1345 
Now an adsorbed substance is displaced by another adsorbed 
substance; this is dependent on the degree to which that second 
substance is itself adsorbed’); if to a suspensoid system is added a 
substance which itself becomes strongly adsorbed it would be asto- 
nishing indeed if it left the stability of the system unmodified. 
As a rule, we possess a measure for the stability of a system in 
the limitation value.*) Meanwhile it is as well to consider in how 
far we must attach value to this relation. A complete coagula- 
tion in a short time occurs when of an added electrolyte so- 
much gets dissolved that the colloid has become isoelectric. But this 
adsorption will also be modified by an added substance. 
If, for instance, we have a As,S, sol this consists of particles of 
arsenious sulphide dispersed in water; these particles at their preparation 
have adsorbed hydrogen sulphide in such a manner that an electric 
double layer has formed in such a way that the layer of S’-ions 
lies at the side of the solid particle and the H-ion layer at that of 
the liquid. If now we add a substance A which is adsorbed posi- 
tively, the condition of that double layer will be modified because A 
displaces H,S, S" as well as H-. When effectuating coagulation by 
means of an electrolyte such as BaCl,, adsorption also takes 
place of BaCl,, Ba" and Cl’ and the limitation value will be attained 
when the quantities of Ba: and 5: are equivalent.*) But this adsorp- 
tion process also experiences a similar influence from the substance 
A. The change in the limitation value under the influence of A is 
therefore the resultant of those two actions. Perhaps these might 
just neutralise each other? This seems to have always been an 
assumption not mentioned. Although we know as yet but little about 
the displacement in the capillary layer, such a symmetry did not 
seem to me probable and therefore the subjoined investigation was 
carried out, provisionally for the purpose of orientation. 
The substance to be admixed should give rise to a strongly positive 
adsorption and hence, according to Gipss’s principle it must strongly 
reduce the surface tension. In this relation account must, of course, 
be taken of the surface tension solid-liquid; the measurement thereof 
is, as yet, almost impracticable, but experience bas taught us up to 
the present (and theoretically this may be expected) that the surface 
tension must as a rule proceed similarly to that for liquid gas. 
Hence, as strongly adsorbable components were chosen those which 
strongly lessen the surface tension of water. 
1) Cf. FREUNDLICH and Masrus, Gedenkboek van BEMMELEN (Helder 1910), 88. 
2) A version of the German word “Schwellenwert’’. 
8) Cf. Wairney and Oper, Zeitschr. f. physik. Chem, 39, 630 (1902). 
