1024 
E , millivolt Wm Es Rl 
1n 
P. em.Hg ‘ 13.6 x 981 
em’, 
x in Ohm-! by 9 x 1011 
1 was put to 0.0108 dyne. 
In the last column of the Tables 1-—4 the electric charge of the 
capillary tube is given per cm? in c.g.s.-units. Fig. 1 represents the 
relations between this charge and the concentration of the liquid 
flowing through the capillary tube. 
3. From these results we may infer that each of these four 
electrolytes can effect a greater charge to the capillary tube than 
pure water. can; only when an optimum charge is reached, higher 
concentrated solutions lower the charge. . 
In the chemistry of colloids much attention has been paid until 
now to the fact that electrolytes lower the potential of contact; this 
now appears to be true only for solutions of higher concentration. 
It is remarkable that in all four cases, mentioned in the Tables 1— 4, 
the current potentials are lowered by the electrolytes, but that the 
contact potentials are modified in the peculiar way with an opti- 
mum value. *) 
A short time after the publication of my previous paper on this 
subject, Frank Powis’) of Donnan’s laboratory communicated (Nov. 
1914) a most interesting investigation about the influence of elec- 
trolytes on the cataphoresis of oil-emulsions. The similarity of 
our results is striking; therefore we came in many respects to the 
same conclusions®). When calculating the contact-potential for oi] 
and water resp. for glass and water, Powis found an optimum only 
in the case of the monovalent cation of potassium, but it is clear 
from our Fig. 1 that he could not have observed such a value as 
regards Ba as he has made no measurements of solutions with a 
concentration below 2004 Mol BaCl, We may now draw the con- 
clusion that the difference between a monovalent and a bivalent 
cation is only quantitative and not qualitative. 
1) It is impossible to make out if the optimum is present in the case of AlCls. 
+ 
As P has reached the value zero at 0.8 » Mol, the optimum should appear at a 
still smaller concentration. I regard the data to be insufficient to decide whether 
we are dealing here with an optimum or not. 
2) Z. f. physik. Chem. 89, 91 (1915). 
3) We gave a.o. the same criticism on the theory of irregular series of floculation. 
With regard to the way in which the final value is reached in each case, | found 
the same progress, as Powis describes (le p. 179). 
