1852) ; 99, 177;(1356). 
6 Pogg.-Ann., 10'7, 1 (1859) ; 110, 38 (1860). 
