36 REPORTS ON THE STATE OF SCIENCE.—1918. 
(2) Any circumstance or condition which changes the adsorption 
produces an effect upon electrical endosmose. LHlectrical endosmose 
varies, therefore, with the condition of the surface (for a given solid), 
with the relative and absolute ion concentrations, with the tempera- 
ture and so forth. 
(3) The direction of endosmose indicates the sign-of the dia- 
phragm ; the rate of endosmose is proportional to the intensity of 
the charge on the diaphragm in case the potential gradient through 
the diaphragm is constant. When the liquid flows to the cathode, 
the diaphragm is negative; when it flows to the anode the dia- 
phragm is positive. No flow at all probably indicates an iso-electric 
condition.” 
(4) A diaphragm tends to become positive by the selective adsorp- 
tion of cations, and negative by the adsorption of anions. 
(5) The positive charge produced by an adsorbed cation is neutral- 
ized more or less by the addition of an adsorbed anion, the effect 
increasing with the concentration of the anion. Similarly, the 
negative charge produced by an anion is neutralized by an adsorbed 
cation. 
(6) Electrical endosmose measures the tendency of a solid to 
form an electrical suspension in a given liquid, but it does not 
measure the tendency of the solid to form a non-electrical suspen- 
sion, such as is produced by adsorbed solvent, solute or neutral 
colloid.*! 
5. Adsorption Potential, Temperature and other Factors. 
Returning to equation 1 it is hardly necessary to point out that «, 
representing the potential of the Quincke-Helmholtz double layer, 
stands also for the ‘adsorption potential’ of the solid-liquid interface. 
Quincke and also Von Tereschin have calculated values® of « fora 
glass-water interface, using data obtained by electro-osmotic experi- 
ments with capillary tubes. The values lie close to 50 millivolts and 
are of the same order of magnitude as those calculated from the 
migration velocities of particles suspended in water (cataphoresis). 
From the beginning it has been recognized that electrical en- 
dosmose is greatly affected by changes of temperature. Perrin found 
that, with rising temperature, the volume of liquid transported under 
otherwise constant conditions increased very rapidly, and he reported 
that temperature had about the same effect on the rate of endosmose as 
it had on the flwidity (reciprocal of viscosity) of the liquid. Equation 
1 indicates that this condition is plausible (since D does not change 
rapidly with the temperature), provided « remains practically con- 
stant as the temperature changes. Perrin’s conclusion that the 
50 Note that Bethe and Toropoff maintain that the ‘ indifferent’ point (zero flow) 
and the isoelectric point do not necessarily coincide exactly. Zeit, Phys, Chem. 89, 
597 (1915). 
a seb has applied this principle in Brit. Pat. 2379 (1911), where in order to 
obtain stable suspensions he adds acids to those substances which migrate to the 
cathode and bases to those which migrate to the anode. In 27930 (1911) he adds 
adsorbed positive or negative colloids (alumina, humic acid, silica, etc.) to obtain the 
same results. 
53 Freundlich, Kapillarchemie, 227 (1909). 
32 Data compiled by Burton, Physical Properties of Colloid Solutions, 135 (1916). 
